Pnictogen-Functionalised C1 Ligands: MC-ARn (n=0, 1, 2, 3).

The chemistry of transition metal carbynes, Ln M≡CR, has historically been dominated by species bearing hydrocarbyl or amino 'R' substituents, with other elements appearing only sporadically. In recent years, carbynes and related 'C1 ' species bearing other main-group substituents, particularly heavier elements of the p-block, have begun to emerge. This review details the chemistry of heavier pnictogen-functionalised C1 ligands, MCARn (A=P, As, Sb, Bi; n=0-3), including their syntheses, properties and reactivities, and how these are distinguished from more traditional carbyne complexes. Recent developments in the closely related phospha-isonitrile Ln M(CPR), cya-phosphide and cya-arside ligands, Ln M(C≡A) (A=P, As), are also discussed.