DOI: 10.1002/chem.201402626

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& Photochemistry

A Theoretical Investigation of Photochemical Reactions of an Isolable Silylene with Benzene Ming-Der Su*[a, b]

Abstract: The mechanisms of photochemical insertion reactions are investigated theoretically using the model system, an isolable dialkylsilylene and benzene, using the CAS(10,10)/6-31G(d) and MP2-CAS-(10,10)/6-311 + + G(df,pd)//CAS(10,10)/6-31G(d) methods. The structures of the conical intersections, which play a key role in such photoinsertion reactions, are determined to provide a qualitative explanation of the reaction pathways. The model investigation demonstrates that the preferred reaction route for the

isolable dialkylsilylene with benzene is as follows: reactants ! Franck–Condon region ! conical intersection ! sevenmembered-ring photoproduct. The theoretical findings suggest that the singlet excited dialkylsilylene should attack benzene in the perpendicular conformation, and that no silyl radicals should exist during these photoinsertion reactions. The results obtained allow a number of predictions to be made.

Introduction Silylenes, the bivalent silicon species corresponding to the well-known carbenes in organic chemistry, are the simplest silicon unsaturated compounds, and have been generated as short-lived intermediates in many thermal and photochemical reactions of organosilicon precursors.[1] Recently, much attention has been focused on the isolable compounds of silylenes, because such heavy carbene analogues are fascinating molecules in their own right, and continue to be the subject of widespread academic research.[2] Thanks to many outstanding synthetic chemists, it is now possible to synthesize and structurally characterize these species bearing a bivalent silicon center if they are kinetically and thermodynamically stabilized by appropriate substitution (see 1,[3] 2,[4] 3,[5] 4,[6] 5,[7] and 6[8]). Because of their unique geometrical and electronic structures, such molecules are particularly interesting and important from both an academic and a practical viewpoint.[1, 2] Nevertheless, there have been very few reports on the excited-state reactions of silylenes because of their intrinsic transient nature.[9] Recently, Kira and co-workers reported the first intermolecular reaction of an excited silylene with benzene [Eq. (1)].[10] That is, the irradiation of the dialkylsilylene 2,2,5,5tetrakis(trimethylsilyl)silacycclopentane-1,1-diyl (1) with filtered light (l > 420 nm) at room temperature in benzene affords [a] Prof. M.-D. Su Department of Applied Chemistry National Chiayi University, Chiayi 60004 (Taiwan) [b] Prof. M.-D. Su Department of Medicinal and Applied Chemistry Kaohsiung Medical University, Kaohsiung 80708 (Taiwan) E-mail: [email protected] Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201402626. Chem. Eur. J. 2014, 20, 9419 – 9423

the corresponding silacycloheptatriene (7) in quantitative yield.[10a] Moreover, the photochemical addition of 1 to various C=C bonds occurs smoothly to produce the substituted silepin (8) if the double bond is not sterically hindered [Eq. (2)].[10b]

By analyzing the multiplicity of the excited state of an isolable dialkylsilylene (1), Kira and co-workers concluded that the singlet nature of the excited state responsible for the photoreaction of 1 is evidenced by fluorescence in the presence of benzene.[10b] They thus proposed a mechanism in which the reaction of 1* with benzene can be estimated by analogy with 9419

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Full Paper silyl radical substitution.[11] Because 1* is a singlet 1,1-biradical in nature, its addition to benzene gives the 1,3-biradical intermediate. As a result, successive cyclization to the corresponding silanorcaradiene followed by CC single-bond cleavage leads to the final silacycloheptatriene 7 (Scheme 1).[2n, 10a] Nevertheless, such a study has not yet been confirmed by any kind of theoretical calculation or experimental evidence. In fact, as far as we are aware, no quantum chemical studies have yet been performed on the photochemical reactions of the first isolable dialkylsilylene 1.

Scheme 1.

