Synthesis and reactivity of η 5-tetramethylcyclopentadienyl-propenyl rhenium complexes: Molecular structure of [(η 5:η 2-C 5Me 4CH 2CH [dbnd]CH 2)Re(CO) 2

Abstract

The fulvene complexes [(η 6-C 5Me 4CH 2)Re(CO) 2(R)] ( 1a, R I; 1b, R C 6F 5) react at the exocyclic methylene carbon with a vinylmagnesium bromide solution to produce the anionic species [(η 5-C 5Me 4CH 2CH CH 2)Re(CO) 2(R)] −. Protonation with HCl at 0 °C produces the hydride complexes [ trans-(η 5-C 5Me 4CH 2CH CH 2)Re(CO) 2(R)(H)] ( 2a, R I; 2b, R C 6F 5). Thermolysis of an hexane solution of the iodo-hydride ( 2a) under a CO atmosphere yields the complex [(η 5-C 5Me 4CH 2CH CH 2)Re(CO) 3] ( 3) and [Re(CO) 5I] as by-product. Thermolysis of 2b produced three new products, mainly the chelated complex [(η 5:η 2-C 5Me 4CH 2CH CH 2)Re(CO) 2] ( 4) and complex 3, with a non-coordinated olefin group, in moderated yield, and traces of [Re(CO) 5(C 6F 5)]. Thermolysis of an hexane solution of 2 in presence of an excess of PMe 3, afforded the phosphine derivative [(η 5-C 5Me 4CH 2CH CH 2)Re(CO) 2(PMe 3)] ( 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 η 2-coordination of the propenyl side arm of the η 5-C 5Me 4 ring.