Abstract
This contribution describes a brief overview of the chemistry of divalent carbon(0) compounds, carbodiphosphoranes (CDPs) and carbodicarbenes (CDCs), which have currently emerged as an important new class of ligands in coordination chemistry. CDPs, which are often depicted as R3P=C=PR3, assume an extremely bent structure rather than a linear structure expected for the allene-like representation. Recent computational studies revealed that the CDPs have two lone pairs in σ and π symmetry on the central carbon(0) atom, providing a better description of their electronic structures as R3P→C0←PR3, in which the P-C bonds come from donor-acceptor interactions. Allenes with strong electron-donating substituents (E) on the terminal carbons also adopt a bent structure and would be best formulated as CDCs, namely E2C→C0←CE2. The central carbon(0) atom in CDPs and CDCs is highly basic, which allows them to serve as attractive ligands for transition metals. They are stronger donors than N-heterocyclic carbene and phosphine ligands, and might be easy to tune their donor properties.
