Reactivity of [RuHCl(PiPr3)2]2 with functionalized vinyl substrates. The H2 ligand as a sensitive probe of electronic structure.

Reaction of [RuHClL2]2 (L = PiPr3) with 2-vinylpyridine gives L2ClRu(eta 2-CH=CHC5H4N) with liberation of H2. Reaction of [RuHClL2]2 with a range of olefins D(H)C=CR(EWG) substituted by electron-donating (D) and -withdrawing (EWG) groups occurs by oxidative addition of a vinyl C-H bond to give the metallacycles L2ClHnRu(eta 2-(++)C(D)=CR(EWG)). The 13C chemical shift of ++C and the fate of the "Hn" unit (decoordination, binding as H2, or binding as two hydrides) are strongly correlated, depend on the donating and withdrawing power of D and EWG, and can be used to decide whether ++C binds to Ru as a carbene or as a vinyl. These results emphasize the reducing power of Ru(II) when pi-acid ligands such as CO are absent.