Synthesis, X-ray structures and solution studies of new organo-rhodium(III) complexes with stibine, pyridine and pyrimidine derivatives

Abstract

The synthesis, X-ray structure and spectroscopic characterization of new organo-rhodium(III) compounds is reported. From the reaction of RhCl 3 with SbPh 3 (Ph−C 6H 5, 1:3–4 molar ratio), in boiling ethanol, a mixture of [ trans-RhCl 2(Ph)(SbPh 3) 3] ( 1) and [ mer-RhCl 3(SbPh 3) 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·(CH 3) 2CO precipitates first. 1 was separated from 2 also through chromatographic techniques (SiO 2 column, CH 2Cl 2 eluent). High yield preparation of 1 was carried out on adding Ag(CF 3SO 3) to the suspension obtained by refluxing a mixture of RhCl 3 and SbPh 3 (Rh/ Sb/Ag molar ratio of 1:4:1). High yield synthesis of 2 was obtained by refluxing an ethanol mixture of RhCl 3 and SbPh 3 (1:3) in the presence of an excess of Cl −, or by refluxing a mixture of RhCl 3 and SbPh 3 (1:10) in ethanol solvent. Orange crystals of 1·0.45(CH 3) 2CO belong to the triclinic system, space group P 1 (No. 2) with a=12.686(2), b=14.906(2), c=15.523(3) Å, α=107.73(2), β=95.10(2), γ=93.62(2)°, 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 SbPh 3 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-RhCl 2(Ph)(Py) 3] ( 3) and [ trans-RhCl 2(Ph)(Lu) 3] ( 4), respectively. 1 reacted also with boiling CH 3CN to produce [RhCl 2(Ph)- (CH 3CN)(SbPh 3) 2] 3 reacted with an excess of 4-methylpyrimidine (Mp) in refluxing methanol to produce [ trans- RhCl 2(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) Å, 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) Å, Z=2, D c=1.39 g cm −3. The structure was refined to R=0.0579 and R w=0.0601. 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 1H NMR spectra show large downfield shifts for the signals relevant to the Py or Lu ligand molecule trans to Ph. The 1H 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 CHCl 3 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-RhCl 2(Py) 4] +.