Detection, determination and identification of allenes and ketenes

Munson, James W.

doi:10.1002/9780470771600.ch5

Cited by 10 publications

(4 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The cleavage of the Rh−C σ-bond in 7 by an equimolar amount of acetic acid in benzene proceeds smoothly and gives, besides the acetatorhodium(I) complex 9 , selectively the new vinylallene 8 (see Scheme ). A characteristic feature of the 13 C NMR spectrum of 8 is the low-field signal at δ 210.2 for the central C C C carbon atom, the position of which is typical for organic allenes …”

Section: Resultsmentioning

confidence: 99%

Unusual Pathways for Metal-Assisted C−C and C−P Coupling Reactions Using Allenylidenerhodium Complexes as Precursors

et al. 2002

View full text Add to dashboard Cite

The rhodium allenylidenes trans-[RhCl[[double bond]C[double bond]C[double bond]C(Ph)R](PiPr(3))(2)] [R = Ph (1), p-Tol (2)] react with NaC(5)H(5) to give the half-sandwich type complexes [(eta(5)-C(5)H(5))Rh[[double bond]C[double bond]C[double bond]C(Ph)R](PiPr(3))] (3, 4). The reaction of 1 with the Grignard reagent CH(2)[double bond]CHMgBr affords the eta(3)-pentatrienyl compound [Rh(eta(3)-CH(2)CHC[double bond]C[double bond]CPh(2))(PiPr(3))(2)] (6), which in the presence of CO rearranges to the eta(1)-pentatrienyl derivative trans-[Rh[eta(1)-C(CH[double bond]CH(2))[double bond]C[double bond]CPh(2)](CO)(PiPr(3))(2)] (7). Treatment of 7 with acetic acid generates the vinylallene CH(2)[double bond]CH[bond]CH[double bond]=C=CPh(2) (8). Compounds 1 and 2 react with HCl to give the five-coordinate allenylrhodium(III) complexes [RhCl(2)[CH[double bond]C[double bond]C(Ph)R](PiPr(3))(2)] (10, 11). An unusual [C(3) + C(2) + P] coupling process takes place upon treatment of 1 with terminal alkynes HC[triple bond]CR', leading to the formation of the eta(3)-allylic compounds [RhCl[eta(3)-anti-CH(PiPr(3))C(R')C[double bond]C[double bond]CPh(2)](PiPr(3))] [R' = Ph (12), p-Tol (13), SiMe(3) (14)]. From 12 and RMgBr the corresponding phenyl and vinyl rhodium(I) derivatives 15 and 16 have been obtained. The previously unknown unsaturated ylide iPr(3)PCHC(Ph)[double bond]C[double bond]C[double bond]CPh(2) (17) was generated from 12 and CO. A [C(3) + P] coupling process occurs on treatment of the rhodium allenylidenes 1, 2, and trans-[RhCl[[double bond]C[double bond]C[double bond]C(p-Anis)(2)](PiPr(3))(2)] (20) with either Cl(2) or PhICl(2), affording the ylide-rhodium(III) complexes [RhCl(3)[C(PiPr(3))C[double bond]C(R)R'](PiPr(3))] (21-23). The butatrienerhodium(I) compounds trans-[RhCl[eta(2)-H(2)C[double bond]C[double bond]C[double bond]C(R)R'](PiPr(3))(2)] (28-31) were prepared from 1, 20, and trans-[RhCl[[double bond]C[double bond]C[double bond]C(Ph)R](PiPr(3))(2)] [R = CF(3) (26), tBu (27)] and diazomethane; with the exception of 30 (R = CF(3), R' = Ph), they thermally rearrange to the isomers trans-[RhCl[eta(2)-H(2)C[double bond]C[double bond]C[double bond]C(R)R'](PiPr(3))(2)] (32, 33, and syn/anti-34). The new 1,1-disubstituted butatriene H(2)C[double bond]C[double bond]C[double bond]C(tBu)Ph (35) was generated either from 31 or 34 and CO. The iodo derivatives trans-[RhI(eta(2)-H(2)C[double bond]C[double bond]C[double bond]CR(2))(PiPr(3))(2)] [R = Ph (38), p-Anis (39)] were obtained by an unusual route from 1 or 20 and CH(3)I in the presence of KI. While the hydrogenation of 1 and 26 leads to the allenerhodium(I) complexes trans-[RhCl[eta(2)-H(2)C[double bond]C[double bond]C(Ph)R](PiPr(3))(2)] (40, 41), the thermolysis of 1 and 20 produces the rhodium(I) hexapentaenes trans-[RhCl(eta(2)-R(2)C[double bond]C[double bond]C[double bond]C[double bond]C[double bond]CR(2))(PiPr(3))(2)] (44, 45) via C-C coupling. The molecular structures of 3, 7, 12, 21, and 28 have been determined by X-ray crystallography.

