Rigid, Fluoroarene-Containing Phosphonium Borates and Boranes: Syntheses and Reactivity Studies

Abstract

The reaction of (C 6 F 5 ) 2 B(OEt) with t Bu 2 P(CH 2 Li) yields the cyclic phosphonium ethoxyborateadduct formation and ortho-fluoride substitution. Treatment of [1]OEt with HCl in Et 2 O gives the chloroborate [1]Cl in almost quantitative yield. The reaction of [1]Cl with Li[AlH 4 ] leads not only to the reduction of the B-Cl bond but also to the selective substitution of one fluorine atom on the tetrafluorophenylene bridge ([4]H). [1]Cl is readily transformed into [1]F, [1]OAc, and [1]OTf upon reaction with Tl[PF 6 ], AgOAc, and AgOTf, respectively (OAc=acetate; OTf=triflate). [1]OTf represents a convenient storage form of [1] þ , because its B-O bond is highly labile. The free Lewis acid [1] þ was prepared in the form of its aluminate salt [1] þ [Al(O t Bu F ) 4 ] -. The phenyl derivative of [1]OEt, (C 6 H 5 )(OEt)B(CH 2 )(C 6 F 4 )P t Bu 2 ([5]OEt), is also accessible and serves as starting material for the preparation of [5]Cl and [5] þ [Al(O t Bu F ) 4 ] -.

A Highly Reactive Geminal P/B Frustrated Lewis Pair: Expanding the Scope to C−X (X=Cl, Br) Bond Activation

“…However, the successful formation of the methylene bridge was accompanied by a cyclization reaction, during which the phosphorus atom displaced an ortho ‐fluorine atom of one of the C 6 F 5 groups. The obtained zwitterionic five‐membered heterocycle A is no longer an FLP (Scheme ) . Shortly thereafter, Erker et al.…”

“…Our initial attempts at the synthesis of af irst geminal P/B FLP relied on the nucleophilic substitution of EtOB(C 6 F 5 ) 2 with tBu 2 PCH 2 Li. [17] However,the successful formation of the methylene bridge was accompanied by ac yclization reaction, during which the phosphorus atom displaced an ortho-fluorine atom of one of the C 6 F 5 groups. Theo btained zwitterionic five-membered heterocycle A is no longeranFLP (Scheme 1).…”

“…Theo btained zwitterionic five-membered heterocycle A is no longeranFLP (Scheme 1). [17][18][19] Shortly thereafter,E rker et al used the hydroboration of (C 6 F 5 ) 2 PCH= CHMe and (C 6 F 5 ) 2 PCCMe with HB(C 6 F 5 ) 2 to make (C 6 F 5 ) 2 PCH(Et)B(C 6 F 5 ) 2 and (C 6 F 5 ) 2 PC(=C(H)Me)B(C 6 F 5 ) 2 ,r espec-tively. [20,21] These geminal FLPs did not undergo the undesired cyclization reaction, likely because the nucleophilicities of the phosphorus atoms are tamed by their electron-withdrawing C 6 F 5 substituents.…”

Donor‐unsupported Phosphanylmethanides Li[CH2PR2] (R = tBu, Ph) – Crystal Structure of Li[CH2PtBu2] Solved by XRPD and DFT‐D Calculations

“…Despite the long existence and common usage of phosphanyl‐substituted lithium organyls,6–9 the molecular structures of the solvent‐free lithium compounds Li[CH 2 P R 2 ] ( R = t Bu, Ph) have not yet been investigated. However, the structures of the donor‐supported lithium methanides Li(D) n [CH 2 PPh 2 ] [D = N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (pmdta; n = 1),10 N,N,N′,N′‐tetramethylethylenediamine (tmeda; n = 1),11,12 dioxane; n = 1.75]13 have been subject to studies in recent years.…”

Synthesis of Cyclic Amine Boranes through Triazole‐Gold(I)‐Catalyzed Alkyne Hydroboration

“…[19] Notably, the Thus, to further extend this methodology as a general protocol for potential cyclic amine borane synthesis, we investigated the post-cyclization derivatization with the expectation of introducing diverse functional groups on boron.…”