Phosphorus ylides properties

Trzcinskabancroft, B., Knachel, H., Dudis, D., Delord, T.J. and Marler, D.O. (1985) Experimental And Theoretical-Studies Of Dinudear Gold(I) And Gold(II) Phosphorus Ylide Complexes - Oxidative Addition, Halide Exchange, And Structural-Properties Including The Crystal And Molecular-Structures Of [Au (CH2)2PPh2]2 And [Au(CH2)2PPh2]2(CH3) Bri. Journal of the American Chemical Society, 107(24), 6908-6915. 

The first kinetically stable dibenzosilafulvene (7), whose structure and properties should more correctly be described by the resonance hybrid 7a 7b with a great contribution of the ylide form 7a, reacts with phosphorus ylide to form betaine (8), which is rearranged, under thermodynamically controlled conditions, into the salt (9) (Scheme 4).24,25... 

The use of phosphorus ylides as ligands was reviewed by Schmidbaur in 1983.315 These ligands are strongly polarized, R3P+—CR,, and thus they bond in the main to transition metals via a C—M bond. Although the phosphorus plays a unique role in the properties of such ligands, it is not the province of this article to describe this M—C type of bonding. An example is given of the type of complex formed with lanthanides (equation 92).316... 

These derivatives have not only provided new synthetic pathways but have shown improved thermal stability (as in the case of arsenic ylides) and a modified pattern of chemical reactivity. The donor properties of ylides 55, 24), and most of their synthetic applications 103), have been covered in other reviews and articles 3, 26) and are not duplicated here. The general organometallic chemistry of arsenic, antimony, and bismuth is the subject of the invaluable monograph by Doak and Freedman 11). The broad scope of phosphorus ylide and pentaorganophosphorane chemistry was covered in the leading multivolume series on organophosphorus chemistry edited by Kosolapoff and Maier 3, 21). Finally, the recent... 

It is too early to decide whether semiempirical computations can successfully evaluate TS models such as 117-124 given the current level of precision. This situation is likely to change as the theoretical methods refine their phosphorus parameters and their ability to mimic solvation effects. Table 22 provides many opportunities to test computational TS predictions. Selectivity in the Wittig reaction depends on substituents, not on some fundamental property of phosphorus ylides. Thus, any successful theoretical analysis of the selectivity issue will need to explain the substituent-induced differences in kinetic Z E ratios. 

Phosphoranes or phosphorus ylides are an extremely useful class of compounds in synthetic chemistry. Several recent studies have been published on the preparation, properties, and applications of ylides as reactants or ligands. Also, mechanistic investigations on the reactivity as well as on the antibacterial, antifungal and/or antitumoral activity of such compounds have been detailed. 

Kawashima and co-workers attempted to prepare the phosphorus ylide-sta-bilized AYC ligand 129 which could, however, not be isolated because of an intramolecular rearrangement giving 130. The intermediate formation of 129 was confirmed by its reaction with sulfur to give 131 and by the formation of the rhodium complexes 132 and 133 (Scheme 1.17). Infrared spectroscopy of the carbonyl complex 133 confirmed the superb donor properties of AYC 129. A palladium complex bearing the phosphorus ylide-stabilized NHC was also prepared. Fiirstner et al. synthesized the analogous... 

The addition of bromine or chlorine to 2,4,6-trialky1-and 2,4,6-triaryl-l -phosphorin affords the corresponding 1,1-dihalogeno-2,4,6-tri(alkyl or aryl)-X -phosophorin. The dihalogeno derivatives may be used to obtain X°-phosphorins with alkyl or aryl groups bound by a heteroatom to the phosphorus. Physical and chemical properties indicate that the dihalogeno derivatives are better formulated as aromatic n delocalized heterocycles with d-orbital participation of the phosphorus than as cyclic 6tt delocalised phosophorus ylides (H. Kanter, W. Mach, and Dimroth, Ber., 1977, 110, 395). 5-... 

Bertrand s approach to the stable earbene problem has been to seareh for a most delieate balance of stability and reaetivify, such that the essential reaetions expeeted of a earbene are not lost. Carbene 42, for example is a distillable red oil that behaves as a nucleophilie earbene despite its phosphaaeefylene eontributing resonance form it undergoes addition to electron poor olefins (e.g., dimethyl fiimarate). The very eleetron-rieh bis(diisopropylamino)phosphino substituent damps the carbene s electrophliie properties by resonanee donation into the ear-benic p orbital. [115] These phosphinosilylcarbenes are therefore best deseribed by phosphorus vinyl ylide structures with a lone pair on earbon (ef, 42, seeond contributor). [116]... 

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