Photo-Driven Si-C Bond Cleavage in Hexacoordinate Silicon Complexes Jörg Wagler, Gerhard Roewer, Daniela Gerlach

Photo-Driven Si-C Bond Cleavage in Hexacoordinate Silicon Complexes Jörg Wagler, Gerhard Roewer, Daniela Gerlach To cite this version: Jörg Wagler, Gerhard Roewer, Daniela Gerlach. Photo-Driven Si-C Bond Cleavage in Hexacoordinate Silicon Complexes. Journal of Inorganic and General Chemistry / Zeitschrift für anorganische und allgemeine Chemie, Wiley-VCH Verlag, 2009, 635 (9-10), pp.1279. 10.1002/zaac.200900080. hal- 00492447 HAL Id: hal-00492447 https://hal.archives-ouvertes.fr/hal-00492447 Submitted on 16 Jun 2010 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. ZAAC Photo-Driven Si-C Bond Cleavage in Hexacoordinate Silicon Complexes Journal: Zeitschrift für Anorganische und Allgemeine Chemie Manuscript ID: zaac.200900080 Wiley - Manuscript type: Article Date Submitted by the 02-Feb-2009 Author: Complete List of Authors: Wagler, Jörg; TU Bergakademie Freiberg, Inst. für Anorganische Chemie Roewer, Gerhard; TU Bergakademie Freiberg, Fak. Chemie und Physik Gerlach, Daniela; TU Bergakademie Freiberg, Inst. für Anorganische Chemie Keywords: Chelate, Hypercoordination, Rearangement, Schiff Base, Tin Wiley-VCH Page 1 of 9 ZAAC 1 2 Full Paper 3 4 5 6 DOI: 10.1002/zaac.200(( please insert the last 6 DOI digits )) 7 8 Photo-Driven Si-C Bond Cleavage in Hexacoordinate Silicon Complexes 9 10 Jörg Wagler*, Gerhard Roewer* and Daniela Gerlach 11 12 Freiberg/Germany, Institut für Anorganische Chemie, TU Bergakademie Freiberg 13 14 Received (( will be filled in by the editorial staff )) 15 16 Dedicated to Prof. Robert J. P. Corriu on the Occasion of his 75 th Birthday 17 18 19 Abstract. Hexacoordinate diorganosilicon complexes of the type accompanied by olefin elimination. Irradiation of compounds (ONNO)SiRX, 20 (ONNO)SiRR’, with (ONNO) being a di-anionic salen-type Schiff base with X being a non-carbon sacrificial ligand, was shown to give rise to 21 ligand, were shown to undergo Si −C bond cleavage and intramolecular further side reactions: In case of X=F the unexpected formation of 22 rearrangement (1,3-shift of R’ to a former imine carbon atom) upon (ONNO)SiF 2 was observed. In analogy to the photo-induced rearrangement 23 irradiation with UV. The course of this reaction depends on the nature of Si- of (ONNO)SiPh 2 the heavier congenor (ONNO)GePh 2 exhibits similar 24 bound substituents: Whereas complexes (ONNO)SiMe 2 and (ONNO)SiPh 2 reactivity, whereas the related tin compound (ONNO)SnPh 2 proved inert 25 give rise to the rearrangement of a methyl and a phenyl group, respectively, under these reaction conditions applied. 26 complexes of the type (ONNO)Si(aryl)(alkyl) were found to undergo 27 Si −C(alkyl) bond cleavage exclusively. Furthermore, such alkyl groups Keywords: Chelate; Hypercoordination; Rearrangement; Schiff Base; Tin bearing β-H atoms may lead to β-H transfer to the imine carbon atom 28 29 30 ligand moieties one into another [10] or even give rise to the Si- 31 Introduction templated formation of novel ligands [11]. 32 Our recent research on hypercoordinate diorganosilanes [12] 33 One of the most intriguing aspects of silicon coordination chemistry revealed remarkably activated Si −C bonds, which, upon irradiation, 34 is the activation of various Si −X bonds upon “hypercoordination” of are cleaved to yield a novel ligand moiety coordinated to the silicon 35 the Si-atom. In particular, one or two additional donor atoms atom (Scheme 1) [13]. Hexacoordination of the silicon atom was 36 brought into closer proximity of a silicon atom, hence giving rise to shown to be one of the keys to this reactivity pattern since 37 silicon penta- and hexacoordination, respectively, may provoke pentacoordinate silicon compounds comprising related ligand 38 Si −X bond splitting, i.e. a lowering of the silicon coordination backbones proved inert under similar reaction conditions [14]. 39 number down to tetra- or pentacoordination, respectively. A great Furthermore, the approach to the ligand within this 1,3-shift reaction 40 variety of reactions following this fundamental scheme can be found proved to proceed towards the sterically less crowded imine carbon 41 in the literature, e.g., the formation of tetracoordinate siliconium atom, as demonstrated with an asymmetric ONN’O’ ligand [15]. In 42 cations from N-methylimidazole and trimethylsilylbromide [1] and our herein presented study we elucidate further parameters which 43 Si −Cl bond dissociation to yield pentacoordinate siliconium cations may control the direction of the reactions following photo-induced 44 [2]. Furthermore, the release of initially Si-bound halides may Si −C bond cleavage. 