Suitable Approach to Prepare N‐Substituted Niobium Complexes – Study of the Factors Controlling the Process

The reactions of the chlorosilyl‐substituted cyclopentadienyl niobium compound [Nb(η 5 ‐C 5 H 4 SiMe 2 Cl)Cl 4 ] ( 1 ) with 1 equiv. of 2‐methoxyethylamine, 3‐methoxypropylamine, and allylamine in toluene specifically afford the corresponding amine adducts [Nb(η 5 ‐C 5 H 4 SiMe 2 Cl){NH 2 (CH 2 ) n OMe}Cl 4 ] ( n = 2, 2 ; 3, 3 ) and [Nb(η 5 ‐C 5 H 4 SiMe 2 Cl)(NH 2 CH 2 CH=CH 2 )Cl 4 ] ( 4 ). In contrast, a similar reaction with 1,2‐phenylenediamine proceeds with the aminolysis of a Nb–Cl bond and the formation of the amido–amine compound [Nb(η 5 ‐C 5 H 4 SiMe 2 Cl)(NHC 6 H 4 ‐2‐κNH 2 )Cl 3 ] ( 5 ). When such reactions are performed in the presence of 2 equiv. of an additional base, they progress through the double deprotonation of the primary amine group and the formation of a single product, the structure of which depends on the coordinating ability of the pendant donor end group. Thus, two different types of derivatives are obtained, constrained‐geometry complexes such as [Nb{η 5 ‐C 5 H 4 SiMe 2 ‐κN(CH 2 ) 2 ‐κOMe}Cl 3 ] ( 6 ) and [Nb(η 5 ‐C 5 H 4 SiMe 2 ‐κNC 6 H 4 ‐2‐κNH 2 )Cl 3 ] ( 7 ) or imido derivatives such as [Nb(η 5 ‐C 5 H 4 SiMe 2 Cl){N(CH 2 ) 3 OMe}Cl 2 ] ( 8 ) and [Nb(η 5 ‐C 5 H 4 SiMe 2 Cl)(NCH 2 CHCH 2 )Cl 2 ] ( 9 ). All of the compounds have been characterized by NMR spectroscopy, and the molecular structures of 2 and 6 have been determined by X‐ray diffraction methods.