Triethylsilanate complex

In a similar fashion, 2-cumyladamantane (12, R = Ph) is formed in nearly quantitative yield upon treatment of the easily synthesized 2-cumyl-2-adaman-tanol (11, R = Ph)154 with triethylsilane and methanesulfonic acid in dichloromethane at —78°.155 The high yield of a single very strained hydrocarbon product in each reaction is quite surprising in view of the very complex interconversions of carbocations known to take place from the alcohol precursors.140,151 152 156... 

Highly diasteroselective and chemoselective reductions may be performed on the hydroxy functions of (r/6-arene)-tricarbonylchromium complexes. Treatment of the chromium-complexed benzylic alcohol 29 with triethylsilane and boron trifluoride etherate in dichloromethane at —78° to 0° gives only diastereomer 30 in 75% yield (Eq. 40).181 In a similar fashion, treatment of the complexed exo-allyl-endo-benzylic alcohol 31 with an excess of Et3SiH/TFA in dichloromethane at room temperature under nitrogen produces only the endo-aflyl product 32 in 92% yield after 1.5 hours (Eq. 41). It is noteworthy that no reduction of the isolated double bond occurs.182... 

Based on the few reported examples, the pattern of ring cleavage that accompanies the ionic hydrogenation of alkylidenencyclopropanes seems to be related to the pattern and degree of substitution on both the ring and the double bond.233 Thus, treatment of l,l-dimethyl-2-methylenecyclopropane with two equivalents of triethylsilane and four equivalents of trifluoroacetic acid for 90 hours at room temperature yields 65% of 2,3-dimethylbutane (Eq. 114).229 Exposure of 1,1-dimethyl-2-isopropylidenecyclopropane to the same ratio of reactants at 50° for 16 hours produces a complex mixture containing 63% of 2,5-dimethylhexane, 18.5% of 2,5-dimethyl-3-hexene, 1.6% of 2,5-dimethyl-2-hexene, and 7% of 2,5-dimethyl-2-hexyl trifluoroacetate (Eq. 115).229... 

Few other examples of such reaction sequences have been described to date. Oh has reported the palladium-catalyzed reductive cyclizations of 1,6-enynes in the presence of formic acid or triethylsilane via an alkylpalladium intermediate and its application to organic synthesis. Palladium complexes also catalyze the conversion of a range of enynes to cyclic 6,7-unsaturated carboxylic acids in the presence of CO.260... 

For example, a dienyl aldehyde reductively cyclizes in the presence of an Ni(0)/PPh3 complex and triethylsilane to give homoallylic cyclopropentanol with high regio- and stereoselectivities, while bishomoallylic cyclopropentanol is obtained as major product under the conditions using stoichiometric Ni(0)-diene complexes (Scheme 85). 

Ruthenium complexes do not have an extensive history as alkyne hydrosilylation catalysts. Oro noted that a ruthenium(n) hydride (Scheme 11, A) will perform stepwise alkyne insertion, and that the resulting vinylruthenium will undergo transmetallation upon treatment with triethylsilane to regenerate the ruthenium(n) hydride and produce the (E)-f3-vinylsilane in a stoichiometric reaction. However, when the same complex is used to catalyze the hydrosilylation reaction, exclusive formation of the (Z)-/3-vinylsilane is observed.55 In the catalytic case, the active ruthenium species is likely not the hydride A but the Ru-Si species B. This leads to a monohydride silylmetallation mechanism (see Scheme 1). More recently, small changes in catalyst structure have been shown to provide remarkable changes in stereoselectivity (Scheme ll).56... 

The [Ir(C0D)( Pr2PCH2CH20Me)]BF4 complex also catalyzes the hydrosilyla-tion of phenylacetylene with triethylsilane, to yield-along with the normal... 

Widenhoefer and co-workers have developed an effective protocol for the asymmetric cyclization/hydrosilylation of functionalized 1,6-enynes catalyzed by enantiomerically enriched cationic rhodium bis(phosphine) complexes. For example, treatment of dimethyl allyl(2-butynyl)malonate with triethylsilane (5 equiv.) and a catalytic 1 1 mixture of [Rh(GOD)2] SbF6 and (i )-BIPHEMP (5 mol%) at 70 °G for 90 min gave the silylated alkylidene cyclopentane 12 in 81% yield with 98% de and 92% ee (Table 4, entry 1). A number of tertiary silanes were effective for the rhodium-catalyzed asymmetric cyclization/hydrosilylation of dimethyl allyl(2-butynyl)malonate with yields ranging from 71% to 81% and with 77-92% ee (Table 4, entries 1-5). Although the scope of the protocol was limited, a small number of functionalized 1,6-enynes including A-allyl-A-(2-butynyl)-4-methylbenzenesulfonamide underwent reaction in moderate yield with >80% ee (Table 4, entries 6-8). 

