Ni(ii) and Fe(ii) complexes based on bis(imino)aryl pincer ligands: synthesis, structural characterization and catalytic activities

Abstract

Bis(imino)aryl NCN pincer Ni(II) complexes 2,6-(ArN=CH)(2)C(6)H(3)NiBr (1: Ar = 2,6-Me(2)C(6)H(3); 2: Ar = 2,6-Et(2)C(6)H(3); 3: Ar = 2,6-(i)Pr(2)C(6)H(3)) were prepared via the oxidative-addition of Ni(0)(Ph(3)P)(4) with bis(N-aryl)-2-bromoisophthalaldimine. These nickel complexes were characterized by NMR and elemental analyses. Their solid molecular structures were established by X-ray diffraction analyses. The nickel metal centers adopt distorted square planar geometries with the bromine atoms acting as one coordinate ligands. The NCN pincer Fe(II) complexes 2,6-(ArN=CH)(2)C(6)H(3)Fe(μ-Cl)(2)Li(THF)(2) (4: Ar = 2,6-Me(2)C(6)H(3); 5: Ar = 2,6-Et(2)C(6)H(3); 6: Ar = 2,6-(i)Pr(2)C(6)H(3)) were synthesized by lithium salt metathesis reactions of the ligand lithium salts with FeCl(2). X-ray structure analyses of 4 and 5 revealed that the Fe(II) complexes are hetero-dinuclear with the iron atoms in trigonal bipyramidal environments. When activated with MAO, the nickel complexes are active for norbornene vinyl polymerization but are inert for butadiene polymerization. The Fe(II) complexes show moderate activities in butadiene polymerization when activated with alkylaluminium, affording the cis-1,4 enriched polymer.

Dienes Polymerization: Where We Are and What Lies Ahead

“…110 Highly trans-1,4 selective polymerization of butadiene was performed with catalyst systems based on the combination of alkylaluminum, MAO, or MMAO, with iron(II) complexes with tridentate bis(imino)pyridyl ligands 111,112 or tridentate 2pyrazolyl substituted 1,10-phenanthroline ligands 113 (Figure 20). Fe(II) complexes with bis(amino)aryl pincer ligands, when activated with an alkylaluminum, showed moderate activities (up to 46 kg polybutadiene (mol Fe) −1 h −1 ) in the polymerization of butadiene, affording cis-1,4-enriched polymer 114 (Figure 21).…”

Cobalt and nickel complexes supported by 2,6-bis(imidate)pyridyl ligands: Synthesis, characterization, and 1,3-butadiene polymerization studies

“…To date, various transition metal complexes supported by imine-type ligands including bis(arylimino)pyridine 15,[17][18][19] , α-diimine 16,[20][21][22] , phenoxyimine [23][24][25] , β-enaminoketonato 26 , and β-diketonato 27 have been extensively studied in the field of olefin polymerization. Recently, such complexes are also studied in 1,3-butdiene polymerization [28][29][30][31][32] . We recently reported that Co(II) complexes bearing bis(imino)pyridine 33 and α-diimine 34 ligands exhibited high catalytic activity and cis-1,4-selectivity for 1,3-butadiene polymerization, and quite interestingly, the addition of phosphines to these systems not only enhanced the catalytic activity but also switched the selectivity from cis-1,4-to 1,2-manner.…”

NCN Nickel(II) Pincer Complexes of 5‐tert‐Butyl‐1,3‐bis(N‐substituted benzimidazol‐2′‐yl)benzenes: Solid and Solution State Behaviour

“…van Koten and co‐workers have reported the synthesis of bis(amine) based NCN nickel(II) pincer complexes, [{2,6‐R‐4‐(Me 2 NCH 2 ) 2 C 6 H 2 NiBr}] (R=H, MeC(O), Cl, MeO, NH 2 ) [ 1 (Scheme )], which have been used as homogeneous catalysts for the addition reaction of polyhalogenated alkanes to alkenes . Related bis(imino) Ni(II) NCN pincer complexes [{2,6‐(ArN=CH) 2 C 6 H 3 NiBr}] (Ar=2,6‐Me 2 C 6 H 3 , 2,6‐Et 2 C 6 H 3 , 2,6‐ i Pr 2 C 6 H 3 ) ( 2 ), have been utilized for the polymerization of butadiene and norbornene . Roester and co‐workers have reported a unique type of NCN nickel(0) pincer complex with six membered N‐heterocyclic carbene as the central ring.…”