Biomedical subjects

Dieter Sellmann

Publications and source records attributed to Dieter Sellmann.

6 recordsLinked to original sources

PubMed2002

Tuning the electronic structure of octahedral iron complexes [FeL(X)] (L = 1-alkyl-4,7-bis(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane, X = Cl, CH(3)O, CN, NO). The S = 1/2 <==>3/2 Spin equilibrium of [FeL(Pr)(NO)].

Two new pentadentate, pendent arm macrocyclic ligands of the type 1-alkyl-4,7-bis(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane where alkyl represents an isopropyl, (L(Pr))(2-), or an ethyl group, (L(Et))(2-), have been synthesized. It is shown that they bind strongly to ferric ions generating six-coordinate species of the type [Fe(L(alk))X]. The ground state of these complexes is governed by the nature of the sixth ligand, X: [Fe(III)(L(Et))Cl] (2) possesses an S = 5/2 ground state as do [Fe(III)(L(Et))(OCH(3))] (3) and [Fe(III)(L(Pr))(OCH(3))] (4). In contrast, the cyano complexes [Fe(III)(L(Et))(CN)] (5) and [Fe(III)(L(Pr))(CN)] (6) are low spin ferric species (S = 1/2). The octahedral [FeNO](7) nitrosyl complex [Fe(L(Pr))(NO)] (7) displays spin equilibrium behavior S = 1/2<==>S = (3)/(2) in the solid state. Complexes [Zn(L(Pr))] (1), 4.CH(3)OH, 5.0.5toluene.CH(2)Cl(2), and 7.2.5CH(2)Cl(2) have been structurally characterized by low-temperature (100 K) X-ray crystallography. All iron complexes have been carefully studied by zero- and applied-field Mössbauer spectroscopy. In addition, Sellmann's complexes [Fe(pyS(4))(NO)](0/1+) and [Fe(pyS(4))X] (X = PR(3), CO, SR(2)) have been studied by EPR and Mössbauer spectroscopies and DFT calculations (pyS(4) = 2,6-bis(2-mercaptophenylthiomethyl)pyridine(2-)). It is concluded that the electronic structure of 7 with an S = 1/2 ground state is low spin ferrous (S(Fe) = 0) with a coordinated neutral NO radical (Fe(II)-NO) whereas the S = 3/2 state corresponds to a high spin ferric (S(Fe) = 5/2) antiferromagnetically coupled to an NO(-) anion (S = 1). The S = 1/2<==>S = 3/2 equilibrium is then that of valence tautomers rather than that of a simple high spin<==>low spin crossover.

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PubMed2002

(NEt(4))(2)[Fe(CN)(2)(CO)('S(3)')]: an iron thiolate complex modeling the [Fe(CN)(2)(CO)(S-Cys)(2)] site of [NiFe] hydrogenase centers.

