Synthesis and DFT calculations of spirooxaphosphirane complexes

Abstract

In situ formed Li/Cl phosphinidenoid complexes [Li(12-crown-4)][M(CO)5(ClPC5Me5)] 3a-c (M = Cr, Mo, W) reacted with cyclobutanone (4), cyclopentanone (5) and cyclohexanone (6) in Et2O to yield the first P-C5Me5 substituted C(3)-spirofused oxaphosphirane complexes 7a-c, 8a and 9a,a'. In the case of cyclopentanone and 1a the outcome of the reaction in THF was different: here the formation of 8a along with (anionic) phosphinoate complexes 14a and 15a was observed, the latter possess an unusual ring-opened oxaphosphirane and 2-cyclopentylidenecyclopentanone as co-ligands to the lithium cation. NMR, IR and MS data as well as single-crystal X-ray structures in the case of 7a-c, 8a, 9a and 15a are reported. DFT calculations on the parent 1-oxa-2-phosphaspiro[2.n]alkane pentacarbonylchromium(0) complexes 10 (a: n = 2; b: n = 3; c: n = 4; d: n = 5) revealed that both ring strain energies and G(r) values decrease significantly as the spiroring size increases. This is caused by an increase in the exocyclic α bond angle at the oxaphosphirane C(3) atom, hence decreasing the s-character of the corresponding orbitals involved in endocyclic bonds at C(3) and thus becoming better suited for accommodation of small ring angles.

Quantum Chemical Calculations on CHOP Derivatives—Spanning the Chemical Space of Phosphinidenes, Phosphaketenes, Oxaphosphirenes, and COP− Isomers

“…As double bonds normally entail enlarged bond angles, their incorporation into small cyclic systems should be expected to result in an increase in the RSE, as occurs, for instance, in moving from cyclopropane to cyclopropene (RSE = 29.0 and 54.5 kcal/mol, respectively [52]). In the case of the parent oxaphosphirene ring system 1a , the RSE was computed by evaluating the energetics of appropriate homodesmotic reactions (Scheme 5), similar to those used for other three- [46,48,51,53,54,55,56,57] or four-membered [47] saturated phosphorus heterocycles. In such reactions, for the cleavage of every endocyclic X–Y (or X=Y) bond, a H n X–YH m (or H n X=YH m ) reagent is used, the valences of X and Y being completed with H atoms.…”

Between Oxirane and Phosphirane: The Spring‐loaded Oxaphosphirane Ring

“…In order to use a well‐suited method for calculating RSE in terms of accuracy and computational cost, a variety of X‐ray structures for reported oxaphosphirane complexes (see the SI) was chosen. A wide set of geometric parameters (only bond distances and bond angles involving the core oxaphosphirane ring moiety) were obtained at the B3LYP−D3/def2−TZVP(ecp) level, often used previously for these and related structures, [24,30,33a,34] as well as the rather computationally efficient Grimme's B97‐3c and PBE‐3c functionals (with the automatically built‐in basis sets) and compared to those in the corresponding (seven) X‐ray structures [30,33a–b,35] . Metrics used to assess the accuracy for the set of parameters studied are the mean absolute error (MAE) and the root mean squared error (RMSE).…”

“…The RSE for parent σ 3 λ 3 ‐oxaphosphirane was estimated [13,24] to be 22.4 kcal mol −1 , halfway between those of oxirane (26.4 kcal mol −1 ) [13,28] and phosphirane (19.4 kcal mol −1 ) [13,28] . κ ‐ P ‐complexation with pentacarbonylmetal(0) units leading to complexes VI turned out to have little effect on RSE, [30] whereas a significant RSE enhancement was found by complexation with BH 3 [24] …”

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

“…Recently, P‐complexes of oxaphosphiranes ( IIIa ; E = O, “CPO” ring), and azaphosphiridines ( IIIb ; E = NR′, “CPN” ring) became readily accessible through the versatile Li/Cl phosphinidenoid complex methodology. This has enabled intense studies on various aspects of closed‐ and open‐shell chemistry of the CPO and CPN rings, and theoretical exploration of the potential energy surface (PES) of these ring systems provided information about relative stabilities of isomers and ring‐strain energies.…”

“…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.…”