The synthesis and characterization of multiply bonded dirhenium(III) alkoxide complexes containing two or three alkoxide ligands, including further studies on complexes of the type Re2Cl4(OMe)(2)(PAr3)(2) (Ar = aryl)

The dirhenium(III) complex cis-Re-2(mu -O2CCH3)(2)Cl-4(H2O)(2) reacts in re fluxing methanol with triarylphosphines (PAr3) with relatively low basiciti es (pK(a) values in the range 1.0-4.6) and moderately large cone angles (14 5-165 degrees) to afford unsymmetrical quadruply bonded dirhenium(III) alko xides of the type Cl-2(MeO)(2)ReReCl2(PAr3)(2) (PAr3=P(p-tolyl)(3) (1), P(m -tolyl)(3) (2), P(p-ClPh)(3) (3), P(p-MeOPh)(3) (4), PPh3). The more basic phosphines PCyPh2 and PBz(3) (Bz = benzyl), with pK(a) values of 5.05 and 6 .50 and cone angles of 153 and 165 degrees, respectively, afford the comple xes Re-2(mu -O2CCH3)Cl-3(OMe)(PCyPh2)(3) (5), with a Re-Re bond order of 4, and Re-2(mu -O2CCH3)Cl-4(PBz(3))(2) (6), with a Re-Re bond order of 3.5, u nder the same conditions. Attempts to incorporate more than two alkoxide li gands about a multiply bonded dirhenium core were successfully achieved in the synthesis of Re2Cl3(OEt)(3)(PPh3)(2) (7) from the reactions of Re2Cl6(P Ph3)(2) and Re2Cl4(OEt)(2)(PPh3)(2) with NaOEt in ethanol. Single-crystal X -ray structure determinations have been carried out on compounds 4, 5 and 7 which have Re-Re bond distances of 2.2476(4), 2.2872(15) and 2.2399(12) An gstrom, respectively. (C) 2000 Elsevier Science S.A. All rights reserved.