Five-Membered Ruthenacycles: Ligand-Assisted Alkyne Insertion into 1,3-N,S-Chelated Ruthenium Borate Species

Building upon previous work, the chemistry of [(η6-p-cymene)Ru{P(OMe)2OR}Cl2], (R=H or Me) has been extended with [H2B(mbz)2]− (mbz=2-mercaptobenzothiazolyl) using different Ru precursors and borate ligands. As a result, a series of 1,3-N,S-chelated ruthenium borate complexes, for example, [(κ2-N,S-L)PR3Ru{κ3-H,S,S’−H2B(L)2}], (2 a–d and 2 a’–d’; R=Ph, Cy, OMe or OPh and L=C5H4NS or C7H4NS2) and [Ru{κ3-H,S,S’-H2B(L)2}2], (3: L=C5H4NS, 3’: L=C7H4NS2) were isolated upon treatment of [(η6-p-cymene)RuCl2PR3], 1 a–d (R=Ph, Cy, OMe or OPh) with [H2B(mp)2]− or [H2B(mbz)2]− ligands (mp=2-mercaptopyridyl). All the Ru borate complexes, 2 a–d and 2 a’–d’ are stabilized by phosphine/phosphite and hemilabile N,S-chelating ligands. Treatment of these Ru borate species, 2 a’–c’ with various terminal alkynes yielded two different types of five-membered ruthenacycle species, namely [PR3{C7H4S2-(E)-N-C=CH(R’)}Ru{κ3-H,S,S’−H2B(L)2}], (4–4’; R=Ph and R’=CO2Me or C6H4NO2; L=C7H4NS2) and [PR3{C7H4NS-(E)-S-C=CH(R’)}Ru{κ3-H,S,S’−H2B(L)2}], (5–5’, 6 and 7; R=Ph, Cy or OMe and R’=CO2Me or C6H4NO2; L=C7H4NS2). All these five-membered ruthenacycle species contain an exocyclic C=C moiety, presumably formed by the insertion of a terminal alkyne into the Ru−N and Ru−S bonds. The new species have been characterized spectroscopically and the structures were further confirmed by single-crystal X-ray diffraction analysis. Theoretical studies and chemical-bonding analyses established that charge transfer occurs from phosphorus to ruthenium center following the trend PCy3<PPh3<P(OPh)3<P(OMe)3.