The RuHClL 2 fragment (L ) P i Pr 3 ) reacts at 25 °C with a dozen different GdCHE compounds (G ) O, E ) R, OR, NR 2 ; G ) NR, E ) R) to give π-acid abstraction products, RuHCl(CG)L 2 , and E-H. For E-H ) C 2 H 5 OH, alcohol is decarbonylated in a second step to give an additional CO ligand and CH 4 . For E-H ) HNR(CR′ 2 H), amine can be dehydrogenated by RuHClL 2 to give RuH(H 2 )ClL 2 and CR′ 2 dNR. X-ray crystallographic studies are presented for the DMF decarbonylation intermediate Ru(H) 2 Cl(η 2 -C(O)NMe 2 )L 2 , where the strong reducing potential of RuHClL 2 is manifested in the formally Ru(IV) species obtained from oxidative addition of H-C(O)NMe 2 . The structure of Ru(H 2 )Cl(η 2 -C 6 H 4 CHdNMe)L 2 , the product from aryl C-H activation of benzylidenemethylamine, PhHCdNMe, is also presented. This ability to abstract CO, isonitrile, or H 2 is traced to the considerable π-basicity of RuHCl(P i Pr 3 ) 2 .

High-valent niobium bis-alkylidene complexes have been structurally authenticated along with the first paramagnetic Nb(IV) alkylidene. The bis-alkylidene complexes presented in this work are thought to be generated via a redox process involving α-hydride elimination from a transient Nb(III) bis-alkyl complex. X-ray diffraction, DFT, and multinuclear NMR studies are consistent with these bis-alkylidenes having drastically different chemical environments.

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.