G.C. van Stein

Dinuclear silver(I) and copper(I) complexes with neutral N2S2 donor ligands and their reactivities towards CO. Structure in solution (1H and INEPT 109Ag NMR) and in the solid (X-ray) of [Ag{m-(R),(S)-1,2-(thiophene-2-CH=N)2-cyclohexane}2] (O3SCF3)2

Abstract The 1/1 reactions of the neutral N2S2 donor system (R)(S)-1,2-(5-R–thiophene-2-CHN)2–cyclohexane (R = H, 1a or Me, 1b) with [M(O3SCF3)] [M = Ag(I) or Cu(I)] yielded ionic complexes, consisting of a dinuclear [M2(1)2]2+ dication and O3SCF3− monoanions. An X-ray crystallographic study characterized the molecular structure of [Ag2–(1a)2](O3SCF3)2, in the monoclinic unit cell, space group P21/n, with Z = 4; a = 17.26(1), b = 15.08(2), c = 19.960(17) A, β = 106.15(4)°, V = 4991 A3. The structure was refined to R is 0.0704. The two N2S2 ligands coor- dinate to the silver(I) centres in a bridging di- bidentate manner with short AgN(imine) [e.g. Ag(1)N(2), 2.152(10); Ag(1)N(7), 2.162(9); Ag(2)N(3), 2.153(10); Ag(2)N(6), 2.158(10) A] and long AgS(thiophene) distances [Ag(1)S(1), 2.961(4); Ag(1)S(8), 2.938(4); Ag(2)S(4), 2.928(4); Ag(2)S(5), 2.995(5) A]. The Ag(1) Ag(I) separation is 2.909(1) A. In solution the coordination properties of the N2S2 ligands to silver(I) and copper(I) have been studied by 1H and INEPT 109Ag NMR spectroscopy. The 1H NMR data revealed, by the presence of two thiophene–imine 1H patterns at 190 K, that at this temperature i) the structural features found for [Ag2(1a)2]2+ in the solid are retained in solution and ii) the silver(I) and copper(I) complexes have similar structures in solution. Furthermore, the presence of 3J(1H107,109Ag) on the imine-H resonances of the silver(I) complexes indicates that at 190 K intermolecular exchange processes are slow on the NMR time scale. From the difference in δ109Ag of the [Ag2(1)2](O3SCF3)2 complexes, R = H (δ + 678) or Me (δ + 659), it was concluded that weak thiopheneSAg(I) interactions are present, and stabilize the formation of the [M2(1)2]2+ dications. However, in the reversible reactions of [Cu2(1)2](O3SCF3)2 with carbon monoxide the thiopheneSCu(I) bonds dissociate and neutral complexes are formed having a [{CuCO(O3SCF3)}2{μ−1}2] type of structure. In these complexes both the carbon monoxide and OSO2CF3 groups are terminally coordinated to Cu(I) (R = H, ν(CO), 2089 cm−1; R = Me, ν(CO) = 2087 cm−1 in CH2Cl2).

Copper(I)and silver(I) ions in unusual poly donor-atom environments; X-ray crystal and molecular structures of [M{(R)(S)-1,2-(5-Me-thiophene-2-CH=N)2 cyclohexane}2]-O3SCF3), M = CuI or AgI