In the search for complexes modeling the [Fe(CN)(2)(CO)(cysteinate)(2)] cores of the active centers of [NiFe] hydrogenases, the complex (NEt(4))(2)[Fe(CN)(2)(CO)('S(3)')] (4) was found ('S(3)'(2-)=bis(2-mercaptophenyl)sulfide(2-)). Starting complex for the synthesis of 4 was [Fe(CO)(2)('S(3)')](2) (1). Complex 1 formed from [Fe(CO)(3)(PhCH=CHCOMe)] and neutral 'S(3)'-H(2). Reactions of 1 with PCy(3) or DPPE (1,2-bis(diphenylphosphino)ethane) yielded diastereoselectively [Fe(CO)(2)(PCy(3))('S(3)')] (2) and [Fe(CO)(dppe)('S(3)')] (3). The diastereoselective formation of 2 and 3 is rationalized by the trans influence of the 'S(3)'(2-) thiolate and thioether S atoms which act as pi donors and pi acceptors, respectively. The trans influence of the 'S(3)'(2-) sulfur donors also rationalizes the diastereoselective formation of the C(1) symmetrical anion of 4, when 1 is treated with four equivalents of NEt(4)CN. The molecular structures of 1, 3 x 0.5 C(7)H(8), and (AsPh(4))(2)[Fe(CN)(2)(CO)('S(3)')] x acetone (4 a x C(3)H(6)O) were determined by X-ray structure analyses. Complex 4 is the first complex that models the unusual 2:1 cyano/carbonyl and dithiolate coordination of the [NiFe] hydrogenase iron site. Complex 4 can be reversibly oxidized electrochemically; chemical oxidation of 4 by [Fe(Cp)(2)PF(6)], however, led to loss of the CO ligand and yielded only products, which could not be characterized. When dissolved in solvents of increasing proton activity (from CH(3)CN to buffered H(2)O), complex 4 exhibits drastic nu(CO) blue shifts of up to 44 cm(-1), and relatively small nu(CN) red shifts of approximately 10 cm(-1). The nu(CO) frequency of 4 in H(2)O (1973 cm(-1)) is higher than that of any hydrogenase state (1952 cm(-1)). In addition, the nu(CO) frequency shift of 4 in various solvents is larger than that of [NiFe] hydrogenase in its most reduced or oxidized state. These results demonstrate that complexes modeling properly the nu(CO) frequencies of [NiFe] hydrogenase probably need a [Ni(thiolate)(2)] unit. The results also demonstrate that the nu(CO) frequency of [Fe(CN)(2)(CO)(thiolate)(2)] complexes is more significantly shifted by changing the solvent than the nu(CO) frequency of [NiFe] hydrogenases by coupled-proton and electron-transfer reactions. The "iron-wheel" complex [Fe(6)[Fe('S(3)')(2)](6)] (6) resulting as a minor by-product from the recrystallization of 2 in boiling toluene could be characterized by X-ray structure analysis.

Binding Sites↗

PubMed2001

[Ru]

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Journal Article↗

PubMed1999

Transition-Metal Complexes with Sulfur Ligands. 132.(1) Electron-Rich Fe and Ru Complexes with [MN(2)S(3)] Cores Containing the New Pentadentate Ligand 'N(2)H(2)S(3)'(2)(-) (= 2,2'-Bis(2-mercaptophenylamino)diethyl Sulfide(2-)).

The new pentadentate amine thioether thiolate ligand 'N(2)H(2)S(3)'-H(2) (= 2,2'-bis(2-mercaptophenylamino)diethyl sulfide) (3) was synthesized in order to obtain iron and ruthenium complexes with high electron densities at the metal centers. The reaction of 'N(2)H(2)S(3)'(2)(-) with Fe(2+) yielded the dinuclear high-spin complex [Fe('N(2)H(2)S(3)')](2) (5). Complex 5 added CO to give the low-spin complex [Fe(CO)('N(2)H(2)S(3)')] (6) whose low frequency nu(CO) (1932 cm(-)(1)) indicates a high electron density at the iron center and a strong Fe-CO bond. However, 6 is labile and readily dissociates CO in solution. Treatment of suitable ruthenium precursor complexes with 'N(2)H(2)S(3)'(2)(-) yielded [Ru(CO)(PCy(3))('N(2)H(2)S(3)')] (7), [Ru(PPr(3))(2)('N(2)H(2)S(3)')] (8), [Ru(PR(3))('N(2)H(2)S(3)')] (R = Pr (9), Ph (10)), and [Ru(NO)('N(2)HS(3)')] (13). In complexes 7 and 8, 'N(2)H(2)S(3)'(2)(-) acts as a tetradentate ligand. When heated in solution, complex 8 dissociates one PPr(3) ligand to give 9. Complex 13 contains the trisanionic 'N(2)HS(3)'(3)(-) resulting from deprotonation of one amine NH function. All [Ru(L)('N(2)H(2)S(3)')] complexes proved inert toward dissociation of the Ru-L bonds. The NH functions of [M(L)('N(2)H(2)S(3)')] complexes are acidic and show H(+)/D(+) exchange reactions with D(2)O. Methylation of the thiolate donors in 10 yielded the thioether derivative [Ru(PPh(3))('N(2)H(2)S(3)'-Me(2))]I(2) (11) whose PPh(3) ligand is as inert to substitution as that of 10. Complex 11 can reversibly be deprotonated to give [Ru(PPh(3))('N(2)HS(3)'-Me(2))]I (12). NMR spectroscopic investigations showed that the deprotonation/protonation reactions of 11 and 12 are stereoselective. In contrast, protonation of 13 with HBF(4) gives two diastereomers of the corresponding [Ru(NO)('N(2)H(2)S(3)')]BF(4) salt (14). X-ray structure analyses of 5, 6, 9, and 11 and NMR spectra showed that the 'N(2)H(2)S(3)'(2)(-) ligand and its derivatives bind to the metal centers in the same fashion which combines fac and mer coordination of the donor atoms. The [MN(2)S(3)] cores of all complexes have an analogous C(1) symmetrical structure in which both the two N and the two terminal S donors assume cis positions.

