A new aliphatic N,C,N’-pincer ligand with pendant guanidine groups

• Published in: Inorganica Chimica Acta 2014-10, Vol.422, p.228-234
• Main Authors: Coles, Martyn P., Khalaf, Majid S., Hitchcock, Peter B.
• Format: Article
• Language: English
• Subjects: Aluminium cation; Crystal structure; Guanidine ligand; Organo-silicon; Pincer ligand; Tin compound
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2014.05.021

A new organometallic ligand derived from a methylene-linked bis(guanidine) is described. Coordination to Si, Sn and Al indicates a tendency for the guanidine-groups to participate in bonding, forming an aliphatic N,C,N′-pincer ligand at tin and aluminium. The bis(guanidine) compound H2C{hpp}2 (hppH=1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) was deprotonated at the bridging methylene group to generate the corresponding carbanion, [CH{hpp}2]−. The in situ reaction with EMe3Cl (E=Si, Sn) afforded the organo-element compounds HC{SiMe3}{hpp}2 (1) and Sn(HC{hpp}2)Me3 (2). Structural characterization of 1 and 2 showed a tendency for the guanidine groups of the organometallic ligand to interact with the heavier group 14 elements, and that the tin compound contained a rare example of an aliphatic N,C,N′-pincer ligand of a main group element. Attempted preparation of the aluminium dichloride instead gave the ionic compound, [Al(HC{hpp}2][AlCl4] (3) that contains a unique six-coordinate, (di)organoalumocenium cation. •A new aliphatic N,C,N′-pincer ligand.•Pendant bicyclic guanidine groups.•Hyper-coordinated silicon and tin(IV) compounds.•A six-coordinate aluminium cation.