Rhodium complexes carboxylate bridged

Dinuclear rhodium(II) carboxylate complexes with cage-like structures 46, in which carboxylate groups bridge the two metals and a... 

Iridium complexes having oxygen ligands are not nearly as extensive as those having nitrogen. Examples include acetylacetonates [Ir(P(C(5H5)3)2 (acac)H2] [64625-61-2], aqua complexes Ir(OH2)6]3+ [61003-29-0], nitrato complexes [Ir(0N02)(NH3),J2 [42482 42-8], and peroxides IrCl(P(C6I fy)3)2(02-/-(>/ I I9)2(CO) [81624-11-5]. Unlike rhodium, very few Ir(II) carboxylate-bridged dimers have been claimed and [Ir,2(OOCCI I3)4 has not been reported. Some Ir(T) complexes exhibit reversible oxidative addition of 02 to form Ir(III) complexes. That chemistry has been reviewed (172). 

Dinuclear aryloxide- and carboxylate-bridged rhodium complexes were tested as catalysts in the hydroformylation of styrene and 1-octene. A regiosdectivity toward the branched aldehyde up to 97 and 45%, respectively, was found [32]. 

The catalytic activity of rhodium diacetate compounds in the decomposition of diazo compounds was discovered by Teyssie in 1973 [12] for a reaction of ethyl diazoacetate with water, alcohols, and weak acids to give the carbene inserted alcohol, ether, or ester product. This was soon followed by cyclopropanation. Rhodium(II) acetates form stable dimeric complexes containing four bridging carboxylates and a rhodium-rhodium bond (Figure 17.8). 

Rhodium(II) forms a dimeric complex with a lantern structure composed of four bridging hgands and two axial binding sites. Traditionally rhodium catalysts faU into three main categories the carboxylates, the perfluorinated carboxylates, and the carboxamides. Of these, the two main bridging frameworks are the carboxylate 10 and carboxamide 11 structures. Despite the similarity in the bridging moiety, the reactivity of the perfluorinated carboxylates is demonstrably different from that of the alkyl or even aryl carboxylates. Sohd-phase crystal structures usually have the axial positions of the catalyst occupied by an electron donor, such as an alcohol, ether, amine, or sulfoxide. By far the most widely used rhodium] 11) catalyst is rhodium(II) acetate [Rh2(OAc)4], but almost every variety of rhodium] 11) catalyst is commercially available. 

The dimeric tetraacetato bridged Rh2(OCOCH3)4 has been obtained by the interaction of ammonium chlororhodate(III) or rhodium (III) hydroxide with acetic acid.1-3 Other (car-boxylato)rhodium(II) compounds were prepared directly in a similar way or from the acetate by exchange.2,3 Halo car-boxylates (RCOO, R = CC13, CF3, CH2C1, etc.) were prepared also by interaction of rhodium trichloride with the appropriate sodium salt in ethanol.4 The carboxylatcs are normally first isolated as a solvent adduct, e.g., [Rh(OCOR)2-C2H5OH]2 but are easily converted to the unsolvated complex. The acetate is readily prepared in a modification of this last procedure. A similar method is satisfactory for the preparation of other lower carboxylates as well as halo carboxylates. 

An interesting series of complexes with antitumour activity is that of the rhodium carboxylates, whose structure is a dimer containing bridging carboxylates ... 

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... 

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