Journal Article↗

PubMed1998

Transition Metal Complexes with Sulfur Ligands. 130.(1) Synthesis, Structure, and Reactivity of the Sulfur-Rich Ruthenium Hydride Complexes [Ru(H)(PR(3))('S(4)')](-) and the eta(2)-H(2) Complex [Ru(H(2))(PCy(3))('S(4)')] (R = Ph, (i)Pr, Cy; 'S(4)'(2-) = 1,2-Bis((2-mercaptophenyl)thio)ethane(2-)).

Hydride and eta(2)-H(2) ruthenium complexes with sulfur-rich coordination spheres were synthesized. Substitution of either DMSO or PPh(3) in [Ru(DMSO)(PR(3))('S(4)')] and [Ru(PPh(3))(2)('S(4)')] by hydride anions from LiAlH(4) or NaBEt(3)H yielded [Ru(H)(PR(3))('S(4)')](-) complexes (R = (i)Pr, Ph, Cy; 'S(4)'(2)(-) = 1,2-bis((2-mercaptophenyl)thio)ethane(2-)). They were isolated as [Li(THF)(Et(2)O)][Ru(H)(PR(3))('S(4)')] (R = (i)Pr (1a), Cy (1b), Na[Ru(H)(PCy(3))('S(4)')].2BEt(3).0.5DMSO (2a), and the solvent-free Na[Ru(H)(PPh(3))('S(4)')].2BEt(3) (2b). X-ray structure determinations of 1a.0.5Et(2)O and 1b.Et(2)O showed that in both complexes pseudooctahedral [Ru(H)(PR(3))('S(4)')](-) anions are bridged to pseudotetrahedral [Li(THF)(Et(2)O)] cations via the hydride ligand and one thiolate donor of the 'S(4)'(2)(-) ligand (crystal data: 1a, monoclinic, P2(1)/n, a = 1401.6(2) pm, b = 1045.2(3) pm, c = 2590.6(4) pm, beta = 95.04(1) degrees, V = 3.780(1) nm(3), Z = 4; 1b, triclinic, P&onemacr;, a = 1264.2(1) pm, b = 1322.9(3) pm, c = 1569.5(2) pm, alpha = 88.96(1) degrees, beta = 83.48(1) degrees, gamma = 62.16(1) degrees, V = 2.3042(6) nm(3), Z = 2). Short intramolecular C-H.H-Ru contacts ( approximately 230 pm) between the hydride ligands, phosphine substituents, and lithium-coordinated Et(2)O molecules indicate "unconventional" hydrogen bonds. They potentially help to decrease the hydridic character of the hydride ligand to such an extent that no structural hydride trans influence can be observed in the solid state. In solution at room temperature, all hydride complexes 1a-2b rapidly release H(2) or HD, when treated with CH(3)OH or CD(3)OD. Low-temperature (1)H and (2)H NMR spectroscopy between -20 and -80 degrees C showed that initially eta(2)-H(2) or eta(2)-HD complexes form. Their formation explains the observed scrambling between protons and hydride ligands, which requires a heterolytic cleavage of dihydrogen. A 1:1:1 triplet at delta = -6.5 ppm ((1)J(HD) = 32 Hz, (2)J(PH) = 5 Hz) and a relaxation time of T(1)(min) = 4 ms (-60 degrees C, 270 MHz) firmly established the formation of the eta(2)-dihydrogen complexes. The reversibility of H(2) release and uptake by [Ru(PCy(3))('S(4)')] fragments and the heterolytic cleavage of H(2) in [Ru(eta(2)-H(2))(PCy(3))('S(4)')] was further ascertained by the reaction of [Ru(DMSO)(PCy(3))('S(4)')] with H(2) in the presence of NaOMe, yielding the [Ru(H)(PCy(3))('S(4)')](-) anion. The relevance of the complexes and their reactions for the heterolytic H(2) activation at the transition metal sulfur sites of hydrogenases is discussed.

