Acylation triphenylphosphine complexes

Palladium chloride and metallic palladium are useful for carbonylating olefinic and acetylenic compounds. Further, palladium is active for decarbonylation of aldehydes and acyl halides. Homogeneous decarbonylation of aldehydes and acyl halides and carbonylation of alkyl halides were carried out smoothly using rhodium complexes. An acyl-rhodium complex, thought to be an intermediate in decarbonylation, was isolated by the oxidative addition of acyl halide to chlorotris(triphenylphosphine)rhodium. The mechanisms of these carbonylation and decarbonylation reactions are discussed. 

While attempting to prepare an T71-(vinylcarbene)iron complex121 by the alkylation or acylation of an a,/3-unsaturated acylferrate, Mitsudo and Wa-tanabe found122 that the major isolated product was in fact an -vinylketene complex (178), formed presumably by the carbonylation of an intermediate V-vinylcarbene, which may then undergo olefin coordination to the vacant metal site. All attempts to isolate such intermediates, or to observe them by 13C NMR spectroscopy, failed. Only in the reaction between potassium tetracarbonyl -cinnamoy ferrate (179.a) and pivaloyl chloride (180.b) was a side product (181) isolated in appreciable yield. In other reactions, only a trace (<1%) of such a compound was detected by spectroscopy. The bis(triphenylphosphine)iminium(l + ) (PPN) salts of 179.a and 179.b also reacted with 2 equiv of ethyl fluorosulfonate to give 178.g and 178.h in 21 and 37% yield, respectively. All products were somewhat unstable to silica gel, hence the low isolated yields in some cases. 

In the absence of triphenylphosphine a tris-SPO platinum complex forms when SPO is reacted with Pt(cod)2, which is insoluble and for which the structure is not known it could be either a hydride (4) or an oligomeric or a dimeric S PO complex (5) lacking one molecule of hydrogen. The reaction with alkene, CO and H2 gives complex 6, which was identified as the acyl tris-SPO complex by NMR. It shows an... 

The oxidative addition is quite general with alkyl, allyl, benzyl, vinyl, and aryl halides as well as with acyl halides to afford the palladium (II) complex VII. The frans-bis( triphenylphosphine )alkylpalladium halides can also be carbonylated in an insertion reaction to give the corresponding acyl complexes, the stereochemistry of which (17, 18) proceeds with retention of configuration at the carbon bonded to palladium. The acyl complex also can be formed from the addition of the corresponding acid halide to tetrakis (triphenylphosphine) palladium (0). 

The facts that the phenylacetyl complex Villa also undergoes a reaction with phenylacetyl chloride under identical experimental conditions to yield dibenzyl ketone, XVIII (218% with respect to Villa), and that XVII was also obtained from the reaction of phenylacetyl chloride with dichlorobis(triphenylphosphine)palladium(0), XIX, implicate XIX in the catalytic cycle. The palladium (II) complex XIX does indeed catalyze the conversion of an acyl halide to the corresponding symmetrical ketone (123% with respect to XIX). The palladium (IV) structures are only... 

The mechanism that has been proposed for the decarbonylation of acid chlorides by chlorotris (triphenylphosphine) rhodium (I) involves acyl- and alkyl- or arylrhodium complexes (2). Three of the intermediates in the catalytic cycle, II, III, and IV (see Reaction 3), can be isolated in this unique reaction. Both acyl complexes (II) and alkyl... 

Carboxylic acid chlorides and chloroformate esters add to tetrakis(triphenylphosphine)palladium(0) to form acylpalladium derivatives (equation 42).102 On heating, the acylpalladium complexes can lose carbon monoxide (reversibly). Attempts to employ acid halides in vinylic acylations, therefore, often result in obtaining decarbonylated products (see below). However, there are some exceptions. Acylation may occur when the alkenes are highly reactive and/or in cases where the acylpalladium complexes are resistant to decarbonylation and in situations where intramolecular reactions can form five-membered rings. 

Reduction of acid chlorides to aldehydes One of the most useful synthetic transformations in organic synthesis is the conversion of an acid chloride to the corresponding aldehyde without over-reduction to the alcohol. Until recently, this type of selective reduction was difficult to accomplish and was most frequently effected by catalytic hydrogenation (the Rosenmund reduction section 6.4.1). However, in the past few years, several novel reducing agents have been developed to accomplish the desired transformation. Among the reagents that are available for the partial reduction of acyl chlorides to aldehydes are bis(triphenylphosphine)cuprous borohydride , sodium or lithium tri-terf-butoxyaluminium hydride, complex copper cyanotrihydridoborate salts °, anionic iron carbonyl complexes and tri-n-butyltin hydride in the presence of tetrakis(triphenylphosphine)palladium(0). ... 

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