The tridentate ligand C6H6P[CH2CH2CH2P(C6H5)2]2, L, forms RhLX complexes (X = Cl, Br, I), which are dissociatively stable in nonaqueous solvents. The chloride complex, RhLCl, reacts readily with a variety of small molecules to form five-coordinate, nonionic derivatives, RhLCl A, where A = BF3, CO, SO2, and O2. The S2 adduct, RhLCl S2, was prepared by treating RhLCl with S8 in benzene. Cationic complexes of RhLCl were made by two general methods: (1) addition of a positively charged ligand (electrophile), or (2) displacement of the chloride ion by a neutral ligand. The most important difference between the two methods is that rhodium remains Rh(I) in the latter case, whereas in the first case oxidation formally to Rh(III) occurs. For example, the five-coordinate, cationic complexes [RhLCl· A]+ were prepared by treating RhLCl with the cationic reagents H+, NO+, N2Ph+, and CH3CO+. Four- and five-coordinate cations [RhL(CH3CN)]+, [RhL(CO)]+, and [RhL(CO)2]+ can be obtained by chloride displacement from RhLCl in polar solvents. The interconversions and chemical reactions of some of the above complexes are presented. The structures of the parent compound, RhLCl, and its nitrosyl derivative, [RhLCl(NO)][PF6], have been determined from three-dimensional X-ray data collected by counter methods. The yellow parent compound crystallizes in space group C2h2-P21/m of the monoclinic system with two molecules in a unit cell of dimensions a = 9.312 (1), b = 21.187 (2), c = 8.851 (3) Á, and β = 105.39 (1)°. The observed and calculated densities are 1.36 (1) and 1.38 g cm-1, respectively. Full-matrix least-squares refinement gave a final value of the conventional R factor (on F) of 0.035 for the 2566 reflections having F2 > 3σ-(F2). The structure consists of discrete monomers, and the coordination geometry around the metal is square planar. The molecule has imposed m symmetry. Some important bond lengths in the parent compound are as follows: Rh-P-(terminal), 2.288 (1); Rh-P(central), 2.201 (2); and Rh-Cl, 2.381 (2) Á. The nitrosyl derivative crystallizes in space group D2h16-Pnma with four molecules in a unit cell of dimensions a = 24.350 (5), b = 15.196 (2), and c = 9.914 (2) Ä. The observed and calculated densities are 1.57 (1) and 1.58 g cm-3, respectively. Full-matrix least-squares refinement gave a final value of the conventional R factor (on F) of 0.055 for the 1282 reflections having F2 > 3σ(F2). The structure consists of discrete monomers. Addition of a nitrosyl ligand to the parent compound, RhLCl, gives a tetragonal pyramidal coordination around the rhodium atom of [RhLCl(NO)][PF6], with imposed mirror symmetry as in the parent compound. The nitrosyl ligand itself is bent, with a Rh-N-O bond angle of 131 (1)°. Some important bond lengths in the nitrosyl derivative are as follows: Rh-P(terminal), 2.374 (3); Rh-P-(central), 2.282 (4); Rh-Cl, 2.408 (4); and Rh-N, 1.91 (2)À. The relationship between structure and reactivity is discussed.
ASJC Scopus subject areas
- Colloid and Surface Chemistry