Aryl C(sp2)-X Coupling (X = C, N, O, Cl) and Facile Control of N-Mono- and N,N-Diarylation of Primary Alkylamines at a Pt(IV) Center.

Xiaoxi Lin,Andrei N Vedernikov,Arkadi Vigalok

doi:10.1021/jacs.0c09452

Xiaoxi Lin, Andrei N Vedernikov + Show 1 more

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https://doi.org/10.1021/jacs.0c09452

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Abstract

We present the first example of an unprecedented and fast aryl C(sp2)–X reductive elimination from a series of isolated Pt(IV) aryl complexes (Ar = p-FC6H4) LPtIVF(py)(Ar)X (X = CN, Cl, 4-OC6H4NO2) and LPtIVF2(Ar)(HX) (X = NHAlk; Alk = n-Bu, PhCH2, cyclo-C6H11, t-Bu, cyclopropylmethyl) bearing a bulky bidentate 2-[bis(adamant-1-yl)phosphino]phenoxide ligand (L). The C(sp2)–X reductive elimination reactions of all isolated Pt(IV) complexes follow first-order kinetics and were modeled using density functional theory (DFT) calculations. When a difluoro complex LPtIVF2(Ar)(py) is treated with TMS–X (TMS = trimethylsilyl; X= NMe2, SPh, OPh, CCPh) it also gives the corresponding products of the Ar–X coupling but without observable LPtIVF(py)(Ar)X intermediates. Remarkably, the LPtIVF2(Ar)(HX) complexes with alkylamine ligands (HX = NH2Alk) form selectively either mono- (ArNHAlk) or diarylated (Ar2NAlk) products in the presence or absence of an added Et3N, respectively. This method allows for a one-pot preparation of diarylalkylamine bearing different aryl groups. These findings were also applied in unprecedented mono- and di-N-arylation of amino acid derivatives (lysine and tryptophan) under very mild conditions.

Highlights

The formation of the new C−X (X = C, heteroatom) bonds via reductive elimination from a group 10 M(IV) atom is the product-forming step in a variety of catalytic oxidative transformations that have attracted much attention in the last two decades.[1,2] As compared to the more common M(II) counterparts, high-valent d6 metal complexes have a greater number of donor atoms at the metal center, which may imply greater competitiveness when it comes to the C−X bond formation and, may require more careful control over the reaction selectivity.[3]
The p-nitrophenoxo complex 2b has been characterized by single-crystal X-ray diffraction (Figure S1), confirming that the reaction of 1 with TMS−4OC6H4NO2 led to the selective replacement of the fluoride ligand Fa, trans to the aryl, giving the product with the mutual trans arrangement of the aryl and 4-nitrophenoxo groups
The remaining fluoride ligand Fb showed the characteristic upfield 19F NMR signals for all three complexes, revealing the same diastereoselectivity of these ligand substitution reactions

Summary

INTRODUCTION

Aryl−F Elimination from a Pt(IV) Center reactions involving heavier halogens, Br and I, are easier to observe.[9] We proposed that the exclusive C−F bond formation was sterically enforced by the presence of the bulky mesityl and 2-[bis(adamant-1-yl)phosphino]phenoxide (P−O) ligands. This ligand scaffold might be efficient for enabling other difficult aryl−X elimination reactions (e.g., X = Cl, CN, O, N(alkyl)) at a Pt(IV) center, hopefully in a selective manner

RESULTS

CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES