Sterically Encumbered Amidinates and Guanidinates of Calcium and Strontium

Abstract

AbstractAn attempt to prepare Tmp‐C(NDipp)2Li by treatment of lithium tetramethylpiperidide (Li‐Tmp) with N,N′‐bis(2,6‐diisopropylphenyl)carbodiimide (Dipp‐N=C=N‐Dipp) failed, and ether degradation occurred instead, allowing the isolation of a few crystals of O=CH–CH=C(NH‐Dipp)2 (1) after hydrolytic work‐up. We then investigated calcium and strontium compounds. Metalation of PrisoH [Priso = iPr2N–C(N‐Dipp)2] with [(thf)2Ca{N(SiMe3)2}2] in refluxing hexane for 18 h yielded [{(Me3Si)2N}(thf)Ca(Priso)] (2). At room temperature, very few crystals of [Ca(Priso)2]·hexane (3) precipitated after several months from a saturated hexane solution of 2. KN(SiMe3)2 was added to a THF solution of [(thf)4CaI2] and PrisoH and heated to 60 °C for several hours yielding [(thf)Ca(Priso)(μ‐I)]2 (4). Metalation of PrisoH with [(thf)2Sr{N(SiMe3)2}2] led to formation of [Sr(Priso)2] (5) regardless of the applied stoichiometry. The reaction of N,N′‐bis(2,6‐diisopropylphenyl)benzamidine with KN(SiMe3)2 and [(thf)4CaI2] in THF followed by recrystallization from 1,2‐dimethoxyethane (dme) solution yielded [(dme)Ca{(Dipp‐N)2C–Ph}2] (6). The molecular structures of these compounds are discussed and compared with those of other encumbered complexes of divalent metal ions.