The cationic ruthenium−alkylidene complex [(PCy3)2(CO)(Cl)RuCHCHC(CH3)2]+BF4 - (1) was found to catalyze both hydrovinylation and [2+2] cycloaddition reactions of alkynes and alkenes. The reaction of R‘C⋮CR‘ ‘ (R‘ = H, Ph, n-Pr; R‘ ‘ = Ph, n-Pr, p-Tol, SiEt3, CH2CH2OH) with ethylene in the presence of 1 (3 mol %) produced the hydrovinylation products 2 and 3. The analogous reaction of dimethyl acetylenedicarboxylate (R‘ = R‘ ‘ = CO2Me) with ethylene and norbornene resulted in the formation of the [2+2] cycloaddition products 4. Based on the experimental evidence, a plausible mechanism of the hydrovinylation reaction has been proposed via a sequential insertion of alkyne and ethylene to the hydride complex 7.

The dehydrogenation of IrH 2 {C 6 H 3 -2,6-(CH 2 PBu t 2 ) 2 } (1) by tert-butylethylene followed by reaction with an excess of water leads to the isolation of IrH(OH){C 6 H 3 -2,6-(CH 2 PBu t 2 ) 2 } (2) in nearly quantitative yield. The hydrido hydroxo complex has been characterized by multinuclear NMR spectroscopy as well as a single-crystal X-ray structure determination. An isotopic labeling study with D 2 O indicates that 2 arises from the oxidative addition of water to the intermediate 14-electron complex Ir{C 6 H 3 -2,6-(CH 2 PBu t 2 ) 2 }. The title complex is an efficient catalyst for the transfer dehydrogenation of cyclooctane to cyclooctene but shows no catalytic activity for the hydroxylation of the alkane by water. The conversion of 1 to 2 can be reversed by placing a solution of 2 under 1 atm of H 2 at 25 °C.

Deuterium-labeling studies show that vinyl C−H oxidative addition of tert-butylethylene (tbe) to IrH2{C6H3-2,6-(CH2PBu t 2)2} (1) is rapid and reversible, while the stoichiometric hydrogenation of tbe by 1 is slower and irreversible. The dinitrogen complex, [Ir{C6H3-2,6-(CH2PBu t 2)2}]2(μ-N2) (3), results from the reaction of 1 with excess tbe under 1 atm of nitrogen. A single-crystal X-ray structure determination of 3 reveals a perpendicular arrangement of the P−C−P pincer ligands, which accounts for the surprising stability of 3 and the inhibiting effect of nitrogen on reactions catalyzed by 1.

The PCP pincer complex, IrH 2 {C 6 H 3 -2,6-(CH 2 P-t-Bu 2 ) 2 } (1) catalyzes the transfer dehydrogenation of primary and secondary alcohols. Dehydrogenation occurs across the C-O bond rather than the C-C bonds and the corresponding aldehydes or ketones are obtained as the sole products arising from the dehydrogenation reactions. Methanol is an exception to this pattern of reactivity and undergoes only stoichiometric dehydrogenation with 1 to give the carbonyl complex, Ir(CO){C 6 H 3 -2,6-(CH 2 P-t-Bu 2 ) 2 } (2). The products are obtained in nearly quantitative yields when the reactions are carried out in toluene solutions. Under the same conditions, 2,5-hexanediol is converted to the annulated product, 3-methyl-2-cyclopenten-1-one which has been isolated in 91% yield in a preparative scale reaction.Résumé : Le complexe PCP en forme de pince, IrH 2 {C 6 H 3 -2,6-(CH 2 P-t-Bu 2 ) 2 } (1) catalyse la réaction de déshydrogé-nation par transfert des alcools primaires et secondaires. La déshydrogénation se fait à travers la liaison C-O plutôt qu'à travers les liaisons C-C et on n'obtient que les aldéhydes et les cétones comme seuls produits de ces réactions de déshydrogénation. Le méthanol est une exception à ce mode de réactivité et il ne subit qu'une déshydrogénation stoechiométrique avec 1 pour conduire à la formation d'un complexe de carbonyle, Ir(CO){C 6 H 3 -2,6-(CH 2 P-t-Bu 2 ) 2 } (2). Lorsqu'on effectue les réactions en solution dans le toluène, les produits sont obtenus en rendements pratiquement quantitatifs. Dans les mêmes conditions, l'hexane-2,5-diol est transformé en produit cyclique, la 3-méthylcyclopent-2-én-1-one qui a été isolée avec un rendement de 91% au cours d'une réaction à l'échelle préparative.

The ruthenium−hydride complex (PCy3)2(CO)(Cl)RuH (1a) was found to catalyze the hydrogenation of terminal and cyclic alkenes. For example, the reaction of 1-hexene with 4 atm of H2 in the presence of 1a (1-hexene:1a = 8300:1) produced the hydrogenation product 2 (TON = 12 000 h-1). The treatment of 1a with excess ethylene led to the observation of both the ruthenium−ethyl and ruthenium−ethylene−hydride species 4a and 5a, respectively. The thermodynamic parameters for the equilibria among 1a, 4a, and 5a were estimated from the VT NMR data. These results are consistent with a monohydride mechanistic pathway.

The reactivity of a series of PCP pincer complexes with carbon monoxide and carbon dioxide has been studied. The reactions of CO 2 with PCP pincer iridium complexes provide the 16electron complex Ir(η 2 -CO 2 ){C 6 H 3 -2,6-(CH 2 PBu t 2 ) 2 } (2). Analogously, reactions with CO yield the 16-electron monocarbonyl compound Ir(CO) is reacted first with CO 2 and then with H 2 O, the reaction affords the same species (3). Thus, compound 3 can be obtained irrespective of the order of addition of the substrates CO 2 and H 2 O to 1a. Similarly, the reaction of 1b with CO affords the insertion product IrH(C(O)OH){C 6 H 3 -2,6-(CH 2 PBu t 2 ) 2 } (5). The identities of 3 and 5 have been confirmed by single-crystal X-ray structure determinations.

The cationic ruthenium-hydride complex [(η 6 -C 6 H 6 )(PCy 3 )(CO)RuH] + BF 4 − was found to be a highly regioselective catalyst for the oxidative C-H coupling reaction of aryl-substituted amides and unactivated alkenes to give ortho-alkenylamide products. The kinetic and spectroscopic analyses support a mechanism involving a rapid vinyl C-H activation followed by a rate-limiting C-C bond formation steps.

The reaction of dicyanamide and Zn(II) leads to Zn[N(CN)2]2, which has a new structure type, namely, a buckled-layer, noninterpenetrating motif.