Boron-phosphorus rings

Two approaches have been used in the synthesis of these types of compounds. Small boron-phosphorus ring compounds can serve as building blocks, and addition and elimination reactions with other main group elements can then extend the cage structure (see Schemes 23 and 24, Section 12.12.6.4.5). Alternatively, an unsaturated carbenoid fragment can be added to the bicyclic fragment as illustrated in Scheme 31 <1998IC490>. 

By analogy with borazines, the initial interest in the analogous unsaturated boron-phosphorus rings focused on the fundamental issue of the extent of... 

The best known boron-containing ring systems are the so-called inorganic benzenes, namely, borazine (71), boroxine (72), and triphosphatriborin (73) (Fig. 46), which are isoelectronic and isostructural with benzene. These ring systems are obtained by the interaction of boron with nitrogen, oxygen, and phosphorus, respectively.4... 

Pyridyllithiums and their benzo analogues can be used for the introduction of other metals, and non-metals, on to the ring, such as mercury, boron, phosphorus, tin and arsenic (Scheme 146) (80JOC1514, 67TL1705, 65RTC439). 

Scheme 2.4 Synthesis of (a) boron-phosphorus and (b) tin-chalcogen rings by salt...

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). ... 

Phosphorus—phosphorus bonds, addition, to alkynes, 10, 751 Phosphorus rings, chromium carbonyl link arsenic rings, 5, 226 As, Sb, Se, Te, Sn rings, 5, 226 boron rings, 5, 222 carbon rings, 5, 224 characteristics, 5, 221 oxygen rings, 5, 227... 

Not many boraphosphenes are known. Salts containing anions of type [R2B = PR ]- where R,R are large groups such as mes, mes, Ph, cyclohexyl and so forth have been isolated (Figure 9.1). The B, P and nearest ring C atoms form a coplanar arrangement and the boron-phosphorus distance corresponds to that expected for a double bond. 

Catenation is defined as the self-linking of an element to form chains and rings. Carbon, then, given the above discussion, is the all-time champion catenator, much better than silicon (or sulfur, boron, phosphorus, germanium, and tin, the other elements that show this ability). Why should this be so A comparison of the relevant carbon and silicon bond energies as shown below is helpful ... 

Riegel B, Pfitzner A, Heckmann G, Pluck E, Binder H (1994) Phosphorus-boron and phosphorus-silicon ring systems functionalization of phosphorus ring systems. Phosphorus Sulfur Silicon 93-94 173-176... 

Unsolvated organomagnesium compounds have been recommended for the synthesis of organometallic derivatives of mercury, boron, aluminum, silicon, germanium, tin, phosphorus, arsenic, and antimony6-8 and have been used in procedures for the alkylation of aromatic rings and for the production of various polymerization catalysts.4 9... 

Electrophilic attack at ring silicon, sulfur, selenium, and phosphorus Nucleophilic attack at ring silicon Nucleophilic attack at ring boron... 

---