An ew class of supramolecular metallacycles capable of undergoing photochemical reactions and in situ release of cyclobutanes in solution is described. The molecular metallacycles were generated through coordination-driven selfassembly of dinuclear metal-carbene complexes as organometallic clips with olefin-functionalized bridging ligands.Photolysis of these molecular metallacycles in situ led to structural interconversion and release of the formed cyclobutane products with quantitative conversion. Further modifications of the obtained cyclobutanes provided as eries of new species containing the cyclobutane skeleton.
Supramolecularcontrolofphotocycloadditionshasemergedas an important strategy for the construction of cyclobutane derivatives by [2+ +2] photodimerizations. [1][2][3][4] However,t he current scope of supramolecular photochemistry is generally restricted to reactions occurring in the solid state. [5][6][7][8][9][10] Contrary to this situation, the control of the outcome of intermolecular photochemical reactions in homogeneous solutions remains asignificant challenge. [1,11] By introduction of suitable templates,i tm ay be possible to achieve similar topochemical control in solution reactions as is possible in the solid state.M olecular flasks and containers have previously been found to influence and enhance the photochemical [2+ +2] cycloadditions of selected olefin substrates in solution. [12][13][14][15] Some cation-p interactions can also facilitate the formation of cyclobutanes in solution, [16] and even adynamic G-quadruplex has been shown to serve as as upramolecular template for photodimerization. [17] By taking advantage of the good solubility of discrete assemblies, [18,19] our recent investigations have demonstrated that supramolecular metallamacrocycles,e specially metalcarbene templates,a llow photochemical [2+ +2] dimerization of olefin-containing ligands in solution (Figure 1a). [20] These scaffolds,although versatile,suffer from difficulties related to the removal of the template metal in the assembled systems, hampering the isolation of the formed cyclobutane derivatives.H erein we report the synthesis of an ew class of supramolecular metallacycles capable of undergoing photochemical reactions in solution (Figure 1b). These new molecular metallacycles were generated by employing dinuclear metal-carbene organometallic clips and olefin-functionalized bridging ligands through coordination-driven self-assembly. Photolysis of these molecular metallacycles in situ led to structural interconversion and release of the formed cyclobutane products with quantitative conversion. In addition, the further application of the obtained cyclobutanes has been investigated, resulting in the synthesis and characterization of as eries of new species containing the cyclobutane skeleton.As proof of our concept, the formation of as uitable molecular metallacycle can easily be realized by combination of two organometallic clips and two linear organic linkers. [18] Different organometallic clips were initially ...
