Five- and Six-Membered Unsaturated Rings

1 Five- and Six-Membered Unsaturated Rings Among the known phosphinine complexes are 

Some of these ring compounds will form jr-type complexes, for example, (8.304b,e) which are similar to those formed by benzene (8.304c) cyclopentadiene (8.304a) and pyridine (8.304d), in which the entire ring is involved in bonding to the metal. 

In the case of 2,4,6 triphenylphosphinine, complexes are formed in which either the lone-pair electrons on the P atom are solely involved in o-bonding, or the whole 6-n electron system of the aromatic-type heterocyclic ring is involved (8.305) [2,3]. 

Both these schemes are involved in (8.306a). Triphosphinine complexes are also known (8.306b) as well as diphosphete (8.306c) [4,5] and triphosphole complexes (8.306d,e) [6]. 

Various biphosphinine complexes such as (8.307a,b) are known [7-9], but complexes of the P analogue of cyclohexapyridyl (8.338g) have not yet been reported. 

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Ultraviolet photoelectron spectroscopy combined with ab initio calculations of the five- and six-membered unsaturated rings containing phosphorus and arsenic have been studied <1995JST57>. Assigning the spectra, no defect of Koopmans theorem has been found in the low-ionization-energy region. Reorganization and correlation effects should be comparable and be considered free from any defects of Koopmans theorem. 

For a set of 329 five- and six-membered unsaturated ring bases Zhang found... 

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