Guanidine Metal Complexes for Bioinorganic Chemistry and Polymerisation Catalysis

Abstract

Guanidines are highly useful ligands which have conquered coordination chemistry within the last 20 years. Their CN 3 moiety allows multiple substitution patterns which enables tailoring them to a large variety of applications, ranging from bioinorganic coordination chemistry via medicinal chemistry to polymerisation catalysis. In bioinorganic chemistry, guanidines gave important stimuli in the modelling of copper type 1, 2 and 3 enzymes. This review provides with a comprehensive overview on complexes which have been reported with neutral guanidine ligands. Peralkylated guanidines as well as bicyclic or more complex guanidine-comprising entities are described in their coordination chemistry with transition and main-group metals. The structural features of the complexes as well as their most prominent features in bioinorganic chemistry or polymerisation catalysis are highlighted. Hereby, the role of the delocalisation of the positive charge within the guanidine unit gained during coordination is discussed in its importance for efficient and robust coordination. The delocalisation within the CN 3 unit can be measured by the structural value ρ which is discussed for numerous systems. The charge delocalisation makes neutral guanidines versatile and efficient for the stabilisation of highly different coordination modes and a large variety of oxidation states.

Implications of Guanidine Substitution on Copper Complexes as Entatic‐State Models

“…This is related to the strong donation of N gua donor atoms to the Cu II centres [see natural bond orbital (NBO) calculations]: the C gua –N imine,gua bond shifts electron density to the N gua donor, which results in an elongation of the C gua –N imine,gua bond and a shortening of the C gua –N amine,gua bond . In all of these complexes, a twist within the guanidine moiety is observed, and this is characteristic of peralkylated guanidine ligands . This twist is a result of the competition between the electronic effects of the intra‐guanidine conjugation and the evasion of the alkyl substituents.…”

“…This twist is a result of the competition between the electronic effects of the intra‐guanidine conjugation and the evasion of the alkyl substituents. The angles between the C gua N 3 and N amine C 3 planes lie in the range 7.7–11.4° and are smaller than those in the corresponding TMGqu Cu complexes because the twist in DMEG complexes is hindered by the rigid ethylene bridge between the amine groups of the guanidine moiety , . In C5 , one triflate anion interacts weakly with the Cu II centre [2.375(3) and 2.786(4) Å for the two molecules in the asymmetric unit].…”

“…The copper complexes reported herein exhibit an interplay between the guanidine and quinoline moieties. The guanidine moiety is generally a slightly harder donor and stabilises the copper centre in both oxidation states, whereas the quinolinyl donor is softer , , . Both bond lengths have to be predicted correctly within DFT calculations.…”

Hand in Hand: Experimental and Theoretical Investigations into the Reactions of Copper(I) Mono‐ and Bis(guanidine) Complexes with Dioxygen

“…[34,35] The preferential stabilisation of O core species in the presence of bidentate guanidine ligands is due to their excellent σand πdonor abilities. [29,[36][37][38] In the context of tetradentate ligands, the steric demands and excellent donor properties of the guanidine groups in the tris(guanidine) ligand TMG 3 tren ( Figure 1) have been successfully used in the last years to stabilise a superoxido end-on monocopper species and to study the subsequent chemistry of this exceptional complex. [39][40][41][42] Some of us previouslyinvestigatedthereactivityofthecopper(I)complexwith 2-[3-(dimethylamino)propyl]-1,1,3,3-tetramethylguanidine (TMGdmap) as ligand towards dioxygen in comparison with copper(I) complexes of the ligands 1,3-bis(N,N,N′,N′-tetramethylguanidino)propane (btmgp) and teramethylpropylenediamine (TMPD).…”

Decay kinetics of sensitive bioinorganic species in a SuperFocus mixer at ambient conditions

“…7 It was shown that bisIJguanidine) ligands are strong N-donors and stabilise high metal oxidation states. 8,9 BisIJguanidine) li-gands represent a ligand class which is intensively investigated for use in biomimetic coordination chemistry. 10,11 Libraries of ligands with different attributes have been synthesised and studied.…”