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Ground-State Geometry Preferences in (Tris(pyrazolyl)borato)- and Cyclopentadienylniobium Alkyne Complexes

1996; American Chemical Society; Volume: 15; Issue: 21 Linguagem: Inglês

10.1021/om960404t

1520-6041

Michel Étienne, B. Donnadieu, René Mathieu, Juan Fernández Baeza, Félix A. Jalón, Antonío Otero, Maria Esther Rodrigo-Blanco,

Electrochemical sensors and biosensors

Reaction of NbCl3(DME)(RC⋮CR') with KTp (DME = 1,2-dimethoxyethane, Tp = hydrotris(pyrazolyl)borate) yields TpNbCl2(RC⋮CR') (R = Ph, R' = Me (2a); R = R' = Me (2b), Et (2c), SiMe3 (2d), Ph (2e)), which has the alkyne in the molecular mirror plane in the solid state (X-ray crystal structure for 2a) and in solution. The barriers to alkyne rotation are low, the highest being measured for complex 2d (52 kJ mol-1 at 273 K), which contains the bulky SiMe3 group on the alkyne. In TpCpNb(Cl)(PhC⋮CMe) (3a), formed by reaction of 2a with NaCp·DME, the alkyne is parallel to the Cp plane, as observed in solution and in the crystal structure. Extended Huckel molecular orbital calculations indicate that in complexes 2 the geometry is mainly governed by steric interactions, whereas in the case of 3a orbital interactions dictate the observed geometry.