T. G. Cherkasova

Carbon-13 nuclear magnetic resonance spectra of rhodium carbonyl complexes

Abstract The 13C NMR spectra of a series rhodium carbonyl complexes were measured. An approximate correlation of δ(13CO) chemical shifts with carbonyl group stretching frequencies ν(CO) was observed. For square planar complexes the variations in ν(CO) parallel that of the coupling constants 1J(RhC). The oxidative addition to planar rhodium(I) complex with formation of octahedral rhodium(III) complex results in opposite trends for ν(CO) and J. The greater ν(CO) value reflects the diminished electron density on the central atom and a lower coupling constant is due to the reduced contribution of the rhodium 5s orbital in the RhCO bond.

Mixed carbonylcyclooctene complexes of rhodium(I). cis-cyclooctene as ligand

Abstract The substitution reactions of carbonyl groups in [Rh(CO) 2 Cl] 2 , Rhacac(CO) 2 , Rhoxq(CO) 2 (acac = acetylacetonate, oxq = 8-hydroxyquinolinate) by cis -cyclooctene, leading to the formation of [Rh(C 8 H 14 )(CO)Cl] 2 , Rhacac- (C 8 H 14 )CO, Rhoxq(C 8 H 14 )CO respectively, are described. Other monoolefins examined do not displace carbonyl groups from rhodium(I) complexes. Mixed carbonylcyclooctene complexes are also formed in the ligand exchange reactions [Rh(CO) 2 Cl] 2 + [Rh(C 8 H 14 ) 2 Cl] 2 and Rhacac(CO) 2 + Rhacac(C 8 H 14 ) 2 . On reaction with triphenylphosphine and triphenylstibine the mixed complexes give Rhacac(L)CO and Rhoxq(L)CO. (Stibine derivatives of this type have not previously been obtained). The chemical and spectroscopic evidence, as well as the thermodynamic data cited from the literature indicate that cyclooctene exhibits comparatively strong donor properties.

Mild decarbonylation of transition metal carbonyls by rhodium(I) complexes

Abstract Transition metal carbonyls have been found to react with rhodium(I) complexes under mild conditions with resultant transfer of carbonyl to rhodium. Partial decarbonylation of Mo(CO)6 and Fe(CO)5 gives Mo(PPh3)2(CO)4, Mo(Arene)(CO)3 (Arene = benzene, toluene or mesitylene, Fe(PPh3)(CO)4, Fe(PPh3)2(CO)3, Fe(Diene)(CO)3 (Diene = butadiene or isoprene). In the absence of ligands capable of stabilizing partially decarbonylated moieties the decarbonylation goes to completion. In hexamethylphosphoramide the exhaustive decarbonylation of Cr(CO)6, Mo(CO)6, W(CO)6, Fe(CO)5 and Ni(CO)4 induced by [Rh(C8H14)2Cl]2 (C8H14 = cyclooctene) proceeds homogeneously and with retention of the oxidation state of rhodium (+1).

Spectral characteristics of products formed by reaction between Rhacac(PPh3)(CO) and methyl iodide