To rationalize the photochemical processes shown in Equations (1) and (2), we performed a theoretical investigation of the photochemical insertion reaction of dialkylsilylene 1. In this work, we provide a deeper insight into the unsolved mechanism of dialkylsilylene photoinsertion reactions. In particular, it will be shown below that the conical intersections (CIs)[12] play a crucial role in the photochemical reactions of isolable dialkylsilylenes. We envision that the present combination of observed experimental works and theoretical examinations will provide a comprehensive understanding of the excited-state behavior of the isolable dialkylsilylene 1.

Methodology The complete active space self-consistent field (CASSCF) calculations were performed by using the multiconfigurational selfconsistent field (MCSCF) program released in Gaussian 09.[13] The active space for describing the photoreaction of an isolable dialkylsilylene comprises ten electrons in ten orbitals, that is, six p-p orbitals plus two CC orbitals (s and s*) for benzene and two frontier orbitals for the dialkylsilylene (9). The CASSCF method was used with the 6-31G(d) basis sets for geometry optimization (vide infra). The optimization of conical intersections was achieved in the (f < M- > 2)-dimensional intersection space using the method of Bearpark et al.[14] implemented in the Gaussian 09 program. Each stationary point was characterized by its harmonic frequencies computed analytically at the CASSCF level. To correct the energetics for dynamic electron correlation, we used the multireference Møller–Plesset (MP2-CAS) algorithm[15] as implemented in the program package Gaussian 09. Unless otherwise noted, the relative energies given in the text are those determined at the MP2-CAS(10,10)/6-311 + + G(df,pd) level using the CAS(10,10)/6-31G(d) (hereafter called MP2-CAS and CASSCF, respectively) geometry. Chem. Eur. J. 2014, 20, 9419 – 9423

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The Geometry of an Isolable Dialkylsilylene The structure of the isolable dialkylsilylene 1 has already been determined by X-ray crystal analysis,[3] so its geometry was first optimized at the CASSCF level of theory using the 6-31G(d) basis set in order to test its reliability. It should be mentioned here that we used the SiH3 substituents in 9 rather than the SiMe3 groups in 1 because of the constraints of available CPU time and disk space. The main geometrical parameters of 9 are summarized in Figure S1 (Supporting Information), together with some known experimental values of 1.[3] From Figure S1, reasonable agreement is seen with calculated and experimental values in the central SiC bond lengths, some SiCH3 bond lengths, and the aCSiC bond angle, with variations of only 0.016  in the bond lengths and 1.18 in the bond angle, bearing in mind that the real molecule 1 possesses bulkier substituents. We therefore believe that the present model with the current method (CASSCF/6-31G(d)) employed in this study should provide reliable information for a discussion of the reaction mechanism, for which experimental data are still not available.

General Considerations According to one experimental study performed by Kira and co-workers,[10b] the triplet 3B1 state of dialkylsilylene 1 does not participate in such photoinsertion reactions because of the strongly forbidden nature of the intersystem crossing from 1B1 to 3B1 of 1.[10b, 16] Triplet states therefore play no role in the reactions studied in the present work. For these reasons, the photochemical reactions of 1 should proceed on singlet surfaces, and should only involve the sp(n) ! 3p transition, as already mentioned in the experimental work.[10b] We shall therefore focus on singlet surfaces from now on. Compound 1 was already determined to be a singlet in the ground state (1A1), and should have one low-lying excited state (1B1) with singlet 1,1-diradical nature.[3] In other words, this singlet excited state of 1 (and 9) has one valence electron in each of two nonbonding orbitals on the silicon center (10 a in Scheme 2). Then, in this singlet excited state, the two valence orbitals can be considered to hybridize to form (s + p) and (sp) orbitals. That is to say, in this singlet excited state, one electron occupies a (s + p) orbital, with the other electron occupying a (sp) or-

Scheme 2.

