1,1‐Ethylboration of alkyn‐1‐yl‐chloro(methyl)silanes: alkenes with chloro(methyl)silyl and diethylboryl groups in cis positions

The 1,1‐ethylboration of alkyn‐1‐yl‐chloro(methyl)silanes, Me₂Si(Cl)? C?C? R ( 1 ) and Me(H)Si(Cl)? C?C? R ( 2 ) [R = Bu ( 2a ), CH₂NMe₂ ( 2b )] requires harsh reaction conditions (up to 20 days in boiling triethylborane), and leads to alkenes in which the boryl and silyl groups occupy cis ((E)‐isomers: 3a , 3b , 5a , 5b ) or trans positions ((Z)‐isomers in smaller quantities: 4b and 6b ). The alkenes are destabilized in the presence of SiH(Cl) and CH₂NMe₂ units ( 5b , 6b ). NMR data indicate hyper‐coordinated silicon by intramolecular N? Si coordination in 3b and 5b , by which, at the same time, weak Si? Cl? B bridges are favoured. Copyright © 2005 John Wiley & Sons, Ltd.     

1,1‐Organoboration of silylethynyltin compounds studied by multinuclear magnetic resonance spectroscopy: isomerization at the CC bonds and electron‐deficient Si?H?B bridges

1,1‐Organoboration, using triethyl‐, triallyl‐ and triphenyl‐borane (BEt₃, BAll₃, BPh₃), of dimethysilylethynyl(trimethyl)stannane, Me₃Sn? C?C? Si(H)Me₂ ( 1 ), affords alkenes bearing three different organometallic groups at the C?C bond. For BEt₃ and BPh₃, the first products are the alkenes 4 with boryl and stannyl groups in cis‐positions. These rearrange by consecutive 1,1‐deorganoboration and 1,1‐organoboration into the isomers 5 as the final products, where boryl and silyl groups are in cis‐positions linked by an electron‐deficient Si? H? B bridge. 1,1‐Ethylboration of bis(dimethylsilylethynyl)dimethylstannane, Me₂Sn[C?C? Si(H)Me₂]₂ ( 2 ), leads to the stannacyclopentadiene 6 along with non‐cyclic di(alkenyl)tin compounds 7 and 8 . 1,1‐Ethylboration of ethynyl(trimethylstannylethynyl)methylsilane, Me(H)Si(C?C? SnMe₃)C?C? H ( 3 ), leads selectively to a new silacyclopentadiene 13 as the final product. The reactions were monitored and the products were characterized by multinuclear magnetic resonance spectroscopy (¹H, ¹¹B, ¹³C, ²⁹Si and ¹¹⁹Sn NMR). Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis and structure of novel spirosilanes. Combination of 1,2‐hydroboration and 1,1‐organoboration

The reaction of tetra(alkyn‐1‐yl)silanes Si(C?C‐R¹)₄ 1 [R¹ = ^tBu ( a ), Ph ( b ), C₆H₄‐4‐Me ( c )] with 9‐borabicyclo[3.3.1]nonane (9‐BBN) in a 1:2 ratio affords the spirosilane derivatives 5a – c as a result of twofold intermolecular 1,2‐hydroboration, followed by twofold intramolecular 1,1‐organoboration. Intermediates 3a–c , in which two alkenyl‐ and two alkyn‐1‐yl groups are linked to silicon, were identified by NMR spectroscopy. The molecular structure of the spiro compound 5c was determined by X‐ray analysis, and the solution‐state structures of products and intermediates follow conclusively from the consistent NMR spectroscopic data sets (¹H, ¹¹B, ¹³C and ²⁹Si NMR). Copyright © 2008 John Wiley & Sons, Ltd.     

