Arylimido niobium(V) complexes: mononuclear and dendritic derivatives

The compound 4-LiC6H4N(SiMe3)2 reacted in tetrahydrofuran with SiMe3Cl or with silicon-chloride groups located at the periphery of carbosilane dendrimers of first, second, and third generation to afford 4-SiMe3C6H4N(SiMe3)2 (3) and functionalized dendrimers Si(CH2CH2CH2SiMe2C6H4N(SiMe3)2)4 (6), Si(CH2CH2CH2SiMe(CH2CH2CH2SiMe2C6H4N(SiMe3)2)2)4 (7), and Si(CH2CH2CH2SiMe(CH2CH2CH2SiMe(CH2CH2CH2SiMe2C6H4N(SiMe3)2)2)2)4 (8). The N,N-bis(trimethylsilyl)aniline groups of 3 reacted with niobium pentachloride in acetonitrile or [NbCp′Cl4] (Cp′=η5-C5H4SiMe3) in dichloromethane to give imido mononuclear complexes [Nb(NC6H4SiMe3-4)Cl3(CH3CN)2] (4) and [NbCp′(NC6H4SiMe3-4)Cl2] (5), respectively. Reaction of dendrimers 6–8 and [NbCp′Cl4] in CH2Cl2 afforded metallodendrimers [Si(CH2CH2CH2SiMe2C6H4NNbCp′Cl2)4] (9), [Si(CH2CH2CH2SiMe(CH2CH2CH2SiMe2C6H4NNbCp′Cl2)2)4] (10), and [Si(CH2CH2CH2SiMe(CH2CH2CH2SiMe(CH2CH2CH2SiMe2C6H4NNbCp′Cl2)2)2)4] (11), in which the metal moieties are linked to the carbosilane framework through imidometal bonds. The structure of complexes 4 and 5 has been determined by X-ray diffraction methods.