title: [Re(eta(5)-C5H5)(CO)3]+ family of 17-electron compounds: monomer/dimer equilibria and other reactions.
abstract: The anodic electrochemical oxidations of ReCp(CO)3 (1, Cp = eta(5)-C5H5), Re(eta(5)-C5H4NH2)(CO)3 (2), and ReCp*(CO)3 (3, Cp* = eta(5)-C5Me5), have been studied in CH2Cl2 containing [NBu4][TFAB] (TFAB = [B(C6F5)4]-) as supporting electrolyte. One-electron oxidations were observed with E(1/2) = 1.16, 0.79, and 0.91 V vs ferrocene for 1-3, respectively. In each case, rapid dimerization of the radical cation gave the dimer dication, [Re2Cp(gamma)2(CO)6]2+ (where Cp(gamma) represents a generic cyclopentadienyl ligand), which may be itself reduced cathodically back to the original 18-electron neutral complex ReCp(gamma)(CO)3. DFT calculations show that the SOMO of 1+ is highly Re-based and hybridized to point away from the metal, thereby facilitating the dimerization process and other reactions of the Re(II) center. The dimers, isolated in all three cases, have long metal-metal bonds that are unsupported by bridging ligands, the bond lengths being calculated as 3.229 A for [Re2Cp2(CO)6]2+ (1(2)2+) and measured as 3.1097 A for [Re2(C5H4NH2)2(CO)6]2+ (2(2)2+) by X-ray crystallography on [Re2(C5H4NH2)2(CO)6][TFAB]2. The monomer/dimer equilibrium constants are between K(dim) = 10(5) M(-1) and 10(7) M(-1) for these systems, so that partial dissociation of the dimers gives a modest amount of the corresponding monomer that is free to undergo radical cation reactions. The radical 1+ slowly abstracts a chlorine atom from dichloromethane to give the 18-electron complex [ReCp(CO)3Cl]+ as a side product. The radical cation 1+ acts as a powerful one-electron oxidant capable of effectively driving outer-sphere electron-transfer reactions with reagents having potentials of up to 0.9 V vs ferrocene.
authors.affiliation: Department of Chemistry, University of Vermont, Burlington, Vermont 05405, USA.
authors.forename: Daesung
authors.initials: D
authors.lastname: Chong
authors.forename: Derek R
authors.initials: DR
authors.lastname: Laws
authors.forename: Ayman
authors.initials: A
authors.lastname: Nafady
authors.forename: Paulo Jorge
authors.initials: PJ
authors.lastname: Costa
authors.forename: Arnold L
authors.initials: AL
authors.lastname: Rheingold
authors.forename: Maria José
authors.initials: MJ
authors.lastname: Calhorda
authors.forename: William E
authors.initials: WE
authors.lastname: Geiger
mesh_terms: D019281:Dimerization; D004563:Electrochemistry; D004573:Electrolytes / Q000737:chemistry; D004583:Electrons; D008024:Ligands; D008956:Models, Chemical; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D012211:Rhenium / Q000737:chemistry*
chemical_list: D004573:Electrolytes; D008024:Ligands; D009942:Organometallic Compounds; D012211:Rhenium