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

The metallostannylene Cp*(^<i>i</i>Pr₂MeP)(H)₂Fe-SnDMP (<b>1</b>; Cp* = η⁵-C₅Me₅; DMP = 2,6-dimesitylphenyl), formed by hydrogen migration in a putative Cp*(^<i>i</i>Pr₂MeP)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, <b>1</b> expels H₂ to generate the coordinatively unsaturated [Cp*(^<i>i</i>Pr₂MeP)Fe═SnDMP][B(C₆F₅)₄] (<b>3</b>), which possesses a highly polarized Fe-Sn multiple bond that involves interaction of the tin lone pair with iron. Evidence from EPR and ⁵⁷Fe Mössbauer spectroscopy, along with DFT studies, shows that <b>3</b> is primarily an iron-based radical with charge localization at tin. Upon reduction of <b>3</b>, C-H bond activation of the phosphine ligand was observed to produce Cp*HFe(κ²-(<i>P,Sn</i>)═Sn(DMP)CH₂CHMePMe^<i>i</i>Pr) (<b>5</b>). Complex <b>5</b> was also accessed via thermolysis of <b>1</b>, and kinetics studies of this thermolytic pathway indicate that the reductive elimination of H₂ from <b>1</b> to produce a stannylyne intermediate, Cp*(^<i>i</i>Pr₂MeP)Fe[SnDMP] (<b>A</b>), is likely rate-determining. Evidence indicates that the production of <b>5</b> 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.