Indenyl Functionalized N-Heterocyclic Carbene Complexes of Chromium: Syntheses, Structures, and Reactivity Studies Relevant to Ethylene Oligomerization and Polymerization

Abstract

The chromium(III) complexes of the type L1CrXY (L1 = 1-(2,6-diisopropylphenyl)-3-[β-(4,7-dimethylindenyl)ethyl]-imidazol-2-ylidene, X, Y = Cl, 2a-Cl; X = Cl, Y = Me, 2a-Me; X = Cl, Y = Ph, 2a-Ph; X, Y = benzyl, 2a-Bz) and L2CrCl2 (L2 = 1-(2,6-diisopropylphenyl)-3-[γ-(4,7-dimethylindenyl)propyl]-imidazol-2-ylidene, 2b-Cl) have been prepared and characterized by analytical and diffraction methods. The salts [L1CrCl(THF)]+[BArF 4]− and [L2CrCl(THF)]+[BArF 4]− (ArF = 3,5-bis(trifluoromethyl)phenyl) were also characterized, having been obtained by abstraction of chloride, or indirectly a methyl, from 2a-Cl or 2a-Me, and 2b-Cl, by NaBArF 4, respectively. Reaction of 2a-Bz with 1 equiv of [H(Et2O)2][BArF 4] in THF gave the thermally unstable salt [L1Cr(Bz)(THF)]+[BArF 4], [2a-Bz] + [BAr F 4 ], which was also characterized crystallographically. The chromium(II) analogue L1CrCl, 3a, was prepared from CrCl2 and L1K, but on prolonged standing in THF, it converted to the dimeric complex 4a. The complexes 2a-Cl, 2b-Cl, 2b-Me, and 2a-Bz in the presence of an Al activator were tested as ethylene polymerization and oligomerization catalysts, in general, showing activity toward polymer formation.

A chromium precursor for the Phillips ethylene trimerization catalyst: (2-ethylhexanoate)2CrOH

“…The solid was soluble in THF, and layering pentane onto the THF solution yielded single crystals of which structure was elucidated to be MeCrCl 2 (THF) 3 via X-ray crystallographic studies. 42,43…”

N-heterocyclic carbene complexes of Group 6 metals

“…CpCr(III)-NHC complexes[169] 4.1.1.3 Indenyl functionalized NHC complexes of CrIn 2012,Danopoulos and Hanton et al[170] reported the synthesis of indenyl functionalized NHC complexes of Cr(II). Complex Cr-51 (Figure 4.5) was synthesized from the reaction of CrCl 2 with the potassium salt of the indenyl functionalized ligand[170].…”

“…Complex Cr-51 (Figure 4.5) was synthesized from the reaction of CrCl 2 with the potassium salt of the indenyl functionalized ligand[170]. It adopts a distorted three coordinate geometry with Cr-C carbene distance of 2.075(4) Å.…”

“…It adopts a distorted three coordinate geometry with Cr-C carbene distance of 2.075(4) Å. Its Cr(III) analogues Cr-52aand Cr-53a(Figure 4.5) were produced from CrCl 3 (THF)3 with the corresponding potassium salt[170]. Both complexes show distorted tetrahedral geometries and the Cr-C carbene bond lengths are 2.154(2) and 2.089(4) Å, respectively.…”

Dehydrogenative coupling of aromatic thiols with Et3SiH catalysed by N-heterocyclic carbene nickel complexes

“…3 During the last few years, our research group in collaboration with Peris and co-workers has developed a new class of bidentate cyclopentadienyl ligands tethered to N-heterocyclic carbenes (NHCs) (A, Scheme 1). [4][5][6][7][8][9][10][11][12] Related indenyl-functionalised NHCs have been described by Danopoulos, [13][14][15][16] Wang 17 and others. 18 An important feature of these Cp-NHC chelating ligands is the possibility of independently varying their structural components, namely the cyclopentadienyl ring, the spacer, and the imidazolium ring in order to fine tune the steric and electronic properties of the ligand.…”