Übergangsmetall-Carbin-Komplexe: CIII. Aktivierung von Ethylisocyanid an elektronenreichen Metallzentren; Synthese von einkernigen Wolfram-Aminocarbin-Komplexen des Typs Tp′(CO)2 WCN(R)Et (R Me, Et)

Abstract A large-scale, high-yield synthesis of the aminocarbyne complexes Tp′(CO) 2 WCN(R)Et (5: R  Me; 6 : R  Et) [Tp′ = hydridotris(3,5-dimethylpyrazol-1-yl)borate] is reported, starting from Tp′W(CO) 3 I ( 2 ). The first step of the synthetic procedure involves thermal decarbonylation of 2 with EtNC to give cis -Tp′W(CO) 2 (CNEt)I ( 3 ). Complex 3 is then reduced with Na/Hg to give the metallate Na[Tp′W(CO) 2 (CNEt)] ( 4 ). Finally, complex 4 is alkylated with RI (R  Me, Et) exclusively at the isocyanide nitrogen to give the aminocarbyne complexes 5 and 6 . In contrast, the metallates Na[(η 5 -C 5 R′ 5 )W(CO) 2 (CNEt)] (R′  H, Me) undergo alkylation with RI at the metal centre to afford the W II alkyl complexes cis / trans -(η-C 5 R′ 5 )W(CO) 2 (CNEt)R. This difference in reactivity is ascribed to the steric demands of the Tp′ ligand, which shields the metal centre from the incoming electrophile.