Rhodium sandwich complexes

In the cobalt and rhodium sandwich complexes MCp Tj -CRCR-BR CHR"BR the acidic proton of the diborole ring was removed and... 

Rhodium Sandwich Complexes and other Decabranched Cyclopentadienyl Complexes, Chem. Eur. J. 1,374,1995 ... 

Buchholz, D., Gloaguen, B., Eillaut, J. L., Cotrait, M., Astruc, D. Mono- and bis (pentaisopropylcyclopentadienyl) cobalt and rhodium sandwich complexes and other decabranched cyclopentadienyl complexes. Chem. Eur. /., 1, 374-381 (1995). 

Brunner et al.98-100 have published a series of papers on epimerisation of chiral rhodium(III) and iridium (III) half-sandwich complexes [39]. 

The enantioselective catalytic 1,3-dipolar cycloaddition of linear or cyclic nitrones to enals was accomplished using the half-sandwich rhodium(III) complex S, Rc)-[(ri -C5Me5)Rh (/ )-Prophos (H20)](SbF6)2 as catalyst precursor [33, 34]. At —25°C, quantitative conversions to the cycloadducts, with up to 95% ee, were achieved (Scheme 10). The intermediate with the dipolarophile coordinated to the rhodium has been isolated and completely characterized, including the X-ray determination of its molecular structure [33, 34]. 

Scheme 10 OCR catalyzed by chiral half-sandwich complexes of rhodium...

The ligands triphos or/ and np in presence of compounds of iron, cobalt, nickel, rhodium, iridium and palladium, by reaction with THF solutions of white phosphorus, P, or yellow arsenic, As, form mononuclear or dinuclear sandwich complexes containing the cyclo-triphosphorus or cyclo-triarsenic units which behave as 3n-electrons rings. 

In addition to 38 and 39, other similar i74-l,3-diphosphacyclobutadiene complexes have been made with iron, rhodium, and iridium (40). Interesting chemistry is observed with rhodium, where two of the molecules appear to have dimerized with a metathetical extrusion of di-tert-butylacetylene to give a sandwich complex with the two rhodium atoms complexing on opposite sides of a twisted 1,2,4,5-tetraphosphacyclo-hexatriene ring (40). 

G. E. Herberich, B. Hessner, G. Huttner, and L. Zsolnai, A Triple-Decker Sandwich Complex of Rhodium with Dibora benzene as the Bridging Ligand, Angew. Chem. Int. Ed. Engl. 20, 472-473 (1981). 

The stability of the / -Cp-cobalt core even allows elemental sulfur to be incorporated in the alkyne co-cyclization. In the presence of excess alkynes the -Cp-cobalt half-sandwich complexes catalyze the formation of thiophenes (eq. (22)) [54]. Kajitani [55] has expanded this work to rhodium complexes and included selenium as an additional heteroatom. 

Interesting electrical properties are to be expected with the stepwise extension of this TT-system. The preparation of multilayered cyclophanes proved to be laborious [6] nevertheless new synthetic methods in transition metal chemistry of arenes have opened up a promising alternative approach via preparation of multidecker sandwich complexes (structure type D in Fig. 3). First row transition metals like chromium, iron and cobalt [51] form strong coordinative bonds with arenes when their oxidation state is low [48a] whereas second and third row elements like ruthenium, rhodium and iridium are strongly bonded towards arenes in higher oxidation states [48a, 51]. Sandwich complexes of cyclophanes can be divided into two groups ... 

Fig. 21, Reaction paths (a tof) to multidecker sandwich complexes of ruthenium, cobalt, rhodium and iridium with [2.2]paracyclophane (8) as ligand...

Dicarba-c/o50-dodecacarborane-containing half—sandwich complexes of ruthenium, osmium, rhodium and iridium Biological relevance and synthetic strategies 12CSR3264. 

Heterobimetallic complexes in which a half-sandwich complex of rhodium ill) is cormected by three bromo-bridges to Re(CO)3 were prepared from metathesis reactions of [Cp RhBr2]2 and [Re( -Br)(C0)3(C4H80)]2- The crystal structure of Cp Rh(/t-Br)3Re(CO)3 was determined by X-ray analysis. The treatment of a mixture of [(rf-CjH8)RuCl2]2 and [Cp RhCl2]2 with silver carboxylates and subsequent hydrogenation afforded mixed metal... 

Most of the rhodium-carbene complexes reported during the period 1984-1994 were half-sandwich-based complexes, as described in COMC (1995). The number of carbene complexes was somewhat scarce in the last decade, but it has increased enormously, widening the variety of carbenes that we can now find in the literature. Some new halfsandwich carbene complexes have been prepared. Irradiation of CpRh(PMe3)(C2H4) in pentafluoroanisole generated a metallacycle that evolved to a cyclic carbene in the presence of an electrophile (Scheme 40). ... 

Cobalt and Rhodium.— Reduction of [( -C Me2)2Rh] + with Zn-HCl affords [( -C6Mee)Rh( 7 -C6H2Me6)]+ and not [( -C6Me6)2Rh]+ as previously claimed the crystal structures of the [PFg]" salts of this ( -cyclohexa-l,3-diene) complex and of the 20-electron sandwich complex [( y -CeMe6)2Co]+ have been determined. ... 

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