The structure and formation of niobocene carbonyl heteronuclear derivatives. The molecular structures of Cp 2[formula omitted](CO) 4, Cp 2Nb(CO)(μ-H)Ni(CO) 3 and [Cp 2Nb(CO)(μ-H)] 2Mo(CO) 4

Abstract

The heteronuclear Cp 2Nb(CO)(μ-CO)Mn(CO) 4 (I), Cp 2Nb(CO)(μ-H)Ni(CO) 3 (II) and [Cp 2Nb(CO)(μ-H)] 2M(CO) 4 (III, M = Mo;IV, M = W) complexes were prepared by reaction of Cp 2NbBH 4/Et 3N with Mn 2(CO) 10 in refluxing toluene, direct reaction of Cp 2NbBH 4 with Ni(CO) 4 in ether, and reaction of Cp 2NbBH 4/Et 3N 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 Cp 2Nb(CO) (with the angle (α) between the ring planes being 44.2(5)°) fragments takes place via a direct NbMn bond (3.176(1) Å) and a highly asymmetric carbonyl bridge (MnC co 1.837(5) Å, NbC co 2.781(5) Å). On the other hand, in complex II the sandwich Cp 2Nb(CO)H molecule (angle α = 37.8°) is combined with the Ni(CO) 3 group generally via a hydride bridge (NbH 1.83 Å, NiH 1.68 Å, NbHNi angle 132.7°) whereas the large Nb⋯Ni distance, 3.218(1) Å, shows the weakening or even absence of the direct NbNi bond. Similarly, in complex III two Cp 2Nb(CO)H molecules (with α angles equal to 41.4 and 43.0°, respectively) are joined to the Mo(CO) 4 group via the hydride bridges (NbH 1.83 and 1.75 Å and MoH 2.04 and 2.06 Å) 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 Å). The effect of electronic and steric factors on the structure of heteronuclear niobocene carbonyl derivatives is discussed.