Tantalum Chloride Species Incorporating Anionic and Cationic Guanidine components

Attempted preparation of tantalum complexes incorporating the anionic guanidinate ligand derived from 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH) are reported. Reaction of (hpp)SiMe3 and TaCl5 in a 1:1 ratio gave the bis-guanidinate compound rather than the expected mono-ligand species. Reaction of 2 equiv. of (hpp)SiMe3 or in situ generated [hpp]Li with TaCl5 afforded a solid which analysed correctly for the compound (hpp)2TaCl3. X-ray structural analysis of the crystallised product identified the coordination isomer [Ta(hpp)4][TaCl6], with a distorted dodecahedral cation and a regular octahedral anion. During the course of this study, two closely related hydrolysis products, [(hppH2)]2[{TaCl6}{Cl}] and [(hppH2)]3[{TaCl6}2{Cl}]eCN were isolated and structurally characterised, each containing [hppH2]+ cations and [Cl]¿ and [TaCl6]¿ anions in extended arrays, linked by intermolecular hydrogen bonds