Rhenium complexes allyl

These -propargyl rhenium complexes undergo kinetic addition of nucleophiles at the central C atom to produce rhenacyclobutenes. The nucleophiles range from PR3 to malonate, acetylides, pyridines, and water. The derivatives of the addition of pyridines, however, are unstable and undergo further rearrangements to allene or acetylene complexes. Protonation of the metaUacyclobutenes produces u -allyl complexes. 

The chiral rhenium complexes of allylic and propargylic alcohols 841 are selectively oxidized by IBX to the unsaturated carbonyl compounds 842 in good yields (Scheme 3.334) [1139]. 

Pseudo-allyl compounds are formed from reactions of [Re(CO)2(PPh3)2(OCHNC6H4-4-Me)] with excess of PhNCO or PhNCS. Whereas carbamate compounds are formed in the former case, a mixture of monothio- and dithiocarbamate compounds is obtained with the sulfur analogue. The formation of the latter complex proceeds via the intermediate formation of the first. The related compounds show similar structural features with distorted octahedral rhenium atoms and... 

Whilst reaction of acyl chloride 303 with Na[Co(CO)3(PEt3)] affords the oxocyclobut-enyl complex 306" by ring expansion and CO loss, analogous treatment with NaRe(CO)5 delivers the non-fluxional // -cyclopropenylrhenium compound 305" . In the latter case, compound 304 loses carbon monoxide with concomitant migration of the cyclopropenyl moiety from carbonyl to rhenium as an allylic rearrangement rather than a 1,2-shift. 

On the other hand a coordinatively unsaturated paramagnetic d metal center could oxidatively add the allyl radical at the metal center to form a labile d° n-aWyl oxo species as organometallic intermediate (step B). The latter may rearrange via a ff-allyl intermediate to a d allyloxy species (step D). The latter is believed to convert to acrolein and a reduced metal center via an /0-hydrogen abstraction by the metal center. In an attempt to gain insight into fundamental reactions involved in this catalytic cycle, some authentic d° allyl 0X0 complexes of rhenium [23] and tungsten... 

Electrophilic attack by trityl cation on olefin complexes cani also occur to abstract a hydride from the allylic position. This process converts a neutral olefin complex into a cationic allyl complex and has been conducted with complexes that are less strongly backbonding than the complexes described in the preceding two paragraphs. One example of such an allylic hydride abstraction from a rhenium-propene complex is shown in Equation 12.69. An early example to form a homoconjugated system is shown in Equation 12.70. ... 

The following metal compounds are used for the preparation of the catalysts oxides, metal carbonyls, halides, alkyl and allyl complexes, as well as molybdenum, tungsten, and rhenium sulfides. Oxides of iridium, osmium, ruthenium, rhodium, niobium, tantalum, lanthanum, tellurium, and tin are effective promoters, although their catalytic activity is considerably lower. Oxides of aluminum, silicon, titanium, manganese, zirconium as well as silicates and phosphates of these elements are utilized as supports. Also, mixtures of oxides are used. The best supports are those of alumina oxide and silica. 

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