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

The bis(imino)quaterpyridine, 6,6'''-{(2,4,6-i-Pr3C6H2)N=CMe}(2)-2,2': 6', 2 '': 6 '', 2'''-C20H12N4 (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-Pr2C6H3)N=CMe}(2)-2,2': 6', 2 '': 6 '', 2'''-C20H12N4 (L-dipp) is also reported. Reactions of L-tripp with 2.5 equivalents of MX2 (MX2 = CoCl2, CoBr2, (DME)(2)NiCl2 and FeCl2) in n-butanol at 100 degrees C overnight results in self-assembly to form the paramagnetic salts [(L-tripp)M2X3](2)[MX4] [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)(OH2) 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)CoBr2CoBr(OH2)(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 similar to 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)(OH2) and 2(NCMe)(3), a single crystal X-ray determination has been performed on the structurally related salt [(L-tripp)Ni2Br3(OH2)(2)][Br] (4).