Bis(imino)quaterpyridine-bearing multimetallic late transition metal complexes as ethylene oligomerisation catalysts

Abstract

The bis(imino)quaterpyridine, 6,6'''-{(2,4,6-i-Pr(3)C(6)H(2))N=CMe}(2)-2,2':6',2'':6'',2'''-C(20)H(12)N(4) (L(tripp)), can be prepared in good yield by the condensation reaction of 6,6'''-bis(acetyl)quaterpyridine with 2,4,6-triisopropylaniline; the 2,6-diisopropylphenyl derivative 6,6'''-{(2,6-i-Pr(2)C(6)H(3))N=CMe}(2)-2,2':6',2'':6'',2'''-C(20)H(12)N(4) (L(dipp)) is also reported. Reactions of L(tripp) with 2.5 equivalents of MX(2) (MX(2) = CoCl(2), CoBr(2), (DME)(2)NiCl(2) and FeCl(2)) in n-butanol at 100 degrees C overnight results in self-assembly to form the paramagnetic salts [(L(tripp))M(2)X(3)](2)[MX(4)] [M = Co, X = Cl (1a); M = Co, X = Br (1b); M = Ni, X = Cl (2); M = Fe X = Cl (3)] in moderate yield. The molecular structures of the acetonitrile/water adducts 1a(NCMe)(2), 1b(NCMe)(OH(2)) and 2(NCMe)(4) reveal that L(tripp) acts as a bis(tridentate) ligand that can support a range of structural motifs for the cationic units including [(L(tripp))CoCl(mu-Cl)CoCl(NCMe)](+), [(L(tripp))CoBr(2)CoBr(OH(2))(NCMe)](+), [(L(tripp))CoBr(mu-Br)CoBr)](+) and [(L(tripp))NiCl(NCMe)(mu-Cl)NiCl(NCMe)](+). On activation with MAO (methylaluminoxane), 1-3 show modest activities for ethylene oligomerisation (1a/MAO approximately 1b/MAO > 2/MAO) or are inactive (3/MAO). Notably, the two cobalt systems (1a/MAO, 1b/MAO) afford highly linear alpha-olefins while the nickel system (2/MAO) yields methyl-branched waxes composed of mostly internal unsaturation along with lower levels of alpha-olefins. In addition to 1a(NCMe)(2), 1b(NCMe)(2)(OH(2)) and 2(NCMe)(3), a single crystal X-ray determination has been performed on the structurally related salt [(L(tripp))Ni(2)Br(3)(OH(2))(2)][Br] (4).