Abstract
Cyclometalated gold(III) complexes Au(L)(OAcF)2 (L = phenylpyridine dicarboxylic diester (ppyde) or phenylpyridine dicarboxylic acid (ppydc)) have been prepared reacting Au(OAc)3 with corresponding phenyl pyridines (ppyde or ppydc) in trifluoroacetic acid (HOAcF) under microwave heating. Further treatment of Au(L)(OAcF)2 with aqua regia resulted in dichloro complexes Au(L)Cl2. Au-functionalized UiO-67 MOF has been synthesized by exchanging linkers of UiO-67 with Au(ppydc)Cl2, furnishing the MOF with (N^C)-cyclometalated Au(III) centers. The catalytic activities of the molecular cyclometalated complexes and the Au-incorporated MOF were studied in gold-catalyzed propargyl ester cyclopropanations. Almost all complexes and the MOF showed catalytic activity to the cyclopropanation product (up to 97% conversion), with a preference for the trans diastereoisomer (up to 14:86 d.r.). The recyclability of the most active molecular complex has also been investigated.
Highlights
Gold catalysis comprises one of the most effective methods for the activation of C–C double and triple bonds leading to broad diversity of follow-up chemical transformations, such as heterocycles and natural compounds syntheses [1,2,3,4,5]
The cyclometalation of ppydc and ppyde with Au(OAc)3 in HOAcF under microwave heating resulted in formation of complexes 1a and 1b in 46% and 65% yields, respectively (Scheme 1)
The inorganic gold species can be removed by washing 1a with aqua regia, in a protocol that was previously employed in our group [31,32]
Summary
Gold catalysis comprises one of the most effective methods for the activation of C–C double and triple bonds leading to broad diversity of follow-up chemical transformations, such as heterocycles and natural compounds syntheses [1,2,3,4,5]. Stable Au(III)-ligated complexes have been developed and studied for their bioactivity, such as anticancer and inhibition of DNA/RNA synthesis [6,7]. Au(III) complexes as catalysts have gained popularity due, in part, to the development of robust synthetic procedures [13]. (N^C)Au complexes bearing a phenyl pyridine ligand (ppy) are extensively studied complexes with various substituents on aromatic rings. This class of cyclometalated complexes has proven to be active in the catalysis of a large range of reactions, including aromatic addition to vinyl ketones [17], AAA-coupling reaction [18,19] and oxazole synthesis [20]
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