Coordination properties of 0.t’ and Cu’ with ligand systems containing N and S donor atoms as potential coordinating sites continue to be of interest as models for the redox active sites in the ‘blue’ proteins [ 1] . The conformation and rigidity of the carbon skeleton connecting the hetero-atoms, as well as the types and number of hetero-atoms in the model ligand systems, are important with respect to both the number of metal atoms which can be bonded and the ultimate configuration at the metal centres. Recently we have shown that the quadridentate N-donor ligands (R)(S)-1 ,2-(6-R-py-2-CH=N)Z-cyclohexane (R = H or Me), in which the inner two N-donor sites are connected by the (R)(S)-1,2cyclohexanediyl ring, act as di-bidentate ligands binding two Cur or Ag’ atoms (see Fig. 1) [2]. The application of INEPT “N and ro9Ag NMR spectroscopy revealed that the structural features found for the silver(I) complex [Ag,{(R@)-1,2(py-2-CH=N)z-cyclohexane),l(03SCF3)2 in the solid, with characteristic alternating two short and two long Ag-N distances around the distorted tetrahedral silver centres [2], are retained in solution [3] . Attempts to form mononuclear Cu’ or Ag’ complexes with these N4donor ligands, using ‘A Curor Agr-to-ligand ratios were unsuccessful. Interpretation of these results requires more information concerning the influence of the donor sites on the coordination properties of these types of potentially quadridentate ligands. For this purpose we have now investigated the bonding features of the N2S, ligand system (R)(S)-1,2-(5-R-thiophene-

Environmental chemistry of PCB-replacement compounds - VI - composition and metabolism of Wemcol ®, an isopropylbiphenyl formulation

Abstract Wemcol is a technical isopropylbiphenyl formulation that is used as a substitute for polychlorobiphenyl. According to the producer Wemcol is 4-isopropylbiphenyl, but we found our sample to consist of 60.3% 3-isopropylbiphenyl, 38.6% 4-isopropylbiphenyl and 3,5-, 3,3′-, 3,4′- and 4,4′-diisopropylbiphenyl in amounts of 0.3%, 0.4%, 0.2% and 0.1% respectively. The two major components of the mixture are metabolized in the rat by two routes : oxidation of the isopropyl group and hydroxylation of the aromatic nuclei. Rats fed the technical mixture retained 3- and 4-isopropylbiphenyl in a ratio 4.3 : 1 in their abdominal fat, whilst the ratio in the mixture is 1.6 : 1. One week after the simultaneous feeding of equal amounts of Wemcol, 4,4′-dichlorobiphenyl, 2,4′,5-trichlorobiphenyl and 2,2′,5,5′-tetrachlorobiphenyl, the isopropylbiphenyls, in contrast to the chlorobiphenyls, could no longer be detected in the abdominal fat of rats.

Structures and reactivities of copper(I) and silver(I) complexes of potentially quadridentate N4 and N2S2 donor ligands.

In designing model complexes for the activities sites in copper proteins it is important to know the influence of the different hetero-atoms and conformational changes of the carbon skeleton on the chemical and physical properties of the metal centre.We have investigated the structure properties of copper(I) and silver(I) complexes with potentially quadridentate N{4} and N{2}S{2} donor ligand system, schematically represented in Fig. 1, which have the connecting (R)(S)-1, 2-diiminocyclohexane group in commonFrom the reaction of the N{4} donor ligand with M(O{3}SCF{3}) (M = Cu}I{ or Ag}I{) we obtained dimeric [M{2}(N{4}){2}]}2{}+{ 2O{3}SCF}-{{3} complexes. The X-ray structure of the silver(I) complex showed that each ligand acts in a di-bidentate manner bridging the two metal centre (see Fig. 2). The silver ions have distorted tetrahedral geometries with each Ag}I{ centre taking part in two short Ag@?N (2.25 A) and two long Ag@?N (2.43 @9) interactions. The N@?Ag@?N bond angle between the two short Ag@?N bonds is circa 150}o{[1].The copper(I) and silver(I) complexes are very stable and do not react further either with excess N{4} ligand or with H{2}O, O{2} and CO. However, detailed }1{H studies have shown that inter- and intramolecular exchange (e.g. metal-ion or ligand exchange) occurs. These will be discussed. In contrast to these result reactions of the N{2}S{2} ligand system with M(O{3}SCF{3}) (M = Cu}I{ or Ag}I{) give rise to two different types of complexes, i.e. a dimeric [M{2}(N{2}S{2}){2}]}2{}+{ 2O{3}SCF}-{{3} and a monomeric [M(N{2}S{2}){2}]}+{ O{3}SCF}-{{3} complex. According to }I{H and }1{}0{}9{Ag NMR data the dimeric complex has a structure similar to that found for the [M{2}(N{4}){2}]}2{}+{ 2O{3}SCF}3{}-{ complex. However, in the [M{2}(N{2}S{2}){2}]}2{}+{ dication the imine-N atoms of the N{2}S{2} ligands have strong intersections with the metal centres, while the thiophene-S atoms coordinate only weakly with the metal-IB centre. This coordination behaviour is reflected by the reactivity of the copper(I) complex, which reacts rapidly with CO(@n{C}{O} = 2092cm}-{}1{. An X-ray study is underway.The X-ray structures of the mononuclear [M(N{2}S{2}){2}]}+{ O{3}SCF}-{{3} complexes have been resolved for M = Cu}I{ and M = Ag}I{ to establish the exact molecular conformations and to test the validity of the assumption that copper(I) can be replaced by silver(I) with retention of the structural features [2]. As a result of the constraint of the N{2}S{2} system, each ligand is primarily bonded to the metal centre (M = Cu or Ag) by one imine-N atom [N(1) and N(3)] with the remaining three hetero-atoms being held in close proximity to the metal centre (see Fig. 3: M = Cu). These complexes do not react with H{2}O, O{2} and CO.

