C–H Activation of Terminal Alkynes by Tris-(3,5-dimethylpyrazolyl)boraterhodiumneopentylisocyanide: New Metal–Carbon Bond Strengths

C–H bond activation of terminal alkynes by [Tp′Rh­(CNneopentyl)]
(Tp′ = hydridotris-(3,5-dimethylpyrazolyl)­borate) resulted
in the formation of terminal C–H bond activation products Tp′Rh­(CNneopentyl)­(CCR)­H
(R = t-Bu, SiMe3, hexyl, CF3, p-MeOC6H4, Ph, and p-CF3C6H4). A combination
of kinetic selectivity determined in competition reactions and activation
energy for reductive elimination has allowed for the calculation of
relative Rh–Calkynyl bond strengths. The bond strengths
of Rh–Calkynyl products are noticeably higher than
those of Rh–Caryl and Rh–Calkyl analogues. The relationship between M–C and C–H bond
strengths showed a linear correlation (slope RM–C/H–C = 1.32), and follows energy correlations
previously established for unsubstituted sp2 and sp3 C–H bonds in aliphatic and aromatic hydrocarbons.