Antonio Mezzetti

Highly Enantioselective Transfer Hydrogenation of Ketones with Chiral (NH)2P2 Macrocyclic Iron(II) Complexes

Bis(isonitrile) iron(II) complexes bearing a C2 -symmetric diamino (NH)2 P2 macrocyclic ligand efficiently catalyze the hydrogenation of polar bonds of a broad scope of substrates (ketones, enones, and imines) in high yield (up to 99.5 %), excellent enantioselectivity (up to 99 % ee), and with low catalyst loading (generally 0.1 mol %). The catalyst can be easily tuned by modifying the substituents of the isonitrile ligand.

Carbon−Fluorine Bond Formationvia a Five-Coordinate Fluoro Complex of Ruthenium(II), Preliminary Communication

The 16-electron, five-coordinate fluoro complex [RuF(dppp)2]PF6 (1a; dppp=propane-1,3-diylbis[diphenylphosphine] smoothly reacts with 1,3-diphenylallyl bromide (=1,1′-(3-bromoprop-1-ene-1,3-diyl)bis[benzene]) in dry CDCl3 to give 1,3-diphenylallyl fluoride and [RuBr(dppp)2]+ in nearly quantitative yield. Under similar conditions, bromide (or chloride)/fluoride exchange also occurs with chlorotriphenylmethane, bromodiphenylmethane, and tert-butyl bromide. The crystal structure of 1a is reported.

Electronic tuning of the PNNP ligand for the asymmetric cyclopropanation of olefins catalysed by [RuCl(PNNP)]+

Abstract Cationic ruthenium complexes of the type [RuCl(L)(PNNP)] + (L=OEt 2 , OH 2 ), where PNNP is the CF 3 -subsituted PNNP ligand N , N ′-bis[ o -(bis(4-trifluoromethylphenyl)phosphino)benzylidene]-(1 S ,2 S )-diaminocyclohexane 1b , catalyse the asymmetric cyclopropanation of styrene, α-Me-styrene, and 1-octene with ethyl diazoacetate. These complexes are more active and give higher cis - and enantioselectivities than their analogues containing the unsubstituted ligand 1a . Thus, [RuCl(OEt 2 )( 1b )]PF 6 cyclopropanates α-Me-styrene with 85% cis selectivity and 86% ee in 94% isolated yield.

Chiral Ru/PNNP complexes in catalytic and stoichiometric electrophilic O- and F-atom transfer to 1,3-dicarbonyl compounds*

The asymmetric hydroxylation and fluorination catalyst [Ru(OEt2)2(PNNP)]2+ (PNNP = chiral tetradentate ligand with a P2N2 donor set) reacts with 1,3-dicarbonyl compounds to give dicationic adducts and, upon deprotonation, the corresponding enolato complexes. The relevance of these species to catalytic O- and F-transfer is investigated.

Crystal structures of the hydrated and dehydrated forms of a partially cesium-exchanged chabazite

Crystal structures of a partially cesium-exchanged chabazite h-Cs-CHA, Cs 3.0 Ca 0.4 Al 3.8 Si 8.3 O 24 .9.5H 2 O and its dehydrated form d-Cs-CHA were determined in the rhombohedral space group R ¯3 m . Unit cell parameters and R -indexes were a =9.441 (1)A, α=94.23(2)° and 0.049 for h-Cs-CHA, and a =9.397(2)A, α=93.74(2)° and 0.046 for d-Cs-CHA, respectively. In both h-Cs-CHA and d-Cs-CHA, site IV, at the centre of the S 8 R window, is nearly fully occupied by the Cs + ions. In h-Cs-CHA, a small number of Cs + ions are located in site 1′, along the [111] direction. The Ca 2+ ions occupy site 1″, along the [111] direction, in h-Cs-CHA and site III, at the centre of the D 6 R cage, in d-Cs-CHA. Only minor distortions of the framework geometry occur upon dehydration, in contrast with the results found for chabazites exchanged with other monovalent cations. The framework stability is discussed and related to the dimensions of the Cs + ion.

Asymmetric Diels-Alder and Ficini reactions with alkylidene β-ketoesters catalyzed by chiral ruthenium PNNP complexes: mechanistic insight.