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Figure 1. The minimum-energy pathway of dialkylsilylene (9) with benzene along the distance coordinate between 9 and benzene optimized for the S0 and S1 states at the CAS(10,10)/6-31G(d) level of theory.

bital (see 10 b). Then, two hybridized orbitals of the singlet excited dialkylsilylene would attack one CC s orbital of benzene (see 11) to give the final product (12). In the present work, we use the molecular orbital model as outlined in Scheme 2 to search for the CI of the photochemical reaction of 9 and benzene. Figure 1 shows the qualitative potential energy surfaces for the S0 and S1 states of the whole system as a function of the distance between 9 and benzene (i.e., the distance r).[17] The geometrical structure of dialkylsilylene (9) attacking benzene, as studied in this work, prefers to adopt the perpendicular (similar to tetrahedral) conformation because of their electronic structures rather than because of any steric effects caused by the substituents (see 11 in Scheme 2). As seen in Figure 1, the potential energy surfaces of S0 and S1 go up when dialkylsilylene 9 approaches benzene. In consequence, S0 and S1 become degenerate at a geometry around r = 1.8  (vide infra), as shown in Figure 1. In other words, this excitation removes the barrier when the excited dialkylsilylene 9 becomes close to benzene. Besides, the formation of such a degenerate point provides further evidence for an enhanced intermolecular closeness between 9 and benzene, and possibly for the existence of a conical intersection, where decay to the ground state can be fully efficient. Accordingly, we utilize the above results to interpret the mechanism for the photochemical insertion reactions of 9 and benzene in the following section.

Results and Discussion According to the above discussion, there is only one kind of reaction pathway for the photochemical insertion reaction on the singlet excited potential energy surface of 9 and benzene. Figure 2 contains all the relative energies of the various points with respect to the energy of the reactant, 9. The structures of the various critical points on the possible mechanistic pathway of Figure 2 are also shown in the same figure. Cartesian coordiChem. Eur. J. 2014, 20, 9419 – 9423

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Figure 2. Energy profiles for the photochemical insertion mode of a stable dialkylsilylene (9) and benzene. The abbreviations FC, TS, and CI stand for Frank–Condon, transition state, and conical intersection, respectively. The relative energies were obtained at the MP2-CAS-(10,10)/6-311 + + G(df,pd)// CAS(10,10)/6-31G(d) and CAS(10,10)/6-31G(d) (in parentheses) levels of theory. The selected geometrical parameters of CASSCF optimized structures of the stationary points are also given. Hydrogen atoms are omitted for clarity. The thick arrows indicate the main atomic motions in the TS-1 eigenvector. The derivative coupling and gradient difference vectors (those which lift the degeneracy) are computed with CASSCF at the conical intersection CI-1. For more information see the text.

nates and energetics calculated for the various points using the CASSCF and MP2-CAS methods are available in the Supporting Information. In the first step, the reactant (9) is promoted to its excited singlet state by a vertical excitation, as shown on the left-hand side of Figure 2. Our MP2-CAS vertical excitation energy to the lowest excited S1 state of 9 was calculated to be 294 kJ mol1. Comparison with the corresponding experimental value of at least 420 nm (= 285 kJ mol1 in energy)[10] indicates that the present calculations provide a good estimate of the relative energies for the isolable dialkylsilylene system. After the vertical excitation process, the molecule is situated on the excited singlet surface but still possesses the S0 (ground-state) geometry (FC). From the point reached by the vertical excitation, the molecule relaxes to reach an S1/S0 CI-1, where the photoexcited system decays nonradiatively to S0.

