SYNTHESIS, X-RAY STRUCTURES AND SOLUTION STUDIES OF NEW ORGANO-RHODIUM(III) COMPLEXES WITH STIBINE, PYRIDINE AND PYRIMIDINE-DERIVATIVES

The synthesis, X-ray structure and spectroscopic characterization of new organo-rhodium(III) compounds is reported. From the reaction of RhCl3 with SbPh3 (Ph=-C6H5, 1:3-4 molar ratio), in boiling ethanol, a mixture of [trans-RhCl2(Ph)(SbPh3)3] (1) and [mer-RhCl3(SbPh3)3] (2) was obtained. A previous hint on this reaction is given by R. Cini, G. Giorgi and E. Periccioli, Acta Crystallogr., Sect. C, 47 (1991) 716. The separation of 1 and 2 was carried out by recrystallizing the mixture from acetone: 1.(CH3)2CO precipitates first. 1 was separated from 2 also through chromatographic techniques (SiO2 column, CH2Cl2 eluent). High yield preparation of 1 was carried out on adding Ag(CF3SO3) to the suspension obtained by refluxing a mixture of RhCl3 and SbPh3 (Rh/Sb/Ag molar ratio of 1:4:1). High yield synthesis of 2 was obtained by refluxing an ethanol mixture of RhCl3 and SbPh3 (1:3) in the presence of an excess of Cl-, or by refluxing a mixture of RhCl3 and SbPh3 (1:10) in ethanol solvent. Orange crystals of 1.0.45(CH3)2CO belong to the triclinic system, space group P1Bar (No. 2) with a=12.686(2), b=14.906(2), c=15.523(3) angstrom, alpha=107.73(2), beta=95.10(2), gamma=93.62(2)-degrees, Z=2, D(c)=1.60 g cm-3. The structure was refined to R=0.0594 and R(w)=0.0651. The complex molecule consists of an octahedrally coordinated Rh(III) center linked to two trans Cl- ions, and to a Ph and to three SbPh3 ligands in the basal plane. A Rh-Sb bond is much lengthened by a strong trans influence from the Ph ligand. 1 reacted with an excess of pyridine (Py) and 3,5-dimethylpyridine (3,5-lutidine, Lu) in refluxing methanol to produce [trans-RhCl2(Ph)(Py)3] (3) and [trans-RhCl2(Ph)(Lu)3] (4), respectively. 1 reacted also with boiling CH3CN to produce [RhCl2(Ph)-CH3CN)(SbPh3)2] 3 reacted with an excess of 4-methylpyrimidine (Mp) in refluxing methanol to produce [trans-RhCl2(Ph)(Py)2(MP)] (5). Yellow needles of 3 belong to the tetragonal system, space group I4(1)/acd (No. 142), with a=15.660(2), c=17.044(2) angstrom, Z=8, D(c)=1.55 g cm-3. The structure was refined to R=0.0402 and R(w)=0.0446. Yellow prisms of 4 belong to the tetragonal system, P4/nnc (No. 126), a=11.522(3), c=10.289(2) angstrom, Z=2, D(c)=1.39 g cm-3 . The structure was refined to R=0.0579 and R(w)=0.060 1. Both 3 and 4 contain two Cl- ligands trans to each other, a Ph group and three Py or Lu molecules in the equatorial sites. Their H-1 NMR spectra show large downfield shifts for the signals relevant to the Py or Lu ligand molecule trans to Ph. The H-1 NMR spectrum of 5 shows that the two Py ligands are trans to each other and that Mp is coordinated through N(1), which occupies the position trans to Ph. The complex molecules of 3, 4 and 5 are stable in CHCl3 solution, at room temperature for periods of hours. The reaction of 2 with an excess of Py in refluxing methanol produced the well known complex [trans-RhCl2(Py)4]+.