H.C. Volger

Nuclear magnetic resonance studies in coordination chemistry V. Kinetic studies of exchange reactions involving 1,5-cyclooctadiene complexes of rhodium(I)☆

Abstract NMR studies showed that the signals of the non-equivalent olefinic protons of the diene complexes (diene) RhCl(L) and (diene) IrCl(L) (diene = 1,5-cyclooctadiene, bicyclo [2.2.1] hepta-2,5-diene and L = PR3, AsR3 or SbR3 with R = aryl or substituted aryl or alkyl) broaden and eventually coalesce to one signal when the temperature of the CDCl3 solutions is raised. Kinetic studies on the monomeric complexes (COD)RhCl(L) (COD 1,5-cyclooctadiene; L = AsPh3, PPh3) showed that this coalescence is caused by monomer-monomer reactions. If, however, ligand L is also present, fast ligand exchange reactions are observed. If along with (COD)RhCl(L) the dimer [(COD)RhCl]2 is present, the olefinic signals of both complexes coalesce. For L = AsPh3 the kinetic behaviour is explained by a reaction between an active intermediate “(COD)RhCl(AsPh3)” and [(COD)RhCl]2, while L = PPh3 reactions occur between (COD)RhCl(PPh3) and the monomeric species (COD)RhCl formed from the dissociation of the dimer. Finally, it is shown that addition of Cl− to (COD)RhCl(AsPh3) also results in the coalescence of the olefinic signals. The chloride effect upon (COD)RhCl(PPh3) is negligible.

Complexes of allenes with platinum (II) and rhodium (I)

Abstract The π-allene-metal linkage in compounds of tetramethylallene (TMA) and 1,1-dimethylallene (1,1-DMA) with platinum (II) and rhodium (I) has been investigated. The compounds were: the dimers [(TMA)PtCl2]2 and [(1,1-DMA)PtCl2]2, prepared by reaction of the allene and [(π-C2H4)PtCl2]2; the monomers (TMA) Cl2Pt(NC5H4p-X), (X = NH2, CH3 C2H5, H, Br, CN), and (1,1-DMA)Cl2Pt(NC5H5, prepared from the respective dimers and (substituted) pyridines; and (Acac)Rh(TMA)2(Acac= acetylacetonato), prepared from the allene and (Acac)Rh(π-C2H4)2. In all these cases NMR results confirmed that the allene group is linked to the metal atom by one of its double bonds. They also indicated that in the TMA-platinum compounds there is a monomolecular reaction in which the metal atom moves back and forth from one double bond to the other. With the monomeric TMA-platinum compounds a linear relation is found between the logarithm of the rate of movement of the metal atom and the Hamett σp parameter of the pyridine substituent.

π-Allyl complexes of rhodium(III) and platinum(II) I. Preparation, properties and structure

Abstract π-Allyl complexes L2X2Rh(π-C3H4R) with L = Ph3P, Ph3As, [p-(CH3)2NC6H4]3As, Ph3Sb; X = Cl, Br and R = H, CH3 and the compound (Ph3P)2Cl2Rh[π-(CH3)2Cue5fbCHue5fbCH2] have been obtained by reaction of the corresponding allyl halides with L3RhX. Treatment of (Ph3P)4Pt with allyl halides yielded uni-univalent complexes [(Ph3P)2Pt(π-R2Cue5fbCHue5fbCH2)]X with X = Cl, Br and R = H, CH3. The configuration of the compounds was destermined by means of electrical conductivity measurements in solution, infrared, proton magnetic resonance and dipole moment measurements. It was shown that the group V donor ligands L are both situated trans to the allyl ligand.

π-Allylic complexes of rhodium(III) and platinum(II) II. Intramolecular rearrangement of the allyl ligand as influenced by group V donor ligands

Abstract A proton magnetic resonance investigation of the temperature dependence of the allyl ligand behaviour in the complexes L 2 Cl 2 Rh(π-C 4 H 7 ) and [(Ph 3 P) 2 Pt(π-C 3 H 5 ]Cl(L is a group V donor ligand) has shown that the syn - and anti -protons of the allyl ligand may become magnetically equivalent owing to the occurrence of a σ-allyl form. The kinetic parameters of this interconversion process were determined for various ligands L. It appears that the increase in total electron donor capacity of L(in the order Ph 3 Sb 3 As p -(CH 3 ) 2 NC 6 H 4 ] 3 As 3 P) decreases the activation energy.

Nuclear magnetic resonance studies in coordination Chemistry VI. Kinetic studies of reactions involving [(1,5-Cyclooctadiene)IrCl]2 and triphenylarsine or triphenylphosphine

NMR kinetic investigations have been carried out on systems containing the 1,5-cyclooctadiene complexes (COD)IrCl(L) as such or in combination with [(COD)IrCl]2 or L(L=AsPh3 or PPh3). n nThe results for mixtures of (COD)IrCl(L) and L indicate that at low temperatures (−70 to −40°) an exchange of L occurs via the five-coordinate species ( COD)IrCl(L)2, which is in equilibrium with much smaller amounts of the ionic species [(COD)Ir(L)2]+Cl−. n nWith (COD)IrCl(AsPh3) and [(COD)IrCl]2 reactions of dissociated triphenylarsine with both the monomeric and dimeric complexes are observed. Linebroadening was not noted when triphenylarsine was replaced by triphenylphosphine. n nFurthermore, it was found that (COD)IrCl(AsPh3) reacts with Cl− and 1,5-cyclooctadiene. The reaction with 1,5-cyclooctadiene does not involve exchange between the coordinated and the free diolefin. n nThe results are compared with those of the isoelectronic and isostructural rhodium systems.

