Lithium phosphide rings

Lateral association is not restricted to lithium amides. Lithium phosphide rings (RR PLi) will have a stereochemistry similar to (RR NLi) rings. The R,R groups perpendicular to the (PLi) ring plane will preclude stacking, but facilitate laddering. The presence of a deficiency of Lewis base (less than one per Li) already precludes the formation of... 

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). ... 

Figures 12.2.7(e)-(g) show the core structures of three lithium phosphide complexes. Li(l t20)2(P Bu)2(Ga 2Bu3) has a puckered Ga2P2 four-membered ring, in which one Ga atom is four- and the other three-coordinated, as shown in Fig. 12.2.7(e). The Li-P bond length is 266 pm(av.).

Lithiophosphide reagents have also found application in the synthesis of a range of chiral phosphines based on carbohydrate systems, e.g., (43), the key step being nucleophilic ring-opening of epoxide derivatives with lithium diphenyl-phosphide. A lithiophosphide-tosylate route has been used in the synthesis of the carbohydrate-based diphosphine (44). Conjugate addition of lithium diphenyl-phosphide to a,P-unsaturated carboxylic esters is the key step in the synthesis of... 

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