A Macrocyclic Gold(I)–Biphenylene Complex: Triangular Molecular Structure with Twisted Au₂(diphosphine) Corners and Reductive Elimination of [6]Cycloparaphenylene

Abstract

The digold(I) complex [Au 2 Cl 2 (Cy 2 PCH 2 PCy 2)] reacts with 4,4'-diphenylene diboronic acid to form a triangular macrocyclic complex with twisted Au-P-C-P-Au groups at the three corners. The synthesis of the complex and its chemical oxidation produced [6]cycloparaphenylene ([6]CPP) in 59 % overall yield. Organogold complexes have attracted attention because of both their characteristic structures and properties potentially useful in catalysis, liquid crystals, devices, bioimaging, and therapies. [1] Gold(III) complexes have common square-planar structures, but they attracted much less attention than complexes of Pt II , the other 5d 8 metal. [2] Gold(I) prefers linear two-coordinated structure, and forms dinuclear complexes with diphosphine ligands such as a,w-bis(diphenylphosphino)alkanes, which are normally used as chelating ligand. [3, 4] Aurophilicity between two Au I centers stabilizes the molecular structure and conformation with close Au I positions (Au À Au distance of about 3.0). [5] Multinuclear organogold(I) complexes with such components are expected to have unique structures. Figure 1 summarizes macrocyclic complexes having more than two Au I ÀC bonds. [6] A dinuclear arylgold(I) complex with a diphosphine ligand [Au 2 (C 6 H 4-F-4) 2 (dppm)] (dppm = bis(diphenylphosphino)methane) was recently reported to cause reductive elimination of 4,4'-difluorobiphenyl upon oxidation with PhICl 2. [7] The reaction involves the oxidative chlorination of two Au I centers, the intramolecular migration of an aryl ligand, forming a chloro(diaryl)gold(III) center, and 1,1reductive elimination of biaryl (Scheme 1). This new kind of C(sp 2)-C(sp 2) bond-forming reaction can be extensively applied to synthesis of conjugated aromatic compounds.

A Fourfold Gold(I)−Aryl Macrocycle with Hyperbolic Geometry and its Reductive Elimination to a Carbon Nanoring Host

“…However, utilizing reversible Pt‐complexation often resulted in complex product mixtures typically containing various ring sizes of the reductively eliminated carbon nanorings [41–46] . We were intrigued by a synthetic protocol for carbon nanorings based on an Au I ‐macrocyclization with a promising size‐selectivity by Tsuchido, Osakada, and co‐workers [47] . This approach is limited to triangular geometries using rigid rod‐shaped aromatic subunits [48] .…”

“…Following this approach, we now used an extended ethylene glycol‐functionalized subunit A in an Au I ‐macrocyclization protocol by Tsuchido, Osakada, and co‐workers (Scheme 1). [47] In this approach, a dinuclear gold(I) complex is used as a corner motif to subsequently obtain an extended carbon nanoring as supramolecular host [50] …”

“…Formation of several ring sizes and low yields are common features observed in other examples following the platinum‐mediated macrocyclization, including our own ethylene glycol‐functionalized cyclo[ n ]pyrenylenes [41, 42, 44, 61, 62] . We therefore turned to gold(I)‐mediated macrocyclization methods and targeted a cyclotrimerization strategy with the initial aim to form a triangular‐shaped macrocycle [47, 48] …”

Ein vierfacher Gold(I)−Aryl‐Makrozyklus mit hyperbolischer Geometrie und dessen reduktive Eliminierung zu einem Kohlenstoffnanoring‐Wirt

“…Diese Werte liegen im gleichen Bereich wie die von literaturbekannten dreieckigen Strukturen. Sie bestimmen hier die hyperbolische Geometrie dieses vierfachen Makrozyklus mit signifikant geringeren Eckenwinkeln als 90° [47, 48] . Die Starrheit zwischen den beiden Au I ‐Zentren ist durch attraktive aurophile Wechselwirkungen begründet, während die Flexibilität aus den [6]CMP‐Untereinheiten resultiert (Torsionsfreiheitsgrade um die Phenyl–Phenanthrenyl‐Bindungen, Abbildung 3a).…”

Combined Approach of Hypervalent Iodine Reagents and Transition Metals in Organic Reactions

“…First the reaction between digold(I)‐complex with 4,4‐diphenylene diboronic acid gave triangular macrocycle with twisting corners (Scheme 123) which on further oxidation produced [6] CPP. The products formed in high yields and reaction proceeded in short steps [127] …”