Chloroacetylenes as Michael acceptors. II. Direct ethynylation and vinylation of tertiary enolates.

The reaction of ClCCCl, PhCCCl and PhSCCCl with a variety of tertiary enolates leads in 43–90% yields to α-chloroethynyl, α-phenylethynyl and α-thiophenylethynyl derivatives. The ?CCCl group is smoothly converted to ?CCH using copper powder in HOAc/THF, or is directly reduced (H₂/Lindlar catalyst) to the ?CHCH₂ group, thus providing facile access to many α-ethynyl and α-vinyl ketones and esters.     

Some unexpected reactions of perfluoroalkynylmagnesium halides

R_FCCMgX reacts with Ac₂O to give not only MeC(O)CCR_F but also MeC(O)CXC(R_F)C(O)Me, and with CF₃COOPr it gives CF₃C(O)CHC(OPr)R_F not CF₃C(O)CCR_F; R_FCCMgBr reacts with Cl₂ to give R_FCCBr rather than R_FCCCl, while with Br₂ R_FCCMgI similarly gives R_FCCI rather than R_FCCBr.     

Reactions of alkynes with bis(triphenylphosphine)platinum-ethylene: A 31P-{1H} NMR study

Internally consistent assignments of the ³¹P-{¹H} NMR parameters of the complexes [Pt(RCCR′)(PPh₃)₂] are proposed, based on the premise that the magnitude of ¹J(PtP) depends mainly on the nature of the moiety CR trans to P. For a given R, ²J(PP) correlates with ¹J(PtP) for thebond trans to CR. The alkynes PhCCSnEt₃, PhCCSnPh₃, Me₃SiCCCl, Me₃SiCCBr, Et₃SiCCI and MeCCI undergo oxidative addition reactions with [Pt(C₂H₄)(PPh₃)₂]; the intermediate alkyne complex was detected for PhCCSnEt₃, Me₃SiCCCl and Me₃CCBr. The triyne Me(CC)₃Me forms platinum(0) complexes by coordination with the central or terminal CC bond and appears also to give a platinum(II) complex by oxidative addition.     

Komplexchemie perhalogenierter Cyclopentadiene und Alkine: III. Reaktion von Pt(PPh3)2(C2H4) mit Monofluoracetylen und Dichloracetylen. Kristallstruktur von Pt(PPh3)2(Cl)(CCCl)

Pt(PPh₃)₂(C₂H₄) reacts with monofluoroacetylene to give the π-complex Pt(PPh₃)₂(FCCH), and with dichloroacetylene under oxidative addition to yield Pt(PPh₃)₂(Cl)(ClCCl), the structure of which was determined by X-ray crystallography.     

Diyne coordination chemistry: Reactions of [RuClH(CO)(PPh3)3] with diphenylbutadiyne and bis(phenylethynyl)mercury

The reaction of the hydridometal complex [RuClH(CO)(PPh₃)₃] with 1,4-diphenyl-butadi-1,3-yne has been investigated and found to proceed with monoinsertion to give a coordinatively unsaturated σ-vinyl complex [Ru-{C(CCPh)CHPh} Cl(CO)(PPh₃)₂], which is also the major product of the reaction of [RuClH(CO) (PPh₃)₃] with [Hg(CCPh)₂].     

Silylation as a protective method for terminal alkynes in organometallic synthesis : Preparation of 1,4-diethynyltetrafluorobenzene and (pentafluorophenyl)acetylene

Hexafluorobenzene reacts with Et₃SiCCLi to give p- Et₃SiCCC₆F₄CCSi-Et₃ and pentafluorophenylcopper couples with BrCCSiEt₃ to give C₆F₅CCSiEt₃ in good yield. Treatment of the products with aqueous methanolic alkali gives p-HCCC₆F₄CCH and C₆F₅CCH respectively.     

Coordinatively unsaturated alkyne complexes: synthesis of mono and bis-alkyne complexes of tungsten (II)

[WBr₂(CO₄]_n reacts with alkynes to give complexes [WBr₂CO(RCCR)₂]₂ (1) (R = R′ = Me, Et, Ph; R = Me, R′ = Ph), which react with nucleophiles L{L = CNBu^t, PPh₃, or P(OMe)₃} to give monoalkyne derivatives (WBr₂(CO)(RCCR′)L₂](2). An intermediate bis-alkyne adduct [WBr₂CO(MeCCMe)₂(CNBu^t)] (3) was isolated in the reaction of [WBr₂CO(MeCCMe)₂]₂ with CNBu^t illustrating that cleavage of the dimer (1) is the first stage in these reactions.     

