Cyclometalated Au(III) Complexes With C*N^N, N^C*N, and C*N Ligands Through C–H Activation

Au(III) complexes with N*C^N, N*C, and N^N*C cyclometalating ligands combining the typical five‐ring chelates N^C or N^N with N*C six‐ring chelates, [Au(QPhPy)Cl][AuCl 4 ] ( 1H ), [Au(QPh CF3 Py)Cl][AuCl 4 ] ( 1CF3 ), [Au(QPh tBu Py)Cl][AuCl 4 ] ( 1tBu ), [Au(QPhPy)Cl]Cl ( 2H ), [Au(QPyPh)Cl 2 ] ( 3H ), [Au(QPyPh CF3 )Cl 2 ] ( 3CF3 ), [Au(QPyPh tBu )Cl 2 ] ( 3tBu ), [Au(bpyAn)Cl][AuCl 4 ] ( 4bpy) , and [Au(phenAn)Cl][AuCl 4 ] ( 4phen ) (Q = 8‐quinolinyl, Ph = phenyl, An = anthracen‐9‐yl, Py = pyridyl, bpy = 2,2′‐bipyridyl, phen = 1,10‐phenanthrolinyl) were studied. Crystal structures of 2H , 3tBu , and 4bpy showed planar coordinated Au(III) centers and distortions within the ligand scaffolds and of [AuCl n ] fragments with the aromatic units of the ligand scaffolds. Cyclic voltammograms showed reduction waves at around –0.7 V vs the ferrocene/ferrocenium couple for the [AuCl 4 ] – anions in compounds 1H to 1tBu , 4bpy , 4phen , and [ n ‐Bu 4 N][AuCl 4 ] ( 5 ). They were followed by a number of ligand‐centered reduction processes in the range 0 to –3.4 V in the complexes. Oxidation processes were recorded for 4bpy and 4phen at around 1 V. The assignments of the electrochemical processes are supported by density functional theory (DFT)‐calculated frontier orbitals compositions and energies at the ωB97XD/6‐311++(2d, 2p)/Def2QZVPP level of theory. The UV–vis absorption spectroscopy of the yellow‐orange compounds 1 is dominated by the Cl‐to‐Au charge transfer (XMCT) bands of the [AuCl 4 ] – anions at 330 nm. This band occurs also for 4phen and 4bpy , but the characteristic feature for these red complexes is the intense long‐wavelength bands at 521 nm (bpy) and 539 nm (phen). The orange C*N cyclometalated complexes 3 take a medium position with absorption maxima at 360 nm. TD‐DFT calculations assign the long‐wavelength bands to transitions with dominant π–π* character and admixtures of XMCT, Cl‐to‐ligand (XLCT), metal‐to‐ligand(π*) (MLCT), and ligand(π)‐to‐metal (LMCT) charge transfer transitions.