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 (η6-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 (μ2-η6,η6-C5H5BOBC5H5)[RuCl(PPh3)2]2 (2), with an oxo-bis(boratabenzene) bridging ligand connected
by the B–O–B linkage. The B-hydroxy
complex (η6-C5H5BOH)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 1a, 1b, 2, and 3 could interconvert
through the nucleophilic substitution reactions. While the reaction
of 1a with phenylacetylene did not successfully afford
the vinylidene complex as expected, reactions of 1a with
terminal ω-alkynols HCC(CH2)
n
CH(R)OH (R = H, n = 1, 2; R = Me, n = 1) proceeded smoothly to provide the neutral oxacyclocarbene
complexes (η6-C5H5BOEt)RuCl(CCH2CH2CH2O)(PPh3) (4), (η6-C5H5BOEt)RuCl(CCH2CH2CH2CH2O)(PPh3) (5), and (η6-C5H5BOEt)RuCl(CCH2CH2CH(Me)O)(PPh3) (6) via intramolecular nucleophilic attack of the hydroxyl
group to the corresponding vinylidene intermediates.