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

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.