Pt-catalyzed addition

A series of carbosilane dendrimers was synthesized by Roovers et al.t 02) by employing the Pt-catalyzed addition of methyldichlorosilane (77) to an alkene, followed by nucleophilic substitution with vinylmagnesium bromide at the terminal dichlorosilane moieties (Scheme 4.22), as the iterative method. Thus, using tetravinylsilane 103-1051 (78) as the ini-... 

The Shibasaki group also demonstrated the potential of their Ca-symmetric diammonium salt catalyst 135 for the syntheses of the alkaloids (+)-cylindricine C (138) and (—)-lepadiformine (139) [22c,68,69], By applying a PT-catalyzed addition of Schiff base 140 to Michael acceptor 141, the key intermediate 142 was obtained in good yield and with good enantiomeric excess. Compound 142 could then be used to obtain selectively either the cylindricine C precursor 143 or the lepadiformine synthon 144 in a very efficient tandem cyclization reaction by choosing the optimum reagents. The impressively short total synthesis of (+)-cylindricine C (138) could be achieved in only two additional steps, whereas the synthesis of the tricyclic intermediate 144 represents a formal total synthesis of (—)-lepadiformine (139) (Scheme 28). 

Pringle et al. have reported Pt-mediated hydrophosphination of acrylonitrile as the first example of transition-metal-catalyzed hydrophosphination of alkenes [111]. Tris(cyanoethyl)phosphine complex of Pt catalyzed addition of H-P(CH2CH2CN)2 with formation of the P(CH2CH2CN)3. The reaction in acetonitrile was carried out at RT. Kinetic measurements and NMR studies suggested two parallel reaction pathways including mononuclear and dinuclear Pt intermediates (Scheme 8.43) [111-113],... 

Notably, half of the tertiary product was the telomer 8, which incorporates an additional equivalent of olefin. In contrast, the Pt(0) precatalyst Pt(norbornene)3 (0.2 mol%) gave a 10 1 mixture of tertiary phosphine 9 and telomer 8 over 11 h at 5 5°C in toluene (Scheme 5-10, Eq. 2). The selectivity was higher (>95%) when only the final step [addition of PH(CH2CH2C02Et)2 to ethyl acrylate] was monitored by NMR. In contrast, Pt[P(CH2CH2CF3)3]2(norbomene) did not catalyze addition of PH, to CH2=CHCF3 thus, the olefin must be a Michael acceptor. [11]... 

This reaction exemplified that the regiochemistry of RS and H introduced by car-bonylahve addition differed from that of those by simple hydrothiolation. In the Rh-catalyzed hydrothiolation, the ArS group added to the terminal carbon and H to the internal carbon (Eq. 7.12). On the other hand, in the Rh-catalyzed thioformylation, RS was placed at internal carbon and formyl at the terminal carbon in spite of using the same catalyst precursor, [RhCljPPhsjs], which was also active for the thioformylation shown in Eq. (7.17). In 1997, the Pt-catalyzed hydrothiocarboxylation using RSH, alkyne and CO was reported to furnish 24 (Eq. 7.18), which showed the same regiochemistry as the Ni-catalyzed reaction shown in Eq. (7.1) [28]. 

Since S03/H2S04 is clearly not the most desirable system for industrial applications, a formidable challenge is to find an oxidant that oxidizes Pt(II) much faster than S03 does, operates in an environmentally friendly solvent, and can be (like SVI/SIV) reoxidized by oxygen from air. Ideally, the reduced oxidant would get reoxidized in a continuous process, such that the oxidant acts as a redox mediator. In addition, the redox behavior has to be tuned such that the platinum(II) alkyl intermediate would be oxidized but the platinum(II) catalyst would not be completely oxidized. Such a system that efficiently transfers oxidation equivalents from oxygen to Pt(II) would be highly desirable. A redox mediator system based on heteropolyacids has been reported for the Pt-catalyzed oxidation of C-H bonds by 02, using Na8HPMo6V6O40... 

