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ortho-Metallated triphenylphosphine chalcogenide complexes of platinum and palladium: synthesis and catalytic activity† Steven H. Privér,a Martin A. Bennett,b Anthony C. Willis,b Srinivas Pottabathula,a,c M. Lakshmi Kantamc and Suresh K. Bhargava*a Treatment of [PtI2(COD)] (COD = 1,5-cyclooctadiene) with 2-LiC6H4P(S)Ph2 gives the complex cis-[Pt{κ22-C6H4P(S)Ph2}2] (1) containing a pair of ortho-metallated triphenylphosphine sulfide rings. The selenium counterpart, [Pt{κ2-2-C6H4P(Se)Ph2}2] (2), which exists as cis- and trans-isomers in solution, and the palladium analogues, cis-[Pd{κ2-2-C6H4P(X)Ph2}2] [X = S (3), Se (4)], are obtained by transmetallation of [MCl2(COD)] with the organotin reagent 2-Me3SnC6H4P(X)Ph2 in a 1 : 2 mol ratio. The reaction of [PdCl2(COD)] with 2-Me3SnC6H4P(X)Ph2 in a 1 : 1 mol ratio, and the reaction of 3 with palladium(II) acetate, give dinuclear, anion-bridged complexes [Pd2(μ-Cl)2{κ2-2-C6H4P(X)Ph2}2] [X = S (5), Se (6)] and [Pd2(μ-OAc)2{κ2-2-C6H4P(S)Ph2}2] (8), respectively. Complexes 5 and 8 could not be made directly from triphenylphosphine sulfide by standard ortho-palladation procedures. The bridging framework in complexes 5 and 6 is cleaved by tertiary phosphines to give mononuclear derivatives [PdCl{κ2-2-C6H4P(X)Ph2}(PR3)] [X = S, R = Ph (11); X = Se, R = Ph (13); X = Se, R = 4-tolyl (15)]. The selenium-containing compounds 13 and 15 decompose slowly in solution giving dinuclear complexes [PdCl(μ2-Se-κ2-P,Se2-SeC6H4PPh2)PdCl(μ-2-C6H4PPh2)(PR3)] [R = Ph (14), 4-tolyl (16)]. The structure of complex 16 establishes that the bridging 2-C6H4PPh2 group is generated by reduction of the phosphine selenide unit, not by ortho-metallation of the coordinated triphenylphosphine. The chloro-bridges of 5 and 6 are also

Received 28th April 2014, Accepted 19th June 2014

cleaved by acetylacetonate (acac) and deprotonated Schiff bases forming mononuclear species [Pd{κ22-C6H4P(X)Ph2}L2] [L2 = acac, X = S (9), Se (10); L2 = 2-OC6H4CHvNC6H4-4-R, X = S, R = OMe (17), NO2

DOI: 10.1039/c4dt01236d

(18); X = Se, R = OMe (19), NO2 (20)]. The ability of complexes 5, 6 and the Schiff base-derivatives 17–20

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to catalyse Heck–Mizoroki and Suzuki–Miyaura C–C bond-forming reactions has also been investigated.

Introduction There are still relatively few examples of ortho-metallated S-donor complexes, especially of Pd(II), compared with the plethora of ortho-metallated complexes derived from N-donors. Following the first synthesis of ortho-palladated and orthoplatinated compounds derived from thiobenzophenone by

a School of Applied Sciences (Applied Chemistry), RMIT University, GPO Box 2476, Melbourne, Victoria 3001, Australia. E-mail: [email protected] b Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia c Inorganic and Physical Chemistry Division, CSIR-Indian Institute of Chemical Technology, Hyderabad, 500 607, India † Electronic supplementary information (ESI) available: Crystal data and details of data collection (Table S1) and X-ray crystallographic data in CIF format for complexes 1, 2, 4, 8, 9, 11–14, 16, 17 and 20. CCDC 999160–999172. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt01236d

12000 | Dalton Trans., 2014, 43, 12000–12012

Alper,1 Pfeffer et al.2,3 showed that thioethers, such as benzyl methyl sulfide, could be metallated in moderate to good yields by palladium(II) acetate in acetic acid (Scheme 1). Previous attempts based on [PdCl4]2− had been unsuccessful, although this reagent, in the presence of sodium acetate, is able to orthometallate the doubly activated compound 1,3-bis(t-butylthiomethyl)benzene, 1,3-C6H4(CH2StBu)2, to form a pincer complex (Scheme 2);4 the bis(methylthiomethyl) analogue can

Scheme 1

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Scheme 2

only be obtained by an exchange reaction between 1,3C6H4(CH2SMe)2 and [Pd2(μ-Cl)2(κ2-2-C6H4CH2NMe2)2].2,3 Selenium analogues of the singly- and doubly-cyclopalladated sulfur compounds have been synthesized and shown to be more powerful catalysts for the Heck–Mizoroki reaction than their sulfur analogues.5 The ortho-palladated compounds formed from [Pd(OAc)2]3 and benzylic tert-butyl thioethers are excellent catalysts for Heck–Mizoroki and Suzuki–Miyaura C–C bond forming reactions.6,7 Cyclopalladated or cycloplatinated thiophosphoryl pincer complexes can be derived by direct metallation of 1,3-disubstituted aromatic compounds containing, for example, two P(S)Ph2 groups, one P(S)Ph2 group and one thioamido group, or one P(S)Ph2 and one P(S)R1R2 group (R1 = R2 = NMe2, NEt2, Ph; R1 = Me, R2 = OBu).8–10 However, there appear to be no reported examples of ortho-palladation or ortho-platination of triphenylphosphine sulfide or its selenium analogue, Ph3PvX (X = S, Se), even though these compounds are readily orthometallated on heating with [PhCH2Mn(CO)5].11 The products are [(OC)4Mn{κ2-2-C6H4P(X)Ph2}] which, in the case of X = S, undergo insertion reactions of the alkynes C2(CO2Me)2 and HCO2Me into the Mn–C σ-bond to form seven-membered manganacycles.12 A possible entry into complexes containing ortho-metallated triphenylphenylphosphine sulfide and triphenylphosphine selenide is transmetallation, as demonstrated, for example, by the preparation of the cycloaurated complexes [AuCl2{κ2-2C6H4P(X)Ph2}] (X = S, Se).13 Transmetallation may provide a general method for the preparation of a new family of complexes containing ortho-metallated triphenylphosphine chalcogenide ligands, thus opening up the burgeoning field of catalysis based on them to further study. In light of this, we report here on transmetallation routes to cycloplatinated and cyclopalladated complexes of triphenylphosphine sulfide and triphenylphosphine selenide, and on the catalytic ability of selected palladium complexes in C–C bond-forming reactions.

showed at least four 31P NMR resonances in the region of δ 43–45. The chemical shifts did not correspond with those of the chloro- or acetato-bridged ortho-palladated complexes of Ph3PvS obtained by transmetallation (see below) and the species present were not investigated further. The failure to achieve direct ortho-palladation of Ph3PvS is surprising because similar procedures have been used successfully in the case of triphenylphosphine imine derivatives.16–18 Bis(chelate) complexes In a reaction similar to that used for the preparation of cis-[Pt(κ2-2-C6H4PPh2)2],19,20 treatment of the organolithium reagent 2-LiC6H4P(S)Ph2 with [PtI2(COD)] (COD = 1,5-cyclooctadiene) gave the cyclometallated bis(chelate) complex cis-[Pt{κ2-2C6H4P(S)Ph2}2] (1) as a pale yellow solid in good yields (Scheme 3). The 1H NMR spectrum showed the expected aromatic multiplets and the 31P NMR spectrum showed a single resonance at δ 51.6, flanked by 195Pt satellites (2JPtP 79.0 Hz). The chemical shift is consistent with a tertiary phosphine sulfide coordinated to Pt(II) and the magnitude of 2JPtP is consistent with the location of the phosphine sulfide group trans to a ligand of high trans influence. For comparison, we cite cis[Pt(SvPPh3)(κ2-C6H3-5-Me-2-PPh2)(PPh2-4-tolyl)] (68.7 Hz)21 and [Pt(dppmS2)(dppe)](ClO4)2 (81.9 Hz)22 in which the phosphine sulfide group is trans to σ-aryl and tertiary phosphine, respectively. In contrast, in cis-[PtCl2(SvPPh3)(DMSO)], where the phosphine sulfide group is trans to chloride, a ligand of relatively low trans-influence, 2JPtP is 116 Hz.23 The spectroscopic data suggest that the phosphine sulfide groups in complex 1 are mutually cis, and this was confirmed by single crystal X-ray diffraction (this and the other structurally characterised complexes will be discussed later). The selenium analogue of 1, [Pt{κ2-2-C6H4P(Se)Ph2}2] (2) could not be prepared by an analogous method; under the reaction conditions, attempted lithiation of 2-BrC6H4P(Se)Ph2 resulted in reduction of the PvSe group. However, 2 could be prepared in good yields by transmetallation of the organotin reagent 2-Me3SnC6H4P(Se)Ph2 with [PtCl2(COD)] in refluxing dichloromethane (Scheme 4). The 31P NMR spectrum of the isolated solid showed two singlet resonances at δ 37.2 and 36.5, suggesting the presence of two species; the ratio of the two peaks varied between preparations but was ca. 3 : 1. The downfield resonance is flanked by broad 195Pt satellites

Results and discussion Attempted ortho-palladation of triphenylphosphine sulfide Under standard conditions,3,14,15 e.g., Li2[PdCl4] (in the presence or absence of NaOAc), [Pd(OAc)2]3, or [Pd2(μ-Cl)2(κ2-2C6H4CH2NMe2)2] (in the presence or absence of CF3COOH) reacted with Ph3PvS to give poorly soluble brown solids that

