Reactivity and kinetic studies of (NH4)2(MoS4) in acidic aqueous solution: possible relevance to the angiostatic function of the MoS4(2-) ligand.

Although addition of mineral acids to WS(4)(2-) in water is known to lead to aggregation and formation of various polynuclear thiotungstate anions, acid hydrolysis of the MoS(4)(2-) anion is reported to give mainly MoS(3) or MoS(2) as hydrolysis products. Knowledge of the resulting product(s) from such reactions has implications on the use of tetrathiomolybdate (MoS(4)(2-)) as both a potential anti-tumor drug and for the treatment of Wilson's disease. In this investigation, reaction of HCl with MoS(4)(2-) in water was monitored as a function of time. Reaction mixtures of both 1:1 and 2:1 mole ratios of the acid to MoS(4)(2-) were examined, as well as MoS(4)(2-) reactions in simulated human stomach fluids at pH of approximately 2 and 3. Monitoring by electrospray mass spectrometry (ESMS), Fourier transform infrared (FTIR), and UV-visible spectroscopy clearly has revealed the formation of complex mixtures of polynuclear thiomolybdates (Mo(2)-Mo(18)). Generally, a two-stage consecutive reaction sequence occurs. A faster stage (k=7.0-7.9 x 10(-2)min(-1)), which seems to extend to trinuclear thiomolybdate species, followed by a slower second stage (k=5.4-15.2 x 10(-4)min(-1)) to higher polynuclear thiomolybdates. Under acidic conditions (e.g. pH approximately 3) that could also mimic some human stomach fluids, and under anaerobic atmosphere where the generated hydrogen sulfide is prevented from escaping from the reaction vessel, Mo(3)S(9)(2-) predominates over an extended reaction period. In similar reactions under aerobic conditions and where the hydrogen sulfide is irretrievably lost from the reaction mixture the binuclear (Mo(2)O(a)S(10-a)(2-);a=0-3) and trinuclear (Mo(3)O(b)S(9-b)(2-);b=1-3) anions predominate.

Rational synthesis of high nuclearity Mo/Fe/S clusters: the reductive coupling approach in the convenient synthesis of (Cl(4)-cat)(2)Mo(2)Fe(6)S(8)(PR(3))(6) [R = Et, (n)Pr, (n)Bu] and the new [(Cl(4)-cat)(2)Mo(2)Fe(2)S(3)O(PEt(3))(3)Cl]-1/2(Fe(PEt(3))(2)(MeCN)(4)) and (Cl(4)-cat)(2)Mo(2)Fe(3)S(5)(PEt(3))(5) clusters.

A general method for the synthesis of high nuclearity Mo/Fe/S clusters is presented and involves the reductive coupling of the (Et(4)N)(2)[(Cl(4)-cat)MoOFeS(2)Cl(2)] (I) and (Et(4)N)(2)[Fe(2)S(2)Cl(4)] (II) clusters. The reaction of I and II with Fe(PR(3))(2)Cl(2) or sodium salts of noncoordinating anions such as NaPF(6) or NaBPh(4) in the presence of PR(3) (R = Et, (n)Pr, or (n)Bu) affords (Cl(4)-cat)(2)Mo(2)Fe(6)S(8)(PR(3))(6) [R = Et (IIIa), (n)Pr (IIIb), (n)Bu (IIIc)], Fe(6)S(6)(PEt(3))(4)Cl(2) (IV) and (PF(6))[Fe(6)S(8)(P(n)Pr(3))(6)] (V) as byproducts. The isolation of (Et(4)N)[Fe(PEt(3))Cl(3)] (VI), NaCl, and SPEt(3) supports a reductive coupling mechanism. Cluster IV and V also have been synthesized by the reductive self-coupling of compound II. The reductive coupling reaction between I and II by PEt(3) and NaPF(6) in a 1:1 ratio produces the (Et(4)N)(2)[(Cl(4)-cat)Mo(L)Fe(3)S(4)Cl(3)] clusters [L = MeCN (VIIa), THF (VIIb)]. The hitherto unknown [(Cl(4)-cat)(2)Mo(2)Fe(2)S(3)O(PEt(3))(3)Cl](+) cluster (VIII) has been isolated as the 2:1 salt of the (Fe(PEt(3))(2)(MeCN)(4))(2+) cation after the reductive self-coupling reaction of I in the presence of Fe(PEt(3))(2)Cl(2). Cluster VIII crystallizes in the monoclinic space group P2(1)/c with a = 11.098(3) A, b = 22.827(6) A, c = 25.855(6) A, beta = 91.680(4) degrees, and Z = 4. The formal oxidation states of metal atoms in VIII have been assigned as Mo(III), Mo(IV), Fe(II), and Fe(III) on the basis of zero-field Mössbauer spectra. The Fe(PEt(3))(2)(MeCN)(4) cation of VIII is also synthesized independently, isolated as the BPh(4)(-) salt (IX), and has been structurally characterized. The reductive coupling of compound I also affords in low yield the new (Cl(4)-cat)(2)Mo(2)Fe(3)S(5)(PEt(3))(5) cluster (X) as a byproduct. Cluster X crystallizes in the monoclinic space group P2(1)/n with a = 14.811(3) A, b = 22.188(4) A, c = 21.864(4) A, beta = 100.124(3) degrees, and Z = 4 and the structure shows very short Mo-Fe, Fe-Fe, Mo-S, Fe-S bonds. The oxidation states of the metal atoms in this neutral cluster (X) have been assigned as Mo(IV)Mo(III)Fe(II)Fe(II)Fe(III) based on zero-field Mössbauer and magnetic measurement. All Fe atoms are high spin and two of the three Fe-Fe distances are found at 2.4683(9) A and 2.4721(9) A.

