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

Abstract

The solid-state reaction of Rh2(O2CCF3)4 with C6Me6 yields a one-dimensional copolymer [Rh2(O2CCF3)4·C6Me6]∞ (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 Rh2(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−Carene 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.

Studies of Dirhodium Tetra(trifluoroacetate). 3. Solid State Isomers of the Compound Rh2(O2CCF3)4(THF) Prepared by Sublimation

“…Several 1:1 adducts of dirhodium(II) carboxylates with donor ligands Rh 2 (O 2 CR) 4 L have been obtained before. Most of them have L ligands with more than one coordination site: IMME ( N , O ), NITMe ( O , O ),2a AAMP ( N , N ),2b DDA ( N , N ), PHZ ( N , N ),2c amp ( N , N ),2d TCNE ( N , N ),2e 1,4-bq ( O , C 2f,g and O , O 2h ), 1,4-nq ( O , C 2f and O , O 2h ), 2,3-Me 2 -1,4-bq ( O , O ),2h C 6 Me 6 ( C , C ) . They all have structures of type II , noted earlier.…”

“…Several years ago we began to examine the behavior of dirhodium(II) tetra(trifluoroacetate), more systematically than had been done before. In our first contribution, which we shall regard as Part 1 of this series, it was established that, in the absence of exogenous donors, Rh 2 (O 2 CCF 3 ) 4 forms a structure in which there are infinite chains of molecules bound end to end ( III ), in a manner well-known for many other M 2 (O 2 CR) 4 compounds. 1a,, More recently (Part 2) it was shown that the compound Rh 2 (O 2 CCF 3 ) 4 ·C 6 Me 6 crystallizes as a one-dimensional copolymer in which bridging hexamethylbenzene molecules alternate with dirhodium units by making π -donor bonds. However, even this unusual 1:1 complex is not different in principle from those of group II since the bridging hexamethylbenzene ligands employ two bonding sites.…”

16 The noble metals

“…The polymeric structure has opposite C 6 ring edges closer to Rh, but the aromatic system is regular. 154 Unlike the paddle-wheel dimeric rhodium(II) carboxylates given by reducing Rh III 4À ; an iridium analogue was also made. 157…”

Electronic and Magnetic Properties of Infinite 1D Chains of Paddlewheel Carboxylates M2(COOR)4 (M = Mo, W, Ru, Rh, Ir, Cu)

“…Typically, the coordination sphere of the Lewis-acidic transition metal center is completed by two weakly bound axial ligands (Figure a). In the absence of donor ligands (e.g., under solventless synthesis conditions , ) acetate paddlewheel complexes associate into infinite 1D chains having an axial interdimer interaction of metal centers with the carboxylate oxygen atoms of neighboring units (Figure b).…”