The structure and dynamic behaviour in solution of the trihydridodienerhenium complexes (Ph3P)2(η-1,3-diene)ReH3

The structure and fluxionality of the trihydridodiene complexes (Ph₃P)₂(η-1,3-<di-ene)ReH₃ have been studied by NMR spectroscopy (η-1-3-diene = buta-1,3-diene, 2-methylbuta-1,3-diene, 2,3-dimethylbuta-1,3-diene, cyclohexa-1,3-diene, penta-1,3-diene, hexa-1,3-diene and hexa-2,4-diene). Several rearrangement processes have been observed; they are, in order of increasing temperature: (a) ligand interchange; (b) reversible migration of a hydride ligand on to the diene ligand, leading to η-allyl species and, in the case of the cyclohexadiene trihydride, degenerate isomerisation of the cyclohexadiene moiety; and (c), in the case of the pentadiene and hexadiene derivatives, isomerisation of the diene ligand.     

Cross-coupling of E,E-1,4-diiodobuta-1,3-diene with nucleophiles catalyzed by Pd or Ni complexes: a new route to functionalized dienes

E,E-1,4-Diiodobuta-1,3-diene can enter into cross-coupling reactions with carbon- or other element-centered nucleophiles in the presence of Pd or Ni complexes as catalysts. Convenient procedures were developed for the stereoselective synthesis of E,E-1,4-dialkenylbuta-1,3-dienes, dienyl-1,4-bisphosphonates, E,E-1,4-bis(diphenylphosphino)buta-1,3-diene, E,E-1,4-diphenylbuta-1,3-diene, and E,E-1,4-bis(thiophenyl)buta-1,3-diene.     

Two-step regioselective synthesis of 1,2-difluorobenzenes from chlorotrifluoroethylene and buta-l,3-dienes

Russian Chemical Bulletin - The gas-phase copyrolysis of chlorotrifluoroethylene with buta-1,3-diene, penta-1,3-diene, or isoprene in a flow reactor at 440–480°C gave...     

The reactivities of diarylbutadienes towards the benzoyloxy radical: the cases of 1-(1′-naphthyl)-4-phenylbuta-l,3-diene and 1,4-Di (1′-Naphthyl)buta-1,3-Diene

A study has been made of end-groups in poly(methyl methacrylate) prepared using benzoyl peroxide as initiator and either 1-(1′-naphthyl)4-phenylbuta-1,3-diene or 1,4-di(1′-naphthyl)buta-1,3-diene as additive. At 60°C, these dienes are 500–600 times as effective as methyl methacrylate in capturing benzoyloxy radicals and more than twice as effective as 1,4-diphenylbuta-1,3-diene.     

Substrate dependence in aqueous Diels-Alder reactions of cyclohexadiene derivatives with 1,4-benzoquinone

A reactivity difference based on the position of substituents on cyclohexa-1,3- diene was observed for the title reaction. The effect of water as solvent was more distinct for 1-methyl-4-isopropylcyclohexa-1,3-diene than for 2-methyl-5-isopropylcyclohexa- 1,3-diene or non-substituted cyclohexa-1,3-diene. The effect of NaCl (salting-out) and guanidium chloride (salting-in) was also large for 1-methyl-4-isopropylcyclohexa-1,3- diene.     

Über den einfluss von chlor-substituenten auf die bildungstendenz und bindungsverhältnisse des tricarbonyl(buta-1,3-dien)eisen: Tricarbonyl(2,3-dichlorbuta-1,3-dien)eisen und tricarbonyl(2-chlorbuta-1,3-dien)eisen

Frequencies of carbonyl stretching vibrations and relative yields in syntheses of tricarbonyl(2,3-dichlorobuta-1,3-diene)iron and tricarbonyl(2-chlorobuta-1,3-diene)iron are discussed with respect to possible steric effects of chloro-substituents on the formation of tricarbonyl(hexachlorobuta-1,3-diene)iron.     

Acetylation of dicarbonyl(η-cyclohexadiene)triphenyl- phosphineiron

Friedel-Crafts acetylation of dicarbonyl(η⁴-cyclohexadiene)triphenylphos-phineiron is accomplished in 96% yield under mild conditions to give dicarbonyl-(η⁴-5-endo-acetylcyclohexa-1,3-diene)triphenylphosphineiron. The structure of the product was established by direct comparison with the epimeric complex dicarbonyl(η⁴-5-exo-acetylcyclohexa-1,3-diene)triphenylphosphineiron produced by reaction of methyl magnesium iodide with dicarbonyl(η⁴-5-exo-cyanocyclohexa-1,3-diene)triphenylphosphineiron.     

