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

The metallostannylene Cp*((Pr2MeP)-Pr-i)(H)(2)Fe-SnDMP (1; Cp* = eta(5)-C5Me5; DMP = 2,6-dimesitylphenyl), formed by hydrogen migration in a putative Cp*((Pr2MeP)-Pr-i)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*((Pr2MeP)-Pr-i)Fe=SnDMP][B-(C6F5)(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 Fe-57 MOssbauer 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(K-2-(P,Sn)=Sn(DMP)(CH2CHMePMePr)-Pr-i) (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*((Pr2MeP)-Pr-i)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.