Synthesis, Structure, and Catalytic Applications for ortho- and meta-Carboranyl Based NBN Pincer-Pd Complexes
Min Ying Tsang, Clara Viñas, Francesc Teixidor, José Giner Planas*, Nerea Conde, Raul SanMartin, María Teresa Herrero, Esther Domínguez, Agustí Lledós, Pietro Vidossich, and Duane Choquesillo-Lazarte.
Inorg. Chem., 2014, 53 (17), pp 9284–9295
o- and m-Carborane-based NBN pincer palladium complexes (oCB-L1)Pd, (oCB-L2)Pd, and(mCB-L1)Pd are synthesized in two steps from commercially available starting materials. The pincer complexes were prepared by the reaction of bis-[R(hydroxy)methyl]-1,2-dicarba-closo-dodecaborane (R = 2-pyridyl oCB-L1, 6-methyl-2-pyridyl oCB-L2) or bis-[2-pyridyl (hydroxy)methyl]-1,2-dicarba-meta-dodecaborane (mCB-L1) with [PdCl2(MeCN)2] under mild conditions. The X-ray structure determination of all carboranyl pincer complexes shows unambiguously B–H activation of the carborane cages. The results agree with the Pd–B bonds in all complexes exhibiting strong σ-electron donation. Theoretical calculations reveal the importance of considering the solid state intermolecular hydrogen bonding when investigating the trans influence in organometallic chemistry. A localized orbitals approach has also been applied to analyze the metal oxidation state in the carboranyl pincer complexes. Catalytic applications of (oCB-L1)Pd and (mCB-L1)Pd have shown the complexes are good catalyst precursors in Suzuki coupling in water and with very low amounts of catalyst loadings.
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