Studies of tetrakis(trifluoroacetate) dirhodium. 2. A pi complex of hexamethylbenzene with tetrakis(trifluoroacetate) dirhodium(II,II)

The solid-state reaction of Rh-2(O2CCF3)(4) with C6Me6 yields a one-dimensional copolymer [Rh-2(O2CCF3)(4). C6Me6]infinity (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(O2CCF3)(4) and C6Me6 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) Angstrom) are the longest for any axial interactions to dirhodium carboxylates known to date. At the same time, the Rh-Rh distance (2.422(1) Angstrom) is not as short as might have been expected in the case of total absence of axial donation.