In heterogeneous catalytic hydrogenations suprafacial (as) addition of hydrogen would be expected, as the transfer of hydrogen atoms from the catalyst surface to the reactant is usually assumed. However, in some Pt catalyzed reactions antarafacial (trans) addition of hydrogen is also observed. The ratio of diastereomeric products formed is determined by the chemisorption equilibrium of the surface intermediates and by the relative rates of hydrogen entrance to the different unsaturated carbon sites. Both effects are influenced by steric factors. 

C4-C6 Alkanes are highly volatile and, hence, of low value as a transportation fuel or a fuel additive. Since high-quality fuels require the generation of liquid hydrocarbons, the fructose-derived HMF and acetone have been converted into their mono- (C9) and bis-aldols (C15), which on Si02-Al203/Pt-catalyzed dehy-dration/hydrogenation produce C9-C15 alkanes (Scheme 2.8). A major drawback of this approach, however, is the fact that HMF, de facto, is a fructose-derived product, and is not producible in an industrially viable price frame at present vide infra. Section 2.3.2). 

Pringle reported that ethyl acrylate also reacts similarly [14]. The radical addition at 70 °C forms a mixture of primary PH2 (CH2CH2COOEt), secondary PH(CH2CH2COOEt)2 and tertiary phosphines. The tertiary phosphine component is not pure P(CH2CH2COOEt)3, but a mixture with telomers. However, Pt complex-catalyzed addition is very clean when PH3 is bubbled through a warmed solution of ethyl acrylate in the presence of 0.002 equiva-... 

The hydrogenation of 1,2-dimethylcyclohexene (17 Pt02, HOAc, 1 atm) yields trans-(19) as well as cis-1,2-dimethylcyclohexane (18), but Ir and Os in t-butyl alcohol are much more selective (equation lb). The addition of hydrogen to (17) competes with isomerization to 1,6-dimethylcyclohexene (20), which not only reacts more rapidly but yields trans (19) as well as the cis product (18) via syn addition of the two hydrogen atoms (equation 17). In the Pt-catalyzed reaction, the intermediate (20) can be observed, although its steady-state concentration remains low (0.21% of the 1,2-isomer 17) because of its... 

SCHEME 18.10 Formation of polycarbosilanes by Pt-catalyzed hydrosilylation of vinyl-silanes. The catalyticaUy active species is [PtCb] which is in situ generated by reduction of HjPtClj with PrOH. Characteristic reaction steps are A Ugand substitution, B oxidative addition of Si-H, C H-migration, and D reductive eUmination of the carbosilane. ... 

In our previous papers we reported the Pt catalyzed Co reduction in Pt-Co/NaY system and formation of bimetallic particles inside NaY-zeolite cages [6, 7]. An additional evidence was found from TPD in high temperature range that the amount of evolved H2 increased with Co loading in Pt-Co/NaY catalysts due to oxidation of reduced Co in bimetallic particles with surface hydroxyl groups [6]. 

The Pt-catalyzed hydrosilylation of trimethyl silane and alkenols or alkenyl-polyethers lead to nonionic silane surfactants, whereas the addition of allylglycidyl ether to trimethylsilane results in a precursor for ionic derivatives. The epoxy group is highly reactive towards nucleophilic agents and can be easily transformed into quaternary ammonium, betaine, or sulfonate complexes. Additionally, cation-anion complexes can be formed by the transformation of two equivalents of epoxy silane with one equivalent of trialkyl ammonium hydrogen sulfite. The reaction of hydroxyalkyltrimethylsilane... 

Extraction of G proteins from membranes usually enhances ADP-ribosylation. In addition, small amounts of detergents like SDS, CHAPS or Lubrol PX facilitate the toxin s enzymatic activity (see above). For detection and identification of G proteins during G protein purification procedures, aliquots are also subjected to PT-catalyzed ADP-ribosylation for detection and identification (Rosenthal... 

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