Synthesis and reactivity of imido niobium complexes containing the functionalized (dichloromethylsilyl)cyclopentadienyl ligand

The niobium complex [NbCpClCl4] (CpCldouble bond; length as m-dashη5-C5H4(SiCl2Me)) (1) with a functionalized (dichloromethylsilyl)cyclopentadienyl ligand was isolated by the reaction of [NbCl5] with C5H4(SiCl2Me)(SiMe3). Complex 1 was a precursor for the imido silylamido derivative [NbCpNCl2(NtBu)] (CpNdouble bond; length as m-dashη5-C5H4[SiClMe(NHtBu)]) (2) after addition of LiNHtBu, which subsequently gave the dichlorosilyl compound [NbCpClCl2(NtBu)] (3) when reacted with SiCl3Me. Addition of LiNHtBu to complex 2 gave the niobium amido complex [NbCpNCl(NHtBu)(NtBu)] (4), which slowly evolved with exchange of the niobium-amido and the silicon-chloro groups to give the dichloroniobium complex [NbCpNNCl2(NtBu)] (CpNNdouble bond; length as m-dashη5-C5H4[SiMe(NHtBu)2]) (5). Reaction of 2 with excess LiNHtBu gave the silyl-η-amido constrained geometry complexes [Nb{η5-C5H4[SiMe(NHtBu)(-η-NtBu)]}(NHtBu)(NtBu)] (6) and [Nb{η5-C5H4[SiClMe(-η-NtBu)]}(NHtBu)(NtBu)] (7), whereas addition of one equimolecular amount of LiNHtBu to 5 in C6D6 afforded complex [NbCpNNCl(NHtBu)(NtBu)] (8). All of the new complexes were characterized by 1H, 13C and 29Si NMR spectroscopy.