Rhodium complexes 1,3-diketones

Haegele et al. (269) have used exact isotope masses and isotope abundances together in determining the detailed fragmentation patterns of square planar rhodium (I) -diketonate complexes. They found that some species postulated by other workers were in error. High resolution is needed to distinguish the 28 mass units for loss of CO (27.9949) from C2H4 (28.0313) (269) or the 69 mass units for PF2 (68.9906) from CFa (68.9952) (90). 

In 2003, Hayashi and his co-workers found that highly enantioselective rhodium-catalyzed allylic alkylation took place with l-aryl-2-propenyl acetates by using an achiral /3-diketonate ligand for the rhodium complexes in the presence of (diphenylphosphino)binaphthyloxazoline 60b. Fine-tuning of the /3-diketonate part resulted in enhancement in enantioselectivity up to 97% ee (Equation (49)). " ... 

The rhodium complex [RhCl(PPh3)3] readily brings about stoichiometric decarbonylation of aldehydes, acyl halides and diketones. A typical aldehyde decarbonylation is illustrated by equation (69). a,3-Unsaturated aldehydes are decarbonylated stereospecifically (equation 70), while with chiral aldehydes the stereochemistry is largely retained (equation 71). ° ... 

By heating above 200 C catalytic decarbonylation is possible using [RhCl(PPh3)3], and is particularly suitable for aromatic aldehydes since aliphatic aldehydes tend to dehalogenate under these conditions to form alkenes (equation 72). Cationic rhodium complexes, for example [Rh(Ph2P(CH2)2PPh2)2], are much more active catalysts and hence reactions can be carried out at below 100 Because of the milder conditions aliphatic aldehydes can be decarbonylated to the alkane using this catalyst system. Rhodium catalysts can also be used to decarbonylate a- and -diketones and keto esters (equations 73 and 74). ... 

Hydrosilylotion of carbonyl compounds. This rhodium complex is an effective catalyst for hydrosilylation of aldehydes, ketones, a,/3-unsaturated aldehydes and ketones, and a-diketones. Hydrosilylation followed by hydrolysis is equivalent to reduction of either the carbonyl group or the a, 3-un-saturation. 

Elongated a-substituted-/3-diketone ligands also form dicarbonylrhodium(l) and dicarbonyliridium(l) complexes, which, when properly elaborated, can yield new metallomesogens. Thus, 68 exhibited a N phase between 84 and 132.5 °C, whereas the existence of the mesomorphic properties in complexes 69 appeared to depend on the linking group. Wan el al. claimed SmC and N phases for the rhodium complexes 69a (M = Rh n = 7-12, 14) between... 

Replacements of ferrocene-substituted p-diketone ligands, p-dik, in cyclooctadiene-rhodium(I) complexes [Rh(p-dik)(cod)] by 1,10-phenan-throline are characterized by large negative activation entropies, indicating the operation of the expected associative mechanism, although the... 

In the above examples, the nucleophilic role of the metal complex only comes after the formation of a suitable complex as a consequence of the electron-withdrawing effect of the metal. Perhaps the most impressive series of examples of nucleophilic behaviour of complexes is demonstrated by the p-diketone metal complexes. Such complexes undergo many reactions typical of the electrophilic substitution reactions of aromatic compounds. As a result of the lability of these complexes towards acids, care is required when selecting reaction conditions. Despite this restriction, a wide variety of reactions has been shown to occur with numerous p-diketone complexes, especially of chromium(III), cobalt(III) and rhodium(III), but also in certain cases with complexes of beryllium(II), copper(II), iron(III), aluminum(III) and europium(III). Most work has been carried out by Collman and his coworkers and the results have been reviewed.4-29 A brief summary of results is relevant here and the essential reaction is shown in equation (13). It has been clearly demonstrated that reaction does not involve any dissociation, by bromination of the chromium(III) complex in the presence of radioactive acetylacetone. Furthermore, reactions of optically active... 

Dichlorotetracarbonyldirhodium reacts readily with ligands such as phosphines, arsines, stibines, and phosphites - to form mononuclear complexes. It reacts with cyclo-pentadienylsodium to form ir-cyclopentadienyldicarbonyl-rhodium. With hydrochloric acid it produces the anion [Rh(CO)2Cl2] , and with /3-diketones in the presence of base forms dicarbonylrhodium /3-diketonates. ... 

Two recent determinations of activation volumes for Mel addition to rhodium(I) 8-diketonate complexes (197) could not discern which type operated. The values, along with those of AS - and the effects of solvent change, clearly indicated development of polar transition states (the charge separation involved in either 29 or 30 would fit) and the authors marginally favored 29. Interestingly, a complex of iridium(III) and Mel, 31, has been structurally characterized and reveals iodide-bonded Mel molecules (198). The Ir-I-C bond angles are 105.5° and 108.2° and although the interaction can be considered nucleophilic... 

Other rhodium(III) complexes which exhibit IL phosphorescence include some 6-diketone complexes, for example, RhL3 (L = aca, tfaca, and hfaca) (185). 

In subsequent investigations, in which solutions of salts the cations of which form complexes with unsaturated organic compounds were used as stationary phases, palladium and platinum derivatives were suggested [76]. Dicarbonylrhodium j3-diketonates show more interesting selectivity relative to olefins [77, 78]. Of the series of the rhodium compounds investigated, the best selectivity was shown by Rh(CO)2(3-trifluoroacetyl-camphorate) (1) [144—149] ... 

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