Organometallic thermodynamics. Redox couples involving metal-metal bonds

(Pentabenzylcyclopentadienyl)molybdenum Complexes: Synthesis, Structures and Redox Properties

“…In this case the value obtained is k F = 30 s -1 , which is significantly higher than that obtained in Bu 4 [41][42][43] Cp*, [44] CpR (CpR = η 5 -C 5 H 4 R), [41,45] Fv [Fv = (η 5 :η 5 -C 5 H 4 ) 2 ] [45,46] and M = Mo and W. Even though the electron-transfer processes in the hexacarbonyl dimers involve the disruption of the dinuclear unit, [35,[41][42][43]45,46] as proposed for 5, and the anodic wave at around 0.5 V compares well with those reported for [MoCpЈ(CO) 3 ] 2 , the cathodic shift observed for the first oxidation wave at 0.26 V in CH 3 CN has no parallel in the hexacarbonyl dimers' oxidation, and the irreversibility of the redox process for 5 contrasts with the reversible processes reported for [MoCpЈ(CO) 3 ] 2 .…”

“…This type of compound has been described by Curtis et + at a lower potential than would be observed for non-stabilized 17-electron species. [34][35][36] However, efforts to identify a solvent adduct by NMR and IR spectroscopy have proved unsuccessful, and the nature of the interaction with the solvent remains unclear, although it is probable that the oxidation of 5 results in metal-metal bond cleavage and the formation of the cation [MoCpBz(CO) 2 + and the anions BF 4 -or PF 6 -, which are present in a large excess in solution. The rate of formation of these species, which are oxidized at the higher potentials (0.52 or 0.54 V), is reflected in the different peaks' intensity ( Figure S3, Supporting Information).…”

The effect of 19-electron formation constants on the electrochemistry and electron transfer induced substitution reactions of cyclopentadienylmetal halide complexes

“…The cyclic voltammograms of the two dimers, Fp 2 and Mp 2 , in CH 3 CN showed chemically irreversible reductions (À2.26 V for Fp 2 ; À1.75 V for Mp 2 ) coupled to anodic peaks on the reverse scans for oxidation of the corresponding anions (À1.30 V for Fp À ; À0.52 V for Mp À ), in good agreement with the literature [13]. Controlled potential electrolyses in CH 3 CN at potentials approximately 200 mV more negative than the CV peak potentials consumed two electrons per mole of dimer reduced (2.0 F/ mol for Fp 2 ; 1.9 F/mol for Mp 2 ) to produce the anions, identified by cyclic voltammetry and IR spectra.…”

“…At platinum electrodes only the latter two options are available. The dissociation of iodide after reduction is presumed to occur so quickly that the Fp is formed in the immediate vicinity of the electrode surface, and at the potentials necessary for reduction of FpI the Fp is reduced to the Fp À anion (E o Fp ¼ À1:27 V [13]). However, the Fp À anion is known to react rapidly with FpI to yield the dimer Fp 2 [2,14,15].…”

Pentabenzylcyclopentadienyl molybdenum and tungsten hydrides: Syntheses, structures and electrochemistry of [MHCpBz(CO)2(L)] (L=CO, PMe3, PPh3)

“…The oxidation of [MoCp Bz (CO) 3 (CH 3 CN)]BF 4 (8), performed in acetonitrile with Bu 4 NPF 6 as electrolyte, showed an irreversible oxidation wave at 1.13 V and a reduction wave at À0.95 V. Upon reduction and scan reverse a new anodic wave appears at À0.57 V. The anodic peak is assigned to the oxidation of 8 to [MCp Bz (CO) 3 The redox potentials obtained for pentabenzylcyclopentadienyl Mo and W complexes are, in general, consistent with results described in the literature for analogous half-sandwich complexes [24,[32][33][34]36,38,40,41,68,69]. The comparison between the first oxidation waves of [MCp Bz (CO) 3 X] where X = H or X = WCp Bz (CO) 3 shows a cathodic shift for the dimer that attests for a higher metal electron density.…”