Phospholes electronic properties

Compared with organic molecules, metal complexes offer a larger variety of molecular structures and a diversity of electronic properties [13]. Since it is well known that phospholes and pyridines behave as classical two-electron donors toward transition metals [13, 14], we have explored the coordination behavior of 2-pyridyl-substituted phospholes with the aim of obtaining complexes exhibiting interesting physical properties. Moreover, original structures can be expected since these heteroditopic P,N-ligands possess two coordination centers with different stereo-electronic properties. The performances of such complexes have been evaluated as catalysts as well as new materials for optoelectronics. 

One key property of pyridylphosphole ligands is their heteroditopic nature. They possess two coordination centers with different stereo-electronic properties, which, in accordance with Pearson s antisymbiotic effect [42a], can control the orientation of a second chelating ligand in the coordination sphere of a square-planar d8-metal center [42b]. This property has been exploited in order to control the in-plane parallel arrangement of ID-dipolar chromophores [42d]. Phospholes... 

Dibenzophospholes A and dithienophospholes B and C (Fig. 4.7) do not display the typical electronic properties and reactivity patterns of phospholes, since the dienic system is engaged in the delocalized benzene or thiophene sextet [7, 10a, 51]. In fact, these building blocks have to be regarded as nonflexible diaryl-phosphines or as P-bridged diphenyl or dithienyl moieties. 

The chemical behavior of phosphole confirms this conclusion at —100 °C it was characterized by NMR spectra, but at room temperature it isomerizes rapidly to 2H-phosphole which dimerizes to a tricyclic compound via a 1,5-sigma tropic H-shift and a [4- -2]-cycloaddition (04ACR9549). Synthetic efforts of Mathey resulted in a lithium-based pathway for obtaining oligophospholes, allowing the investigation of electronic properties of such promising compounds. 

The Zr polymers 201 are not just of intrinsic interest but they also permit chemical modification reactions in which the Zr atom is replaced.This allows for the introduction of diene, thiophene, phosphole, and aromatic functionalities, to yield novel vr-conjugated organic polymers 202-205 with controlled structures and electronic properties (Scheme 18). 

Hay, C., C. Fischmeister, M. Hissler, L. Toupet, and R. Reau. 2000. Electropolymerization of IT-conjugated oligomers containing phosphole cores and terminal thienyl moieties Optical and electronic properties. Angew Chem Int Ed Engl 345 1812-1815. 

Interest in functional ji-conjugated phosphole-based compounds of interest as the basis of electroluminescent and other devices has been the stimulus for a considerable volume of published work in the past year. Included among this is a series of papers on the synthesis and properties of 2,5-di(hetero)arylphospholes (207), the tuning of their electronic properties by P-functionalisation, and their... 

In fact, calculations have shown that phospholes with a planar P-atom would be more aromatic than pyrrole, due to the good 7i-donor ability of planar-P centers. However, this stabilization is not sufficient to overcome the high planarization barrier of the P-atom (35 kcal mol ), but is responsible for the reduced P-inversion barrier in phosphole (ca. 16 vs. 36 kcal mol for phospholanes) [67-69]. Low barrier inversion is another key property of phospholes since inversion at phosphorus can occur at room temperature. Together, these electronic properties (low aromatic character, a-n hyperconjugation) set phosphole apart from pyrrole and thiophene. In other words, this P-heterole has its own chemistry (synthetic routes, methods of functionalization, etc.) that cannot be predicted by simply extrapolating that of its aromatic S- and N-analogues [1-5, 32 0, 51-53, 70-72]. 

However, it is a potential drawback in our approach since the pathway of the 7t-system, and therefore the electronic property of the ligand, is altered on going from phosphole to phospholene subunits (Scheme 11.4). 

Lemau de Talance V, Hissler M, Zhang LZ, Karpati T, Nyulaszi L, Caras-Quintero D, Bauerle P, Reau R (2008) Synthesis, electronic properties and electropolymerisation of EDOT-capped sigma(3)-phospholes. Chem Commun 2200... 

Not only the absorption behaviour, but also all the physical properties of derivatives (32) are related to the nature of the 2,5-substitution pattern. For example, a blue-green emission is observed for di(2-pyridyl)phosphole (32b) whereas the emission of di(2-thienyl)phosphole (32a) is red-shifted (AAj,nj= 35 nm) [36]. Likewise, cyclic voltammetry (CV) revealed that derivative (32a), featuring electron-rich thienyl substituents, is more easily oxidised than compound (32b), which possesses electron-deficient pyridyl substituents [36]. 

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