Cationic methyl complexes of rhodium(III): synthesis, structure, and some reactions

Reactivity of cationic methyl rhodium(III) complexes cis-[Rh(β-diket)(PPh3)2(CH3)(CH3CN)][BPh4] toward ligands of different character: pyridine, carbon monoxide, and triphenylphosphine

“…In the case of isomerization 2 ð3Þ ! 4 ð5Þ the process seems to include only the methyl ligand migration within the equatorial plane, and moreover, the presence of b-diketonate ligand with a bite angle value of $90° [6,[29][30][31][32][33][34][35][36] could facilitate this migration making two other equatorial angles more capacious then in the ideal tbp [37]. Observed incompleteness of the isomerization reactions for 24 h may be caused either by equilibrium between acyl and methyl carbonyl complexes [9,24,26,27] or by kinetic reasons.…”

“…Recently [6], we detected two dynamically exchanged isomeric forms of the cation in solution of the salt cis-[Rh (b- There is no doubt that this dynamic isomerization proceeds through acetonitrile dissociation, which produces a variety of undetectable fluxional pentacoordinate species of sp and tbp configurations. The adjunction of carbon monoxide molecule to some of these species may generate short-lived intermediates containing methyl and carbonyl ligands in cis position and thus appropriate to the transformation into acetyl complexes by migratory insertion.…”

“…Recently, we isolated and characterized two cationic methyl complexes of rhodium(III), cis-[Rh(b-diket)(PPh 3 ) 2 -(CH 3 )(CH 3 CN)] + [BPh 4 ] À (b-diket is acetylacetonate or benzoylacetonate ligand) [6], which may be considered as stable analogs of unstable ionic intermediates. According to X-ray data, both phosphines in these cations in the solid state lie in the same (''equatorial'') plane with the b-diketonate ligand.…”

“…Here, we report reactions of the complexes cis-[Rh(b-diket)(PPh 3 ) 2 (CH 3 )(CH 3 4 ] with three ligands, pyridine, carbon monoxide and triphenylphosphine, widely differing in their electronic properties and reactivity. [6]. The 1 H NMR spectrum of complex 1 consists of a group of signals of phenyl protons (d 6.8-7.5 ppm), signals of coordinated pyridine (d 6.74 and 8.09 ppm), 1 a signal from methine proton of the acetylacetonate ligand (d 4.37 ppm) and a number of signals from methyl protons in the region d 1-2 ppm.…”

“…The coupling to 103 Rh and two inequivalent 31 P nuclei is not resolved. On the basis of NMR spectra, we assign to the cation of 1 the following structure, akin to the structure of cation cis-[Rh(Acac)(PPh 3 ) 2 (CH 3 )(NH 3 )] + , which has been determined by NMR spectra and X-ray analysis [6]. The IR spectra of complexes 2 and 3 display intense bands with maxima at 1726 cm À1 (2) and 1728 cm À1 (3), which correspond to the m(CO) stretching vibration in the -C(@O)Me group of acetyl rhodium(III) complexes [3,5,[8][9][10][11][12][13][14][15][16][17].…”