Metalation of Aryl‐bis(3‐alkyl‐5‐methylpyrazol‐1‐yl)‐ methane (Alkyl=Me, Ad; Aryl=Ph, C₆H₄‐2−OH) with NaN(SiMe₃)₂, KN(SiMe₃)₂, and Ca{N(SiMe₃)₂}₂

Abstract

Deprotonation of phenyl‐bis(3,5‐dimethylpyrazolyl)methane (HC(Ph)(PzMe2)2, 1 a) with [(thf)2Ca{N(SiMe3)2}2] in THF at −40 °C yields heteroleptic [(thf)2Ca{N(SiMe3)2}{C(Ph)(PzMe2)2}] (2 a) and finally homoleptic [(thf)Ca{C(Ph)(PzMe2)2}2] (2 b). However, these complexes degrade at room temperature to calcium bis(pyrazolate) and 2‐phenyl‐4,6‐dimethylpyrimidine (3 a). This degradation is accelerated when bulky phenyl‐bis(3‐adamantyl‐5‐methylpyrazolyl)methane (HC(Ph)(PzAd,Me)2, 1 b) is treated similarly and 2‐phenyl‐4‐adamantyl‐6‐methylpyrimidine (3 b) forms quickly. Sodiation of 1 a and 1 b with NaN(SiMe3)2 yields [{HC(Ph)(PzMe2)2}Na{C(Ph)(PzMe2)2}] (4 a) and [{HC(Ph)(PzAd,Me)2}Na{C(Ph)(PzAd,Me)2}] (4 b). The stronger metalation reagent benzylpotassium is able to quantitatively deprotonate 1 b leading to dinuclear [K{C(Ph)(PzAd,Me)2}]2 (4 c). The metathetical approach and the reaction of 4 c with metal(II) halides of Mg, Ca and Zn again leads to degradation and formation of pyrimidine 3 b. This decomposition of the ligand can be circumvented when the sidearm contains the anionic charge. Thus, 2‐hydroxyphenyl‐bis(3‐adamantyl‐5‐methylpyrazol‐1‐yl)methane (1 c) reacts with [(thf)2Ca{N(SiMe3)2}2] in THF to the homoleptic complex [(thf)4Ca{O−C6H4−CH(PzAd,Me)2}] (2 c). In this complex, THF and pyrazolyl bases compete in the coordination sphere and preparation of a heteroleptic complex fails. To avoid the binding competition between THF and pyrazolyl bases and to stabilize heteroleptic calcium complexes, the reaction has been repeated in toluene yielding [Ca{N(SiMe3)2}{O−C6H4−CH(PzAd,Me)2}]2 (2 d).