Arene-ruthenium complexes

An arene ruthenium complex with polymerizable side chains for the... 

AN ARENE RUTHENIUM COMPLEX WITH POLYMERIZABLE SIDE CHAINS FOR THE SYNTHESIS OF IMMOBILIZED CATALYSTS... 

Auzias M, Therrien B, Siiss-Fink G, Stepnicka P, Ang WH, Dyson PJ (2008) Ferrocenoyl pyridine arene ruthenium complexes with anticancer properties synthesis, structure, electrochemistry, and cytotoxicity. Inorg Chem 47 578-583... 

Therrien B (2009) Functionalised T 6-arene ruthenium complexes. Coord Chem Rev 253 493-519... 

Binuclear [RuX2(arene)]2 (1) and mononuclear RuX2(L) (arene) (3) derivatives have been shown to be useful precursors for access to alkyl-or hydrido(arene)ruthenium complexes. The latter are key compounds for the formation of arene ruthenium(O) intermediates capable of C—H bond activation leading to new hydrido and cyclometallated ruthenium arene derivatives. Arene ruthenium carboxylates appear to be useful derivatives of alkyl-ruthenium as precursors of hydrido-ruthenium complexes their access is examined first. 

The first example of an optically active arene ruthenium complex was obtained by Brunner and Gastinger (68). The reaction of la with HgMe2 (44) and then (R)-(+)Ph2PNHCH(Me)Ph afforded a pair of diastereoisomers, 116 and 117, which were separated by chromatography (68,69) (Scheme 9). Complexes 116 and 117 (X = Cl) react with SnCl2 to give complexes 118 and 119, but the stereoselectivity depends on reaction... 

The best method of preparing pentamethylcyclopentadienyl arene ruthenium complexes is that of Kaganovich etal. (89). Three complexes of type 125 have been prepared in good yield directly from the commercial reagent ruthenium trichloride, pentamethylcyclopentadiene, and arenes (89). 

Cyclophane ruthenium complexes have been prepared by the methods developed to make arene ruthenium complexes (Section II,A). Treatment of the solvated complexes of type 7, obtained from the dimers 1 and silver tetrafluoroborate in acetone, with 1 equiv of cyclophanes a-j in the presence of trifluoroacetic acid gives the double-layered (i76-arene)-(i76-cyclophane)ruthenium(II) complexes 263 in good yield (Scheme 26, p. 222). When 7 is used in excess, the triple-layered complex 264 is formed (159-162). 

An electrochemical study of the reduction of the double-layered (arene)-(cyclophane)ruthenium complexes 263 and of bis(arene)ruthenium complexes 235c has been reported (160,166). The compounds show in... 

A. Formation of Mixed-Metal Derivatives from Arene Ruthenium Complexes... 

B. Arene Ruthenium Complexes as Precursors of Ruthenium/Metal Derivatives... 

Although arene ruthenium complexes appear to be efficient catalyst precursors for the activation of alkynes, no evidence for the role or even the presence of the arene ligand in the active species has been obtained yet. 

In the first part of this article, focusing attention on polymer-supported cobalt phosphine complex 1 and arene ruthenium complex 2, we review contributions from our laboratory that show how organometallics can be efficiently attached to derivitised polystyrene and we outline their synthetic versatility.2,3 Following this, we discuss the preparation of a supported ruthenium complex, 3, and its use in oxidation and transfer hydrogenation catalysis. 

Arene ruthenium complexes are used frequently in metal-mediated organic synthesis for a wide range of reactions.5 For the purposes of our studies we have focused attention mainly on enol formate synthesis as a representative reaction for comparing the activity of 2 with its non-supported analogue 5. As with the supported cobalt complex, we find that attachment of 5 to a polymer support has little effect in its catalytic activity with a range of enol formates being prepared in high yield. 

Bis(arene) ruthenium complexes (99) + are electrophilic and add various nucleophiles (see Nucleophile), including hydride, to form (100) (Scheme 24). Methyl groups of methylated arene rings are acidic and can be deprotonated, giving the corresponding exo-methylene complexes (101). This is similar to the chemistry developed for analogous iron complexes, and is reminiscent of the a-mthenocenyl carbonium ions (Section 4.5). 

Fig. 48. Redox potentials of bis( j -arene)ruthenium complexes as a function of the ligand...

Keywords Arene chromium complexes Arene ruthenium complexes Enantioselective total synthesis Planar-chiral metal complexes Natm-al products... 

In addition to transfer hydrogenation reactions, arene ruthenium complexes also display excellent activity in the catalytic hydrogenation of olefins and alkynes including asymmetric reduction [40]. Remarkably, this process occurs under milder conditions, than required for catalysis with the dissociation of arene-metal bond. Lately, arene iridium complexes have also been found to be effective hydrogenation catalysts [41 ]. It is noteworthy that iridium can also promotes addition to the carbon-nitrogen double bond. 

Several arene-ruthenium complexes containing bidentate phosphine ligands have been shown to be useful catalyst precursors for the hydration of terminal aryl alkynes 105 to afford acetophenones 106 (Scheme 29) [52]. For example, the cationic complex 104, when activated by AgSbH5, promoted addition of water to a carbon-carbon triple bond. It was found that such reactions proceeded slowly but in good to excellent yields. It is remarkable, that the water in commercial acetone was sufficient to achieve complete conversion to the product. 

In a series of fascinating studies, Dixneuf s group has demonstrated the capability of arene-ruthenium complexes for promoting the intramolecular cyclization of (Z)-3-methylpent-2-en-4-yn-l-ols, such as 116 and 118, to furan derivatives 117 and 119 (Scheme 32) [53,55-57]. This reaction corresponded to the intramolecular Markovnikov addition of a hydroxyl group to a non-activated terminal triple bond. It was found that the czs-geometry of double bond is crucial for the... 

Recent refinements in hydride transfer reductions have enhanced the utility of oxazaborolidine- and BINAP-Ru (II) complex-catalyzed reductions. A review by Wills describes the development of catalysts for the syntheses of chiral nonracemic secondary alcohols from aryl ketones [5]. Among the more interesting catalysts discussed were f/ -arene ruthenium complexes, which utilize diamine and monotosylated diamine ligands. 

Scheme 1 Hydride transfer mechanism of -arene ruthenium complexes. Reduction of the active catalyst 2 results in the formation of 3. Approach of the incoming ketone proceeds through a six-membered transition state to form the secondary alcohol and regenerate 2.

Figure 1.21 Structures of the encapsulated pyrenyl-arene ruthenium complexes and of pyrenyl-Floxuridine of Therrien and coworkers.

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