Überführung eines carben- in einen isocyanid-komplex

Pentacarbonyl(diphenylcarbene)tungsten, (CO)₅WCPh₂ (I), reacts with diethylamino(dimethyl)acetonitrile, Me₂(Et₂N)CCN (II), to give pentacarbonyl(diphenylmethylisocyanide)tungsten, (CO)₅W[CNC(H)Ph₂] (III). In the reaction of I with diethylaminoacetonitrile, H₂(Et₂N)CCN, and dimethylamino(methoxy)acetonitrile, H(MeO)(Me₂N)CCN, respectively, complex III is also formed in small amounts.     

The reaction of 3,3-dichloroallyltrimethylsilane with n-butyllithium

n-Butyllithium reacts with 3,3-dichloroallyltrimethylsilane to metalate the vinyl proton. Under the reaction conditions the Me₃SiCH₂C(Li)CCl₂ formed undergoes β-elimination of LiCl to give ClCCCH₂SiMe₃ whose subsequent reaction with n-butyllithium produces LiCCCH₂SiMe₃. Addition of trimethylchlorosilane gives Me₃SiCCCH₂SiMe₃. When two molar equivalents of n-butyllithium are used, further metalation of LiCCCH₂SiMe₃ gives LiCCCH(Li)SiMe₃. The action of N-bromosuccinimide on Me₃SiCH₂CHCCl₂ resulted in formation of Me₃SiCHCHCCl₂Br.     

Electrochemical disk generation and ring identification of carbanions from organomercurials in acetonitrile

A rotating disk-ring electrode was used for study of a series of organomercury compounds R₂Hg, where R = CN, CF(NO₂)₂, C₆F₅, PhCC, p-NO₂C₆H₄OCC, PhSCH₂CC, PhCOCH₂, CH₂CN, CCl₂CCl, 2-phenyl-o-carboranyl. Reduction of these compounds at a Pt-disk in acetonitrile is a two-electron process and results in generation of the carbanion R^?. The carbanions generated at the disk interact with the solvent during their convective diffusion to the ring electrode where there may be oxidized. The main reaction in solution, shown using chromatography-mass spectrometry techniques, is acid-base interaction of carbanions with the solvent acetonitrile, which acts as a Brönsted acid. Reaching the ring, the carbanions may be oxidized at anodic potentials of the ring; oxidation potentials depend significantly on carbanion structure (e.g.+0.28 V (vs. SCE), for PhCC^? and +2.20 V for CN^?. It is shown that PK_a value of the carbanions do not correlate with the oxidation potentials, however, a linear correlation is observed between pK_a values and a special parameter called the efficiency coefficient.     

Silicon in organic synthesis. 12. trans-1-benzenesulfonyl-2-(trimethylsilyl)ethylene,a Diels-Alder dienophile equivalent of acetylene and monosubstituted acetylenes

$\text{trans}$-1-Benzenesulfonyl-2-(trimethylsilyl)ethylene and its 1,2-$\text{d}$₂ derivative enter into Diels-Alder cycloaddition to give products which are smoothly eliminated with fluoride ion. Alkylation of the α-sulfonyl carbanion can precede elimination, such that synthetic equivalents for HCCH, HCCD, DCCD, RCCH, and RCCD are now available.     

ÜbergangsmetallCarbin-Komplexe: LXXXVI. Synthese mono-, bis-, und tris-Trimethylphosphan-substituierter Diethylaminocarbin-Komplexe des Wolframs

The reaction of trans-I(CO)₄WCNEt₂ (I) with a slight excess of PMe₃ results in the replacement of one carbonyl group to give mer-I(CO)₃(PMe₃)WCNEt₂ (II). Complex II reacts at room temperature with additional PMe₃ under CO replacement to give a mixture of cis- and trans-dicarbonyl-I(CO)₂(PMe₃)₂WCNEt₂ (III, IV). Complexes III and IV, which can be separated by column chromatography, isomerize slowly at room temperature, the thermodynamic equilibrium favouring the more stable trans complex IV. The cis isomer III can be obtained from I(CO)₂py₂WCNEt₂ (V) and PMe₃. Another CO ligand can be eliminated from III or IV by an excess of PMe₃ in boiling hexane and gives mer-I(CO)(PMe₃)₃WCNEt₂ (VI). Moreover complex VI can be prepared by oxidative decarbonylation from III or IV by iodine and subsequent reduction of the intermediate, an isolable, seven-coordinated carbyne complex formulated as (I)₃(CO)(PMe₃)₂WCNEt₂ (VII), by two equivalents of PMe₃.     

