m-Terphenylphosphines: Synthesis, structures and coordination properties

Abstract A series of m -terphenylphosphines TerphPCl 2 , TerphPH 2 and TerphPMe 2 (Terph = 2,6-Mes 2 C 6 H 3 –, 2,6-(4- t -BuC 6 H 4 ) 2 C 6 H 3 –, 2,6-(3,5-Me 2 C 6 H 3 ) 2 C 6 H 3 –, 2,6-(2,6-Et 2 C 6 H 3 ) 2 C 6 H 3 –, and 2,6-(2,6- i -Pr 2 C 6 H 3 ) 2 C 6 H 3 –; Mes = 2,4,6-Me 3 C 6 H 2 –) 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-Mes 2 C 6 H 3 PH 2 , 6 , and the dimethylphosphine 2,6-(3,5-Me 2 C 6 H 3 ) 2 C 6 H 3 PMe 2 , 9 , readily form complexes with the Cl 2 Ru( p -cymene) complex fragment, whereas the larger phosphine 2,6-Mes 2 C 6 H 3 PMe 2 , 8 , does not. Heating of the complexes TerphPR 2 Ru(Cl 2 )( p -cymene) 11 and 12 and the mixture of 8 and {( p -cymene)RuCl 2 } 2 lead to expulsion of the p -cymene ligand and intramolecular η 6 coordination of one of the flanking arene rings to the ruthenium center to afford the complexes Cl 2 RuP(H 2 )C 6 H 3 -2-η 6 -Mes-6-Mes, 13 , Cl 2 RuP(Me 2 )C 6 H 3 -2-η 6 -Mes-6-Mes, 14 , and Cl 2 RuP(H 2 )C 6 H 3 -2-η 6 -(3,5-Me 2 C 6 H 3 )-6-(3,5-Me 2 C 6 H 3 ), 15 . All complexes were characterized by NMR spectroscopy and complexes 14 and 15 also by X-ray crystallography.