Scheme 3

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Scheme 4

(2JPtP 70.6 Hz) and two sets of 77Se satellites (1JSeP 534 Hz, 3 JSeP 26.9 Hz). The 77Se satellites are further split into doublets of 2.2 Hz due to four-bond P–P coupling, arising from inequivalence of the phosphorus atoms in the isotopomer containing only one 77Se nucleus. The upfield resonance at δ 36.5 shows broad 195Pt satellites of 73.0 Hz and one set of 77Se satellites (1JSeP 506 Hz) which are further split into doublets of ca. 0.7 Hz due to P–P coupling. By comparison to the spectroscopic data for its palladium analogue (see later), the upfield resonance is tentatively assigned to cis-[Pt{κ2-2-C6H4P(Se)Ph2}2], and the less shielded resonance at δ 37.2 to the trans isomer. The Se–P couplings are also reproduced in the 77Se NMR spectrum, which shows a pair of resonances at δ −130.2 and +42.5. The former resonance is flanked by 195Pt satellites of 230 Hz; due to the low intensity of the downfield peak, coupling to platinum was not observed. The structure of cis[Pt{κ2-2-C6H4P(Se)Ph2}2] was confirmed by X-ray diffraction. Complexes 1 and 2 could also be prepared in lower yields by heating toluene solutions of [Pt(κ2-2-C6H4PPh2)2] with elemental sulfur or selenium, respectively. The palladium analogues of complexes 1 and 2 were prepared by transmetallation of 2-Me3SnC6H4P(X)Ph2 with [PdCl2(COD)] to give cis-[Pd{κ2-2-C6H4P(X)Ph2}2] [X = S (3), Se (4)] as pale yellow solids in high yields (Scheme 4). The 31 P NMR spectrum of 3 showed a singlet resonance at δ 46.9, comparable to that of complex 1. In contrast to its platinum analogue 2, the 31P NMR spectrum of 4 showed only a singlet resonance at δ 32.6 with 77Se satellites of 29.8 and 557 Hz which were further split by 4.0 Hz due to 4JPP coupling and the 77 Se NMR spectrum showed the expected doublet of doublets centred at δ −119.5. The structures of 2 and 4 have been confirmed by X-ray crystallography. Anion-bridged dipalladium complexes and their derivatives When stirred in dichloromethane at room temperature, equimolar amounts of 2-Me3SnC6H4P(X)Ph2 (X = S, Se) and [PdCl2(COD)] gave the poorly soluble chloro-bridged dimers [Pd2(μ-Cl)2{κ2-2-C6H4P(X)Ph2}2] [X = S (5), Se (6)]. Both complexes showed a pair of singlet resonances in their 31P NMR spectra (δ 46.7 and 47.8 for 5; δ 25.8 and 26.8 for 6), consistent with the presence of syn- and anti-isomers. The direct orthopalladation of triphenylphosphine imines by Li2[PdCl4]16 or [Pd(OAc)2]317 has also been reported to give chloro- or acetato-

12002 | Dalton Trans., 2014, 43, 12000–12012

complexes similar to 5 and 6, while treatment of the organolithium reagent 2-LiC6H4P(vNPh)Ph2 with [PdCl2(COD)] gives a mixture of the chloro-bridged species [Pd2(μ-Cl)2{2-C6H4P(vNPh)Ph2}2] and the bis(chelate) complex cis-[Pd{κ2-C,N2-C6H4P(vNPh)Ph2}2].18 Attempts to prepare the chlorobridged platinum complexes [Pt2(μ-Cl)2{κ2-2-C6H4P(X)Ph2}2] (X = S, Se) analogous to 5 and 6 using the appropriate organotin reagent and [PtCl2(COD)] were unsuccessful and only unreacted starting materials were recovered. The mixed-ligand bis(chelate) complex [Pd{κ2-2-C6H4P(S)Ph2}{κ2-2-C6H4P(Se)Ph2}] (7) could be prepared in an impure state by treating a dichloromethane suspension of 5 or 6 with two equivalents of 2-Me3SnC6H4P(X)Ph2 (X = Se, S, respectively); also formed are the bis( phosphine sulfide) and bis( phosphine selenide) complexes 3 and 4. The ratio of 3 : 4 : 7 was 1 : 1 : 2 and attempts to separate the three species by chromatography were unsuccessful. Complex 7 shows a pair of resonances in the 31P NMR spectrum at δ 31.1 and 48.1 assignable to the phosphine selenide and phosphine sulfide, respectively, split into doublets of 1.0 Hz due to coupling of the inequivalent phosphorus nuclei. The two resonances also show 77Se satellites of 555 and 27.4 Hz, respectively, consistent with one- and three-bond coupling (cf. 557 and 29.8 Hz in 4). Attempts to make 7 by refluxing equimolar amounts of 3 and 4 in toluene for 24 h were unsuccessful and only unreacted started materials were detected by 31P NMR spectroscopy. The acetato-bridged dimer [Pd2(μ-OAc)2{κ2-2-C6H4P(S)Ph2}2] (8) was prepared in good yields from the reaction of 3 with [Pd(OAc)2]3. The 1H NMR spectrum showed the expected aromatic multiplets together with a methyl singlet at δ 2.09 due to the acetate group and the 31P NMR spectrum showed a singlet resonance at δ 47.0, comparable to that observed for 3 (δ 46.9). The IR spectrum of 8 (nujol mull) showed bands at 1588, 1578 and 1415 cm−1, corresponding to the CvO and C–O stretching vibrations, respectively; the separation of ca. 170 cm−1 is consistent with the presence of bridging acetate groups24 which was confirmed by X-ray diffraction. Reaction of [Pd2(μ-Cl)2{κ2-2-C6H4P(X)Ph2}2] [X = S (5), Se (6)] with Na(acac) gave the mononuclear complexes [Pd(κ2-O,O′acac){κ2-2-C6H4P(X)Ph2}] [X = S (9), Se (10)]. The 1H NMR spectra for 9 and 10 each showed three singlet resonances at ca. δ 1.9, 2.0 and 5.3 due to the acac ligand, assignable to the two inequivalent methyl and methine groups, respectively, together with aromatic multiplets. The 31P NMR spectra each showed a single resonance, the chemical shifts of which are comparable to those of the appropriate bis(chelate) complexes (3 or 4) and chloro-bridged dimers (5 or 6). The chloro-bridges in 5 are also cleaved by PPh3, giving the mononuclear complex [PdCl{κ2-2-C6H4P(S)Ph2}(PPh3)] (11) as a mixture of cis and trans isomers (Scheme 5), these terms referring to PPh3 cis and trans, respectively, to the sulfur atom of PvS. The 31P NMR spectrum of 11 showed a pair of singlet resonances at δ 34.4 and 43.8 assignable to the cis isomer and a pair of doublets at δ 17.5 and 50.2 due to the trans isomer, split by ca. 60 Hz due to P–P coupling. In both cases, the high field resonance was due to the phosphorus atom of the coordinated

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Scheme 5

PPh3 ligand and the low field resonance to the phosphorus in the phosphine sulfide chelate group. The first attempt to obtain X-ray quality crystals of 11 unexpectedly gave the trinuclear complex [Pd3Cl3(μ2-S-κ2-P,S-2-SC6H4PPh2)3] (12), which is formally derived by loss of PPh3, reduction of the phosphine sulfide group and insertion of the sulfur atom into the palladium–carbon bond (Scheme 5); a second attempt gave crystals of the expected structure. It is not clear how 12 was formed from a spectroscopically pure sample of 11 and it could not be detected by 31P NMR spectroscopy when a sample of 11 in 3 : 1 CD2Cl2–MeOH was set aside; even after four weeks, only 11 was present. A low-yielding synthesis of 12 has been reported25 and other complexes containing a six-membered Pd3S3 ring are known.26,27 The selenium analogue of 11, [PdCl{κ2-2-C6H4P(Se)Ph2}(PPh3)] (13) was prepared similarly from [Pd2(μ-Cl)2{κ2-2C6H4P(Se)Ph2}2] (6) and PPh3 (Scheme 6). Like its sulfur analogue, the 31P NMR spectrum of 13 showed a pair of singlet resonances at δ 27.3 and 32.6 with additional couplings to 77Se of 529 and 96.2 Hz, respectively, and a second pair of resonances at δ 16.4 and 31.1, split into doublets of ca. 60 Hz. In this case, no 77Se satellites were observed owing to the low abundance of this isomer. The former pair of resonances are assigned to the cis isomer and the latter to the trans (cis : trans ratio ca. 10 : 1). Slow crystallization of a solution of 13 from CH2Cl2–MeOH gave crystals with two different morphologies, yellow blocks and yellow prisms. The blocks proved to be the expected complex [PdCl{κ2-2-C6H4P(Se)Ph2}(PPh3)] (13) while

the prisms were those of a rearranged product, [PdCl(μ2-Se-κ2P,Se-2-SeC6H4PPh2)PdCl(μ-2-C6H4PPh2)(PPh3)] (14). Dinuclear complex 14 is structurally different from the trinuclear complex 12 (Scheme 5); it is formally obtained by loss of a PPh3 ligand and selenium atom ( possibly as Ph3PvSe), and reduction of the phosphine selenide group and insertion of the selenium atom into a Pd–C bond. In contrast to the stability of 11, when a 3 : 1 CD2Cl2–MeOH solution of 13 was left to stand at ambient temperature, three new resonances began to appear in the 31P NMR spectrum after 24 h. These resonances, a doublet of doublets at δ 20.9 ( JPP 6.1, 478 Hz) and doublets at δ 27.6 ( JPP 6.1 Hz) and 49.0 ( JPP 478 Hz), are consistent with the formation of 14 and are assigned to the phosphorus atoms in the six-membered ring, PPh3 ligand and five-membered chelate ring, respectively. Additionally, a small singlet resonance at δ 35.2 was observed, which is tentatively assigned to Ph3PvSe (δP 35.8 in CDCl3).28 The remaining selenium atom has evidently migrated into the Pd–C σ-bond and the transformation can be described by the equation: 2 ½PdClf2-C6 H4 PðSeÞPh2 gðPPh3 Þ ! ½Pd2 Cl2 ð2-SeC6 H4 PPh2 Þð2-C6 H4 PPh2 ÞðPPh3 Þ þ Ph3 PvSe After five weeks, the new resonances comprised ca. 25% of the reaction mixture, as estimated by integration of the 31P

