Phosphole spectrum

Figure 8 Comparison of experimental and predicted Raman spectrum for thiophene-phosphole oligomer. Reprinted from Casado et al. [61], Figure 4, with permission from Elsevier. Copyright (2005).

Photoelectron.—n-Orbital energies appear to be unsuitable to discern the aromatic nature of phospholes (120) due to combined nn and ttn interactions. It is concluded that n conjugative and P-Cw hyperconjugative interactions stabilize the phos-phole system relative to the interrupted cw-butadiene and phosphorus subunits, and that the p.e. spectrum can be interpreted in favour of an aromatic phosphole ring.143 Other workers have discussed144 and reviewed145 this aromaticity problem, and there has been a quantum-chemical study of the aromatic nature of phosphorus hetero-cycles.144 The p.e. spectrum of the ylide (121) contains peaks at 6.19, 8.32, and... 

Fig. 38. The agreement between simulated and experimental CD spectra for the PD complex was very good after a red-shift of 0.25 eV was applied to the excitation energies. Analysis of the computed spectrum showed the intense bands to originate predominately from n-to-n transitions within an extended n framework of the phosp-hole-helicene ligands. Unlike initially expected, the various bands in the CD spectrum cannot be assigned to transitions centered separately on the helicene and phosphole moieties, respectively. The experimentally measured molar rotation of the Pd complex was 23.1 103 deg cm2 dmol 1 2% in dichloromethane. For an analogous Cu complex it was 13.1 103 2%, a staggering 104 deg cm2 dmol 1 lower.

Fig. 38 Top Structure of the Pd-bis(phosphole-helicene) complex and a comparison of the BHLYP/SV(P) computed and experimental CD spectra. Bottom Two-dimensional structure of the phosphole-helicene ligand as well as the experimental UV-Vis vs the Boltzmann averaged spectrum computed at the BHLYP/SV(P) level of theory, red-shifted 0.25 eV. Data to prepare the plots were taken from [260]...

A phosphole is essentially a cyclopentadiene where one of the CH units is substituted by a phosphorus atom. It results a compound of the formula C H P with two conjugated C=C double bonds. The chemical shift range is shown in Table 5.11, and can be found around [Pg.65]

Little use has been made of the IR spectra of phospholes. A few reports exist on such spectral measurements, but primarily they have been made for the purpose of characterizing functional groups on the ring. From the spectrum reported for methyl l-methylphosphole-3-carboxylate (vch3110, 1535, 1250 and 1186, unassigned at 1075, 1062, 888, 793, 740, 700 cm ... 

C (10 mmHg). In CeD, the PNMR shift was <5 +159, entirely consistent with the presence of a C=P double bond, and this was confirmed by the C NMR spectrum, which showed phosphorus to be directly coupled to an sp carbon (<5 194.7, Jfc 68.7 Hz) and to an sp carbon 37.1, /pc 51.4 Hz). The 27f-phospholes where the 2-phenyl was replaced by 2,4,6-trimethylphenyl, 2,4,6-trimethoxyphenyl, and methyl were also made in good yield by this method. These 2 -phospholes are thermally stable but very sensitive to water and were hydrated on attempted chromatography on Kieselgel to form the phospholanone (204). Other reactions observed (Scheme 46) included a Diels-Alder cycloaddition with methyl propiolate (giving (205)), and a 1,3-dipolar cycloaddition with mesityl nitrile oxide that formed (206). 

XXX) has a UV spectrum similar to the corresponding phosphole and to the silicon analog (XXXI) (84), indicating little aromatic character. Brown has suggested that conjugation could occur in the arsole (493). 

At this stage, only 151c bears a helicene moiety that is configurationally stable. The last step is the synthesis of the phosphole derivatives 152a—e in 27—73% yields (Scheme 40). In solution, a rapid inversion of conf yiration is observed for phospholes 152a,b,d, while for 152e, two diastereomers are observed in the P-NMR spectrum. 

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