Arylcalcium‐Verbindungen: Synthesen, Strukturen, physikalische Eigenschaften und chemisches Verhalten

Abstract

Die Organocalciumchemie steht noch immer am Anfang ihrer Entwicklung. Die Direktsynthese aus Iodarenen und aktiviertem Calciumpulver eröffnet einen einfachen Zugang zu Arylcalciumiodiden in guten Ausbeuten. Der Einfluss des Substitutionsmusters der Phenylgruppe, des Halogens und des Lösungsmittels wird diskutiert. Die Arylcalciumhalogenide zeigen ein Schlenk‐Gleichgewicht, das die Isolierung von Diarylcalciumderivaten ermöglicht. Wegen der hohen Reaktivität der Arylcalciumhalogenide müssen während der Herstellung und Handhabung tiefe Temperaturen aufrechterhalten werden. Eine geringere Reaktivität und höhere Beständigkeit können durch sterisches Abschirmen des Calciumatoms erreicht werden, z. B. durch Erhöhung der Koordinationszahl des Metallzentrums oder Substitution des Iodidions durch sperrige Gruppen.

Bis(trimethylsilyl)methyl Derivatives of Calcium, Strontium and Barium: Potentially Useful Dialkyls of the Heavy Alkaline Earth Elements

“…H and 13 C NMR spectroscopic analysis of the isolated crystals in C 6 D 6 provided data, including a characteristic high-field methine signal observed at d = À1.62 ppm, similar to that communicated by Lappert for the complex identified as [Ca{CH- 3 ] en route to compound V. [7] Notably, no degradation of the coordinated THF molecules was observed upon extended monitoring of the NMR spectroscopy samples. An X-ray crystallographic diffraction identified compound 1 as a pseudo-tetrahedral complex that contained two molecules of THF ( Figure 1).…”

“…[2] Despite spectacular recent advancements by Westerhausen and co-workers in the area of arylcalcium analogues of Grignard reagents [3] (e.g., compound I) [4] and reports of a variety of triorganosilyl-substituted and donorstabilised benzyl-, diphenyl-and triphenylmethyl complexes (e.g., II and III), [5] a well-defined chemistry of comparable alkyl derivatives is still virtually non-existent. Only two alkyl calcium species have been successfully characterised by X-ray diffraction analysis.…”

Heavy Grignard Reagents: Challenges and Possibilities of Aryl Alkaline Earth Metal Compounds

“…In the last years the organocalcium chemistry has experienced a rapid development in many fields such as aryl, [17] alkynyl, [74] benzyl, [19][20][21] alkanediyl, [75] and triorganylsilyl calci- um compounds. [76] The majority of these compounds was prepared by means of metathesis reactions from potassium derivatives and now, the easy access of aryl calcium derivatives from the direct synthesis (Grignard reaction) might accelerate the development of the organic chemistry of the heavy alkaline earth metals.…”

“…However, after isolation and determination of the molecular structure 2 ] by Lappert and co-workers (Ca À C 248.3(5) pm), [15] organocalcium chemistry experienced a rapid growing interest. [16,17] Solvent-free [Ca{C-…”

“…[19][20][21] In contrast to this tremendous success in preparing alkyl calcium derivatives, the synthesis of aryl calcium compounds remained challenging up to very recently. [17] To raise the stability of aryl calcium compounds, the aryl moiety was incorporated into a crown ether such as 2-(phenylcalcio)-1,3-xylylene [18]crown-5; however, this sparingly soluble compound had to be characterized by derivatization reactions. [22] The co-condensation of calcium with benzene and alkylbenzenes yielded the insertion products, namely the arylcalcium hydrides.…”