Scandium, titanium and vanadium complexes supported by PCP-type pincer ligands: synthesis, structure, and styrene polymerization activity.

A series of first-row early transition metal dialkyl complexes bearing pincer ligands [(POCOP)M(CH 2 SiMe 3 ) 2 ] (POCOP: (2,6-( t Bu 2 PO) 2 -C 6 H 3 ); 1-Sc: M = Sc; 1-Ti: M = Ti; 1-V: M = V) and [(PCP)M(CH 2 SiMe 3 ) 2 ] (PCP: (2,6-( t Bu 2 PCH 2 ) 2 -C 6 H 3 ); 2-Sc: M = Sc; 2-Ti: M = Ti) have been synthesized. These dialkyl complexes were characterized by single-crystal X-ray diffraction, NMR spectroscopy, and solution magnetic susceptibility (Evans method) analyses appropriately. All the complexes exhibited square pyramidal geometries with different extents of distortion. The activities of these complexes were further explored in styrene polymerization, in which combinations of scandium complexes (1-Sc or 2-Sc) with [Ph 3 C][B(C 6 F 5 ) 4 ] were found to be active catalytic systems for highly syndiospecific (>99% rrrr ) polymerization of styrene. Meanwhile, the Ti(III) complexes 1-Ti and 2-Ti showed rather low activity in styrene polymerization, which stands in sharp contrast to those in previous reports involving Ti(III) catalysts bearing cyclopentadienyl derivative ligands.