Allyl Rhodium Research Articles

Rhodium(I)-Catalyzed C-C Bond Activation of Siloxyvinylcyclopropanes with Diazoesters.

The rhodium(I)-catalyzed C-C bond activation reaction of siloxyvinylcyclopropanes with diazoesters demonstrates a novel mode of C-C bond cleavage of siloxyvinvylcyclopanes. The alkene products were obtained as single E-configured isomers in good yields. A σ,η3 -allyl rhodium complex, which has been previously proposed as the key intermediate in rhodium(I)-catalyzed cycloaddition of vinylcyclopropanes, has been isolated and characterized by X-ray crystallography.

Syn‐Selective Rhodium(I)‐Catalyzed Allylations of Ketimines Proceeding through a Directed CH Activation/Allene Addition Sequence

Rhodium(I)-catalyzed C-H functionalization of aryl ketimines and subsequent carborhodation of a terminal allene resulted in the formation of allyl rhodium intermediates, which underwent allylation of the imine to give cyclized products, e.g., I, with high regioselectivity and diastereoselectivity. Preliminary attempts to develop an enantioselective variant were also successful.

Rhodium‐Catalyzed Allylation of Aldehydes with Homoallylic Alcohols by Retroallylation and Isomerization to Saturated Ketones with Conventional or Microwave Heating

The treatment of an aldehyde with a tertiary homoallylic alcohol at 100-250 degrees C in the presence of cesium carbonate and a rhodium catalyst leads to allyl transfer from the homoallylic alcohol to the aldehyde. The process includes Rh-mediated retroallylation to form an allyl rhodium species as the key intermediate. The homoallylic alcohol formed initially through allyl transfer is converted under the reaction conditions into the corresponding saturated ketone when bulky ligands are used. Microwave heating at 250 degrees C accelerates the reaction significantly.

The competitive and non-competitive hydroformylation of conjugated dienes starting with tetrarhodium dodecacarbonyl. An in-situ high-pressure infrared spectroscopic study

It is well known that the liquid-phase homogeneous unmodified rhodium catalysed hydroformylation of alkenes is poisoned by the presence of trace quantities of conjugated dienes. Nevertheless, some hydroformylation of conjugated dienes is possible with unmodified rhodium, and this reaction is in general slower than alkene hydroformylations at comparable reaction conditions. In the present contribution, we examined (A) the catalytic behaviour of alkenes in the presence of trace conjugated diene impurities and (B) the catalytic behaviour of a variety of dienes using Rh 4(CO) 12 in n-hexane solvent at 293 K under 1.0–4.0 MPa CO and 0.5–2.0 MPa H 2. The analytic method was in-situ high-pressure infrared spectroscopy. It was observed that (I) in the hydroformylation of poisoned alkenes, most of the rhodium reacts with the trace quantity of conjugated dienes and not the alkenes in this competitive situation and (II) the metal carbonyl spectra of the hydroformylation of a variety of dienes are very similar. The primary absorbance maxima observed in the hydroformylations of conjugated dienes occur at circa 2109, 2091, 2087, 2064, 2049, 2037, 2030, 2020, 2012, 1999, and 1990 cm −1. Given the known chemistry of Rh 4(CO) 12 under syngas, and the very well documented chemistry of Rh 4(CO) 12 under alkene hydroformylation conditions, the lack of bridging carbonyls in the present experiments strongly suggested that the new infrared vibrations are due to mononuclear rhodium species. Preliminary analysis suggests the presence of at least three new species. In particular, the formation of observable η 3 allyl rhodium tricarbonyl species, σ allyl rhodium tetracarbonyl species and even acyl rhodium tetracarbonyl species RCORh(CO) 4 (R=alkenyl and/or formylalkyl) seems probable. Characteristic wavenumbers of 2108, 2064, 2037, 2020 and 1700 cm −1 are tentatively assigned to the latter. The reduced hydroformylation activity in the competitive hydroformylation of alkenes arises due to the much higher affinity of rhodium complexes for conjugated dienes than for alkenes under otherwise similar reaction conditions.

ChemInform Abstract: C—C Bond Cleavage of 8‐Quinolinyl Alkyl Ketone by σ,η3‐Allyl Rhodium(III) Complex.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.