Palladium-Catalysed Cross-Coupling Reactions Controlled by Noncovalent Zn⋠⋠⋠N Interactions.

Non-covalent interactions between halopyridine substrates and catalytically inert building blocks, namely zinc(II)-porphyrins and zinc(II)-salphens, influence the catalytic outcome of Suzuki-Miyaura and Mizoroki-Heck palladium-catalysed cross-coupling reactions. The weak Zn⋅⋅⋅N interactions between halopyridine substrates and zinc(II)-containing porphyrins and salphens, respectively, were studied by a combination of 1 H NMR spectroscopy, UV/Vis studies, Job-Plot analysis and, in some cases, X-ray diffraction studies. Additionally, the former studies revealed unique supramolecular polymeric and dimeric rearrangements in the solid state featuring weak Br⋅⋅⋅N (halogen bonding), C-H⋅⋅⋅π, Br⋅⋅⋅π and π⋅⋅⋅π interactions. The reactivity of halopyridine substrates in homogeneous palladium-catalysed cross-coupling reactions was found to correlate with the binding strength between the zinc(II)-containing scaffolds and the corresponding halopyridine. Such observation is explained by the unfavourable formation of inactive over-coordinated halopyridine⋅⋅⋅palladium species. The presented approach is particularly appealing for those cases in which substrates and/or products deactivate (or partially poison) a transition-metal catalyst.

The synthesis, crystal structure and spectroscopic properties of luminescent Zn(II) complex.

A luminescent Zn(II) complex 1, ZnL2Cl2.2H2O has been synthesized where L=2,2',2''-(1,3,5-benzenetriyltrimethylidyne) as a yellow crystal. Single crystal X-ray analysis of the compound 1 shows a distorted tetrahedral structure. The compound 1 crystallizes in monoclinic, space group C2/c with a = 20.3151(19), b = 8.7299(9), c = 24.626(2) angstroms, beta = 107.474(2) degrees , V = 4165.9(7) A3. At room temperature, the complex 1 exhibits an intense blue emission at 474 nm upon 380 nm excitation.