The ruthenium aqua complexes [Ru(H(2)O)(2)(bipy)(2)](OTf)(2), [cis-Ru(6,6'-Cl(2)-bipy)(2)(OH(2))(2)](OTf)(2), [Ru(H(2)O)(2)(phen)(2)](OTf)(2), [Ru(H(2)O)(3)(2,2':6',2''-terpy)](OTf)(2) and [Ru(H(2)O)(3)(Phterpy)](OTf)(2) (bipy = 2,2'-bipyridine; OTf(-) = triflate; phen = phenanthroline; terpy = terpyridine; Phterpy = 4'-phenyl-2,2':6',2''-terpyridine) are water- and acid-stable catalysts for the hydrogenation of aldehydes and ketones in sulfolane solution. In the presence of HOS(O)(2)CF(3) (triflic acid) as a dehydration co-catalyst they directly convert 1,2-hexanediol to n-hexanol and hexane. The terpyridine complexes are stable and active as catalysts at temperatures > or = 250 degrees C and in either aqueous sulfolane solution or pure water convert glycerol into n-propanol and ultimately propane as the final reaction product in up to quantitative yield. For the terpy complexes the active catalyst is postulated to be a carbonyl species [(4'-R-2,2':6',2''-terpy)Ru(CO)(H(2)O)(2)](OTf)(2) (R = H, Ph) formed by the decarbonylation of aldehydes (hexanal for 1,2-hexanediol and 3-hydroxypropanal for glycerol) generated in the reaction mixture through acid-catalyzed dehydration. The structure of the dimeric complex [{(4'-phenyl-2,2':6',2''-terpy)Ru(CO)}(2)(mu-OCH(3))(2)](OTf)(2) has been determined by single crystal X-ray crystallography (Space group P1 (a = 8.2532(17); b = 12.858(3); c = 14.363(3) A; alpha = 64.38(3); beta = 77.26(3); gamma = 87.12(3) degrees, R = 4.36 %).

Gentle thermolyses of CpW(NO)(CH 2 CMe 3 )-(η 3 -allyl) complexes (Cp = η 5 -C 5 Me 5 (Cp*), η 5 -C 5 Me 4 H (Cp′)) in neat hydrocarbon solutions result in the loss of neopentane from the metal's coordination spheres and the transient formation of the 16-electron (16e) intermediate species CpW(NO)(η 2 -allene) and/or CpW(NO)(η 2 -diene). These transient intermediates can react with hydrocarbon substrates, RH (R = alkyl, aryl), to form three different types of organometallic products. The first products are the desired CpW(NO)(η 3 -allyl)(η 1 -R) complexes that result from the selective single activation of a C−H bond of RH. The second class of products involves CpW(NO)(H)[η 3 -(R)-allyl] complexes that are isomers of the CpW(NO)(η 3 -allyl)(η 1 -R) compounds resulting from an intramolecular R/allyl H exchange. Finally, the third type of products contains CpW(NO)(H)[η 3 -hydrocarbyl] species that result from three successive C−H activations of hydrocarbon substrates such as R′CH 2 CH 2 CH 3 and loss of the original allyl ligand. Just which organometallic products ultimately result from the reactions of the CpW(NO)(CH 2 CMe 3 )(η 3 -allyl) complexes with hydrocarbons depends on several factors, including the natures of the cyclopentadienyl and allyl ligands, the hydrocarbon substrates themselves, the electron density at the metal centers, and the experimental conditions employed. This article documents these dependences and identifies the optimum CpW(NO)(CH 2 CMe 3 )(η 3 -allyl) compounds and experimental conditions for effecting the selective single C−H bond activations of hydrocarbon substrates such as benzene as a representative arene and methylcyclohexane as a representative alkane. During the course of these investigations all new organometallic complexes have been characterized by conventional spectroscopic methods, and the solid-state molecular structures of several of them have been established by singlecrystal X-ray crystallographic analyses.

