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)2 OR}Cl2 ], (R=H or Me) has been extended with [H2 B(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)PR3 Ru{κ3 -H,S,S'-H2 B(L)2 }], (2 a-d and 2 a'-d'; R=Ph, Cy, OMe or OPh and L=C5 H4 NS or C7 H4 NS2 ) and [Ru{κ3 -H,S,S'-H2 B(L)2 }2 ], (3: L=C5 H4 NS, 3': L=C7 H4 NS2 ) were isolated upon treatment of [(η6 -p-cymene)RuCl2 PR3 ], 1 a-d (R=Ph, Cy, OMe or OPh) with [H2 B(mp)2 ]- or [H2 B(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 {C7 H4 S2 -(E)-N-C=CH(R')}Ru{κ3 -H,S,S'-H2 B(L)2 }], (4-4'; R=Ph and R'=CO2 Me or C6 H4 NO2 ; L=C7 H4 NS2 ) and [PR3 {C7 H4 NS-(E)-S-C=CH(R')}Ru{κ3 -H,S,S'-H2 B(L)2 }], (5-5', 6 and 7; R=Ph, Cy or OMe and R'=CO2 Me or C6 H4 NO2 ; L=C7 H4 NS2 ). 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 .