Application of INEPT 109Ag and 15N NMR Spectroscopy for the study of metal-ligand interactions of silver analogues of copper(I) model compounds

Because of the presence of copper (in its reduced state) at active sites in protein it has become very important to study copper(I) model complexes by spectroscopic techniques.We now report that if copper(I) in model complexes can be substituted by silver(I) with retention of the structural features then }1{}0{}7{Ag or }1{}0{}9{Ag NMR spectroscopy (natural abundances 50% I = 12) using the recently developed polarization transfer sequence INEPT (Insensitive Nuclei Enhanced by Polarization Transfer) [1] provides an excellent tool for studying the metal IB-ligand interaction}1{H NMR studies show that the analogous copper(I) and silver(I) complexes of potentially quadridentate N{4} (R)(S)-1, 2-(6-R-pyridine-2-CH@?N){2}-cyclohexane (R = H or Me) as well as the N{2}S{2} donor ligand (R)(S)-1,2-(5-R-thiophene-2-CH@?N){2}-cyclohexane (R = H or Me) have similar structures (confirmed by X-ray studies [2]). However, study of the direct coordination sphere and copper(I)-ligand interactions in these model complexes by Cu NMR is hampered by the large quadropole moments of both }6{}3{Cu and }6{}5{Cu (natural abudances 70 and 30% respectively, I = 32).We have measured directly }1{}0{}9{Ag NMR (INEPT) spectra with large enhancements in signal to noise and enormous experimental time saving (a factor 400-500) as compared to the conventional methods (see Fig. 1) [3]. the influence of the nature of the hetero-atoms coordinating the metal centre is directly reflected in the chemical shift differences of the }1{}0{}9{Ag resonances.It is shown that for silver(I) coordination complexes information about the ligand-to-metal interaction can be obtained by using not only direct }1{}0{}9{Ag NMR, but also INEPT }1{}5{N NMR spectroscopy. In particular the }1{}5{N NMR (INEPT) spectra of the silver(I) complexes [M{2}(N{4}){2}]}2{}+{ 2O{3}SCF}-{{3} show that the structure of these complexes as found in the solid by X-ray methods, in which each metal ion has a distorted tetrahedral coordination geometry of four N-atoms, is fully retained in solution. From different }1{J(}1{}5{N@?}1{}0{}7{},{}1{}0{}9{Ag) coupling constants the relative bond strengths of the various Ag@?N interactions can be deduced.Where Cu}I{ can be substituted by Ag}I{ either in coordination (model) complexes or biological systems (bovine superoxide dismutase [4]) INEPT }1{}0{}9{Ag NMR spectroscopy has potential as a novel technique for the study of the coordinating properties of the metal centres.