Phosphathioketenes

Cycloaddition phosphathioketenes, 33 332 reactions, in preparation of fluoroalicyclic derivatives, 15 327-328 reactions, of iminoboranes, 31 159-165 [2-1-2] Cycloaddition phosphaalkenes, 33 271-272 phosphathioketenes, 33 334 [2-t-l] Cycloaddition, phosphaalkenes, 33 269-271... 

A sterically hindered (2,4,6-tri-t-butylphenyl)[bis(trimethylsilyl)]phosphine (9), whose crystal structure has been reported84, was utilized to form a 1-phosphabuta-l,3-diene (equation 67)36. Mes -substituted phosphaketene was obtained from the reaction of 9 with phosgene (equation 68)4. Reaction of 9 with thiophosgene afforded dimeric phosphathioketene, [Mes P=C=S]2 (equation 69)85. A."V3-Dithioxophosphorane was also isolated by introduction of the bulky substituent (equation 70)86. 

X-ray structure analysis of the 1,3-diphosphaallene was carried out by Karsch and coworkers118, who prepared the diphosphaallene according to equation 92119. The diphosphaallene was also prepared independently by Appel and coworkers by reaction of silylphosphide 11a and phosphaketene Mes P=C=0 (equation 93)90. Appel and Knoll mentioned the reaction of the silylphosphide 11a with carbon disulfide8a and an intermediary formation of phosphathioketene Mes P=C=S was postulated in this reaction (equation 94). 

Insertion into the phosphorus silicon bond primarily generates a phosphaalkene, which splits off trimethylsilylthiolate and frees the phosphathioketene 1. A renewed addition of the phosphide followed by a splitting off of thiolate finally yields the diphosphaallene 2 [Eq. (54)]. 

Attempts to produce phosphathioketenes analogous to the synthesis of phosphaketenes in a reaction of Ar—P(SiMe3)2 with thiophos-... 

Its structure as determined by an X-ray investigation is shown in Fig 21. It may be understood as a dimer of the assumed phosphathio-ketene intermediate. The cycloaddition of the phosphathioketene corresponds to the behavior of unsubstituted carbaketenes (146) and so is different from that of the phosphaketenes described earlier, while thioketenes dimerize to 1,3-dithietanes (147,148). An asymmetric retro ring cleavage can be initiated if l-thia-3-phosphetane is irradiated by a mercury lamp generating carbon disulfide and the 1,3-diphosphaallene [Eq. (78)] (117, p. 33). 

Conversions in pentane proceed in an nonuniform manner at high temperatures. In addition to unidentified products exhibiting different 31P NMR AX patterns, as well as the main product dichlorophosphane and another unknown substance, which exhibits a 31P NMR shift of + 301 ppm, one obtains a red compound, of which elemental analysis and the molecular mass point to the trimer phosphathioketene. The number of isomer compounds of this composition is limited by the 31P NMR spectrum. The A2X system, of which the X triplet is split into a double doublet if detected in solution in chloroform, indicates two acyclic PC double bonds and one phosphorus atom as a ring member (117). A possible explanation is given in Fig. 22. This could be in agreement with the addition of a monomer to the dimer, forming the six-membered ring compound with the proposed structure. 

Another possibility to generate phosphathioketenes on a larger scale for intercept reactions starts with the lithium phosphide [Eq. (80)]. Lithium phosphide reacts with CS2, which is inserted into the LiP bond... 

If a suitably reactive reagent for the interception is missing, a [2 + 2] cycloaddition of the phosphathioketene is observed, which takes place with the precursor and leads to the phosphathietane [Eq. (81)] (118, p. 30). 

Replacement of P=C in an unstable monomer by P-C in the dimeric form is fairly common (13.280). Similarly, P C monomers will dimerise as in Equation 13.281. The dimer may in some cases be capable of undergoing further reaction (called 2-1-2 cycloaddition or cyclotetramerisation) to form a cubane molecule (13.282). Further examples of dimerisations are provided by phosphake-tenes (13.283), phosphathioketenes (13.284) and phosphaallyl derivatives (13.285) and (13.286). 

A phosphaketene RP=C=0 (R = 2,4,6-tris-t-butylphenyl) and a 1,3-phosphaazaallene RP=C=N-t-Bu are stable compounds, while the phosphathioketenes, RFMZ =S (R = t-butyl or tris-t-butylphenyl) are only obtained as dimers. Phosphoarsaallenes, P =As and diarsaaUenes, As=C=As, are also known... 

The trivalent phosphaketenes and phosphathioketenes are usually not stable as monomers because they undergo rapid dimerization, even at low temperatures. For example, t-butylphosphaketene, t-BuP=C=0, is only stable below -60 °C. Above this temperature. 

In the generation of the unstable phosphathioketene 7 (R = 2,4,6-tributylphenyl) dimerization occurs to give the unsymmetrical dimer 8 as red crystals. ... 

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