Aminoethynyl‐silanes, ‐germanes and ‐stannanes: novel organometallic‐substituted enamines via 1,1‐organoboration

The reactions of diethylaminoethynyl(trimethyl)silane (1), bis(diethylaminoethynyl)methylsilane (2), diethylaminoethynyl(trimethyl)germane (3), dimethylaminoethynyl(triethyl)germane (4), diethylaminoethynyl(trimethyl)stannane (5) and methyl(phenyl)aminoethynyl(trimethyl)stannane (6) with trialkylboranes [BEt₃ (7b), BPr₃ (7c), BⁱPr₃ (7d) and 9‐alkyl‐9‐borabicyclo[3.3.1]nonanes 9‐Me‐9‐BBN (8a) and 9‐Et‐9‐BBN (8b)] were studied. The alkynes 1 and 2 did not react even with boiling BEt₃, whereas the reactions of 3–6 afforded mainly novel enamines [(E)‐1‐amino‐1‐trialkylgermyl‐2‐dialkylboryl‐alkenes (9, 10), (E)‐1‐diethylamino‐1‐trimethylstannyl‐2‐dialkylboryl‐alkenes (11, 12), (E)‐1‐methyl(phenyl)amino‐1‐trimethylstannyl‐2‐dialkylboryl‐alkenes (13, 14)]. This particular stereochemistry is unusual for products from 1,1‐organoboration reactions, indicating a special influence of the amino group. The starting materials and products were characterized by multinuclear magnetic resonance spectroscopy (¹H, ¹¹B, ¹³C, ¹⁵N, ²⁹Si, ¹¹⁹Sn NMR). Copyright © 2003 John Wiley & Sons, Ltd.     

1‐Silacyclopent‐2‐enes and 1‐silacyclohex‐2‐enes bearing functionally substituted silyl groups in 2‐positions. Novel electron‐deficient Si?H?B bridges

The reactions of alkyn‐1‐yl(vinyl)silanes R₂Si[C?C‐Si(H)Me₂]CH?CH₂ [R = Me (1a), Ph (1b)], Me₂Si[C?C‐Si(Br)Me₂]CH?CH₂ (2a), and of alkyn‐1‐yl(allyl)silanes R₂Si[C?C‐Si(H)Me₂]CH₂CH?CH₂ (R = Me (3a), R = Ph (3b)] with 9‐borabicyclo[3.3.1]nonane in a 1:1 ratio afford in high yield the 1‐silacyclopent‐2‐ene derivatives 4a, b and 5a, and the 1‐silacyclohex‐2‐ene derivatives 6a, b, respectively, all of which bear a functionally substituted silyl group in 2‐position and the boryl group in 3‐position. This is the result of selective intermolecular 1,2‐hydroboration of the vinyl or allyl group, followed by intramolecular 1,1‐organoboration of the alkynyl group. In the cases of 4a, b, potential electron‐deficient Si? H? B bridges are absent or extremely weak, whereas in 6a,b the existence of Si? H? B bridges is evident from the NMR spectroscopic data (¹H, ¹¹B, ¹³C and ²⁹Si NMR). The molecular structure of 4b was determined by X‐ray analysis. Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis and molecular structures of 1‐boracyclopent‐2‐enes

The reaction of 1‐silyl‐1‐borylalkenes with alkyn‐1‐yltin compounds affords borol‐2‐enes, organometallic‐substituted allenes, mixtures thereof or even more complex mixtures with buta‐1,3‐dienes, depending on the third substituent at the C?C bond (Bu or Ph), on the number of Si? Cl functions (two or three) and the nature of the alkyn‐1‐yltin compound. Six new borol‐2‐enes were isolated in pure state, and two of them were characterized by X‐ray structural analysis. The solution‐state structures of all major products were clearly established by multinuclear magnetic resonance methods (¹H, ¹¹B, ¹³C, ²⁹Si, ¹¹⁹Sn NMR). Copyright © 2009 John Wiley & Sons, Ltd.     

1,1‐allylboration of bis(silyl)ethynes: electron‐deficient Si?H?B bridges and novel heterocycles via intramolecular hydrosilylation

