REARRANGEMENT OF A PROPARGYL VINYL RHENIUM COMPLEX TO A RHENIUM ALLENYL VINYL KETONE COMPLEX

An eta1- to eta3-propargyl rearrangement promotes vinyl migration to CO in trans-C5H5(CO)2Re(CH2C=CH)-((E)-CH=CHCH2CMe3) (7) which eventually leads to the formation of allenyl vinyl ketone complex C5H5(CO)Re(eta2,eta2-H2C=C=CHCOCH=CHCH2CMe3) (8). This allenyl vinyl ketone complex 8 undergoes additional transformations at room temperature leading to the diastereomeric allenyl vinyl ketone complex C5H5(CO)Re(eta2,eta2-H2C=C=CHCOCH= CHCH2CMe3) (9) by complexation of rhenium to the opposite face of the vinyl group and to the pi-allyl sigma-vinyl rhenium complex C5H5(CO)Re[eta3(exo,syn)-H2CCHCHCOCH=CH2CMe3] (10) by a net [1,5] hydrogen migration. Upon heating at 105-degrees-C, allenyl vinyl ketone complex 9 rearranged to the isomeric pi-allyl sigma-vinyl rhenium complex C5H5(CO)Re[eta3(endo,-syn)-H2CCHCHCOCH=CCH2CMe3] (11). When the first formed pi-allyl sigma-vinyl rhenium complex 10 was heated at 105 105-degrees-C, it first rearranged to allenyl vinyl ketone complex 9 and then to the more stable pi-allyl sigma-vinyl rhenium complex 11. Two different mechanisms can account for the interconversion of allenyl vinyl ketone complexes with pi-allyl sigma-vinyl rhenium complexes. One involves a [1,5] sigmatropic hydrogen shift over the unsaturated organic fragment and the second involves transfer of hydrogen via a rhenium hydride intermediate.