Putting cyaphide in its place: determining the donor/acceptor properties of the κC-cyaphido ligand

The synthesis of group 9 pyridine–diimine complexes M((Dipp)PDI)X and [M((Dipp)PDI)L](+) (M = Co, Rh; (Dipp)PDI = 1,1′-(pyridine-2,6-diyl)bis(N-(2,6-diisopropylphenyl)ethan-1-imine); X = CP(−), CCH(−); L = CO, (t)BuNC) bearing a series of strong-field ligands, including the cyaphide ion (C[triple bond, length as m-dash]P(−)), is reported. A combined experimental and computational comparative study of the group 9 PDI cyaphide complexes Co((Dipp)PDI)(CP) and Rh((Dipp)PDI)(CP), as well as the N-heterocyclic carbene (NHC) gold(i) cyaphide complex Au(IDipp)(CP) (IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), reveals the σ donor and π acceptor properties of the κC-cyaphido ligand, and allow us to suggest a position for this ion in the spectrochemical series.