Dearomatization of the PCP Pincer Ligand in a ReV Oxo Complex.

A high-valent, rhenium(V) oxo complex (PCP)ReOCl2 (1; PCP=bis(2,6-di-tert-butylphosphinomethyl)phenyl) undergoes a deprotonation and "dearomatization" upon treatment with LiN(SiMe3 )2 to give (P*CP)ReOCl (2 a), in which Re is bound to a new dianionic P*CP ligand. Compound 2 a was studied spectroscopically, structurally, and computationally and was determined to have non-negligible Re=C multiple bond character, leading to its formulation as a new pseudo-carbenoid species. Reaction of 2 a or its iodo analogue (P*CP)ReOI (2 b) with CO2 provided access to (PCP)ReOX(CO2 ) (X=Cl or I, 3 a/b), the product of 1,3-cycloaddition and C-C bond formation.