Novel dinuclear ruthenium(I) and osmium(I) complexes containing poly(pyrazolyl)borato ligands. X-Ray crystal structure of [{Ru[HB(C3H3N2)3](CO)2}2]

Abstract

Reaction of the precursors catena-[Ru(O₂CMe)(CO)₂](1) and [{Os(O₂CMe)(CO)₃}₂](2) with tris- and tetrakis-(pyrazolyl)borato salts yields the neutral dimers [{M[RB(pz)₃](CO)₂}₂][M = Ru, R = H, (3); M = Ru, R = pz, (4); M = Os, R = pz, (5); M = Os, R = H, (6)](pz = C₃H₃N₂). Compounds (3)–(6) react with chlorinated organic solvents or Br₂ to give moderate yields of monomeric [M{RB(pz)₃}X(CO)₂](7)–(10)(X = Cl or Br). The X-ray structure of compound (3) has been determined and shows that the two tris(pyrazolyl)borato ligands co-ordinate as tridentate chelates in a cis staggered configuration around the dimetal core. The compound crystallizes in the monoclinic space group P2₁/n with a= 12.439(2), b= 15.380(2), c= 15.571 (3)Å, β= 100.85(2)°, and Z= 4. The structure has been refined to R= 0.039 and R′= 0.029. The Ru–Ru distance of 2.882(1)Å corresponds to a normal single bond. Variable-temperature n.m.r. studies revealed interconversion of co-ordinated pyrazolyl groups in solution with ruthenium dimers (3) and (4) showing greater dynamic behaviour than the osmium analogues (5) and (6).