Scheme 6

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Scheme 7

NMR spectrum. Longer reaction times led to further decomposition and unidentified products. To determine if the bridging 2-C6H4PPh2 group in 14 was derived by deselenisation of a phosphine selenide group or by ortho-metallation of the coordinated PPh3 ligand, [PdCl{κ2-2C6H4P(Se)Ph2}{P(4–tolyl)3}] (15) was prepared analogously to 13 using P(4-tolyl)3. The spectroscopic parameters for 15 are generally comparable to those of 13. Yellow crystals deposited from a 3 : 1 CH2Cl2–MeOH solution of 15 over a period of several weeks. One of them proved to be [PdCl(μ2-Se-κ2-P,Se-2SeC6H4PPh2)PdCl(μ-2-C6H4PPh2){P(4–tolyl)3}] (16), the 4-tolyl analogue of 14, thus confirming that the bridging 2-C6H4PPh2 unit is derived by reduction of coordinated 2-C6H4P(Se)Ph2, not by metallation of coordinated PPh3 in the parent complex. Cleavage of PvSe bonds has been observed in the reactions of tertiary phosphine selenides with metal carbonyl clusters.29

structure of 1 is shown in Fig. 1 and selected bond lengths and angles for complexes 1, 2 and 4 are listed in Table 1. Crystals of the bis(chelate) complexes 2 and 4 obtained from 1,2-dichloroethane were isomorphous (monoclinic C2/c) and contained one disordered solvent molecule per asymmetric unit, whereas crystals of complex 1 (monoclinic P21/c) were solvent-free. In all three complexes, the metal atom is bound by two mutually cis metallated aryl groups and two phosphine chalcogenides, the geometry being approximately square planar. The Pt–C bond lengths in 1 [2.003(4), 2.014(4) Å]

Schiff base derivatives The chloro-bridges in [Pd2(μ-Cl)2{κ2-2-C6H4P(X)Ph2}2] [X = S (5), Se (6)] are also cleaved by bidentate anionic ligands. Thus, reaction of 5 and 6 with the Schiff bases 2-HOC6H4CHvNC6H4-4-R (R = OMe, NO2) in the presence of a base gave mononuclear species of the type [Pd{κ2-2-C6H4P(X)Ph2}(κ2-2-OC6H4CHvNC6H4-4-R)] {X = S, R = OMe (17), NO2 (18); X = Se, R = OMe (19), NO2 (20)} (Scheme 7) as yellow (R = OMe) or orange-red (R = NO2) solids in high yields. The 31P NMR spectra of complexes 17 and 18 each showed a singlet resonance at ca. δ 45, and complexes 19 and 20 a singlet at ca. δ 26, the chemical shifts of which are comparable to those of other complexes containing the 2-C6H4P(X)Ph2 chelate group. As expected, the resonances for complexes 19 and 20 show additional coupling to 77Se of about 500 Hz; this coupling is also reproduced in the 77Se NMR spectra. The structures of 16 and two different modifications of 19 have been confirmed by X-ray diffraction. X-ray crystallography The structures of cis-[Pt{κ2-2-C6H4P(S)Ph2}2] (1), cis-[Pt{κ2-2C6H4P(Se)Ph2}2] (2) and cis-[Pd{κ2-2-C6H4P(Se)Ph2}2] (4) were confirmed by single crystal X-ray diffraction. The molecular

12004 | Dalton Trans., 2014, 43, 12000–12012

Fig. 1 Molecular structure of cis-[Pt{κ2-2-C6H4P(S)Ph2}2] (1). Ellipsoids show 30% probability levels and hydrogen atoms have been omitted for clarity.

Table 1 Selected bond lengths (Å) and angles (deg) in cis-[Pt{κ2-2C6H4P(S)Ph2}2] (1), cis-[Pt{κ2-2-C6H4P(Se)Ph2}2]·2(C2H4Cl2) (2) and cis[Pd{κ2-2-C6H4P(Se)Ph2}2]·2(C2H4Cl2) (4)

M(1)–C(2) M(1)–C(32) M(1)–X(1) M(1)–X(2) C(2)–M(1)–X(2) C(32)–M(1)–X(1) C(2)–M(1)–X(1) C(32)–M(1)–X(2) C(2)–M(1)–C(32) X(1)–M(1)–X(2) a

Complex 1a

Complex 2b

Complex 4c

2.003(4) 2.014(4) 2.4107(10) 2.4014(10) 176.46(11) 175.94(12) 87.22(11) 88.79(12) 94.22(16) 87.84(4)

2.028(7)

2.030(2)

2.5045(8)

2.5158(3)

172.57(19)

172.37(6)

90.1(2)

90.75(6)

92.6(4) 88.01(4)

91.725(13) 87.716(13)

M = Pt, X = S. b M = Pt, X = Se. c M = Pd, X = Se.

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are similar to those observed in the phosphine sulfide pincer complex [PtCl(4-CH3C6H2-2,6-{P(S)Ph2}2)] [2.02(2) Å].11 In contrast, the Pt–S bond lengths are significantly longer in 1 than in the pincer complex [2.4107(10), 2.4014(10) Å vs. 2.307(5) Å], owing to the greater trans-influence of the σ-C groups relative to that of the phosphine sulfide moiety. The Pt–C bond lengths in 2 and 4 [2.028(7), 2.030(2) Å, respectively] are comparable to those in 1, while the M–Se bond lengths [2.5045(8), 2.5158(3), respectively] are ca. 0.1 Å greater than the Pt–S bond lengths in 1; a similar trend was observed for the cyclometallated manganese carbonyl complexes [(OC)4Mn{κ2-2-C6H4P(X) Ph2}] [X = S, 2.410(1) Å; Se, 2.514(1) Å].8 In the structure of [Pd2(μ-OAc)2{κ2-2-C6H4P(S)Ph2}2] (8), shown in Fig. 2 (together with selected bond lengths and angles), each palladium atom is bound by a chelating C6H4P(S)Ph2 group and two bridging acetate ligands. The two C6H4P(S)Ph2 groups adopt a face-to-face orientation that brings the metal atoms into close contact, the Pd⋯Pd separation [2.92983(19) Å] being similar to those observed in the structurally similar complexes [Pd2(μ-OAc)2(κ2-2-C6H4CH2SMe2)2]30 [2.9483(3) Å] and [Pd2(μ-OAc)2(κ2-2-C6H4CHMeStBu2)2]31 [2.9565(4) Å] containing cyclopalladated thioether ligands. In general, the bond lengths and angles about the Pd atoms in 8 are also similar to those in the thioether complexes, although the Pd–S bond lengths are significantly longer [ca. 2.29 Å vs. 2.25 Å], consistent with the poorer donor strength of the sulfur atom in the phosphine sulfide group. The bond lengths and angles about the metal atom in [Pd(κ2-O,O′-acac){κ2-2-C6H4P(S)Ph2}2] (9) (Fig. 3) are generally similar to those observed in the acetato complex 8, although the Pd–O bond lengths are ca. 0.05 Å shorter. In both cases, the Pd–O bond lengths trans

Fig. 2 Molecular structure of [Pd2(μ-OAc)2{κ2-2-C6H4P(S)Ph2}2] (8). Ellipsoids show 30% probability levels and hydrogen atoms have been omitted for clarity. One phenyl group is disordered by rotation about the P–C bond and only one orientation is shown. Selected bond lengths (Å) and angles (deg): Pd(1)–Pd(2) 2.92983(19), Pd(1)–C(2) 1.9801(18), Pd(1)– S(1) 2.2977(6), Pd(1)–O(11) 2.0745(15), Pd(1)–O(21) 2.1456(15), Pd(2)– C(32) 1.9827(17), Pd(2)–S(2) 2.2936(5), Pd(2)–O(12) 2.1372(13), Pd(2)– O(22) 2.0661(15), C(2)–Pd(1)–O(21) 177.22(7), S(1)–Pd(1)–O(11) 166.87(5), C(2)–Pd(1)–S(1) 92.08(5), C(2)–Pd(1)–O(11) 90.79(7), S(1)–Pd(1)–O(21) 87.58(5), O(11)–Pd(1)–O(21) 90.16(7), C(32)–Pd(2)–O(12) 175.42(7), S(2)– Pd(2)–O(22) 176.83(5), C(32)–Pd(2)–S(2) 90.63(6), C(32)–Pd(2)–O(22) 90.52(7), S(2)–Pd(2)–O(12) 88.13(5), O(12)–Pd(2)–O(22) 90.50(6).

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to S are about 0.06 Å shorter than those trans to C, as expected on the basis of relative trans-influences. Although the complexes are isostructural, crystals of trans[PdCl{κ2-2-C6H4P(X)Ph2}(PPh3)] [X = S (11), Se (13)] (Fig. 4), grown from CH2Cl2–methanol, were not isomorphous (11: triˉ, 13: monoclinic P21/n). As expected, the geometry clinic P1 about the metal centres is approximately square planar and the Pd–X bond length is ca. 0.1 Å longer for X = Se compared to X = S (Table 2), similar to that observed in the bis(chelate) complexes 1, 2 and 4. The metrical parameters in the trinuclear complex [Pd3Cl3(μ2-S-κ2-P,S-2-SC6H4PPh2)3] (12), obtained as a methanol solvate, are comparable to those of the reported dichloromethane solvate.25

Fig. 3 Molecular structure of [Pd(κ2-O,O’-acac){κ2-2-C6H4P(S)Ph2}] (9). Ellipsoids show 30% probability levels and hydrogen atoms have been omitted for clarity. Only one molecule in the asymmetric unit is shown. Selected bond lengths (Å) and angles (deg): Pd(1)–C(2) 1.994(4), Pd(1)–S(1) 2.3075(11), Pd(1)–O(11) 2.023(3), Pd(1)–O(12) 2.084(3), C(2)– Pd(1)–O(12) 178.28(14), S(1)–Pd(1)–O(11) 178.56(9), C(2)–Pd(1)–S(1) 90.08(12), C(2)–Pd(1)–O(11) 89.18(14), S(1)–Pd(1)–O(12) 89.31(8), O(11)– Pd(1)–O(12) 91.47(11).

