Oxapentadienyl−Rhodium−Phosphine Chemistry1

Abstract

Treatment of [(PR3)2Rh(μ-Cl)]2 (R = Me or Et) with potassium oxapentadienide leads to the production of ((1−3-η)-5-oxapentadienyl)Rh(PR3)2 (1, R = Me; 2, R = Et) as equilibrium mixtures of anti and syn isomers. Similarly, treatment of [(PR3)2Rh(μ-Cl)]2 (R = Me, Et) with potassium 2,4-dimethyloxapentadienide generates ((1−3-η)-2,4-dimethyl-5-oxapentadienyl)Rh(PR3)2 (3, R = Me; 4, R = Et). Compounds 3 and 4 exist predominantly as the anti isomer but upon cooling exhibit two rotameric forms, the sickle-shaped and U-shaped rotamers. Treatment of 1 with an additional 1 equiv of PMe3 produces the 18e species ((1−3-η)-5-oxapentadienyl)Rh(PMe3)3 (5), which is stable at room temperature. In contrast, when 2 is treated with an additional 1 equiv of PEt3, no reaction can be detected by NMR at room temperature. However, upon cooling to −70 °C, the characteristic signals for the phosphine adduct ((1−3-η)-5-oxapentadienyl)Rh(PEt3)3 (6) are observed by NMR. Compound 3, like 1, reacts with an additional 1 equiv of PMe3 t...