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C-H activation of benzene at 26 °C by (η(5)-C(5)Me(5))W(NO)(CH(2)CMe(3))(η(3)-CH(2)CHCHMe) results after 4 h in the production of five new organometallic complexes, only two of which are isomers of the desired (η(5)-C(5)Me(5))W(NO)(C(6)H(5))(η(3)-CH(2)CHCHMe) compound. In contrast, the identical reaction involving the η(5)-C(5)Me(4)H analogue affords only the phenyl complexes during the first 24 h, thereby facilitating their isolation in good yields. This striking difference in reactivity can be attributed to the lesser steric demands of the η(5)-C(5)Me(4)H ligand that result in its complexes reacting at a significantly slower rate.

Cp*W(NO)(CH 2 CMe 3 )(η 3 -CH 2 CHCHMe) (1) is known to initiate facile and selective aliphatic C-H bond activations of hydrocarbons at ambient temperatures. Its ability to effect C-H activations of unfunctionalized hydrocarbon portions of more complex molecules containing various functional groups has now been investigated in some detail. In addition, molybdenum analogues of 1 have also been examined in order to see how the C-H activation chemistry is affected when the central metal is changed. Thermolyses of 1 in neat 1-chloropropane, 1-chlorobutane, and 1-bromobutane at room temperature result in activation of the terminal C-H bonds at the end opposite the carbon-halogen linkage and the clean formation of the alkyl-allyl complexes Cp*W(NO)(CH 2 CH 2 CH 2 Cl)(η 3 -CH 2 CHCHMe) (2), Cp*W(NO)(CH 2 (CH 2 ) 2 -CH 2 Cl)(η 3 -CH 2 CHCHMe) (3), and Cp*W(NO)(CH 2 (CH 2 ) 2 CH 2 Br)(η 3 -CH 2 CHCHMe) (4), respectively. No reaction occurs with the C-Cl or C-Br bonds in the haloalkanes even though they are weaker than the C-H bonds that are activated. Similarly, treatment of 1 with n-Bu 2 O yields exclusively the terminal 5), whereas the reaction with THF results in the single activation of a secondary sp 3 C-H bond R to the oxygen atom in THF and the formation of Cp*W(NO)(C 4 H 7 O)(η 3 -CH 2 CHCHMe) (6). Consistently, reaction of 1 with ethylcyclohexane results in preferential activation of one of the primary sp 3 C-H linkages of the ethyl group and the formation of Cp*W(NO)(CH 2 CH 2 C 6 H 11 )(η 3 -CH 2 CHCHMe) (7). The Cp*Mo(NO)(alkyl)(η 3allyl) complexes analogous to 1 are generally thermally unstable and react at or slightly above room temperature. The first member of this family of complexes to be studied was Cp*Mo(NO)(CH 2 CMe 3 )(η 3 -C 3 H 5 ) (8), whose thermolysis in the presence of pyridine at 35 °C over 3 days leads to the formation of Cp*Mo(NO)(C 5 H 5 N)(η 2 -CH 2 dCHCH 2 CH 2 -t-Bu) (9), an η 2 -olefin complex in which the allyl and neopentyl ligands have coupled. The related Cp*Mo(NO)(CH 2 SiMe 3 )(η 3 -CH 2 CHCHMe) complex (11) exists as a 2:1 mixture of isomers distinguishable by the orientation of the endo, syn allyl ligand. In the less sterically congested major isomer, the methyl group on the allyl ligand is adjacent to the NO ligand, but in the minor isomer the methyl group is adjacent to the more sterically demanding CH 2 SiMe 3 ligand. In general, the thermal reaction of 11 is similar to that of 1. Spectroscopic monitoring indicates that the loss of TMS from 11 at room temperature results in the formation of a 16e η 2 -diene intermediate complex that can be trapped with PMe 3 as an 18e adduct, Cp*Mo(NO)(η 2 -CH 2 dCHCHdCH 2 )(PMe 3 ) (12). However, reactions of 11 with various substrates (e.g., pentane, Et 2 O, and mesitylene) all lead to a single product, Cp*Mo(NO)(η 4 -trans-butadiene) (13). Evidently, the formation of the 18e butadiene complex is favored over the activation of a relatively electron-poor C-H bond by this molybdenum system. The results of DFT calculations on the model reaction ...