Transition-metal complexes with sulfur ligands. 88. Dependence of spin state, structure, and reactivity of [FeII(L) ('NH)S4')] complexes on the coligand L (L = CO, N2H2, N2H4, NH3, pyridine, NHCH3NH2, CH3OH, THF, P(OCH3)3, P(OPh)3): model complexes for iron nitrogenases ('NHS4'2-dianion of 2,2'-bis[(2-mercaptophenyl)thio]diethylamine)

Abstract

In search of complexes exhibiting functional and structural characteristics of the active centers of nitrogenases, the Fe" complexes [Fe(L)('bi~Sl)] with the pentadentate amine-thioether-thiolate ligand ' N H S~)~-(L = N2H4, CH3-OH, THF, pyridine, NH3, NHCH3NH2, P(OMe)3, P(OPh)3; ' N~s 4 '~-= dianion of 2,2'-bis[(2-mercaptophenyl)-thioldiethylamine), [Fe('N&)],, and the free ligand ['N&'-H2].HCl were synthesized and characterized. The molecular structures of the complexes with L = N2H4, NH3, and CH3OH have been elucidated by X-ray structure analyses. The crystal data for [ F~( N~H~) ( " H S~' ) ] (la) are orthorhombic space group Pbca, a = 1102.1 (7), b = 1567.2 (8), c = 2206.6 (14) pm, 2 = 8, and R / R , = 0.046/0.046. The crystal data for [Fe(CH30H)('NHSl)] (2) are orthorhombic space group Pbca, a = 1152.8 (3), b = 1471.5 (9, c = 2237.0 (5) pm, 2 = 8, and R / R , = 0.069/0.054. The crystal data for [Fe(NH3)('NHS,')] (5) are orthorhombic space group Pbca, a = 1107.0 (9, b = 1547.1 (8), c = 2171.9 (9) pm, 2 = 8, and R / R , = 0.040/0.035. u donor ligands (N2H4 or NHj) cause high-spin states; u donor, T acceptor ligands (CO, NO, or N z H~) , however, cause low-spin states of the iron centers. The high-spin 18e-complexes (L = N&, NH3, CH3OH) exhibit considerably larger F e S and Fe-N distances than the low-spin 18e-compounds (L = CO, '/2(N2H2)). The 19e-complex [F~(NO)("HS~')] with low-spin FelI takes an intermediate position.The correlation between coligands L, spin states, and bond lengths is interpreted in terms of molecular orbital schemes, which also explain why the 18e-low-spin complexes are highly substitution inert and the 18e-high-spin complexes are very labile. With regard to the active centers of "Fe-only" nitrogenases, [Fe-('NHS~)] complexes provide a model. Interrelation of iron spin states, coordination of either u or u -~ ligands, and substitution lability or inertness may not only support the reduction steps leading from N2 via N2Hz over N2H4 to NH3, but also enable the final step in a catalytic cycle, the substitution of NH3 by N2.

Inert and Labile [Ru(L)(‘pyS4’)] Complexes with Rigid [RuNS4] Cores andtrans-Thiolate Donors [L = PPh3, PEt3, DMSO, CO, NO+, N2H4; ‘pyS4’2– = 2,6-Bis(2-mercaptophenylthio)dimethylpyridine(2–)]

“…[4] It has yielded a large number of [Fe(L)('N H S 4 ')] complexes with L comprising the nitrogenase-relevant molecules CO, NO, N 2 H 2 , N 2 H 4 , and NH 3 , although not N 2 . This prompted us to investigate the coordination behaviour of 'N H S 4 ' 2-towards ruthenium as well; it was anticipated that with the kinetically more inert ruthenium, species that 423 (5); in the presence of PEt 3 or N 2 H 4 mononuclear [Ru(PEt 3 )-('pyS 4 ')] (6) and [Ru(N 2 H 4 )('pyS 4 ')] (7) were formed. Template alkylation of NBu 4 [Ru(NO)(S 2 C 6 H 4 ) 2 ] with 2,6-bis(tosyloxymethyl)pyridine gave [Ru(NO)('pyS 4 ')]Tos (8).…”

“…This prompted us to investigate the coordination behaviour of 'N H S 4 ' 2-towards ruthenium as well; it was anticipated that with the kinetically more inert ruthenium, species that 423 (5); in the presence of PEt 3 or N 2 H 4 mononuclear [Ru(PEt 3 )-('pyS 4 ')] (6) and [Ru(N 2 H 4 )('pyS 4 ')] (7) were formed. Template alkylation of NBu 4 [Ru(NO)(S 2 C 6 H 4 ) 2 ] with 2,6-bis(tosyloxymethyl)pyridine gave [Ru(NO)('pyS 4 ')]Tos (8). Complex 8 proved to be the best suited precursor for L exchange reactions.…”

“…Complex 8 proved to be the best suited precursor for L exchange reactions. Under reducing conditions, 8 releases its NO ligand and the resulting [Ru('pyS 4 ')] fragments can combine either with each other to give 5, or with PEt 3 and N 2 H 4 to yield 6 and 7, respectively. All complexes have been characterized by spectroscopic methods and elemental analysis; 1, 2, 3, and 4 have also been submitted to X-ray structure analysis.…”

Übergangsmetallkomplexe mit Schwefelliganden, XCl+ Fell-Komplexe des fünfzähnigen Thioether-Thiolat-Aminliganden ′buNHS4′-H2: Synthese, Charakterisierung, Reaktivität und Stereochemie (′buNHS4′-H2 = 2,2′-Bis(2-mercapto-3,5-di-tertiärbutyl-phenylthio)diethylamin) / Transition Metal Complexes with Sulfur Ligands, XCI+ Fell Complexes of the Pentadentate Thioether-Thiolate-Amine L

“…lc . Die unsubstitu ierte Stammverbindung ['NhS4'-H 2]-HC1 weist ein < SSH = 4,28 ppm auf [5]. Im Gegensatz dazu beträgt Die weitgehend ähnlichen Eigenschaften der tertiärbutyl-substituierten Derivate [Fe(L)('buN HS4')] erlauben somit nunm ehr die detaillierte U ntersu chung von Reaktionen, die bislang durch die Schwerlöslichkeit der [Fe(L)('NHS4')]-Komplexe behindert wurden.…”

“…N H 3 oder weichen <7-7r-Donoren wie CO bzw. N 2H 2 erlaubte beispielsweise Rückschlüsse au f den A blauf von Elem entarreaktionen der N 2-Fixierung [5]. Durch die K oordination von N 2H 2 an [Fe('NHS4')]-Fragmente und Isolierung des zwei kernigen [//-N2H 2{Fe('N HS4')}2] gelang erstmals die Stabilisierung der Schlüsselstufe des Diazens an Eisen-Schwefel-Zentren [6].…”