Dimeric Iridium/ruthenium dimer

The dichlororuthenium arene dimers are conveniently prepared by refluxing ethanolic ruthenium trichloride in the appropriate cyclohexadiene [19]. The di-chloro(pentamethylcyclopentadienyl) rhodium dimer is prepared by refluxing Dewar benzene and rhodium trichloride, whilst the dichloro(pentamethylcyclo-pentadienyl)iridium dimer is prepared by reaction of the cyclopentadiene with iridium trichloride [20]. Alternatively, the complexes can be purchased from most precious-metal suppliers. It should be noted that these ruthenium, rhodium and iridium arenes are all fine, dusty, solids and are potential respiratory sensitizers. Hence, the materials should be handled with great care, especially when weighing or charging operations are being carried out. Appropriate protective clothing and air extraction facilities should be used at all times. 

A special type of reaction is observed with the platinum(IV) complex [PtI(Me)3] which cleaves the Af,N,Af, A -tetraphenyltetraaminoethylene under reduction to form the dimeric cyclometallated mono(NHC) complex of platinum(II) iodide [Eq. (31)]. Cyclometallation with the same ligand is also observed for ruthe-nium. Additional cyclometallations with various substituents of NHCs have been reported for ruthenium(II), rhodium(III), iridium(I), palladium(II), " and platinum(II). In the case of iridium, alkyl groups can be activated twice. In rare cases like for nickel(II) /x-bridging NHCs have been obtained. ... 

The first examples of C-H activation of an NHC ligand by TMs were reported by Hitchcock and Lappert and centered on ruthenium and iridium. [RuCl2(PPh3)3] reacted with the dimeric carbene (217) in xylene at 140 °C to give the five-coordinate monocarbeneruthenium (II) complex (218),... 

Norbornene or norbornadiene-type substrates with nickel, ruthenium or cobalt catalysts undergo stereoselective dimerization or codimerizations with other substrates. Numerous examples have been reported15. Stoichiometric use of an iridium complex in the cyclodimerization of norbornadiene results in an isolable c.vo-rrans-c.ro-metallacyclopentane 7, formed from two norbornadiene units18. Upon heating in the presence of triphenylphosphanc, the exo-trans-e.YO-dimer 8 is liberated from complex 7. 

The first synthetic, non-proteic molecular catalyst capable to oxidize water was reported about 30 years ago [69]. This was the so-called blue dimer, [(bpy)2Ru (H20)(p-0)Ru(H20)G>py)2] - Once electrochemically or chemically activated, the blue dimer undergoes the stepwise loss of four electrcms and four protons, producing an intermediate reactive species that oxidizes water [70,71]. Unfortunately, the blue dimer loses its catalytic efficiency after a few cycles due to the degradation of the organic ligands. However, the blue dimer paved the way to the discovery of other water oxidation catalysts, most of them still based on ruthenium centers [72—78]. In the last few years, molecular catalysts based on iridium centers [79] as well as on cheaper metals such as manganese [80-84], cobalt [85], and iron [86] were also developed. 

Iridium dimer complexes catalyse the 3 + 2-cycloaddition reactions of organic azides with bromoalkynes to furnish 1,5-disubstituted 4-bromo-1,2,3-triazoles in excellent yields under mild conditions. Ruthenium(II)-azido complexes undergo 3 + 2-cycloaddition reactions with strained cyclooctynes under ambient temperatures. No reaction was observed with non-activated terminal or internal alkynes under the same conditions. Dithioic acid copper catalysts (60) catalyse the 3 + 2-cycloaddition reaction of azides with alkynes to form 1,4-disubstituted-1,2,3-triazoles in various solvents and under various temperatures. Thermal Huisgen 3 + 2-cycloaddition reactions of azides and bis(trimethylsilyl)acetylene formed 4,5-bis(trimethylsilyl)-l/f-l,2,3-triazoles in low to high yields (15-95%). The Cu(I)-catalysed 3 + 2-cycloaddition... 

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