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
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Abstract
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 <i>trans</i>-[PdBr<sub>2</sub>(iPr<sub>2</sub>-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 <sup>1</sup>H and <sup>13</sup>C 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
