Thioesters metal complexes

Metal complexes are known to insert CO into carbon-sulfur bonds [118], even catalytically [119], Stoichiometric precedents exist for the formation offhioesters from nickel-alkyls, CO, and thiols [120], For example, NiMe2(bipy) reacts with thiols to afford mefhylnickel(ll) fhiolates, which carbonylate to afford acetyl-nickel(ll) fhiolates. These acetylnickel(II) thiolates reductively eliminate fhioester in the presence of CO [121], More biologically relevant is the reactivity of nickel acyls toward fhiolates, which gives fhe thioester concomitant with reduction to Ni(0) (Eq. 12.10) [122]. Thiolates are known to reduce Ni(II) to Ni(0) under an atmosphere of CO [123]. 

Polarographic studies are reported on thioesters, mainly of the type (140) and (141), and on trichloroethylphosphonites. In the field of nucleotides and nucleosides it is found that ATP has a very high surface activity at the mercury electrode, which is strongly dependent upon complex formation with transition metals. The polarographic behaviour of cobalt complexes with triphenylphosphine and its oxide has been studied in order to estimate extraction efficiencies. 

The / -mercapto thioesters (69 R = Et, Pr1) and the o-mercaptobenzoic acid thioesters (68 R = Et, Pr1, Pe ) form complexes with Cu1, Ni11 and Co111.255,258 Since several (b) class and borderline metals form more stable complexes with the S-esters (68) than with the O-esters (67), it is likely that the S-esters behave as S,S-bidentates. 

If this conjecture is correct, the intermediate form of MPT would be bound to the synthase protein via thioester linkages. Given the hydrolytic instability of thioesters, the synthase bound MPT derivative should serve as an ideal precursor to metal-containing MPT derivatives that could be generated either by hydrolysis of the thioester followed by complexation or by direct reaction with molybdate, tungstate, or a simple derivative of these oxyanions. 

The mechanism of these reactions was proposed to take place by initial electron transfer to the carbonyl group of the thioester, generating a ketyl-like radical anion such as 103 (Scheme 7.43). Subsequent radical addition to the electron-deficient alkene (acrylamide or acrylate), possibly guided by pre-complexation to a Sm(III) metal ion, generates a new radical centre, which is reduced to the corresponding Sm(III) enolate by a second equivalent of Sml2. Protonation of this enolate and hydrolysis of the hemithioacetal upon work-up then lead to the y-ketoamide or ester. 

Complexes of dmit2- are commonly generated either via ligand transfer from [Zn(dmit)2]2- (see Section III.G) or by salt metathesis using Na2dmit. Alkali metal salts of dmit2- are prepared by hydrolysis of the thioester dmit[C(0)Ph)]2. This dithioester is prepared by treatment of [Zn(dmit)2]2- with PhC(Q)Cl and... 

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