Ruthenium alkyl

Ruthenium alkyls were also formed via chlorine-alkyl interchange. An enhancement of the activity of RhCl(PPh3)3 by AlBr3 was simply due to formation of the more active bromo complex, while enhancement by addition of Al(i-Bu)3 was attributed to formation of HRh(PPh3)3 (see Section II,B,1). 

Casey has suggested that the hydrogenation of alkenes by Shvo s catalyst may proceed by a mechanism involving loss of CO from the Ru-hydride complex, and coordination of the alkene. Insertion of the alkene into the Ru-H bond would give a ruthenium alkyl complex that can be cleaved by H2 to produce the alkane [75], If this is correct, it adds further to the remarkable chemistry of this series of Shvo complexes, if the same complex hydrogenates ketones by an ionic mechanism but hydrogenates alkenes by a conventional insertion pathway. 

The alkylruthenium species obtained in eq. 5.1 is very stable in water, neither the addition of strong acids nor boiling for several hours lead to its decomposition. In aqueous solution it exists as a monomeric cation, however, it was isolated in solid state and characterized by X-ray crystallography as a dimer [ Ru(C2Hs)(CO)2(H20)2 2] - The stabiUty of this ruthenium alkyl is attributed to the stabihzation effect of strong hydrogen bonds which could be detected in the crystal structure and are postulated also in its aqueous solutions. Finally, elimination of propionic acid from the acyl could be induced by raising the temperature this reaction closes the catalytic cycle ... 

Noyori also observed that under high pressure of H2, the solvolysis of the ruthenium-alkyl species was less important for the product formation. In our study of the Ru(H)-catalyzed hydrogenation of 2-(6 -methoxy-2 -naphthyl)acrylic acid in CH3OD, we found the deuterium labelling in the naproxen product to be similar to those reported on the hydrogenation of tiglic acid ... 

Reaction of the ruthenium alkyl complexes with bromine or iodine also cleaves the ruthenium-carbon bond to form the alkyl halides in reasonable yield [Eq. (102)]. Attempts to decomplex the organic substrate using... 

Reaction between alkynes with electron-withdrawing groups and ruthenium alkyl or hydride complexes results in complexes containing alkenyl or... 

More specifically, calculations have suggested that the ruthenium-alkyl complex in Equation 6.53 reacts with arene to exchange covalent ligands by a process closely related to a a-bond metathesis mechanism. Computational studies of the reactions of a simple iridium-alkyl and alkoxo complex with alkanes to generate new metal-alkyl complexes have also suggested that a mechanism is followed that involves many of the characteristics of a classic a-bond metathesis transition state. However, calculations of the mechanisms of these two processes imply that the transition state contains some degree of M-H bonding. 

A ruthenium(II)-catalysed oxidative cross-coupling of phenylpyridine substrates with cycloalkanes has been reported (Scheme 31) [22]. The proposed mechanism involves directed metalation of phenylpyridine and formation of a ruthenium alkyl species in the presence of ferf-butyl peroxide as an oxidizing reagent. The reaction required an excess of oxidizing reagent (4 equiv. with respect to phenylpyridine) as... 

Reactions which appear to be closely related are the reversible exchange of hydrogen in some ruthenium-aryls and in some ruthenium-alkyl phosphine complexes (see p. 232). They may be represented as follows ... 

---