SYNTHESIS, STRUCTURE, AND CHEMISTRY OF NIOBIUM CATIONIC KETENIMINE COMPLEXES, [NB(ETA(5)-C5H4SIME3)2(ETA(2)-PHRCCNPH-C,N)(L)]+ - MOLECULAR-STRUCTURE OF [NB(ETA(5)-C5H4SIME3)2(ETA(2)-PH2CCNPH-C,N)(CH3CN)][PF6]

Reaction of NbCp'2(eta2-PhRCCNPh-CN) (2a, R = Ph; 2b, R = Me; 2c, R = Et) (Cp' = eta5-C5H4SiMe3) with 1 equiv of [Cp2Fe]+X- (X = PF6, BPh4) in the presence of nitriles or isonitriles produces the cationic ketenimine niobiocene complexes [NbCP'2(eta2-PhRCCNPh-CN)(L)][X] (3a R = Ph, L = CH3CN,X=PF6; 3a'R = Ph, L = CH3CN, X = BPh4-; 3b R = Me, L = CH3CN, X = BPh4-; 3c R = Et, L = CH3CN, X = BPh4-; 3d R = Ph, L = tBuCN, X = BPh4-; 3e R = Ph, L = PhCN, X = BPh4-; 3f R = Ph, L = tBuNC, X = BPh4-; 3g R = Me, L = tBuNC, X = BPh4-; 3h R = Et, L = tBuNC, X = BPh4-) in practically quantitative yields. We have also studied the electrochemical oxidation process of 2a by means of cyclic voltammetry experiments. The structures of these compounds have been determined by spectroscopic methods. The structure of 3a was determined by single-crystal diffractometry. Compound 3a crystallizes in the triclinic space group P1BAR (No. 2) with a = 9.468(3) angstrom, b = 10-641(2) angstrom, c = 19.852(2) angstrom, alpha = 86.30(1)degrees, beta = 88.79(1)degrees, gamma = 74.64(2)degrees, Z = 2, V = 1924.6 angstrom3, D(calcd) = 1.420 g/mL, and R = 0.069, based on 5647 reflections. The molecular structure shows a typical bent-sandwich geometry around the niobium atom with the ketenimine and CH3CN ligands arrayed in the plane between the two cyclopentadienyl rings. Cationic ketenimine complexes 3 isolated as nitrile adducts are readily converted to the corresponding isonitrile compounds by treatment with an excess of isonitrile. However, the inverse reaction does not occur under the same conditions. Complexes 3a'-c react with water from wet acetone to produce the hydroxo iminoacyl complexes [NbCp'2(OH)(eta2-PhRHCCNPh-C,N)][BPh4] (5a, R = Ph; 5b, R = Me; 5c, R = Et), and 3a' reacts with methanol in the same manner to yield the corresponding methoxide complex [NbCp'2(OCH3)(eta2-Ph2HCCNPh-C,N)][BPh4], 6.