Benno Bildstein

IMIDAZOLINE-2-YLIDENE METAL COMPLEXES WITH PENDANT FERROCENYL SUBSTITUENTS

Abstract Imidazolium and benzimidazolium salts with ferrocenylated alkyl side chains are prepared as progenitors of N-[(ferrocenyl)alkyl](benz)imidazoline-2-ylidene carbenes, which form metal complexes of W(0), Pd(II), and Hg(II). X-ray structures and other spectroscopic properties show that these carbene precursors and complexes are analogous to published non-ferrocenylated complexes with regard to the coordination sphere at the metal, but different in terms of steric protection of the central metal by the bulky ferrocenyl substituents and in terms of distinguishable redox potentials of the ferrocene/ferrocenium couple.

N-HETEROCYCLIC CARBENES WITH N-FERROCENYL-N'-METHYL-SUBSTITUTION : SYNTHESIS, REACTIVITY, STRUCTURE AND ELECTROCHEMISTRY

Abstract Benzimidazolium salts with one N -ferrocenyl substituent and with one N -methyl substituent are prepared by a synthetic sequence involving coupling of the metallocenyl group to a non-cyclic orthophenylene-diamine precursor, ring closure, and oxidation. From these carbene progenitors a range of carbene derivatives are synthesized, including thiourea, azine, and metal complexes with W(0), Pd(II) and Hg(II). Spectroscopic, structural and electrochemical properties in this series of compounds are compared with those of recently published analogous but methylene-spacered benzimidazoline-2-ylidene derivatives, indicating significant electronic communication between the carbene moiety and the N -ferrocenyl substituent.

Efficient telomerization of 1,3-butadiene with alcohols in the presence of in situ generated palladium(0)carbene complexes

The palladium-catalyzed telomerization of 1,3-butadiene with alcohols has been studied in presence of palladium and imidazolium salts, which form in situ carbene ligands. Among the different imidazolium salts tested 1,3-dimesitylimidazolium chloride (7), 1,3-bis(ferrocenylmethyl)benzimidazolium tetraphenylborate (12) and 1,3-bis(2-ferrocenylethyl)benzimidazolium bromide (13) gave the best yields of the desired octadienyl ethers. Significantly improved regioselectivities for the linear octadienylethers are obtained in the reaction of 1,3-butadiene and methanol compared to the previously optimized palladium/triphenylphosphine catalyst. Using n-butanol and iso-propanol the palladium carbene catalysts lead to a considerable increase in the corresponding telomerization products compared to standard palladium/triphenylphosphine catalysts.

Cationic and neutral cumulene sp-carbon chains with ferrocenyl termini

Abstract The synthesis, physical and chemical properties of cationic (Fc)2CCnC(Fc)+ and neutral (Fc)2CCnC(Fc)2 cumulenes with ferrocenyl substituents and with up to ten cumulated carbons is summarized. In comparison to metallacumulenes and to purely organic cumulenes, the combination of a cumulenic backbone with directly attached ferrocenyl substituents significantly alters the usually observed reactivity and/or stability. The terminal metallocenyl groups serve as redox-active centers, inductive donors, and sterically encumbered groups, effecting (i) electronic coupling through the bridging cumulene ligand, (ii) stabilization of adjacent electron-deficient carbenium centers, (iii) increased nucleophilic reactivity of the cumulene moiety, and (iv) steric hindrance with accompanying reduced reactivity for shorter cumulenes and enhanced stability for longer cumulenes. The chemical reactivity of sterically unhindered neutral cumulenes (Fc)2CCnC(Fc)2 includes complex formation with late transition metals, ferrocenophane formation with zero-valent Ni, and cycloadditions with olefins, alkynes, and fullerenes. (Fc)2CCnC(Fc)+ salts are novel organometallic non-linear optical materials which show significant second-order non-linear optical properties.

