Cycloaddition of P−C Single Bonds: Stereoselective Formation of Benzo‐1,3,6,2‐trioxaphosphepine Complexes via a Ditopic van der Waals Complex

Abstract

While phosphaalkenes and phosphanes are known to participate in [4+n] cycloaddition reactions, P-C single bonds are inert in this respect. Herein, reactions of oxaphosphirane complexes with tetrachloro-ortho-benzoquinone are presented that reveal a stereoselective reaction of the endocyclic P-C bond to afford benzo-1,3,6,2-trioxaphosphepine complexes. High-level DFT calculations provide evidence that the final product is derived from a sequence of three consecutive steps involving a ditopic van der Waals complex.

A Computational Study on the Stability of Oxaphosphirane Rings towards Closed‐Shell Valence Isomerization

“…In the case of P ‐M(CO) 5 complexes 2a – i , ring opening arising from C–O cleavage reaction leads to the corresponding side‐on complexes 4 , as first reported for model P ‐Cr(CO) 5 complexes,[14a] and later on extended to tungsten analogues. [14b], [14c], These complexes 4 display single P–C bonds (0.952–1.097) and double P=O bonds (1.829–1.909). The only example of an unstable oxaphosphirane complex is the derivative having electron‐releasing C‐substituents, 2d , which spontaneously undergoes ring opening to give the valence isomer structure 4′ (Scheme ), featuring a rather acute geometry at P in the ligand part (Σ<P = 310.1°).…”

“…Very close values between these two levels has been systematically reported for close‐shell systems with rmsd (root mean square deviation) typically below 0.2 kcal mol –1 . [14c], , , Also, SCS‐MP2 and PWPB95‐D3 methods were checked for comparison. LPNO‐NCEPA1 and PWPB95‐D3 were found to be the most accurate methods for a set of 110 energy values, as shown by the low rmsd (root mean square deviation) values (0.20 and 0.21 kcal mol –1 , respectively), computed taking DLPNO‐CCSD(T) as the reference, using the def2‐TZVPP basis set.…”

“…Interestingly, further insights into bond weakening upon simple transformations (protonation, complexation, one‐electron oxidation or reduction, etc.) was garnered,, , and a variety of synthetic applications of oxaphosphiranes have been explored, thus creating an active field of ongoing research . Virtually all synthetic applications of oxaphosphiranes rely on the energetically accessible ring‐opening reaction, either by endocyclic C–O[14a] or P–C[14b], [14c], cleavage reaction.…”

Mn2(CO)10-Catalyzed Intramolecular Dimerization of Diphosphirane Complexes

“…A C–P bond [1,5] shift was observed in cyclooctatriene-fused phosphirane . A [4 + 3] cycloaddition reaction of oxaphosphiranes with tetrachloro- o -benzoquinone led to the stereoselective formation of benzo-1,3,6,2-trioxaphosphepine complexes …”

“…7 A [4 + 3] cycloaddition reaction of oxaphosphiranes with tetrachloro-obenzoquinone led to the stereoselective formation of benzo-1,3,6,2-trioxaphosphepine complexes. 8 We recently disclosed an unusual rearrangement of 1iminylphosphirane complexes under a CO atmosphere, and the subsequent cycloaddition with olefins gave 7-aza-1-phosphanorbornanes. 9 More interestingly, thermolysis of 1,1′-biphosphirane led to 3,4-dihydro-1,2-diphosphete and diphosphorus (P 2 ) intermediates.…”