Synthesis and Coordination Chemistry of 3,4-Ethylene-Bridged 1,1,2,5-Tetrasubstituted Biguanides

Abstract

The synthesis of 3,4-ethylene-bridged 1,1,2,5-tetrasubstituted biguanides is reported, which are accessible by three alternative routes. Exemplary molecular structures of the ligand and an observed side product have been elucidated by X-ray diffraction analysis. Mono-and dinuclear complexes of the biguanide in both its neutral and monoanionic forms were obtained, including examples of aluminum, copper, magnesium, potassium, tin, and zinc, indicating a versatile coordination behavior, as evidenced by means of single-crystal X-ray diffraction analysis.Article pubs.acs.org/IC

Mono- and Dinuclear Aluminium Complexes Derived from Biguanide and Carbothiamide Ligands

“…Hence, each tetracoordinated potassium ion binds to the nitrogen atom N1 and the phenyl ring of the related Dipp group of one ligand in a κ 1 and η 6 mode, in κ 1 fashion to the N4 nitrogen atom of the next ligand and to one molecule of THF. The respective potassium-nitrogen bond lengths in the range of 2.695(2) to 2.735(2) Å, as well as the distance of the potassium ion to the centre of the C 6 perimeter (2.857(2) Å), are in good agreement with previously reported potassium complexes [22,26]. Hence, deprotonation occurs exclusively at N1, while the amino function at N5 remains intact, which is most likely due to the stabilization of H5 by the intramolecular N5H1•••N3 hydrogen bridge.…”

“…The crystalline yield of 1 amounts to 16%, although 1 is formed in 40% based on the crude 1 H NMR besides the carbothiamide 2 and the unsymmetric thiourea carrying one 2,6-diisopropylphenyl (Dipp) and one cyclohexyl substituent. Notably, such side products have also been observed in the synthesis of monoprotic biguanides [22]. Scheme 1.…”

“…Based on the synthetic protocol previously established for monoprotic biguanide ligands, [22] biguanide 1 could be obtained from the ethylene-bridged bis(thiourea), cyclohexylamine, and lead(II) oxide in a one-pot procedure, Scheme 1. The crystalline yield of 1 amounts to 16%, although 1 is formed in 40% based on the crude 1 H NMR besides the carbothiamide 2 and the unsymmetric thiourea carrying one 2,6-diisopropylphenyl (Dipp) and one cyclohexyl substituent.…”

“…This behavior is beneficial in terms of metal-ligand cooperativity [17,18], and the addition of hydrogen or protic substrates to gallium(III) β-diketiminate complexes generates an additional protic side within the ligand [19,20]. During our recent studies on dianionic bis(guanidine)s [21], we were able to isolate monoprotic biguanides as well as diprotic carbothiamides depending on the experimental conditions [22], and we wondered if diprotic biguanides are available as well when using a primary instead of a secondary amine. In here, we report the synthesis of the unprecedented biguanide 1 along with its reactivity towards trimethylaluminium and potassium bis(trimethylsilyl)amide.…”

Conjugated Bis‐Guanidines (CBGs) as β‐Diketimine Analogues: Synthesis, Characterization of CBGs/Their Lithium Salts and CBG Li Catalyzed Addition of B−H and TMSCN to Carbonyls

“…[27] At the time of drafting our manuscript, Kretschmer et al reported the 3,4-ethylene bridged 1,1,2,5-tetrasubstituted biguanides (Scheme 1, v). [28] As far as we know, tetra aryl-substituted conjugated bis-guanidines (CBG) are not known in the literature (Scheme 1). [29] Therefore, herein, we report a synthesis of structurally characterized CBGs by the reaction of amidoxime or aqueous (aq.)…”