Phospholes fused ring systems

In the case of the phosphindole system, a C-bromo P-oxide (256) may be generated as a precursor to the phosphole oxide, which is then reduced to the phosphole group by a silane <7ICJC530>. In this fused ring system, the phosphole oxide moiety is stable and does not undergo the rapid dimerization characteristic of most monocychc phospholes. The entire synthesis is shown in Scheme 76. 

Incorporation of other heteroatoms to phosphole-containing heteroarenes also leads to interesting molecular properties. One common example is the incorporation of thiophene units (Figure 12.10). These phospholes have high photoluminescence quantum yields due to their limited degrees of freedom from the rigid, fused ring system. Like many of the compounds discussed herein, these... 

Like phospholes, phosphinines can also be part of extended jr-systems. In a recent work, Mathey et al. have synthesized and characterized by X-ray crystallography a dithienophosphinine 103 (Scheme 55) [308], The electronic interaction between the fused rings has been shown on the orbitals and by the decreased NICS(l) value (from -10.8 ppm to -8.8 ppm) of the phosphinine ring. 

The influence of the heteroatom on the structure of a series of dinaphtho-fused five membered potentially aromatic ring systems (317), including the phosphorus and arsenic systems, has been studied by crystallographic techniques. A theoretical study has shown that the incorporation of two o, X -phosphorus atoms into the phosphole ring system decreases the ring strain and significantly lowers the inversion barrier about the phosphole pyramidal phosphorus. Pyramidalisation at phosphorus in phospholes has been shown to increase on... 

The parent phosphole ring can be fused to a number of other cyclic structures for many of these compounds the coordination number can be varied, but most of the known compounds are found in phosphole form, or as the oxide derivative. The ring systems that are the most common are shown below. By far the most widely studied is the dibenzo derivative, because it is easily synthesized and worked with. However, the system displays few properties of a phosphole and is more like a diphenylphosphine. This system is accorded abbreviated attention for current interest, a series of papers by Cornforth et al. starting in 1982 should be consulted <82JCS(p1)2289>. 

Interest in potentially aromatic heterocyclic systems has continued at a similar level to the previous year, with most work again relating to the chemistry of fused ring phospholes and phospholyl anions. Activity in the phosphirene area, however, has again been minimal, the only significant... 

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