Oxaphospholes and Bisphospholes from Phosphinophosphonates and α,β‐Unsaturated Ketones

Abstract

The reaction of a {W(CO)5}-stabilized phosphinophosphonate 1, (CO)5WPH(Ph)–P(O)(OEt)2, with ethynyl- (2 a–f) and diethynylketones (7–11, 18, and 19) in the presence of lithium diisopropylamide (LDA) is examined. Lithiated 1 undergoes nucleophilic attack in the Michael position of the acetylenic ketones, as long as this position is not sterically encumbered by bulky (iPr)3Si substituents. Reaction of all other monoacetylenic ketones with lithiated 1 results in the formation of 2,5-dihydro-1,2-oxaphospholes 3 and 4. When diacetylenic ketones are employed in the reaction, two very different product types can be isolated. If at least one (Me)3Si or (Et)3Si acetylene terminus is present, as in 7, 8, and 19, an anionic oxaphosphole intermediate can react further with a second equivalent of ketone to give cumulene-decorated oxaphospholes 14, 15, 24, and 25. Diacetylenic ketones 10 and 11, with two aromatic acetylene substituents, react with lithitated 1 to form exclusively ethenyl-bridged bisphospholes 16 and 17. Mechanisms that rationalize the formation of all heterocycles are presented and are supported by DFT calculations. Computational studies suggest that thermodynamic, as well as kinetic, considerations dictate the observed reactivity. The calculated reaction pathways reveal a number of almost isoenergetic intermediates that follow after ring opening of the initially formed oxadiphosphetane. Bisphosphole formation through a carbene intermediate G is greatly favored in the presence of phenyl substituents, whereas the formation of cumulene-decorated oxaphospholes is more exothermic for the trimethylsilyl-containing substrates. The pathway to the latter compounds contains a 1,3-shift of the group that stems from the acetylene terminus of the ketone substrates. For silyl substituents, the 1,3-shift proceeds along a smooth potential energy surface through a transition state that is characterized by a pentacoordinated silicon center. In contrast, a high-lying transition state TS(E′–F′)R=Ph of 37 kcal mol−1 is found when the substituent is a phenyl group, thus explaining the experimental observation that aryl-terminated diethynylketones 10 and 11 exclusively form bisphospholes 16 and 17.

Organophosphorus Compounds in Organic Electronics

“…The very mild and reversible reduction (ca. −1.35 V vs. Fc 0/1+ ) supports the stabilization of the LUMO levels; however, no emission has been noted in this class of compounds …”

“…À1.35 Vv s. Fc 0/1 + ) supports the stabilization of the LUMO levels;h owever,n o emission has been noted in this class of compounds. [26,85]…”

Facile Phenylphosphinidene Transfer Reactions from Carbene–Phosphinidene Zinc Complexes

“…Such an unprotected fivemembered heterocycle has only been prepared once before, through atwo-step procedure using an electrophilic phosphinidene complex followed by demetallation. [22] Themolecular structure of 8 firmly establishes the phenyl rings to be in the trans position and shows that the third phenyl ring (on C3) is in conjugation with the C1 = C2 double bond in the ring [C2-C3-C10-C11 À3.2(3)8 8;F igure 1]. [8] We turned to DFT calculations to provide insight into the formation of 8.…”

Phospholones from Diacetylenic Ketones: Synthesis, Properties, and Reactivity

“…Recently, we have reported a method for the preparation of persubstituted 1,2-oxaphospholes and ethylene-bridged bisphospholes starting from readily available diynones and tungsten-coordinated phosphanyl phosphonates. , This approach allowed the preparation of the target compounds in one step and in moderate to high yields. The final compounds showed interesting optoelectrochemical properties and can be used as electrochromic switches .…”