Functionalized pentamethylferrocenes: Synthesis, structure, and electrochemistry

Abstract The advantageous properties of the Cp * ligand — intensified electron donation, steric bulk, and enhanced solubility in comparison to the ubiquitous Cp ligand — are finding increasing use in organometallic chemistry. A systematic evaluation of synthetic routes to pentamethylferrocene compounds with a wide range of functionalities, including carboxyl, carbonyl, aminomethyl, vinyl, ethynyl, fulvenyl, cyclopentadienylmethyl, and others is reported. Spectroscopic, structural, and electrochemical properties of such functionalized pentamethylferrocenes Fc */2 —R are compared to those of non-methylated ferrocenes Fc—R. The electronic influence of the Cp * ligand in these unsymmetricalferrocenes Fc */2 —R has been studied by cyclic voltammetry measurements, demonstrating a decrease in oxidation potential of −0.276 V in direct comparison to non-methylated ferrocenes Fc—R.

Carbenes with ferrocenyl substituents

Abstract Carbenes containing ferrocenyl substituents are interesting target compounds due to the stereoelectronic influence of the metallocenyl groups in terms of steric protection, electron-donation, and reversible redox chemistry. Synthetic approaches to ferrocenyl-substituted methylidenes and N-heterocyclic carbenes are summarized, the reactivity of these carbenes is explored, and the spectroscopic, structural and electrochemical properties of the carbene derivatives are discussed.

Synthesis and electrochemistry of ferrocenyldiazabutadiene metal carbonyl complexes (Fc-DAB)M(CO)4 [M=Cr,Mo,W]

Abstract The synthesis, characterization (UV–Vis, IR, MS, NMR), and electrochemistry (CV, DPV) of ferrocenyl diazabutadienes and their chromium, molybdenum, and tungsten tetracarbonyl complexes are reported in this study. The properties of these compounds are compared to those of p -methoxyphenyl diazabutadiene analogues, (a) allowing the clear distinction between ferrocene-based and diazabutadiene metal carbonyl localized redox processes in these multimetallic complexes, and (b) showing that the electronic interaction between the peripheral ferrocenyl substituents increases upon complexation to the Group 6 transition metal tetracarbonyl moieties.

First Examples of a New Family of Redox‐Functionalised Chelate Complexes Based on a 1,1′‐Ferrocenediyl‐Bridged Di(amido) Ligand

Treatment of Fe[(C5H4)NHPh]2 (1H2) with M(NMe2)4 (3a: M = Ti, 3b: M = Zr) in benzene afforded the chelates (1)Ti(NMe2)2 (4) and (1)Zr(NMe2)2(HNMe2) (5), respectively. Chelate 5 was cleanly oxidised by ferrocenium hexafluorophosphate in acetonitrile. Treatment of 5 with two equivalents of [Me2NH2]Cl (6) in benzene afforded (1)ZrCl2(HNMe2) (7). The chelates 5 and 7 were characterised by X-ray structure analyses. The new redox-active chelate complexes are precatalysts for the polymerisation of ethylene.

Synthese und reaktivität von diferrocenyl-thio-,-seleno- und -telluro-keton

Abstract Chalcogenoketones (Fc) 2 CX 1a (X  S, Fc = Ferrocenyl), 1b (X  Se), and 1c (X  Te) are synthesized by reaction of diferrocenylketone with P 4 S 10 , bis(dimethylaluminum)-selenide, bis(dimethylaluminum)-telluride, respectively. Reaction with [tetrahydrofurane][M(CO) 5 ](M  Cr, Mo, W) yields, for 1a , the complexes [(Fc) 2 CS][M(CO) 5 ] 2ad (M  Cr), 2af (M  W), and [H 3 C-C(OH)S][W(CO) 5 ] 3 ; and for 2b , the complex [(Fc) 2 CSe][W(CO) 5 ] 2bf . Telluroketone 1c does not form a complex; instead detelluration takes place and tetraferrocenylethylene (Fc) 2 CC(FC) 2 is obtained quantitatively. The structure of compound 3 has been determined by X-ray diffraction study. All compounds, except the extremely air-sensitive chalcogenoketones 1b and 1c , have been characterized by the usual spectroscopic and analytical methods.

Tris(trimethylsilyl)methyl-polyselenides and -polytellurides. X-Ray structure of (Me3Si)3CTeTeTeC(SiMe3)3

Novel polyselenides and polytellurides have been prepared by means of the stabilizing tris(trimetylsilyl)methyl group; [(Me3Si)3C]2Te3, the first compound containing a three tellurium atom chain, crystallizes as a trans-rotamer with a bonding angle of 103.8(1)° at the central tellurium atom and Te–Te bond distances of 2,710(1)A.