Synthesis, Structure, and Polymerization Activity of Cyclopentadienylnickel(II) N‐Heterocyclic Carbene Complexes: Selective Cross‐Metathesis in Metal Coordination Spheres

Abstract

The N-heterocyclic carbene (NHC) complexes [(RC 5 H 4 )Ni-(X)(NHC)] (2-5) have been prepared by treating nickelocene [or 1,1Ј-bis(alkenyl)nickelocene] with a suitable carbene precursor. The alkenylcyclopentadienido complexes 4 and 5 undergo chemoselective cross-metathesis with methyl acrylate or methyl vinyl ketone in the presence of the seocnd-generation Grubbs catalyst to yield complexes 6-8, which bear an α,β-unsaturated carbonyl substituent on the cyclopentadienido ligand. The X-ray crystal structure of 2 [monoclinic,

Synthesis, Structures and Properties of Half‐Sandwich Nickel(II) Complexes with Backbone‐Modified NHC Ligands

“…Similar dynamic behaviour was observed for some dialkyl or mixed alkyl‐aryl nickel NHC complexes 6c,6f,10,23. The nature of such restricted rotation has been attributed mainly to steric factors related to the bulkiness of halogen or Cp ligands, although electronic factors cannot be completely excluded 6d,6f. Restricted rotation of the Ni–C carbene and N–C R bond could be also caused by a CH ··· XNi interaction, as observed in the solid state for [Ni(η 5 ‐C 5 H 5 )(Cl)(NHC)] [NHC = 1‐cyclohexyl‐3‐(2,4,6‐trimethylphenyl)‐4,5‐dihydroimidazol‐2‐ylidene] 6f.…”

“…Non‐equivalence of these hydrogen atoms bonded to the same carbon atom originates from the restricted rotation of the Ni–C carbene or N–C Bn bonds. Similar dynamic behaviour was observed for some dialkyl or mixed alkyl‐aryl nickel NHC complexes 6c,6f,10,23. The nature of such restricted rotation has been attributed mainly to steric factors related to the bulkiness of halogen or Cp ligands, although electronic factors cannot be completely excluded 6d,6f.…”

“…This procedure, developed by Abernethy et al, has proved to be versatile and has resulted in a considerable number of different NHC complexes of the general formula [Ni(η 5 ‐C 5 H 4 R)(X)(NHC)] ( 1 , R = H or alkyl; X = Cl, Br or I) 6,7. These complexes serve as precatalysts in a remarkably broad range of transformations, such as amination of aromatic halides,6a,6i polymerization of styrene,6b,6f polymerization of methyl methacrylate,8 Suzuki–Miyaura cross‐coupling,6g,9,10 polymerization of phenylacetylene,6f regioselective hydrothiolation of alkynes,11 hydrosilylation of aldehydes, ketones and imines,12 and α‐arylation of acyclic ketones 13…”

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

“…The nickel complexes (172−173), (175) and (182) were used in the polymerization of phenylacetylene [85].…”

“…The direct method of synthesis is sufficiently popular for the neutral [(NHC)(Cp)NiX], (X = anion) type complexes as the following [CpNi(NHC)X] (X = Cl, Br, I) type complexes, (172), [81] (173−175), [82] (176−177), [83] (178), [84] (179−182),[85] …”