Triphenyl phosphite rhodium complexes

The hydridotetrakis(triphenyl phosphite)rhodium complex described below is the first example of a rhodium hydride complex stabilized by phosphite ligands.2... 

PC sH,g, Triphenyl phosphite, cobalt complex, 29 178 iron complexes, 28 171,29 159 nickel complex, 28 101 ruthenium complex, 26 178 03PC2 H2, Tris(4-methylphenyl) phosphite, ruthenium complex, 26 277,278,28 227 03P2RhC2,H45, Rhodium(I), (acetato)car-bonylbis(triisopropylphosphine)-, 27 292... 

In 2001, Van den Hoven and Alper reported the unexpected 2(Z)-6(ft)-47/-[l,4]-thiazepin-5-one 215, as the major product, from the reaction of acetylenic thiazole 214 with carbon monoxide and hydrogen in presence of a zwitterionic rhodium complex and triphenyl phosphite. After optimization of the reaction condition, the pressure, and the temperature, up to 90% yield is achieved with good selectivity for thiazepine 215 over thiazole side products 216-218 (Scheme 38) <2001 JA1017>. 

The preparations described here are developed from published work by Malatesta et al.5 and from more recent studies in the contributors own laboratory.2 The cobalt and nickel complexes are prepared by reduction of the corresponding metal nitrates with sodium tetrahydroborate in the presence of excess ligand, whereas the syntheses of the rhodium and platinum complexes involve simple ligand exchange processes. The preparative routes are suitable for use with triphenyl- or p-substituted triphenyl phosphites reactions involving o- or m-substituted triphenyl phosphites give much reduced yields of products which are difficult to crystallize and are very air-sensitive. These features probably reflect the unfavorable stereochemistry of the o- and m-substituted ligands. 

POCisHis, Phosphine, triphenyl-, oxide cerium complexes, 23 178 P03C3H, Trimethyl phosphite chromium complexes, 23 38 cobalt and rhodium complexes, 25 162-163... 

Some insight into the mechanisms of the iodine-promoted carbonylation has been obtained by radioactive tracer techniques [17] and low-temperature NMR spectroscopy [18]. The mechanism involves the formation of HI, which in a series of reactions forms with rhodium a hydrido iodo complex which reacts with ethylene to give an ethyl complex. Carbonylation and reductive elimination yield propionic acid iodide. The acid itself is then obtained after hydrolysis. The rate of carboxylation was reported to be accelerated by the addition of minor amounts of iron, cobalt, or manganese iodide [19]. The rhodium catalyst can be stabilized by triphenyl phosphite [20]. However, it is doubtful whether the ligand itself would meet the requirements of an industrial-scale process. 

PO2WC2SH21, Tungsten, dicarbonyl(T) -cyclopentadienyl)hydrido(triphenyl-phosphine)-, 26 98, 28 7 PO3C3H, Trimethyl phosphite, cobalt and rhodium complexes, 28 283, 284 iron complexes, 26 61, 28 171, 29 158 nickel complex, 28 101 P03C,H,5, Triethyl phosphite, iron complexes, 26 61, 28 171, 29 159 nickel complexes, 28 101,104-106 P03C,H2, Isopropyl phosphite, nickel complex, 28 101... 

In addition to dimerization and clustering to multinuclear rhodium carbonyl complexes, active catalyst can also be removed from the reaction mixture by orthometallation. Several reports have appeared on orthometallation of rhodium triphenyl phosphite complexes in literature but... 

Ligand metallation. In early transition metal polymerization catalysis often metalation of the ligand occurs leading to inactive catalysts. In late transition metal chemistry the same reactions occur, but now the complexes formed represent a dormant site and catalyst activity can often be restored. Work-up of rhodium-phosphite catalyst solutions after hydroformylation often shows partial formation of metallated species, especially when bulky phosphites are used [50]. Dihydrogen elimination or alkane elimination may lead to the metallated complex. The reaction is reversible for rhodium and thus the metallated species could function as a stabilized form of rhodium during a catalyst recycle. Many metallated phosphite complexes have been reported, but we mention only two, one for triphenyl phosphite and rhodium [51, 52] (see Figure 19) and one for a bulky phosphite and iridium [53]. 

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