Chemical bond hypervalent compounds

A review on the chemistry of thio derivatives of trivalent phosphorus acids which covers the literature to 1986, includes a section on pentaco-ordinate phosphorus compounds derived from addition to a-diketones and unsaturated systems activated to nucleophilic attack by electron withdrawing groups. Chemical bonding in hypervalent molecules has been discussed and qualitative bonding concepts developed to supersede the dsp and d sp models. A review on the mechanism and stereochemistry of the Wittig olefination reaction inevitably includes a discussion of the equilibrium between betaine and 1,2-oxaphosphetane intermediates. A correction has been published to reference 19 of Chapter 2 in SPR14, Vol.21, concerning the Mitsunobu Reaction. ... 

The ultimate extension of the hypervalency concept involves bonding to group 18 rare-gas elements. The rare gases were long considered to be chemically inert until Neil Bartlett and coworkers synthesized XeF2, XeF4, and other RgF compounds (particularly for Rg = Xe, Kr) in the 1960s.145 Many more such compounds are now known.146... 

The structure and reactivity of several specific classes of hypervalent iodine compounds have been investigated theoretically. Varvoglis, Tsipis and coauthors have studied the geometry and electronic stmcture of some hypervalent iodine compounds PhIX2 by means of extended Hlickel and CNDO/2 quantum chemical approaches [200], The bonding was analyzed in terms of both the model of delocalized MOs on the basis of interactions between fragment MOs derived from EHMO-SCCC calculations and that of localized MOs derived by the CNDO/2 method. The ability of these compounds to afford c -addition products with alkenes via a synchronous molecular addition mechanism was found to be theoretically feasible [200]. 

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