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-Ph2PCH2P­(Ph)­(CH2) n P­(Ph)­CH2PPh2 (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/NH4PF6 or [Cu­(CH3CN)4]­PF6 in the presence of NaBH4 afforded trinuclear copper hydride complexes, [Cu3(μ3-H)­(meso-dpmppe)2]­(PF6)2 (1) and [Cu3(μ3-H)­(meso-dpmppp)2]­(PF6)2 (2), while a similar reaction with rac-dpmppe resulted in the formation of a tetranuclear copper dihydride complex, [Cu4(μ3-H)2(rac-dpmppe)2]­(PF6)2 (5). Complexes 1 and 5 further reacted with RNC (R = t Bu, Cy, Xyl) to give [Cu3(μ3-H)­(meso-dpmppe)2(XylNC)]­(PF6)2 (3), [Cu4(μ3-H)2(meso-dpmppe)2(RNC)2]­(PF6)2 (R = t Bu (4a), Cy (4b)) and [Cu4(μ3-H)2(rac-dpmppe)2(RNC)2]­(PF6)2 (R = t Bu (6a), Cy (6b), Xyl (6c)), respectively. Complexes 1–6 were characterized by ESI-MS and 1H and 31P NMR spectroscopy and X-ray diffraction analyses, demonstrating that a hydride ligand is located at the center of triangular Cu3 plane of 1–3, while two μ3-hydride-capped Cu3 planes are fused to result in rhombic Cu4H2 structures in 4a,b, 5, and 6a–c. Complexes 1–6 in CD3CN solutions notably showed high thermal stability and no reactivity toward H2O and CO2. 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.