Arylglyoxylrhodium Complexes, Their Thermolysis, and Attempted Generation by Carbonylation of an Aroylrhodium Complex

Abstract

Reactions of ArCOCOCl (Ar = p-ClC6H4, Ph) with Rh(acac)(CO)2 proceeded readily to afford dimeric arylglyoxyl rhodium complexes [Rh(μ-Cl)(acac)(CO)(COCOAr)]2. [Rh(μ-Cl)(acac)(CO){COCO(p-ClC6H4)}]2 was characterized by X-ray diffraction. Thermolysis of the products showed that [Rh(μ-Cl)(acac)(CO){COCO(p-ClC6H4)}]2 was more stable than [Rh(μ-Cl)(acac)(CO)(COCOPh)]2. The reaction of p-CH3OC6H4COCOCl with Rh(acac)(CO)2 did not form a similar dimeric complex as final product, but gave p-CH3OC6H4COCl as major product, showing thermal instability of corresponding arylglyoxyl and aroyl rhodium complexes. The reaction of C6F5COCOCl did not form a simlar dimeric complex either, but a mononuclear complex RhCl(acac)(COCOC6F5)(CO)2 was generated as a transient intermediate, which was readily transformed to a furanone arising from reductive elimination of the acac ligand and C6F5COCO moiety followed by cyclization. In the thermolysis of [Rh(μ-Cl)(acac)(CO)(COCOAr)]2, only ArCOCl and Rh(acac)(CO)2 were formed, and any ArCORh species could not be detected during the thermolysis process. However, the reaction of Rh(acac)(CO)2 with PhCOCl formed RhCl(acac)(CO)2(COPh), albeit only to a small extent, suggesting that the reaction is not thermodynamically favored. The reaction of RhCl(CO)(PMe3)2 with p-ClC6H4COCOCl also proceeded cleanly to furnish p-ClC6H4COCORhCl2(CO)(PMe3)2. Thermolysis of the complex formed p-ClC6H4CORhCl2(CO)(PMe3)2, indicating slow reductive elimination of ClC6H4COCl as compared with the ArCORh species, generated in the thermolysis of [Rh(μ-Cl)(acac)(CO)(COCOAr)]2. Treatment of ClC6H4CORhCl2(CO)(PMe3)2 with carbon monoxide generates p-ClC6H4COCORhCl2(CO)(PMe3)2, although the yield was low.

Rhodium‐Catalyzed Addition of α‐Keto Acid Chlorides with Terminal Alkynes

“…This reactivity trend agrees with our previous observation that, unlike the reaction of 1a, for instance, the reaction of 1f with RhA C H T U N G T R E N N U N G (acac)(CO) 2 at room temperature (in the absence of an alkyne) did not form 2 , but proceeded all the way to p-anisoyl chloride and Rh-A C H T U N G T R E N N U N G (acac)(CO) 2 , indicative of rapid decarbonylation from p-AnCOCORhCl to p-AnCORhCl and reductive elimination. [4] (iii) Only 1e and 1f formed 5 in appreciable quantities. As is mentioned in the introduction section, we have reported that electron-withdrawing substituents bound to acid chlorides suppress the decarbonylation from RCORhCl to RRhCl.…”

“…Since oxidative addition of 6 with RhA C H T U N G T R E N N U N G (acac)(CO) 2 is not a thermodynamically favored process, [4] once compound 6 has been extruded from 9, regenaration of 9 through the backward process can take place only marginally.…”

“…[4] Indeed, a preliminary reaction of 6a with 2A under CO atmosphere (50 atm) in the presence of RhA C H T U N G T R E N N U N G (acac)(CO)A C H T U N G T R E N N U N G (AsPh 3 ) (5 mol%) at 100 8C for 12 h in toluene gave (Z)-3aA in 21% GC yield, which encouraged us to further studies, although the yield is not satisfactory at this stage.…”

“…[3] In our continued study on the reactivity of acid chlorides with rhodium complexes, we have encountered mono-and dinuclear a-keto acyl rhodium complexes being formed in the reaction of RhA C H T U N G T R E N N U N G (acac)(CO) 2 with a-keto acid chlorides. [4] Although there are several papers reporting on the generation of a-keto acyl complexes, special conditions or procedures to circumvent the difficulty of generation are required in most cases. [5] Accordingly, since the publication of Sen and co-workers, [5e] we have tacitly considered that a-keto acyl complexes are usually thermally labile.…”