Hydride abstraction from the β-position of the enolato ligand of the previously reported complex [Ru(3a-H)(PNNP)]PF(6) (5a; 3a-H is the enolate of 2-tert-butoxycarbonylcyclopentanone) with (Ph(3)C)PF(6) gives the dicationic complex [Ru(6a)(PNNP)](2+) (7a) as a single diastereoisomer, which contains the unsaturated β-ketoester 2-tert-butoxycarbonyl-2-cyclopenten-1-one (6a) as a chelating ligand. The methyl analogue 2-methoxycarbonylcyclopentanone (3b) gives [Ru(3b-H)(PNNP)]PF(6) as a mixture of noninterconverting diastereoisomers (ester group of 3b trans to P, 5b; or to N, 5c), which were separated by column chromatography. Hydride abstraction from 5b (or 5c) yields diastereomerically pure [Ru(6b)(PNNP)](2+) (7b or 7c). Complexes 7b and 7c do not interconvert at room temperature in CD(2)Cl(2) and form opposite enantiomers of the Diels-Alder adduct upon reaction with Danes diene (1 equiv). X-ray studies of 7a, 5b, and 5c give insight into the origin of enantioselection and the sense of asymmetric induction in the previously reported asymmetric Diels-Alder and Ficini cycloaddition reactions with 2,3-disubstituted butadienes and ynamides, respectively. Stoichiometric reactions (substrate coordination, cycloaddition, and product displacement) between [Ru(OEt(2))(2)(PNNP)](2+) (2), 6b (or 6a), and Danes diene (15, to give estrone derivatives) or N-benzyl-N-(cyclohexylethynyl)-4-methylbenzenesulfonamide (17, to give cyclobutenamides) suggest that product displacement from the catalyst is turnover limiting.

Isonitrile iron(II) complexes with chiral N2P2 macrocycles in the enantioselective transfer hydrogenation of ketones.

Bis(isonitrile) iron(II) complexes bearing a C2-symmetric N2P2 macrocyclic ligand, which are easily prepared from the corresponding bis(acetonitrile) analogue, catalyze the asymmetric transfer hydrogenation (ATH) of a broad scope of ketones in excellent yields (up to 98%) and with high enantioselectivity (up to 91% ee).

Cation sites and framework deformations in dehydrated chabazites. Crystal structure of a fully silver-exchanged chabazite

A sample of silver-chabazite, Ag3.7Al3.8Si8.3O24.10H2O, was completely dehydrated at suitable conditions of vacuum and temperature (2 × 10−6 Torr, 60°C). After dehydration, the symmetry of the Ag-CHA crystals was reduced from the usual rhombohedral space group R3m to the monoclinic C2m, with the following cell dimensions: a = 19.240(6)A, b = 13.771(4)A, c = 11.868(4)A, β = 113.28(3)A, Full matrix least-squares refinement reduced R index to 0.093 on the basis of 2305 reflections. The framework of d-Ag-CHA can be described as a tridimensional linkage of D6R units in alternate layers rotated about the monoclinic b-axis. The silver ions occupy eight independent positions, related to sites I, III and IV of the rhombohedral cell, near the centre of the 6-ring, at the centre (0, 12 12) of the D6R cage and near the 8-ring aperture, respectively. The positions and the populations of the cation sites of d-Ag-CHA are compared with those of h-Ag-CHA and related with the relevant variation of the framework.

Synthetic methodologies for tripodal phosphines. The preparation of MeSi(CH2PPh2)3 and n-BuSn(CH2PPh2)3 and a comparison of their rhodium(I) and ruthenium(II) coordination chemistry. The X-ray crystal structures of [Rh(NBD){n-BuSn(CH2PPh2)3}](OTf) and [Rh(NBD){MeSi(CH2PPh2)3}](OTf)☆

Abstract The preparation of the new tripodal ligands MeSi(CH2PPh2)3 (Si-triphos) and n-BuSn(CH2PPh2)3 (Sn-triphos) and their complexes of rhodium(I) of the type [Rh(NBD)(tripod)](OTf) (NBD  norbornadiene, OTf  triflate) and of ruthenium(II) of the type [Ru(O2CCF3)2(tripod)], is reported. The coordination chemistry of the new tripodal phosphines, and in particular that of Sn-triphos, differs significantly from that of MeC(CH2PPh2)3 (triphos). A comparison of the X-ray structure of [Rh(NBD)(triphos)](OTf) with those of the new complexes [Rh(NBD)(Sn-triphos)](OTf) and [Rh(NBD)(Si-triphos)](OTf) shows that the steric requirements of the ligands RE(CH2PPh2)3 (E  C, Si and Sn), increas from the carbon to the tin compound. The coordination chemistry of ruthenium(II) indicates that, relative to triphos, Sn-triphos displays an enhanced steric bulk which, however, is not sufficient to stabilize the mononuclear, five-coordinate dichloro complexes.

P-Stereogenic diphosphines in the ruthenium-catalysed asymmetric hydrogenation of CC and CO double bonds

Abstract Bis(acetato) and dichloro complexes of ruthenium(II) containing P -stereogenic ligands have been prepared and tested in the asymmetric catalytic hydrogenation of functionalised olefins and keto esters. The best performance (52.6% ee) has been obtained in the hydrogenation of ethyl acetoacetate with [RuCl(PPh 3 )(( S , S )-1,1′-bis(1-naphthylphenylphosphino)ferrocene)] 4 .