REACTION OF VINYLACETYLENE WITH [MO(ETA-5-C5H5)(CO)2]2 - REACTIVITY OF [(MO(ETA-5-C5H5)(CO)2)(MU-HCCCH=CH2)] - CRYSTAL-STRUCTURES OF [(MO(ETA-5-C5H5)(CO)2)2(MU-ETA-2,ETA-3-HCCCHCH3)][BF4] AND OF [[(MO(ETA-5-C5H5)(CO)2)2]2-MU-(MU-HCCCH2CH2)2]

The reaction of vinylacetylene with [Mo(eta(5)-C5H5)(CO)2]2 affords the adduct [Mo(eta(5)-C5H5)(CO)2}2(mu-HC = CCH = CH2)] (1). The electrophilic attack of HBF4 gives the ionic allylic complex [{Mo(eta(5)-C5H5)-(CO)2}2(mu-eta(2),eta(3)-HC = CCHCH3)][BF4] (2). An unexpected reaction occurs with CPh3PF6 leading to [{Mo(eta(5)-C5H5)(CO)2}2(mu-eta(2),eta(3)-HC = CCHCH2CPh3)][PF6] (3). Complex 2 undergoes nucleophilic attack with NaBH4 and LiCH3 exclusively on the carbon atom bearing the methyl group, giving mu-alkyne complexes [{Mo(eta(5)-C5H5)(CO)2}2(mu-HC = CCH2CH3)] (6) and [{Mo(eta(5)-C5H5)(CO)2}2(mu-HC = CC(CH3)2)] (7), respectively. However, in the case of complex 3, the delocalization of the positive charge allows NaBH4 to react in two different ways to give the mu-alkyne species [{Mo(eta(5)-C5H5)(CO)2}2(mu-HC = CCH2CH2CPh3)] (9) and allylic [{Mo(eta(5)-C5H5)(CO)2}2(mu-sigma,eta(3)-HC-CH-CHCH2CPh3)] (10). The reduction of 1 with sodium amalgam leads to the formation of the sigma-eta(3) allylic complex [{Mo(eta(5)-C5H5)(CO)2}2(mu-sigma,eta(3)-HC-CH-CHCH3)] (5) and tetrametallic [[{Mo(eta(5)-C5H5)(CO)2}2]2-mu-(mu-HC = CCH2CH2)2] (4). Another dimerization occurs in the reaction of 2 with sodium amalgam, leading to [[{Mo(eta(5)-C5H5)(CO)2}2]2-mu-(mu-HC = CCH(CH3)-)2] (8). This product exists as three isomers, the meso 8A (R*S*) and a racemic mixture of 8B (SS) and 8C (RR). The action of base (DBU) on 3 gives the mu-substituted vinylacetylene complex [{Mo(eta(5)-C5H5)(CO)2}2(mu-HC = CCH = CHCPh3)] (11E). The structures of 2 and 4 have been solved by single-crystal X-ray diffraction methods. Crystallographic data [space group, a/angstrom, b/angstrom, c/angstrom, beta/deg, Z, number of observed reflections, R(w)]: for 2, P2(1)/n, 12.924 (7), 18.339 (18), 8.431 (6), 95.36 (5), 4, 2239, 0.0568; for 4, P2(1)/n, 8.308 (6), 14.457 (4), 14.664 (9), 102.97 (3), 2, 1558, 0.046.