45 provoke reactions at the ligand backbone [3]. As soon as Si −X 46 bonds other than Si-Halide are getting activated by Si- 47 hypercoordination, the groups X may exhibit reactivities of 48 camouflaged nucleophiles, i.e., group X may attack electrophilic 49 centres in the ligand backbone such as carbonyl and imine carbon 50 atoms. Such reactivity was shown for hexacoordinate 51 silacyclobutanes [4], allylsilanes [5], disilanes [6], cyanosilanes [7] 52 and H-silanes [8]. Even an unexpected alkyl group shift towards an Scheme 1 . 1,3-Shift of an initially Si-bound ethyl group upon UV irradiation. 53 imine ligand was reported recently [9]. Furthermore, coordination to 54 silicon as central atom may induce rearrangements of isomeric 55 Results and Discussion 56 57 ____________ As reported earlier, a variety of hexacoordinate diorganosilanes ( 2- * Dr. J. Wagler, Prof. Dr. Gerhard Roewer 58 Institut für Anorganische Chemie 8) was accessible via reaction between the tetradentate Schiff base 59 TU Bergakademie Freiberg ligand 1 and the respective diorganodichlorosilanes (Scheme 2) [12]. 60 Leipziger Str. 29 In accord with the exclusive 1,3-shift of the Si-bound alkyl group of D-09596 Freiberg, Germany Fax: (+49) 3731 39 4058 2 and 3 upon UV irradiation under formation of 2a and 3a , E-mail: [email protected] , [email protected] respectively [13], in compound 4, which comprises a sterically more freiberg.de 1 Wiley-VCH ZAAC Page 2 of 9 1 2 demanding alkyl substituent (i.e., a cyclohexyl group) the 1,3-alkyl 3 shift is still favored. 4 5 6 N2 C22 C7 7 N1 8 O2 9 Si1 O1 10 C31 O3 11 12 13 14 15 O4 16 17 Figure 1. Molecular structure of 4a in the crystal. (Thermal ellipsoids at the 20% 18 probability level, H-atoms omitted, selected atoms labeled). Selected bond lengths [Å] 19 and angles [deg.]: Si1 −O1 1.706(1), Si1 −O2 1.716(1), Si1 −N1 1.989(1), Si1 −N2 1.738(1), Si1 −C31 1.886(2), N1 −C7 1.295(2), N2 −C22 1.496(2), O1 −Si1 −N2 126.3(1), 20 O1 −Si1 −C31 108.9(1), N2 −Si1 −C31 123.5(1), O2 −Si1 −N1 171.5(1). For comparison Scheme 2 . Synthesis of hexacoordinate diorganosilanes 2-8 and their photo-assisted 21 the corresponding bond lengths and angles in molecule 5a in an isostructural crystal rearrangement into pentacoordinate silicon complexes 2a -8a . For 2a -8a (not applicable lattice: Si1 −O1 1.711(1), Si1 −O2 1.719(1), Si1 −N1 1.987(1), Si1 −N2 1.740(1), 22 for 5a ) the diastereomer with swapped positions R’ vs. Ph was observed 29 Si NMR Si1 −C31 1.889(2), N1 −C7 1.295(2), N2 −C22 1.495(2), O1 −Si1 −N2 126.1(1), spectroscopically as a minor component (< 10 %) of the reaction mixture. For 3a and 4a 23 O1 −Si1 −C31 109.6(1), N2 −Si1 −C31 123.0(1), O2 −Si1 −N1 171.7(1). 24 the product of β-hydride transfer (R’ = H) was also observed NMR spectroscopically as a minor component (< 10%) [13]. 25 26 Even β-hydride transfer to the imine carbon atom, which was 27 29 Table 1. Si NMR shifts ( δ in ppm relative to SiMe 4) detected in the product mixture found as a minor side reaction when 3 was irradiated, did not play 28 after irradiation of compounds 2-9, 11 and 13 . any pronounced role. Table 1 reveals the formation of 29 pentacoordinate silicon complexes upon UV irradiation of 2, 3, 4 29 [a] 29 [b] 29 [a] 29 [b] 30 δ( Si)1 δ( Si)2 δ( Si)1 δ( Si)2 and 5. The very narrow 29 Si NMR shift range underlines the 31 2 -113.3 -115.8 7 -115.5 -116.7, -101.5 formation of silicon compounds bearing very similar Si-bound 32 3 -114.5 -114.8 [c] , -117.4 8 -116.3 -113.3, -113.6, -114.6, -117.9 moieties, i.e., compounds comprising the (ONN’O’)Si-Ph pattern. 33 4 -112.7 -114.8 [c] , -118.2 9 -114.8 [c] Other signals as for 8 On the formation of a minor diasteromeric product in case of 2 and 34 5 -113.9 11 -114.3 -117.3 3 as well as the β-hydride transfer product in case of 3 ( δ29 Si 35 6 -101.8 -103.1 13 -129.5 d = -114.8 ppm) we have reported earlier [13]. These features can also 36 a) Predominant signal b) Additional signal(s) c) corresponds to the β-H transfer product. be found for compound 4, whereas the rearrangement product of 5 37 reveals only one 29 Si NMR signal, as expected.

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