1,2-Thiaphosphetanes: The Quest for Wittig-Type Ring Cleavage, Rearrangement, and Sulfur Atom Transfer

Abstract

The potential energy surface for opening and ring-enlargement reactions of 1,2-thiaphosphetane with different oxidation states and coordination at phosphorus has been computationally explored. The most favored [2 + 2] cycloreversions are the so-called normal Wittig-type reactions furnishing an alkene and a PS-containing component. Somewhat unfavored are reactions involving the P−S bond cleavage and a C-to-P hydrogen shift as well as a ring enlargement to a 1,3,2-dithiaphospholane in the case of high coordinate derivatives. Apart from a twostep P-to-S oxygen transfer in 1,2σ 4 λ 5 -thiaphosphetane P-oxide, an interesting reaction is the P−S bond cleavage leading to a thiabetaine which, alternatively, can be formed by the C-attack of a phosphinidene oxide on a thiirane. A similar route, energetically more favored, was found for 1,2σ 5 λ 5 -thiaphosphetane starting from thiirane and the corresponding phosphane. For a wide set of P(III) reagents including HPR 2 (R = Me, Ph), PR 3 (R = Me, Ph, NMe 2 , OMe, F, Cl), and HPO, the competitive direct S-attack was found to be the preferred pathway for the desulfurization of thiiranes, and the relative tendency for these P(III) reagents to act as an S-atom acceptor, the thermodynamic S-transfer potential (TSP) scale, was defined using the S 8 /S 7 couple as a point of reference. Article pubs.acs.org/IC

1,2σ3λ3-Oxaphosphetanes and Their P-Chalcogenides—A Combined Experimental and Theoretical Study

“…Elongation of the less activated, non-benzylic C-O bond of 9 gives exergonically styrene 10 and phosphinidene oxide complex 11 through a moderate barrier (18.41 kcal mol −1 ). A similar result was found previously for a terminal phosphinidene molybdenum(0) thiirane complex, giving rise to ethylene and a side-on complexed phosphinidene sulfide [ 33 ]. On the contrary, P insertion into the benzylic C-O bond proceeds through a lower-energy TS (9.81 kcal mol −1 ) affording 1,2-oxaphosphetane 12* ( C 3 -substituted) in a markedly exergonic process.…”

“…The 77 Se{ 1 H}-NMR spectrum showed two doublets at −10.7 and 79.4 ppm. A comparison to the (acyclic) tert -butyl-ethoxyphenylphosphane- P -selenide[ 33 ] (δ ( 31 P{ 1 H}) = 111.0 ppm, 1 J (Se,P) = 786.3 Hz) showed very similar values for the phosphorus chemical shifts and coupling constants, whereas the selenium resonances of 16a,a’ are downfield-shifted (cf. δ ( 77 Se{ 1 H}) = −350.3 ppm [ 35 ]).…”

Terminal Phosphinidene Complex Adducts with Neutral and Anionic O-Donors and Halides and the Search for a Differentiating Bonding Descriptor

“…Both the singlet oxygen ( 1n ) and N-donor ligands ( 1r and 1s ) form a PE (E = O, N) double bond, which creates a trigonal-planar geometry at the P center (∑<P in the range 359.5–360.0°; Scheme ). Adduct 1n can exergonically cyclize to the dioxaphosphirane complex 2 , which can convert (via O–O bond cleavage) to the more stabilized dioxophosphorane side-on complex 3 , thus paralleling the high exergonicity recently reported for the parent free ligand and P -aryl derivatives . Similarly, the most stable NO N-adduct 1r , featuring a spin density well delocalized between the ligand N and O atoms (Figure ), can cyclize to the more stable, mostly N-centered, radical oxazaphosphiridine complex 4 .…”

Deoxygenation of Oxiranes by λ3σ3‐Phosphorus Reagents: A Computational, Mechanistic, and Stereochemical Study

“…[15] FLP (frustrated Lewis pair) combinations of phosphanes with boranes induce ring opening of epoxides affording zwitterionic products III (Figure 1), as recently shown by Slootweg. [16] This study reveals the high barrier (ΔG � = 44.4 kcal/mol) computed (ωB97X-D/6-31G**) for ring opening by direct P-attack of t Bu 2 P- The analogous desulfurization reaction of thiiranes [11] by tervalent phosphorus reagents was recently studied computationally [17] and the existence of two different transition states (TSs) from the direct P•••S interaction was demonstrated. For twelve PZ 3 reagents analyzed in the desulfurization of parent thiirane, a lowest barrier TS (ΔG � = 19.9 to 30.3 kcal/mol) was found for the nucleophilic P-to-S attack, whereas in some cases a second higher-energy TS (ΔG � = 61.9 to 68.9 kcal/mol) corresponding to the inverse S-to-P attack could be located.…”

“…A similar scale for the sulphur atom transfer ability (TSP) was later reported using the S 8 /S 7 couple as reference. [17] Herein a wide set of acceptor compounds "B:" bearing either an atomic lone pair (LP) or an unsaturation that is prone to oxidation by oxygen atom transfer are studied using state-ofthe-art single-reference computational methods, by evaluation of the enthalpy change corresponding to the reaction B: 8). Obviously, according to this definition, the couple H 2 O 2 /H 2 O used as reference has TOP H = 0.0 kcal/mol.…”