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Full Paper Along the contacting distance r, a conical intersection, S1/S0 CI1, is obtained (Figure 1). The geometry at the conical intersection S1/S0 CI-1 of C1 symmetry is given in Figure 2. Its contacting distances were calculated to be 2.18 and 2.55  for Si(central)C3 and Si(central)C4, respectively. Our computational results predicted that the energy of S1/S0 CI-1 lies 213 kJ mol1 above 9 and benzene and 81 kJ mol1 below FC and benzene at the MP2-CAS level of theory. Funneling through the CI, different reaction pathways on the ground-state surface may be predicted by following the derivative coupling vector or the gradient difference vector directions.[12] According to the results presented in Figure 2, the gradient difference vector is mainly related to the SiC3C4 stretching mode that gives the seven-membered-ring product (12) on the S0 surface, whereas the derivative coupling vector gives the asymmetric C3C4 bending motion that may lead to a vibrationally hot 9-S0 species. In addition, our present computational results demonstrate that this path channel is a one-step process (the direct route), which only involves the S1/S0 CI-1 point. The computations also predict that the path of the photochemical insertion reaction should be a barrierless process. That is, starting from the FC point, dialkylsilylene (9) reacts with benzene and then enters an extremely efficient decay channel, S1/S0 CI-1. After decay at this conical intersection point, the insertion photoproduct 12 as well as the initial reactants (9 and benzene) can be reached through a barrierless ground-state relaxation pathway. Accordingly, the process of the photochemical reaction path can be represented as follows: Path (photo): 9 + benzene!FC + benzene!S1/S0 CI-1!12. The dark reaction on the ground-state potential energy surface is also examined. The search for transition states on the S0 surface near the structure of S1/S0 CI-1 gives TS-1. As seen in Figure 2, for the dark reaction, the energy of the TS-1 connecting 9 + benzene and 12 on the S0 surface lies 21 kJ mol1 below the energy of the S1/S0 CI-1. Note that the computational results predict the energy barriers for 9 + benzene ! 12 and 12 ! 9 + benzene to be 192 and 255 kJ mol1, respectively. This finding suggests that it would be difficult to produce the seven-membered-ring molecule 12 using the thermal (dark) reaction, which is in good agreement with the experimental observations.[10] Finally, one may wonder whether it is possible to find the alternative reaction path via the silyl radicals, as shown in Scheme 1. However, the proposed scheme posed a number of unsolved mechanistic and logical questions, as it did not consider photoreaction pathways from the excited to the ground state. Moreover, the mechanism given in Scheme 1 consists of multistep processes, which would produce radical intermediates. Nevertheless, no experimental detections of these intermediates or side products have been reported yet.[10] Indeed, repeated attempts to search for the silyl radicals in the photoreaction of 9 and benzene using the MCSCF methodology have always failed. On the basis of these findings, it is therefore concluded that no silyl radicals exist on the MCSCF surface for such photochemical insertion reactions.

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Conclusion The reaction mechanisms for the photoreaction of the isolable dialkylsilylene (1) have been studied with respect to the formation of two chemical bonds between two rings. This study provides the first theoretical demonstration of the reaction trajectory and a theoretical estimation of the activation energy and reaction enthalpy for these photochemical insertion processes. Our model investigations demonstrate that upon absorption of a photon of light, the isolable dialkylsilylene (1) is excited vertically to S1 (FC) through a 1(n ! 3p) transition. Then, this singlet excited molecule 1 can enter an extremely efficient channel, which takes the form of a CI between the excitedand ground-state potential energy surfaces. After decay at the CI point, the molecule continues its evolution on the groundstate potential surface to produce the final insertion product through the radiationless decay route as well as returning to the reactants in the ground state. Besides, on the basis of the molecular orbital analysis, the singlet excited dialkylsilylene (1) should attack benzene in the perpendicular conformation. Moreover, the theoretical evidence indicates that the silyl radicals proposed in previous works[10, 11] do not exist in such photoinsertion reactions. All these theoretical findings can explain successfully the available experimental findings.[10] It is hoped that the present theoretical results will convince experimental chemists that conical intersection mechanisms play a crucial role in photochemical reactions of isolable dialkylsilylenes. It is therefore expected that successful schemes for the photoexcited chemical reactions of some related silylene species will be devised soon.