show abstract

Section: Resultsmentioning

confidence: 99%

Unusual Pathways for Metal-Assisted C−C and C−P Coupling Reactions Using Allenylidenerhodium Complexes as Precursors

et al. 2002

View full text Add to dashboard Cite

show abstract

“…Under optimized conditions, 5a was obtained, while 6a was obtained in a low yield under conditions of lower temperature or shorter reaction times (Table , entries 2, 3). The spectra of 6a was typical of a terminal allene .…”

Section: Resultsmentioning

confidence: 99%

Reaction of Allenyl Selenoketene, Generated by [3,3] Sigmatropic Rearrangement, with Amines

et al. 2001

View full text Add to dashboard Cite

Many syntheses of heterocyclic compounds containing selenium have been extensively investigated because of their interesting reactivities 1 and potential pharmaceutical significance. 2 We are interested in the synthesis of novel heterocyclic compounds containing selenium. 3 We found a new evidence for allenyl selenoketene formation via a [3,3] sigmatropic rearrangement by trapping with primary amines and its cyclization by new pathway. To the best of our knowledge, though there are examples of a ketene-allene cycloaddition in the literature, 4 a selenoketene-allene cycloaddition has not been reported. 5 Reactions with various kinds of secondary amines also were investigated. We describe here the reaction of 2-pentynyl phenylethynyl selenide with primary and secondary amines.

show abstract

“…From the point of view of the local molecular symmetry and of the n-π* orbital origin of the lowest electronic transition, the ketene and diazo (diazoalkane) groups are analogues of the carbonyl group, investigations of chiroptical and conformational properties of which are a cornerstone of modern stereochemistry. , Nevertheless, this aspect of ketenes and diazoalkanes has not been studied so far. To the best of our knowledge, there is no published CD spectrum of a compound with an isolated ketene or diazo chromophore …”

Section: Introductionmentioning

confidence: 99%

Chiroptical Properties of the Ketene and Diazo Chromophores. 1. Conformation and Optical Activity of 1-Alken-1-ones and 1-Diazoalkanes vs Aldehydes

et al. 1998

View full text Add to dashboard Cite

Ab initio methods have been employed to study the conformational behavior and chiroptical properties of acyclic, structurally related aldehydes, ketenes, and diazoalkanes of the type MeCHRCH=XY. The study involved aldehydes 1, 4, and 7 (XY = O, R = H, Me, Et, correspondingly), ketenes (1-alken-1-ones) 2, 5, and 8 (XY = CO, R = H, Me, Et), and 1-diazoalkanes 3, 6, and 9 (XY = NN, R = H, Me, Et). Geometries were optimized at the B3LYP/6-31G level, stationary points were characterized by vibrational frequency analysis, and final energies of 7-9 were obtained at the B3LYP/6-311+G//B3LYP/6-31G level. The chiroptical properties were calculated by the CIS/6-31+G method. It was found that rotational barriers of the functional group (CHXY) about the CC bond are lowered in the following order: aldehydes (1.5-2.1 kcal mol(-1)) > ketenes (1.3-1.6) > diazoalkanes (0.5-0.7). A conformer with the C=X bond eclipsed by an alpha-hydrogen is the global minimum of the ketenes and diazoalkanes, unlike the aldehydes where eclipsing by an alpha-alkyl group is preferred over a hydrogen. In all three classes of compounds, the optical rotational strength of the n-pi transition is greatest for conformers with the dihedral angle, CCCX, in the range 80-100 degrees. Within this range, the signs of the n-pi rotational strengths for the ketenes and diazoalkanes are opposite to ones for the aldehydes. As a whole, the torsional dependencies of the n-pi rotational strength of the ketene and diazo chromophores can be explained within the framework of a model of "through-bond" perturbation. CD spectra of (S)-alpha-methyl-substituted butanal (7), 1-penten-1-one (8), and 1-diazobutane (9) were obtained experimentally. The calculated chiroptical properties of equilibrium mixtures of conformers of compounds 7-9 are in agreement with experimental data.

show abstract

Detection, determination and identification of allenes and ketenes

Cited by 10 publications

References 8 publications

Unusual Pathways for Metal-Assisted C−C and C−P Coupling Reactions Using Allenylidenerhodium Complexes as Precursors

Unusual Pathways for Metal-Assisted C−C and C−P Coupling Reactions Using Allenylidenerhodium Complexes as Precursors

Reaction of Allenyl Selenoketene, Generated by [3,3] Sigmatropic Rearrangement, with Amines

Chiroptical Properties of the Ketene and Diazo Chromophores. 1. Conformation and Optical Activity of 1-Alken-1-ones and 1-Diazoalkanes vs Aldehydes

Contact Info

Product

Resources

About