m-Terphenyl Anchored Palladium Diphosphinite PCP-Pincer Complexes That Promote the Suzuki-Miyaura Reaction Under Mild Conditions

Diphosphinite PCP-pincer pro-ligands anchored by a meta-terphenyl backbone were synthesized. These pro-ligands, [2,6-(2-Ph2POC6H4)(2)C6H3X] (3a X = 1, 3b X = Br) and [2,6-(2-(Pr2POC6H4)-Pr-i)(2)C6H3X] (4a X = 1, 4b X = Br) upon reaction with Pd-2(dba)(3) yield PCP palladium pincer complexes [2,6-(2Ph(2)POC(6)H(4))(2)C6H3PdX] (5a X = I, 5b X = Br) and [2,6-(2-(Pr2POC6H4)-Pr-i)(2)C6H3PdX] (6a X = 1, 6b X = Br). The structures of 5a-b and 6a-b were determined by single crystal X-ray diffraction analyses. Complexes 5b and 6b were evaluated for their efficacy in promoting catalytic Suzuki-Miyaura CC coupling reactions. A variety of aryl bromides efficiently underwent CC coupling reactions with p-tolylboronic acid with high yields in the presence of either 5b or 6b. Compound 6b also proved to be a very active pro-catalyst for the coupling of aryl chlorides with p-tolylboronic acid. Excellent to good yields (in some cases greater than 90%) were achieved even with electron rich or sterically hindered aryl chlorides.