Approaches to Sigma Complexes via Displacement of Agostic Interactions: An Experimental and Theoretical Investigation

A series
of coordinatively unsaturated, 16-electron, cationic ruthenium
complexes bearing PNP pincer ligands of the type [RuH­(L)­(PNRP)]+ (L = PPh3, R = PhCH2 (3), Ph (4); L = CO, R = PhCH2 (5); PNRP = RN­(CH2CH2PPh2)2) has been prepared and characterized. These
complexes exhibit agostic interaction in the sixth coordination site.
The binding of various X–H (X = H, Si, B, and C) bonds in small
molecules such as H2, silanes, tetracoordinate boranes,
and CH4 to the ruthenium center via displacement of the
relatively weak agostic interaction in these complexes has been studied.
Structures of [RuH­(L)­(PNRP)]+ (L = PPh3, R = PhCH2 (3), Ph (4); L =
CO, R = PhCH2 (5); PNRP = RN­(CH2CH2PPh2)2) complexes and
the sigma-borane complex trans-[RuH­(CO)­(η1-H-BH2·NMe3)­(PNRP)]+ (R = PhCH2 (15)) have been established
by X-ray crystallography. The relative binding strengths of the X–H
bonds to ruthenium center in these complexes has been studied using
computational methods.