Half-sandwich Mo(III) complexes with asymmetric diazadiene ligands

The asymmetric 1,4-diazadiene ligands (RN)-N-*=CHCH=NR* [R-* = (S)-CH(CH3)Ph], R(2)(*)dad, and 2,2'-bis(4-ethyloxazoline), as-ox, have been used to generate half-sandwich Mo-111 derivatives by addition to CP2Mo2Cl4. Ligand R(2)(*)dad affords a mononuclear, paramagnetic 17-electron product, CpMoCl2(R(2)(*)dad), whereas as-ox leads to the isolation of a dinuclear compound where only one molecule of ligand has been added per two Mo atoms, Cp2Mo2Cl4(as-ox). In the presence of free as-ox, this compound coexists with the paramagnetic mononuclear complex in solution. Both products are capable of controlling the radical polymerization of styrene under typical atom transfer radical polymerization (ATRP) conditions. However, the tacticity of the resulting polystyrene does not differ from that given by conventional free radical polymerization. (c) 2006 Elsevier B.V. All rights reserved.