INDUCED INTERNAL ELECTRON-TRANSFER CHEMISTRY IN RHENIUM SULFIDE SYSTEMS

This paper demonstrates the proclivity with which high-valent rhenium sulfur complexes undergo internal electron transfer. Specifically, reaction of [Et(4)N][ReS4] with 1.5 molar equiv of tetraalkylthiuram disulfide in acetonitrile gives the dinuclear Re(TV) complexes, Re-2(mu-S)(2)(S(2)CNR(2))(4), 1, in very high yield. This dimer reacts with an additional equivalent of tetraalkylthiuram disulfide in the presence of excess Lewis acids, or with 0.5 molar equiv of tetraalkylthiuram disulfide and 1 molar equiv of [Cp(2)Fe][PF6], to give the dinuclear Re(III) species [Re-2(mu-S-S(2)CNR(2))(2)(S(2)CNR(2))(3)](+), 2, in high yield. The reaction of [ReS4](-) with 3 molar equiv of tetraalkylthiuram disulfide in a mixture of dichloromethane and acetonitrile gives the mononuclear Re(V) species [Re(S2CN(R)(2))(4)]-[Cl], 3, in high yield. Each of these reactions involves induced internal electron transfer in which the formal oxidation state of the metal center is reduced by the addition of an oxidant (i.e., tetraalkylthiuram disulfide). The bound sulfide is the reductant both for the metal and the external oxidant. The reformation of 1 from 2, in which the metal is oxidized, can be effected using reductants such as H-2. Electrochemical properties and chemical reactivities of the complexes are presented. The Re-2(mu-S)(2)(S(2)CNR(2))(4) dimer undergoes a reversible one-electron oxidation to produce Re-2(mu-S)(2)(S(2)CNR(2))4(+), 1(+) This species can be generated chemically and, in the presence of excess sulfur, forms a novel Re(TV) sulfur-bridged dicationic dimer-of-dimers, [(Re-2(mu-S)(S(2)CNR(2))(4))(2)S-4](2+), 4. The reaction of 1(+) with tetraalkylthiuram disulfide give 2, which can be reconverted to 1 electrochemically via an EEC reaction. Single crystal X-ray diffraction studies of 1-i-Bu (P2(1)/c (No. 14), a = 11.084(2) Angstrom, b = 13.815(3) Angstrom, c = 19.945(4) Angstrom, beta = 92.23(2)degrees, V = 3052(2) Angstrom(3)), [2-Me][O3SCF3] (P ($) over bar 1 (No. 2), a = 14.238(4) Angstrom, b = 11.476(4) Angstrom, c = 14.977(5) Angstrom, alpha = 112.28(2)degrees beta = 117.70(2)degrees gamma = 89.14(2)degrees, V = 1966(1) Angstrom(3)), [3-Me][Cl] (C2/e (No. 15), a = 13.174(4) Angstrom, b = 18.736(6) = Angstrom, c = 9.826(3) Angstrom, beta = 96.46(2)degrees, V = 2410(1) Angstrom(3)), and [4-i-Bu][PF6](2) (P2(1) (No. 4), a = 15.754(3) Angstrom, b = 22.505(5) Angstrom, c = 20.278(6) Angstrom, beta = 115.12(2)degrees, V = 6510(3) Angstrom(3)), are described where the symbols after the number designate the alkyl group, R, of the particular complex.