Gotthelf Wolmershäuser

Umsetzung von P4 mit (η5-C5H5)(CO)2MoMo(CO)2(η5-C5H5) zu den tetraedrischen molybdänkomplexen Pn[Mo(CO)2(η5-C5H5)]4-n (n = 2,3)

Abstract Interaction of (η 5 -C 5 H 5 ) 2 Mo 2 (CO) 4 , (I) with P 4 affords the tetrahedral molybdenum complexes P n [Mo(CO) 2 (η 5 -C 5 H 5 )] 4- n (II, n = 3 and III, n = 2). The structure of III has been elucidated by X-ray analysis.

(E2)2-einheiten (E = P, As) als clusterbausteine

Abstract The interaction of [C p ★ 2(CO)4Mo2](MoMo) (I) with As4 gives the Mo-As clusters [C p ★ (CO)2Mo(η3-As3)] (II), [C p ★ (CO)4Mo2(μ,η2-As2)] (III) and cis-[C p ★ (CO)Mo(μ,η2-As2)]2 (IV). IV probably has the same structure as cis-[C p ★ (CO)Mo(μ,η2-P2)]2 cis-[C p ★ (CO)Mo(μ-η2-P2)]2 (V) whose derivative, cis-[C p ★ (CO)Mo(μ,η2-P2){Cr(CO)5}2]2 (VI) (C p ★ = η5-C5Me5) has been characterized by an X-ray structure analysis.

Temperature-Induced Spin-Transition in a Low-Spin Cobalt(II) Semiquinonate Complex†

Spin crossover and valence tautomerism are examples of processes that can be utilized as a basis for achieving molecular switches. Whereas the spin-crossover process is characterized by a temperature-, pressure-, or light-induced change of the electronic state of the metal ion to one with a different spin multiplicity, valence tautomerism entails an intramolecular redox reaction between a metal ion and a coordinated ligand, which, in a few instances, is accompanied by a change in the spin state of the metal ion. Various reported low-spin cobalt(III) catecholate complexes, which can be transformed into high-spin cobalt(II) semiquinonate complexes by raising the temperature, provide excellent examples of the latter process. In contrast, spin-crossover chemistry is dominated by octahedral iron(II) complexes with a FeN6 coordination sphere; [2] however, there are only very few known octahedral cobalt(II)-containing spin-crossover complexes. Herein we describe the first cobalt(II) semiquinonate complex that displays spin-crossover properties rather than valence tautomerism. The starting point of our investigation was the olive-green cobalt(III) 3,5-di-tert-butylcatecholate (dbc ) complex [Co(L-N4Me2)(dbc)](BPh4)·0.8MeCN·0.2Et2O (1) containing the dimethyl derivative of the tetraazamacrocyclic ligand 2,11diaza[3.3](2,6)pyridinophane (L-N4Me2) as coligand. This complex was obtained in 42 % yield by oxidation of the red cobalt(II) catecholate complex [Co(L-N4Me2)(dbc)] (prepared in situ from equimolar solutions of cobalt(II) perchlorate, L-N4Me2, and 3,5-di-tert-butylcatecholate) with ferrocenium tetrafluoroborate ([Fe(Cp)2](BF4); Cp = cyclopentadienyl), followed by a metathesis reaction with sodium tetraphenylborate (Scheme 1). In accordance with the description of 1 as a cobalt(III) catecholate complex, solutions and solids of this substance are diamagnetic. X-ray

Ferrocene mit einem Pentaarsacyclopentadienyl-Liganden

Abstract Thermolysis of [(η 5 -C 5 Me 4 R)Fe(CO) 2 ] 2 ( 1a : R = Me, 1b : R = Et) with yellow arsenic, As 4 , gives the sandwich complexes [(η 5 -As 5 )Fe(η 5 -C 5 Me 4 R)] ( 2a : R = Me, 2b : R = Et) with a pentaarsacyclopentadienyl ligand. In a stacking reaction 2a forms the triple-decker sandwich cation [(η 5 -C 5 H 5 )Fe(μ, η 5 -As 5 )Fe(η 5 -C 5 Me 5 )]PF 6 ( 3 ) with 30 valence electrons. 2b und 3 have been characterized by X-ray diffraction studies.

Metallocenes of Samarium, Europium, and Ytterbium with the Especially Bulky Cyclopentadienyl Ligands C5H(CHMe2)4, C5H2(CMe3)3, and C5(CHMe2)5

Octaisopropylmetallocenes of the lanthanoids Sm (1-Sm), Eu (1-Eu), and Yb (1-Yb) can be obtained easily from the diiodides of the rare earth elements. Like the hexa(tert.-butyl)metallocenes 2-Sm, 2-Eu, and 2-Yb, they show no tendency towards coordination of donor solvent molecules or alkali salts. The decaisopropylmetallocenes 3-Sm, 3-Eu und 3-Yb have been synthesized from the metal and the free pentaisopropylcyclopentadienyl radical. The three europocenes 1-Eu, 2-Eu, and 3-Eu show fluorescence in daylight or under UV irradiation (336 nm). Crystalline 1-Eu and 2-Eu are bent sandwich complexes, whereas for the decaisopropyl derivative 3-Eu axial symmetry with parallel five-membered rings has been observed.