Fig. 4 Molecular structure of trans-[PdCl{κ2-2-C6H4P(S)Ph2}(PPh3)] (11). Ellipsoids show 30% probability levels and hydrogen atoms have been omitted for clarity.

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Table 2 Selected bond lengths (Å) and angles (deg) in trans-[PdCl{κ22-C6H4P(S)Ph2}(PPh3)] (11), and trans-[PdCl{κ2-2-C6H4P(Se)Ph2}(PPh3)] (13)

Pd(1)–C(2) Pd(1)–X(1) Pd(1)–Cl(1) Pd(1)–P(2) C(2)–Pd(1)–Cl(1) X(1)–Pd(1)–P(2) C(2)–Pd(1)–X(1) C(2)–Pd(1)–P(2) X(1)–Pd(1)–Cl(1) Cl(1)–Pd(1)–P(2) a

Complex 11a

Complex 13b

2.0391(18) 2.3894(4) 2.3703(5) 2.2842(4) 171.13(5) 169.659(16) 89.74(5) 93.06(5) 84.596(16) 93.713(16)

2.013(3) 2.4906(3) 2.3947(7) 2.2947(7) 170.53(7) 163.93(2) 88.24(2) 93.02(7) 88.24(2) 92.34(3)

X = S. b X = Se.

In the molecular structure of 14, shown in Fig. 5, the selenium atom asymmetrically bridges two palladium atoms [Pd(1)–Se(1) 2.3872(2), Pd(2)–Se(1) 2.4869(2)], in an arrangement similar to that observed for the sulfur atoms in complex 12,25 and the Pd⋯Pd separation [3.2760(2) Å] suggests little or no metal–metal interaction. The metrical parameters in the P(4-tolyl)3 analogue 16 are generally similar to those observed in 14 (Table 3), although the Pd⋯Pd separation [3.1872(3) Å] is significantly smaller, presumably due to the greater donor strength of P(4-tolyl)3 compared to PPh3. The structures of the Schiff base complexes [Pd{κ2-2-C6H4P(S)Ph2}(κ2-2-OC6H4CHvNC6H4-4-OMe)] (17) and [Pd{κ2-2C6H4P(Se)Ph2}(κ2-2-OC6H4CHvNC6H4-4-NO2)] (20) were confirmed by X-ray diffraction, and in the case of 20, two crystal modifications were obtained. The structures of 20a (shown in Fig. 6) and 20b differ by rotation of the nitrophenyl group along the N–Caryl bond by approximately 30°. In all cases, the metrical parameters of 17, 20a and 20b are unremarkable (Table 4).

Table 3 Selected bond lengths (Å) and angles (deg) in [PdCl(μ2-Se-κ2P,Se-2-SeC6H4PPh2)PdCl(μ-2-C6H4PPh2)(PPh3)]·0.376(CH3OH) (14) and [PdCl(μ2-Se-κ2-P,Se-2-SeC6H4PPh2)PdCl(μ-2-C6H4PPh2){P(4–tolyl)3}]·CH2Cl2· CH3OH (16)

Pd(1)–Se(1) Pd(1)–P(1) Pd(1)–P(2) Pd(1)–Cl(1) Pd(2)–Se(1) Pd(2)–P(3) Pd(2)–C(32) Pd(2)–Cl(2) Pd(1)⋯Pd(2) Se(1)–Pd(1)–Cl(1) P(1)–Pd(1)–P(2) Se(1)–Pd(1)–P(1) Se(1)–Pd(1)–P(2) P(1)–Pd(1)–Cl(1) P(2)–Pd(1)–Cl(1) Se(1)–Pd(2)–P(3) C(32)–Pd(2)–Cl(2) Se(1)–Pd(2)–C(32) Se(1)–Pd(2)–Cl(2) C(32)–Pd(2)–P(3) P(3)–Pd(2)–Cl(2)

Complex 14

Complex 16

2.3872(2) 2.2949(5) 2.3296(5) 2.3350(5) 2.4869(2) 2.2905(5) 2.0137(17) 2.3933(5) 3.2760(2) 175.863(16) 175.731(18) 87.241(14) 90.214(13) 91.617(19) 90.682(18) 172.845(14) 172.24(5) 81.50(5) 95.726(14) 92.10(5) 91.029(18)

2.4023(4) 2.2823(9) 2.3420(8) 2.3390(9) 2.4744(4) 2.2760(8) 2.007(3) 2.4037(9) 3.1872(3) 175.82(3) 172.08(3) 86.27(2) 90.92(2) 89.90(3) 92.66(3) 170.99(2) 173.34(9) 82.41(8) 96.35(2) 91.63(8) 90.33(3)

Fig. 6 Molecular structure of [Pd{κ2-2-C6H4P(Se)Ph2}(κ2-2OC6H4CHvNC6H4-4-NO2)] (20a). Ellipsoids show 30% probability levels and hydrogen atoms have been omitted for clarity.

Table 4 Selected bond lengths (Å) and angles (deg) in [Pd{κ2-2-C6H4P(S)Ph2}(κ2-2-OC6H4CHvNC6H4-4-OMe)] (17) and [Pd{κ2-2-C6H4P(Se)Ph2}(κ2-2-OC6H4CHvNC6H4-4-NO2)] (20a)

Fig. 5 Molecular structure of [PdCl(μ2-Se-κ2-P,Se-2-SeC6H4PPh2)PdCl(μ-2-C6H4PPh2)(PPh3)]·0.376(CH3OH) (14). Ellipsoids show 30% probability levels. Hydrogen atoms and methanol of crystallisation have been omitted for clarity.

12006 | Dalton Trans., 2014, 43, 12000–12012

Pd(1)–X(1) Pd(1)–C(2) Pd(1)–N(1) Pd(1)–O(1) X(1)–Pd(1)–O(1) C(2)–Pd(1)–N(1) X(1)–Pd(1)–C(2) X(1)–Pd(1)–N(1) N(1)–Pd(1)–O(1) C(2)–Pd(1)–O(1) a

Complex 17a

Complex 20ab

2.3138(5) 2.017(2) 2.1057(17) 2.0325(15) 176.65(5) 175.22(7) 89.17(6) 93.18(5) 90.04(6) 87.68(7)

2.4195(3) 2.015(3) 2.115(2) 2.0283(18) 175.62(6) 174.14(9) 90.11(7) 93.87(6) 88.40(8) 87.92(9)

X = S. b X = Se.

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Catalysis The catalytic activities of selected palladacycles were investigated in the Heck–Mizoroki coupling reaction (Scheme 8). To determine optimal reaction conditions, the coupling of 4-bromoanisole (1 mmol) and styrene (2 mmol) was carried out in the presence of the chloro-bridged complex 5 as catalyst (0.5 mol %) using a variety of solvents (3 mL) and bases (2 mmol) at 140 °C. As shown in Table 5, a 75% conversion (66% isolated yield) of the coupled product 4-methoxy-trans-stilbene was obtained after 10 h using DMF as solvent and K2CO3 as base; good yields were also obtained using DMA as solvent. Using these reaction conditions, selected palladacycles (5, 6, 17–20) were further investigated (Table 6) and it was shown that a good isolated yield of coupled product was obtained for the chloro-bridged phosphine sulfide complex 5 (Table 6,

Scheme 8

Table 5 Heck–Mizoroki coupling of 4-bromoanisole and styrene catalysed by complex 5a

Entry

Solvent

Base

Conversionb (%)

1 2 3 4 5 6 7 8 9

DMF DMF DMF DMF DMF DMSO 1,4-Dioxane DMA DMA

K2CO3 NaHCO3 LiOH·H2O K3PO4 Cs2CO3 K2CO3 K2CO3 K2CO3 LiOH·H2O

75 0 29 0 12 58 30 63 18

entry 1). Only low yields of coupled product were obtained when the Schiff base-containing complexes 17 and 18 were used as catalysts (Table 6, entries 4 and 6) owing to the formation of palladium black; the yields of coupled products were improved significantly when LiOH as base and DMA as solvent were used, and no formation of palladium black was observed (Table 6, entries 5 and 7). High yields of coupled product could also be obtained from bromobenzene and 4-bromotoluene (Table 6, entries 10 and 11) using LiOH–DMA. Under the reaction conditions, all complexes containing the phosphine-selenide group were catalytically inactive (Table 6, entries 3, 8 and 9) due to thermal decomposition. The Suzuki–Miyaura coupling reaction (Scheme 9) of 4-bromoanisole and phenylboronic acid was also investigated. Using complex 5 as a test catalyst, the optimal reaction conditions were determined similarly to that of the Heck–Mizoroki reaction above, and, as shown in Table 7, excellent conversions were obtained using K2CO3 or LiOH·H2O in MeOH (Table 7, entries 1 and 3, respectively). Using LiOH as base and methanol as solvent, compounds 5, 6 and 17–20 were tested for their activity to catalyse the coupling of aryl bromides and phenylboronic acid (Table 8). Isolated yields of greater than 85% of the coupled products were obtained using the phosphine sulfide-containing complexes (Table 8, entries 1, 3, 4, 7 and 8). In contrast, yields of 50% or less were obtained when the phosphine selenide complexes were used (Table 8, entries 2, 5 and 6), owing to their poor thermal stability.