Polyfluoro-compounds based on the cycloheptane ring system. Part 7. Ethoxypolyfluorocycloheptenes and polyfluorocycloheptenones

Dodecafluorocycloheptene and ethanolic potassium hydroxide afforded 1- ethoxyundecafluorocycloheptene which at 410°C decomposed to decafluorocyclohept-2-enone. Decafluorohepta-l,3-diene likewise gave mainly 1-ethoxynona- fluoro-, together with some 1,4-diethoxyoctafluoro-cyclohepta-1,3-diene. The 1-ethoxy-1,3-diene was photoisomerised to 1-ethoxynonafluorobicyclo- (3,2,0)hept-6-ene (proving its structure), and was decomposed on pyrolysis at 430°C to give a complex mixture, from which octafluorocyclohepta-2,4- dienone was isolated.     

Skeletal isomerism within 1,3-disilabicyclo[1.1.0]butane and 2,3-disilabuta-1,3-diene derivatives

A bis-adamantane-spiro-fused 1,3-bis(triisopropylsilyl)-1,3-disilabicyclo[1.1.0]butane equilibrates with the corresponding 2,3-bis(triisopropylsilyl)-1,3-disilabuta-1,3-diene with a ratio of 1:19. The 1,3-disilabuta-1,3-diene was fully characterized by a combination of multinuclear NMR and UV-VIS spectroscopies, elemental analysis, and single-crystal X-ray diffraction analysis.     

Diels-Alder reaction of eight-membered cyclic siloxydienes

Eight-membered cyclic siloxydienes, 2-(tert-butyldimethylsiloxy)-1-methyl-5-oxacycloocta-1,3-diene and 2-(tert-butyldimethylsiloxy)-5-oxacycloocta-1,3-diene, were prepared from δ-valerolactone, and their Diels-Alder reactions with various dienophiles are reported.     

Oxidative trifluoroacetamidation of (1<Emphasis Type="Italic">E</Emphasis>,3<Emphasis Type="Italic">E</Emphasis>)-1,4-diphenylbuta-1,3-diene and 1,1,4,4-tetraphenylbuta-1,3-diene

Reactions of trifluoroacetamide with (1E,3E)-1,4-diphenylbuta-1,3-diene and 1,1,4,4-tetraphenylbuta-1,3-diene in the oxidative system t-BuOCl–NaI have been studied. The reaction with (1E,3E)-1,4-diphenylbuta-1,3-diene afforded three products, N,N′-(phenylmethylene)bis(trifluoroacetamide), 3-chloro-4-iodo- 2,5-diphenyl-1-(trifluoroacetyl)pyrrolidine, and trifluoro-N-[(3E)-2-hydroxy-1,4-diphenylbut-3-en-1-yl]acetamide, with a high overall yield. 1,1,4,4-Tetraphenylbuta-1,3-diene failed to react with trifluoroacetamide.     

Ab initio studies of

Ab initio calculations of the [1,5]-H shift in (3Z)-penta-1,3-diene and other substituted pentadienes and heteroanalogues using the hybrid density functional Becke3LYP with the 6-31G basis set are presented. Electron-donating substituents, such as methoxy in (3Z)-3-methoxypenta-1,3-diene 1, or heteroatoms such as a nitrogen atom in (Z)-ethylidenevinylamine 2, (1Z)-buta-1,3-dienylamine 3, (2Z)-but-2-enylideneamine 4, (Z)-allylidenemethylamine 5, and methylene-(Z)-propenylamine 6 are introduced. The electron-withdrawing fluoride is substituted for the hydrogen atoms in (3Z)-3-fluoropenta-1,3-diene 7, (3Z)-2,4-difluoropenta-1,3-diene 8, (3Z)-1,1',2,3,4,5,5'-heptafluoropenta- 1,3-diene 10, (1E,3E)-1,3,5-trifluoropenta-1,3-diene 11, and (1Z,3E)-1,3,5- trifluoropenta-1,3-diene 13. A detailed analysis of the geometries, energies, and electronic characteristics of the sigmatropic transposition compared to those of the unsubstituted case provides insights into substituent effects of this prototype of pericyclic reaction. The inductive and mesomeric effects of heteroatoms or heterosubstituents are of a great importance and in a continuous balance in the energetics of the transformation. Sterics can also play an important role due to the geometrical constraints of the reaction. As a general trend, decreasing the electron density of the phi system destabilizes the aromatic transition structure and increases the activation energy, and vice versa.     