The reaction of bis(silyl)ethynes 2 – 4 , bearing one, two and three hydrides at one of the silicon atoms, with triallylborane 1 leads primarily to alkenes 5 , 8 and 11 respectively by 1,1‐allylboration. In these alkenes, the diallylboryl and the silyl group bearing one or more Si? H functions are in cis‐positions at the C?C bond, giving rise to the formation of an electron‐deficient Si? H? B bridge. This follows unambiguously from the consistent set of NMR data, in particular from the observation of isotope‐induced chemical shifts ²Δ^10/11B(²⁹Si). The activation of the Si? H bond in 5 , 8 and 11 induces intramolecular hydrosilylation under very mild reaction conditions to give 1,4‐silabora‐cyclo‐2‐heptenes 7 , 10 and 13 respectively. Upon heating, these seven‐membered heterocycles undergo ring contraction by 1,1‐deallylboration to give the 1‐sila‐cyclo‐2‐hexenes 14 – 16 , and bear an exocyclic diallylboryl group in 3‐position. All proposed structures are based on consistent ¹H, ¹¹B, ¹³C and ²⁹SiNMR data. Copyright © 2004 John Wiley & Sons, Ltd.     

A novel 4‐methylene‐3‐borahomoadamantane: 1,1‐organoboration of an alkyn‐1‐ylsilane using 1‐boraadamantane

1,1‐Dibromo‐2,2‐bis(trimethylsilylethynyl)ethene ( 2 ) reacts with two equivalents of 1‐boraadamantane ( 1 ) by 1,1‐organoboration of both trimethylsilylethynyl groups to give a triene 3 bearing two 4‐methylene‐3‐borahomoadamantane moieties in terminal positions. The triene was characterized by one‐ and two‐dimensional ¹H, ¹¹B, ¹³C and ²⁹Si NMR spectroscopy in solution and X‐ray structural analysis in the solid state. The planes of the C double bond are strongly twisted against each other as a result of the bulky substituents, and the surroundings of the boron atoms deviate from the ideal trigonal planar geometry owing to the tension in the tricyclic frameworks. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis and molecular structures of 1‐chloro‐1‐silacyclopent‐2‐enes. Combination of 1,2‐hydroboration, 1,1‐organoboration and protodeborylation

The reaction of alkyn‐1‐yl(chloro)(methyl)vinyl‐ and alkyn‐1‐yl(chloro)(phenyl)‐vinylsilane with 9‐borabicyclo[3.3.1]nonane (9‐BBN) afforded selectively 1‐silacyclopent‐2‐ene derivatives containing a Si? Cl function, as a result of consecutive 1,2‐hydroboration and 1,1‐organoboration. Protodeborylation with acetic acid left the Si? Cl functions in various 1‐silacyclopent‐2‐enes untouched, whereas acetic acid in the presence of dipropylamine led to conversion of the Si? Cl into the Si? OAc function. New starting materials and all products were characterized in solution by multinuclear NMR spectroscopy (¹H, ¹¹B, ¹³C and ²⁹Si NMR), and the molecular structures of two 1‐silacyclopent‐2‐ene derivatives were determined by X‐ray analysis. The gas phase geometries of 1‐silacyclopent‐2‐enes were optimized by DFT calculations [B3LYP/6‐311 + G(d,p) level of theory], found to be in reasonable agreement with the results of the crystal structure determination, and NMR parameters were calculated at the same level of theory. Copyright © 2009 John Wiley & Sons, Ltd.     

Boryl‐substituted 1‐silacyclobutenes. Formation and molecular structure

The 1,2‐hydroboration of the chloro(hexyn‐1‐yl)‐ ( 1a ) and chloro(phenylethyn‐1‐yl)diphenylsilanes ( 1b ) with 9‐borabicyclo[3.3.1]nonane afforded selectively the alkenylsilanes 2a, b , in which the boryl and the silyl groups are linked to the same olefinic carbon atom. In case of 2a , treatment with phenylethynyl lithium gave a mixture of the alkyn‐1‐ylborate 3a and the alkenyl(phenylethynyl)diphenylsilanes 4a . In the case of 2b , only the alkyn‐1‐ylsilane 4b was identified as an intermediate. Both 4a, b slowly rearranged by intramolecular 1,1‐vinylboration into the silacyclobutenes 5a, b . The intermediates were characterized by ¹H, ¹¹B, ¹³C and ²⁹Si NMR spectroscopy in solution, and the molecular structure of the 1‐silacyclobutene 5a was determined by X‐ray analysis. The gas phase geometries of model molecules corresponding to 5a were optimized by MO calculations using DFT methods [B3LYP/6‐311 + G(d,p) level of theory], found to be in reasonable agreement with the results of the crystal structure determination, and NMR parameters were calculated at the same level of theory. Copyright © 2006 John Wiley & Sons, Ltd.     

