Phosphite ligands, triaryl

The first examples of five-coordinate platinum(II) complexes of the type [Pt(PR3)L]2+ (L = tris(2-(diphenylphosphino)ethyl)phosphine R = Et, OMe, OEt) (104) containing only P-donor atoms have been prepared by the reaction of [PtClL]+ with an appropriate monodentate tertiary phosphine or phosphite ligand.284 Triaryl phosphines and phosphites do not react with the precursor complex, even at elevated temperatures, most probably due to the considerable steric interactions that would occur upon the approach of the P-donor ligand to the platinum(II) center. 

The trialkyl or triaryl phosphite complexes are more accessible than those of tertiary phosphines. The phosphite ligands complex strongly to rhodium, and easily displace alkene, alkadiene and even carbonyF ligands from [RhCl(CO)2]2 (equations 41 and 42), a displacement that cannot be achieved by tertiary phosphines. Indeed, even tertiary phosphine ligands themselves can be displaced by the phosphite ligands (equation 43).The phosphite complexes can also be prepared by cleaving [RhX(P(OR)3 2]2 complexes with additional ligand (equation 26). 

When the reaction was promoted by the unmodified catalysts [(cod) Rh(hfacac)] (hfacac = hexafluoroacetylacetonate CF3COCHCOCF3, cod = cyclooctadiene), the superiority of SCCO2 in the hydroformylation rates was demonstrated very well. The modified catalytic systems formed with perfluoroalkyl-substituted triarylphos-phine and triaryl phosphite ligands exhibited higher regioselectivities in scCOj than in conventional solvents. The olefin isomerization is a typical side reaction for phosphite-modified systems in conventional solvents, while it is suppressed effectively in SCCO2. 

Bedford and colleagues found that phosphines, diphosphines, arsines, and bulky triaryl phosphites are convenient ligands [51]. Best results were obtained with... 

Tris- and tetrakis(triaryl phosphite)platinum(O) complexes have been prepared by reduction of platinum(II) phosphite derivatives with hydrazine.5 The tetrakis complexes have also been prepared by ligand exchange processes, and the synthesis described here is based on this latter procedure. The chemistry of platinum phosphite complexes has not been extensively studied. 

The next most important complexes of this type are trialkyl or triaryl phosphite complexes. These are best prepared by allowing the ligands to react with [RhH(CO)(PPh3)3] (equations 60 and 61). 

Based on the extensive studies reported for the triaryl phosphite-nickel complex catalyzed hydrocyanation of alkenes [1] and our own findings, we propose a general catalytic cycle shown in Scheme 5 for the Ni(COD)2/L/MVN system. This simplified catalytic cycle is meant to encompass the various diastereomeric pathways generated by the ligand Cj symmetry. 

Intramolecular Hydrogen Transfer. It is possible to transfer groups from the metal to ligand by insertion reactions, but a rather special case of transfer reactions is one between certain ligands and the metal atom in which a hydrogen atom is initially transferred and is then subsequently lost. Such reactions are especially important for triarylphosphines and triaryl phosphites.30 Some examples are the following ... 

Under more severe conditions, mononuclear products can be obtained from the reaction of Group V ligands with second- and third-row metal carbonyl clusters. Ru3(CO)i2 reacts with L at 140°C to produce Ru(C0)sL2 [L = PPhs, PBus, P(OPh)3] (326, 327). Similar reactions occur with Os3(CO)i2 (46), Ru3(CO)g(PPh3)3, and Os3(CO)9(PPh3)3 (326). Ir4(CO)i2 produces Ir2(C0)4Lg with trialkyl and triaryl phosphites (386). It is reported that Rh4(CO)i2 and Rhe(CO)i6 react with Ph3P to form Rh4(CO)io(PPh3)2, which subsequently decomposes to Rh2(CO)4(PPh3)4 (88). 

In a related process, formation of benzofuranone from carbonylation of 2-iodobenzyl alcohol in supercritical carbon dioxide was recently reported by Kayaki et al. The rate of reaction in supercritical CO2, using palladium chloride in combination with trialkyl or triaryl phosphites as ligands, was reported to be higher than that in typical organic solvents. 

Rhodium and nickel have been by far the most common metals aside from palladium employed in Suzuki-Miyaura carbon-carbon bond-forming reactions. Platinum has been used on several occasions, for example Bedford and Hazelwood showed that platinum complexes with n-acidic, ortfto-metalated triaryl phosphite and phosphinite ligands exhibited what they termed unexpectedly good activity in Suzuki biaryl coupling reactions with aryl bromide substrates (Scheme 13.22). Application to aryl chlorides resulted in low conversion to the desired biaryl products. 

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