Investigation of Electronic Communication and Guest Inclusion Using Photoluminescent Macrocyclic Receptors with RuII Centers and Ph2P−C≡C−C≡C−PPh2 Spacers

Abstract

The study of photoluminescent and redox-active supramolecular systems has attracted recent attention as a consequence of a rapid growing interest in designing artificial arrays for applications in photonic and electronic devices. [1, 2] Systems with various designs have been studied using the assembly of active (for example, metal-based chromophores and redox-active moieties) and passive components (for example, rigid or flexible spacers) as a basis. [1±7] Such systems are constructed to gain a practical insight into parameters and factors that govern processes, such as signal transportation, by electron/energy transfer, electronic and excitonic interaction, as well as guest inclusion and selective molecular sensing.We have become interested in investigating the photoluminescent and redox-active macrocyclic inorganic cyclophanes for their dual capability in molecular recognition through host ± guest interaction and electronic communication between multiple redox centers within a macrocyclic platform. Monomeric model complex [RuCl(tpy)(C 4 P 2 ) 2 ]-(PF 6 ) (1), rectangular dimer [{RuCl(tpy)(C 4 P 2 )} 2 ](PF 6 ) 2 (2), and triangular macrocycle [{RuCl(tpy)(C 4 P 2 )} 3 ](PF 6 ) 3 (3) have been prepared from [RuCl(tpy)]-based moieties (tpy 2,2':6',2''-terpyridine) and rigid ditopic phosphane spacer Ph 2 P À C C À C C À PPh 2 (C 4 P 2 ), in order to study the redox interaction and guest inclusion by electrochemical and optical methods. The short alkyne bridge affords the desired structural rigidity to provide controllable cavity sizes in the systems. The Ru II -based moieties with polypyridine and polyphosphane ligands also have well-behaved reversible redox properties and photoluminescence characteristics. Such properties are extremely important for the design and applications of new spectral and electrochemical sensory agents for organic guests based on organometallic and coordination receptor systems. [4] Herein, the synthesis, chromatographic separation, and characterization of 1 ± 3 are reported. Other properties have also been studied, including the ground-state absorption, excited-state emission, redox characteristics, and guest inclusion using anisole and 1,4-dimethoxybenzene as guest molecules. Specifically, the emission intensities of hosts 2 and 3 increase steadily upon addition of guest molecules, and the binding constants of both guest molecules increase significantly when the trimeric system 3 with the larger cavity is used. In addition, the redox interaction between the metalbased corner units is also investigated using cyclic and squarewave voltammetry. The best electronic communication is observed between the two terminal Ru II centers in the doubly bridged complex 2.The spacer C 4 P 2 is prepared from Me 3 Si À C C À CCÀSiMe 3 by treatment with 2.5 equivalents of MeLiĹ iBr and then 2.5 equivalents of ClPPh 2 . Complexes 1 ± 3 are obtained upon reaction of C 4 P 2 and [RuCl 3 (tpy)] (3/1 ratio, with an excess NH 4 PF 6 ) in refluxing THF/ethylene glycol mixture (4/1), in yields of 15, 30, and...

Unexpected Photochemical Reactivity of Ruthenium(II) Polypyridine Complexes Induced by a Bis(bidentate) Phosphine

“…In this work, we report that the bis(bidentate) phosphine cis , trans , cis -1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb) (see Chart 1) prepared in our laboratory only recently and designed as a spacer having two bidentate sets of coordination sites to incorporate molecular components such as [Ru(bipy) 2 ] 2+ , where bipy is 2,2‘-bipyridine, leads to a completely unexpected photochemical reactivity of the resulting homobimetallic complexes [Ru 2 (dppcb)(bipy) 4 ] 4+ . To the best of our knowledge, no other phosphine combined with the building block [M(bipy) 2 ] 2+ (M = Ru, Os) shows this reactivity. − Both diastereoisomerically pure forms of [Ru 2 (dppcb)(bipy) 4 ] 4+ undergo a photochemical ligand exchange reaction, where in the presence of acetonitrile [Ru 2 (dppcb)(bipy) 2 (MeCN) 4 ] 4+ is produced (see Chart 1), and all three complexes have been fully characterized by X-ray diffraction methods. Hitherto, this type of reaction has been mainly restricted to carbonyl complexes of Ru(II), − [Ru(bipy) 3 ] 2+ , Ru(II)−arene systems, and Ru(II) compounds containing Schiff base ligands …”