Scheme 9

a Reaction conditions: 4-bromoanisole (1 mmol), styrene (2 mmol), complex 5 (0.5 mmol%), base (2 mmol), solvent (3 mL), 140 °C, 10 h. b GC-conversion with respect to 4-bromoanisole; average of two runs.

Table 6

Heck–Mizoroki coupling of an aryl bromide and styrenea

Entry

Aryl bromide

Catalyst

Isolated yieldb (%)

1 2 3 4 5 6 7 8 9 10 11

4-Bromoanisole 4-Bromoanisole 4-Bromoanisole 4-Bromoanisole 4-Bromoanisole 4-Bromoanisole 4-Bromoanisole 4-Bromoanisole 4-Bromoanisole Bromobenzene 4-Bromotoluene

5 5 6 17 17 18 18 19 20 18 18

66 12c 0 11 69c 6 72c 0 0 84c 78c

a

Reaction conditions: aryl bromide (1 mmol), styrene (2 mmol), catalyst (0.5 mol%), K2CO3 (2 mmol), DMF (3 mL), 140 °C, 10 h. b Average of two runs. c Using LiOH·H2O (2 mmol) and DMA (3 mL).

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Table 7 Suzuki–Miyaura coupling of 4-bromoanisole and phenylboronic acid catalysed by complex 5a

Entry

Solvent

Base

Conversionb (%)

1 2 3 4 5 6 7 8 9 10 11

MeOH MeOH MeOH MeOH MeOH DMF 2-Propanol t-Butanol DMSO Toluene THF

K2CO3 KF LiOH·H2O K3PO4 Cs2CO3 LiOH·H2O LiOH·H2O LiOH·H2O LiOH·H2O LiOH·H2O LiOH·H2O

97 75 99 72 72 20 85 0 3 16 24

a Reaction conditions: 4-bromoanisole (1 mmol), phenylboronic acid (1.5 mmol), complex 5 (0.5 mol%), base (2 mmol), solvent (3 mL), 80 °C, 10 h. b GC-conversion with respect to 4-bromoanisole; average of two runs.

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Table 8 Suzuki–Miyaura coupling of an aryl bromide and phenylboronic acida

Entry

Aryl bromide

Catalyst

Isolated yieldb (%)

1 2 3 4 5 6 7 8

4-Bromoanisole 4-Bromoanisole 4-Bromoanisole 4-Bromoanisole 4-Bromoanisole 4-Bromoanisole Bromobenzene 4-Bromotoluene

5 6 17 18 19 20 5 5

92 50 85 84 20 16 94 91

a Reaction conditions: aryl bromide (1 mmol), phenylboronic acid (1.5 mmol), catalyst (0.5 mol%), LiOH·H2O (2 mmol), methanol (3 mL), 80 °C, 10 h. b Average of two runs.

Conclusions ortho-Metallated platinum and palladium complexes of triphenylphosphine sulfide and selenide were prepared by transmetallation procedures, either from the appropriate organolithium or organotin reagent. Unaccountably, the methods that have been applied successfully to the direct ortho-palladation of thioethers and triphenylphosphine imines failed for triphenylphosphine sulfide. Over a period of weeks at room temperature, the complex trans-[PdCl{κ2-2-C6H4P(Se)Ph2}(PPh3)] (13) in solution undergoes reduction of its coordinated triphenylphosphine selenide, accompanied by migration of selenium into a Pd–C σ-bond, to give [PdCl(μ2-Seκ2-P,Se-2-SeC6H4PPh2)PdCl(μ-2-C6H4PPh2)(PPh3)] (14). Selected palladacycles were also shown to catalyse Heck–Mizoroki and Suzuki–Miyaura coupling reactions, the triphenylphosphine selenide-based complexes being generally less efficacious owing to their poorer thermal stability.

Experimental section General comments All experiments involving organolithium and organotin reagents were performed under an atmosphere of dry argon with use of standard Schlenk techniques. Diethyl ether, dichloromethane, toluene and hexane were dried by passage through solvent drying columns. The compounds 2-BrC6H4PPh2,32 [PtI2(COD)]33 and [PdCl2(COD)]34 were prepared by literature methods and the methoxy- and nitro-substituted Schiff bases by the usual condensation reaction between salicylaldehyde and the appropriate amine;35 all other reagents were commercially available and used as received. 1 H (300 MHz), 13C (75 MHz), 31P (121 MHz) and 77Se (57 MHz) NMR spectra were measured on a Bruker Avance 300 spectrometer at room temperature in CDCl3. Coupling constants are given in Hertz (Hz) and chemical shifts (δ) in ppm, internally referenced to residual solvent signals (1H and 13C), external 85% H3PO4 (31P) or external Ph3PvSe (77Se, δ −262). Infrared spectra were obtained on a Perkin Elmer Spectrum 100 FT-IR spectrometer as KBr discs or nujol mulls, Raman spectra on a

12008 | Dalton Trans., 2014, 43, 12000–12012

Perkin Elmer Station 400F Raman spectrometer and MALDI mass spectra on a Bruker Biflex II spectrometer. Electrospray (ESI) mass spectra were measured on HP 5970 MSD and Waters spectrometers in the Mass Spectrometry Unit of the Research School of Chemistry, ANU. Elemental analyses were carried out by the Microanalytical Unit at the same School. X-ray crystallography Crystals suitable for X-ray crystallography were grown by slow evaporation of 1,2-dichloroethane (1, 2, 4), dichloromethane layered with methanol (8, 9, 11–14, 16) or dichloromethane layered with hexane (17, 20). Data were collected at 200 K on a Nonius-Kappa CCD diffractometer using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). Crystal data and details of data collection are given in Table S1.† Data were measured by use of COLLECT.36 The intensities of reflections were extracted and the data were reduced by use of the computer programs Denzo and Scalepack.37 The crystal structures were solved by direct methods38 and refined by use of the program CRYSTALS.39 Neutral atom scattering factors,40 the values of Δf‘ and Δf″, and mass attenuation coefficients41 were taken from standard compilations. Catalysis General procedure for the Heck–Mizoroki reaction. A mixture of aryl bromide (1 mmol), styrene (2 mmol), catalyst (0.005 mmol), base (2 mmol) and solvent (3 mL) was heated to 140 °C for 10 h and the progress of the reaction was monitored by GC. After the mixture had been cooled to room temperature, ethyl acetate (30 mL) was added and the mixture was washed successively with 1 M HCl and water. The organic phase was separated, dried (Na2SO4) and the solvents evaporated. The residue was passed down a silica gel column, eluting with ethyl acetate, to afford the coupled product in high purity. General procedure for the Suzuki–Miyaura reaction. A mixture of aryl bromide (1 mmol), phenylboronic acid (1.5 mmol), catalyst (0.005 mmol), base (2 mmol) and solvent (3 mL) was heated to 80 °C for 10 h, monitoring the progress of the reaction by GC. After the mixture had been cooled to room temperature, ethyl acetate (30 mL) was added and the mixture was washed successively with 1 M HCl and water. The organic phase was separated, dried (Na2SO4) and the solvents evaporated. Purification by column chromatography (silica gel, ethyl acetate) gave the coupled product in high purity. Attempted direct cyclopalladation of triphenylphosphine sulfide (a) A mixture of PdCl2 (0.1 g, 0.56 mmol) and LiCl (0.05 g, 1.12 mmol) in MeOH (5 mL) was stirred with gentle warming for 30 min. The red-brown solution was filtered through Celite into a solution of Ph3PvS (0.16 g, 0.56 mmol) in THF (7 mL). Almost immediately the mixture became turbid and a yellow orange precipitate slowly formed. After stirring the mixture at room temperature for 24 h, the solid was isolated by filtration,

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washed with MeOH and dried (225 mg). 31P NMR: δ 45.1, 44.9, 44.3, 43.3. (b) In a similar reaction to (a) above, a solution of NaOAc (0.093 g, 1.13 mmol) in MeOH (3 mL) was added to the THF solution of Ph3PvS prior to the addition of the palladium solution. After stirring at room temperature for 24 h, a dark brown/black mixture was obtained. Filtration of this suspension gave a dark brown solid which was washed with MeOH and dried (236 mg). 31P NMR: δ 45.1, 44.9, 44.3, 43.3.

