Aminothiolate Ligands Research Articles

The importance of nitrogen substituents in chiral amino thiol ligands for the asymmetric addition of diethylzinc to aromatic aldehydes

A new series of N,S-chelate ligands derived from (S)-valine, which possess the capability of a stereogenic nitrogen donor atom, are catalysts for the addition of diethylzinc to aromatic aldehydes and gave the product secondary alcohols in up to 82% ee.

Displacement of ligands in [PtBr2(en)](en = ethylenediamine) by β- and γ-mercaptoamines

The reactions of [PtBr2(en)](en = ethylenediamine) with 2-(dimethylamino)ethanethiol, 3-dimethylaminopropane-1-thiol and 4-mercapto-1-methylpiperidine in alkaline aqueous solution give different types of complexes depending on the nature of the mercaptoamine. With the N-substituted β-mercaptoamine the product is cyclo-[{Pt(µ-SCH2CH2NMe2-N,µ-S)Br}3], consisting of discrete trimeric molecules with a central Pt3S3 ring. Each platinum atom is square-planar co-ordinated by a S2NBr donor set; the aminothiolate ligands are simultaneously chelating, through S and N, and bridging, through S, while bromine is terminally bonded. With the two γ-mercaptoamines, three crystalline products have been obtained, of formulae [(en)Pt(µ-SR)2Pt(en)]n+Brn·xH2O [R =(CH2)3NMe2, n= 2, x= 0; R = C5H9NMe, n= 2, x= 6; R = C5H9NHMe, n= 4, x= 2]. The three cations differ chemically only in the nature of the thiolate substituent group R, and their core geometries are essentially identical, consisting of a central exactly planar Pt2S2 ring linked to two five-membered chelate Pt(en) rings. There is extensive hydrogen bonding in the hydrated complexes. The different chelating ability of the β- and γ-mercaptoamines results in total displacement of ethylenediamine from the starting material by the β-mercaptoamine, but substitution of only bromine by the γ-mercaptoamines.

Dipalladium and diplatinum bis(µ-alkanethiolato) complexes with a planar M2S2ring

Mononuclear complexes of formula [M(SR)2(dppe)](M = Pd 1 or Pt 2; R = C5H9NMe, dppe = Ph2PCH2CH2PPh2) are formed in reactions of [MCl2(dppe)] with the sodium salt of 4-mercapto-1-methylpiperidine NaSR in acetonitrile–methanol solution. Subsequent reaction of 1 with [PdCl2(dppe)] and of 2 with [PtCl2(dppe)] in acetonitrile solution produces the bridged dinuclear cationic complexes [M2(µ-SR)2(dppe)2]2+, which are obtained as crystalline salts with tetraphenylborate anions (M = Pd 3 or Pt 4). An apparently mixed PtPd product 5 is formed in an analogous reaction from 1 and [PtCl2(dppe)] or from 2 and [PdCl2(dppe)]. The structures of complexes 1–5 have been determined crystallographically. Complexes 1 and 2 are isostructural, with a slightly distorted square-planar cis-MP2S2 co-ordination geometry. The isostructural complexes 3–5 also show square-planar co-ordination; the two aminothiolate ligands act as bridges between the metal atoms, giving a precisely planar central M2S2 ring. In all five structures the MP2C2 chelate rings have a twist conformation. The nitrogen atoms of the aminothiolates are not co-ordinated to the metal atoms. Infrared and 1H, 31P and 195Pt NMR spectra are presented and discussed. The combined evidence suggests that 5 is essentially a simple solid-solution mixture of pure complexes 3 and 4 in variable proportions, with at most a minor component of a genuinely heterobimetallic complex.

Synthesis and structures of tetranuclear 2-(dimethylamino)ethanethiolato complexes of zinc, cadmium and mercury involving both primary and secondary metal–halogen bonding

Two series of complexes of Zn, Cd and Hg with 2-(dimethylamino)ethanethiolate (L) ligands have been prepared. Complexes [M4L4X4](series I)(X = Cl or Br) are obtained from anhydrous MX2, HL·HX and triethylamine in acetonitrile, and also from the metal acetate, HL·HX and sodium hydroxide in aqueous solution. Treatment of [Cd4L4X4] with NaL in acetonitrile–methanol gives [Cd4L6X2](series II, Cd only). The structures of two complexes of series I, [Cd4L4Br4]1 and [Hg4L4Cl4]2, and of the series II complex [Cd4L6Cl2]3, have been determined crystallographically, and are probably representative of the two series. All have a central centrosymmetric M4S4 eight-membered ring in an extended-chair conformation with two opposite M atoms disposed one on each side of the M′2S4 plane, and with aminothiolate ligands which are both S,N-chelating to M′ atoms and S-bridging between M and M′ atoms. The additional L ligands in 3 chelate the out-of-plane M atoms. The halogen atoms in 1 and 2 are terminally bonded to the M atoms, but two of them are also weakly bonded to both M′ atoms to give incipient triple bridging. In complex 3 the Cl atoms bridge the two M′ atoms and are only weakly bonded to one M atom each. These patterns of primary and secondary M–X bonding are compared with those in other structures having a similar central X2M2M′2S4 core.

Preparation and crystal structure of the unprecedented octameric zinc–aminothiolate complex [Zn8{S(CH2)3NMe2}16

[Zn8{S(CH2)3NMe2}16], prepared by anodic oxidation of zinc in acetonitrile containing 3-dimethylamino-1-propanethiol, contains zinc atoms coordinated tetrahedrally by either four sulphur or one nitrogen and three sulphur atoms; the aminothiolate ligands function variously as terminal, µ2-bridging, or both chelating and bridging ligands.

A novel hexachelating amino-thiol ligand and its complex with gallium(III)

The ligand 1,4,7-tris(2-mercaptoethyl)-1,4,7-triazacyclononane, TS-TACNH{sub 3} (1), was synthesized from the parent amine, TACN, by reaction with ethylene sulfide in benzene. TS-TACNH{sub 3} undergoes reaction with Ga(NO{sub 3}){sub 3}{times}9H{sub 2}O in ethanol to give the neutral complex Ga(TS-TACN) (2). The complex may be recrystallized from dichloromethane as pale pink needles of the disolvate and the crystal structure is reported. There are four molecules of complex and two molecules of solvation (CH{sub 2}Cl{sub 2}) present per unit cell. The gallium is fully chelated in a slightly distorted octahedral environment by the three amine nitrogens and the three thiolate sulfurs. For comparison, the Ga{sup 3+} complex of the similarly hexachelating ligand 1,4,7-triazacyclononane-1,4,7-triacetic acid, NOTA, is also presented. The complex Ga(NOTA) (3), crystallizes from boiling water also as pale pink needles. Again, the metal center is fully chelated in a slightly distorted octahedral environment. The degree of distortion may be expressed as trigonal twist, {phi}, where {phi} = 0{degree} for a true octahedron and {phi} = 60{degree} for a trigonal prism. While both Ga(TS-TACN) and Ga(NOTA) are potentially isostructural, in regard to coordination geometry, with trigonal-prismatic Fe(NOTA) ({phi} = 34.8{degree}), the gallium(III) complexes are only slightly distorted from a regular octahedral coordination sphere (Ga(NOTA)more » {phi} = 12.4{degree} and Ga(TS-TACN) {phi} = 10.4{degree}). Preliminary results indicate {sup 68}Ga(TS-TACN) to be stable in vivo versus the blood protein transferrin, indicating a relatively high stability constant for this hexachelating ligand. 14 refs., 7 figs., 3 tabs.« less