Rhodium, pentamethylcyclopentadienyl

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. 

Several dyes or transition-metal complexes can be used as redox mediators in indirect electrolyses. Pentamethylcyclopentadienyl-rhodium(bipyridine) complexes [Cp Rhnl(bpy)(H20)]2+ 9 [33], which were pioneered and intensively studied by Steckhan et al. [34—36], are very versatile catalysts for the reduction of cofactors. 

Systems which fulfil these conditions are tris(2,2 -bipyridyl)rhodium complexes [63] and, more effectively, substituted or unsubstituted (2,2 -bipyridyl) (pentamethylcyclopentadienyl)-rhodium complexes [64], Electrochemical reduction of these complexes at potentials between — 680 mV and — 840 mV vs SCE leads to the formation of rhodium hydride complexes. Strong catalytic effects observed in cyclic voltammetry and preparative electrolyses are... 

Some rhodium complexes are more promising in the hydrogenation of arenes. The pentamethylcyclopentadienyl rhodium complex [ RhCUCi -CsMes) ], for instance, is stereoselective in the reduction of CgD6, yielding the all-m product almost exclusively, without the formation of cyclohexene.179... 

The pyrazolate ligand plays an important role in the addition of HPPh2 to complexes containing the (C5Me5)RhH1 fragment, allowing new links to the pentamethylcyclopentadienyl-rhodium(III) phosphido chemistry, which is very scarcely represented. 

Recently, it was also shown [74] that pentamethylcyclopentadienyl rhodium and iridium complexes with labile dative ligands catalyze the borylation of alkanes at the terminal position under thermal conditions (Scheme 9). It was proposed that Ir(V) and Rh(V) boryl complexes act as intermediates in these reactions. Reaction of Cp IrH4 with HBpin gives Cp Ir(Bpin)(H)3 and Cp Ir(Bpin)2(H)2. Both of the two Ir(V) boryl complexes react with octane to give octylboronate ester [75], though it is still unclear regarding the role... 

C5Me5)Rh]4[V40l9], Inorg. Chem. 28 1423 (1989) b) Y. Hayashi, Y. Ozawa, K. Isobe, The first vanadate hexamer capped by 4 pentamethylcyclopentadienyl-rhodium or pentamethylcyclopentadienyl-iridium groups, Chem. Lett. 425 (1989). 

R1 = Me, R2 = H), however, an unexpected inversion took place to afford a mixture of two phosphines (59, and 592). The phosphines (59, and 592) were reacted with bis[(pentamethylcyclopentadienyl)rhodium dichloride to furnish the corresponding rhodium(III) complexes (60, and 602) (Scheme 27) [38],... 

Partial or complete displacement of the coordinated acetonitrile ligands may be achieved with monodentate ligands (e.g., phosphines ), bidentate ligands (e.g., dienes), or tridentate ligands, providing a convenient entry to a range of (i -pentamethylcyclopentadienyl)rhodium and -iridium complexes. 

Pentamethylcyclopentadienyl-Rhodium and -Iridium Complexes as Catalysts for Olefin and Arene Hydrogenation... 

We find that the pentamethylcyclopentadienyl-rhodium compounds, and particularly the chloride (la), are useful catalysts for arene hydrogenation at 50°C and 50 atm H2 (19), Again, base (Et3N) is a necessary co-catalyst and the reactions proceed well in 2-propanol as solvent, where turnover numbers in excess of 200 per rhodium can easily be obtained for benzene-to-cyclohexane hydrogenation. The reactions also proceed in benzene, where turnover numbers in excess of 800 per rhodium are found, and even in the presence of water. No metal is formed under these conditions. 

Dichloro(T] -pentamethylcyclopentadienyl)rhodium(III) dimer di-p-chloro-dichlorobi (Ti -pentamethyl-... 

Rigby W, Bailey PM, McCleverty JA, MaitUs PM (1979) Pentamethylcyclopentadienyl-rhodium and -iridium complexes 19. Preparation and reactions of azido-, cyanato-, tMocya-nato-, nitrito-, and nitrato-rhodium complexes. J Chem Soc Dalton Trans 371—381... 

The structures of the ( 7 -pentamethylcyclopentadienyl)rhodium aqua complexes, as a function of pH, were studied by H, and 2D NOESY NMR spectroscopic techniques as well as by FAB mass spectrometry... 

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