Palladium complexes phosphine-phosphite

Metal carbon insertions of C02 occur in both main group and transition metal complexes.5,19 The reactions result in a strong M—O bond at the expense of a weak M—C bond (together with a C C a bond at the expense of a C O n bond). Insertion into t/weo-W(CO)5 CHDCHDPh gave the threo carboxylate, indicating retention of configuration at the o-carbon, as with CO insertion.29 Cis- RW(CO)4L (R = Me, Et or Ph) showed second-order kinetics toward C02 insertion, first order in anion and in C02. Replacement of CO by a phosphine or phosphite increased the insertion rate.30 Palladium catalysis of C02 insertion into unreactive Sn C bonds in allyl stannanes provided three isomeric tetra-carboxylates from tetraallyl tin. Attempted reactions of tetraalkyl, vinyl or aryl tin complexes did not proceed. Insertion into an intermediate rf -allyl palladium complex was suggested to lead to carboxylate products.31,32... 

Musco [92] and Consiglio [93] have used palladium-oxazoline complexes (28,29) to produce styrenic copolymers that exhibit high optical rotations. Takaya has briefly noted the use of his novel phosphine-phosphite bi-dentate ligands for the enantioselective production of aromatic polyketones [82]. 

Apart from palladacycles, a number of catalyst systems are currently known that show productivities up to 100,000 for Heck and Suzuki reactions of all kinds of aryl bromides. It is important to note that coupling reactions of electron-deficient aryl bromides (e.g., 4-bromoacetophenone), which are often used in academic laboratories, are not suitable as test reactions to judge the productivity of a new catalyst, because simple palladium salts without any Ugand give turnover numbers up to 100,000 with these substrates. Recently, palladium complexes in combination with sterically congested basic phosphines (e.g., tri-tcrt-butylphosphine), carbenes, and also phosphites led to productive palladium catalysts for the activation of various aryl chlorides. 

The idea of metal-metal bond establishment in the excited state of this complex has also stimulated the interest on the photophysical and photochemical investigations of related d -d complexes. In 1970, Dori and co-workers first reported the luminescence properties of phosphine complexes of d metal centers such as copper(I), silver(I), gold(I), nickel(0), palladium(0), and platinum(0) [12]. Later in 1985, Caspar reported the luminescence properties of polynuclear nickel(O), palladium(O), and platinum(O) complexes of phosphine, phosphite, and arsine [13]. Similar to the related d -d systems, the emissive states of [Pd2(dppm)3] and [Pd Cdpam),] have been suggested to be metal-centered (d-p) in nature modified by metal-metal interaction. 

Reactions.—Desulphurization of thiirans to alkenes remains an important strategy for the preparation of hindered alkenes, e.g. (14), and is the most typical thiiran reaction. Phosphines and phosphites are the reagents that are most often used. Lithium reagents desulphurize rra s-2,3-diphenylthiiran to ( )-stilbene, while the ds-isomer is converted into a 1 1 mixture of (Z)-stilbene and the two isomers of tr-mercaptostilbene. 2-Phenylthiiran is desulphurized by cf-metallated isocyanides. Thermal extrusions of sulphur include the conversion of (15) into (16), amongst others. Desulphurizations using zinc and acetic acid, molybdenum or palladium complexes, and the oxaziridine (17) have been reported. 

Maleic anhydride monomer cont.) oxime adducts, 228 palladium complexes, 213 peracid formation, 246 phenols photochemical reaction, 180 phosphine reactions, 230 phosphite reactions, 206 photo-adduct applications, 213 photo-adduct sterochemistry, 182, 183, 192-194 photochemical dimerization, 188 photochemical polymerization, 195, 239, 241-243, 247, 248... 

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. 

The chemistry of phosphite, phosphonite and phosphinite complexes of palladium(II) generally resembles that of their phosphine analogues. Its description here will therefore be brief, attention being paid to those areas where differences in behaviour are apparent. 

Preparation of phosphine and phosphite complexes of palladium ) have been reported to result from reduction of palla-dium(II) complexes in the presence of the desired ligand.1" The products are generally formulated as PdL4 (where n = 0, 1), depending upon the nature and amount of the ligand used. A related complex, [Pd P(C6H5)3 2]re, has also been reported.6... 

Ligand size determines coordination numbers as well as reactivity. Thus phosphine complexes of Pd°, frequently used as precursors in palladium catalyzed reactions, may be 4-, 3-, or 2-coordinate, as in Pd(PMe3)4, Pd(PPr )3, and Pd(PPhBu 2)2, respectively. For nickel phosphine and phosphite complexes, the dissociation constant Kd for the equilibrium... 

Cyclometalation is one of the most reliable and versatile methods for the synthesis of stable Pd-C a-bonds. In this reaction, a palladium (or other metal) complex is reacted with a ligand possessing a donor atom. The metal is directed by the donor atom to insert into a C-H bond, forming a chelate ring. This donor is usually the nitrogen of a tertiary amine, heterocyclic amine, or imine, or a phosphorus in a tertiary phosphine or phosphite. Other donor atoms, such as O and S, are occasionally encountered. The chelate ring size is normally five. ... 

The ethylenebis(tricyclohexylphosphine)palladium(0) and ethylenebis(tri-u-tolyl phosphite)palladium(0) complexes dissolve in diethyl ether when argon is passed through the suspension. Upon evaporation of these solutions in vacuo, the corresponding bis(tert-phosphine)palladium(0) complexes are obtained. ... 

Trialkyl phosphines and phosphites generally form with palladium (II) chloride well-defined square planar complexes of the type [PdCl2L2], which exist as either cis or trans isomers. 

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