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‐1 H ‐naphtho[1,8‐ ef ][1,3]diazocin‐3(2 H )‐ylidene; Ar: Mes=2,4,6‐trimethylphenyl, Dipp=2,6‐diisopropylphenyl or Xyl=2,6‐dimethylphenyl; X=Cl, NCCH 3 , NTf 2 ) 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 1 H and 13 C 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 + NTf 2 − 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 +AgNTf 2 ).