Journal Article↗

PubMed1997

Synthesis, Structure, and Reactivity of Ruthenium and Osmium Nitrido Complexes with 1,2-Benzenedithiolate Ligands: N- versus S-Alkylation.

The reactivity of the nitrido complexes (N(n)Bu(4))[Ru(N)(S(2)C(6)H(4))(2)] (1) and (N(n)Bu(4))[Os(N)(S(2)C(6)H(4))(2)] (2) (C(6)H(4)(SH)(2) = 1,2-benzenedithiol) toward electrophiles, R(+) (R = Me, Et, Ph(3)C), is described. While 1 yielded intractable mixtures of products, 2 could be cleanly alkylated. The synthesis of 1 has been reported previously (Z.Naturforsch. 1987, 42B, 341); complex 2 can be synthesized by treating (N(n)Bu(4))[Os(N)Cl(4)] with deprotonated 1,2-benzenedithiol in acetone/MeOH at 0 degrees C. Complexes 1 and 2 are isostructural and crystallize in the orthorhombic space group Pna2(1), Z = 8, with a = 36.881(6) Å, b = 9.402(2) Å, and c = 17.652(2) Å for 1 and a = 37.042(4) Å, b = 9.375(2) Å, and c = 17.671(2) Å for 2. The anions of both compounds consist of a five-coordinate mononuclear center with a distorted square-pyramidal geometry; a terminal nitrido ligand occupies the apical position and two chelating (S(2)C(6)H(4))(2)(-) ligands form the basal plane. Treatment of 2 with R(3)OBF(4) in CH(2)Cl(2) yields [Os(N)(S(2)C(6)H(4))(SC(6)H(4)SR)] (R = Me, 3; R = Et, 4) where one thiolate donor is alkylated. Alkylation of the sulfur of the 1,2-benzenedithiolate ligand was confirmed by NMR spectroscopy and X-ray crystallography (for 3). Complex 3.CH(2)Cl(2) crystallizes in the orthorhombic space group P2(1)2(1)2(1), Z = 4, with a = 8.551(1) Å, b = 10.772(2) Å, and c = 19.716(3) Å. In contrast, treatment of 2 with Ph(3)CPF(6) in CH(2)Cl(2) yields [Os(NCPh(3))(S(2)C(6)H(4))(2)] (5), whose (1)H and (13)C NMR spectra indicate that the terminal nitride is the site of electrophilic attack. X-ray crystallography further confirms the alkylation at the nitrogen atom; complex 5 crystallizes in the triclinic space group P&onemacr;, Z = 2, with a = 9.338(8) Å, b = 10.001(3) Å, c = 16.280(6) Å, alpha = 75.88(3) degrees, beta = 74.29(6) degrees, and gamma = 69.55(5) degrees.

Journal Article↗