PREPARATION OF NEW ZIRCONIUM BENZAMIDINATES - ALKYL DERIVATIVES AND LOW-VALENT CHEMISTRY YIELDING METALLACYCLES VIA COUPLING OF ALKYNES ANDETHYLENE

A wide range of new zirconium(IV) derivatives utilizing the N,N'-bis(t rimethylsilyl)benzamidinato ligand are reported. The previously report ed dichloride, L2ZrCl2 [L = PhC(NSiMe3)(2)], reacted cleanly with 1 eq uivalent of Me2Mg in Et2O to give L2ZrMe2 which was isolated as colorl ess crystals from CH2Cl2 or Et2O. Attempting to prepare the methyl chl oride derivative using 0.5 equivalent of Me2Mg yielded mixtures of dic hloride, dimethyl and methyl chloride derivatives. The compound L2ZrCl 2 reacted cleanly with 1 equivalent of the bulkier alkyl LiCH2SiMe3 gi ving L2Zr(CH2SiMe3)Cl. Reactivity of methyl derivatives with a variety of small molecules (CO, CO2 or acetone) is reported. The dimethyl com pound, L2ZrMe2, reacted cleanly with B(C6F5)(3) to form the methyltria rylborate complex L2Zr[MeB(C6F5)(3)]Me which is moderately active towa rds ethylene polymerization. Additionally, several other derivatives a re conveniently prepared by salt-metathesis reactions with the dichlor ide including; L2Zr(CH2Ph)(2), L2Zr(OSO2CF3)(2), L2Zr[NH(C6H3Pr21-2,6) ]Cl, L2Zr(BH4)2, L2Zr[ESi(SiMe3)(3)]Cl (E = Se or Te). The 1% Na-Hg am algam reduction of L2ZrCl2 in the presence of diphenylacetylene or tri methysilyl-acetylene yielded orange zirconacyclopentadienes L2Zr(C4Ph4 ) and L2Zr[C4H2(SiMe3)(2)-2,4] in moderate yields. The compound L2Zr(C 4Ph4) reacted readily with CO to give the dark red eta(2)-cyclopentadi enone L2Zr[eta(2)-C(O)C4Ph4]. Analogous the formation of the zirconacy clopentadienes, reduction in the presence of ethylene gave the zircona cyclopentane, L2Zr(C4H8), in good yield. When the reduction is carried out in the absence of any trapping ligands, however, a benzamidinate ligand is oxidatively cleaved and the dimeric imido-iminoacyl compound , [LZr(eta(2)-PhCNSiMe3)(mu-NSIMe3)](2), is isolated as orange crystal s in moderate yield. Single-crystal X-ray diffraction data are reporte d for L2ZrCl2, L2ZrMe2 and L2Zr(C4H8).