The benzobisdithiazole system in its various oxidation states: a new building block for organic conductors

Abstract The title compound can be isolated in at least three distinct oxidation states. Synthesis and characterization of these species are presented in this paper. The dication is easily reduced to the radical cation by a variety of reducing agents. Partial reduction occurs during its preparation, yielding a mixed valence compound showing a conductivity of ≈2 × 10 −1 S cm −1 . Further reduction yields a neutral paramagnetic species that forms a conducting 2:1 complex with TCNQ.

Highly conducting charge transfer complexes of benzo-1,3,2-dithiazol -2yl and its derivatives with teracyanoquinodimethane

Benzo-1,3,2-dithiazol-2yl and its derivatives form charge transfer complexes with tetracyanoquinodimethane; their powder conductivities are as high as 3Ω–1/cm.

Bis(2,4-di-t-butyl-η4-1,3-diphosphacyclobutadiene)nickel

t-Butylphosphaacetylene 2 reacted with nickel acetylacetonate/n-butyllithium to furnish the title compound 4, the structure of which has been elucidated by X-ray crystallography.

Cation size dependent reactivity of lanthanide trihalides with bulky alkylcyclopentadienyl anions

Reactions of NdCl3 and PrCl3 with two equivalents of sodium tri-tert-butylcyclopentadienide furnished base- and salt-free [Cp′2NdCl] and [Cp′2PrCl] (Cp′ = 1,2,4-(Me3C)3C5H2) in good yield. Trimethylaluminium has been added to the neodymium complex to form [Cp′2NdClAlMe3]. With LaCl3 or CeCl3 base-free bis(ring) complexes were not obtained, but in the latter case the salt adduct [(4Cp2Ce)(μ-Cl)2Na(tmeda)2]∞ (4Cp = (Me2CH)4C5H) could be extracted from the product mixture with tetramethylethylenediamine and crystallized as a zigzag chain polymer. [4Cp2SmCl2Na(dme)2] retained the coordinated sodium chloride even when dissolved in non-polar solvents. Attempted preparation of [Cp′2YbCl] gave the mono(ring) complex [Cp′YbCl(μ-OCH2CH2OCH3)]2 from cleavage of the dimethoxyethane solvent and with lutetium trichloride the hexanuclear complex [(4CpLu)5LuCl13(OEt2)5] was prepared in low yield. For lanthanum and thulium use of the triiodide as a starting compound enabled synthesis of the corresponding bis(tetraisopropylcyclopentadienyl)metal iodide, bis{tri-tert-butylcyclopentadienyl}lanthanum iodide was also prepared from LnI3. [4Cp2TmI] shows a unique conformation of one of the tetraisopropylcyclopentadienyl ligands with two isopropyl neighbours rotated towards each other indicating extreme steric congestion. Oxidation of [Cp′2Sm] with copper(I) iodide gave [Cp′2SmI] in high yield. Mono(ring) complexes are readily available from trichlorides of thulium, ytterbium, and lutetium. Apart from the donor solvent adducts [4CpTmCl2(dme)], [Cp′YbCl2(thf)2], and [4CpLuCl2(dme)], which were isolated from solutions in the corresponding donor solvent, the salt- and donor-free dihalides [Cp′TmCl2]n and [Cp′YbCl2]n were obtained as oligomers from pentane or petroleum ether extracts. The thulium compound gave [Cp′Tm{N(SiMe3)2}2] with two equivalents of Na[N(SiMe3)2] and the ytterbium complex underwent ring exchange with lithium tert-butylcyclopentadienide and formation of the bis(tert-butylcyclopentadienyl)ytterbium complex [(Me3CC5H4)2Yb(μ-Cl)]2.

[(C5Me4R)Co(As2)]-Molekülbausteine

Abstract The co-thermolysis of [(η5-C5Me4R)Co(CO)2] (1a: R  Me, 1b: R  Et) with yellow arsenic, As4, affords the binuclear and trinuclear complexes [(η5-C5Me4R)CO(As2)]2 (2a, 2b), [(η5-C5Me4 R)2CO2(As6)] (3a,3b) and [(η5-C5Me4R)CO(As2)]3 (4a,4b). The structure of 2b, 3a and 4a has been elucidated by X-ray crystallography.