MODULATION OF AGOSTIC B-H-]RU BONDS IN EXO-MANOPHOSPHINO-7,8-DICARBA-NIDO-UNDECABORATE DERIVATIVES

The series of compounds [7-PP2-8-R-7,8-C2B9H10](-) behaves as tricoord inating ligands toward Ru(II). The coordination takes place by means o f the exo-cluster PPh(2) group and boran atoms B(2) and E(11) through B-H --> Ru agostic bonds. The three remaining Ru(II) positions may be occupied by two equivalent or distinct neutral ancillary ligands and o ne coordinating anion. The H-1 NMR spectra of these complexes provide evidence for the participation of two B-H's in bonding to Ru(II). A re sonance near -3 ppm is indicative of a B-H --> Ru agostic bond with a large contribution of B-H, while a resonance dose to -15 ppm is indica tive of a B-H --> Ru agostic bond with a large contribution of Ru-H. A gradation of agostic bonds with intermediate situations may be produc ed. These have been achieved by synthesizing a series of complexes [Ru X(7-PPh(2)-8-R-C2B9H10)LL], where X=Cl or H, R=H, Me, or Ph, L=PPh(3), and L'=PPh(3), CO, tetrahydrothiophene, or ethanol. Combinations have been done. The study has shown that the nature of R at the 8-cluster position practically has little effect on the B-H-Ru resonance; howeve r, the nature of the trans ancillary ligand is highly perturbing. The effect has been compared to the trans influence, The study has permitt ed evaluation of the trans influence (I) of a series of ligands. The o rder I(H) >I(PR(3)) >I(CO) >I(BH) >I(Cl) is followed. An NMR quantitat ive figure of this trans influence is given; however, due to the limit ed number of complexes tested it must be taken as only of qualitative value. The structural assignments are supported by the molecular struc tures of [RuCl(7-PPh(2)-8-Me-7,8-C2B9H10)(PPh(3))(2)] (1) and [RuCl(7- PPh(2)-8-Me-7,8-C2B9H10)(EtOH)(PPh(3))]. 0.64 (Me)(2)CO (2).