A boron-pendant ruthenium Species forms a unique agostic methyl bridge between the boron and ruthenium atoms in the presence of a ligating solvent, acetonitrile. NMR inversion-recovery experiments enabled the activation and equilibrium thermochemistry for formation of the agostic bridge to be measured. The mechanism for bridge formation involves displacement of an acetonitrile ligand; thus, this is a rare example of a case where an agostic C-H ligand competitively displaces another tightly binding ligand from a coordinatively saturated complex. Characterization of this complex gives unique insights into the development of C-H activation catalysis based oil this ligand-metal bifunctional motif.