IrHCl2P2 (P = P'Pr3) reacts rapidly with H2 at 25 °C to set up an equilibrium where H2 binds trans to the original hydride ligand (trans-2). A second slower reaction forms IrH(H2)Cl2P2 (cis-2), where the cis disposition of the chlorides, and also H cis to H2, was established by neutron diffraction. This molecule (unlike trans-2), shows rapid site exchange between coordinated H and H2. cis-2 can be induced to lose HC1 to form Ir(H)2ClP2 (3). The structure of Ir(H)2Cl(PlBu2Ph)2, an analog of 3, was shown by neutron diffraction to have a planar H2IrCl in a Y shape, with Cl at the base of the Y and a H-Ir-H angle of only 73°. ECP ab initio calculations of IrH2Cl(PH3)2 show that the

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For the species RuHXP2(CO), IrH2XP2, and Cp*RuXP (P = bulky phosphine, X = halide or pseudohalide), bothM]'X) are found to be quite rapid. In addition, hydride exchange occurs for RuHCl-(CO)P2 and RuDC1(CO)P'2, as well as for IrH2Cl(P'Bu2Ph)2 and IrD2Cl(PtBu2Me)2. Exchange is generally faster for halides than for hydrides yet is much slower for the groups phenoxide, OSiPh3, and C2Ph. These equilibria favor the better donating halide being bonded to the less electron-rich metal center. A variable-temperature NMR study of the degenerate exchange Cp*Ru(P*Bu2Me)Cl + Cp*Ru'(P*Bu2Me)Br <=t Cp*Ru(P'Bu2Me)Br + Cp*Ru'-(PtBu2Me)Cl establishes a second-order rate law with AH* = 8.6 ± 0.8 kcal/mol and AS* = -20 ± 3 cal/(mol K). These results clearly indicate the transient existence in solution of halideand/or hydride-bridged dimers of monomeric metal complexes.

Alkoxide (MeO -, EtO -, i PrO -) attack occurs at the coordinated olefin of Ir(Tripod)(COD) (Tripod ) MeC(CH 2 PPh 2 ) 3 , COD ) 1,5-cyclooctadiene) in CH 2 Cl 2 to give Ir(Tripod)(2-alkoxycyclooct-5-en-1-yl), primarily as the exo isomer. These products slowly eliminate alcohol to give Ir(Tripod)((1,2-η 2 )-6-σ-cycloocta-1,4-dienyl), which is the only product detected when the alkoxide is t BuO -. Addition of excess methanol to exo-Ir(Tripod)(2-methoxycyclooct-5-en-1-yl) abstracts MeO -(i.e., heterolytic O-C bond cleavage), and thus a hydrogen-bonding solvent reverses the nucleophilic attack on coordinated olefin. Alkoxide (MeO -, i PrO -, t BuOand 2-BuO -) addition occurs at an olefinic carbon of Rh(Tripod)(NBD) + (NBD ) norbornadiene) to give Rh(Tripod)(2-alkoxynorborn-4-en-1-yl). The crystal structure of the exo/ methoxy example has been determined. While this product cannot unimolecularly eliminate alcohol, attempts to protonate the norbornyl ether in the presence or absence of added NBD were not successful. Here again, acid abstracts RO -from the ligand ether.