Mori has reported the nickel-catalyzed cyclization/hydrosilylation of dienals to form protected alkenylcycloalk-anols." For example, reaction of 4-benzyloxymethyl-5,7-octadienal 48a and triethylsilane catalyzed by a 1 2 mixture of Ni(GOD)2 and PPhs in toluene at room temperature gave the silyloxycyclopentane 49a in 70% yield with exclusive formation of the m,//7 //i -diastereomer (Scheme 14). In a similar manner, the 6,8-nonadienal 48b underwent nickel-catalyzed reaction to form silyloxycyclohexane 49b in 71% yield with exclusive formation of the // /i ,// /i -diastereomer, and the 7,9-decadienal 48c underwent reaction to form silyloxycycloheptane 49c in 66% yield with undetermined stereochemistry (Scheme 14). On the basis of related stoichiometric experiments, Mori proposed a mechanism for the nickel-catalyzed cyclization/hydrosilylation of dienals involving initial insertion of the diene moiety into the Ni-H bond of a silylnickel hydride complex to form the (7r-allyl)nickel silyl complex li (Scheme 15). Intramolecular carbometallation followed by O-Si reductive elimination and H-Si oxidative addition would release the silyloxycycloalkane with regeneration of the active silylnickel hydride catalyst. 

Although the cofacial diporphyrins represent a vibrant and innovative direction in dioxygen activation, simple porphyrins and their derivatives also remain an important research area. The dichlorophenyl-substituted porphyrin tdcpp [5,10,15,20-tetrakis(2,6-dichlorophenyl)-porphyrin] forms a complex with cobalt(II), [Co(tdcpp)], and catalyzes the oxidation of conjugated olefins to (after experimental workup) ketones in the presence of dioxygen and triethylsilane (80) a hydroperoxide intermediate has been isolated from these reactions (81). 

In 1993, Murai s group examined the effectiveness of the iron-triad carbonyl complexes Fe(CO)5, Fe2(CO)9 and Fe3(CO)12 as catalysts for the reaction of styrene with triethylsilane [47]. Whereas Fe(CO)5 showed no catalytic activity, Fe2(CO)9 and Fe3(CO)12 formed selectively P-silylstyrene 57a and ethylbenzene 58. Interestingly, Fe3(CO)12 is the catalyst that exhibited the highest selectivity. This trinuclear iron carbonyl catalyst was also successfully applied in the reaction of different para-substituted styrenes with Et3SiH giving only the (E)-P-triethylstyrenes in 66-70% yield (Scheme 4.23). 

Treatment of this complex with triethylsilane gives the corresponding ASMA in moderate yield.199 200... 

A convenient two-step method for tetrahydropyran synthesis from tetrahydropyran-2-ones can be achieved by using a titanocene complex in the presence of a stoichiometric reducing agent, followed by treatment with Amberlyst 15 and triethylsilane <1998JOC2360>. 

The [Mn(CO)3(P)2(CH2Cl2)][BArF] complex, 23, also catalyzes reaction of phenol with triethylsilane, presumably by a mechanism similar to that proposed for the Fe system (Scheme 9). The ratio of silane to the catalyst was about 24 1, and a slight deficiency of phenol was added at —78°C in an NMR tube reaction. XH NMR spectra recorded from... 

The reactivity of platinum silylenoid 27 was explored with traditional silylene trapping reagents. While the silylenoid did not react with triethylsilane or 2,3-dimethyl-1,3-butadiene, phenylacetylene was a viable substrate, providing the me-tallocyclohexadiene 29 (Scheme 7.4).54 The formation of platinum complex 29 was hypothesized to occur via platinum cyclobutene intermediate 28, which formed on insertion of the acetylene into the platinum-silicon bond. A second molecule of phenylacetylene was then inserted into the remaining platinum-silicon bond to provide the observed product. 

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