Tri- and Tetranuclear Copper Hydride Complexes Supported by Tetradentate Phosphine Ligands.

Three types of tetradentate phosphine ligands with different central methylene chains and configurations, meso- and rac-PhPCHP(Ph)(CH) P(Ph)CHPPh ( n = 2, meso- and rac-dpmppe; n = 3, meso-dpmppp) were utilized to synthesize a new series of tri- and tetranuclear copper hydride complexes. Reactions of meso-dpmppe or meso-dpmppp with CuCl/NHPF or [Cu(CHCN)]PF in the presence of NaBH afforded trinuclear copper hydride complexes, Cu(μ-H)( meso-dpmppe) (1) and Cu(μ-H)( meso-dpmppp) (2), while a similar reaction with rac-dpmppe resulted in the formation of a tetranuclear copper dihydride complex, Cu(μ-H)( rac-dpmppe) (5). Complexes 1 and 5 further reacted with RNC (R = Bu, Cy, Xyl) to give Cu(μ-H)( meso-dpmppe)(XylNC) (3), Cu(μ-H)( meso-dpmppe)(RNC) (R = Bu (4a), Cy (4b)) and Cu(μ-H)( rac-dpmppe)(RNC) (R = Bu (6a), Cy (6b), Xyl (6c)), respectively. Complexes 1-6 were characterized by ESI-MS and H and P NMR spectroscopy and X-ray diffraction analyses, demonstrating that a hydride ligand is located at the center of triangular Cu plane of 1-3, while two μ-hydride-capped Cu planes are fused to result in rhombic CuH structures in 4a,b, 5, and 6a-c. Complexes 1-6 in CDCN solutions notably showed high thermal stability and no reactivity toward HO and CO. DFT calculations indicated an interesting correlation between the Wiberg bond indices (WBI) of Cu-H bonds and their natural atomic charge (NAC), where the isocyanide ligands had an appreciable influence on the Cu-H interactions.