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

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Abstract
A wide range of new zirconium(IV) derivatives utilizing the N,N′-bis(trimethylsilyl)benzamidinato ligand are reported. The previously reported dichloride, L 2 ZrCl 2 [L = PhC(NSiMe 3 ) 2 ], reacted cleanly with 1 equivalent of Me 2 Mg in Et 2 O to give L 2 ZrMe 2 which was isolated as colorless crystals from CH 2 Cl 2 or Et 2 O. Attempting to prepare the methyl chloride derivative using 0.5 equivalent of Me 2 Mg yielded mixtures of dichloride, dimethyl and methyl chloride derivatives. The compound L 2 ZrCl 2 reacted cleanly with 1 equivalent of the bulkier alkyl LiCH 2 SiMe 3 giving L 2 Zr(CH 2 SiMe 3 )Cl. Reactivity of methyl derivatives with a variety of small molecules (CO, CO 2 or acetone) is reported. The dimethyl compound, L 2 ZrMe 2 , reacted cleanly with B(C 6 F 5 ) 3 to form the methyltriarylborate complex L 2 Zr[MeB(C 6 F 5 ) 3 ]Me which is moderately active towards ethylene polymerization. Additionally, several other derivatives are conveniently prepared by salt-metathesis reactions with the dichloride including: L 2 Zr(CH 2 Ph) 2 , L 2 Zr(OSO 2 CF 3 ) 2 , L 2 Zr[NH(C 6 H 3 Pr i 2 -2,6)]Cl, L 2 Zr(BH 4 ) 2 , L 2 Zr[ESi(SiMe 3 ) 3 ]Cl (E = Se or Te). The 1% Na–Hg amalgam reduction of L 2 ZrCl 2 in the presence of diphenylacetylene or trimethylsilylacetylene yielded orange zirconacyclopentadienes L 2 Zr(C 4 Ph 4 ) and L 2 Zr[C 4 H 2 (SiMe 3 ) 2 -2,4] in moderate yields. The compound L 2 Zr(C 4 Ph 4 ) reacted readily with CO to give the dark red η 2 -cyclopentadienone L 2 Zr[η 2 -C(O)C 4 Ph 4 ]. Analogous to the formation of the zirconacyclopentadienes, reduction in the presence of ethylene gave the zirconacyclopentane, L 2 Zr(C 4 H 8 ), 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(η 2 -PhCNSiMe 3 )(µ-NSiMe 3 )] 2 , is isolated as orange crystals in moderate yield. Single-crystal X-ray diffraction data are reported for L 2 ZrCl 2 , L 2 ZrMe 2 and L 2 Zr(C 4 H 8 ).

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