Synthesis of new chloro methyl niobium and tantalum complexes with silyl-cyclopentadienyl ligands: X-ray crystal structure of [Ta{η5-C5H3(SiMe3)2}Cl2Me2]

Trichloro methyl [Nb{η5-C5H3(SiXMe2)(SiMe3)}Cl3Me] (X = Cl, 2; Me, 3), dichloro dimethyl [Nb{η5-C5H3(SiXMe2)(SiMe3)}Cl2Me2] (X = Cl, 4; Me, 5) and tetramethyl [Nb{η5-C5H3(SiXMe2)(SiMe3)}Me4] (X = Me, 6; Cl, 7) niobium complexes were synthesized by treatment of starting tetrachloro derivatives [Nb{η5-C5H3(SiXMe2)(SiMe3)}Cl4] (X = Cl, 1a; Me, 1b) with dimethyl zinc or chloro methyl magnesium in different proportions and conditions. A mixture of trichloro methyl and dichloro dimethyl tantalum complexes [Ta{η5-C5H3(SiClMe2)(SiMe3)}Cl4−xMex] (x = 1, 8; 2, 9) in a 2:1 molar ratio was obtained in the reaction of [Ta{η5-C5H3(SiClMe2)(SiMe3)}Cl4] (1c) with 0.5 equivalents of ZnMe2 in toluene at low temperature. 8 could be isolated as single compound when 1 equivalent of 1c was added to the mixtures of 8 and 9, while the reaction of 1c with 1.5 equivalents of dimethyl zinc gave 9 as unitary product. However, [Ta{η5-C5H3(SiMe3)2}Cl4] (1d) reacts with 0.5 equivalents of alkylating reagent giving the trichloro methyl compound [Ta{η5-C5H3(SiMe3)2}Cl3Me] (10) in good yield. On the other hand, [Ta{η5-C5H3(SiMe3)2}Cl4] (1d) reacts with 2 equivalents of MgClMe in hexane at room temperature giving a mixture of dichloro dimethyl and chloro trimethyl complexes[Ta{η5-C5H3(SiMe3)2}Cl4−xMex] (x = 2, 11; 3, 12), while the use of 4 equivalents of MgClMe converts 1c into the tetramethyl derivative [Ta{η5-C5H3(SiClMe2)(SiMe3)}Me4] (13). Finally, a tetramethyl tantalum complex [Ta{η5-C5H3(SiMe3)2}Me4] (14) was prepared by reaction of [Ta{η5-C5H3(SiXMe2)(SiMe3)}Cl4] (X = Cl, 1c; Me, 1d) with 5 (X = Cl) or 4 (X = Me) equivalents of MgClMe in diethyl ether (X = Cl) or hexane (X = Me), respectively, as solvent. All the complexes were studied by IR and NMR spectroscopy and the molecular structure of the complex 11 was determined by X-ray diffraction methods.