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

The
metallostannylene Cp*­(iPr2MeP)­(H)2Fe-SnDMP (1; Cp* = η5-C5Me5; DMP = 2,6-dimesitylphenyl), formed
by hydrogen migration in a putative Cp*­(iPr2MeP)­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
H2 to generate the coordinatively unsaturated [Cp*­(iPr2MeP)­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 57Fe 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(κ2-(P,Sn)Sn­(DMP)­CH2CHMePMeiPr) (5). Complex 5 was also accessed via thermolysis of 1, and kinetics
studies of this thermolytic pathway indicate that the reductive elimination
of H2 from 1 to produce a stannylyne intermediate,
Cp*­(iPr2MeP)­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.