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.
This study investigated the dynamic photoresponse of pseudorotaxane crystals with azobenzene and ferrocenyl groups in the axle component. X-ray crystallography showed pseudorotaxanes with a methylazobenzene group and a dibromophenylene ring in the cyclic component to exhibit twisting of the trans-azobenzene groups at torsion angles of 17° and 38°, respectively. Repeated alternating laser irradiation of the crystals at 360 and 445 nm produced bending of 20-30° in opposite directions, with no evidence of decay. Under 445 nm irradiation, bending took place within 0.3 s. A crystal of nonsubstituted pseudorotaxane showed bending of only 2° under 360 nm irradiation due to multiple π-π interactions between the planar trans-azobenzene groups. The pseudorotaxane crystals have two chromophores, bent rapidly and reversibly on irradiation at rates depending on the molecular structure.
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