| 1. |
- Carlsson, Håkan, et al.
(författare)
-
Hydrolytically active tetranuclear nickel complexes with structural resemblance to the active site of urease
- 2002
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 41:20, s. 4981-4983
-
Tidskriftsartikel (refereegranskat)abstract
- Reaction of the new asymmetric ligand 2-(N-isopropyl-N-((1-methylimidazolyl)methyl)aminomethyl)-6-(N-carboxylm ethyl-N-((1-methylimidazolyl)methyl) aminomethyl)-4-methylphenol (ICIMP) with nickel perchlorate and diphenylacetic acid leads to the formation of tetranuclear nickel complexes, whose crystal structures reveal that they consist of dimers of dimers in which each Ni-2 unit has a coordination environment that is similar to the active site of urease. One complex has been shown to coordinate urea and catalyze the hydrolysis of an organophosphate monoester.
|
|
| 2. |
- Carlsson, Håkan, et al.
(författare)
-
Nickel Complexes of Carboxylate-Containing Polydentate Ligands as Models for the Active Site of Urease
- 2004
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 43:26, s. 8252-8262
-
Tidskriftsartikel (refereegranskat)abstract
- Two new carboxylate-containing polydentate ligands have been synthesized, the symmetric ligand 2,6-bis[N-(N-(carboxylmethyl)-N-((1-methylimidazol)methyl)amine)methyl]-4-methylphenolate (BCIMP) and the corresponding asymmetric ligand 2-(N-isopropyl-N-((1-aminomethyl)-4-methylphenol (ICIMP). The ligands have been used to prepare model complexes for the active site of the dinuclear nickel enzyme urease, viz. [Ni2(BCIMP)Ac2]- (6), [Ni2(BCIMP)(Ph2Ac)2]- (7), [Ni2(ICIMP)(Ph2Ac)2] (14), [Ni4(ICIMP)2(Ph2Ac)2][ClO4]2 (15), [Ni4(ICIMP)2(Ph2Ac)2(DMF)2][ClO4]2 (16), and [Ni4(ICIMP)2(Ph2Ac)2(urea)(H2O)][ClO4]2 (17), where the latter complex contains urea coordinated in a unidentate fashion through the carbonyl oxygen. The N2O-N2O2 donor set of ICIMP provides a good framework for the preparation of urease models, but in some cases tetranuclear nickel complexes are formed due to coordination of the carboxylate moiety of one dinickel-ICIMP unit to one or both of the nickels of a second Ni2 unit. Reactivity and kinetics studies of 7 and 15 show that these model complexes catalyze hydrolysis of 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) at basic pH. In this assay, complexes based on the asymmetric ligand ICIMP exhibit a significantly faster rate of hydrolysis than the corresponding BCIMP complexes. Magnetic measurements indicate that there are weak antiferromagnetic interactions between the nickel ions in complex 16.
|
|
| 3. |
- Carlsson, Håkan, et al.
(författare)
-
Structural and Functional Models of the Active Site of Zinc Phosphotriesterase
- 2004
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 43:18, s. 5681-5687
-
Tidskriftsartikel (refereegranskat)abstract
- In an attempt to prepare structural and functional models for the active site of the hydrolytic enzyme zinc phosphotriesterase, five new zinc complexes of the ligands 2,6-bis[N-(N-(carboxylmethyl)-N-((1-methylimidazol)methyl)amine)methyl]-4-methylphenolate (BCIMP) and the corresponding asymmetric ligand 2-(N-isopropyl-N-((1-methylimidazolyl)methyl)aminomethyl)-6-(N-carboxylmethyl-N-((1-methylimidazolyl)methyl)aminomethyl)-4-methylphenol (ICIMP) have been synthesized, viz. Na[Zn2(BCIMP)Ac2] (1), [Zn2(BCIMP)(Ph2Ac)] (2), [Zn2(ICIMP)Ac2] (3), [Zn4(ICIMP)2(Me3Ac)2][ClO4]2 (4), and [Zn4(ICIMP)2(Ph2Ac)2][ClO4]2 (5). The X-ray structure of complex 5 has been determined and reveals that the complex is a dimer of dimers in the solid state, which in solution dissociates to potent structural models. Studies using NMR show that only one carboxylate coligand bridges the dizinc units in the case of diphenyl acetate and pivalate, while the steric bulk of acetate is sufficiently small to permit the coordination of two acetates/dizinc unit. Functional studies involving the hydrolysis/transesterification of 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) show that the complex with ICIMP (compound 5) has a significantly higher rate of catalysis than the BCIMP complex (compound 2). This is attributed to the vacant/labile coordination site that is available in the ICIMP complex but not the BCIMP complex.
|
|
| 4. |
- Homanen, Pertti, et al.