Abstract 13C, 31P and 1H NMR spectra revealed that in reaction mixtures Rhacac(PPh3)(CO) and MeI there were present two methylcarbonyl (MC) complexes of RhIII. These were presumably isomers of Rhacac(PPh3)(CO)(Me)I: MC-I (δ 13C 185. 3 ppm, 1J(CRh) 64.0 Hz, 2J(CRhP) 18.1 Hz; δ 31P 33.7 ppm, 1J(PRh) 124.4 Hz; δ 1H (MeRh) 1.36 ppm, 2J(HCRh) 1.9 Hz, 3J(HCRhP) 2.1 Hz) and MC-II (δ 13C 185.6 ppm, 1J(CRh) 62.5 Hz, 2J(CRhP)11.0 Hz; δ 31P 28.4 ppm, 1J(PRh) 117.4 Hz δ 1H (MeRh) 1.65 ppm, 2J (HCRh) 1.9 Hz, 3J(HCRhP) 3.8 Hz). The third product is an acetyl complex, presumably the dimer [Rhacac(PPh3)(MeCO)I] 2 (δ 13C 212.4 ppm, 1J(CRh) 28.0 Hz, 2J(CRhP) ∼ 7 Hz; δ 31P 37.6 ppm, 1J(PRh) 153.0 Hz; δ 1H (MeCO) 2.94 ppm, 2J(HCC) 5.9 Hz). The MC-I complex is able to transform partially into MC-II. Oxidative addition of MeI to Rhacac (AsPh3)(CO) and to Rhoxq(PPh3)(CO) (hoxq = 8-hydroxyquinoline; oxq its residue) yielded similar methylcarbonyl and acetyl complexes. All species present in the reaction mixtures are identified spectroscopically without isolation.

31P-NMR and X-ray studies of new rhodium(I) β-ketoiminato complexes Rh(R1C(O)CHC(NH)R2)(CO)(PZ3) where PZ3=PPh3, PCy3, P(OPh)3 or P(NC4H4)3

Abstract The substitution of the CO ligand in rhodium(I) β-ketoiminato complexes Rh(R1{O,N}R2)(CO)2 ({O,N}=R1C(O)CHC(NH)R2; R1, R2=CF3, Me, CMe3 in several combinations) by phosphorus ligands PZ3 (PZ3=PCy3, PPh3, P(OPh)3, P(NC4H4)3) leads to Rh(R1{O,N}R2)(CO)(PZ3) complexes characterised by 31P{1H}-NMR and X-ray methods. The stronger σ-donor PZ3 ligands (PZ3=PCy3, PPh3) substitute almost exclusively the CO group trans to N, forming P-trans-to-N isomers. The complexes Rh(CF3{O,N}Me)(CO)(PCy3) (II), Rh(CF3{O,N}CMe3)(CO)(PCy3) (III), Rh(CF3{O,N}Me)(CO)(PPh3) (IV) and Rh(CF3{O,N}CMe)(CO)(PPh3) (V) are of a square-planar geometry with a slight tetrahedral distortion around the rhodium atom in II, III and V. The RhP(PCy3) bonds are slightly longer than the RhP(PPh3) bonds. The reaction of stoichiometric amounts of the less basic P(OPh)3 or P(NC4H4)3 ligands leads to the formation of both isomers of the Rh(R1{O,N}R2)(CO)(P(OPh)3) or Rh(R1{O,N}R2)(CO)(P(NC4H4)3) complex in comparable yields. The RhP(P(OPh)3) distance (2.195(2) A) in the isomer of Rh(CF3{O,N}CMe3)(CO)(P(OPh)3) with P(OPh)3 coordinated trans to N (VI) is ca. 0.04 A longer than in the isomer of that complex with P(OPh)3 coordinated trans to O (VII). The CO substitution in Rh(R1{O,N}R2)(CO)2 by PZ3 ligands (PPh3, PCy3, P(OPh)3) causes the shortening of the RhC(CO) bond by ca. 0.04 A compared to Rh(CF3{O,N}Me)(CO)2 (I), making difficult the coordination of another PZ3 ligand, especially one with stronger σ-donor properties. The more π-acceptor P(OPh)3 ligands form bis-phosphito complexes and Rh(CF3{O,N}CMe3){P(OPh)3}2 (VIII) exhibits inequivalence of the two P(OPh)3 ligands in solution (31P-NMR) as well as in solid form (X-ray).

The nature of the product of the reaction [Rh(CO)2Cl]2 with PPh3 at 11 mole ratio of PPh3/Rh

Oxidation of the compounds1 RhAcac(CO)2 and RhAcacPPh3CO with halogens affords rhodium(III) carbonyl chloride, [Rh(CO)2Cl3]3, and binuclear phosphine-containing complexes (RhPPh3COX3)2 (X = Cl, Br). The nature of the reaction product of [Rh(CO)2Cl]2 with triphenylphosphine at a 11 mole ratio of PPh3/Rh is discussed.

