MECHANISM OF REARRANGEMENT OF AN ALLYLVINYLRHENIUM COMPLEX TO AN (ALLYL VINYL KETONE)RHENIUM COMPLEX - ROLE OF CONCERTED ORGANOMETALLIC REACTIONS IN AVOIDING HIGH-ENERGY COORDINATIVELY UNSATURATED INTERMEDIATES

Deprotonation of C5H5(CO)2Re=CHCH2CH2CMe3 (1) with KOCMe3 Produced the vinylrhenium anion K+C5H5(CO)2Re[(E)-CH=CHCH2CMe3]- (2), which reacte d with Mel at the rhenium center to produce trans-C5H5(CO)2Re(CH3)[(E) -CH=CHCH2CMe3](3). Reaction of 2 with allyl bromide led to a similar a llylvinylrhenium complex trans-C5H5(CO)2Re(CH2CH=CH2)[(E)-CH=CHCH2CMe3 ] (4). However, unlike methylvinylrhenium complex 3 which was kinetica lly very stable, the allylvinylrhenium compound 4 reacted rapidly at r oom temperature to produce the (allyl vinyl ketone)rhenium complex C5H 5(CO)Re(eta2,eta2-CH2=CHCH2COCH=CHCH2CMe3) (5), which was characterize d spectroscopically and by X-ray crystallography. The conversion of 4 to 5 was not affected by added PMe3. Net inversion of allylic regioche mistry was observed in the conversion of deuterated allylvinylrhenium complex 4-alphad2 to 5-gammad2. The allylisopropylrhenium compound tra ns-C5H5(CO)2Re(CH2CH=CH2)[CH(CH3)2] (9) rearranged to give the stable eta3-allyl isobutyryl complex C5H5(CO)Re(eta3-CH2CHCH2)[COCH(CH3)2] (1 0), which was resistant to reductive elimination to a ketone. A mechan ism involving two consecutive concerted organometallic reactions is pr oposed.