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-dimensi onal copolymer [Rh-2(O2CCF3)(4). C6Me6]infinity (1), which constitutes the first example of a dirhodium (II,II) carboxylate complex with arene. Compou nd 1 has been characterized by elemental analysis and IR and mass spectrosc opy, and its structure has been determined by X-ray diffraction. In the cry stal structure of 1 the alternating arrangement of Rh-2(O2CCF3)(4) and C6Me 6 units forms infinite chains extended along the [100] direction. The coord ination of hexamethylbenzene to the dirhodium unit is unsymmetrical, with t wo opposite edges of the arene ring approaching the axial sites of the dime rs. This off-centered complexation causes no distortion of the aromatic sys tem, The closest Rh-C-arene contacts (2.770(6) and 2.787(6) Angstrom) are t he longest for any axial interactions to dirhodium carboxylates known to da te. At the same time, the Rh-Rh distance (2.422(1) Angstrom) is not as shor t as might have been expected in the case of total absence of axial donatio n.