Silanes palladium complexes

Cationic palladium complex 121 reductively coupled enynes (Eq. 20) using trichlorosilane as the stoichiometric reductant [71]. This combination of catalyst and silane afforded silylated methylenecyclopentanes such as 122 in good yield from enynes such as 123. Attempts to develop an enantioselective version of this reaction were not successful [71]. When enediyne 124 was cyclized in the presence of trichlorosilane, the reaction favored enyne cycli-zation 126 by a 3 1 ratio over diyne cyclization to 125 (Eq. 21). In contrast, when the more electron-rich dichloromethylsilane was used as the reductant, diyne cyclization product 125 was preferred in a ratio of 4 1 [71]. Selectivities of up to 10 1 for enyne cyclization were observed, depending on the substrate employed [72],... 

The asymmetric hydrosilylation that has been most extensively studied so far is the palladium-catalyzed hydrosilylation of styrene derivatives with trichlorosilane. This is mainly due to the easy manipulation of this reaction, which usually proceeds with perfect regioselectivity in giving benzylic silanes, 1-aryl-1-silylethanes. This regioselectivity is ascribed to the formation of stable 7t-benzylpalladium intermediates (Scheme 3).1,S Sa It is known that bisphosphine-palladium complexes are catalytically much less active than monophosphine-palladium complexes, and, hence, asymmetric synthesis has been attempted by use of chiral monodentate phosphine ligands. In the first report published in 1972, menthyldiphenylphosphine 4a and neomenthyldiphenylphosphine 4b have been used for the palladium-catalyzed reaction of styrene 1 with trichlorosilane. The reactions gave l-(trichlorosilyl)-l-phenylethane 2 with 34% and 22% ee, respectively (entries 1 and 2 in Table l).22 23... 

A new type of asymmetric hydrosilylation which produces axially chiral allenylsilanes has been reported by use of a palladium catalyst coordinated with the bisPPFOMe ligand 51b.64 The hydrosilylation of l-buten-3-ynes substituted with bulky groups such as tert-butyl at the acetylene terminus took place in a 1,4-fashion to give allenyl(trichloro)-silanes with high selectivity. The highest enantioselectivity (90% ee) was observed in the reaction of 5,5-dimethyl-T hexen-3-yne with trichlorosilane catalyzed by the bisPPFOMe-palladium complex (Scheme 13). 

The application of this approach to phosphorus dendrimers is readily applied11111 to the creation of a tetrahedral series via the use of a four-directional silane core (Scheme 4.26). The treatment of tetravinylsilane (78) with phosphine 98 quantitatively gave the desired small dendrimer 99, which can be transformed to the tetrakis(square planar palladium) complex see Chapter 8. 

The presence of five-membered rings such as cyclopentanes, cyclopentenes, and dihydrofurans in a wide range of target molecules has led to a variety of methods for their preparation. One of the most successful of these is the use of trimethylenemethane [3 + 2] cycloaddition, catalysed by pal-ladium(O) complexes. The trimethylenemethane unit in these reactions is derived from 2-[ (trimethylsilyl)methyl]-2-propen- 1-yl acetate which is at the same time an allyl silane and an allylic acetate. This makes it a weak nucleophile and an electrophile in the presence of palladium(0). Formation of the palladium 7t-allyl complex is followed by removal of the trimethylsilyl group by nucleophilic attack of the resulting acetate ion, thus producing a zwitterionic palladium complex that can undergo cycloaddition reactions. 

The hydrosilylation of butadiene with low-valent palladium complexes gives an alkylsilane formed by addition of 2 molecules of butadiene to 1 molecule of silane (271, 272) [Eq. (95)]. Compounds Pd(maleic anhydride)(PPh3)2 and Pd(p-benzoquinone)(PPh3)2 were particularly effective catalysts for this reaction. Halopalladium(II) compounds and Pd(PPh3)4 were less effective as catalysts. The proposed mechanism is... 

Palladium-catalyzed cross couplings of organofluorosilanes with vinyl [37] and aryl [38] halides and triflates are known, where the activation of the Si—C bond by fluoride ion plays an essential role in the coupling. The pentacoordinated fluoroorganic silanes promote the transmetallation to the aryl halide-palladium complexes strongly. At least one fluorine... 

Synthesis of homoallylamines by catalytic asymmetric allylation of imines with allyl silanes using a chiral bis x-allyl palladium complex, also using allylstannanes (see 1st edition). 

Cross coupling. Biaryls are obtained from aryl halides and aryl(halo)silanes in the presence of the palladium complex and KF. 

In 2007, synthesis and complexation of a PSiP-pincer hgand, in which a sihcon atom and two phosphorus atoms are tethered by a phenylene group, was first reported by Turculet and coworkers [11-19]. They reported that the PSiP-ruthenium complex exhibited catalytic activity for transfer hydrogenation of ketones [11], and the PSiP-platinum and -palladium complexes efficiently catalyzed reduction of COj to methane by silanes [18[. Shortly after the Turculefs first report in 2007, we reported the first example of utilization of the phenylene-bridged PSiP-pincer complex in carbon-carbon bond formation reactions of unsaturated hydrocarbons [20[. 

Heterogeneous palladium catalysts have been prepared by covalent immobilization of palladium (11) complexes onto SBA-15 sdica. The heteroannu-lation of 2-iodoaniline with triethyl(phenylethynyl)silane using these preformed palladium complexes gives excellent yields in Larock synthesis of indoles. These palladium catalysts have been demonstrated to be recyclable through multiple recycling experiments (2010MI179). 

But whether the cis (Z) or trans E) isomer of the product is generated depends upon the catalyst used (151). The addition of trisubstituted silanes to aliens occurs predominantly across the 1,2-position in the presence of palladium complexes and also H2PtCl6. The bis-silyl product is also obtained but to a lesser extent (3) ... 

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