Synthesis of group 4 organometallic complexes that contain the bis(borylamide) ligand [Mes(2)BNCH(2)CH(2)NBMes(2)](2-)

Titanium and zirconium derivatives of the new chelating bis(borylamido) ligand [Mes(2)BNCH(2)CH(2)NBMes(2)](2-) ([Ben](2-)) are prepared by treating MCI(4)(THF)(2) (M = Ti, Zr) with (Ben)Mg(THF)(2). Nitrogen-boron pi-interactions in (Ben)TiCl2 and (Ben)ZrCl2(THF) result in one mesityl group in each BMes(2) unit occupying space roughly above and below the MCl(2) plane. (Ben)TiCl2 is smoothly alkylated by Grignard reagents in dichloromethane to give (Ben)Ti(R)Cl (R = CH(2)Ph, CH(2)CMe(3)) and (Ben)TiR(2) (R = Me, CH(2)Ph), while unstable (Ben)-ZrMe(2) can be prepared from (Ben)ZrCl2(THF) and methyllithium in toluene. An X-ray study of (Ben)Ti(CH(2)Ph)Cl confirms the proposed ligand conformation and features a highly distorted ''eta(2)'' benzyl ligand with a Ti-C-a-C-ipso angle of only 87.0(5)degrees. (Ben)MMe(2) complexes cleanly decompose by metalation of the ortho methyl groups from mesityl rings on different borons at room temperature (for Zr) or upon heating (for Ti). An X-ray crystal structure of (TwistBen)Zr shows it to be a dimer in which the two zirconium centers are bridged by two mesityl o-methylene groups. B(C6F5)(3) binds to a methyl group in (Ben)MMe(2) complexes in dichloromethane, but such compounds show little polymerization activity toward ethylene at 25 degrees C and 1-2 atm as a consequence of strong anion binding.