Photochemical reactions of [CH2(eta5-C5H4)2][Rh(C2H4)2]2 with silanes: evidence for Si-C and C-H activation pathways

Photochemical reaction of CH2(eta5-C5H4)2]Rh(C2H4)2]2 1 with dmso led to the stepwise formation of CH2(eta5-C5H4)2]Rh(C2H4)2]Rh(C2H4)(dmso)] 2a and CH2(eta5-C5H4)2]Rh(C2H4)(dmso)]2 2b. Photolysis of 1 with vinyltrimethylsilane ultimately yields three isomeric products of CH2(eta5-C5H4)2]Rh(CH2=CHSiMe3)2]2, 3a, 3b and 3c which are differentiated by the relative orientations of the vinylsilane. When this reaction is undertaken in d6-benzene, H/D exchange between the solvent and the alpha-proton of the vinylsilane is revealed. In addition evidence for two isomers of the solvent complex CH2(eta5-C5H4)2]Rh(C2H4)2]Rh(C2H4)(eta2-toluene)] was obtained in these and related experiments when the photolysis was completed at low temperature without substrate, although no evidence for H/D exchange was observed. Photolysis of 1 with Et3SiH yielded the sequential substitution products CH2(eta5-C5H4)2]Rh(C2H4)2]Rh(C2H4)(SiEt3)H] 4a, CH2(eta5-C5H4)2]Rh(C2H4)(SiEt3)H]2 4b, CH2(eta5-C5H4)2]Rh(C2H4)(SiEt3)H]Rh(SiEt3)2(H)2] 4c and CH2(eta5-C5H4)2]Rh(SiEt3)2(H)2]2 4d; deuteration of the alpha-ring proton sites, and all the silyl protons, of 4d was demonstrated in d6-benzene. This reaction is further complicated by the formation of two Si-C bond activation products, CH2(eta5-C5H4)2]RhH(mu-SiEt2)]2 5 and CH2(eta5-C5H4)2](RhEt)(RhH)(mu-SiEt2)2] 6. Complex 5 was also produced when 1 was photolysed with Et2SiH2. When the photochemical reactions with Et3SiH were repeated at low temperatures, two isomers of the unstable C-H activation products, the vinyl hydrides CH2(eta5-C5H4)2]{Rh(SiEt3)H}{Rh(SiEt3)}(mu-eta1,eta2-CH=CH2)] 7a and 7b, were obtained. Thermally, 4c was shown to form the ring substituted silyl migration products (eta5-C5H4)CH2(C5H3SiEt3)]Rh(SiEt3)2(H)2]2 8 while 4b formed CH2(C5H3SiEt3)2]Rh(SiEt3)2(H)2]2 (9a and 9b) upon reaction with excess silane. The corresponding photochemical reaction with Me3SiH yielded the expected products CH2(eta5-C5H4)2]Rh(C2H4)2]Rh(C2H4)(SiMe3)H] 10a, CH2(eta5-C5H4)2]Rh(C2H4)(SiMe3)H]2 10b, CH2(eta5-C5H4)2]Rh(C2H4)(SiMe3)H]Rh(SiMe3)2(H)2] 10c and CH2(eta5-C5H4)2]Rh(SiMe3)2(H)2]2 10d. However, three Si-C bond activation products, CH2(eta5-C5H4)2](RhMe)(RhH)(mu-SiMe2)2] 11, CH2(eta5-C5H4)2](Rh{SiMe3})(RhMe)(mu-SiMe2)2] 12 and CH2(eta5-C5H4)2](Rh{SiMe3})(RhH)(mu-SiMe2)2] 13 were also obtained in these reactions.