THE STRUCTURE AND FORMATION OF NIOBOCENE CARBONYL HETERONUCLEAR DERIVATIVES. THE MOLECULAR STRUCTURES OF AND 2Nb(CO)(μ-H)Ni(CO)3 AND 2Nb(CO)(μ-H)>2Mo(CO)4

Article abstract of DOI:10.1016/S0022-328X(00)92887-0

The heteronuclear Cp₂Nb(CO)(μ-CO)Mn(CO)4 (I), Cp₂Nb(CO)(μ-H)Ni(CO)3 (II) and 2Nb(CO)(μ-H)>2M(CO)4 (III, M=Mo; IV, M=W) complexes were prepared by reaction of Cp₂NbBH4/Et3N with Mn2(CO)10 in refluxing toluene, direct reaction of Cp₂NbBH4 with Ni(CO)4 in ether, and reaction of Cp₂NbBH4/Et3N with M(CO)5*THF complexes (M=Mo or W) in THF/benzene mixture.An X-ray investigation of compounds I-III was performed.It is established that in I the bonding between Mn(CO)5 and Cp₂Nb(CO) (with the angle (α) between the ring planes being 44.2(5) deg) fragments takes place via a direct Nb-Mn bond (3.176(1) Angstroem) and a highly asymmetric carbonyl bridge (Mn-C_CO 1.837(5) Angstroem, Nb-C_CO 2.781(5) Angstroem).On the other hand, in complex II the sandwich Cp₂Nb(CO)H molecule (angle α=37.8 deg) is combined with the Ni(CO)3 group generally via a hydride bridge (Nb-H 1.83 Angstroem, Ni-H 1.68 Angstroem, NbHNi angle 132.7 deg) whereas the large Nb...Ni distance, 3.218(1) Angstroem, shows the weakening or even absence of the direct Nb-Ni bond.Similarly, in complex II two Cp₂Nb(CO)H molecules (with α angles equal to 41.4 and 43.0 deg, respectively ) are joined to the Mo(CO)4 group via the hydride bridges (Nb-H 1.83 and 1.75 Angstroem and Mo-H 2.04 and 2.06 Angstroem) producing a cis-form. The direct Nb-Mo bonds are probably absent, since the Nb...Mo distances are rather long (3.579 and 3.565 Angstroem).The effect of electronic and steric factors on the structure of heteronuclear niobocene carbonyl derivatives is discussed.