Synthesis and Reactivity of Ene-Diamido and Ene-Diolato [(Trimethylsilyl)cyclopentadienyl]niobium(V) Complexes and a Comparative DFT Study of the Bonding Capabilities of Diazabutadiene and Butadiene Ligands

摘要: The reactions of [NbCp′Cl2(Me3SiCCSiMe3)] (Cp′ = η5-C5H4SiMe3) with 2,3-dimethyl-1,4-diphenyl-1,4-diazabuta-1,3-diene (Me,Ph-DAD) and diketones R−CO−CO−R (R Me, Ph) gave ene-diamido complexes [NbCp′Cl2(Me,Ph-DAD)] (1) ene-diolato [NbCp′Cl2{O(R)CC(R)O}] 2; Ph, 3), respectively, simultaneous elimination bis(trimethylsilyl)acetylene. NMR spectroscopic data these compounds are in agreement a supine conformation, respect to the Cp′ ring, ligands. In order gain further information concerning bonding capabilities ligand, DFT study model complex [NbCpCl2(HNCHCHNH)] (I) was performed. For comparison, analysis compound [NbCpCl2(η4-CH2CHCHCH2)] (II) also carried out. Differences description diazabutadiene butadiene ligands bonded common [NbCpCl2] moiety discussed. A detailed fragment orbital interactions I provides no evidence for any positive overlap between Nb centre inner carbon atoms DAD ligand. Dialkylation dichloro 1 dialkyl derivatives [NbCp′R2(Me,Ph-DAD)] 4; CH2SiMe3, 5; CH2C6H5, 6), which suggests prone conformation Treatment dimethyl derivative 4 monoxide 2,6-dimethylphenyl isocyanide led formation oxa- azaniobacyclopropane [NbCp′{η2-(E)CMe2}(Me,Ph-DAD)] [E O, 7; N(2,6-Me2C6H3), 8], respectively. Subsequent insertion into Nb−C bond 7 proceeds [NbCp′{η2-(O)CMe2-(CNAr)x}(Me,Ph-DAD)], (Ar 2,6-Me2C6H3; x 1, 9; 2, 10). All isolated were characterized by IR (1H, 13C{1H}) spectroscopy. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)