Tungstacyclobutadiene complexes

Table 2 Comparative computational results for selected tungstacyclobutadiene complexes ...

Cyclopropenyl systems can be formed from metallacyclobutadiene complexes. Here no decomplexation of unsaturated cyclopropanes is observed. The tungstacyclobutadiene complex 12 is converted into a cyclopropenyl complex 13 upon addition of a nitrogen nucleophile. ... 

McCullough, L.G., Ustemann, M.L, Schrock, R.R., Churchill, M.R., and Ziller, J.W. (1983) Multiple metal-carbon bonds. 34. Why terminal alkynes cannot be metathesized. Preparation and crystal structure of a deproto-nated tungstacyclobutadiene complex, W(eta.5-C5H5)[Cj(CMe3)2]a./. Am. Chem. Soc., 105, 6729-6730. 

Further support for this mechanism has also been provided by Schrock et al [37] who have synthesized stable tungstacyclobutadiene complexes. 

The motives underlying the original synthesis of 3 were based on the observation that certain tungstacyclobutadienes react with internal acetylenes to give (substituted) cyclopentadienyl complexes.Consequently, alkynyl-substituted organometallics were deemed to be appropriate for use in the syntheses of heterobimetallic complexes. To this end, the alkynyl-substituted (ii -C5Me4CH2CH2C CEt)Rh(CO)2 (4), was synthesized via reaction of [RhCl(CO)2l2 with 3 (Scheme III). Subsequent treatment with... 

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