Two-Coordinate d~9 Complexes. Synthesis and Oxidation of NHC Nickel(Ⅰ) Amides

摘要

Divalent, square-planar group 10 complexes with π-donor ligands are precluded from forming π-bonds since the empty d_(x~2-y~2) orbital is M-L σ~* in nature and does not have the proper symmetry for π-overlap. Trigonal planar geometry, however, affords a metal fragment having an empty in-plane orbital that can participate in π-bonding, exemplified by the low-spin, d~8 nickel complex-cations [(dtbpe)Ni=NHAr~+] and [(dtbpe)Ni=P'Bu_2~+] (dtbpe = l,2-bis(di-tert-butylphosphino)ethane; Ar = 2,6-di-isopropylphenyl). The synthetic strategy to these molecules involved preparing unusual d~9 L_2NiX complexes and subsequent l-e~- oxidation to the d8 cations. Due in part to their low coordination number and cationic charge, these complexes exhibit interesting reactivities. We were intrigued about the possible consequences for reactivity of lowering the coordination number of Ni to two. Power and Arduengo have described examples of neutral, two-coordinate nickel in high spin, d~8 Ni(NMesBMes_2)_2 and the d~(10) N-heterocyclic carbene (NHC) complex Ni(IMes)_2. Herein we report unique two-coordinate, 13-electron d~9 nickel amides of the type (NHC)Ni(NR_2) and their oxidations to afford interesting and surprising low-spin d~8 products.