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 Re 2Cl 4(OMe) 2(PAr 3) 2 (Ar=aryl)

Abstract

The dirhenium(III) complex cis-Re 2(μ-O 2CCH 3) 2Cl 4(H 2O) 2 reacts in refluxing methanol with triarylphosphines (PAr 3) with relatively low basicities (p K a values in the range 1.0–4.6) and moderately large cone angles (145–165°) to afford unsymmetrical quadruply bonded dirhenium(III) alkoxides of the type Cl 2(MeO) 2ReReCl 2(PAr 3) 2 (PAr 3=P( p-tolyl) 3 ( 1), P( m-tolyl) 3 ( 2), P( p-ClPh) 3 ( 3), P( p-MeOPh) 3 ( 4), PPh 3). The more basic phosphines PCyPh 2 and PBz 3 (Bz=benzyl), with p K a values of 5.05 and 6.50 and cone angles of 153 and 165°, respectively, afford the complexes Re 2(μ-O 2CCH 3)Cl 3(OMe)(PCyPh 2) 3 ( 5), with a Re–Re bond order of 4, and Re 2(μ-O 2CCH 3)Cl 4(PBz 3) 2 ( 6), with a Re–Re bond order of 3.5, under the same conditions. Attempts to incorporate more than two alkoxide ligands about a multiply bonded dirhenium core were successfully achieved in the synthesis of Re 2Cl 3(OEt) 3(PPh 3) 2 ( 7) from the reactions of Re 2Cl 6(PPh 3) 2 and Re 2Cl 4(OEt) 2(PPh 3) 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) Å, respectively.