The synthesis of a full series of group 4/nickel complexes supported by a 2-(diphenylphosphino)pyrrolide (NP) ligand is reported. Treatment of the homoleptic, 8-coordinate M(NP)4 monometallic precursors with Ni(COD)2 (COD = 1,5-cyclooctadiene) yielded the heterobimetallic complexes (κ2-NP)M(μ2-NP)3Ni (M = Ti, Zr, Hf). Although X-ray crystallographic analysis reveals similarly short metal-metal distances in all three complexes, quantum chemical calculations indicate that ZrNi (5) and HfNi (6) contain only single Ni → M dative bonds while TiNi (4) has an additional Ti-Ni π-bond. All three complexes have quasireversible reductions by cyclic voltammetry, and 1-electron chemical reduction of 4 by Na(Hg) yields the anion, [Na][(κ2-NP)Ti(μ2-NP)3Ni] (7). X-ray and computational analysis indicate that the 1-electron reduction of 4 completely breaks the metal-metal bond, yielding a formally TiIII-Ni0 complex. Ti-Ni bonding can also be disrupted by coordination of CO, wherein Ni → CO backbonding effectively outcompetes Ni → Ti dative bonding.
Bibliographical noteFunding Information:
Financial support was provided by the University of Minnesota (start up funds) and the ACS Petroleum Research Fund (ACS-PRF 54225-DNI3). Victor G. Young, Jr. is thanked for assistance with X-ray diffraction data interpretation. The Bruker-AXS D8 Venture diffractometer was purchased through a grant from NSF/MRI (1224900) and the University of Minnesota. Equipment purchases for the NMR facility were supported through a grant from the NIH (S10OD011952) with matching funds from the University of Minnesota. R. K. C. thanks the National Science Foundation for a Graduate Research Fellowship under Grant No. 00039202. The authors acknowledge the Minnesota Supercomputing Institute (MSI) at the University of Minnesota for providing resources that contributed to the research results reported within this paper.
© 2016 The Royal Society of Chemistry.