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Syntheses 2-BrC6H4P(S)Ph2. To a solution of 2-BrC6H4PPh2 (4.0 g, 11 mmol) in CH2Cl2 (30 mL) was added elemental sulfur (0.4 g, 12 mmol) and the mixture was stirred at room temperature for 2 h. The slightly turbid solution was filtered and the solvent was removed in vacuo. The yellow gummy solid was recrystallised from hot EtOH to give the product as colourless crystals (4.15 g, 95%). M.p.: 124–126 °C. 1H NMR: δ 7.12–7.24 (m, 1H, aromatic), 7.24–7.38 (m, 2H, aromatic), 7.42–7.60 (m, 6H, aromatic), 7.64–7.72 (m, 1H, aromatic), 7.78–7.92 (m, 4H, aromatic). 13C NMR: δ 126.7 (d, 6.2 Hz), 126.9 (d, 11.1 Hz), 128.4 (d, 11.9 Hz), 131.3 (d, 87.2 Hz), 131.5 (d, 2.0 Hz), 132.0 (d, 11.1 Hz), 132.7 (d, 3.1 Hz), 132.8 (d, 88.0 Hz), 134.8 (d, 11.3 Hz), 135.4 (d, 7.0 Hz). 31P NMR: δ 46.4 (s). IR (KBr, cm−1): 636 (PvS str). ESI-MS (m/z): 375 [M + H]+. Anal. Calcd for C18H14BrPS: C 57.92, H 3.78, Br 21.41, P 8.30, S 8.59. Found: C 57.96, H 3.94, Br 21.19, P 8.42, S 8.87. 2-BrC6H4P(Se)Ph2. This was prepared similarly to the corresponding sulfide, with use of selenium powder (1.2 g, 15 mmol) in place of sulfur and the mixture was stirred at room temperature for 24 h. Recrystallisation from hot EtOH gave the product as colourless crystals (5.1 g, 92%). M.p.: 134–135 °C. 1H NMR: δ 7.12–7.22 (m, 1H, aromatic), 7.24–7.38 (m, 2H, aromatic), 7.42–7.58 (m, 6H, aromatic), 7.64–7.72 (m, 1H, aromatic), 7.82–7.96 (m, 4H, aromatic). 13C NMR: δ 127.0 (d, 7.0 Hz), 127.1 (d, 11.1 Hz), 128.5 (d, 12.6 Hz), 130.1 (d, 78.4 Hz), 131.6 (d, 3.0 Hz), 131.6 (d, 79.8 Hz), 132.7 (d, 10.8 Hz), 132.8 (d, 1.5 Hz), 135.0 (d, 11.2 Hz), 135.6 (d, 7.0 Hz). 31 P NMR: δ 37.7 (s, JSeP 744 Hz). 77Se NMR: δ −263.2 (d, JSeP 745 Hz). IR (KBr, cm−1): 567 (PvSe str). ESI-MS (m/z): 421 [M + H]+. Anal. Calcd for C18H14BrPSe: C 51.46, H 3.36, Br 19.02, P 7.37. Found: C 51.62, H 3.43, Br 19.12, P 7.24. 2-Me3SnC6H4PPh2. To a solution of 2-BrC6H4PPh2 (6.8 g, 20 mmol) in Et2O (100 mL), cooled to 0 °C, was added nBuLi (1.6 M in hexanes, 12.5 mL, 20 mmol) dropwise. After stirring for 30 min, Me3SnCl (1.0 M in hexanes, 20 mL, 20 mmol) was added slowly and the mixture was allowed to come to room temperature with stirring. The suspension was hydrolysed and the Et2O layer separated. The aqueous phase was extracted with Et2O (3 × 20 mL) and the combined organic phases were dried (MgSO4). After filtration, the solvent was removed in vacuo and the gummy solid, after recrystallisation from hot MeOH, gave the title compound as colourless crystals (6.7 g, 80%). M.p.: 55–56 °C. 1H NMR: δ 0.29 (d, JPH 1.1 Hz, JSnH 52.9, 55.1 Hz, 9H, Me), 7.10–7.20 (m, 1H, aromatic), 7.20–7.39 (m, 12H, aromatic), 7.49–7.70 (m, 1H, aromatic). 13C NMR: δ −6.8

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(d, JPC 9.9 Hz, JSnC 339, 355 Hz), 128.3 (d, JPC 6.3 Hz), 128.4 (s, JSnC 43.9 Hz), 128.8 (s, JSnC 9.7 Hz), 133.3 (d, JPC 18.5 Hz), 134.2 (s, JSnC 39.9 Hz), 136.0 (d, JPC 20.2 Hz, JSnC 39.2 Hz), 137.9 (d, JPC 10.8 Hz), 144.8 (d, JPC 1.8 Hz, JSnC 39.0, 41.6 Hz), 152.8 (d, JPC 66.0 Hz, JSnC 449, 470 Hz). 31P NMR: δ −3.5 (s, JSnP 40.9, 43.1 Hz). ESI-MS (m/z): 427 [M + H]+. Anal. Calcd for C21H23PSn: C 59.34, H 5.45 P 7.29. Found: C 59.68, H 5.08 P 7.00. This compound, m.p. 58–59 °C, was first prepared by Weichmann and Schmoll,42 who treated 1,2-dichlorobenzene successively with LiSnMe3 and LiPPh2. Our 1H and 31P NMR spectroscopic data agree reasonably well with those reported. 2-Me3SnC6H4P(S)Ph2. To a solution of 2-Me3SnC6H4PPh2 (1.8 g, 4.2 mmol) in CH2Cl2 (20 mL) was added elemental sulfur (0.15 g, 4.6 mmol) and the mixture was stirred at room temperature for 24 h. After filtration, the solvent was removed in vacuo and the gummy solid was recrystallised from hot EtOH (hot filtration) to give the product as colourless crystals (1.65 g, 85%). M.p.: 98–100 °C. 1H NMR: δ 0.14 (s, JSnH 53.1, 55.6 Hz, 9H, Me), 6.96–7.03 (m, 1H, aromatic), 7.18–7.24 (m, 1H, aromatic), 7.40–7.54 (m, 7H, aromatic), 7.58–7.65 (m, 4H, aromatic), 7.83–7.85 (m, 1H, aromatic). 13C NMR: δ −3.95 (s, JSnC 353.8, 371.0 Hz), 127.1 (d, 12.7 Hz), 128.4 (d, 11.4 Hz), 130.1 (d, 3.5 Hz), 131.4 (d, 2.4 Hz), 132.4 (d, 10.3 Hz), 132.7 (d, 15.1 Hz), 133.3 (d, 84.0 Hz), 138.6 (d, 18.4 Hz), 139.5 (s), 149.6 (d, 24.3 Hz). 31P NMR: δ 48.3 (s, JSnP 46.6, 48.7 Hz). IR (KBr, cm−1): 636 (PvS str). ESI-MS (m/z): 459 [M + H]+. Anal. Calcd for C21H23PSSn: C 55.18, H 5.07, P 6.78, S 7.01. Found: C 54.97, H 5.13, P 6.53, S 7.18. 2-Me3SnC6H4P(Se)Ph2. This was prepared similarly to the corresponding sulfide, with use of selenium powder (0.35 g, 4.4 mmol) in place of sulfur. After 24 h, the dark suspension was filtered through Celite and the filtrate was evaporated to dryness. Recrystallisation from hot EtOH gave the product as colourless crystals (2.0 g, 94%). M.p.: 138–140 °C. 1H NMR: δ 0.13 (s, JSnH 54.4, 55.2 Hz, 9H, Me), 6.88–6.95 (m, 1H, aromatic), 7.15–7.21 (m, 1H, aromatic), 7.37–7.53 (m, 7H, aromatic), 7.61–7.68 (m, 4H, aromatic), 7.82–7.84 (m, 1H, aromatic). 13C NMR: δ −3.64 (s, JSnC 354.0, 370.1 Hz), 127.2 (d, 11.4 Hz), 128.5 (d, 11.0 Hz), 130.0 (d, 3.5 Hz), 131.5 (d, 2.4 Hz), 132.4 (d, 17.1 Hz), 132.6 (d, 11.7 Hz), 132.9 (d, 10.6 Hz), 137.8 (s), 138.7 (d, 20.3 Hz), 150.6 (d, 24.7 Hz). 31P NMR: δ 40.83 (s, JSeP 712 Hz, JSnP 50.0, 52.0 Hz). 77Se NMR: δ 71.8 (d, JSeP 712 Hz, unresolved JSeSn 10.1 Hz). IR (KBr, cm−1): 565 (PvSe str). ESI-MS (m/z): 505 [M + H]+. Anal. Calcd for C21H23PSeSn: C 50.04, H 4.60, P 6.15. Found: C 50.40, H 4.69, P 6.07. cis-[Pt{κ2-2-C6H4P(S)Ph2}2] (1). (a) To a solution of 2-BrC6H4P(S)Ph2 (0.6 g, 1.6 mmol) in Et2O (100 mL) cooled to −78 °C was added nBuLi (1.6 M in hexanes, 1.0 mL, 1.6 mmol) and the mixture was stirred for 30 min. To the clear yellow solution was added solid [PtI2(COD)] (0.4 g, 0.7 mmol) and stirring was continued at −78 °C for 4 h, then at room temperature overnight. The very pale yellow solid was filtered off, extracted with CH2Cl2, and the solution was filtered. Methanol was added to the filtrate and the volume was reduced in vacuo. The pale yellow solid that precipitated was isolated by fil-

