Isocyanide insertion reactivity of dinuclear niobium and tantalum imido complexes: X-ray crystal structure of [{Nb(η5-C5H4SiMe3)(CH2Ph)2}2(μ-1,4-NC6H4N)]

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