Acknowledgements The author is grateful to the National Center for High-Performance Computing of Taiwan for generous amounts of computing time, and the National Science Council of Taiwan for the financial support. The author also wishes to thank Professor Michael A. Robb, Dr. S. Wilsey, Dr. Michael J. Bearpark, (University of London, UK) and Professor Massimo Olivucci (Universita degli Studi di Siena, Italy), for their encouragement and support during his stay in London. Special thanks are also due to reviewers 1 and 2 for very helpful suggestions and comments. Keywords: conical intersections photochemistry · silicon · silylenes

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[1] For reviews of transient silylenes, see: a) W. H. Atwell, D. R. Weyenberg, Angew. Chem. 1969, 81, 485; Angew. Chem. Int. Ed. Engl. 1969, 8, 469; b) Reactive intermediates, Vol. 1 (Eds.: P. P. Gaspar, M. Jones, R. A. Moss), John Wiley & Sons, New York, 1978; c) Reactive intermediates, Vol. 2 (Eds.: P. P. Gaspar, M. Jones, R. A. Moss), John Wiley & Sons, New York, 1978; d) Reactive intermediates, Vol. 3 (Eds.: P. P. Gaspar, M. Jones, R. A. Moss), John Wiley & Sons, New York, 1978; e) M. Ishikawa, M. Kumada, Adv. Organomet. Chem. 1981, 19, 51; f) The Chemistry of Organic Silicon Compounds, Vol. 2, Part 3 (Eds.: P. P. Gaspar, R. West, Z. Rappoport, Y. Apeloig), John Wiley & Sons, Chichester, 1998; g) W. H. Atwell, Organometallics 2009, 28, 3573.  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper [2] For recent reviews, see: a) W. P. Neumann, Chem. Rev. 1991, 91, 311; b) M. F. Lappert, Main Group Met. Chem. 1994, 17, 183; c) M. Driess, H. Grutzmacher, Angew. Chem. 1996, 108, 900; Angew. Chem. Int. Ed. Engl. 1996, 35, 828; d) J. Barrau, R. Ghassoub, Coord. Chem. Rev. 1998, 178 – 180, 593; e) P. P. Gaspar, R. West, The Chemistry of Organic Silicon Compounds, Vol. 2, Part 3, (Eds.: Z. Rappoport, Y. Apeloig), John Wiley & Sons, New York, 1998, Chapter 43, p. 2463; f) P. Jutzi, N. Burford, Chem. Rev. 1999, 99, 969; g) J. Barrau, J. Escudi, J. Satg, Chem. Rev. 1999, 99, 283; h) N. Tokitoh, R. Okazaki, Coord. Chem. Rev. 2000, 210, 251; i) M. J. Weidenbruch, Organomet. Chem. 2002, 646, 39; j) M. Weidenbruch, Organometallics 2003, 22, 4348; k) N. J. Hill, R. West, J. Organomet. Chem. 2004, 689, 4165; l) Y. Mizuhata, T. Sasamori, N. Tokitoh, Chem. Rev. 2009, 109, 3479; m) M. Kira, Chem. Commun. 2010, 46, 2893; n) M. Kira, J. Chem. Sci. 2012, 124, 1205. [3] a) M. Kira, S. Ishida, T. Iwamoto, C. Kabuto, J. Am. Chem. Soc. 1999, 121, 9722; b) M. Kira, J. Organomet. Chem. 2004, 689, 4475; c) M. Kira, S. Ishida, T. Iwamoto, Chem. Rec. 2004, 4, 243; d) M. Kira, T. Iwamoto, S. Ishida, Chem. Bull. Soc. Jpn. 2007, 80, 258. [4] a) P. Jutzi, D. Kanne, C. Krger, Angew. Chem. Int. Ed. Engl. 1986, 25, 164; b) P. Jutzi, U. Holtmann, D. Kanne, C. Krueger, R. Blom, R. Gleiter, I. HylaKryspin, Chem. Ber. 1989, 122, 1629; c) P. Jutzi, A. Becker, H. G. Stammler, B. Neumann, Organometallics 1991, 10, 1647. [5] a) M. Denk, R. Lennon, R. Hayashi, R. West, A. V. Belyakov, H. P. Verne, A. Haaland, M. Wagner, N. Metzler, J. Am. Chem. Soc. 1994, 116, 2691; b) R. West, M. Denk, Pure Appl. Chem. 1996, 68, 785. [6] a) M. Denk, J. C. Green, N. Metzler, M. J. Wagner, Chem. Soc. Dalton Trans. 1994, 2405; b) T. A. Schmedake, M. Haaf, Y. Apeloig, T. Mller, S. Bukalov, R. West, J. Am. Chem. Soc. 1999, 121, 9479. [7] a) B. Gehrhus, M. F. Lappert, J. Heinicke, R. Boese, D. Blser, J. Chem. Soc. Chem. Commun. 1995, 1931; b) B. Gehrhus, P. B. Hitchcock, M. F. Lappert, J. Heinicke, R. Boese, D. Blser, J. Organomet. Chem. 1996, 521, 211. [8] J. Heinicke, A. Opera, M. K. Kindermann, T. Karbati, L. Nyulszi, T. Veszprmi, Chem. Eur. J. 1998, 4, 541. [9] For reviews on the photochemistry of silylenes, see: a) A. G. Brook, The Chemistry of Organic Silicon Compounds, Vol. 2, Part 2 (Eds.: Z. Rappoport, Y. Apeloig,), Wiley, New York, 1998, 21, p. 1233; b) M. Kira, T. Miyazawa, The Chemistry of Organic Silicon Compounds, Vol. 2, Part 2 (Eds.: Z. Rappoport, Y. Apeloig,), Wiley, New York, 1998, 22, p. 1311. [10] a) M. Kira, S. Ishida, T. Iwamoto, C. Kabuto, J. Am. Chem. Soc. 2002, 124, 3830; b) M. Kira, S. Ishida, T. Iwamoto, A. de Meijere, O. Ito, M. Fujitsuka, Angew. Chem. 2004, 116, 4610; Angew. Chem. Int. Ed. 2004, 43, 4510;

