Ruthenium hydride complexe

Ruthenium hydride complexes, e.g., the dimer 34, have been used by Hofmann et al. for the preparation of ruthenium carbene complexes [19]. Reaction of 34 with two equivalents of propargyl chloride 35 gives carbene complex 36 with a chelating diphosphane ligand (Eq. 3). Complex 36 is a remarkable example because its phosphine ligands are, in contrast to the other ruthenium carbene complexes described so far, arranged in a fixed cis stereochemistry. Although 36 was found to be less active than conventional metathesis catalysts, it catalyzes the ROMP of norbornene or cyclopentene. 

As a final example in this section, a contribution by Grubbs et al. is discussed. The chloride-free ruthenium hydride complex [RuH2(H2)2(PCy3)2] (37) is believed to react, in the presence of alkenes, to form an unidentified ruthenium(O) species which undergoes oxidative additions with dihalo compounds, e.g., 38, to give the corresponding ruthenium carbene complex 9 (Eq. 4) [20]. 

Clapham, S.E., Hadzovic, A. and Morris, R.H. Review Mechanisms of the H2-Hydro-genation and Transfer Hydrogenation of Polar Bonds Catalyzed by Ruthenium Hydride Complexes. Coord. Chem. Rev., 2004, 248, 2201-2237. 

Non-activated aromatic and aliphatic esters have beeen efficiently hydrogenated to the corresponding alcohols under relatively mild, neutral conditions using a [2-(di-i-butylphosphinomethyl)-6-(diethylaminomethyl)pyridine]-ruthenium hydride complex... 

The mixed coupling of two different alkenes allows the formation of new functional unsaturated products but requires high regioselectivity. A ruthenium hydride complex, generated in situ from the reaction of RuHCl(CO)(PCy3)2 with HBF4.OEt2, was found to be an effective catalyst for the hydrovinylation of alkenes [8]. The reaction of styrene with ethylene produced the hydrovinylation compound 10 in 93% yield (Eq. 5). Initial hydrometallation of the alkene and insertion of ethylene seemed to be a plausible mechanism. 

In contrast to the silyl-ruthenium complexes including triisopropylphosphine, the ruthenium hydride complex with triphenylphosphine directs the stereoselectivity toward the E product according to Eq. (14) (Table 2) [27]. 

A similar approach was performed using the alkene metathesis catalyst RuCl2(= CHPh)(PCy3)2 [76]. It was known that this complex reacts with hydrogen in THF to give ruthenium hydride complexes capable of catalytic alkene hydrogenation [77] (Scheme 32). 

It is noteworthy that computational and experimental studies have shown that the formation of ruthenium-vinylidenes from terminal alkynes and ruthenium hydride complexes also proceeds via the formation of t -vinyl intermediate (Scheme 8.4) [14]. Thus, in this case the vinylidene ligand is not formed directly from the alkyne, and its /3-hydrogen atom arises from the hydrido ligand. 

Ruthenium hydride complexes such as RuH(Cl)(PPh3)3(tol) (to = toluene) and RuH(Cl)(CO)(PPh3)3 can effect isomerization of propargyl alcohols and propargyl ethers to a,/l-unsaturated carbonyl compound and dienol ether, respectively [13]. 

Acetylenic silyl ethers are converted to the conjugated dienol silyl ethers by the catalysis of ruthenium hydride complexes (Eq. 12.8). 

Allyl silyl ethers 29 derived from the corresponding allylic alcohols 28 are selectively isomerized to silyl enol ethers 30 via carbon-carbon double bond migration catalyzed by a ruthenium hydride complex, RuH2(PPh3)4 (Eq. 12.11) [17], The generality of the reaction was demonstrated for the silyl ethers of methallyl alcohol, ciima-myl alcohol, 2,4-pentadienyl alcohol, and so on. 

Isomerization of N-allyl amide to N-propenyl amide is a key step of the deprotection of an amino group. ( )-N-Aryl-N-(l-propenyl)ethanamides 35 are obtained via the double bond migration of N-aryl-N-allylamide 34 catalyzed by a ruthenium hydride complex [19]. The configuration of the N-propenyl moiety in the product is almost E, and the high E selectivity is probably due to the steric repulsion between the aryl group and the methyl substituent of the propenyl group (Eq. 12.13). 

With nickel(II) 2-ethylhexanoate and triethylaluminum, tetralin (59) is obtained by hydrogenation of naphthalene (55). Polycyclic aromatics, such as anthracene (57 equation 8), 9-methylanthracene and 9-trifluoroacetylanthracene, are partially hydrogenated to 1,2,3,4-tetrahydroanthracene derivatives by use of [Rh(DPPE)(arene)]+ in methanol and by ruthenium hydride complexes having triphenylphosphine ligands... 

It is well known that silylation of allyl derivatives with vinylsilane catalyzed by a ruthenium hydride complex is accompanied by isomerization ofpropen-l-yl to propen-2-yl derivatives as well as homo-coupling of vinylsilane when equimolar amounts of the initial substances are used. If catalyst I was used in the SC of allyl amide and allyl amine with vinylsilanes, a S-fold excess of olefin to vinylsilane was used to stop homocoupling of vinylsilane, but simultaneously no more than 5% of isomerization of allyl compound was observed [19, 26]. When allyl boronate is used instead of allylamine under mild conditions (20 - 40 °C), the two reactions catalyzed by I and IV yield stereoselectively -product (see Scheme 4) [26]. 

Therefore, the aim of this work was to synthesize new silacyclic and oligomeric organosilicon compounds containing easily modifiable Sl-O-R bonds, via competitive silylative coupling cyclization and polycondensation of divlnyl-substltuted silyl ethers in the presence of ruthenium hydride complex. 

The ruthenium hydride complex can be readily converted to a thiolate-containing product through S-H bond activation. ... 

A ruthenium hydride complex, RuH2(PPh5)4, has been employed for polymerization of mefhyl methacrylate (MMA) in conjunction wifh a chloride-type initiator, CHCl2COPh, and Al(()t-lh) j in toluene at 80°C (Scheme 6.180) [232]. Although RuH2(PPh3)4 is active even in the absence of Al(Oi-Pr)3, this aluminum additive has a substantial accelerating effect on the reaction rate. The polymers obtained had narrow MWD [M /M = 1.1). 

A review of homogeneous hydrogenation by Ru catalysts was published in 1970 and the synthesis and properties of ruthenium-hydride complexes known prior to 1977 have been reviewed . An up to date review of ruthenium-hydride complexes appeared in 1984 . We concern ourselves here with hydrogenation reactions that involve Ru(II) species as catalyst precursors or catalytic intermediates. 

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