Abstract
Four C8-halogenated theophyllines (1–4) featuring N7-methyl or N7-allyl and C8-chloro or C8-bromo substituents have been prepared. The halogenotheophyllines react with [Pd(PPh3)4] in an oxidative addition to give complexes of type trans-[Pd(theophyllinato)X(PPh3)2] (trans-[5]–trans-[8]). The protonation of the unsubstituted theophyllinato ring-nitrogen atom to give the pNHC complexes was achieved either by performing the oxidative addition of 1 in the presence of NH4BF4 to give complex trans-[9]BF4 or by N-protonation of the coordinated theophyllinato ligand in trans-[6]–trans-[8] with HBF4·Et2O to give complexes trans-[10]BF4–trans-[12]BF4. The molecular structures of trans-[5], trans-[7], trans-[9]BF4, trans-[11]BF4 and trans-[12]BF4 were determined by X-ray diffraction showing significant differences of comparable metric parameters in the theophylline-derived five-membered diaminoheterocycles. No interaction of the N-allyl substituents with the metal center was observed.
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