Synthesis and Structural Characterization of Nickel(II) Complexes with Imino-N-heterocyclic Carbene Heteroditopic Ligands

Abstract

Two different heteroditopic bis(aryl)-substituted imino-N-heterocyclic carbene ligands were coordinated to nickel using new copper carbene dimers as transmetalating agents. The oxidative addition of an imidazolium salt precursor with Ni(COD) 2 led to the unexpected bis(carbene)NiCl 2 complex, presumably through a putative nickel hydride intermediate. All new complexes were isolated in good yield and were structurally characterized. The size of the iminic carbon substituent was found to have a profound impact on the bond angles and bond lengths about the metal center. All nickel complexes were tested for ethylene polymerization activity at standard temperature and pressure and were found to be inactive.

Nickel N-heterocyclic carbene complexes and their utility in homogeneous catalysis

“…The first route is the transmetallation method (Scheme 13), which was used for preparing the following complexes (336), [120] (337), [121] (338), [122] (339−340) and [123] (341) [124] from the respective Ag−NHC complexes and (342) [125] from a Cu−NHC complex by the treatment with the Ni(II) precursors namely, (DME)NiX 2 (X = Cl, Br) and (PPh 3 ) 2 NiX 2 (X = Br, Cl).…”

“…A large number of the benzimidazole, imidazole and the triazole based N-heterocyclic carbene complexes of the type (NHC) 2 NiX 2 (343−359), [122,126] (360), [127] (361−364), [128] (365−366), [122] (367), [129] (368), [50,129] (369−371), [129] (372), [130] (373), [127] (374), [131] (375), [132] (376−377), [133] (378), [134] (379), [135] (380), [136] (381−382), [86] (383−384), [137] (385−386), [138] (387−388), [124] (389−392), [110] (393), [139] (394), [47] (395−396), [140] (397−398) [141] and (399−400) [127] were conveniently synthesized by the direct method from the reaction of a free or an in situ generated NHC ligand with a Ni(II) precursor namely, Ni(OAc) 2 , bis-indenyl nickel (Ind) 2 In the third approach, the oxidation method has been used in the preparation of the (402), [125] (403−404), [143] (405), [144] (441) [32] and (446−447) [62] Additional notable examples of the oxidation method include a large number of complexes (367−368), [145] (406−409), [146] (410−411), [40] (412), [147] (413−416), [21] (417−420), [41] (421−422), [148] (423−...…”

Coordination and reactivity study of titanium phenoxo complexes containing a bulky bidentate imino-N-heterocyclic carbene ligand

“…The steric constraint imposed by the formation for the metallacycle leads to a yaw distortion of 10.0 , slightly higher than that observed in TiCl 4 (C^Imine) (9.1 ) [12] but considerably smaller than in square planar nickel complexes of C^Imine (14.5e15.7 ) [9], further illustrating the effect of having a sixcoordinate metal centre and sterically-demanding phenoxide ligands.…”

“…Nucleophilic attack of adventitious water on the iminic carbon of the bidentate ligand, which has become a better electrophile through replacement of two chlorides in TiCl 4 (C^Imine) with the more electronegative phenoxide ligands, likely accounts for its decomposition to mesitylimidazole and N-(2,6-dimethylphenyl)pivaloylamide. Interestingly, such cleavage of the N1eC4 bond has not been reported for more electron-rich late transition metal analogues [9]. Compound 2 was independently synthesized by reacting 2 equiv of 1-(2,4,6-trimethylphenyl)imidazole with TiCl 2 (2,6-OC 6 H 3 -Me 2 ) 2 (THF) 2 .…”

Nickel(II) Complexes with Tritopic NimineCNHCNamine Pincer Ligands

“…Using a potentially bidentate N imine C NHC ligand, Lavoie's group also observed monodentate C NHC behavior [Eq. (2)] …”