Theoretical study of reaction pathways to borazine

Four reaction pathways from diborane and ammonia to borazine, (HBNH)3, have been studied computationally at the density functional level (B3LYP/6-311+G(2d,p)//B3LYP/6-31G(d)). The cycloaddition of H2BNH2 to 1,3-diaza-2,4-diborabuta-1,3-diene and subsequent elimination of two molecules of H2 was found to be the lowest-energy pathway to (HBNH)3. In the other pathways, the formation and conversion of the intermediates 1,3,5-triaza-2,4,6-triborahexatriene, cyclotriborazane, and 1,3,5-triaza-2,4,6-triborahexa-1,5-diene into (HBNH)3 were investigated. The formation of 1,3-diaza-2,4-diborabuta-1,3-diene and, subsequently, the formation and electrocyclization of 1,3,5-triaza-2,4,6-triborahexatriene and the cycloaddition of H2BNH2 to 1,3-diaza-2,4-diborabuta-1,3-diene are predicted to be the kinetically favored pathways to (HBNH)3 in the gas phase. At low concentrations of 1,3-diaza-2,4-diborabutene, high concentrations of H2BNH2, and a temperature of 298.15 K, the formation of the polyolefins H3BNH2(H2BNH2)nNHBH2 (n=1,2) is predicted to be competitive with the formation of 1,3-diaza-2,4-diborabuta-1,3-diene.     

Low-lying excited states and primary photoproducts of [Os3(CO)10(s-cis-L)] (L=cyclohexa-1,3-diene, buta-1,3-diene)] clusters studied by picosecond time-resolved UV/Vis and IR spectroscopy and by density functional theory

Combined picosecond transient absorption and time-resolved infrared studies were performed, aimed at characterising low-lying excited states of the cluster [Os(3)(CO)(10)(s-cis-L)] (L=cyclohexa-1,3-diene, 1) and monitoring the formation of its photoproducts. Theoretical (DFT and TD-DFT) calculations on the closely related cluster with L=buta-1,3-diene (2') have revealed that the low-lying electronic transitions of these [Os(3)(CO)(10)(s-cis-1,3-diene)] clusters have a predominant sigma(core)pi*(CO) character. From the lowest sigmapi* excited state, cluster 1 undergoes fast Os-Os(1,3-diene) bond cleavage (tau=3.3 ps) resulting in the formation of a coordinatively unsaturated primary photoproduct (1 a) with a single CO bridge. A new insight into the structure of the transient has been obtained by DFT calculations. The cleaved Os-Os(1,3-diene) bond is bridged by the donor 1,3-diene ligand, compensating for the electron deficiency at the neighbouring Os centre. Because of the unequal distribution of the electron density in transient 1 a, a second CO bridge is formed in 20 ps in the photoproduct [Os(3)(CO)(8)(micro-CO)(2)(cyclohexa-1,3-diene)] (1 b). The latter compound, absorbing strongly around 630 nm, mainly regenerates the parent cluster with a lifetime of about 100 ns in hexane. Its structure, as suggested by the DFT calculations, again contains the 1,3-diene ligand coordinated in a bridging fashion. Photoproduct 1 b can therefore be assigned as a high-energy coordination isomer of the parent cluster with all Os-Os bonds bridged.     

Selenosulfonation of 1,3-dienes: One-pot synthesis of 2-(phenylsulfonyl)-1,3-dienes

A one-pot procedure for the transformation of a 1,3-diene into the corresponding 2-(phenylsulfonyl)-1,3-diene was developed. The reaction involves a 1,2-selenosulfonation-oxidation sequence.     

