Carbodicarbenes: Divalent Carbon(0) Compounds

摘要

Is it possible to coordinate two donor ligands L to a carbon(0) atom, and what would be the properties of such a carbon atom? These questions have been of interest to chemists for many years. First answers to this question have been obtained with the synthesis and structural characterization of carbodiphosphoranes (CDPs) A using donor ligands of type L=R3P. Carbodiphosphoranes can be formulated as bisphosphine complexes of a naked carbon atom (Aa). Alternatively, a heterocumulene R3PCPR3 (Ab) resonance structure and the description as a carbenoid species (Ac) are possible. The bonding parameters and reactivity of the carbodiphosphoranes indicate that the electronic situation of these compounds is reasonably described by a polar structure with two electron lone pairs at the central carbon atom (Aa, Scheme 1).