β-Diketones derived from cyclopentadienyl rhenium tricarbonyl

The acetyl complex (η5–C5H4COCH3)Re(CO)3 reacts with KOtBu and an excess of appropriate ester to provide cyrhetrenyl-β-diketones complexes (η5–C5H4COCH2COR)Re(CO)3 (R = CF3, 1a; CH3, 1b; Ph, 1c). These new 1,3-diketones exist predominantly as enol tautomer, although a enol/keto mixture of approx. 10:1 is present in complexes 1b–c, in chloroform-d solution. The complexes have been characterized by spectroscopic techniques IR, 1H and 13C NMR and mass spectrometry. X-ray crystallography of complex 1b shows that only the enol form occurs in the solid state. The O–C–C–C–O fragment of the molecule is planar with asymmetric enolisation in the direction furthest from the cyrhetrenyl group.