Tuning of Copper(I)–Dioxygen Reactivity by Bis(guanidine) Ligands

Abstract

A series of bis(guanidine) ligands designed for use in biomimetic coordination chemistry, namely bis(tetramethylguanidino)‐, bis(dipiperidinoguanidino)‐, and bis(dimethylpropyleno)propane (btmgp, DPipG2p and DMPG2p, respectively), has been extended to include bis(dimethylethyleneguanidino)propane (DMEG2p), which has both Namine atoms of each guanidine functionality connected by a short ethylene bridge, as a member. From this series, a family of novel bis(guanidine)copper(I) compounds – [Cu2(btmgp)2][PF6]2 (1), [Cu2(DPipG2p)2][PF6]2 (2), [Cu2(DMPG2p)2][PF6]2 (3), and [Cu2(DMEG2p)2][PF6]2·2MeCN (4) – has been synthesised. Single‐crystal X‐ray analysis of 1–4 demonstrated that these compounds contain dinuclear complex cations that contain twelve‐membered heterocyclic Cu2N4C6 rings with the Cu atoms being more than 4 Å apart. Each copper atom is surrounded by a set of two N‐donor functions from different ligands, resulting in linear N–Cu–N coordination sites. Depending on their individual substitution patterns, the guanidine moieties deviate from planarity by characteristic propeller‐like twists of the amino groups around their N–Cimine bonds. The influence of these groups on the reactivity of the corresponding complexes 1–4 with dioxygen was investigated at low temperatures by means of UV/Vis spectroscopy. The reaction products can be classified into μ‐η2:η2‐peroxodicopper(II) or bis(μ‐oxo)dicopper(III) complex cations that contain the {Cu2O2}2+ core portion as different isomers. The electronic properties of the specific bis(guanidine) ligands are discussed from the viewpoint of their σ‐donor and π‐acceptor capabilities, and it is shown that μ‐η2:η2‐peroxodicopper(II) complexes are stabilised relative to the bis(μ‐oxo)dicopper(III) ones if π conjugation within the guanidine moieties is optimised. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

New Guanidine-Pyridine Copper Complexes and Their Application in ATRP

“…The ρ-value of 0.95 shows a small degree of charge delocalization within the guanidine unit. The intra-guanidine torsion is small (14.8°(av)), as expected for a DMEG unit [12].…”

“…This parameter amounts in both complexes to 0.95, indicating a low charge delocalization within the CN 3 guanidine framework. The intra-guanidine torsion is rather small, as expected for DMEG units, with N amin,gua C 3 ,C gua N 3 plane angles of 14.7(av) (1) and 14.6(av) (2) [12]. The reaction of one equivalent of DMEGpy with one equivalent of CuCl 2 gives the mono(chelate) complex, [Cu(DMEGpy)Cl 2 ] (3) (Figure 3).…”

“…The donor properties can be tuned through the choice of guanidine substituents, amine and spacers. These ligands have already been intensely investigated in bioinorganic coordination chemistry [12][13][14][15][16][17][18], but also in the ATRP of styrene [19][20][21][22][23][24]. In all of these studies, it appeared that the polyfunctional guanidines support the oxidation state change from Cu(I) over Cu(II) to Cu(III) and stabilize the corresponding complexes excellently.…”

Novel Tin(IV) Complexes with the Hybrid Guanidine Ligand DMEGqu

“…The Sn-N imine bonds (2.184(4), 2.191(4)Å) are shorter than the Sn-N qu bonds (2.234(4), 2.214(4)Å), and both are longer than the corresponding bonds in C1 and C4, In known complexes with the DMEG guanidine moiety, the torsion of the N amine C 3 planes versus the C gua N 3 plane, also known as the intra-guanidine twist, is less pronounced than in similar complexes with other guanidines due to the bridging ethylene group of DMEG. In the literature, for transition metal complexes torsion values of about 12 • are found [16,20]. However, in the presented structures a more pronounced planarity of the DMEG moiety is observed [23].…”

Transition‐Metal Complexes with Ferrocene‐Bridged Bis(imidazolin‐2‐imine) and Bis(diaminocyclopropenimine) Ligands

“…However, the same connectivity was found by Herres-Pawlis for propylene-bridged guanidine complexes with Cu I . [24] Scheme 4. Synthesis of dimeric (5a/b) and polymeric (6) Cu I complexes.…”