Igor Shevchenko

Insights into the Staudinger Reaction: Experimental and Theoretical Studies on the Stabilization of cis‐Phosphazides

The Staudinger-model reaction H3P (1) + HN3 (2) H3P=NH (5) + N2 (6) has been investigated at the CCSD(T)/6-31G**//MP2(Full)/6-31G* level. Primary products formed in this reaction are the phosphazides H3P=N–N=NH (3) which exist as trans and cis isomers. In contrast to some previous assumptions, cis-3is 8.2 kcal mol−1 more stable than trans-3 but decomposes rather easily into the expected products H3P=NH and N2. This decomposition can be effectively hampered by intramolecular donor–acceptor interactions as shown by calculations on model compounds as well as by experiments. Thus the reaction of a methylene-σ3,λ3-phosphanyl-σ5,λ5-phosphorane with PhN3 led to a new four-membered heterocycle containing a thermally remarkable stable cis-phosphazide moiety.

AN UNUSUAL REACTION OF HEXAFLUOROACETONE WITH METHYLENEDIPHOSPHANES : FACILE SYNTHESIS OF CARBODIPHOSPHORANES

The oxidation of the methylenediphosphanes 3a,b with hexafluoroacetone does not lead to the expected dioxaphospholane heterocycles, but yields quantitatively the carbodiphosphoranes 5a,b. Compounds 5a,b easily add HCl, HF or Cl2 to the ylidic bonds. The chloro derivative 14b, and its analogue 17 were used for the synthesis of phosphonium substituted carbenes.

An Unusual Oxidation of 1,5‐Dimethyl‐2,4‐bis(dialkylamino)‐1,5‐diaza‐2,4‐diphosphinan‐6‐one with Hexafluoroacetone

The oxidation of heterocycles 5a,b, or 9 containing a methylenediphosphane unit, with hexafluoroacetone does not lead to the expected dioxaphospholane heterocycles, but yields unstable carbodiphosphoranes 6a,b or ylide 10 respectively, which then react easily with HFA to give the stable intermediate products 7a,b or 11 of the Wittig reaction.

Compounds Featuring the Structural Fragment P-C-P

Abstract This article summarizes some of our investigations of compounds featuring the structural fragment P‒C‒P. Phosphorus atoms in different oxidation states and coordination numbers display different chemical behaviors. This may lead to unique chemical properties when they are bridged by a methylene group in a P‒CH2‒P system. For example, the PIII‒CH2‒PVunit is able to add different unsaturated compounds to give zwitterionic products with oppositely charged phosphorus atoms. In addition, the two hydrogen atoms in P‒CH2‒P may also take part in different transformations, resulting in the formation of carbodiphosphoranes or in the formation of a direct P-P bond to give three-membered ring diphosphiranes.

Ylides and Carbenes: the First Carbene Catalyzed Reaction

For example, ylide 3 obtained from diphosphane 1 and acyl imines 2 is capable of reversible cleavage of the P C bond in solution to give carbene (nitrile ylide) 4 and the phosphane, respectively.1 Carbene 4 can be trapped by Ph3P to give ylide 5. Trying to obtain ylide 5 from Ph3P and acyl imine 2 we found that under certain conditions the reaction leads to the formation of difluorophosphorane 6 and carbene 7. The latter can display not only carbene-like but also biradical-like properties to give dimer 8. Ylides 3 and 5 can be used as a source of carbene (or nitrile ylide) 4 in different reactions under mild conditions. However, the interaction of ylide 5 with diaminocarbene 9 did not give the expected alkene 10, but led to a quantitative transformation into compound 11 which can be considered as an unsymmetrical dimer of carbene 4.2 This is the first example of a reaction in which carbene acts as a catalyst. Similarly to phosphanes, diaminocarbene 9 can react with acyl imine 2. Although this reaction should also include the intermediate

A novel type of formation of zwitterionic compounds, containing two phosphorus atoms of opposite charge and different coordination number

The oxidation of bis[bis(dialkylamino)phosphinyl]methane 1 with 5,5,5-trifluoro-4-(trifluoromethyl)penta-3-en-2-one 2 unexpectedly gave zwitterionic compound 7 which according to X-ray analysis contains two phosphorus atoms of opposite charge and different coordination number (lambda 4P(+); lambda 6P(-)) with a direct P-H bond at the hexacordinated phosphorus.

TAKING A BITE OF PHOSPHORUS: UNUSUAL CLEAVAGE OF A PHOSPHORUS-CARBON BOND

Abstract The diphosphine (Me2N)2PCH2P(NMe2)2 reacts with the tetraamino macrocycle cyclen at about 100 °C in a closed system via cleavage of the P-C bond to yield cyclenphosphorane and bis(dimethyl-amino)methylphosphine. The presence of dimethylamine in this reaction is necessary, since a similar reaction which allows the amine to escape, produces an oligomeric product of formula [(C8H16N4)PCH2P]n.