Coordination of neutral, methylene bridged bis-guanidyls at palladium

Abstract

The bis-guanidyl compound H(2)C{hpp}(2) (hppH = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) coordinates to palladium(ii) as a neutral, chelating N,N'-bidentate ligand. Structural analysis of PdMeCl(H(2)C{hpp}(2)) shows a non-planar metallacycle that is twisted relative to the square plane of the metal and an "anagostic" interaction with a C-H from the bridging methylene group. Generation of the cationic palladium complex, [PdCl(H(2)C{hpp}(2))][OTf] was achieved by halide abstraction from the dichloride PdCl(2)(H(2)C{hpp}(2)) using NaOTf. The product was identified as a mixture of different species in solution; in the solid-state, the molecular structure is dimeric, consisting of the mu,mu'-dichlorobridged dication. The new bis-guanidyl compound H(2)C{tbo}(2) (Htbo = 1,4,6-triaza-bicyclo[3.3.0]oct-4-ene) was synthesized, and structurally characterized. Coordination of this compound at palladium dichloride was accompanied by ionization of the Pd-Cl bond, and formation of the dication [Pd(H(2)C{tbo}(2))(2)][Cl](2). Structural analysis shows a significant reduction in the twisting of this ligand.