Acidato Ligands Research Articles

Rhodium(I)-NHC Complexes Bearing Bidentate Bis-Heteroatomic Acidato Ligands as gem-Selective Catalysts for Alkyne Dimerization.

A series of Rh(κ2 -BHetA)(η2 -coe)(IPr) complexes bearing 1,3-bis-hetereoatomic acidato ligands (BHetA) including carboxylato (O,O), thioacetato (O,S), amidato (O,N), thioamidato (N,S), and amidinato (N,N), have been prepared by reaction of the dinuclear precursor [Rh(μ-Cl)(IPr)(η2 -coe)]2 with the corresponding anionic BHetA species. The RhI -NHC-BHetA compounds catalyze the dimerization of aryl alkynes, showing excellent selectivity for the head-to-tail enynes. Among them, the acetanilidato-based catalyst has shown an outstanding catalytic performance reaching unprecedented TOF levels of 2500 h-1 with complete selectivity for the gem-isomer. Investigation of the reaction mechanism supports a non-oxidative pathway in which the BHetA ligand behaves as proton shuttle through intermediate κ1 -HBHetA species. However, in the presence of pyridine as additive, the identification of the common RhIII H(C≡CPh)2 (IPr)(py)2 intermediate gives support for an alternative oxidative route.

(Piperidinomethyl)silylmethyl cyclopalladated complexes with amino acidato ligands

The reactions of [Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(μ-Cl)]2 with the tetra-n-butylammonium NnBu4+ salts of different deprotonated α-amino acids (N,N-dimethylglycine, (S)-(+)-alanine, (R)-(−)-2-phenylglycine, and (S)-(+)-valine) lead to the amino acidato complexes [Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}{NR2CH(R′)C(O)O-κ2N,O}] (R = Me, R′ = H; R = H; R′ = Me, Ph, iPr), where both nitrogen donor atoms are coordinated trans, as shows the crystal structure of [Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}{NH2CH(iPr)C(O)O-κ2N,O}].

A cyclic tetranuclear Ni2Gd2 complex bridged by amino acidato ligands, with an S = 9 ground state, derived from ferromagnetic spin-coupling between nickel(ii) and gadolinium(iii) ions

Synthesis and structure of a cyclic tetranuclear Ni(2)Gd(2) complex bridged by amino acidato ligands, with an S = 9 spin ground state, derived from ferromagnetic spin-coupling between S(Gd) = 7/2 and S(Ni) = 1 are reported.

Dinickel Complexes Bridged by Unusual (N,O,O )-Coordinated α-Amino Acids: Syntheses, Structural Characterization and Magnetic Properties

Four novel dinickel complexes, coordinated by mixed ligands of tren and racemic amino acids, namely [Ni2(tren)2(dl-alaninato)(H2O)]I3·2H2O (1), [Ni2(tren)2(dl-leucinato)(H2O)]I3·2.5H2O (2), [Ni2(tren)2(dl-phenylalaninato)(H2O)]I3·H2O (3), and {[Ni2(tren)2(dl-histinato)](ClO4)3·1.5H2O}n(4), have been synthesized and structurally characterized by X-ray crystallography, FTIR, u.v. and e.s. spectra. They represent the first series of dinickel(II) complexes bridged by the unusual (N,O,O′)-coordinated α-amino acids. In complexes (1–3), one of the nickel(II) centers is coordinated by four N-atoms of the tren ligand, one O-atom of the carboxylate group of the amino acidato ligand and one H2O molecule. The other nickel(II) center is also coordinated by the four N-atoms of the tren ligand, one carboxylic O-atom and the amino N-atom of the amino acidato ligand, resulting in an asymmetric dinuclear core with chromophores of NiN4O2 and NiN5O. In the polymeric {[Ni2(tren)2(dl-histinato)](ClO4)3·1.5H2O}n(4), the imidazole N-atom is also involved in ligation with nickel(II) and both nickel(II) centers have the same chromophore described as NiN5O. The Ni...Ni distances are in the 5.5199(10)–5.5807(15)A range. Analyses of the magnetic properties of complexes (1), (3) and (4) show that a weak ferromagnetic interaction exists between the two nickel(II) centers.

Preparation and Stereoselectivity of [Cr(L‐Amino Acidato)2(L‐Amino Acidato‐N)(H2O)

New complexes of the bis‐type [Cr(AA)2(AA‐N)(H2O)], where AA stands for L‐amino acidato ligands (L‐leucine, L‐methionine, L‐phenylalanine, L‐serine, L‐threonine) and AA‐N represents monodentate L‐amino acidato ligand with an amino nitrogen as a donor atom, were prepared by heating mixtures of [Cr(NH3)6](OOCCH3)3 and L‐amino acid in alcoholic solution. In the case of L‐leucine and L‐phenylalanine, the mixture of (+)546‐ and (−)546‐[Cr(AA)2(AA‐N)(H2O)] were obtained. The optical resolution of the phenylalanine complex was tried by column chromatography and the (+)546‐bis‐type complex was obtained. With the other amino acids, only (+)546‐bis‐type complexes were stereoselectively obtained.

