A RE(I)-RE(VII) COMPLEX BY THE OXYGENATION REACTIONS OF RE(I) SPECIES - REACTIVITY AND X-RAY STRUCTURAL CHARACTERIZATION OF RE(CO)3(PPH3)2(OREO3)

The hydrido complex HRe(CO)2(PPh3)3 reacts with tertiary amines, in the presence of O2 and H2O, to give Re(CO)2(PPh3)2(O2CR), containing a chelating carboxylato group originated by oxidation of the alkyl group of the amine. NEt3, N(n-Pr)3 and N(n-Bu)3 have been used, the acetato, propionato and butyrato derivatives being respectively obtained. In the absence of the amine, the reaction gives the Re(I)-Re(VII) complex Re(CO)3(PPh3)2(OReO3), 1, containing a coordinated perrhenate ion. The same species was obtained by reaction of Re(CO)3(PPh3)2(NHCOC6H4Me) with O2/H2O. Complex 1 has been alternatively prepared by reacting ReCl(CO)3(PPh3)2 with AgReO4. Crystals of 1 have been shown by single crystal X-ray analysis to be monoclinic, space group P2(1)/n (No. 14 with a = 10.248(6), b = 27.487(5), c = 13.247(2)angstrom, beta = 97.55(2)-degrees and Z = 4. The refinement performed by full-matrix least-squares methods, for 4651 independent significant reflections, gave a final R value of 0.029. The crystals contain discrete dinuclear molecules with an octahedrally coordinated Re(I) atom bearing three carbonyls, two mutually trans triphenylphosphine ligands and a coordinated ReO4- moiety. Complex 1 was shown to be partially dissociated in acetone solution and the value of the dissociation constant has been estimated by means of the Ostwald relationship [K = 6(1)x10(-5)]. The addition Of NEt3 to an acetone solution of 1 at room temperature causes its complete dissociation. Complete dissociation was also observed in acetonitrile, with formation of the ionic species [Re(CO)3(PPh3)2-(MeCN)][ReO4], 2. Complex 1 reacts with NEt3, at 55-degrees-C under an inert atmosphere, to give the rhenium(I) acetato derivative Re(CO)2(PPh3)2(O2CCH3), showing that the perrhenate anion is able to perform the oxidation of alkyl groups of tertiary amines to carboxylato groups.