ETS study of the negative ion states of t-butyl and trimethylsilyl derivatives of ethylene and benzene

Modelli, Alberto; Jones, Derek; Distefano, Giuseppe

doi:10.1016/0009-2614(82)83539-2

Cited by 108 publications

(101 citation statements)

References 16 publications

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“…The ET spectroscopy apparatus was in the format devised by Sanche and Schulz, [30] as has been described previously. [31] Microanalyses were performed by M-H-W Laboratories (Phoenix, AZ) and at the Centro de Investigaciones Químicas, Universidad Autó noma de Hidalgo (Pachuca, Hgo., Mexico). Analytical thin-layer chromatography was performed using E. Merck silica gel 60 F 254 coated plates (0.25 mm), and spots were visualized using long-and short-wavelength UV lamps.…”

Section: Resultsmentioning

confidence: 99%

Synthesis of New Captodative Alkenes: Alkyl 2-Aroyloxy Acrylates − Structure, and Reactivity in Diels−Alder Cycloadditions

et al. 2001

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Section: Resultsmentioning

confidence: 99%

Synthesis of New Captodative Alkenes: Alkyl 2-Aroyloxy Acrylates − Structure, and Reactivity in Diels−Alder Cycloadditions

et al. 2001

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“…The VAE of the Ł NC MOs of aliphatic isonitriles is higher than those of CO (1.5 eV) 30 and N 2 (1.89 eV), 31 being in the range 2.69-2.77 eV, similar to CH 3 NC (2.81 eV). 24 In aromatic isonitriles the out-of-plane Ł NC orbital mixes with the  Ł b 1 orbitals of the phenyl ring. This lowers the corresponding VAE considerably, i.e.…”

Section: Discussionmentioning

confidence: 99%

“…24 To enhance the visibility of the sharp resonance structures, the impact energy of the electron beam is modulated with a small a.c. voltage, and the derivative of the electron current transmitted through the gas sample is measured directly by a synchronous lock-in amplifier. The present spectra were obtained by using the apparatus in the 'high-rejection' mode 25 and are, therefore, related to the nearly total scattering cross-section.…”

Section: Methodsmentioning

confidence: 99%

“…The ET spectrum of 2,6-dimethylphenyl isonitrile (VI), where the degeneracy of the 24 ). The first resonance of the spectrum (0.73 eV) is associated with the a 2 component of the benzene LUMO (VAE D 1.12 eV in benzene 24 ), which possesses a node at the substituted carbon atom and is stabilized by the inductive electron-withdrawing effect of the NC substituent.…”

Section: Electron Transmission Spectramentioning

confidence: 99%

“…In contrast, the VAE of the Ł LUMO (largely localized at the benzene ring) is overestimated by 0.2-0.3 eV in 4-methoxyphenyl isonitrile and probably even more in 2,6-dimethylphenyl isonitrile. For the latter, this result is partly due to the fact that the calculations (both HF and B3LYP) predict a destabilizing effect (0.2-0.3 eV) of the methyl groups on the lowest ring Ł anion state (see Table 2, where the VOEs of phenyl isonitrile are also reported for comparison), whereas ETS data show that methyl substitution causes a slight (if any) stabilization of the lowest anion states of benzene 24 and pyridine. 33 Therefore, it seems reasonable to evaluate the first VAE of 2,6-dimethylphenyl isonitrile from the scaled VOE (0.2-0.3 eV) obtained for phenyl isonitrile.…”

Section: Electron Transmission Spectramentioning

confidence: 99%

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Donor–acceptor properties of isonitriles studied by photoelectron spectroscopy and electron transmission spectroscopy