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tration, washed with MeOH, and dried (0.45 g, 80%). 1H NMR: δ 6.79–6.86 (m, 1H, aromatic), 6.89–6.95 (m, 1H, aromatic), 7.05–7.10 (m, 1H, aromatic), 7.37–7.41 (m, 1H, aromatic), 7.43–7.57 (m, 6H, aromatic), 7.73–7.80 (m, 4H, aromatic). 31 P NMR: δ 51.6 (s, JPtP 79.0 Hz). IR (KBr, cm−1): 623 (PvS str). ESI-MS (m/z): 782 [M + H]+. Anal. Calcd for C36H28P2PtS2: C 55.31, H 3.61, P 7.92, S 8.20. Found: C 55.13, H 3.71, P 8.14, S 8.11. (b) To a solution of [Pt(κ2-2-C6H4PPh2)2] (45 mg, 0.06 mmol) in toluene (10 mL) was added sulfur (4 mg, 0.12 mmol) and the mixture refluxed for 24 h. The pale yellow solution was evaporated to dryness and the residue was recrystallised from CH2Cl2–MeOH to give 1 as a pale yellow solid (38 mg, 78%). 31P NMR: δ 51.6 (s, JPtP 78.9 Hz). cis-[Pd{κ2-2-C6H4P(S)Ph2}2] (3). To a solution of 2-Me3SnC6H4P(S)Ph2 (0.46 g, 1.0 mmol) in CH2Cl2 (10 mL) was added [PdCl2(COD)] (0.14 g, 0.5 mmol) and the yellow solution was refluxed for 24 h. Hexane was added to the cooled suspension and the sandy-coloured solid was filtered off, washed with hexane and extracted with CH2Cl2. Methanol was added to the filtered extract and the volume was reduced in vacuo to precipitate complex 3 as a pale yellow solid, which was filtered off, washed with MeOH and dried (0.32 g, 94%). 1H NMR: δ 6.72–6.79 (m, 1H, aromatic), 6.84–6.91 (m, 1H, aromatic), 7.05–7.11 (m, 1H, aromatic), 7.32–7.35 (m, 1H, aromatic), 7.43–7.57 (m, 6H, aromatic), 7.73–7.81 (m, 4H, aromatic). 31 P NMR: δ 46.9 (s). IR (KBr, cm−1): 625 (PvS str). ESI-MS (m/z): 693 [M + H]+. Anal. Calcd for C36H28P2PdS2: C 62.39, H 4.07, S 9.25. Found: C 62.30, H 4.13, S 9.09. cis-[M{κ2-2-C6H4P(Se)Ph2}2] [M = Pt (2), Pd (4)]. To a solution of 2-Me3SnC6H4P(Se)Ph2 (0.48 g, 0.95 mmol) in CH2Cl2 (10 mL) was added [MCl2(COD)] (M = Pt, 0.17 g, 0.45 mmol; Pd, 0.13 g, 0.46 mmol) and the mixture was refluxed for 24 h. Hexane was added to the suspension and the yellow solid was filtered off, washed with hexane and dissolved in CH2Cl2. Addition of methanol and evaporation of the solution in vacuo caused the product (2 or 4) to precipitate as a pale yellow solid, which was filtered off, washed with MeOH and dried. Complex 2: (0.27 g, 68%). 1H NMR: δ 6.72–6.24 (m, 14H, aromatic), 7.34–7.78 (m, 34H, aromatic), 8.22–8.34 (m with broad Pt satellites, JPtH ca. 31 Hz, 1H, aromatic). 31P NMR: δ 36.5 (s, JPtP 73.0 Hz, 1JSeP 506 Hz, 3JSeP not observed, 4JPP 0.7 Hz) (trans isomer), 37.2 (s, JPtP 70.6 Hz, 1JSeP 534 Hz, 3JSeP 26.9 Hz, 4JPP 2.2 Hz) (cis isomer). cis/trans ratio ca. 3 : 1. 77Se NMR: δ −130.2 (dd, 1JSeP 532 Hz, 3JSeP 26.7 Hz, JSePt 230 Hz) (cis isomer), 42.5 (d, 1JSeP 505 Hz, 3JSeP and JSePt not observed) (trans isomer). IR (KBr, cm−1): 551 (PvSe str). ESI-MS (m/z): 876 [M]+. Anal. Calcd for C36H28P2PtSe2: C 49.38, H 3.22, P 7.08. Found: C 49.01, H 3.23, P 7.02. Complex 2 could also be prepared as follows. To a solution of [Pt(κ2-2-C6H4PPh2)2] (50 mg, 0.07 mmol) in toluene (10 mL) was added selenium powder (11 mg, 0.14 mmol) and the mixture was refluxed for 24 h. The solvent was removed in vacuo and the residue was extracted with CH2Cl2. The suspension was filtered through Celite to remove some insoluble black material, and MeOH added to the filtrate. Partial evaporation resulted in the pre-

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cipitation of a pale orange solid, which was isolated by filtration, washed with MeOH and dried in vacuo (23 mg, 38%). 31 P NMR: δ 37.2 (s, JPtP 68.2 Hz, 1JSeP 532 Hz, 3JSeP 26.6 Hz, 4 JPP 3.0 Hz) (cis isomer). Complex 4: (0.33 g, 92%). 1H NMR: δ 6.45–6.71 (m, 1H, aromatic), 6.80–6.86 (m, 1H, aromatic), 6.99–7.04 (m 1H, aromatic), 7.17–7.19 (m, 1H, aromatic), 7.43–7.55 (m, 6H, aromatic), 7.72–7.79 (m, 4H, aromatic). 31P NMR: δ 32.6 (s, 1 JSeP 557 Hz, 3JSeP 29.8, 4JPP 1.9 Hz). 77Se NMR: δ −119.5 (dd, 1 JSeP 557 Hz, 3JSeP 29.7 Hz). IR (KBr, cm−1): 552 (PvSe str). ESI-MS (m/z): 787 [M]+. Anal. Calcd for C36H28P2PdSe2: C 54.95, H 3.59. Found: C 54.72, H 3.62. [Pd2(μ-Cl)2{κ2-2-C6H4P(S)Ph2}2] (5). To a solution of 2-Me3SnC6H4P(S)Ph2 (0.16 g, 0.35 mmol) in CH2Cl2 (10 mL) was added [PdCl2(COD)] (0.10 g, 0.35 mmol) and the mixture was stirred for 24 h. The yellow precipitate of 5 was filtered off, washed with MeOH and dried in vacuo (0.13 g, 82%). 1H NMR: δ 6.6–6.8 (m, 2H, aromatic), 6.9–7.1 (m, 2H, aromatic), 7.4–7.9 (m, 10H, aromatic). 31P NMR: δ 46.7 (s), 47.8 (s). Raman (cm−1): 306, 282 (Pd–Cl str). MALDI-MS (m/z): 835 [M − Cl]+. Anal. Calcd for C36H28Cl2P2Pd2S2: C 49.68, H 3.24, Cl 8.15, S 7.37. Found: C 49.56, H 3.25, Cl 8.37, S 7.14. [Pd2(μ-Cl)2{κ2-2-C6H4P(Se)Ph2}2] (6). This was prepared analogously to 5 from 2-Me3SnC6H4P(Se)Ph2 (0.20 g, 0.4 mmol) and [PdCl2(COD)] (0.11 g, 0.4 mmol) to give an orange precipitate which was filtered off, washed with MeOH and dried (0.12 g, 87%). 1H NMR: δ 6.5–7.2 (m, 6H, aromatic), 7.4–7.8 (m, 8H, aromatic). 31P NMR: δ 25.8 (s, 77Se satellites not observed), 26.8 (s, 77Se satellites not observed). Raman (cm−1): 301, 269 (Pd–Cl str). MALDI-MS (m/z): 929 [M − Cl]+. Anal. Calcd for C36H28Cl2P2Pd2Se2: C 44.85, H 2.93, Cl 7.35. Found: C 44.80, H 2.96, Cl 7.72. [Pd{κ2-2-C6H4P(S)Ph2}{κ2-2-C6H4P(Se)Ph2}] (7). (a) A suspension of 3 (45 mg, 0.06 mmol) and 4 (51 mg, 0.06 mmol) in CH2Cl2 (40 mL) was refluxed for 24 h, during which time the solid dissolved. Methanol was added and the solution was evaporated in vacuo, causing a pale yellow solid to precipitate. This was isolated by filtration, washed with MeOH and dried in vacuo (89 mg). 31P NMR spectroscopy showed this to be a 1 : 1 : 2 mixture of 3 : 4 : 7. Attempts to separate this mixture by chromatography were unsuccessful. 1H NMR: δ 6.6–7.9 (m, 28H, aromatic). 31P NMR: δ 31.3 (d, 4JPP 1.0 Hz, JSeP 555 Hz), 48.1 (d, 4JPP 1.0 Hz, JSeP 27.4 Hz) (complex 7), 32.6 (s, 1JSeP 557 Hz, 3JSeP 29.8, 4JPP 1.9 Hz) (complex 4), 46.9 (s) (complex 3). 77Se NMR: δ −114.2 (dd, 1JSeP 555 Hz, 3JSeP 26.4 Hz) (complex 7), −119.6 (dd, 1JSeP 556 Hz, 3JSeP 29.8 Hz) (complex 4). ESI-MS (m/z): 693 [M + H]+ (complex 3), 741.0 [M + H]+ (complex 7), 786.9 [M + H]+ (complex 4). (b) To a suspension of 5 (50 mg, 0.05 mmol) in CH2Cl2 (40 mL) was added 2-Me3SnC6H4P(Se)Ph2 (60 mg, 0.1 mmol) and the mixture was refluxed for 24 h. The solution was evaporated to dryness and the residue was dissolved in CH2Cl2. Addition of MeOH and partial evaporation caused a pale yellow solid to precipitate, which was isolated, washed with MeOH and dried in vacuo (80 mg). The 31P NMR spectrum was identical to that in (a).

