Bonds ruthenium hydrides

Since activation of the N-H bond of PhNHj by Ru3(CO)i2 has been reported to take place under similar conditions [306], it has been proposed that the reaction mechanism involves (i) generation of an anUido ruthenium hydride, (ii) coordination of the alkyne, (iii) intramolecular nucleophilic attack of the nitrogen lone pair on the coordinated triple bond, and (iv) reductive ehmination of the enamine with regeneration of the active Ru(0) center [305]. 

An olefin metathesis/double bond isomerization sequence can be promoted by the catalysis of in situ generated ruthenium hydride species from ruthenium complex 1 (Scheme 41 ).68... 

The postulated mechanism involves a directing effect of the carbonyl group to the metal center, ideally positioning this metal for insertion into the ortho-G-H bond. The resulting ruthenium hydride undergoes hydridometallation of the olefin followed by reductive elimination to give the new C-C bond. 

A detailed review of the mechanisms of the hydrogenation of polar double bonds by ruthenium hydride species have been published by Clapham et alP The article examines the properties of over 100 catalyst systems for transfer and... 

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. 

Conjugated dienes were thus selectively obtained by hydrovinylation of alkynes catalyzed by a cationic ruthenium alkylidene complex [43] (Eq. 31). This reaction is thought to be promoted by the ruthenium hydride species resulting from the deprotonation of the <5-methyl group of the metallic precursor, followed by the sequential insertion of alkyne and ethylene into the metal-hydride and metal-vinyl bonds. 

Cycloisomerization of allyl propargyl ethers takes place under mild conditions when performed with a ruthenium hydride catalyst obtained from Cp RuCl(COD) in the presence of acetic acid or ethanol. 3,4-Dialkylidenete-trahydrofurans were produced in good yields [ 71 ] (Eq. 53). It is noteworthy that the C-H and C-C bonds formed are always syn. This is the result of the cis addition of the Ru-H bond to the C=C bond. 

The catalytic activation of allylic carbonates for the alkylation of soft car-bonucleophiles was first carried out with ruthenium hydride catalysts such as RuH2(PPh3)4 [108] and Ru(COD)(COT) [109]. The efficiency of the cyclopen-tadienyl ruthenium complexes CpRu(COD)Cl [110] and Cp Ru(amidinate) [111] was recently shown. An important catalyst, [Ru(MeCN)3Cp ]PF6, was revealed to favor the nucleophilic substitution of optically active allycarbonates at the most substituted allyl carbon atom and the reaction took place with retention of configuration [112] (Eq. 85). The introduction of an optically pure chelating cyclopentadienylphosphine ligand with planar chirality leads to the creation of the new C-C bond with very high enantioselectivity from symmetrical carbonates and sodiomalonates [113]. 

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. 

Ruthenium hydride-catalyzed carbon-carbon double bond migration is applicable to isomerization of allylic acetals and ketals 31 to vinylic ones 32, which undergo selective cross-aldol type reaction by treatment with Bp3-Et20 to yield 33 (Eq. 12.12) [18]. 

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). 

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 silylative coupling reaction of l,2-bis(dimethyIvinylsiloxy)ethane was effectively catalyzed by 1 mol% of ruthenium hydride catalyst, and the divinyl compound was completely consumed within 1 h at 80 °C. The reaction successfully proceeded without the solvent under air, but toluene could also be employed without affecting either the activity of the catalyst or the selectivity of this process. Application of this catalytic system for silylative coupling cyclization of l,2-bis(dimethyl-vinylsiloxy)ethane gave exclusively a cyclic product (Isolated yield 85%) with the exo-methylene bond between two silicon atoms in the molecule (2,2,4,4-tetramethyl-3-methylene-l,5-dioxa-2,4-dlsilacycloheptane) accompanied only by trace amounts of oligomers. 

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

Joe Chatt has been a pioneer of modern organometallic chemistry involving transition metal phosphine derivatives and in particular hydride complexes. In this article, we will emphasise the link between the pioneering work of Joe Chatt and the present interest in (T-bond complexes and their reactivity. This article concentrates on the chemistry of ruthenium derivatives and is divided into a brief historical overview, giving a perspective of the evolution of the chemistry of ruthenium hydride complexes and a part describing recent achievements in this field, mainly from our research group. 

These insertions are regiospecific, forming the least substituted ruthenium carbon a bond. The relative rates for additions of these ruthenium hydrides to various alkenes are ... 

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