Nickel(II) complexes of amino acids in comparison with the cobalt(III) analogues: interesting structural aspects relative to intermolecular hydrogen bonds and chiral recognition

The crystal and packing structures of three racemic compounds with the formula, [Ni(tren)( dl-aminoacidato)]Cl· nH 2O have been investigated, aiming to compare the homochiral–heterochiral assembly process of the nickel(II) chiral complex cations with their well-studied cobalt(III) analogues. Due to the inherent hydrogen bonding donors–acceptors carried by the complex cations, infinite 1-dimensional (1-D) chains are generated by complementary inter-cationic H- bonds in both the Ni(II) and Co(III) analogues, but with different H- bond patterns. In all the Co(III) analogues studied by this group, the cations are linked together via the same pattern and strength of H- bonds which are designated as C6[R 2 1(6)]. They are homochiral, irrespective of the nature of the amino acidato ligands. In the Ni(II) analogues, the cations are linked by H- bonds described as C 2 1(6)[R 2 2(12)]. However, when the side chain of the amino acid is bulkier, the homochiral assembly of the cations becomes ambiguous due to the observed disorder of the asymmetric carbon. Additionally, it is interesting to note that the deprotonated carboxylic group of the amino acid coordinates with Ni(II) and Co(III) in different modes, as a delocalized and localized anion, respectively.

Facile Dehydrogenation of alpha-Amino Acids Chelated to a Ruthenium(II) Ion: (alpha-Imino acidato)ruthenium(II) Complexes.

(alpha-Imino acidato)ruthenium(II) complexes, [Ru(II){N(R(1))=C(R(2))CO(2)}L(2)](+) (R(1) = R(2) = Me or R(1) = R(2) = -(CH(2))(3)-; L = 2,2'-bipyridine (=bpy) or 1,10-phenanthroline (=phen)), were obtained by anodic oxidation at a constant potential of the corresponding (alpha-amino acidato)ruthenium(II) complexes, N-methylalaninato or prolinato complexes, in good to excellent yields. (alpha-Imino acidato)ruthenium(II) complexes are stable in neutral or acidic aqueous solution. The half-wave potentials of alpha-imino acidato complexes are 0.73-0.78 V (vs SCE), which are more positive than those of the corresponding alpha-amino acidato complexes, 0.55-0.59 V. The crystal structure of [Ru(pro-H(2))(bpy)(2)]ClO(4).3H(2)O (pro-H(2) = 1,2-didehydroprolinato) has been determined by single-crystal X-ray analysis. Crystallographic data: space group C2/c, a = 21.73(1) Å, b = 19.33(1) Å, c = 14.58(1) Å, beta = 114.91(5) degrees, Z = 8, R = 0.0352. The length of the C=N double bond of the alpha-imino acidate moiety is 1.294(5) Å, and Ru-N(imino nitrogen) = 2.042(3) Å. The chelate ring of the alpha-imino acidato ligand is planar.

Metal complexes of biologically important ligands: Synthesis of amino acidato complexes of Pd II containing a C, N-cyclometallated group as an ancillary ligand

New amino acidato complexes of Pd II of stoichiometry [Pd(CN)(Aa)] (CN C, N-cyclometallated ligand, Aa = N, O-amino acidato ligand) have been obtained by reaction of [Pd(CN)(acac)] (CN N, N-dimethylbenzylamine- C 2, N (dmba) ( 1) or N, N-dimethyl( S- α-phenylethyl)amine- C 2, N ( S-dmphea) ( 2)) with glycine, chiral amino acids (alanine, phenylalanine and valine), and amino acid derivatives ( N-acetylglycine and N-acetyl- α, β-dehydroalanine) in MeOH. The compounds are characterized by IR, 1H and 13C NMR. The geometry of these complexes has been unambiguously determined by NOE difference experiments and NOESY measurements.

Stereoselective Preparation and Characterization of [Cr(amino acidato)2(amino acidato-N)(Me2SO)] Complexes

Abstract New complexes of the type [Cr(AA)2(AA-N)(Me2SO)], where AA stands for l-amino acidato ligands (valinato, isoleucinato, and leucinato) and AA-N represents monodentate l-amino acidato ligands with an amino nitrogen as a donor atom, were prepared by heating mixtures of Cr(NO3)3·9H2O and sodium salts of amino acids in Me2SO. For all the amino acids used, only complexes of the type (+)546-[Cr(AA)2(AA-N)(Me2SO)] were obtained. The presence of a Me2SO molecule as a ligand was shown by the IR spectra of the crystals of the complexes. The bis-type complexes with l-valine and l-isoleucine were converted to (−)546-isomers in MeOH and the resulting products were isolated. All the new complexes were confirmed to have facial configuration, [Cr(O)3(N)3] from their UV-vis absorption spectra, as well as the corresponding tris-type complexes, [Cr(AA)3].

