Structural diversity in the coordination of amidines and guanidines to monovalent metal halides

Abstract

A series of structurally characterised, monovalent metal-halide complexes incorporating neutral amidine and guanidine ligands is reported. N,N′-diphenylbenzamidine reacted with copper(I) chloride to afford the bis-ligand complex [CuCl(PhC{NPh}{NHPh})₂]₂ (1), that exists as a chlorine bridged dimer in the solid state, with a non-symmetrical distribution of NH⋯Cl interactions within the ‘Cu₂Cl₂’ metallacycle. In contrast, only one equivalent of the guanidine, Me₂NC{NⁱPr}{NHⁱPr} (2), is coordinated in the copper(I) iodide complex [CuI(Me₂NC{NⁱPr}{NHⁱPr})]₂ (3), which was also isolated as the dimer with bridging halide atoms. The molecular structure of the bicyclic guanidine, 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH), is reported, revealing a hydrogen bridged dimer with extensive delocalisation throughout the ligand framework. Coordination of hppH to lithium chloride afforded the dimeric bis-ligand complex [LiCl(hppH)₂]₂ (4) in which each hppH molecule interacts with a different chlorine atom of the central ‘Li₂Cl₂’ core of the molecule via NH⋯Cl hydrogen bonding. In contrast the 2 ∶ 1 ligand to metal complex is formed with silver(I) chloride to afford AgCl(hppH)₂ (5), a unique example of a monomeric, three-coordinate silver chloride supported by nitrogen-based ligands. The series of mixed ligand complexes [CuX(hppH)(PPh₃)]_n (6, X = Cl, n = 1; 7, X = Br, n = 2; 8 X = I, n = 2) have also been synthesised and structurally characterised, allowing comparisons of the relative coordinating behaviour of hppH and PPh₃ as neutral donors at copper(I) centres to be made.