Monoanionic fac-k3 ligands derived from 6-amino-1,4-diazepine:: Ligand dependence of stability and catalytic activity of their scandium alkyl derivatives

Two new monoanionic fac-kappa(3) tridentate ligands [6-RN-1,4,6-trimethyl-1,4-diazepine](-) (R = CH3, L-1; R = PhMe2Si, L-2) were prepared. Reactions of ligands HL1 and HL2 with Sc(CH2SiMe3)(3)(THF)(2) yielded (L-1)Sc(CH2SiMe3)(2)(THF) (1) and (L-2)SC(CH2SiMe3)(2)(THF) (2), respectively. In toluene solvent, 1 loses a THF molecule and decomposes via metalation of the methyl group of the amido functionality to give {[CH2(mu-N)-1,4,6-trimethyl-1,4-diazepine]SC(CH2SiMe3)}(2) (3), whereas 2 loses a THF molecule to give stable (L-2)Sc(CH2SiMe3)(2) (4). In THF, both 1 and 2 react with [PhNMe2H][B(C6H5)(4)] to generate the ionic monoalkyl compounds [(L)Sc(CH2SiMe3)(THF)(2)][B(C6H5)(4)] (5, L = L-1, 6, L = L-2). Nevertheless, only the THF-free system 4/[PhNMe2H][B(C6F5)(4)] shows good ethylene polymerization activity, showing that a single THF molecule per Sc suffices to quench the catalysis. Dinuclear 3 reacts with ethylene via stoichiometric insertion into the Sc-CH2N bond to yield {[CH2CH2CH2(mu-N)-1,4,6-trimethyl-1,4diazepine]Sc(CH2SiMe3)}(2) (7).