EARLY-TRANSITION-METAL KETENIMINE COMPLEXES - SYNTHESIS, REACTIVITY, AND STRUCTURAL CHARACTERIZATION OF COMPLEXES WITH ETA-2(C,N)-KETENIMINE GROUPS BOUND TO THE HALOGENOBIS((TRIMETHYLSILYL)CYCLOPENTADIENYL)NIOBIUM UNIT - X-RAY STRUCTURE OF NB(ETA-5-C5H4SIME3)2CL(ETA-2(C,N)-PHN=C=CPH2)

The reaction of Nb(η5-C5H4SiMe3)2X (X = Cl Br) with 1 equiv of various ketenimines, R1N═C═CR2R3, leads to the niobium derivatives Nb(η5-C5H4SiMe3)2X(η2(C,N)-R1N═C═CR2R3) (1, X = Cl, R1 = R2 = R3 = C6H5; 2, X = Cl, R1 = p-CH3-C6H4, R2 = R3 = C6H5; 3, X = Br, R1 = R2 = R3 = C6H5; 4, X = Br, R1 = p-CH3-C6H4, R2 = R3 = C6H5; 5, X = Cl, R1 = R2 = C6H5, R3 = CH3; 6, X = Br, R1 = R2 = C6H5, R3 = CH3) with the expected ketenimine C═N bonding mode. Reduction of 1 with 1 equiv of Na/Hg gives the complex Nb(η5-C5H4SiMe3)2(η2(C,N)-PhN═C═CPh2) (9) as a paramagnetic compound. The reduction of 9 with 1 equiv of Na/Hg and the subsequent addition of a proton source (ethanol) leads to the iminoacyl compound Nb(η-C5H4SiMe3)2(CRNR1) (10, R = CH(Ph2), R1 = Ph). The one- and two-electron reductions of 1 have been studied by cyclic voltammetry experiments. The structure of 1 was determined by single-crystal X-ray diffractometry: a = 24.4904 (14) Å, b = 11.0435 (04) Å, c = 26.6130 (15) Å, β = 109.890 (5)°, monoclinic, space group C2/c, Z = 8, V = 6768.4 (5) Å3, ρcalcd = 1.3194 g/mL, R = 0.048, Rw = 0.060 based on 4806 observed reflections. The structure contains a niobium atom bonded to two cyclopentadienyl rings in a η5 fashion; the coordination of the metal is completed by a Cl atom and a η2(C,N)-bonded ketenimine ligand. © 1990, American Chemical Society. All rights reserved.