Preparation of new zirconium benzamidinates: alkyl derivatives and low-valent chemistry yielding metallacycles via coupling of alkynes and ethylene

A wide range of new zirconium(IV) derivatives utilizing the N,N'-bis(trimethylsilyl)benzamidinato ligand are reported. The previously reported dichloride, L2ZrCl2 [L = PhC(NSiMe3)(2)], reacted cleanly with 1 equivalent of Me2Mg in Et2O to give L2ZrMe2 which was isolated as colorless crystals from CH2Cl2 or Et2O. Attempting to prepare the methyl chloride derivative using 0.5 equivalent of Me2Mg yielded mixtures of dichloride, dimethyl and methyl chloride derivatives. The compound L2ZrCl2 reacted cleanly with 1 equivalent of the bulkier alkyl LiCH2SiMe3 giving L2Zr(CH2SiMe3)Cl. Reactivity of methyl derivatives with a variety of small molecules (CO, CO2 or acetone) is reported. The dimethyl compound, L2ZrMe2, reacted cleanly with B(C6F5)(3) to form the methyltriarylborate complex L2Zr[MeB(C6F5)(3)]Me which is moderately active towards ethylene polymerization. Additionally, several other derivatives are conveniently prepared by salt-metathesis reactions with the dichloride 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 amalgam reduction of L2ZrCl2 in the presence of diphenylacetylene or trimethysilyl-acetylene yielded orange zirconacyclopentadienes L2Zr(C4Ph4) and L2Zr[C4H2(SiMe3)(2)-2,4] in moderate yields. The compound L2Zr(C4Ph4) reacted readily with CO to give the dark red eta(2)-cyclopentadienone L2Zr[eta(2)-C(O)C4Ph4]. Analogous the formation of the zirconacyclopentadienes, reduction in the presence of ethylene gave the zirconacyclopentane, 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 crystals in moderate yield. Single-crystal X-ray diffraction data are reported for L2ZrCl2, L2ZrMe2 and L2Zr(C4H8).