Niobium‐ and Tantalum‐Based Ethylene Polymerisation Catalysts Bearing Methylene‐ or Dimethyleneoxa‐Bridged Calixarene Ligands

Abstract

Treatment of p-tert-butylcalix[6]areneH(6) (H(6)tBu-L) or p-tert-butylcalix[8]areneH(8) (H(8)tBu-L(1)) with [MCl(5)] (M=Nb, Ta) in refluxing toluene or dichloromethane affords, after work-up, the complexes [{M(NCMe)Cl(2)}(2)(tBu-L)] (M=Nb (1), Ta (2)) and [(MCl(2))(2)(tBu-L(1)H(2))] (M=Nb (4), Ta (5)), respectively. Complex 1, as well as [{Nb(2)(mu-O)(2)(mu-Cl)(tBu-LH)}(2)] (3), is also available from [NbOCl(3)] and H(6)tBu-L. Reaction of [MOCl(3)] (M=Nb, Ta) with Li(3)(tBu-L(2)) in diethyl ether, where H(3)tBu-L(2) is p-tert-butylhexahomotrioxacalix[3]areneH(3), affords, after work-up, the trimeric complexes [{M(tBu-L(2))(mu-O)}(3)] (M=Nb (6), Ta (7)). The behaviour of 1 to 7 (not 3), as well as the known complexes [{(MCl)p-tert-butylcalix[4]arene}(2)] (M=Nb (8), Ta (9)) and [(MCl(2))p-tert-butylcalix[4]arene(OMe)] (M=Nb (10), Ta (11)), as pro-catalysts for the polymerisation of ethylene has been investigated. In the presence of dimethyl (or diethyl)aluminium chloride, methylaluminoxane or trimethylaluminium, these niobium and tantalum procatalysts are all active (<35 g mmol(-1) h(-1) bar(-1)), for the polymerisation of ethylene affording high-molecular-weight linear polyethylene. The dimethyleneoxa-bridged systems (derived from 6 and 7) are more active (84 and 46 g mmol(-1) h(-1) bar(-1), respectively) than the methylene-bridged systems. The molecular structures of 1-6 and 10 (acetonitrile solvate) are reported.

Activated Niobium and Tantalum Imido Complexes: From Tuneable Polymerization to Selective Ethylene Dimerization Systems

“…However, these values are less than half those achieved using the analogous niobium pre‐catalysts. This parallels reports in the literature that identify the same trends in relative performance between analogous Nb‐ and Ta‐based polymerization systems ,…”

INSIGHTS into the structures adopted by titanocalix[6 and 8]arenes and their use in the ring opening polymerization of cyclic esters

“…The coordination of the metal to the calix [6]arene and the conformation adopted by the macrocycle are reminiscent of that observed for the group V complexes {[M(NCMe)Cl 2 ] 2 L 1 } (M = Nb, Ta). 16 When THF was employed as solvent, the orange/red complex [Ti 4…”

“…The hexane molecule lies in the cleft between the two aromatic rings. There is a weak intermolecular C-H⋯Br interaction between the methyl group at C (16) and Br (1) with an H(16A)⋯Br(1) distance of 3.05 Å.…”

Calix[8]arenes Solid-State Structures: Derivatization and Crystallization Strategies

“…The niobium complex reported was prepared from NbCl 5 as metal source, and crystallized from hot acetonitrile solution as two polymorphs, only one of which was refined as (NbCl 2 ) 2 (p-tert-butylcalix[8]arene-6H). The macrocycle adopts a twisted conformation, and no oxygen bridges between the metal centers are observed; the two OH protons on the phenolic units are H-bonded to acetonitrile molecules in the lattice (Redshaw et al, 2007). Not surprisingly, late transition metals are hardly represented among structurally characterized calix [8]arene complexes.…”