Synthesis of Marasin and 9-Me-Marasin, (Nona- and Deca-6,8-diyne-3,4-dienol).

3,4-Pentadienol was protected with ethyl vinyl ether and regioselectively (70%) deprotonated at the terminal position by treatment with BuLi in THF at low temperature. Starting from the so obtained lithium compound, Marasin (nona-6,8-diyne-3,4-dienol) (1a) and 9-Me-Marasin (deca-6,8-diyne-3,4-dienol) (1b) were prepared by two metal-mediated synthetic routes. Route A involves transmetallation of the lithium compound with LiCuBr₂, followed by reaction with Me₃Si-CC-CC-l or Me-CC-CC-l. Route B involves transmetallation with ZnCl₂, followed by a palladium-catalyzed coupling reaction with Me₃Si-CC-CC-Br or Me-CC-CC-Br. Before removal of the protecting groups the yield of C-C coupled products, Me₃Si-CC-CC-CHCCH-CH₂CH₂OCH(Me)OEt and Me-CC-CC-CHCCH-CH₂CH₂-OCH(Me)OEt (6a and 6b) was 95 % via route A. Route B afforded (6a) and for (6b) in 75% and 50 % yield, respectively. After removal of the trimethylsilyl group with AgNO₃ and the acetal group with trace of acid, (1a) and (1b) were obtained by route A in 20 % and 65 % overall yield, respectively, and by route B in 13 % and 30 % overall yield, respectively. The antibiotic activity of both compounds was tested against Staphylococcus aureus and the MIC (Minimal Inhibiting Concentration) for Marasin was 0.2 (fesol|μg/ml) 9-Me-marasin was not active suggesting that the free acetylene function of the allenediyne is essential for the antibiotic activity.     

Molecular structures of acetylene derivatives of tin: Part IV. Gas-phase electron-diffraction study of tetraethynyltin,Sn(CCH)4, and triethynyltin iodide,ISn(CCH)3

The geometrical parameters of tetraethynyltin and triethynyltin iodide have been determined by gas-phase electron diffraction. Triethynyltin iodide was present as an admixture in both the tetraethynyltin samples studied. Because the samples differed significantly in percentage of the iodide (17.4 ± 4.0 and 47.1 ± 3.5 mol %, in samples A and B, respectively), it was possible to determine the structures of both molecules to a sufficient degree of accuracy.The r_α, structures were solved by the least-squares treatment of the molecular intensities, using mean amplitudes and shrinkage corrections calculated from the force fields of a number of tin derivatives.The T_d-symmetry model of Sn(CCH)₄ was refined to give the following parameters: Sn-C, 2.068(5); CC, 1.228(8); CH, 1.079(51). The structural parameters for ISn(CCH)₃ (on the basis of the C_3v model with linear Sn-CC-H fragments) are as follows: Sn-I, 2.646(4); Sn-C, 2.062(17); CC, 1.226(6); ∠ISnC 108.0(2.8). (The thermal average bond distances, r_g, are given in Å, and the valence angle, rα, in degrees; the values in paren- theses are three times the standard deviations, 3σ.)The Sn-C bonds in Sn(CCH)₄, and ISn(CCH)₃ are shorter than the corresponding bonds in the monoethynyltin derivatives, Me₃SnCCH and Me₃SnCCSnMe₃. The SnI bond in ISn(CCH)₃ is noticeably shorter than those in stannane iodide and trimethylstannane iodide.     

Double addition du methanol sur des complexes η5-cyclopentadienyl η1-hexadiyne-2,4-yl tricarbonyl molybdene et dicarbonyl fer

The η¹-diacetylenic molybdenum complexes η-C₅H₅(CO)₃MoCH₂CCCCCH₃ (Ia) can add two methanoi molecules successively. The first addition, with CO insertion, gives a usual η³-allyl-alkoxycarbonylated compound, gh⁵-C₅H₅(CO)₂Mo-η₃CH₂C(COOCH₃)CHCCCH₃ (IIa). The second reaction needs propargyl bromide as catalyst. It is a 1,5-methanol addition on the unsaturated η³-allyl ligand to give the new complex η⁵-C₅H₅(CO)₂Mo-η³-CH₃OCH₂C(COOCH₃)CHCCHCH₃ (IIIa). The synthesis of the two unstable cationic intermediates and their reactions with methoxide yielding the same addition products have been achieved and have confirmed the mechanism postulated. With the iron analogue (η⁵-C₅H₅)(CO)₂FeCH₂CCCCCH₃ (Ib), direct addition of methanoi is not possible, but the same reactions are obtained by protonation followed by methoxide addition to give complexes IIb and IIIb. In this case, the more stable cationic intermediates IVb and Vb can be fully characterised.     

