Tuning the Bonding of a μ-Mesityl Ligand on Dicopper(I) through a Proton-Responsive Expanded PNNP Pincer Ligand

Abstract

We report the synthesis and characterization of a series of cationic, neutral, and anionic dicopper­(I) complexes featuring a μ-mesityl ligand and a naphthyridine-derived PNNP expanded pincer ligand. Structural characterization showed that the protonation state of the dinucleating ligand has a pronounced effect on the bending and tilting of the μ-mesityl ligand. DFT calculations indicate that the varying orientations of the μ-mesityl ligand are inherent due to changes in electronic structure rather than crystal-packing effects. NBO analysis reveals how the interactions that contribute to the three-center–two-electron bond between the μ-mesityl ligand and the dicopper core change for the various degrees of observed bending and tilting.

Diphosphino‐Functionalized 1,8‐Naphthyridines: a Multifaceted Ligand Platform for Boranes and Diboranes

“…Due to the absence of coordinating solvents, the phosphines are found to coordinate to the potassium centers. The four NC=CH bonds range from 1.377 to 1.397 Å, fitting well with those of NDP‐Cu 2 derivatives with full‐dearomatization (1.380(5)‐1.399(5) Å, [4f,12] Scheme 1) and confirming the successful two‐fold deprotonation.…”

Unexpected reactivity of a PONNOP ‘expanded pincer’ ligand

“…3 Yet, relatively few ligands derived thereof have been reported that are capable of both binding two metal centers in close proximity while also providing accessible adjacent coordination sites on both metals to enable metal-metal cooperativity. 4 In the pursuit of such new platforms we recently reported a dinucleating 'expanded PNNP pincer' ligand, 5 which was inspired by the mononucleating PNP pincer ligands 6 (Scheme 1, top). Similar to the PNP ligands the CH 2 linkers in the PNNP ligand can be deprotonated concomitant with dearomatization of the naphthyridine core, and this enabled the cooperative activation of H 2 to give a tetranuclear copper dihydride cluster.…”

A Well‐Defined Anionic Dicopper(I) Monohydride Complex that Reacts like a Cluster

“…The Cu…Cu distance (2.4229(7) Å) in 1 is shorter than the Cu…Cu distances in A (2.4778(5)-3.4144(6) Å), [11] which is in line with the trend observed for the dearomatization of the analogous mesityl complexes. [12] Dearomatization of the backbone is evident from the short C1-C2 and C9-C10 bond lengths (1.387(3) and 1.386(3) Å, respectively) which are consistent with localized C=C double bonds. This dearomatization leads to a rigid backbone structure in which the methine linkers are in plane with the naphthyridine backbone (P1-C1-C2-N1 = 2.7(3)°).…”

“…[11] This ligand can bind two Cu(I) atoms in close proximity, and can be deprotonated once or twice concomitant with partial or full dearomatization of the naphthyridine core. [11,12] The latter enabled the synthesis of tetracopper dihydride complex A (Scheme 1) through bifunctional activation of hydrogen gas. [11] Recently, Tilley and coworkers reported penta-and trinuclear cationic CuH complexes supported by a naphthyridine based ligand (Scheme 1, B).…”