C(sp³)–N Bond‐Forming Reductive Elimination of Amines: Reactions of Bisphosphine‐Ligated Benzylpalladium(II) Diarylamido Complexes

Abstract

Reductive elimination is a common organometallic transformation that is the key product-forming step in many catalytic cycles. [1] Although many examples of reductive elimination from aryl palladium amido complexes to form C(sp 2 ) À N bonds have been reported as part of catalytic processes and as stoichiometric reactions, [2,3] reductive elimination to form a bond between an amide ligand and an sp 3hybridized carbon atom is less common. Reductive elimination from methylplatinum(IV) sulfonamido complexes by dissociation of the sulfonamide has been reported, [4] as has reductive elimination from alkyl nickel amido complexes after the addition of an oxidant. [5,6] Reactions of free amines with allyl-and benzylpalladium complexes are also known. [7][8][9] However, despite several attempts, [10,11] reductive elimination to form an C(sp 3 )ÀN bond of any type through the simple thermal reaction of an isolated organometallic amido complex has not been reported.Herein, we report a purely thermal reductive elimination to form a C(sp 3 ) À N bond in an amine from a benzylpalladium amido complex. An assessment of the stereochemical course of this process showed that it occurs by a stepwise pathway that is distinct from the accepted concerted pathway for the reductive elimination of aromatic amines from aryl palladium(II) species, and an assessment of the effect of the electronic properties of the amido group on the reaction rate showed that this effect is distinct from that observed for reductive elimination to form CÀO bonds from methylplatinum(IV) carboxylate and phenoxide complexes.We prepared a series of benzylpalladium amido complexes to investigate their ability to undergo reductive elimination to form C(sp 3 ) À N bonds without competing bhydrogen elimination. We chose complexes containing chelating ligands to enforce a cis configuration of the benzyl and the amido ligands for reductive elimination; complexes containing a 1,1'-bis(diphenylphosphanyl)ferrocene (dppf) ligand displayed the appropriate balance of stability, reac-tivity, and synthetic accessibility. Dppf-ligated benzylpalladium amido complexes 1-7 were synthesized by treatment of the known complex [(cod)Pd(Bn)Cl] [9] (Bn = benzyl) with dppf followed by the appropriate potassium diarylamide in THF (Scheme 1). Complexes 8 and 9, which contain naphthylmethyl and mesitylmethyl groups, respectively, were synthesized by the treatment of [CpPd(h 3 -allyl)] [12] with dppf followed by naphthylmethyl or mesitylmethyl bromide. The resulting bromide complexes were then converted into the diarylamido complexes by treatment with the appropriate potassium diarylamide. The benzylpalladium arylamido complex 10 and methylpalladium diarylamido complex 11 were synthesized by analogous methods involving the treatment of [(cod)Pd(Bn)Cl] with dppf followed by the potassium anilide, and the treatment of [(cod)Pd(Me)Cl] [13] with dppf followed by the potassium diarylamide. These compounds were characterized by conventional one-and two-dimensional NMR spectroscopic methods and el...

Synthesis of Methylene‐Bridged Biscarbazole Alkaloids by using an Ullmann‐type Coupling: First Total Synthesis of Murrastifoline‐C and Murrafoline‐E

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Determination of the Metastable Zone Width by a Simple Optical Probe

“…Early studies on the generation of π‐benzylpalladium complexes used benzyl halides2 as electrophilic partners. Hartwig reported the thermal reductive elimination to form a C( sp 3 )N bond in an amine from a benzylpalladium amido complex 2c. Recently, benzyl esters,3 carbonates,4 and phosphates5 have been developed.…”

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