Abstract
We report a new air‐stable PdI dimer, [Pd(μ‐I)(PCy2 tBu)]2, which triggers E‐selective olefin migration to enamides and styrene derivatives in the presence of multiple functional groups and with complete tolerance of air. The same dimer also triggers extremely rapid C−C coupling (alkylation and arylation) at room temperature in a modular and triply selective fashion of aromatic C−Br, C−OTf/OFs, and C−Cl bonds in poly(pseudo)halogenated arenes, displaying superior activity over previous PdI dimer generations for substrates that bear substituents ortho to C−OTf.
Highlights
PdI dimers have emerged as especially powerful catalysts for these challenges.[7]
As part of our ongoing program with dinuclear metal catalysts,[7,9g,h,13,14] we questioned whether a hybrid version of the dimers D1 and D2 could potentially be created, which would combine the practical air-stability feature of D2 with the reactivity modes of D1 and D2 to enable rapid and selective cross-coupling reactions as well as olefin migrations under complete tolerance of air
We focused especially on the E-selective generation of enamides, which owing to their exquisite reactivity and stability features make them tuneable enamine equivalents for a wide variety of transformations.[16]
Summary
When we performed the isomerization of allyl benzene 44 a in deuterated methanol (CD3OD), we observed only very little D incorporation in the substrate (< 5 %, Figure 2 C) This suggests that the L1Pd(II)(H)(X) [L = PCy2tBu] that is initially formed via cyclopalladation barely undergoes exchange with the solvent. The newly developed [Pd(m-I)(PCy2tBu)]2 D3 allowed for the first efficient E-selective olefin migrations in air in just 2 h reaction time to generate E-enamides or styrene derivatives in the presence of various functionalities, including sulfones, (phosph)amides, aldehydes, ester, stereocenters, and even tolerating the frequently reactive aromatic CÀI bonds or ortho-OH groups. Dimer D3 was shown to trigger rapid and chemoselective Csp2 -Csp as well as Csp2 -Csp cross coupling reactions of poly(pseudo)halogenated arenes in air, showing superior reactivity compared to previous dimer generations for triflate substrates that contain ortho substituents
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