Silylcarbonylation

Silylcarbonylation is a known term describing formally the silicon version of hydroformylation (cf. Section 2.1.1) discovered by Collenille [147] and later developed by Murai and co-workers, in which hydrogen is replaced by trialkylsilane, eq. (10) [148]. The silylformylation of alkenes is catalyzed by Co2(CO)g [148], [RhCl(CO)2]2 [149], RhCl(PPh3)3 [150], Ru3(CO)i2, and HRujfCO),- [151] to give silyl enol ethers of the homologous aldehydes as the sole products. 

The silylformylation of oxygen-containing compounds such as aldehydes and cyclic ethers in the presence of Co2(CO)g and [Rh(COD)Cl]2 affords siloxy derivatives according to eqs. (11) and (12) [148, 152]. 

In contrast to hydroformylation of olefin derivatives, the addition of carbon monoxide and trialkylsilane to alkynes gives carbon-centered silanes exclusively when catalyzed by, for example, rhodium and Rh-Co carbonyl clusters [153, 154] and Rh2(pfb)4 (pfb = perfluorobutyrate) (eq. (13) [153]). 

The reactions include the extremely regio-, stereo-, and chemoselective insertion of 1-alkyne into the (M)-Si bond of the silyl(hydrido)metal intermediate to form a 2-silylvinyl-(M ) complex, followed by a facile insertion of CO into the 

Rhodium cationic and zwitteiionic complexes proved to be superior catalysts for the hydroformylation of vinylsilanes, producing either a- or ff-silyl aldehydes depending on the reaction conditions [162], On the other hand, carbonylation of vinylsilanes in the reaction related to hydrocarboxylation and hydroesterification afforded P- and a-silyl esters in high yields (eq. (14) [163]). 

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When substituted silanes are used instead of hydrogen, the process is referred to as silylformylation or silylcarbonylation. Only rhodium complexes catalyze the transformation of unsaturated compounds to silylaldehydes via the silylformylation reaction. Iridium complexes also are able to catalyze the simultaneous incorporation of substituted silanes and CO into unsaturated compounds, although during the reaction other types of product are formed. In the presence of [ IrCl(C03) ] and [Ir4(CO)i2]) the alkenes react with trisubstituted silanes and CO to give enol silyl ethers of acyl silanes [58] according to Scheme 14.10. 

The iridium cluster [Ir4(CO)i2], which was used successfully as an olefin silylcarbonylation catalyst, also appeared effective in the formation of nitrogen hetero-... 

Other silicon derivatives containing Si—X—C bonds (where X is O and/or N) can be successfully prepared by using iridium-catalyzed reachons such as the asymmetric hydrosilylation of ketones and amines, the silylcarbonylation of alkenes, and the alcoholysis of Si—H bonds. Indeed, oxygenation of the latter bond to silanol also proceeds smoothly in the presence of iridium compounds. 

Use of a hydrosilane instead of molecular hydrogen in combination with a transition metal has opened the door leading to hydrosilylation and dehydrogenative silylation of unsaturated bonds. Thus, replacement of hydrogen by a hydrosilane is a reasonable strategy to improve serious issues in hydroformylation of alkenes. Along this line, some types of silylcarbonylation were extensively studied by Murai and his co-workers. However, the silicon moiety always attaches to the oxygen atom of incorporated GO molecule (Scheme 1). 

These precedents of silylcarbonylation made Matsuda and his co-workers hesitate to verify this route because intensive financial support for the research of -chemistry in Japan has ended. Fascination to create a new reaction and acquisition of a small fund to purchase a pressure bottle, however, prompted them to embark on exploration of this synthetic plan without any chart. Thus, diphenylacetylene 2 and triethylsilane in almost equal amounts were allowed to interact in the presence of 3mol% of Rh4(GO)i2 and Et3N under GO pressure (20 atm) as the first trial. The isolated products turned out to be 3 (85%, Z = 90 10) and 4 (10%) (Equation (1)). 

Insertion of unsaturated molecules into a transition metal-silyl bond has been suggested for the catalytic reactions related to hydrosilylation and silylcarbonylation. However, there is little direct evidence supporting such a process for unsaturated molecules to insert into a metal-silyl bond in organometallic complexes. " Thus, the fact that 108 is readily derived from 11 and 13 demonstrates the participation of this process in the catalytic cycle of silylformylation. 

In sharp contrast to simple alkenes that undergo silylcarbonylation, genuine silylformylation of an olefinic moiety is attained only by an intramolecular technique (Equation (33)). Since the most serious competitive reaetion is an intermolecular hydrosilylation reaction to form 192, the key for the successful transformation depends on an appropriate combination of substituents R and R. ... 

The silylcarbonylation of alkenes catalyzed by Co2(CO)s giving homologous silyl enol ethers was reported by Murai and coworkers in 1977 as a silicon version of hydro-formylation of alkenes, and developed as a unique synthetic method302-304. Although... 

Regioselective silylcarbonylation of enamines (305) with HSiEt2Me is promoted by [Rh(CO)2Cl]2, giving o -(siloxymethylene)amines (306) as a E/Z mixture (E/Z = 51/49-84/16) in modest to high yields, which are readily hydrolyzed to afford a-siloxyketones (307) (equation 114)313. Enamines of morpholine give much better results than those of diethylamine or benzyl(methyl)amine in this reaction. 

The 1,3-silyl migrations from O to C in lithiated silyl enol ethers 205 afforded a-silylcarbonyl compounds 206 after hydrolysis (equation 134)326 -330. 

Formal silylcarbonylation and silylformylation reactions are mainly catalyzed by cobalt and rhodium complexes (clusters) yet, Chatani et al. [158] have found a new type of carbonylation of diynes with trialkylsilanes leading to catechols (Eq. 100). 

Carbamoyl silanes 100 could be prepared by reaction of lithium silylamides 97 with CO at room temperature and under pressure (30 atm) followed by reaction with methyl iodide (Scheme 25)101. The intermediate carbamoyllithium 98 suffers a rearrangement of the silyl group to afford a new lithium (silylcarbonyl)amide 99, which is finally methylated. 

Bicyclo 4.1.0]heptan 7-Trimethyl-silylcarbonyl- E17b, 1393 (7-Br/7-SiR3 — 7-H/7-CO—SiR3) Cyclohexan trans-2-Hydroxy-1-(trimethylsilyl-ethinyl)- E19d, 146 (sp-CH - C - Li/Oxiran) Cyclopenten 2-Ethyl-4-methylen-l-trimethylsilyl- E17c, 2251 (Methylen-cyclo propan + In) Ethen l-(l-Cyclohexenyl)- -trimethylsilyloxy- E1S/1, 441 (Keton 4- RjSi—O —S02 —R) Furan 2-Methyl-5-propyl-3-trimethylsilyl- E18, 674 (In-Hydromagnesier./+ R —CN)... 

Cyclopropan 2-Butyl-l -trimethyl-silylcarbonyl- E17b, 1393 (2-Br/2-SiRj -> 2-H/2-CO—SiR3)... 

Cyclopropan 2-Acetyl-l-(tert.-butyl-dimethyl-silylcarbonyl)- E21c, 3225 (En + C1-CH2-CO-SiR3)... 

On the action of Grignard compounds, a, 3-epoxysilanes undergo rearrangement to a-silylcarbonyl compounds, eo f/tra-lS-hydroxysilanes being formed in a very stereoselective reaction. ... 

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