Vinylidene complexes ligand exchange

Various modes of reactivity of vinylidene complexes are illustrated in Scheme 1. The first four modes of reactivity shown in Scheme 1 are (1) simple substitution of the ligands bound to the metal [6] (2) oxidation of the metal [7] (3) modification or exchange of a vinylidene substituent [8] and (4) transfer of the vinylidene ligand [9]. The last two modes... 

Scheme 10.14 rationalizes the divergent behavior of the two catalytic systems in these selective transformations of pent-l-yn-ols. The presence of phosphine ligands promotes the formation of ruthenium vinylidene species which are key intermediates in both reactions. The more electron-rich (p-MeOC6Fl4)3P phosphine favors the formation of a cyclic oxacarbene complex which leads to the lactone after attack of the N-hydroxysuccinimide anion on the carbenic carbon. In contrast, the more labile electron-poor (p-FC6H4)3P) phosphine is exchanged with the N-hydroxysuccinimide anion and makes possible the formation of an anionic ruthenium intermediate which liberates the cyclic enol ether after protonation. 

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