Thiolates tridentate

Thiolates are strong ligands and a rich coordination chemistry with cobalt(III) exists. Normally, thiols are employed directly in synthesis, and this is the usual entry into their coordination chemistry. However, alternative approaches do appear from time to time, and recently the cobalt-mediated direct thiolation of an aromatic ring in bidentate phenyl(2-pyridyl)diazene using dithiocarbamate ion to produce a coordinated tridentate thiolate has been reported.1034... 

An S4 coordination sphere of the type seen in the Ada protein, where four cysteines coordinate, was achieved with the tridentate tris(2-mercapto-l-phenylimidazolyl)hydroborato ligand. The zinc thiophenolate derivative showed reactivity of the thiolate linkage (Figure 8).506... 

A tridentate SNO ligand coordinates with a bipyridine to give ((2,2 -bipyridine)[2-(2-mercapto-phenyl)iminophenoxy])zinc. The monomeric complex has a distorted trigonal bipyramidal geometry with a phenolate and a thiolate coordinated. The synthesis was carried out electrochemically from anodic zinc in the presence of a disulfide-linked ligand precursor.867... 

Methyl- l-[methyl-(2-pyridin-2-yl-ethyl)amino]propane-2-thiol (108) is a tridentate N2S ligand with an aliphatic thiolate ligand. The single-crystal X-ray structures demonstrate that the zinc complexes are close structural analogs of the His2Cys site found in peptide deformylase.873... 

A number of neutral mixed-ligand oxorhenium(V) complexes containing tridentate [SC2H4YC2Lt4S] (Y = S,0) (95) and monodentate, monoanionic thiolate ligands have been prepared from [ReOCU] and a mixture of the ligands (Scheme The intermediate... 

Rheniumi ) 0x0 bioconjugates have been prepared with chelating NjS donor ligands such as amino/amido/thiolates, mixed-ligand complexes of tridentate ligands with... 

Tomioka et al. reported the asymmetric Michael addition of lithium thiolates catalyzed by chiral aminoether 31 (Scheme 8D. 18) [39]. Thus, in the presence of catalytic amounts of 31 (10 mol %) and lithium 2-(trimethylsilyl)thiophenolate 32-Li (8 mol %), thiol 32 (3 equiv.) reacted with a,p-unsaturated esters at -78°C in toluene-hexane solvent to give the Michael adduct with up to 97% ee. In the ahsence of 31, the reaction of thiophenol proceeded in only 0.5% yield at room temperature. A monomeric complex consisting of 31 and lithium is proposed as the key reactive species in this asymmetric reaction. The trimethylsilyl group at the ortho-po-sition of the thiol moiety in 32 contributes to the formation of the stereochemically defined monomeric chelated structure, wherein the lithium cation is coordinated with the three heteroatoms of the tridentate ligand 31. The reactions of acyclic /nmv-a,P-unsaturated esters (R1 = Me, Et, Pr, Bu, Bu, PhCH9 R2 = H) proceeds with high enantioselectivity in... 

Lithium thiolates add well to activated olefins, generating /i-sulfuri/cd lithium eno-lates175. Those can be used in tandem inter-176 or intra-177 molecular addition-aldolisation processes. In the presence of a catalytic amount of bi- or tridentate chiral ligands178, this addition becomes enantioselective and the newly created asymmetric center(s) can be almost totally controlled, provided the thiolate and the enone structures are well chosen (Scheme 40)179 l82. 

C104) crystallizes in 96% yield in a second-order asymmetric manner. The solution actually contains the equilibrium mixture A(jR) A(jR) = 7 3.1036 Both Co2, and OH- effect rapid mutarota-tion about the metal in this complex but not about the chiral carbon. With (S)-penicillamine a similar equilibrium obtains (A A[Co (S)pen (en)2]2+ = 7 3) but preferential crystallization does not occur.1037 X-Ray structures confirm equatorial and axial dangling carboxylate functions in A-[Co (R)cys (en)2](C104) and A-[Co (7 )cy s (en)2 ] (C104) H2 O respectively.1037 (N,S) bonding seems to be preferred in (N,S,0) systems (cysteine, penicillamine) but (N,0)[Co (R)cys (en)2]2+ has been prepared by reduction of the tridentate sulfenamide complex (285 equation 159).1038 This (N.O) chelate lacks the extended charge transfer absorptions in the near UV characteristic of thiolate coordination. 

Condensation of ketones or aldehydes with the methyl ester of dithiocarbazic acid produces hgands with S,N,0 or S,N donor sets. An example is (142), which acts as both a didentate and a tridentate to ReO. Nickel(II)-templated reactions of pentanedione or salicylaldehyde with aminoethanethiol produce N,0,S ligands such as (143) and (144) these form simple mononuclear complexes or else dinuclear species with thiolate bridging two Ni centers. Mixed donor Schiff-base hgands including other heteroatoms such as P (145) and Te (146) have appeared. 

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