N-Phosphanyl- and N,N′-Diphosphanyl-Substituted N-Heterocyclic Carbene Chromium Complexes: Synthesis, Structures, and Catalytic Ethylene Oligomerization

Abstract

The chromium(II) complexes [CrCl2(t-BuNHC,P-κC)2] (1), [CrCl2(MesNHC,P-κC)2] (2), [CrCl2(DippNHC,P-κC)2] (3), and [CrCl2(P,NHC,P-κC)2] (4) containing the N-phosphanyl- or N,N′-diphosphanyl-substituted N-heterocyclic carbene (NHC) hybrid ligands t-BuNHC,P (1-(di-tert-butylphosphino)-3-tert-butylimidazol-2-ylidene), MesNHC,P (1-(di-tert-butylphosphino)-3-mesitylimidazol-2-ylidene), DippNHC,P (1-(di-tert-butylphosphino)-3-(2,6-diisopropylphenyl)imidazol-2-ylidene), and P,NHC,P (1,3-bis(di-tert-butylphosphino)imidazol-2-ylidene), respectively, were prepared from CrII ([CrCl2(thf)2]) or CrIII ([CrCl3(thf)3] or [Cr(Me)Cl2(thf)3]) precursors. The solid-state structures of these four complexes show square-planar CrII centers, with two trans chloride and two monodentate CNHC donors. Alkylation of 3 and 4 with [Mg(benzyl)2(thf)2] led to the formation of the σ complexes [Cr(benzyl)3(DippNHC,P-κC,κP)] (5) and [Cr(benzyl)3(P,NHC,P-κC,κP)] (6), respectively, with five-coordinate distorted-square-pyramidal CrIII coordin...