Facile Hydrometalation of Alkynes by <i>n</i><i>ido</i>-1,2-(Cp*RuH)₂B₃H₇ Yielding Novel Ru−B Edge-Bridging Alkylidenes. Stepwise Conversion of HC⋮CC(O)OMe into <i>n</i><i>ido-</i>1,2-(Cp*RuH)₂-3-HOB-4-MeC-5-MeOC-BH₃, Cp* = η⁵-C₅Me₅

The reaction of the alkyne HC⋮CC(O)OMe with 7 sep 1,2-(Cp*RuH)2B3H7 leads to hydroboration plus hydroruthenation to produce nido-1,3-μ-Me{C(O)OMe}C-1,2-(Cp*Ru)2B3H7, a compound with an exocluster ruthenium−boron μ-alkylidene that exists in two isomeric forms. Both isomers undergo rearrangement with intramolecular chelation of the carbonyl oxygen at a boron site, thereby opening the cluster and generating arachno-2,3,-μ(C)-5-η(O)-Me{C(O)OMe}C-1,2-(Cp*Ru)2B3H7. Further heating leads to deoxygenation of the carbonyl fragment by a boron center concurrent with insertion of the carbon atom into the metallaborane cage to give nido-1,2-(Cp*RuH)2-3-HOB-4-MeC-5-MeOC-BH3.