m-Terphenylphosphines: Synthesis, structures and coordination properties

A series of m-terphenylphosphines TerphPCl2, TerphPH2 and TerphPMe2 (Terph = 2,6-Mes2C6H3–, 2,6-(4-t-BuC6H4)2C6H3–, 2,6-(3,5-Me2C6H3)2C6H3–, 2,6-(2,6-Et2C6H3)2C6H3–, and 2,6-(2,6-i-Pr2C6H3)2C6H3–; Mes = 2,4,6-Me3C6H2–) was prepared and fully characterized. The structural investigation by X-ray crystallography and density functional theory revealed significant distortions in the environment of the ipso carbon and phosphorus centers. These can be traced back to steric interactions and repulsions of the chlorine and methyl substituents on phosphorus with one of the flanking arenes of the m-terphenyl substituents. The primary phosphine 2,6-Mes2C6H3PH2, 6, and the dimethylphosphine 2,6-(3,5-Me2C6H3)2C6H3PMe2, 9, readily form complexes with the Cl2Ru(p-cymene) complex fragment, whereas the larger phosphine 2,6-Mes2C6H3PMe2, 8, does not. Heating of the complexes TerphPR2Ru(Cl2)(p-cymene) 11 and 12 and the mixture of 8 and {(p-cymene)RuCl2}2 lead to expulsion of the p-cymene ligand and intramolecular η6 coordination of one of the flanking arene rings to the ruthenium center to afford the complexes Cl2RuP(H2)C6H3-2-η6-Mes-6-Mes, 13, Cl2RuP(Me2)C6H3-2-η6-Mes-6-Mes, 14, and Cl2RuP(H2)C6H3-2-η6-(3,5-Me2C6H3)-6-(3,5-Me2C6H3), 15. All complexes were characterized by NMR spectroscopy and complexes 14 and 15 also by X-ray crystallography.