Studies of Tetrakis(trifluoroacetate) Dirhodium. 2. A Pi Complex of Hexamethylbenzene with Tetrakis(trifluoroacetate) Dirhodium(II,II)

The solid-state reaction of Rh 2 (O 2 CCF 3 ) 4 with C 6 Me 6 yields a one-dimensional copolymer [Rh 2 (O 2 CCF 3 ) 4 ·C 6 Me 6 ] ∞ ( 1 ), which constitutes the first example of a dirhodium(II,II) carboxylate complex with arene. Compound 1 has been characterized by elemental analysis and IR and mass spectroscopy, and its structure has been determined by X-ray diffraction. In the crystal structure of 1 the alternating arrangement of Rh 2 (O 2 CCF 3 ) 4 and C 6 Me 6 units forms infinite chains extended along the [100] direction. The coordination of hexamethylbenzene to the dirhodium unit is unsymmetrical, with two opposite edges of the arene ring approaching the axial sites of the dimers. This off-centered complexation causes no distortion of the aromatic system. The closest Rh−C arene contacts (2.770(6) and 2.787(6) Å) are the longest for any axial interactions to dirhodium carboxylates known to date. At the same time, the Rh−Rh distance (2.422(1) Å) is not as short as might have been expected in the case of total absence of axial donation.