Gold(I) Complexes with Eight‐Membered NHC Ligands: Synthesis, Structures and Catalytic Activity

A series of expanded‐ring NHC gold complexes of the formula (NaphtDHD−Ar)Au−X (NaphtDHD=4,5‐dihydro‐1H‐naphtho[1,8‐ef][1,3]diazocin‐3(2H)‐ylidene; Ar: Mes=2,4,6‐trimethylphenyl, Dipp=2,6‐diisopropylphenyl or Xyl=2,6‐dimethylphenyl; X=Cl, NCCH3, NTf2) have been synthesized, including the first gold(I) triflimidate complex (5) stabilized by an eight‐membered NHC ligand. The new organogold compounds have been characterized by mass spectrometry, IR spectroscopy, and 1H and 13C NMR spectroscopy. The structural geometries of 3 b–c and 5 have been unequivocally established by crystallographic analysis revealing broad N‐C‐N angles (>121°) and high buried volume values (46–54%). The first catalytic studies were carried out on the cycloisomerization of 1,6‐enynes, obtaining full conversions (0.5 mol% catalyst loading) and excellent endo/exo selectivity (up to 99:1), and on the gold‐catalyzed phenol synthesis. Lastly, the (NaphtDHD‐Dipp)Au+ NTf2− species was subjected to a kinetic experiment in the cyclization of a N‐propargyl carboxamide to evaluate the efficiency of the pre‐formed catalyst (5) and the in situ activated gold complex (3 b+AgNTf2).