Hydrophosphinations platinum

Although a wide variety of metals were claimed as active catalysts for formaldehyde hydrophosphination, platinum salts were preferred. Similarly, Group 10 metal salts were used to catalyze acrylonitrile hydrophosphination. Russian workers showed that Ni(II) or Co(II) salts in the presence of ammonia or amines would also catalyze the addition of phosphine to formaldehyde [6]. More recently, academic and industrial interest in these reactions was sparked by a series of papers by Pringle, who investigated late metal phosphine complexes as hydrophosphination catalysts. These and related studies are arranged below by substrate. 

Scheme 5-4 Platinum-catalyzed hydrophosphination of acrylonitrile using PH3 (Eq. I) and PH (CH2CH2CN)2 (Eq. 2). The proposed structure of a telomeric by-product of this reaction (I) Is also shown...

The mononuclear mechanism is similar to the one proposed for platinum-catalyzed hydrophosphination of formaldehyde (Scheme 5-3), but also includes a second P-C bond-forming pathway nucleophilic (Michael) attack of the phosphido ligand on coordinated acrylonitrile. The binuclear mechanism is similar, but P-C bond formation is proposed to occur by cooperative action of two Pt centers, with complexes 4 - 6 as possible intermediates [8]. 

Scheme 5-12 Platinum-catalyzed hydrophosphination of ethyl acrylate as a route to biden-tate diphosphines (Eq. 1). Stoichiometric reac-...

Scheme 5-13 Platinum(Me-Duphos)-catalyzed asymmetric hydrophosphination...

Hydrophosphination of ethyl acrylate using PH3 (R = C02Me, Equation (17)) is catalyzed by a mixture of the zero-valent platinum complexes (72a c), which are formed upon addition of P CH2CH2C02Et 3 to Pt(norbornene)3] (Scheme 44). Failure of these complexes to bring about P H addition to CH2 = CHCF3 indicates that Michael activation of the alkene through I and R effects of the substituents is crucial for catalytic activity in this class of metal complexes.190... 

Hoye, P.A.T., Pringle, P.G., Smith, M.B., and Worboys, K., Hydrophosphination of formaldehyde catalyzed by tris(hydroxymethyl)phosphine complexes of platinum, /. Chem. Soc., Dalton Trans., 269, 1993. 

In view of excess phosphine being inhibitory in many catalytic reactions, it is surprising that the hydrophosphination reaction is not suppressed by the phosphines formed. In agreement with this, the product phosphine P(CH2CH2CN)3 is reluctant to form tetrakis(phosphine)platinum species, allowing the metal complex to be coordinatively unsaturated. Likewise, the... 

The mechanistic study on the hydrophosphination of activated olefins, in conjunction with rapid inversion of the configuration at the phosphorus center, was elaborated to develop asymmetric hydrophosphination catalyzed by a chiral phosphine platinum complex although the % ee is not excitingly high yet (Scheme 9) [15]. 

The binuclear palladium complex [(tBu2PH)PdPtBu2]2 with oxygen gave a very efficient catalyst for the hydrogenation of a,/3-unsaturated carbonyls. 0 Glueck and co-workers have undertaken studies on aspects of platinum-catalyzed hydrophosphinations of activated olefins.71,72... 

The Duphos ligand (157) has been used to prepare organometallic complexes of palladium.385 Rhodium complexes of ligands (156), (157), or (159) are efficient catalysts for enantioselective hydrogenations337-341,343,345,386-388 and furthermore, in the case of platinum complexes with (157), as catalysts for the asymmetric hydrophosphination of activated olefins.71... 

Examples of electrophilic addition of secondary phosphines to alkenes or alkynes were described. [114, 124, 125, 135]. Glueck [124-126] reported enantioselective tandem reaction of alkylated/arylation of primary phosphines catalyzed by platinum complex, proceeding with formation of chiral phosphaace-naphthenes. Palladium-catalyzed hydrophosphination of alkynes 219 tmder kinetic resolution conditions gave access to 1,1-disubstituted vinylphosphine boranes 220. However, despite screening several chiral ligands, temperatures, and solvents, the... 

