Reaction scope and mechanism of sterically induced ruthenium-mediated intramolecular coupling of o-carboranyl with cyclopentadienyl.: Synthesis and structure of ruthenium complexes incorporating doubly linked cyclopentadienyl-carboranyl Ligands

Reactions of [Me(R-1)A(C5H3R2)(C2B10H10)]Li-2 (A = C, Si; R-1 = H, Me; R-2 = H, Me) with 1 equiv of RuCl2(PPh3)(3) in THF afforded the corresponding doubly linked cyclopentadienyl-carboranyl ruthenium(II) hydride complexes [eta(5)-Me2C(C5H3)(C2B10H10)]RuH(PPh3)(2) (6), [eta(5)-MeHC(C5H3)(C2B10H10)]RuH(PPh3)(2) (7), [eta(5)-Me2C(5-Me-C5H2)(C2B10H10)]RuH(PPh3)(2) (8), [eta(5)-Me2C(3/4-Me-C5H2)(C2B10H10)] RuH(PPh3)(2) (9a/9b), and [eta(5)-Me2Si(C5H3)(C2B10H10)]RuH(PPh3)(2) (10) in 72-85% isolated yields. On the other hand, interaction of [Me2C(C5H4)(C2B10H10)]Li-2 with 1 equiv of RuCl2[PPh2(OEt)](3) produced only [eta(5): sigma-Me2C(C5H4)(C2B10H10)]Ru[PPh2(OEt)](2) (14). An equimolar reaction of [Me2C(C5H4)(C2B10H10)]Li-2 with RuCl2(PPh3)(3) in the presence of dppe (dppe = 1,2-bis(diphenylphosphino) ethane) generated [eta(5):sigma-Me2C(C5H4)(C2B10H10)]Ru(dppe) (15). No ruthenium hydride complexes were detected in the latter two cases. Treatment of [eta(5)-Me2C(C5H3)(C2B10H10)]RuH(PPh3)(2) (6) with excess HBF4 center dot OEt2 in toluene gave the neutral ligand Me2C(C5H4)(C2B10H10) (12). This work showed that such intramolecular coupling reactions were driven by steric factors. A possible reaction mechanism was proposed to account for these ruthenium-mediated coupling reactions. All new complexes were fully characterized by multinuclear NMR techniques and elemental analyses. Molecular structures of 6, 7, and 8 were further confirmed by single-crystal X-ray analyses.