ORGANOMETALLIC OXIDES - PREPARATION, STRUCTURE, AND CHEMICAL AND PHYSICAL-PROPERTIES OF PARAMAGNETIC [(ETA-C5H5)NBCL(MU-A)]3(MU-3-OH)(MU-3-O) (A = CL, OH) AND OTHER OXO-HYDROXO CLUSTERS OF NIOBIUM

Hydrolysis of Cp'NbCl4 (Cp’ = 7)5-C5H5 (Cp), i7-C5H4Me (Cp1)) in tetrahydrofuran (THF) gave a mixture of products of general formula [Cp'NbL4]2^-0), where L4 is a combination of H20 and terminal or bridging CI that gives eight-coordinate, pentavalent, niobium. For Cp’ = Cp, a major constituent of the mixture is [CpNb(H20)Cl3]2(M-0)'2THFO.5Et20 (1), the structure of which was determined by X-ray diffraction. Crystal data: monocliniC.; C2/C.; α = 22.105 (4) Â, b = 11.366 (1) Â, c = 15.563 (2) Â, β = 124.71 (1)° R = 0.056 for 165 parameters and 1444 observed |F0|. The Nb-O-Nb angle in 1 is 173.7 (7)°, and the torsion angle between the [CpNb(H20)Cl3] units is 78.8 (3)°. The H20 ligands are hydrogen-bonded to lattice THF. Reduction of [Cp'NbL4]2(M-0) with aluminum powder gave the cluster [Cp'NbCl(,ii-Cl)]3(M3-OH)(M3-0) (2). The structure of 2 (Cp’ = Cp) as the THF adduct was determined by X-ray diffraction. Crystal data: monocliniC.; P2j/C.; α = 9.966 (l) Â, b = 12.471 (2) Â, c = 20.321 (2) Â, β = 93.86 (1)° R = 0.027 for 307 parameters and 3507 observed \F0\. 2 has an isosceles triangle of CpNbCl groups (Nb-Nb = 2.823 (1), 3.239 (1), 3.252 (1) Â) with edge-bridging CI and face-bridging OH and O ligands. The OH is hydrogen-bonded to the lattice THF. The Nb-Nb distances indicate a single Nb-Nb bond between Nb(l) and Nb(2) but no interaction between Nb(l) or Nb(2) and Nb(3). This model is borne out by the magnetic moment of 2,1.39 (295 K), and by the ESR spectrum. The g and93Nb hyperfine interaction tensors, derived from a spectral analysis of 2, are parallel and axial within experimental error (g« = 1.9232, g±= 1.9832; c^93 = 649 MHz, ax93 = 303 MHz) and show that the unpaired electron is located on Nb(3) in a d„ orbital that makes an angle of approximately 45° to the Nb3 plane. There is no coupling to the other Nb nuclei or to CI. Extended Hückel calculations confirm this assignment. The ESR spectrum also shows that 2 exists as two isomers with the proton attached to an oxygen atom either above or below the plane of the Nb atoms. [Cp'NbCl(M-Cl)]3(ju3-OH)(M3-0) decomposed slowly in THF solution to give a species formulated as Cp'4Nb5Cl5(OH)90(THF)2 (5) on the basis of spectroscopy, analysis, and a partial structure determination; 5 has an adamantane-like Nb4(0H)6 core and a magnetic moment of 1.86 μB. Reduction of [CpNbL4]2(M-0) with zinc powder gave units of [CpNbCl(M-OH)]3(M3-OH)(M3-0) (3) connected by ZnCl(OH)(THF). Spectroscopic and magnetic methods establish that 3 has a structure similar to that of 2, with edge-bridging OH instead of CI. © 1990, American Chemical Society. All rights reserved.