Scriban C, Kovacik I, Glueck DS (2005) A protic additive suppresses formation of byproducts in platinum-catalyzed hydrophosphination of activated olefins. Evidence for P-C and C-C bond formation by Michael addition. Organometallics 24 4871-4874... 

More than 20 years ago, Pringle and co-workers showed that hydrophosphination is a suitable reaction to prepare useful phosphine ligands for homogeneous catalysis by using platinum metal complexes. More recently, this reaction has been extended to the preparation of P-stereogenic phosphines and derivatives. 

The previously accepted pathway consisted of P-H oxidative addition to Pt(0) to form 19 followed by coordination and insertion of the alkene in the Pt-P bond to form 20 and a final reductive elimination to furnish the product and regenerate the catalyst. Another possibility is the nucleophilic attack of phosphido complex 19 to the alkene ( Michael addition mechanism, as in anionic polymerisation) to generate the zwitterionic intermediate 21. This complex can yield the hydrophosphination product 11 via one of two complementary pathways. Carbanion attack at the cationic platinum hydride i.e. intramolecular hydrogen transfer) would yield the final phosphine complexed to Pt(0) that would be displaced by an equivalent of PHR R to furnish, after oxidative addition, starting complex 19. Alternatively, the anionic carbon atom in 21 could attack the platinum centre directly, forming the cyclic intermediate 22. From here Pt-P bond dissociation would generate 20, which would furnish the product after reductive elimination. 

Platinum catalysts of the preceding section activate only the nucleophile (a secondary phosphine), which then reacts with the electrophile (an activated alkene). There are, however, interesting examples of lanthanide complexes activating both the nucleophile and the electrophile towards intramolecular diastereoselective hydrophosphination/cyclisations. In 2000 Marks and co-workers found that certain lanthanide complexes catalyse the intramolecular hydrophosphination of alkenes and alkynes (Scheme 6.13). 

Glueck s group has reported catalytic DKR processes in which secondary phosphines were converted into the corresponding enantio-enriched tertiary phosphines by platinum-catalysed asymmetric hydrophosphination of acrylonitrile, or by platinum-catalysed asymmetric alkylation of secondary phosphines. The key intermediates were diastereomeric phosphide complexes with chiral ancillary ligands (L -Pd PRR )- Their relative rates of P-inversion and phosphorus-carbon bond formation controlled the enantioselectivity of the product formation. As shown in Scheme 2.66, the reactions allowed moderate enantioselectivities of up to 71% ee and 77% ee, respectively, to be achieved. 

Hydroxo-bridged dinuclear complexes, [Pt(P-P)(/u-OH)]2 (where P-P = DIOP, BINAP, NORPHOS, MeDUPHOS, and BPPM) as precursors have been used for the enantioselective Baeyer-Villiger oxidation of ketones (290). The platinum(O) catalyst precursor, Pt(MeDUPHOSXfrans-stylbene), catalyzes the asymmetric hydrophosphination of activated olefins (291). 

A route to non-racemic P-stereogenic vinylphosphine-boranes, e.g., (100), is afforded by the addition of methylphenylphosphine-borane with alkynes in the presence of a chiral diphosphine-palladium catalyst. The ehiral diphosphine-platinum complex-catalysed addition of diethylphosphine to the diene cis,cis-muco-nitrile has given the new diphosphine (101) as a 3 2 mixture of diastereoisomers. Further work has been reported on the use of cyclopentadienyliron complexes that act as metal templates for the intramolecular hydrophosphination of coordinated vinylphosphines with 1,2-diphosphino-alkanes and -benzenes, leading to 1,4,7-triphosphacyclononanes, e.g., (102), capable of further elaboration to form new cyclic phosphines. 

Wicht DK, Kourkine IV, Lew BM, Nthenge JM, Glueck DS (1997) Platinum-catalyzed acrylonitrile hydrophosphination via olefin insertion into a Pt-P bond. J Am Chem Soc 119 5039-5040... 

Pringle PG, Smith MB (1990) Platinum(0)-catalysed hydrophosphination of acrylonitrile. J Chem Soc Chem Commun 1701-1702... 

Costa E, Pringle PG, Worboys K (1998) chemoselective platinum(0)-catalysed hydrophosphination of ethyl acrylate. Chem Commun 49-50... 

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