Erica Farnetti

Alternative intermediates for glycerol valorization: iridium-catalyzed formation of acetals and ketals

The organoiridium derivatives [Cp*IrCl2]2 (Cp* = pentamethylcyclopentadienyl) and [Cp*Ir(Bu2-NHC)Cl2], (Bu2-NHC = 1,3-di-n-butylimidazolylidene) catalyzed glycerol acetalization with several ketones and aldehydes, as well as transacetalization. All the catalytic reactions produced the five-membered cyclic ketals, i.e. the 1,3-dioxolanes, as main products, with selectivities of 94–100% for ketals, and up to 83% for acetals.

A novel glycerol valorization route: chemoselective dehydrogenation catalyzed by iridium derivatives

Organoiridium derivatives of the type Ir(diene)(N-N)X (diene = 1,5-hexadiene,1,5-cyclooctadiene; N-N = 2,2′-bipyridine, 1,10-phenanthroline and substituted derivatives; X = Cl, I) catalyze the hydrogen transfer reaction from glycerol to acetophenone, yielding dihydroxyacetone and phenylethanol. The catalytic reactions are performed at temperatures of 100 °C or higher, in the presence of a basic cocatalyst. The effect of experimental conditions on overall conversion and catalyst lifetime is discussed, as well as on the degradation of dihydroxyacetone, which can lead to an apparent decrease of selectivity of the catalytic reaction.

Stereoselective living polymerization of phenylacetylene promoted by rhodium catalysts with bidentate phosphines

Abstract Polymerization of phenylacetylene to give highly stereoregular cis-transoid polyphenylacetylene is accomplished by use of [Rh(nbd)(OMe)]2 (nbd=norbornadiene) and Ph2P(CH2)xPPh2 (x=2, dppe; x=3, dppp; x=4, dppb). The catalytic system employing the ligand dppb promotes formation of polymer products with low polydispersities. The polymerization is of living nature, as proved by the dependence of polymer molecular weight on conversion and on initial monomer concentration, with molecular weight distributions always maintained within a narrow range. NMR studies of the catalytic system provide information on the rhodium chemistry involved, as well as useful means of comparison to other rhodium–phosphine catalytic systems.

Dehydrogenation of glycerol to dihydroxyacetone catalyzed by iridium complexes with P–N ligands

The chemoselective dehydrogenation of glycerol was catalyzed by organoiridium derivatives of the type [HIr(cod)L] (cod = 1,5-cyclooctadiene; L = Prn-N(CH2CH2PPh2)2, Et2NCH2CH2N(CH2CH2PPh2)2, o-Me2NC6H4PPh2) using hydrogen acceptors such as acetophenone, cyclohexanone, styrene and benzaldehyde. The catalytic reactions were performed in the absence of a basic cocatalyst in order to avoid decomposition of the desired product, i.e. dihydroxyacetone. Acceptor-less dehydrogenation was also observed either in the absence of a hydrogen acceptor, or as a parallel route, when the reaction was performed in the presence of acetophenone.

Hydrogenation of α,β-unsaturated aldehydes and ketones to the unsaturated alcohols catalysed by hydridoiridium phosphine complexes

Unusual selective hydrogenation of cinnamaldehyde and benzylideneacetone to the corresponding unsaturated alcohols is catalysed by [H2Ir(phosphine)4]+ complexes in toluene; use of a chiral phosphine gives a 7.4% enantiomeric excess of (S)-(–)-1-phenylbut-1-en-3-ol.

Polymerization of phenylacetylene catalyzed by organoiridium compounds

Abstract The compounds [Ir(cod)X] 2 (cod=1,5-cyclooctadiene; X=Cl, OMe) catalyze the polymerization of phenylacetylene, with negligible formation of oligomeric products. At variance, the monoolefin analogue [Ir(cot) 2 Cl] 2 (cot=cyclooctene) only promotes alkyne cyclotrimerization. The polymerization reaction proceeds in various solvents such as tetrahydrofuran (THF), chloroform and benzene, but it is most favored when using NEt 3 as reaction medium. The role of the diene in the catalytic reaction is investigated, also in relation to a deactivation process of the catalyst with time. Spectroscopic studies of the catalytic reaction indicate the formation of monomeric iridium-solvent adducts, which are likely to be the initiators of the polymerization reaction. A possible reaction mechanism is proposed, according to the data reported in the literature and the results of the present investigation.

