Direct synthesis of cis-dihalido-bis(NHC) complex of nickel(II) and catalytic application in olefin addition polymerization: effect of halogen co-ligands and density functional theory study

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 42; no. 33; pp. 12020 - 12030
• Main Authors: Zhang, Dao, Zhou, Sen, Li, Zhiming, Wang, Quanrui, Weng, Linhong
• Format: Journal Article
• Language: English
• Published: England 01.01.2013
• Subjects: Addition polymerization; Alkenes - chemistry; Catalysis; Chlorides; Crystallography, X-Ray; Ethylene; Halogens; Halogens - chemistry; Heterocyclic Compounds - chemistry; Ligands; Methane - analogs & derivatives; Methane - chemistry; Models, Molecular; Molecular Structure; Nickel; Nickel - chemistry; Olefins; Organometallic Compounds - chemical synthesis; Organometallic Compounds - chemistry; Polymerization; Quantum Theory
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c3dt50957e

Two novel amine-containing N-heterocyclic carbene ligand precursors [H(1a-b)]Br have been prepared in good yield and fully characterized. Direct syntheses of cis- and trans-dihalido-bis(NHC) nickel complexes [Ni(NHC)2X2] (X = Cl, Br) are reported. The solid structures of trans-[Ni(1a-b)2Br2] (2a-b) and cis-[Ni(1a)2Cl2] (3) were determined by single-crystal X-ray analysis and 3 was found to be the first example of cis-configuration coordination of monodentate NHC ligands to a metal center for dihalido-bis(NHC) nickel complexes. DFT calculations were conducted to determine the energy difference between cis- and trans-isomers of complexes 2a and 3 bearing bromide and chloride co-ligands. The cis-[Ni(1a)2Cl2] (cis-3) is 1.77-1.55 kcal mol(-1) lower in energy than its trans-isomer in polar solvents including CH2Cl2 and THF, while the trans-[Ni(1a)2Br2] (trans-2a) is more stable than the cis-isomer similarly in the gas phase. The cis nickel complex 3 with two coordinated monodentate NHCs was tested for olefin addition polymerization at standard conditions. It was found that cis-3 was inactive in ethylene polymerization but showed moderate catalytic activities (0.5-3.0 × 10(6) g of PNB (mol of Ni)(-1) h(-1)) in the addition polymerization of norbornene in the presence of methylaluminoxane (MAO) as cocatalyst.