Isocyanide insertion reactivity of dinuclear niobium and tantalum imido complexes: X-ray crystal structure of [{Nb(η 5-C 5H 4SiMe 3)(CH 2Ph) 2} 2(μ-1,4-NC 6H 4N)

Abstract

The reactivity of dinuclear niobium and tantalum imido complexes with the isocyanide compound 2,6-Me 2C 6H 3NC has been studied. The trialkyl complexes [{NbR 3(CH 3CN)} 2(μ-1,3-NC 6H 4N)], [{NbR 3(CH 3CN)} 2(μ-1,4-NC 6H 4N)] and [{TaR 3(CH 3CN)} 2(μ-1,4-NC 6H 4N)] (R=CH 2SiMe 3) gave [{Nb(η 2-RCNAr) 2R} 2(μ-1,3-NC 6H 4N)] ( 1), [{Nb(η 2-RCNAr) 2R} 2(μ-1,4-NC 6H 4N)] ( 2) and [{Ta(η 2-RCNAr) 2R} 2(μ-1,4-NC 6H 4N)] ( 3) (R=CH 2SiMe 3; Ar=2,6-Me 2C 6H 3), from the isocyanide insertion in two of the metal alkyl carbon bonds. The reaction of the isocyanide reagent with the di-alkyl mono-cyclopentadienyl derivatives [{Nb(η 5-C 5H 4SiMe 3)R 2} 2(μ-1,3-NC 6H 4N)] (R=Me, CH 2Ph, CH 2SiMe 3), [{Nb(η 5-C 5H 4SiMe 3)R 2} 2(μ-1,4-NC 6H 4N)] (R=Me, CH 2Ph ( 4), CH 2SiMe 3) and [{Ta(η 5-C 5Me 5)(CH 2SiMe 3) 2} 2(μ-1,4-NC 6H 4N)] yielded [{Nb(η 5-C 5H 4SiMe 3)(η 2-RCNAr)R} 2(μ-1,3-NC 6H 4N)] (R=Me ( 5), CH 2Ph ( 6), CH 2SiMe 3 ( 7)), [{Nb(η 5-C 5H 4SiMe 3)(η 2-RCNAr)R} 2(μ-1,4-NC 6H 4N)] (R=Me ( 8), CH 2Ph ( 9), CH 2SiMe 3 ( 10)) and [{Ta(η 5-C 5Me 5)(η 2-Me 3SiCH 2CNAr)CH 2SiMe 3} 2(μ-1,4-NC 6H 4N)] ( 11) (Ar=2,6-Me 2C 6H 3), respectively, from a single insertion process. The reaction with the mono-alkyl complex [{Nb(η 5-C 5H 4SiMe 3)(Me)Cl} 2(μ-1,4-NC 6H 4N)] gave [{Nb(η 5-C 5H 4SiMe 3)(η 2-MeCNAr)Cl} 2(μ-1,4-NC 6H 4N)] ( 12), produced from the isocyanide insertion in the metal-alkyl carbon bond. The alkyl-amido complex [{Nb(η 5-C 5H 4SiMe 3)(Me)NMe 2} 2(μ-1,4-NC 6H 4N)] gave, from the preferential isocyanide insertion in the metal-amide nitrogen bond, [{Nb(η 5-C 5H 4SiMe 3)(η 2-Me 2NCNAr)Me} 2(μ-1,4-NC 6H 4N)] ( 13). The molecular structure of one of the alkyl precursors, [{Nb(η 5-C 5H 4SiMe 3)(CH 2Ph) 2} 2(μ-1,4-NC 6H 4N)] ( 4), has been determined.