Paul Alexander Cameron

Controlled polymerization of lactides at ambient temperature using [5‐Cl‐salen]AlOMe

The Schiff-base aluminium complex [5-Cl-salen]AlOMe (2) is shown to be a room temperature initiator for controlled ring-opening polymerization of D,L- and L-lactides; the molecular structure of the precursor [5-Cl-salen]AlMe (1) reveals a distorted trigonal bipyramidal geometry.

Pendant arm Schiff base complexes of aluminium as ethylene polymerisation catalysts

The potentially tridentate Schiff base ligands [3,5-But2-2-(HO)C6H2CHNL] 1, on reaction with Me3Al at room temperature, afford the complexes [(3,5-But2-2-(O)C6H2CHNL)AlMe2] [L = CH2CH2NMe2 2a, (2-PhO)C6H4 2b, 2-CH2C5H4N 2c and 8-C9H6N (quinoline) 2d], 2a and 2c have been characterised crystallographically; further reaction of the dimethyl compounds with B(C6F5)3 affords the cationic systems [(3,5-But2-2-(O)C6H2CHNL)AlMe]+ 3a–d of which 3a and 3b are ethylene polymerisation catalysts.

Synthesis and characterisation of neutral and cationic alkyl aluminium complexes bearing N,O-Schiff base chelates with pendant donor arms

The Schiff base ligands [3,5-But2-2-(OH)C6H2CHNL] [L = CH2CH2NMe2 (1a), 2-(PhO)C6H4 (1b), 2-CH2C5H3N (1c), 8-C9H6N (quinoline) (1d) and 2-(PPh2)C6H4 (1e)] are accessed in good yields (>85%) via standard imine condensation reactions. Reaction of 1a–e with Me3Al at room temperature affords the corresponding complexes [(3,5-But2-2-(O)C6H2CHNL)AlMe2] (2a–e); in the case of L = 8-quinoline, the same reaction conducted in refluxing toluene affords binuclear {[3,5-But2-2-(O)C6H2CHMeN-8-C9H6N]AlMe}2 (3) by methyl migration from metal to ligand. Further reaction of the dimethyl compounds with B(C6F5)3 in CD2Cl2 or C6D6 affords the cationic systems [(3,5-But2-2-(O)C6H2CHNL)AlMe]+ (4a–e). The crystal structures of 2a, 2c, 2e and 3 have been determined. In 2a and 2c the respective ligands bind to the metal centre via all three heteroatoms, the aluminium having a trigonal bipyramidal geometry, whereas in 2e coordination is via nitrogen and oxygen only, and the aluminium is tetrahedral. Complex 3 has a dimeric structure with the ligand adopting both tridentate and binucleating roles; the aluminium centres are trigonal bipyramidal.

Surprises in enolate binding at high valent molybdenum

Treatment of [Mo(NAr)2Cl2(DME)] (Ar = 2,6-diisopropylphenyl; DME = 1,2-dimethoxyethane) with LiOC(OBut)CMe2 at low temperature affords the unexpected carbon-bound molybdenum(VI) enolate complex [Mo(NAr)2Cl{η2-C(Me2)CO2But}] 1; the novel α-aminoenolate derivative [Mo(NAr)2Cl{η2-CH(NMe2)CO2Et}] 2 is obtained under analogous conditions using LiNPri2/Me2NCH2CO2Et; the structures of 1 and 2 confirm the carbophilic nature of the [Mo(NAr)2] core.