2,4-Pentanedione, complex with rhodium

Thermolysis of (cycloheptatrienylmethyl)carbene complexes 554 [toluene, 1-2 h, 80-100°C MLn = Cr(CO)5, W(CO)5] affords an equilibrium mixture of 4,5-homotropilidenes 555 and 556. According to the NMR data and the results of AMI calculations, the formation of isomer 556 (equation 218) is strongly favored277. This course of events was called intramolecular cyclopropanation , and it was shown that the equilibrium between the 4,5-homotropilidene complexes is significantly different from that of the metal-free ligands. By reaction of the latter (555 and 556) with bis(ethylene)rhodium 1,3-pentanedionate 557, the complexes 558 and 559 of both 4,5-homotropilidenes were obtained in a 1 3 ratio. These complexes are non-fluxional and are configurationally stable at room temperature (equation 219)277. 

A system kinetically very similar to the phosphine-free rhodium carbonyl catalyst is obtained with bulky phosphites (Fig 6.3). At temperatures from 50 to 80°C, and CO and H2 partial pressures ranging from 10 to 70 bar, the rate of aldehyde formation is first order in H2 and approximately minus one order in CO. The reaction rate is independent of the concentration of 1-octene at conversions below 30%. The reaction was found to be first order in rhodium concentration and insensitive to the phosphite/rhodium ratio, provided that the absolute concentration was sufficiently high to generate a hydride complex from the pentanedionate precursor (reaction 9). 

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