Versatile Fe-Sn Bonding Interactions in a Metallostannylene System: Multiple Bonding and C-H Bond Activation.

The metallostannylene Cp*( i Pr 2 MeP)(H) 2 Fe-SnDMP ( 1 ; Cp* = η 5 -C 5 Me 5 ; DMP = 2,6-dimesitylphenyl), formed by hydrogen migration in a putative Cp*( i Pr 2 MeP)HFe[Sn(H)DMP] intermediate, serves as a robust platform for exploration of transition-metal main-group element bonding and reactivity. Upon one-electron oxidation, 1 expels H 2 to generate the coordinatively unsaturated [Cp*( i Pr 2 MeP)Fe═SnDMP][B(C 6 F 5 ) 4 ] ( 3 ), which possesses a highly polarized Fe-Sn multiple bond that involves interaction of the tin lone pair with iron. Evidence from EPR and 57 Fe Mössbauer spectroscopy, along with DFT studies, shows that 3 is primarily an iron-based radical with charge localization at tin. Upon reduction of 3 , C-H bond activation of the phosphine ligand was observed to produce Cp*HFe(κ 2 -( P,Sn )═Sn(DMP)CH 2 CHMePMe i Pr) ( 5 ). Complex 5 was also accessed via thermolysis of 1 , and kinetics studies of this thermolytic pathway indicate that the reductive elimination of H 2 from 1 to produce a stannylyne intermediate, Cp*( i Pr 2 MeP)Fe[SnDMP] ( A ), is likely rate-determining. Evidence indicates that the production of 5 proceeds through a concerted C-H bond activation. DFT investigations suggest that the transition state for this transformation involves C-H cleavage across the Fe-Sn bond and that a related transition state where C-H bond activation occurs exclusively at the tin center is disfavored, illustrating an effect of iron-tin cooperativity in this system.