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(c) To a suspension of 6 (50 mg, 0.05 mmol) in CH2Cl2 (40 mL) was added 2-Me3SnC6H4P(S)Ph2 (50 mg, 0.1 mmol) and the mixture was refluxed for 24 h. The orange solution was evaporated to dryness and the residue was taken up in CH2Cl2. Methanol was added to the solution and the volume was reduced in vacuo, causing an orange solid to precipitate. This was filtered off, washed with MeOH and dried in vacuo (51 mg). The 31P NMR spectrum was identical with that in (a). [Pd2(μ-OAc)2{κ2-2-C6H4P(S)Ph2}2] (8). A solution containing a mixture of 3 (105 mg, 0.15 mmol) and [Pd(OAc)2]3 (34 mg, 0.05 mmol) in CH2Cl2 (60 mL) was stirred at room temperature for 48 h. Hexane was then added and the volume was reduced in vacuo. The precipitated yellow solid was filtered off, washed with hexane and dried (120 mg, 86%). 1H NMR: δ 2.09 (s, 6H, Me), 6.6–8.1 (m, 28H, aromatic). 31P NMR: δ 47.0 (s). IR (nujol, cm−1): 1588, 1578 (COO), 1415 (C–O), 622 (PvS str). ESI-MS (m/z): 941 [M + Na]+. Anal. Calcd for C40H34O4P2Pd2S2: C 52.36, H 3.73, S 6.99. Found: C 52.10, H 3.75, S 6.79. [Pd(κ2-O,O′-acac){κ2-2-C6H4P(S)Ph2}] (9). To a suspension of 5 (100 mg, 0.1 mmol) in CH2Cl2 (20 mL) was added Na(acac) (50 mg, 0.4 mmol) in MeOH (20 mL). Almost immediately the solid dissolved and after being stirred for 10 min, the solution was evaporated to dryness. The yellow solid was dissolved in CH2Cl2, the solution was filtered through Celite, and MeOH added to the filtrate. The yellow solid that precipitated when the solution was evaporated in vacuo was isolated, washed with MeOH and dried (106 mg, 93%). 1H NMR: δ 1.95 (s, 3H, Me), 2.07 (s, 3H, Me), 5.33 (s, 1H, CH), 6.7–6.8 (m, 1H, aromatic), 6.95–7.05 (m, 1H, aromatic), 7.2–7.3 (m, 1H, aromatic), 7.45–7.65 (m, 6H, aromatic), 7.7–7.9 (m, 5H, aromatic). 31P NMR: δ 48.5 (s). ESI-MS (m/z): 399 [M − acac]+. Anal. Calcd for C23H21O2PPdS: C 55.38, H 4.24, S 6.43. Found: C 55.40, H 4.40, S 6.43. [Pd(κ2-O,O′-acac){κ2-2-C6H4P(Se)Ph2}] (10). To a suspension of 6 (100 mg, 0.1 mmol) in CH2Cl2 (20 mL) was added Na(acac) (50 mg, 0.4 mmol) in MeOH (20 mL). Almost immediately the solid dissolved and after the mixture had been stirred for 10 min, the solvent was removed in vacuo. The residue was dissolved in CH2Cl2 and the solution, after filtration through Celite, was treated with MeOH. The volume of the solution was reduced in vacuo, and the solution became turbid. After 24 h at −18 °C, 10 had formed as a golden-yellow solid, which was isolated, washed with MeOH and dried (93 mg, 82%). 1 H NMR: δ 1.92 (s, 3H, Me), 2.06 (s, 3H, Me), 5.32 (s, 1H, CH), 6.6–6.7 (m, 1H, aromatic), 6.95–7.05 (m, 1H, aromatic), 7.2–7.3 (m, 1H, aromatic), 7.45–7.7 (m, 6H, aromatic), 7.7–7.8 (m, 4H, aromatic), 7.8–7.9 (m, 1H, aromatic). 31P NMR: δ 27.0 (s, JSeP 501 Hz). 77Se NMR: δ −61.7 (d, JSeP 501 Hz). ESI-MS (m/z): 447 [M − acac]+. Anal. Calcd for C23H21O2PPdSe: C 50.62, H 3.88. Found: C 50.36, H 4.05. [PdCl{κ2-2-C6H4P(S)Ph2}(PPh3)] (11). To a suspension of 5 (100 mg, 0.1 mmol) in CH2Cl2 (20 mL) was added solid PPh3 (61 mg, 0.23 mmol). Almost immediately, a clear yellow solution was obtained, which was stirred for 10 min. Hexane was added and the solution was evaporated in vacuo. The precipitated pale yellow solid was isolated by filtration, washed with hexane and dried (150 mg, 94%). 1H NMR: δ 6.4–6.5 (m, 1H,

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aromatic), 6.6–6.8 (m, 3H, aromatic), 7.2–7.7 (m, 21H, aromatic), 7.8–8.0 (m, 4H, aromatic). 31P NMR: δ 34.4 (s), 43.8 (s) (cis isomer), 17.5 (d, JPP 58.2 Hz), 50.2 (d, JPP 58.5 Hz) (trans isomer). cis/trans ratio: 12 : 1. MALDI-MS (m/z): 661 [M − Cl]+. Anal. Calcd for C36H29ClP2PdS: C 61.99, H 4.19, Cl 5.08, S 4.60. Found: C 61.90, H 4.27, Cl 4.64, S 4.35. [PdCl{κ2-2-C6H4P(Se)Ph2}(PR3)] {R = Ph (13), 4-tolyl (15)}. In a similar reaction to that of complex 11 described above, complex 6 (100 mg, 0.10 mmol) in CH2Cl2 (20 mL) was treated with solid PR3 (PPh3, 55 mg; P(tolyl)3, 65 mg; 0.22 mmol) to give the title products as yellow solids. R = Ph (13): 151 mg, 98%. 1H NMR: δ 6.3–6.8 (m, 4H, aromatic), 7.1–7.7 (m, 21H, aromatic), 7.7–7.9 (m, 4H, aromatic). 31 P NMR: δ 27.3 (s, JSeP 529 Hz), 32.6 (s, JSeP 96.2 Hz) (cis isomer), 16.4 (d, JPP 61.9 Hz), 31.1 (d, JPP 61.6 Hz) (trans isomer). cis/trans ratio: 10 : 1. 77Se NMR: δ 65.4 (dd, JSeP 96.4, 529 Hz) (cis isomer); trans isomer not observed. MALDI-MS (m/z): 709 [M − Cl]+. Anal. Calcd for C36H29ClP2PdSe: C 58.09, H 3.93, Cl 4.76. Found: C 58.36, H 4.18, Cl 4.42. R = tolyl (15): 145 mg, 87%. 1H NMR: δ 2.28 (s, 9H, Me), 6.3–6.5 (m, 1H, aromatic), 6.5–6.6 (m, 2H aromatic), 6.7–6.8 (m, 1H, aromatic), 6.9–7.0 (m, 6H, aromatic), 7.2–7.4 (m, 6H, aromatic), 7.4–7.6 (m, 6H, aromatic), 7.8–7.9 (m, 4H, aromatic). 31P NMR: δ 26.6 (d, JPP 5.6 Hz, JSeP 532 Hz), 30.5 (d, JPP 5.6 Hz, JSeP 98.4 Hz) (cis isomer). 77Se NMR: δ 52.3 (dd, JSeP 98.7, 532 Hz) (cis isomer); trans isomer not observed. ESI-MS (m/z): 751 [M − Cl]+. Anal. Calcd for C39H35ClP2PdSe: C 59.56, H 4.49, Cl 4.51. Found: C 59.25, H 4.41, Cl 4.32. [Pd{κ2-2-C6H4P(X)Ph2}(κ2-OC6H4CHvNC6H4-4-R)] {X = S, R = OMe (17), NO2 (18); X = Se, R = OMe (19), NO2 (20)}. Typical procedure for complexes containing Schiff base ligands: to a solution of Schiff base (0.2 mmol) in a 4 : 1 mixture of CH2Cl2–MeOH (10 mL) was added LiOH (0.25 mmol) followed by the chloro-bridged palladium complex (0.1 mmol). After stirring at room temperature for 24 h the solvent was removed in vacuo and the residue was taken up in CH2Cl2. The suspension was filtered through Celite, hexane was added to the filtrate and the volume was reduced. The precipitated solid was isolated by filtration, washed with hexane and dried in vacuo. Complex 17: yellow solid, 94% yield. 1H NMR: δ 3.83 (s, 3H, OMe), 6.52–6.57 (m, 1H, aromatic), 6.76–6.82 (m, 1H aromatic), 6.89 (d, J 8.7 Hz, 2H, aromatic), 6.99–7.00 (m, 5H, aromatic), 7.26–7.34 (m, 2H, aromatic), 7.44–7.70 (m, 10H, aromatic), 7.93 (s, 1H, CHvN), 8.19–8.22 (m, 1H, aromatic). 31P NMR: δ 45.5 (s). ESI-MS (m/z): 626 [M + H]+. Anal. Calcd for C32H26NO2PPdS: C 61.40, H 4.19, N 2.24. Found: C 61.63, H 4.35, N 2.11. Complex 18: orange-red solid, 92% yield. 1H NMR: δ 6.54–6.59 (m, 1H, aromatic), 6.76–6.82 (m, 1H, aromatic), 7.01–7.11 (m, 2H, aromatic), 7.17 (dd, J 1.8, 8.1 Hz, 1H, aromatic), 7.25–7.29 (m, 2H, aromatic), 7.31–7.38 (m, 2H, aromatic), 7.46–7.52 (m, 4H, aromatic), 7.58–7.67 (m, 6H, aromatic), 7.92 (s, 1H, CHvN), 8.15–8.19 (m, 1H, aromatic), 8.23–8.28 (m, 2H, aromatic). 31P NMR: δ 45.9 (s). ESI-MS (m/z): 641 [M + H]+. Anal. Calcd for C31H23N2O3PPdS: C 58.07, H 3.62, N 4.37, S 5.00. Found: C 57.92, H 3.62, N 4.13, S 4.87.

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Complex 19: yellow solid, 86% yield. 1H NMR: δ 3.82 (s, 3H, OMe), 6.53 (dd, J 7.2, 7.5 Hz, 1H, aromatic), 6.70 (dd, J 8.1, 10.2 Hz, 1H, aromatic), 6.88 (d, J 8.6 Hz, 2H, aromatic), 6.98–7.16 (m, 5H, aromatic), 7.27–7.35 (m, 2H, aromatic), 7.42–7.70 (m, 10H, aromatic), 7.88 (s, 1H, CHvN), 8.24 (dd, J 2.7, 7.8 Hz, 1H, aromatic). 31P NMR: δ 25.8 (s, JSeP 501 Hz). 77 Se NMR: δ −45.7 (d, JSeP 501 Hz). ESI-MS (m/z): 674 [M + H]+. Anal. Calcd for C32H26NO2PPdSe: C 57.12, H 3.89, N 2.08. Found: C 56.98, H 4.07, N 1.87. Complex 20: orange-red solid, 86% yield. 1H NMR: δ 6.52–6.58 (m, 1H, aromatic), 6.67–6.73 (m, 1H, aromatic), 7.00–7.08 (m, 2H, aromatic), 7.16 (dd, J 1.8, 8.1 Hz, 1H, aromatic), 7.25–7.36 (m, 4H, aromatic), 7.45–7.51 (m, 4H, aromatic), 7.56–7.68 (m, 6H, aromatic), 7.87 (s, 1H, CHvN), 8.19 (dd, J 0.9, 3.3 Hz, 1H, aromatic), 8.21–8.26 (m, 2H, aromatic). 31 P NMR: δ 25.9 (s, JSeP 497 Hz). 77Se NMR: δ −41.6 (d, JSeP 497 Hz). ESI-MS (m/z): 689 [M + H]+. Anal. Calcd for C31H23N2O3PPdSe: C 54.13, H 3.37, N 4.07. Found: C 54.09, H 3.45, N 3.45.

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