Rhodium carbonyl complexes triarylphosphine

In 2007, Trost and McClory reported the rhodium-catalyzed cycloaromatization of terminal alkynes bearing an amino or a hydroxy group (61 and 63) into the corresponding indoles and benzofurans (62 and 64) (Scheme 21.27) [36]. As described in the preceding section, McDonald et al. reported a similar transformation catalyzed by molybdenum carbonyl complex as a catalyst [10] (see Schemes 21.23 and 21.25). Use of rhodium catalyst provided some advantages in terms of the catalyst turnover and the selectivity. The combination of [RhCl(cod)]2 and a fluorinated triarylphosphine promoted the cyclization efficiently. Later, a ruthenium version of this cyclization was reported, as shown in Scheme 21.22 [31]. 

Most hydroformylation investigations reported since 1960 have involved trialkyl or triarylphosphine complexes of cobalt and, more recently, of rhodium. Infrared studies of phosphine complex catalysts under reaction conditions as well as simple metal carbonyl systems have provided substantial information about the postulated mechanisms. Spectra of a cobalt 1-octene system at 250 atm pressure and 150°C (21) contained absorptions characteristic for the acyl intermediate C8H17COCo(CO)4 (2103 and 2002 cm-1) and Co2(CO)8. The amount of acyl species present under these steady-state conditions increased with a change in the CO/ H2 ratio in the order 3/1 > 1/1 > 1/3. This suggests that for this system under these conditions, hydrogenolysis of the acyl cobalt species is a rate-determining step. 

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