Phosphorus heterocycles, structure

Keywords Aromaticity, Delocalization, Phosphorus heterocycles, Structure... 

Silicon-phosphorus heterocyclic structures (rings, cages, polycyclic ladders) are also well investigated. ... 

Yamashita M (2007) Preparation, Structure, and Biological Properties of Phosphorus Heterocycles with a C - P Ring System. 8 173-222... 

Diazaphospholes constitute the most widely investigated class of heterophospholes, the 67t-aromatic phosphorus heterocycles [1,2]. Diazaphospholes are unique in the manner that the five-membered ring incorporates one phosphorus atom. First diazaphosphole representative, i.e. 2//-[l,2,3 diazaphospholc was obtained as early as 1967 [3] and until 1980s the interest of organophosphorus chemists remained in the development of different synthetic routes and in investigating their varied reactivity due to the structural diversity within the class [4], On the basis of the relative positions of the three heteroatoms in the five-membered ring, six monocyclic diazaphosphole systems (A-F) are possible and all of them have been reported (Structure 1). 

Electron.—The determination of the molecular structure of phosphorus heterocycles by electron diffraction has been reviewed.176 The structures of trimethylphosphine oxide, and the corresponding sulphide in the gaseous phase, have been compared. The rotational freedom of the methyl group appears to be greater for the sulphide, which also has the longer P—C bonds, i.e. 181.8 pm for (144 Ch = S)and 180.9 pm for (144 Ch = O).177 The trifluoromethylphosphoranes (145) and (146) adopt the... 

This type of compound (152 to 155) containing one Pni, or tetra- and penta-coordinated Pv atom have been described.(1967,138anai39 1968,123 1969, ii6) Heterocycles with two P-heteroatom bonds in the ring have been more commonly reported. In addition to the numerous Pv oxyphos-phoranes and homologs, synthetised by Ramirez and co-workers (see 1968,124 for a review of these compounds) and by others,(1967,121,140 and 141 1969,147) parent tri-, tetra- and penta- coordinated phosphorus heterocyclics with various structures (156 to 162) are known.<1965,32 ... 

A fascinating feature of the chemistry of boron-phosphorus heterocycles is the existence of stable singlet biradicals, e.g. fBuBP Pr2)2 (for a discussion of the electronic structure, see Section 5.4.2.2). The synthesis of this four-membered ring is illustrated in Scheme 5.2. Related derivatives of the type (RBPR 2)2 are also prepared by a salt-elimination reaction of the appropriate lithium phosphide with a 1,2-dichlorodiborane or, in the case of the perphenylated derivative (PhBPPh2)2, by reduction of the cyclic dimer [Ph(Cl)BPPh2]2 with lithium naphthalenide (Scheme 9.11). ... 

The sixth chapter, Preparation, Structure and Biological Property of Phosphorus Heterocycles with a C-P Ring System by Mitsuji Yamashita presents a very critical review of novel phosphorus heterocycles. The review discusses aliphatic 4-, 5-, 6- and 7-membered C-P-C heterocycles, aromatic C-P-C heterocycles, and various C-P-0 type heterocycles including phospha sugars. Synthetic aspects, structural studies, and the biological properties of these phosphorus heterocycles are also addressed. This chapter may attract the interest of synthetic chemists as well as heterocyclic and heteroatom chemists in the life science fields. 

Chapter 2 by Laszlo Nyulaszi and Zoltan Benko deals with the chemistry and physical organic chemistry of aromatic phosphorus heterocycles and is divided into four subchapters dealing with three-, four-, five-, and six-membered rings, in which there may be more than one phosphorus atom. The chapter begins with a clear presentation of the electronic structure that phosphorus may achieve in molecules with CP bonds. For cyclopentadiene and phosphole eight aromaticity indices are collected. Almost all of them indicate that phosphole is more aromatic than cyclopentadiene. It is also shown that even small structural effects (substituent, bonding modes) can have a substantial impact on the chemistry of the reported systems. 

Table 1(a) Selected structural parameters of representative three-membered phosphorus heterocycles bond angles (... 

Gates DP (1997) The synthesis, structure, reactivity and polymerization behavior of boron- and sulfur-nitrogen-phosphorus heterocycles and highly strained chalcogen- and boron-bridged [1], ferrocenophanes. PhD thesis, University of Toronto... 

Silylphosphines, (R3Si)3P, are well known. On the basis of electronegativity (Table 1) they are weaker n acids than organophosphines. With the isolation of R2Si=PR compounds, an increased variety of structures is available. Six-membered silicon-phosphorus heterocycles (1) have been proposed as ligands for catalyst candidates, owing to the steric accessibility of the transition metal. 

Figure 7 Typical structural types of hypervalent phosphorus heterocycles.

---