Kinetic Lability, Structural Diversity, and Oxidation Reactions of New Oligomeric, Anionic Carboxylate-Pyridine Complexes.

The dimeric [M(2)(OAc)(5)(py)(2)&mgr;-(OH(2))]Et(4)N complexes, I (M = Mn, Fe, Co), have been isolated from pyridine solutions of M(II)(OAc)(2).xH(2)O and Et(4)N(OAc).4H(2)O. The X-ray structures of I (M = Mn, Fe, Co) have been determined and show the metal ions asymmetrically bridged by two acetate ligands and a water molecule. One of the metal ions is bound by a pyridine ligand and two monodentate acetate ligands that are hydrogen bonded to the bridging water molecule. The second metal ion is bound to a bidentate acetate ligand and a pyridine ligand. Recrystallization of I from acetonitrile leads to the reorganization of I and isolation of the M(3)(OAc)(8)(Et(4)N)(2) complexes, II (M = Mn, Fe, Co). The X-ray structure of II (M = Mn, Co) has been determined and shows the three metal ions connected by four bridging acetate ligands in a &mgr;(1), &mgr;(2) mode and two acetate ligands in the &mgr;(1),eta(1) mode, with a bidentate acetate ligand on each of the external metal ions completing the distorted octahedral geometry. Air oxidation of I-Fe in propionitrile leads to the formation of the mixed-valence [Fe(3)&mgr;(3)-(O)(OAc)(7)(OH(2))]Et(4)N(III). The X-ray structure of III has been determined and resembles the core of the basic acetate complexes; however, it has five bridging acetate ligands. The Mössbauer spectrum of III shows two quadrupole doublets in a 1:2 ratio with delta(Fe) = 1.29(1) and 0.48 mm/s; DeltaE(q) = 1.89 and 0.71 mm/s. The oxidation of I-Fe by H(2)O(2)/O(2) in pyridine solution in the presence of Cl(-) ligands affords Fe(4)&mgr;(3)-(O)(2)(OAc)(6)(py)(4)Cl(2) (IV). The X-ray structure of IV shows a rhombic {Fe(III)(4)(&mgr;(3)-O)(2)} core previously found in iron and manganese chemistry. The reaction of ferrocenium ion with I-Fe under basic conditions in dichloromethane solution led to the formation of the familiar mixed-valence Fe(3)&mgr;(3)-(O)(OAc)(6)(py)(3) complex (V) with the basic acetate structure. Complexes I-Fe, II-Fe, III, and IV catalyze the reaction of O(2) with adamantane under GiF conditions to give adamantanols and adamantanone. The similarity of the results in comparison to similar studies previously reported for iron/carboxylate complexes are noted and discussed.