Reduktive CC-kupplung von zwei isocyanid-liganden an Mo(II)- und W(II)-zentren,eine reaktionssequenz über isocyanid- und aminocarbin-komplexe von Mo(0) und W(0)

The octahedral alkylisocyanide complexes M(RNC)₆ and alkylisocyanide-substituted aminocarbyne complexes [(RNC)₅MCN(Et)R]BF₄ (M = Mo, W; R = Et, ^tBu) have been found to be key intermediates in the reductive coupling of two isocyanide ligands to a complexed alkyne. The crucial step in the reaction sequence leading from the seven-coordinate starting materials [M(RNC)₆Br]Br to the bis(amino)acetylene products [I(RNC)₄M[η²-R(Et)NCCN(H)R]]BF₄ and [I(RNC)₄M[η²-R(H)NCCN(H)R]]I involves an aminocarbyne-isocyanide coupling reaction induced by HI. The composition and structure of the intermediates and the products have been fully characterized.     

Reactions of diphosphineplatinum(II) oxalate complexes with phenylacetylene. Formation of phenylalkynylplatinum complexes

[Pt(C₂O₄)(dppe)] reacts thermally with PhCCH to produce [Pt(CCPh)₂(dppe)], which has been prepared by alternative routes. Similar treatment of [Pt(C₂O₄)(dppm)] initially produces [Pt(CCPh)₂(dppm)], which rearranges to give cis,cis-[Pt₂(CCPh)₄(μ-dppm)₂]. Reaction of [PtCl₂(dppm)] with PhCCH/KOH/18-crown-6, or with (PhCC)SnMe₃, gives [Pt(CCPh)₂(dppm)], which may be converted to the cis,cis-dimer by addition of oxalic acid. Ultraviolet irradiation or refluxing with a trace amount of dppm converts [Pt(CCPh)₂(dppm)] to trans,trans-[Pt₂(CCPh)₄(μ-dppm)₂], but the cis,cis-dimer is stable under these conditions. [Pt(C₂O₄)L₂] (L = PPh₃, PEt₃) complexes also react thermally with PhCCH to yield [Pt(CCPh)₂L₂] species.     

Synthesis of mononuclear and oligomeric ruthenium(II) acetylides

The complexes trans-[Ru(PMe₃)₄(CCPh)₂] and trans-[Ru(PMe₃)₄(CCC₆H₄C₆H₄CCSnMe₃)₂] have been prepared from the reaction between trans-[Ru(PMe₃)₄Cl₂] and an excess of either Me₃SnCCPh or Me₃SnCCRCCSnMe₃ (R = p-C₆H₄C₆H₄), respectively. However, if only one equivalent of the latter reagent is used the rod-like polymeric species trans-[-Ru(PMe₃)₄CCRCC-]_n can be isolated.     

Carbonyl(cyclopentadienyl)(trimethylphosphin)tolylcarbin-komplexe von Molybdän und Wolfram

Special reaction conditions enable dicarbonyl(η⁵-cyclopentadienyl)tolylcarbyne complexes of molybdenum and tungsten to react with trimethylphosphine by the replacement of one carbonyl ligand to give Cp(CO)(PMe₃WC-Tol (M = Mo, W). The preparation and spectroscopic data of these complexes as well as structural parameters of the tungsten complex are reported.     

The gas-phase molecular structure of silyl chloroacetylene,determined by electron diffraction

The molecular structure of SiH₃CCCl in the gas phase has been investigated using electron diffraction. Mean amplitudes of vibration and perpendicular amplitude correction factors calculated from spectroscopic data enabled refinement of both r_a and r_α structures to be carried out. The r_α refinement leads to a linear skeleton, with r_α parameters: r(Si-C) 181.2(5) pm, r(CC) 123.4(6) pm, r(C-Cl) 162.0(5) pm, r(Si-H) 148.8(12) pm, ∠HSiC 109.4(20)°. The r_a structure shows an apparent angle in the skeleton of 172(3)° (∠CCCl) owing to shrinkage.