Synthesis and reactivity of η5-tetramethylcyclopentadienyl-propenyl rhenium complexes: Molecular structure of [(η5:η2-C5Me4CH2CHdouble bond; length as m-dashCH2)Re(CO)2]

The fulvene complexes [(η6-C5Me4CH2)Re(CO)2(R)] (1a, Rdouble bond; length as m-dashI; 1b, Rdouble bond; length as m-dashC6F5) react at the exocyclic methylene carbon with a vinylmagnesium bromide solution to produce the anionic species [(η5-C5Me4CH2CHdouble bond; length as m-dashCH2)Re(CO)2(R)]−. Protonation with HCl at 0 °C produces the hydride complexes [trans-(η5-C5Me4CH2CHdouble bond; length as m-dashCH2)Re(CO)2(R)(H)] (2a, Rdouble bond; length as m-dashI; 2b, Rdouble bond; length as m-dashC6F5). Thermolysis of an hexane solution of the iodo-hydride (2a) under a CO atmosphere yields the complex [(η5-C5Me4CH2CHdouble bond; length as m-dashCH2)Re(CO)3] (3) and [Re(CO)5I] as by-product. Thermolysis of 2b produced three new products, mainly the chelated complex [(η5:η2-C5Me4CH2CHdouble bond; length as m-dashCH2)Re(CO)2] (4) and complex 3, with a non-coordinated olefin group, in moderated yield, and traces of [Re(CO)5(C6F5)]. Thermolysis of an hexane solution of 2 in presence of an excess of PMe3, afforded the phosphine derivative [(η5-C5Me4CH2CHdouble bond; length as m-dashCH2)Re(CO)2(PMe3)] (5). All the complexes were characterized by IR, 1H, 13C and 31P NMR spectroscopies and mass spectrometry. The molecular structure of 4 has also been determined. The molecule exhibits a formal three-legged piano-stool structure, with two CO groups, and the third position corresponding to the η2-coordination of the propenyl side arm of the η5-C5Me4 ring.