Thermal Isomerization of Fac-Tris(L-amino Acidato)chromium(III) in Solid State

Abstract The thermal isomerization of fac-Δ- and/or fac-Δ-tris-[Cr (AA)3] in solid state, where AA stands for an L-amino acidato ligand (L-alaninato, L-norvalinato, L-norleucinato, L-valinato, L-leucinato and L-isoleucinato), was studied under an isothermal heating at 180 °C for 5 h. The isomerization behavior of those complexes was classified into two groups, though all the resulting products at equilibria were of facial configuration. In the case of [Cr(ala)3], [Cr (norval)3] and [Cr (norleu)3], only fac-Δ-[Cr(AA)3] was obtained irrespective of configurations of the starting complexes, while [Cr(val)3], [Cr(ile)3] and [Cr(leu)3] gave mixtures of diastereoisomers on heating. By separating those products into each diastereoisomer, fac-Δ-[Cr(val)3] and fac-Δ-[Cr(ile)3], which had not been previously obtained, were prepared satisfactorily.

Regulation of the ligand field strength of a cobalt(III) complex by methyl substitutions on a tetraamine ligand: an important factor for the dissociation of a generally inert chelated amino acidato ligand from a cobalt(III) complex

Regulation of the ligand field strength of a cobalt(III) complex by methyl substitutions on a tetraamine ligand: an important factor for the dissociation of a generally inert chelated amino acidato ligand from a cobalt(III) complex

Stereoselectivity in the Polarographic Reduction of Chromium(III) Complexes with L-α-Amino Acids

Abstract Polarographic reduction behaviors of fac-[Cr(AA)3] complexes, where AA is an L-α-amino acidato ligand, have been studied in Me2SO. These complexes showed two reduction waves at mercury electrode and the first corresponded to Cr(III) → Cr(II). This reduction potential was found to be more positive for the (+)546-isomer than for the corresponding (−)546-isomer in the presence of Et4N+.

Optically active pseudoctahedral rhodium(III), iridium(III), and ruthenium(II) complexes with α-amino acidato ligands. Crystal structures of RIrSCSN- and SIrSCSN-[(C 5Me 5)Ir(pro)Cl] · [formula omitted]H 2O (Hpro = l-proline)

The synthesis and characterization of optically active amino acidato complexes of the types [(C 5Me 5)M(aa)Cl], [( p-cymene)Ru(aa)Cl], [(C 5Me 5)M(aa)(PPh 3)]BF 4, and [( p-cymene)Ru(aa)(PPh 3)]BF 4 (M = Rh, Ir; Haa = l-alanine, l-proline), in which the metal is a chiral centre, are reported. The cationic species were prepared via the solvato-complexes [(C 5Me 5)M(aa)(MeOH)] + and [( p-cymene)Ru(aa)(MeOH)] +, which epimerize rapidly on the 1H NMR time scale. The crystal structure of the complex [(C 5Me 5)Ir(pro)Cl] is reported; the asymmetric unit contains two independent molecules differing in the configuration at the metal.

CONFORMATION OF COORDINATED AMINO ACIDS. I. TETRAMMINE(l-PHENYLALANINATO)COBALT(III) ION

Abstract The ABX type spectrum of three CH protons of l-phenylalanine in tetrammine(l-phenylalaninato)cobalt(III) ion was analysed and it was found that fractional populations of three rotational isomers of the amino acidato ligand are significantly different from those in the free amino acid.

Preparation and Circular Dichroism of trans(N)- and cis(N)-Isomers of (Ammoniatriacetato)(amino-acidato)cobalt(III) Complexes

Abstract Eleven new complexes, trans(N)- or cis(N)-isomers of (ammoniatriacetato)(amino-acidato)cobalt(III) ions, have been synthesized as their potassium salts, where the amino acids are glycine, β-alanine, γ-aminobutyric acid, sarcosine, l-alanine, l-serine, l-valine and l-proline. The geometrical isomers have been separated by ion-exchange column chromatography and their structures determined on the basis of their absorption spectra and proton magnetic resonance spectra. Stereoselectivity about the formation of the trans and cis isomers was found. The circular dichroism of the complexes containing optically active amino acidato ligands has been measured and discussed in relation to so-called vicinal contribution by the optically active ligands.