Platinum complexes phosphites

The discussion of the activation of bonds containing a group 15 element is continued in chapter five. D.K. Wicht and D.S. Glueck discuss the addition of phosphines, R2P-H, phosphites, (R0)2P(=0)H, and phosphine oxides R2P(=0)H to unsaturated substrates. Although the addition of P-H bonds can be sometimes achieved directly, the transition metal-catalyzed reaction is usually faster and may proceed with a different stereochemistry. As in hydrosilylations, palladium and platinum complexes are frequently employed as catalyst precursors for P-H additions to unsaturated hydrocarbons, but (chiral) lanthanide complexes were used with great success for the (enantioselective) addition to heteropolar double bond systems, such as aldehydes and imines whereby pharmaceutically valuable a-hydroxy or a-amino phosphonates were obtained efficiently. 

A study of sequential Arbuzov-type demethylation reactions of the platinum(II)-phosphite complex [Pt P(OMe)3 4]2+, in which the phosphite ligands are converted to phosphonates, has been described.285 Many of the products of the reaction were characterized by NMR spectroscopy and X-ray crystallography.286 The X-ray structures are the first reported for trialkylphosphite complexes of platinum(II). 

CsHuN, Ethanamine, A-ethyl-A-methyl-tungsten complex, 26 40, 42 C6HF5, Benzene, pentafluoro-gold complexes, 26 86-90 C H4I2, Benzene, 1,2-diido-iridium complex, 26 125 CJT, Phenyl platinum complex, 26 136 C,H,N, Pyridine osmium complex, 26 291 OHtS, Benzenethiol osmium complex, 26 304 QH7P, Phosphine, phenyl-cobalt-iron complex, 26 353 QH 1-Butyne, 3,3-dimethyl-mercury-molybdenum-ruthenium complex, 26 329-335 C6H 4P, Phosphine, triethyl-platinum complex, 26 126 platinum complexes, 26 135-140 CsHisPO, Triethyl phosphite iron complex, 26 61... 

The platinum complex is reasonably air stable, but the palladium complex is moderately air sensitive, turning to a black powder overnight if stored in air. Their solubilities are similar to those of the nickel analogue. There is a tendency for both the palladium and platinum complexes to lose a phosphite ligand on recrystallization. 

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. 

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 platinum(II) phosphite complex [Pt2(P205H2)4]4 has a tetrabridged structure. It is readily oxidized to Ptm dimers [PL OsH LJ2. On photolysis they oxidize organic substrates and are capable of cleaving DNA.16... 

Table 5.3 Coordination chemical shifts for phosphanes and phosphites in group 6 and platinum complexes...

Asymmetric hydroformylation of prochiral olefins has been investigated both for the elucidation of reaction mechanism and for development of a potentially useful method for asymmetric organic synthesis. Rhodium and platinum complexes have been extensively studied, and cobalt complexes to a lesser extent. A variety of enantiopure or enantiomerically enriched phosphines, diphosphines, phosphites, diphosphites, phosphine-phosphites, thiols, dithiols, P,A-ligands, and P,5-ligands have been developed as chiral modifiers of rhodium and platinum catalysts. - " ... 

C5H15O3P, Triethyl phosphite, iron complex, 26 61, 28 171 nickel complexes, 28 101, 104-106 CjHijP, Phosphine, triethyl-, gold-osmium complexes, 27 209, 211 gold-platinum complex, 27 218 nickel complex, 28 101 platinum complexes, 26 126, 135-140, 27 32, 34,28 27, 120, 122, 133, 29 191 C5H16N4, l,2-Ethanediamine,AfJVJV Af -tetramethyl-, lithium complex, 26 148 CjH,6P2, Phosphine, l,2-ethanediylbis(di-methyl-, nickel complex, 28 101 CjHijSi, Silane, triethyl-, ruthenium complex, 26 269... 

NdC4jHj9, Neodymium, tris(2,6-dwert-butyl-4-methylphenoxo)-, 27 167 O3PC3H, Trimethyl phosphite, cobalt and rhodium complexes, 28 283,284 iron complexes, 28 171, 29 158 nickel complex, 28 101 O3PCJH15, Triethyl phosphite, iron complexes, 28 171, 29 159 nickel complex, 28 101 nickel, palladium, and platinum complexes, 28 104-106 03PC,H2i, Isopropyl phosphite, nickel complex, 28 101... 

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. 

The d phosphine and phosphite complexes of zerovalent nickel, palladium and platinum possess long-lived emissive excited states in both fluid solution and in the solid state.The lifetimes of the Ni and Pd complexes are in the 1.39-5.38 ps range, with the platinum complex Pt(PPh3)4 having the shorter excited state lifetime of 0.07 //s because of spin-orbit coupling. These long lifetimes allow for bimolecular reactions to occur, and under photochemical conditions chlorobenzene will add to the complex Pd(PPh3)3 (Ref. 75) ... 

Other notable examples are the orthometallation (orthophenylatioti) reactions of many complexes of aryl phosphines (PAr3) and aryl phosphites P(OAr)3 with platinum metals in pailiculai, e,g, ... 

Tri-ra-butylphosphite, tri-ra-butylarsine, and tri-ra-butylstibine complexes of platinum(O) have been prepared by the reaction of the ligand with pt(COD)2] or, in the case of the phosphite, by reaction with [Pt(PPh3)4].38 All form four-coordinate complexes when 4 mole-equivalents of ligand are used, but when 2 or 3 mole-equivalents of the phosphite ligand are used, mixtures of three- and four-coordinate complexes are observed.38... 

Phosphite complexes of platinum(0) have received substantially less attention than have phosphine complexes.44 [Pt P(OC6H4OMe-2)3 3] can be prepared by reduction of the [PtCl2 P-(OC6H4OMe-2)3 2] complex in the presence of the phosphite or by the reaction of the phosphite with Lris(//2-norbornene)platinum(II) 44 Alkene complexes of bis(phosphite)platinum(II) can be prepared in a similar manner to the analogous phosphine complexes. 

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. 

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