Breaking bonds and breaking rules: inert-bond activation by [( i Pr 3 P)Ni] 5 H 4 and catalytic stereospecific norbornene dimerization.

The facile carbon atom abstraction reaction by [( i Pr 3 P)Ni] 5 H 6 (1) with various terminal alkenes to give [( i Pr 3 P)Ni] 5 H 4 (μ 5 -C) (2) occurs via a common highly reactive intermediate [( i Pr 3 P)Ni] 5 H 4 (3), which was isolated by the reaction of 1 with norbornene. Temperature dependent 1 H and 31 P{ 1 H} NMR chemical shifts of 3 are consistent with a thermally populated triplet excited state only 2 kcal mol -1 higher energy than the diamagnetic ground state. Complex 3 catalyzes the dimerization of norbornene to stereoselectively provide exclusively ( Z ) anti-(bis-2,2'-norbornylidene).