REACTIONS OF COORDINATED LIGANDS .54. SYNTHESIS OF (1,2,3-ETA)-TRANS-BUTADIENYL COMPLEXES BY DEPROTONATION OR DESILYLATION OF CATIONIC MOLYBDENUM 1,3-DIENE COMPLEXES - FORMATION OF ETA-4-VINYLKETENE COMPLEXES AND CRYSTAL-STRUCTURES OF [MO((1,2,3-ETA)-TRANS-CH2CHC=CH2)(CO)2-(ETA-C5ME5)], [MO(ETA-3-CH2CC(ME)CH2CO)(CO)2(ETA-C5ME5)] AND [MOI(ETA-4-CH2=CHC(ME)=C=O)(CO)(ETA-C5ME5)]

One of the products of the reaction of the base Li[N(SiMe3)2] with (Mo(eta4-C4H6)(CO)2(eta-C5Me5)][BF4] is the exo-orientated (1,2,3-eta)-trans-butadienyl complex (Mo{(1,2,3-eta)-trans-CH2CHC=CH2}(CO)2(eta-C5Me5)]. A single-crystal X-ray diffraction study of the latter has revealed that the two adjacent n systems, allyl and C=CH2 within the butadienyl fragment are orthogonal to each other. This complex can be formed selectively and in high yield by reaction of [NBun4]F with the cation [Mo{eta4-CH2= CHC(SiEt3)=CH2}(CO)2(eta-C5Me5)][BF4]. The desilylation reaction has also been used to transform (Mo{eta4-syn-CH(Ph)=CHC(SiMe3)=CH2}(CO)2(eta-C5Me5)][BF4] into a mixture of exo- and endo-(Mo{(1,2,3-eta)-trans-syn-CH(Ph)CHC=CH2}(CO)2(eta-C5Me5)]. An alternative synthetic route to (1,2,3-eta)-trans-butadienyl complexes was explored involving reaction of Li[Mo(CO)3(eta-C5Me5)] with CH2=C=C(Me)CH2Cl. In the event an unusual cyclisation reaction occurred leading to the formation of the X-ray crystallographically identified complex [Mo{eta3-CH2CC(Me)CH2CO}(CO)2(eta-C5Me5)). Extended Huckel molecular orbital calculations on (Mo{(1,2,3-eta)-trans-CH2CHC=CH2}(CO)2(eta-C5Me5)] using the complete set of crystallographic coordinates shows that reaction with protons should occur on the end carbon of the butadienyl ligand to form a cationic eta3-vinylcarbene complex. However, protonation with CF3SO3H affords a vinylketene complex [Mo(OSO2CF3){eta4-CH2=CHC(Me)=C=O)(CO)(eta-C5Me5)] the structural identity of which was established by an X-ray crystallographic study of the analogue [Mol{eta4-CH2=CHC(Me)=C=O}(CO)(eta-C5Me5)] obtained from the triflate complex via metathesis. The mechanisms of these reactions are discussed.