2004

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Some alkyl and aryl isonitriles, considered as CO analogue sigma-donor and pi-acceptor ligands in transition metal chemistry, were studied by means of HeI photoelectron spectroscopy and electron transmission spectroscopy, in order to evaluate their donor-acceptor properties from the measured ionization energies (IE) and vertical electron attachment energies (VAE). The investigated molecules were 2-propyl, 1-butyl, tert-butyl, 1-pentyl, cyclohexyl, 2,6-dimethylphenyl, 4-methoxyphenyl and 4-chorophenyl isonitrile. By interpreting the spectra on the basis of literature data and quantum chemical calculations, the spectral features associated with the molecular orbitals mainly involved in coordination and back-donation were identified. The results show that the IE (10.62-10.95 eV) of the sigma electron pair (n(c)) responsible for the sigma-donor capability is substantially lower than that of CO. The VAEs of the empty pi* orbitals involved in the d/pi* back-donation indicate that aryl isonitriles are better acceptors (VAE <0.3 eV) than their aliphatic counterparts (VAE >2.7 eV). In the case of aryl derivatives, the pi-donor ability could also play some role in metal-ligand bonding (IE 8.74-9.34 eV). Isonitrile coordination characteristics are also compared with those of CO, N(2) and CH(3)CN.

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γ‐Silyl Group Effect in Hydroalumination and Carbolithiation of Propargylic Alcohols

Igawa

Tomooka

2005

Angewandte Chemie

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The hydrometalation reaction of an alkynyl group is a valuable process, not only for functionalized alkene synthesis but also for alkenyl metal preparations.[1] Among the numerous variants of this class of reaction, hydroalumination of propargylic alcohols is especially well utilized in many facets of organic synthesis owing to its promising chemo-and stereoselectivity [Eq. (1); L = ligand, E = electrophile]. [2,3] Herein, we report a noticeable accelerating effect of a gsilyl substituent on the hydroalumination reaction, an effect that can substantially enhance the synthetic utility of this classical transformation. By proper choice of the silyl group, highly group-selective functionalization in polyalkynyl alcohols A has been accomplished by overcoming the steric influences, to provide valuable multifunctionalized alcohols B through hydroalumination and also carbolithiation [Eq. (2)].We have found this unprecedented silyl effect during the course of our synthetic study of zaragozic acid A.[4] As one of the key steps in this total synthesis, we faced the problem of group-selective functionalization of intermediate 1, which has three alkynyl groups on C4 and C5 [Eq. (3); Bn = benzyl, TBDPS = tert-butyldiphenylsilyl, TBS = tert-butyldimethylsilyl, TMS = trimethylsilyl]. Surprisingly enough, hydroalumination of alcohol 1 with sodium bis(2-methoxyethoxy) aluminum hydride (Red-Al) provides vinylsilane 2 exclusively. [5] Our purpose for the total synthesis was achieved by this group-selective transformation; however, a question that immediately arose was why the reaction preferentially occurred at the alkyne substituted with the bulkier TBDPS group, rather than one substituted with the less bulky TMS group.[6] At an earlier stage, we suspected an influence of the multiple oxy functionalities on 1 to be the origin of the peculiar selectivity; these functionalities may exert chelation control on the aluminum reagent.[7] Thus, in order to eliminate this confusing factor, we examined a competitive hydroalumination in a series of simplified 1,1-bis(alkynyl) alcohols 3 bearing TBDPS and TMS groups at the g and g' positions (Table 1).The reaction of sec-alcohol 3 a (R = H) with Red-Al in toluene at 0 8C provides vinylsilane (E)-4 a (95 %) predominantly, along with a trace amount of (E)-5 a (3 %; TBDPS side/TMS side 97:3; Table 1, entry 1).[8] Similar selectivity was [a]

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ETS study of the negative ion states of t-butyl and trimethylsilyl derivatives of ethylene and benzene

Cited by 108 publications

References 16 publications

Synthesis of New Captodative Alkenes: Alkyl 2-Aroyloxy Acrylates − Structure, and Reactivity in Diels−Alder Cycloadditions

Synthesis of New Captodative Alkenes: Alkyl 2-Aroyloxy Acrylates − Structure, and Reactivity in Diels−Alder Cycloadditions

Donor–acceptor properties of isonitriles studied by photoelectron spectroscopy and electron transmission spectroscopy

γ‐Silyl Group Effect in Hydroalumination and Carbolithiation of Propargylic Alcohols

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