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Khamker Q, Champouret YD, Singh K, Solan GA: Bis (imino) quaterpyridine-bearing multimetallic late transition metal complexes as ethylene oligomerisation catalysts. Dalton Trans. 2009 Nov 7;(41):8935-44. Epub 2009 Sep 24.
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). |
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