Boron hydride reduction of transition metal—acetyl complexes

Abstract Acetyl complexes of iron(II) and ruthenium(II) of the type (π-C 5 H 5 )(CO)LM(COCH 3 ), where L = PPh 3 , P(OPh) 3 , P(cyclohexyl) 3 , PMe 2 Ph or CO for M = Fe, and PPh 3 for M = Ru, are rapidly reduced to the corresponding ethyl complexes by BH 3 · THF or B 2 H 6 /C 6 H 6 . In some cases hydrido complexes of the type (π-C 5 H 5 )(CO)LMH are also formed. The reaction has been studied by use of 1 H NMR and the spectrum of (π-C 5 H 5 )(CO)(PPh 3 )FeC 2 H 5 , which shows several unusual features, is discussed in detail. It is suggested that the rate of reduction increases with increasing electron density at the metal centre. Acetyl complexes of other transition metals, i.e. Ir, Pt, Pd, Co and Mo, are also reduced to the corresponding ethyl compounds by B 2 H 6 /C 6 H 6 .

The stereospecific addition of dienes to palladium chloride

Abstract Using 2,4-hexadiene as a model compound we have shown that dienes add to palladium chloride in a stereospecific way. The three diene isomers react to give a pair of epimeric π-allylpalladium diastereomers, one of which is formed from the cis,trans-diene, the other from either the trans,trans or the cis,cis-isomer. The mechanisms of the epimerization and solvolysis of the products have been studied, and the reactions found to proceed via a diene-palladium complex.

Nuclear magnetic resonance studies in coordination chemistry : VII. Kinetic studies of exchange reaction involving Bicyclo[2.2.1]hepta-2.5-diene complexes of rhodium(I)

Abstract NMR studies of the coalescence of the signals of the inequivalent olefinic protosn of the monomer (Nor)RhCl(PPh 3 ) (Nor=bicyclo[2.2.1]hepta-2,5-diene) have indicated the occurance of monomer-monomer reactions. In the presence of free triphenylphosphine a fast ligand exchange reaction was observed with the monomer. When, however, besides the monomer the dimeric [(Nor)RhCl] 2 was present, below + 20° monomer-dimer reactions took place without exchange of PPh 3 . Above +20° phosphine-exchange reactions occured between (Nor)RhCl(PPh 3 ) and (Nor)RhCl, the latter being formed by dissociation of the dimer. Addition of Cl− to solution of the monomer, and to mixtures of monomer and dimer, resulted in halide-exchange reactions, while addition of free norbornadiene had no observable effect. With the triphenylarsine system we could only study reactions of the monomer (Nor)RhCl(AsPh 3 )in the presence of dimer. The arsine system is different from the phosphine one in that reactions were found of dissociated AsPh 3 with the arsine compound and the dimer, respectively. The result for these systems are compared with those for the 1.5-cyclooctradiene system of Rh 1 and Ir 1 and the π-allylpalladium systems.

π-allylic complexes of rhodium(III) and platinum(II) IV. Chemical reactivity of π-allylic platinum complexes

Abstract The reactions of {[C6H5)3P]2Pt(π-C3H5)}+Cl− and of the π-1,1-dimethylallylic analogue with hydrogen, hydrogen chloride, sulfur dioxide, carbon monoxide, ethene and 1,3-butadiene were studied. With hydrogen and hydrogen chloride the corresponding saturated and unsaturated hydrocarbons were formed respectively. The reactions with sulfur dioxide and carbon monoxide gave rise to insertion products. The ease of these reactions is ascribed to the very low concentration of the coordinatively unsaturated platinum σ-allyl complex. Ethene and 1,3-butadiene yielded small amounts of dimerization products.

π-allylic complexes or rhodium(III) and platinum(II) III. Chemical reactivity of π-allylic rhodium(III) complexes

Abstract The reactions of L2Rh(π-C3H4R)Cl2 [L = (C6H5)3P, (C6H5)3As or (C6H5)3Sb and R = H or CH3] with sulfur dioxide, ethene and carbon monoxide were studied. Sulfur dioxide gives rise to the formation of a σ-allylic rhodium-sulfur dioxide complex. With carbon monoxide L2Rh(π-C3H4R)Cl2 (L = triphenylphosphine or arsine) produces L2(CO)RhCl and (methyl)allyl chloride in quantitative yields. The reaction proceeds via a number of intermediates (trivalent rhodium π- and σ-allyl and insertion products). Ethylene dimerizes into a mixture of butenes; the catalytic activity of the complex is rather poor. The ease of displacement of the ligand by either ethylene or carbon monoxide decreases in the order (C6H5)3As > Cl # (C6H5)3P. No specific correlation has been found between the destabilizing influence of the ligand L on the metal-π-methallyl bond and the rate of the reaction with carbon monoxide.