Exploring new superstructures in homoleptic gold-thiolate, gold-alkynyl complexes and ruthenium molecular wheels

Abstract

Transition metal-thiolate and -alkynyl complexes are of special interest for their structural diversity, intriguing chemical and physical properties, and broad applications in supramolecular chemistry. This thesis describes self-assembly of novel types of supramolecular ensembles that adopt fascinating structures, including ring-in-ring, trefoil knot, and wheel, based on Au-thiolate, Au-alkynyl, or Ru-thiolate coordination. A dodecanuclear Au(I)-thiolate cluster [Au(SC4)]12 (Au12, C4 = 9,9-dibutyl-9H-fluorene-2-yl) was prepared by recrystallization of the [2]catenane [Au(SC4)]10 (Au10) from alkane solvents such as hexane. The Au12 cluster possesses an unprecedented ring-in-ring structure with its two rings held together by weak, metallophilic (AuI•••AuI) interactions, unlike previously reported ring-in-ring structures formed by hydrogen bonding, donor-acceptor, host-guest, or metal-ligand interactions. The Au12 ring-in-ring cluster underwent cluster core change to give the thermodynamically more stable Au10 [2]catenane upon dissolving in, or recrystallization from, other solvents such as DCM and CHCl3. Both the ring-in-ring and [2]catenane structures have been characterized by NMR spectroscopy, ESI-MS spectrometry, elemental analysis, and X-ray crystal structure determination. The cluster-to-cluster transformation process in solution was monitored by 1H NMR and ESI-MS measurements. Density functional theory (DFT) calculations were performed to provide insight into the mechanism of the ‘ring-in-ring↔[2]catenane’ interconversions, which could be rationalized by considering various interactions including ligand-ligand and metal-ligand dispersive interaction as well as metallophilic interaction. Two pentadecanuclear Au(I)-alkynyl clusters [Au(C≡C-Cn)]15 (Au15), wherein Cn = C4 or 9,9-dihexyl-9H-fluorene-2-yl (C6), with trefoil knot structures featuring metallophilic interactions between the loops of each trefoil knot strand, were synthesized by reaction of [Au(THT)Cl] (THT = tetrahydrothiophene) with monoalkynes Cn-C≡CH (n = 4 or 6). This contrasts with the required use of bi- or multidentate/multipodal ligands for preparing previously reported metal trefoil knot structures, which have metal nuclearity of ≤8 and do not feature inter-loop metallophilic interactions. The Au15 trefoil knots, characterized by X-ray crystal structure determination and also NMR and ESI-MS analysis and constituting unique type of gold compounds and homoleptic metal-alkynyl complexes, underwent cluster core change to [Au(C≡C-Cn)]12 (Au12′; n = 4 or 6) upon dissolving in DCM or benzene, and were re-assembled by recrystallization from acetone. A dynamic equilibrium was established in acetone-d6 solution between the Au15 and Au12′ clusters according to 1H NMR measurements. The Au15↔Au12′ inter-conversion was studied by NMR and UV-vis measurements. Trefoil knots Au15 can react with Cu(I)- or Ag(I)-alkynyl complexes, producing hetero-bimetallic trefoil knots [Au9M6(C≡C-Cn)15] (M = Ag, Cu; n = 4, 6); similar reactions for Au12′ gave two hetero-bimetallic [2]catenanes, [Au6M6(C≡C-Cn)12] (M = Ag, Cu; n = 6). In addition, a series of hexnuclear Ru6 and octanuclear Ru8 molecular wheels, including [Ru(CO)2(μ-STrip)(μ-X)]n (n = 6, X = Cl-, Br-; n = 8, X = I-; Trip = 2,4,6-triisopropylphenyl), based on edge-shared octahedra were prepared. These Ru6 and Ru8 wheels feature mixed bridging ligands (RS-/X-), different from previously reported [Ru(SR)2(CO)2]n (n = 6, 8) wheels with RS-bridging ligands exclusively. Use of the bulky TripS- along with MeS- ligands enabled the formation of a cubane-type complex, [Ru(CO)2(μ3-SMe)(STrip)]4. The molecular wheels and cubane-type complex were characterized by NMR, UV-vis and IR spectroscopy and ESI-MS spectrometry.