Half-Sandwich B-Oxy Boratabenzene Ruthenium Complexes: Synthesis, Characterization, and Reactivity of (η6-C5H5BOR)RuCl(PPh3)2 (R = Et, Me)

The first examples of half-sandwich boratabenzene ruthenium complexes have been prepared and well-characterized. Treatment of RuCl2(PPh3)(3) with the anionic boratabenzene ligands C5H5BORNa (R = Et, Me) produced the B-alkoxy complexes (eta(6)-C5H5BOR)RuCl((PPh3)(2) (R = Et, 1a; Me, 1b), while the reaction of RuCl2(PPh3)(3) with the neutral borabenzene-PPh3 adduct C5H5BPPh3 led to the formation of the dinuclear complex (mu(2)-eta(6),eta(6)-C3H5BOBC5H5)-[RuCl(PPh3)(2)], (2), with an oxo-bis(boratabenzene) bridging ligand connected by the B-O-B linkage. The B-hydroxy complex (eta(6),C5H3BOH)RuCl(PPh3)(2) (3) was obtained from the nucleophilic substitution of complexes 1a, 1b, or 2 with water at the boron atoms, and the complexes la, 1b, 2, and 3 could interconvert through the nucleophilic substitution reactions. While the reaction of la with phenylacetylene did not successfully afford the vinylidene complex as expected, reactions of 1a with terminal omega-alkynols HC C(CH2)(n)CH(R)OH (R = H, n = 1, 2; R = Me, n = 1) proceeded smoothly to provide the neutral oxacyclocarbene complexes (eta(6)-C5H5BOEt)RuCl(= CCH2CH2CH2O)(PPh3) (4), (eta(6)-C5H5BOEt)RuCl(=CCH2CH2CH2CH2O)(PPh3) (5), and (eta(6)-C5H5BOEt)RuCl(=CCH2-CH2CH(Me)O)(PPh3) (6) via intramolecular nucleophilic attack of the hydroxyl group to the corresponding vinylidene intermediates.