Heteroleptic Phenylcalcium Derivatives via Metathesis Reactions of PhCa(thf)₄I with Potassium Compounds

Abstract

The metathesis reactions of (thf)4Ca(Ph)I with the corresponding potassium compounds KR yield the heteroleptic arylcalcium derivatives (thf)3Ca(Ph)[N(SiMe3)2] (1) and (thf)4Ca(Ph)PPh2 (2), due to the insolubility of KI in common organic solvents. However, the reaction of KCp and KOC6H2-2,6-tBu-4-Me with (thf)4Ca(Ph)I give the homoleptic compounds (thf)2CaCp2 (3) and (dme)CaCp2 (4) (depending on the solvent) as well as (thf)3Ca(OC6H2-2,6-tBu-4-Me)2 (5). Diphenylcalcium decomposed under these reaction conditions. The reaction of K[(Me3SiN)2CPh] with (thf)4Ca(Ph)I yields [{(thf)3Ca}2{4,4-Ph2-2,6-(C6H4)2C3N3}(μ-I)] (6). This dihydrotriazine derivative forms due to a slow liberation of benzonitrile from the starting N,N'-bis(trimethylsilyl)benzamidinate. A solvent change in order to shift the Schlenk equilibrium (2 PhCaICaPh2 + CaI2) toward the homoleptic diphenylcalcium leads immediately to ether cleavage reactions and the formation of [{(Et2O)CaPh2}4·(Et2O)CaO] (7), which precipitates from diethyl ether. This cage compound contains an oxygen-centered Ca5 square pyramid with the phenyl groups bridging all Ca···Ca edges.

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

“…[44] An investigation to verify whether the ether cleavage reaction was occurred by hydrolysis from traces of moisture has been undertaken. Several samples of different aryl calcium iodides in THF were stored at 0 8C or room temperature for several days.…”

“…This is a consequence of the repulsion between the lone pair with the anionic charge and the neighboring CÀC bonds. [43,44] This effect should increase with increasing ionic character of the heteropolar metal-carbon bonds.…”

“…[44] The bulky bis(trimethylsilyl)amido group reduces the tendency of ether cleavage reactions. This general principle allowed the synthesis of various organocalcium compounds.…”

Ein effizientes, allgemeines Verfahren zur Synthese von Halogen‐freiem Diarylcalcium

“…[4] Die Ursache für diese widersprüchlichen Berichte über die Synthese und Stabilität der Arylcalcium-Verbindungen in Etherlösungen liegt an der großen Diskrepanz zwischen der Reaktionsträgheit des Metalls und der hohen Reaktivität der metallorganischen Derivate, der Notwendigkeit zur Aktivierung des Metalls vor der Verwendung und schließlich an der Neigung zur Etherspaltung während der Direktsynthese der Arylcalciumhalogenide. Eine erneute Untersuchung der Synthese von Arylcalcium-Verbindungen führte zur Isolierung von Sauerstoff-zentrierten Arylcalcium-Käfigverbin-dungen, [5][6][7] Calciumvinylat-Derivaten [8] und (nach längerem Erhitzen von Phenylcalciumiodid in THF) sogar zu Arylfreiem [(CaO) 4 {(thf) 3 Ca(m-I) 2 } 4 ]. [8] Aus diesen Gründen muss die Direktsynthese von Arylcalciumiodiden bei tiefen Temperaturen erfolgen.…”

Reduction of Bromo- and Iodo-2,6-bis(diphenylphosphanylmethyl)benzene with Magnesium and Calcium

“…The isolation of [(thf) 3 Ca(Br)(µ-O 2 PPh 2 )] 2 (3a) from these reduction reactions proves that the P-C bond to the methylene unit has been cleaved, finally leading to the diphenylphosphinate anions. Earlier findings already demonstrated that oxide ions can be trapped in calcium cage compounds in the absence of low-valent phosphorus species [25][26][27][28]. In summary, the very reactive calcium-based heavy Grignard reagents quickly attack the ether molecules, leading to arene and diverse ether degradation products.…”