James M. Mayer

Imido and amido complexes of hydrotris(pyrazolyl)borate-rhenium

Rhenium(V) para-tolylimido complexes TpRe(NTol)X2 (X = Cl (2a); I (2b)) are formed on refluxing the oxo derivatives TpRe(O)X2 (X = Cl (1a); I (1b)) with para-toluidine (Tp = hydrotris(pyrazalyl)borate; Tol = para-tolyl). Reaction of 2a with ZnEt2 in benzene gives the imido-ethyl complex TpRe(NTol)(Et)Cl ((3) Et = CH2CH3), which was characterized by an X-ray crystal structure. Photolysis of 2a and 3 apparently lead to ReI and ReC bond homolysis, as in their oxo congeners, but the analogous photoproducts are not observed. Reaction of 1a with amines at ambient temperatures leads to the oxo-amido compounds TpReO(NRR′)Cl. Complexes with primary amido ligands, TpReO(NHR)Cl (R = Et (4); nPr (5); iPr (6)) exist as two isomers by 1H NMR. Similarly, NMR spectra of compounds with symmetrical amido ligands, TpReO(NR2)Cl (R = H (7); Et (8); NR2 = piperidyl (9)), show inequivalent substituents. These data indicate restricted rotation about the ReN amido bond. Based on the X-ray crystal structure of 8, the barrier to rotation is electronic as well as steric in origin.

Molybdenum(VI) dioxo complexes with macrocyclic amine ligands

Abstract Reaction of MoO2Cl2 with the tetradentate amine ligand 1,4,8,12-tetraazacyclopentadecane ([15]aneN4) yields the molybdenum(VI) dioxo complex [MoO22+ unit. The oxo ligands are cis and the macrocyclic amine coordinates in a non-planar fashion, as revealed by X-ray crystal structure and NMR data. One of the nitrogen donors cis to the oxo groups has been deprotonated to give an amide ligand (NR2−). In contrast, reaction of MoO2Cl2 with tetramethylcyclam (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane, TMC) yields the neutral adduct MoO2Cl2(η2-TMC) (III), in which only two of the amine nitrogens are coordinated. An X-ray structure of III shows it to have an all-cis octahedral geometry, very unusual for MoO2X2L2 complexes, with one oxo ligand trans to an amine and the other trans to a chloride. Compounds [MoO2([15]aneN4-H)]BPh4 II and III are not very stable in solution; II is not reduced electrochemically or by PPh3.

Molybdenum oxychlorides I. Electrochemistry of MoO2Cl2: oxidation, dimerization, and electrodeposition at a platinum electrode

Abstract This paper describes the electrochemical behavior of MoO 2 Cl 2 at a platinum electrode in acetonitrile, methylene carbonate, and propylene carbonate solvents. Cyclic voltammetry, bulk electrolysis, and chemical reduction are used to show that on one-electron reduction of MoO 2 Cl 2 , MoO 2 Cl − 2 reacts with MoO 2 Cl 2 to form an unusual Mo(VI)Mo(V) dimer. This dimer can undergo both oxidation and further reduction. Oxidation to the Mo(VI)Mo(VI) oxidation state is irreversible at low scan rates but reversible at high scan rates. Reduction of the dimer occurs in a reversible one-electron process to yield an Mo(V)Mo(V) dimer which can be reduced further in a one-electron irreversible process. MoO 2 Cl 2 partially ionizes in these solvents to give MoO 2+ 2 , MoO 2 Cl 2− 4 and possibly MoO 2 Cl − 3 : MoO 2+ 2 and MoO 2 Cl 2− 4 are electrochemically active. Reduction of MoO 2+ 2 leads to electrodeposition of MoO 2 (s). An unusual irreversible oxidation wave is observed for MoO 2 Cl 2 , a d 0 species, which is due to oxidation of MoO 2 Cl 2− 4 . Solutions of MoO 2 Cl 2 oxidize ferrocene: the solid obtained on drying was characterized by elemental analysis and IR spectroscopy.