A Fumaronitrile Complex of Rhodium(I). Structure of iodo(Fumaronitrile)(triphenyl phosphite)bis(p-methoxyphenyl isocyanide)rhodium(I), RhI(trans-H(NC)C═C(CN)H)(P(OC₆H₅)₃)(P-CH₃OC₆H₄NC)₂

The solid-state structure of the title complex which exhibits dynamic solution behavior has been determined from three-dimensional X-ray data collected by counter techniques. The material crystallizes in space group C_2h⁵-P2₁/c of the monoclinic system with four molecules of the complex in the unit cell. Crystal data are a = 15.252 (7) Å, b = 11.454 (6) Å, c = 21.933 (11) A, β = 103.62 (2)°, and V = 3723.7 Å3. The observed and calculated (Z = 4) densities are 1.57 (2) and 1.577 g/cm³, respectively. The structure, including the H atoms of the fumaronitrile ligand, has been refined (on F) by a full-matrix least-squares procedure to a conventional agreement index of 0.040 for 4357 observations having F_o²3σ(F_o²). The structural results reveal trigonal-bipyramidal coordination about the Rh atom with trans-axial isocyanide ligands (C-Rh-C = 177.7 (2)°) situated at 1.964 Å (average) from the metal. The equatorial plane contains an iodo, a triphenyl phosphite, and a symmetrically Π-bonded fumaronitrile ligand. The olefinic carbon atoms lie almost exactly in the plane defined by Rh, I, and P (average deviation 0.05 Å) and are equidistant from the metal: Rh-C = 2.139 A (average). The distance from the Rh atom to the midpoint of the olefinic bond (Ct) is 2.013 Å. There is considerable angular distortion in the equatorial plane: I-Rh-P = 102.37 (5)°, I-Rh-Ct = 118.9 (2)°, and P-Rh-Ct = 138.7 (2)°. The distortions within the olefin are about as expected: the olefinic C-C distance is 1.444 (10) Å and the substituents are bent back and away from the metal center by 28° (average). Other distances of interest are Rh-P = 2.265 (2) Å and Rh-I = 2.739 (2) Å. The implications of the solid-state structure on the interpretation of the dynamic solution behavior of this and related complexes are discussed.