1,2-diphosphaallyl anion

The first step - a 1,2-diphosphaallyl anion [49] In contrast to the syntheses of dimeric l-(l,2-dimethoxyethane-0,0 )lithoxyaikylidenephosphanes from ethyl formate or 2,4,6-trimethyl-benzoyl chloride and (l,2-dimethoxyethane-0,0 )lithimn phosphanide already mentioned (Eq. 13), the reaction of ethyl benzoate with lithium bis(trimethylsilyl)phosphanide at about 0 °C in... 

Recently, detailed P NMR studies of the formation of the 1,2-diphosphaallyl anion were carried out in order to increase its unacceptably low yield. This led to the very surprising discovery that an unstable ElZ- (5 P-Si +41.4 5 P-C +454.2 ppm jpp 460.6 Hz) as well as the finally isolated EIE- sova.er (8 P-Si +8.0 8 P-C 411.1 ppm jpp 461.2 Hz l,2-dimethoxyethane/[D5]-benzene solution) are present in the reaction mixture. An X-ray structure determination shows the solid compound to be built up of discrete tris(l,2-dimethoxyethane-0,0 )lithium cations and / -isomeric 3-phenyl-l,3-bis(trimethylsilyl)-l,2-diphosphapropenide anions (Fig. 6). 

Red crystals of compound 134 were isolated from the lithiation of diphosphirane 133 with -butyllithium in diethyl ether at -70°C. The formation of the 1,3-diphosphaallyl anion results from a P-P bond cleavage. In the product the exo-exo position of the aryl groups confirms the theoretically predicted conrotatory anionic ring opening. A cr-allyl character agrees with the P-Li coupling constants (Equation 11) <1996JOM(514)37>. 

Unlike the cyanocyclopropyl anion <77JA263l>, the cyclic diphosphiranyl anion intermediate is not detectable, but the 1,3-diphosphaallyl anion is observed when the progress of the reaction is followed by 31P NMR at low temperature. It appears at 5 31P = 64.4 with a yP Li = 40 Hz, characteristic of covalent phosphorus-lithium bonds <89NJC315>. The exo-exo configuration of this intermediate was confirmed by x-ray diffraction <93PS(77)230>. This anion, recrystallized with two molecules of diethylether, has a rr-allyl structure (d c = 1.71 A) and the lithium atom is located in... 

Through a rather complicated sequence of meanwhile fully understood reaction steps ethyl benzoate and lithium bis(trimethylsilyl)phosphanide form tris(l,2-dimethoxyethane-0,0 )-lithium 3-phenyl-l,3-bis(trimethylsilyl)-l,2-diphosphapropenide and 3,5-diphenyl-l,2-bis(tri-methylsilyl)-l,2,4-triphospholide. X-ray structure determinations on orange or green, metallically lustrous, crystals show the compoxmds to be ionic in the solid and to contain a 1,2-diphosphaallyl and a 2-phosphaallyl anion, respectively. Dark red tetrakis(tetra-... 

The phosphonium phosphaalkenes are formed via the diphosphaallyl cation after the cationic rupture of an extracyclic C—Cl bond. Contrary to the photochemical or anionic ring-opening reactions, the cationic intermediates are not detected. The theoretical calculations performed on unsubstituted derivatives reveal for this reaction a P—P bond rupture by a disrotatory process leading directly to an exo-exo open chain structure <92IC2414>. 

The reaction of anionic transition metal complexes (M = Mo, W, Co) with monohalogenated diphosphiranes (2f-g) occurs upon heating and leads to the o- or 7t-diphosphaallyl complexes as a result of preferential P—P bond rupture, depending on the reaction conditions, the nature of the intracyclic carbon substituents, and the transition metal complexes (Scheme 10) <93PS(76)4i, 93JOM(453)77>. rc-Donor substituents (R3 = Ph) promote the >/3-form, whereas u-donor (R3 = Me) afford the t] -complex. 

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