Synthesis and Characterization of a Family of POCOP Pincer Complexes with Nickel: Reactivity Towards CO2 and Phenylacetylene |
| |
Authors: | Klara J Jonasson Dr Ola F Wendt |
| |
Institution: | Centre for Analysis and Synthesis, Department of Chemistry, Lund University, P.O. Box 124, 22100 Lund (Sweden) |
| |
Abstract: | A cyclohexyl‐based POCOP pincer ligand (POCOP=cis‐1,3‐bis(di‐tert‐butylphosphinito)cyclohexyl) cyclometalates with nickel to generate a series of new POCOP‐supported NiII complexes, including the halide, hydride, methyl, and phenyl species. trans‐NiCl{cis‐1,3‐bis(di‐tert‐butylphosphinito)cyclohexane}], (POCOP)NiCl] ( 1 a ) and the analogous bromide complex ( 1 b ) were synthesized and fully characterized by NMR spectroscopy and X‐ray crystallography. Cyclic voltammetry measurements of 1 a and 1 b alongside their bis(phosphine) analogues (PCP)NiCl] ( 2 a ) and (PCP)NiCl] ( 2 a ) (PCP=cis‐1,3‐bis(di‐tert‐butylphosphino)cyclohexyl) indicate a reduced electron density at the metal center upon introducing electron‐withdrawing oxygen atoms in the pincer arms. The methyl (POCOP)NiMe] ( 3 ) and phenyl (POCOP)NiPh] ( 4 ) complexes were formed from 1 a by reaction with the corresponding organolithium reagents. 1 a also reacts with LiAlH4 to give the hydride complex (POCOP)NiH] ( 5 ). The methyl complex 3 reacts with phenyl acetylene to give the acetylide complex (POCOP)NiCCPh] ( 6 ). The reactivity of compounds 3 – 5 towards CO2 was studied. The hydride complex 5 and the methyl complex 3 both underwent CO2 insertion to form the formate species (POCOP)NiOCOH] ( 7 ) and acetate species (POCOP)NiOCOCH3] ( 8 ), respectively, although with a higher barrier of insertion in the latter case. Compound 4 was unreactive towards CO2 even at elevated temperatures. Complexes 3 – 8 were all characterized by NMR spectroscopy and X‐ray crystallography. |
| |
Keywords: | CO2 insertion cyclometalation nickel pincer complexes P ligands |
|
|