Cobalt complexes of a sterically encumbered bis(phosphino)silyl pincer-type ligand are reported, including a base-free cobalt silylene. Introduction of tert-butyl groups on the phosphine donors significantly impacts the reactivity of resulting complexes, leading to hindered reactions both at the cobalt and at the silicon center and changing the free-energy profile for the silylene-catalyzed formation of adamantyl isocyanate from adamantyl azide and carbon monoxide. Ultimately, destabilization of 6-coordinate intermediates renders the catalytic reaction significantly less effective than for smaller-profile analogues with isopropyl and cyclohexyl phosphine substituents.
Whited et al. (Tue,) studied this question.