Gold(I) and Palladium(II) Complexes of 1,3,4-Trisubstituted 1,2,3-Triazol-5-ylidene “Click” Carbenes: Systematic Study of the Electronic and Steric Influence on Catalytic Activity

The
synthesis of a small family of six electronically and sterically
modified 1,3,4-trisubstituted 1,2,3-triazol-5-ylidene gold­(I) chloride
complexes is described. Additionally, the corresponding trans-[PdBr2(iPr2-bimy)­(1,3,4-trisubstituted 1,2,3-triazol-5-ylidene)]
complexes are also generated and used to examine the donor strength
of the 1,3,4-trisubstituted 1,2,3-triazol-5-ylidene ligands. All compounds
have been characterized by 1H and 13C NMR and
IR spectroscopy, high-resolution electrospray mass spectrometry (HR-ESI-MS),
and elemental analysis. The molecular structures of four of the gold­(I)
and four of the palladium­(II) complexes were determined using X-ray
crystallography. Finally, it is demonstrated that these 1,2,3-triazol-5-ylidene
gold­(I) chloride complexes (Au­(trz)­Cl) are able to catalyze the cycloisomerization
of 1,6-enynes, in high yield and regioselectivity, as well as the
intermolecular direct etherification of allylic alcohols. Exploiting
the Au­(trz)Cl precatalysts allowed the etherification of allylic alcohols
to be carried out under milder conditions, with better yield and regioselectivity
than selected commercially available gold­(I) catalysts.