Novel Hemilabile (Phosphinoalkyl)arene Ligands: Mechanistic Investigation of an Unusual Intramolecular, Arene−Arene Exchange Reaction

The novel, hemilabile (phosphinoalkyl)arene ligands ArX(CH 2 ) 2 PPh 2 ( 1a, Ar = C 6 H 5, X = O; 1b, Ar = C 6 H 5, X = CH 2; 1c, Ar = FC 6 H 4, X = CH 2 ) were synthesized and complexed to Rh(I) to form the bis(phosphine), η 6 -arene piano stool complexes [(η 6:η 1 -ArX(CH 2 ) 2 PPh 2 )Rh(η 1 -ArX(CH 2 ) 2 PPh 2 )]BF 4 ( 2a − c ). Complexes 2a − c were fully characterized in solution, and complex 2a was characterized by single-crystal X-ray diffraction methods. Two of these complexes, 2a, c, undergo an unusual, degenerate η 6 -arene, free arene exchange reaction which was studied by 2-D NMR EXSY experiments. A mechanism for the exchange reaction of 2a which involves the formation of a square planar, cis -phosphine, cis -ether Rh(I) complex, [Rh(η 2 -PhO(CH 2 ) 2 PPh 2 ) 2 ]BF 4 ( 13 ), is proposed.