Electron Transfer and Chemical Reactions Associated with the Oxidation of an Extensive Series of Mononuclear Complexes [M(CO)₂(κ¹-P-P)(κ²-P-P)X] and Binuclear Complexes [{M(CO)₂(κ²-P-P)X}₂(μ-P-P)] (M = Mn, Re; P-P = Diphosphine or Related Ligand; X = Cl, Br)

Abstract

The electrochemical oxidation of an extensive series of cis,mer-M(CO) 2 (κ 1 -dpm)(κ 2 -P-P)X (M ) Mn, Re; dpm ) Ph 2 PCH 2 PPh 2 ; P-P ) dpm, Ph 2 PCH 2 CH 2 PPh 2 (dpe), o-(Ph 2 P) 2 C 6 H 4 -(dpbz); X ) Cl, Br) complexes has been investigated on both the voltammetric and bulk electrolysis time scales. At short time domains or low temperatures, the manganese complexes undergo a reversible one-electron oxidation to cis,mer-[Mn(CO) 2 (κ 1 -dpm)(κ 2 -P-P)X] + . These compounds isomerize under slow scan rate voltammetric conditions at room temperature to give trans-[Mn(CO) 2 (κ 1 -dpm)(κ 2 -P-P)X] + , which on even longer bulk electrolysis time scales slowly lose Xto form a reactive trans-[Mn(CO) 2 (κ 2 -dpm)(κ 2 -P-P)] 2+ intermediate. In turn, this complex is reduced either at the electrode surface (X ) Cl) or in a homogeneous chemical reaction (X ) Br) to form trans-[Mn(CO) 2 (κ 2 -dpm)(κ 2 -P-P)] + , which is the final product observed under conditions of bulk electrolysis. In contrast, the first oxidation step for the corresponding rhenium complexes involves oxidation of the pendant phosphorus atom and reaction with traces of water to give cis,mer-Re(CO) 2 (κ 1 -dpmO)(κ 2dpm)X and then cis-[Re(CO) 2 (κ 2 -dpmO) 2 ] + , with the rhenium center subsequently being oxidized at more positive potentials. Methylation of the pendant phosphorus of cis,mer-Re-(CO) 2 (κ 1 -dpm)(κ 2 -dpm)X gives cis,mer-[Re(CO) 2 (κ 1 -dpmMe)(κ 2 -dpm)X] + . The ligand-based oxidation pathway is blocked by the methylation, so that only the usual metal-centered Re-(I)/Re(II)-based oxidation processes are observed in the voltammetry of these compounds. The compounds cis,mer-Re(CO) 2 (κ 1 -ape)(κ 2 -ape)X and cis,mer-[Re(CO) 2 (κ 1 -apeMe)(κ 2 -ape)X] + (ape ) Ph 2 AsCH 2 CH 2 PPh 2 ) exhibit electrochemistry similar to that of the dpm analogues. The major products of the interaction of dpe with the metal pentacarbonyl halides (2:1) are the new binuclear species {M(CO) 2 (κ 2 -dpe)X} 2 (µ-dpe), whose structures have been determined by IR and 31 P NMR spectroscopy and electrospray mass spectrometry (ESMS). The stereochemistry of the manganese complexes is cis,fac, and upon voltammetric oxidation, first one and then the second manganese atom are oxidized. Bulk oxidative electrolysis at low temperature leads to the generation of cis,fac-[{Mn(CO) 2 (κ 2 -dpe)X} 2 (µ-dpe)] + and cis,fac-[{Mn(CO) 2 (κ 2 -dpe)X} 2 (µ-dpe)] 2+ . The stereochemistry of the oxidized metal centers isomerizes to trans + at room temperature, but the binuclear structure is retained. Bulk reductive electrolysis at low temperature after bulk oxidative electrolysis at room temperature leads to the characterization of trans-{Mn(CO) 2 (κ 2 -dpe)X} 2 (µ-dpe). The binuclear rhenium complexes cis,mer-{Re(CO) 2 (κ 2 -P-P)X} 2 (µ-P-P) (P-P ) dpe, Ph 2 P(CH 2 ) 3 PPh 2 (dpp)) were isolated, and they each undergo two successive one-electron oxidations to generate the monoand dications without any isomerization on the voltammetric time scale. ESMS provides independent proof of the bin...

A Rare Type of Rhenium(I) Diimine Complexes with Unsupported Coordinated Phosphine Oxide Ligands: Synthesis, Structural Characterization, Photophysical and Theoretical Study

“…That's why the family of coordination compounds containing phosphine oxides consists mainly of the complexes with hard Lewis acids like lanthanides and actinides ions, first row transition metals,, , , and heavy metals in high oxidation states: Re V , Re III[17,18] and Au III , which are complementary partners for the hard donor oxygen in the phosphine oxides. In the complexes of soft metal ions the coordinated phosphine oxide moiety is commonly presented as a component of a polydentate ligand, where the phosphine oxide oxygen often plays the role of labile function in catalytic processes …”

“…The Re I ion is a typical representative of the soft Lewis acids and similarly to the other soft metal centers coordinates the phosphine oxide mostly in combination with the other suitable soft functions, which support the Re–O bond . In general, the Re I organometallic compounds attract considerable attention particularly due to their unique photophysical and photochemical characteristics, which open a way to a wide range of practical applications.…”

Synthesis and Structural Characterization of a TCNQ Based Organic Semi-Conducting Material with a 2:5 Stoichiometry

“…7,7′,8,8′-Tetracyanoquinodimethane (TCNQ) is well-known to be an electron acceptor which readily forms charge–transfer (CT) complexes. ,, These TCNQ-based materials are found with a number of different cation:anion stoichiometries and are of considerable interest because of their extensive and novel electrical, electrochemical, and magnetic properties arising from the characteristic π-stacking of the TCNQ moieties into columns. Accordingly they offer exciting applications as molecular devices. ,− …”

Homoleptic Tris-Diphosphine Re(I) and Re(II) Complexes and Re(II) Photophysics and Photochemistry

“…Chemical oxidation of [(dmpm) 3 Re] + with 2 equiv of (4-BrC 6 H 4 ) 3 N + SbF 6 − in CH 3 CN produced an orange solid, which was shown by Xray diffraction to be a seven-coordinate Re III complex having a coordinated solvent molecule. The crystallographic data of this seven-coordinate complex, [(dmpm) 3 Re(MeCN)] 3+ (15), is given in the Supporting Information.…”

“…In comparison to the wide variety and scope of d 6 Re(I) coordination compounds, relatively few stable low-spin d 5 Re II monomeric complexes are known. 1−11 Heteroleptic diimine and diphosphine carbonyls [(diimine)(CO) 3 ReX] + , 12,13 trans-[(PP) 2 (CO) 2 Re] 2+ and trans-[(dppe) 2 (CO)ReBr] + , 14,15 have been generated electrochemically and have generally limited stabilities (PP = 1,2-bis(dimethylphosphino)ethane (dmpe),…”