Copper‐Mediated Aromatic 1,1‐Difluoroethylation with (1,1‐Difluoroethyl)trimethylsilane (TMSCF2CH3)

A new method for the formation of 1,1‐difluoroethyl copper species (“CuCF₂CH₃”) with 1,1‐difluoroethylsilane (TMSCF₂CH₃) has been developed. The “CuCF₂CH₃” species can be applied to the efficient 1,1‐difluoroethylation of diaryliodonium salts under mild conditions, affording (1,1‐difluoroethyl)arenes in good to excellent yields. This convenient procedure tolerates a wide range of functional groups and thus serves as a practical synthetic tool for the introduction of CF₂CH₃ group(s) into complex molecules.     

Amine‐bis(phenolate) Iron(III)‐Catalyzed Formal Hydroamination of Olefins

A practical synthesis of highly functionalized amines by the formal hydroamination reaction of alkenes with nitroarenes catalyzed by an air stable amine‐bis(phenolate) iron(III) complex is reported. The reaction uses an easily handled silane, low catalyst loadings, and mild reaction conditions. A wide range of substrates are transformed with synthetically useful yields (21 examples).     

Metal‐Free Polymerization of Phenylsilane: Tris(pentafluorophenyl)borane‐Catalyzed Synthesis of Branched Polysilanes at Elevated Temperatures

The strong organoborane Lewis acid B(C₆F₅)₃ catalyzes the polymerization of phenylsilane at elevated temperatures forming benzene and SiH₄ as side‐products. The resulting polymer is a branched polysilane with an irregular substitution pattern, as revealed by 2D NMR spectroscopy. Having explored the mechanism of this novel metal‐free polymerization by computational chemistry methods at the DFT level, we have suggested that unusual cationic active species, namely monomer‐stabilized silyl cations, propagate the polymerization. Hydride abstraction of SiH₃ moiety by the catalyst in the initiation step was found to be kinetically preferred by around 9 kcal mol^?1 over activation by coordination of the monomer at the aromatic ring. The formation of linear Si? Si bonds during propagation was calculated to be less favorable than branching and ligand scrambling, which accounts for the branched and highly substituted form of the polymer that was obtained. This novel type of polymerization bears the potential for further optimization with respect to degree of polymerization and structure control for both primary as well as secondary silanes, which can be polymerized by sterically less hindered boranes.     

Synthesis and characterization of sodium bis(trimethylstannyl) amide and bis(trimethylsilyl) bis(trimethylstannyl) -phospha-tetrazene

Sodium bis(trimethylstannyl)amide NaN(SnMe₃)₂, isolated by the reaction of trimethylstannyldiethylamine with sodium amide, reacts with tris(trimethylsilyl)hydrazino—dichloro-phosphine to form bis(trimethylsilyl)bis(trimethylstannyl)-2-phospha-2-tetrazene, (Me₃Si)₂N-N=P-N(SnMe₃)₂. Both the molecules have been isolated and characterized.     

ZnI2‐promoted homologation of ferrocenylacetylene and aldehydes: an efficient synthesis of ferrocene‐containing allenes

A concise and efficient protocol for the first synthesis of ferrocene‐containing allenes based on the homologation reaction of ferrocenylacetylene and aldehydes promoted by ZnI₂ was developed. The present method was applicable to many kinds of substituted aldehydes, providing good to excellent yields of ferrocene‐containing allenes. Copyright © 2012 John Wiley & Sons, Ltd.     

