The impact of P-substituents on the structures, spectroscopic properties, and reactivities of POCOP-type pincer complexes of nickel(II).

The room temperature reaction of NiBr(2)(NCCH(3))(x) with the pincer-type ligand POCHOP(Ph) gave the new pincer complex (POCOP(Ph))NiBr (1, POCOP(Ph) = κ(P), κ(C), κ(P)-2,6-{Ph(2)PO}(2)C(6)H(3)). Complex 1 reacts with AgX to give the analogous Ni-X derivatives (X = CN, 2; OSO(2)CF(3), 3; OC(O)CH(3), 4; ONO(2), 5), whereas complex 3 reacts with phenylacetylene and NEt(3) to give the Ni-CCPh derivative 6. On the other hand, reaction of 1 or 3 with RLi or RMgI did not afford the desired Ni-R derivatives, giving instead the corresponding iodo and hydroxo derivatives. Complexes 1-6 have been characterized by NMR, IR, and UV-Vis spectroscopy and X-ray crystallography. The solid state structural and IR data indicate that Ni-C(sp) interaction is dominated by ligand-to-metal σ-donation in 2 and 6. Cyclic voltammetry measurements indicate that complexes 3 and 4 display reversible redox behaviour (Ni(II)/Ni(III)); comparison of the E(0)(1/2) values for these complexes and their POCOP(i-Pr) analogues shows that both the X ligands and the P-substituent have a considerable impact on the ease of oxidation in this family of complexes. This journal is © The Royal Society of Chemistry 2011