Evaluation of the donor ability of phenanthrolines in iridium complexes by means of synchrotron radiation photoemission spectroscopy and DFT calculations

Synchrotron radiation XPS measurements of Ir 4f, N 1s and I 4d core levels for the compounds Ir(cod)(N-N)X (cod=1,5-cyclooctadiene; N-N=1,10-phenanthroline and substituted derivatives; X=Cl, I) are reported. The compounds Ir(cod)(3,4,7,8-Me4phen)X (3,4,7,8-Me4phen=3,4,7,8-tetramethyl-1,10-phenanthroline) were structurally characterized by single crystal X-ray analyses. The comparison among the binding energies shows differences that are interpreted in terms of electron density variations due to the change of the phenanthroline substituents. Such analysis provides a quantitative evaluation of the ligand donor properties. The trend in the measured binding energies is confirmed by the results obtained by DFT DeltaSCF calculations, which include final state relaxation effects, while the specific role of initial state effects has been assessed in terms of the Kohn-Sham eigenvalues analysis.

Hybrid PN phosphines as participative ligands in iridium hydrogenation catalysts

Iridium complexes formed in situ from [Ir(cod)(OMe)]2 and a potentially bidentate ligand such as P(o-C6H4NH2) Ph2 ( = PNH2) or P(o-C6H4NMe2)Ph2 ( = PNMe2) catalyze the chemoselective hydrogenation of benzylideneacetone. In the presence of HIr(PNH2(PNH2) the substituted allylic alcohol is obtained in 92% yield, whereas in the presence of H2Ir(PNMe2) there is a much poorer selectivity. The features of the catalysis are discussed in relation to the nature of the iridium species formed; steric factors appear to play a crucial role in determining the selectivity. Monitoring of the progress of the reaction catalyzed by the IrPNHz system by NMR spectroscopy has revealed the sequence of reactions, including ready intramolecular NH activation. The crystal structure of Ir-(PNH2)3 has been determined.

Chemoselective Reduction of Enones to Allylic Alcohols

Summary Chemoselective reduction of conjugated enones to allylic alcohols via hydrogen transfer from propan-2-ol over metal oxides is investigated in vapour phase conditions. The unique ability of MgO to reduce exclusively carbonyl group is observed. However, because of the high basicity of MgO side reactions are present. It is shown that by doping the MgO catalyst with HCl a significant decrease of its basicity occurs and consequently side reactions are minimized.

Selective hydrogenation of benzylideneacetone catalyzed by iridium diphosphine complexes

Hydrogenation of benzylideneacetone (PhCH=CHCOCH3) is catalysed by iridium diphosphine complexes of the type [Ir(P-P)2]+ (P-P = dpe, dpp, dpb, (S, S)-chiraphos, (R)-prophos,, (+)-diop and (S)-prolophos) and by systems formed in situ from [Ir(cod)Cl]2 or [Ir(cod)(OCH3)]2 (cod = 1,5-cyclooctadiene) and diphosphines. 1-Phenyl-1-buten-3-ol [PhCH=CHCH(OH)CH3] is selectively produced in high yields using [Ir(P-P)2]+ (P-P=diop, prolophos) as catalyst precursor or high P/Ir ratios in the systems prepared in situ. Optical yields up to 30% in the S(−)-unsaturated alcohol are obtained with chiral diphosphines as ligands. Catalytic results are given together with spectroscopie data and some equilibria are proposed to account for the different activities and selectivities observed in the hydrogenation. The length of the carbon atom chain in the diphosphine seems to play a crucial role in determining the distribution of products.