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

摘要

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_2PO} _2C_6H_3). Complex 1 reacts with AgX to give the analogous Ni-X derivatives (X = CN, 2; OSO_2CF_3, 3; OC(O)CH_3, 4; ONO_2, 5), whereas complex 3 reacts with phenylacetylene and NEt3 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 _1/2~0 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.