Studies on gold(III) coordination of a series of prepared polydentate pyridine and quinoline based ligands are reported. Characterization ( 1 H, 13 C, 15 N NMR, and XRD) of the novel gold(III) complexes, prepared in 31-98 % yield, revealed different coordination ability of the pyridine and quinoline nitrogen atoms. Testing of catalytic activity in cyclopropanation [a] Ligated gold(III) complexes based on bisoxazoline, [14,15] pyridinyl-oxazolines [16] and 2,6-bisoxazoline-pyridine [17] have previously been prepared with different counterions. Given the affinity of gold(III) to coordinate to such heterocyclic ligands, we initially studied the coordination ability of gold(III) to (S)-4-isopropyl-2-(quinolin-2-yl)-4,5-dihydrooxazole, 1a, and (S)-4phenyl-2-(quinolin-2-yl)-4,5-dihydrooxazole, 1b, (Scheme 1a). The coordination of the alkyl-substituted ligand (R = iPr) to AuCl 3 seemed to give a mixture of two complexes ( 1 H NMR). Addition of NH 4 PF 6 has been reported [18] to activate gold(III)
EurJOCEuropean Journal of Organic Chemistry for coordination. This method allowed successful formation of the oxazole mono-coordinated crystalline 1a-Au(III) complex as the only product (74 % yield, Scheme 1a). Addition of NH 4 PF 6 was not required to efficiently obtain the corresponding 1b-Au(III) complex (98 %) with the phenyl-substituted ligand (R = Ph). Scheme 1. Preparation of (a) 1-Au(III), (b) 2-Au(III) complexes [19] and (c) Pyr-/ Qu-oxazoline ring opened product.As 15 N NMR chemical shifts have proven to give valuable information on metal coordination, [20] the observed coordina-Eur.