Stereospecific synthesis of a family of novel (E)‐2‐aryl‐1‐silylalka‐1,4‐dienes or (E)‐4‐aryl‐5‐silylpenta‐1,2,4‐trienes via a cross‐coupling of (Z)‐silyl(stannyl)ethenes with allyl halides or propargyl bromide

Stereospecific synthesis of a family of novel (E)‐2‐aryl‐1‐silylalka‐1,4‐dienes or (E)‐4‐aryl‐5‐silylpenta‐1,2,4‐trienes via a cross‐coupling of (Z)‐silyl(stannyl)ethenes with allyl halides or propargyl bromide is described. In the reaction with allyl bromide, either a Pd(dba)₂? CuI combination (dba, dibenzylideneacetone) in DMF or copper(I) iodide in DMSO–THF readily catalyzes or mediates the coupling reaction of (Z)‐silyl(stannyl)ethenes at room temperature, producing novel vinylsilanes bearing an allyl group β to silicon with cis ‐disposition in good yields. Allyl chlorides as halides can be used in the CuI‐mediated reaction. CuI alone much more effectively mediates the cross‐coupling reaction with propargyl bromide in DMSO–THF at room temperature compared with a Pd(dba)₂? CuI combination catalysis in DMF, providing novel stereodefined vinylsilanes bearing an allenyl group β to silicon with cis ‐disposition in good yields. Copyright © 2008 John Wiley & Sons, Ltd.     

Electrochemical Reduction of 4,4′‐(2,2,2‐Trichloroethane‐1,1‐diyl)‐ bis(chlorobenzene) (DDT) and 4,4′‐(2,2‐Dichloroethane‐1,1‐diyl)‐ bis(chlorobenzene) (DDD) at Carbon Cathodes in Dimethylformamide

In dimethylformamide containing tetramethylammonium tetrafluoroborate, cyclic voltammograms for reduction of 4,4′‐(2,2,2‐trichloroethane‐1,1‐diyl)bis(chlorobenzene) (DDT) at a glassy carbon cathode exhibit five waves, whereas three waves are observed for the reduction of 4,4′‐(2,2‐dichloroethane‐1,1‐diyl)bis(chlorobenzene) (DDD). Bulk electrolyses of DDT and DDD afford 4,4′‐(ethene‐1,1‐diyl)bis(chlorobenzene) (DDNU) as principal product (67–94%), together with 4,4′‐(2‐chloroethene‐1,1‐diyl)bis(chlorobenzene) (DDMU), 1‐chloro‐4‐styrylbenzene, and traces of both 1,1‐diphenylethane and 4,4′‐(ethane‐1,1‐diyl)bis(chlorobenzene) (DDO). For electrolyses of DDT and DDD, the coulometric n values are essentially 4 and 2, respectively. When DDT is reduced in the presence of a large excess of D₂O, the resulting DDNU and DDMU are almost fully deuterated, indicating that reductive cleavage of the carbon–chlorine bonds of DDT is a two‐electron process that involves carbanion intermediates. A mechanistic scheme is proposed to account for the formation of the various products.     

Platinum Complexes of a Borane‐Appended Analogue of 1,1′‐Bis(diphenylphosphino)ferrocene: Flexible Borane Coordination Modes and in situ Vinylborane Formation

A bis(phosphine)borane ambiphilic ligand, [Fe(η⁵‐C₅H₄PPh₂)(η⁵‐C₅H₄PtBu{C₆H₄(BPh₂)‐ortho})] (FcPPB), in which the borane occupies a terminal position, was prepared. Reaction of FcPPB with tris(norbornene)platinum(0) provided [Pt(FcPPB)] ( 1 ) in which the arylborane is η³BCC‐coordinated. Subsequent reaction with CO and CNXyl (Xyl=2,6‐dimethylphenyl) afforded [PtL(FcPPB)] {L=CO ( 2 ) and CNXyl ( 3 )} featuring η²BC‐ and η¹B‐arylborane coordination modes, respectively. Reaction of 1 or 2 with H₂ yielded [PtH(μ‐H)(FcPPB)] in which the borane is bound to a hydride ligand on platinum. Addition of PhC₂H to [Pt(FcPPB)] afforded [Pt(C₂Ph)(μ‐H)(FcPPB)] ( 5 ), which rapidly converted to [Pt(FcPPB′)] ( 6 ; FcPPB′=[Fe(η⁵‐C₅H₄PPh₂)(η⁵‐C₅H₄PtBu{C₆H₄(BPh‐CPh=CHPh‐Z)‐ortho}]) in which the newly formed vinylborane is η³BCC‐coordinated. Unlike arylborane complex 1 , vinylborane complex 6 does not react with CO, CNXyl, H₂ or HC₂Ph at room temperature.