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

The synthesis of group 9 pyridine-diimine complexes M(PDI)X and [M(PDI)L] (M = Co, Rh; PDI = 1,1'-(pyridine-2,6-diyl)bis(-(2,6-diisopropylphenyl)ethan-1-imine); X = CP, CCH; L = CO, 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(PDI)(CP) and Rh(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 κ-cyaphido ligand, and allow us to suggest a position for this ion in the spectrochemical series.