Oxidation of the [Rh(CO)2Cl2] anion in aqueous solution

Abstract The reaction of rhodium(I) carbonyl chloride, [Rh(CO)2Cl]2, with dichromate, cerium(IV) sulfate, hexachloroplatinic acid or p-benzoquinone in aqueous hydrochloric acid proceeds by consumption of 4 equivalents of oxidizing agent per mole or rhodium(I) in accordance with the equation RhI(CO)2  4e + H2O → RhIII(CO) + 2H+ + CO2 A “cyclic” oxidation mechanism is suggested.

Dirhodium(II) dicarboxylato complexes containing carbonyl and C-bonded methoxycarbonyl ligands

Abstract Oxidation of rhodium(I) carbonyl chloride, [Rh(CO) 2 Cl] 2 , with copper(II) acetate or isobutyrate in methanol solutions yields binuclear double carboxylato bridged rhodium(II) complexes with RhRh bonds, [Rh(μ-OOCRκO)(COOMeκC)(CO)(MeOH)] 2 , where R=CH 3 or i -C 3 H 7 . According to X-ray data, surrounding of each rhodium atom in these complexes is close to octahedral and consists of another rhodium atom, two oxygens of carboxylato ligands, terminal carbonyl group, C-bonded methoxycarbonyl ligand, and axial CH 3 OH. Methoxycarbonyl ligand is shown to originate from CO group of the parent [Rh(CO) 2 Cl] 2 and OCH 3 group of solvent. N- and P-donor ligands L ( p -CH 3 C 6 H 4 NH 2 , P(OPh) 3 , PPh 3 , PCy 3 ) readily replace the axial MeOH yielding [Rh(μ-OOCRκO)(COOMeκC)(CO)(L)] 2 . The X-ray data for the complex with R= i -C 3 H 7 , L=PPh 3 showed the same molecular outline as with L=MeOH. Electronic effects of axial ligands L on the spectral parameters of terminal carbonyl group are essentially the same as in the known series of rhodium(I) complexes (an increase of δ 13 C and a decrease of ν (CO) with strengthening of σ-donor and weakening of π-acceptor ability of L).

Direct 13C-31P coupling constant of coordinated triphenylphosphine as a characteristic of electron-withdrawing power of the metal center

It is known that C signals of phenyl groups attached to a phosphorus atom are split due to coupling with the P nucleus. The direct C–P coupling constant (JCP) sharply increases in going from aromatic phosphines to the corresponding phosphine oxides. In keeping with our and published data [1–10], the JCP value of PPh3 is negative and is –11 Hz, and the JCP value of Ph3P=O is positive (104 Hz). It is reasonable to rationalize increase of JCP by change of the valence state of the phosphorus atom. The phosphorus atom in the triphenylphosphine molecule possesses a lone electron pair (LEP), whereas the latter is involved in interaction with a strong electron acceptor (oxygen atom) in the phosphine oxide molecule.

Binuclear rhodium organometallic complexes as catalysts of the liquid-phase 1-octene oxidation

The reaction of catalytic liquid-phase oxidation of olefins by molecular oxygen belongs to the most promising processes of organic synthesis and is a subject of numerous publications (see [1–3] for example). We have shown recently [4] that mononuclear rhodium organometallic complexes are active catalysts of the 1-octene oxidation by molecular oxygen. In this communication we present preliminary results of studying catalytic properties of complexes containing several metal centers, namely binuclear complexes of rhodium (+1), rhodium (+3), iridium (+1), palladium (+2), and triad complexes containing the ruthenium (+2) complex trans-[Ru(py)4(CN)2] as a central unit and rhodium (+1) or palladium (+2) complexes as terminal fragments.