Crystal size 0.35 x 0.20 x 0.19 mm Theta range for data collection 3.33 to 27.51 deg. Limiting indices -18<=h<=18, -12<=k<=12, -14<=l<=14 Reflections collected / unique 34587 / 3713 [R(int) = 0.0509] Completeness to theta = 27.51 99.6 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.785 and 0.597 Refinement method Full-matrix least-squares on F^2

Reaction of Ti{η 5 -C 5 H 4 SiMe 2 -η-N(CH 2 ) 2 NRR′}Cl 2 with Nb(η 5 -C 5 H 4 SiMe 2 Cl)Cl 4 affords the tethered heterodinuclear complexes TiCl 2 {η 5 -C 5 H 4 SiMe 2 -η-N(CH 2 ) 2 -κ-NRR′}Nb(η 5 -C 5 H 4 SiMe 2 -Cl)Cl 4 , which are thermally unstable in solution and evolve to render an equimolar mixture of Ti(η 5 -C 5 H 4 SiMe 2 Cl)Cl 3 and the corresponding cyclopentadienyl-amido niobium compounds, Nb{η 5 -C 5 H 4 SiMe 2 -η-N(CH 2 ) 2 NRR′}Cl 3 . These compounds are straightforwardly obtained from the reaction of Nb(η 5 -C 5 H 4 SiMe 2 Cl)Cl 4 with 1 equiv of the appropriate diamine, NH 2 (CH 2 ) n -NRR′, in the presence of 2 equiv of NEt 3 , in high yield. In this reaction, the presence of the functional pendant chain plays a central role not only in determining the course of the reaction but also in stabilizing the final product, from both an electronic and a steric point of view. The molecular structure of Nb{η 5 -C 5 H 4 SiMe 2 -η-N(CH 2 ) 3 -η-NH 2 }Cl 3 has been determined by X-ray diffraction methods.

The reaction of the cyclopentadienyl-silyl-amido titanium compound [Ti{η5-C5H4SiMe2-η-N(CH2)2-η-NH2}Cl2] with group 5 metal monocyclopentadienyl complexes [MCpRCl4] (M = Nb, Ta; CpR = C5H4SiMe3 (Cp‘), C5Me5 (Cp*)) afforded the heterobimetallic complexes [TiCl2{η5-C5H4SiMe2-η-N(CH2)2-κ-NH2}MCpRCl4] (M = Nb, CpR = Cp‘, 2a; Cp*, 2b; M = Ta, CpR = Cp‘, 3a; Cp = Cp*, 3b). Compounds 2 evolve at room temperature to give a three-component mixture, the chlorosilyl-substituted cyclopentadienyl titanium compound [Ti(η5-C5H4SiMe2Cl)Cl3], the corresponding mononuclear amido-amino, [NbCpR{NH(CH2)2-η-NH2}Cl3] (CpR = Cp‘, 4a; Cp*, 4b), and the dinuclear imido niobium complexes [{NbCpRCl2}2(μ-N(CH2)2-η-N)] (CpR = Cp‘, 5a; Cp*, 5b). In contrast, the analogue tantalum complexes thermally degraded, when CpR = Cp‘ at normal temperature, whereas when CpR = Cp* at temperatures higher than 50 °C, they gave a unique tantalum complex, the corresponding mononuclear amido-amino derivative [TaCpR{NH(CH2)2-η-NH2}Cl3] (CpR = Cp‘, 6a; Cp*, 6b). Alternatively, these group 5 complexes were prepared by direct reaction of the monocyclopentadienyl derivatives with the corresponding organic diamine, in the appropriate proportion and reaction conditions. Tantalum amino adducts were observed as intermediate species in the course of such reactions, and even the dinuclear derivative [{TaCp*Cl4}2(μ-NH2(CH2)2NH2)] (8) could be isolated. Hydrolysis of the dinuclear imido complex 5a yielded the tricyclic tetranuclear niobium oxo derivative [{NbCp‘Cl(μ2-O)}4(Cl)2(μ3-O)] (9), which displays an asymmetrical structure as a consequence of the triply connected oxygen site. These compounds were characterized by elemental analysis and NMR spectroscopy, and the crystal structures of 4a and 9 were determined by X-ray diffraction methods.

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