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

The chemistry of transition metal carbynes, L_nM≡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, MCAR_n (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 L_nM(CPR), cya-phosphide and cya-arside ligands, L_nM(C≡A) (A=P, As), are also discussed.