13C,13C coupling constants of conjugated dienes

One bond ¹³C,¹³C- and ¹³C,¹H-coupling constants have been measured for some 1,2-dimethylene-cycloalkanes, as well as for 2,3-dimethylbuta-1,3-diene and methylenecyclobutane. The results for 2,3-dimethylbuta-1,3-diene confirm the findings for buta-1,3-diene, i.e. that J(C-1, C-2) is smaller for the diene than for the correspondingly substituted monoene. No differences have been found between the ¹J(CC) exocyclic coupling constants of the dimethylene and monomethylene cycloalkanes.     

Die Pyrolyse von (+)-Verbenen

The pyrolysis of verbenene has been found to give rise to 39% of isobutenylcyclohexa-1,3-diene ( 3 ), 29% of o-mentha-1 (7),5,8-triene ( 2 ) together with two double bond-isomers ( 4 and 5 ) of the cyclohexadiene ( 3 ). The structures were proved by catalytic reduction to the saturated hydrocarbons, and isobutenylcyclohexa-1,3-diene was synthesized from 2,3-dihydrobenzaldehyde.     

Reaktion von konjugierten doppelbindungsystemen mit dihalogen(diorganylamino)boranen und Na/K-legierung

The reaction of 2,3-dimethylbuta-1,3-diene or 2-methylbuta-1,3-diene with Na/K-alloy and dichloro(diisopropylamino)borane in n-hexane yielded the 1-bora-cyclopent-3-enes, A and II, and 1-bora-cyclonona-1,3-diene, I, respectively. Cycloocta-3,7-diene reacts with dibalogeno(diorganylamino)boranes and Na/K-alloy in n-hexane to yield the 9-bora-bicyclo[4,2,1]non-7-enes III, V, VI and the 1,6-bis(diorganylaminofluoroboryl)-cyclooct-7-enes IV and VH. When 1,2-dimethoxyethane was the solvent, only the dimeric cyclooctene, C, was obtained. The compounds were characterized by elemental analyses and spectroscopy [MS; NMR (¹H, ¹¹B, ¹³C, ¹⁹F)]. An X-ray analysis is presented for I, MNDO-calculations have been carried out for III and III.     

Effect of basic set quality and electron correlation on the scale factors of a harmonic force field

The completely optimized structure and harmonic force field of s-trans-buta-1,3-diene are reported at the MP2/6-31G and MP2/6-31G* levels of computation. Sets of empirical scale factors for the calculated force fields are derived and compared with the corresponding values computed at the RHF/4-31G and RHF/6-31G levels. Changes in the scale factors for this series of force fields are discussed. The vibrational frequencies are also reported for thirteen isotopomers of s-trans-buta-1,3-diene using the MP2/6-31G* force field. Some characteristics of the gauche and cis forms of buta-1,3-diene are also given.     

Substituent Effects on Fe+-Mediated [4+2] Cycloadditions in the Gas Phase

The Fe⁺-mediated [4+2] cycloaddition of dienes with alkynes has been examined by four-sector ion-beam and ion cyclotron resonance mass spectrometry. Prospects and limitations of this reaction were evaluated by investigating several Me-substituted ligands. Me Substitution at C(2) and C(3) of the diene, i.e., 2-methylbuta-1,3-diene, 2,3-dimethylbuta-1,3-diene, hardly disturbs the cycloaddition. Similarly, variation of the alkyne by use of propyne and but-2-yne does not affect the [4+2] cycloaddition step, but allows for H/D exchange processes prior to cyclization. In contrast, Me substituents in the terminal positions of the diene moiety (e.g., penta-1,3-diene, liexa-2,4-diene) induce side reactions, namely double-bond migration followed by [3+2] and [5+2] cycloadditions, up to almost complete suppression of the [4+2] cycloaddition for 2,4-dimethylhexa-2,4-diene. Similarly, alkynes with larger alkyl substituents (pent-1-yne, 3,3-dimethylbut-1-yne) suppress the [4 + 2] cycloaddition route. Stereochemical effects have been observed for the (E)- and (Z)-penta-1,3-diene ligands as well as for (E,E)- and (E,Z)-hexa-2,4-diene. A mechanistic explanation for the different behavior of the stereoisomers in the cyclization reaction is developed. Further, the regiochemical aspects operative in the systems ethoxyacetylene/pentadiene/Fe⁺ and ethoxyacetylcne/isoprene/Fe⁺ indicate that substituents avoid proximity.