Bisguanidines with Biphenyl, Binaphthyl, and Bipyridyl Cores: Proton‐Sponge Properties and Coordination Chemistry

Abstract

Herein, we report on the synthesis, protonation, and coordination chemistry of chelating guanidine ligands with biphenyl, binaphthyl, and bipyridyl backbones. The ligands are shown to be proton sponges, and this protonation was studied experimentally and by using quantum-chemical calculations. Group 10 metal (Ni, Pd, and Pt) complexes with different metal/ligand ratios were synthesized. In the case of the bipyridyl systems, coordination occurs exclusively at the pyridine N atoms, as opposed to protonation. The spin-density distribution and the magnetism were evaluated for a series of paramagnetic Ni(II) complexes with the aid of paramagnetic NMR spectroscopic studies in alliance with quantum-chemical calculations and magnetic (SQUID) measurements. Through direct delocalization from the singly occupied molecular orbitals (SOMOs), a significant amount of spin density is placed on the guanidinyl groups, and spin polarization also transports spin density onto the aromatic backbone.

A Copper(I) Complex with Two Unpaired Electrons, Synthesised by Oxidation of a Copper(II) Complex with Two Redox‐Active Ligands

“…Paramagnetic NMR spectroscopy has been established as a powerful tool for the analysis of paramagnetic molecules in solution;[ 41 , 42 ] we applied this technique previously for complexes with guanidine ligands. [ 43 , 44 , 45 ] Figure 7 shows the 1 H NMR spectra for [Cu(L1) 2 ] + and [Cu(L2) 2 ] + at various temperatures (see 13 C NMR spectra in the Supporting Information). The signal dispersion is much larger for [Cu(L1) 2 ] + , indicating more spin density on the ligands.…”

Switching from Metal‐ to Ligand‐Based Oxidation in Cobalt Complexes with Redox‐Active Bisguanidine Ligands

“…On the other hand, well resolved signals appeared in the paramagnetic NMR spectra of these compounds. Paramagnetic NMR is well established as powerful tool for the analysis of paramagnetic molecules in solution, [50,51] and has previously been applied by us to study paramagnetic metal‐guanidine complexes [52–54] . The 13 C NMR spectra of [Co(hfacac) 2 (L1)](PF 6 ) are shown in Figure 5a.…”

“…Paramagnetic NMR is well established as powerful tool for the analysis of paramagnetic molecules in solution,[ 50 , 51 ] and has previously been applied by us to study paramagnetic metal‐guanidine complexes. [ 52 , 53 , 54 ] The 13 C NMR spectra of [Co(hfacac) 2 (L1)](PF 6 ) are shown in Figure 5 a. The temperature dependence of the 13 C as well as the 1 H NMR signals clearly differ from the Curie‐Law, mainly due to magnetic coupling between the two spin centers in the molecule.…”

Synthese eines Kupfer(I)‐Komplexes mit zwei ungepaarten Elektronen durch Oxidation eines Kupfer(II)‐Komplexes mit zwei redoxaktiven Liganden

“…[39] Charakteristisch fürd ie letztgenannte Spezies ist außerdem eine intensive Satellitenstruktur im post-peak Bereich, [39,40] Die paramagnetische NMR-Spektroskopie hat sich als leistungsfähige Methode fürd ie Analyse paramagnetischer Moleküle in Lçsung bewährt, [41,42] wir haben diese Te chnik bereits fürK omplexe mit Guanidin-Liganden angewendet. [43][44][45]…”

“…[39] Charakteristisch fürd ie letztgenannte Spezies ist außerdem eine intensive Satellitenstruktur im post-peak Bereich, [39,40] Die paramagnetische NMR-Spektroskopie hat sich als leistungsfähige Methode fürd ie Analyse paramagnetischer Moleküle in Lçsung bewährt, [41,42] wir haben diese Te chnik bereits fürK omplexe mit Guanidin-Liganden angewendet. [43][44][45] Abbildung 7z eigt die 1 [19,20,24,25,54] Zusätzliche Experimente (siehe Hintergrundinformationen) zeigen, dass die katalytische Aktivität(Umsatz/Zeit) der beiden Komplexe innerhalb der ersten 5Stunden der Reaktion vergleichbar ist. Interessanterweise wird mit [Cu(L2) 2 ] schließlich ein hçherer Umsatz erzielt, obwohl L1 ein besserer Elektronendonor ist als L2 (Tabelle 2).…”