(författare)
-
A Cluster-based Catalytic Hydrogenation System with High Conversion and Reversible Enantioselectivity
- 2000
-
Ingår i: Organometallics. - : American Chemical Society (ACS). - 1520-6041 .- 0276-7333. ; 19:26, s. 5568-5568
-
Tidskriftsartikel (refereegranskat)abstract
- Four tetranuclear ruthenium carbonyl hydrido clusters consisting of the enantiomeric pairs [H4Ru4(CO)10{-1,2-(R/S,R/S)-bdpp}] and [H4Ru4(CO)10{1,1-(R/S,R/S)-bdpp}] containing chiral (R,R)- or (S,S)-bdpp [bdpp = (2R/S,4R/S)-2,4-bis(diphenylphosphino)pentane] have been prepared and fully characterized. These clusters catalyze asymmetric hydrogenation of tiglic acid [trans-2-methyl-2-butenoic acid] with high conversion rates (75-100%) under relatively mild reaction conditions. Enantiomeric excesses of 40-46% were observed; the predominating enantiomeric form of the hydrogenated product is dependent on the configuration of the diphosphine ligand, indicating strong chiral induction.
|
|
| 5. |
- Kiriakidou-Kazemifar, Nitsa, et al.
(författare)
-
Formation of Rhodium Carbonyl Cluster Thiolates with Concomitant H2 evolution
- 2001
-
Ingår i: Journal of Organometallic Chemistry. - 0022-328X. ; 623:1-2, s. 65-73
-
Tidskriftsartikel (refereegranskat)abstract
- Reaction of [Rh6(CO)15(NCMe)] with p-thiocresol [(4-Me)C6H4SH] leads to the formation of [Rh2(CO)4(μ-SC6H4CH3)2] as the main product along with a small amount of [Rh6(CO)16]. An approximately 30-fold excess of the thiol is required in order to obtain a good yield of the thiolate-bridged dimer while reaction of [Rh4(CO)12] with an excess of p-thiocresol leads to an apparently clean conversion to the dimeric Rh(I) complex. Mass spectrometric measurements show that the latter reaction involves evolution of H2, and CO evolution is indicated by the retardation of the reaction in CO saturated solution; these results suggest the following reaction stoichiometry: [Rh4(CO)12]+4RSH→2[Rh2(CO)4(μ-SR)2]+2H2+4CO. Kinetic measurements show that the reaction proceeds in three stages which are proposed to involve two rapid pre-equilibria and a final irreversible and relatively slow conversion to the products. The crystal and molecular structure of [Rh2(CO)4(μ2-SC6H4CH3)2] is reported.
|
|
| 6. |
- Tunik, Sergey, et al.
(författare)
-
Reactions of Diacetylene Ligands with Trinuclear Clusters; Cyclization of Diynes with beta-amino moieties on the surface of H2Os3(CO)10
- 2001
-
Ingår i: Organometallics. - : American Chemical Society (ACS). - 1520-6041 .- 0276-7333. ; 20:18, s. 3854-3863
-
Tidskriftsartikel (refereegranskat)abstract
- Reactions of [H2Os3(CO)10] with the substituted diynes R-C2-C2-R' (1, R = Ph, R' = CH2NHPh; 2, R = Ph, R' = CH2NHCH2Ph; 3, R = R' = CH2NHPh) afford the clusters [HOs3(CO)10(L)] (L = {-1:2-PhCH2C(H)=C-C(H)=C-NPh} (4), {-1:2-PhCH2C(H)=C-C(H)=C-NCH2Ph} (5), and {-1:1-CH3CC=C-C(H)=C(H)-NPh} (6), which have been characterized by single-crystal X-ray diffraction analyses as well as by various spectroscopic methods. In clusters 4-6, the starting diynes 1-3 have been rearranged to form substituted pyrrolyl rings which bridge two osmium atoms in 1:2- (4, 5) or 1:1- (6) coordination modes depending on the nature of substituents in 1-3. A possible reaction pathway for the diyne cyclization reactions that yield 4-6 involves initial transfer of a hydride onto a coordinated diyne followed by a series of 1,3-shifts and subsequent nucleophilic attack of the nitrogen on the third carbon atom of the diyne system to afford the five-membered pyrrolyl ring. Cluster 6 and its previously characterized furanyl analogue [HOs3(CO)10{-1:1-(OCHCHCC)-C-CH3)}] (7) undergo facile thermal transformation accompanied by the loss of a CO ligand to give the clusters [HOs3(CO)9{3,3-CH3CC=C-C(H)=C(H)-NPh}] (8) and [HOs3(CO)9{3,3-(OCH=CHC=CCCH3)}] (9). In both 8 and 9, single-crystal X-ray analysis revealed the presence of pentagonal pyramid cluster cores containing three osmium and three carbon atoms.
|
|
