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

The metallostannylene Cp*(PrMeP)(H)Fe-SnDMP (; Cp* = η-CMe; DMP = 2,6-dimesitylphenyl), formed by hydrogen migration in a putative Cp*(PrMeP)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, expels H to generate the coordinatively unsaturated [Cp*(PrMeP)Fe═SnDMP][B(CF)] (), which possesses a highly polarized Fe-Sn multiple bond that involves interaction of the tin lone pair with iron. Evidence from EPR and Fe Mössbauer spectroscopy, along with DFT studies, shows that is primarily an iron-based radical with charge localization at tin. Upon reduction of , C-H bond activation of the phosphine ligand was observed to produce Cp*HFe(κ-()═Sn(DMP)CHCHMePMePr) (). Complex was also accessed via thermolysis of , and kinetics studies of this thermolytic pathway indicate that the reductive elimination of H from to produce a stannylyne intermediate, Cp*(PrMeP)Fe[SnDMP] (), is likely rate-determining. Evidence indicates that the production of 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.