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[11]

[12]

[13]

[14] [15] [16]

[17]

c) K. Uchiyama, S. Nagendran, S. Ishida, T. Iwamoto, M. Kira, J. Am. Chem. Soc. 2007, 129, 10638. For instance, see: a) H. Sakurai in Free Radicals, Vol. II (Ed.: J. K. Kochi), John Wiley & Sons, New York, 1973; b) C. Chatgilialoglu, Chem. Rev. 1995, 95, 1229; c) M. Kira, H. Sugiyama, H. Sakurai, J. Am. Chem. Soc. 1983, 105, 6436. a) F. Bernardi, M. Olivucci, M. A. Robb, Isr. J. Chem. 1993, 33, 265; b) M. Klessinger, Angew. Chem. 1995, 107, 597; Angew. Chem. Int. Ed. Engl. 1995, 34, 549; c) F. Bernardi, M. Olivucci, M. A. Robb, Chem. Soc. Rev. 1996, 25, 321; d) F. Bernardi, M. Olivucci, M. A. Robb, J. Photochem. Photobiol. A 1997, 105, 365; e) M. Klessinger, Pure Appl. Chem. 1997, 69, 773; f) M. Klessinger, J. Michl in Excited States and Photochemistry of Organic Molecules, VCH Publishers, New York, 1995. Gaussian 09, Revision A.02, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, . Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian, Inc., Wallingford CT, 2009. M. J. Bearpark, M. A. Robb, H. B. Schlegel, Chem. Phys. Lett. 1994, 223, 269. J. J. W. McDouall, K. Peasley, M. A. Robb, Chem. Phys. Lett. 1988, 148, 183. For heavy-atom effect, see: a) S. P. McGlynn, T. Azumi, M. Kinoshita, The Triplet State, Prentice-Hall, New York, 1969, pp. 190 – 198; b) M. A. ElSayed, J. Phys. Chem. 1963, 38, 2834; c) M. A. El-Sayed, Acc. Chem. Res. 1968, 1, 8. For the molecule picture containing fixed geometrical parameters, see the Supporting Information.

Received: March 16, 2014 Published online on July 2, 2014

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A theoretical investigation of photochemical reactions of an isolable silylene with benzene.

The mechanisms of photochemical insertion reactions are investigated theoretically using the model system, an isolable dialkylsilylene and benzene, us...
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