Protic Ruthenium Tris(pyrazol-3-ylmethyl)amine Complexes Featuring a Hydrogen-Bonding Network in the Second Coordination Sphere

Abstract

We synthesized ruthenium complexes bearing a tris(pyrazol-3-ylmethyl)amine ligand LH3 and revealed that this tripodal ligand allows predictable accumulation of three proton-delivering NH groups around a coordination site. The Brønsted acidity of the NH groups in LH3 led to the formation of multiple hydrogen bonds with the substrate ligand and deprotonation. The chlorido complex ligated by LH3 catalyzed disproportionation of 1,2-diphenylhydrazine.

Stereoselective synthesis of chlorido–phosphine ruthenium complexes bearing a pyrazole-based protic tripodal amine ligand

“…The notable difference in the product selectivity prompted us to further investigate the reaction of the protic LH 3 ligand, which led to the finding that use of methanol as the solvent completely switches the product selectivity to the cis isomer. The 1 H NMR spectrum of this complex, confirming the C s symmetry in solution, exhibits no remote coupling between the phosphorus nuclei and the methylene protons in the tripodal ligand[11], in agreement with the cis-orientation of the phosphine ligand and the amine nitrogen atom. Subsequent anion exchange to hexafluorophosphate resulted in isolation of the cis(P,N amine )-2 as crystals.…”

“…Crafting coordination spaces with tripodal ligands has been the focus of intense research to develop activation and selective transformation of substrates therein [1][2][3][4][5][6][7][8]. In [11]. Given that the metal-ligand cooperation in activation and transformation of substrate molecules is envisaged, the tunable phosphine ligand should be installed at the position cis to the amine nitrogen atom to fix the substrate-binding site surrounded by the three Brønsted acidic NH groups in LH 3 .…”

“…chlorido-bridged diruthenium(II) complex 1 with triphenylphosphine in toluene leads to exclusive formation of the chlorido-phosphine complex trans(P,N amine )-2, wherein the incoming phosphine ligand lies in the position trans to the amine nitrogen atom in the tripodal ligand LH 3[11]. The result sharply contrasts with the reaction of a related aprotic tripodal ligand, tris(pyridylmethyl)amine (TPA), with [RuCl 2 (PPh 3 ) 3 ], which affords a mixture of cis(P,N amine )-and trans(P,N amine )-[RuCl(PPh 3 )(tpa)] +[29].…”

Tuning the Fe(II/III) Redox Potential in Nonheme Fe(II)–Hydroxo Complexes through Primary and Secondary Coordination Sphere Modifications

“…Nam and Que have demonstrated that varying the axial ligand in nonheme iron complexes changes their electronic structures and reactivities. − Work from the Long and Chang groups has shown that altering the donor strength of a pyridine ligand framework can produce analogous differences in the metal complexes’ properties . Although a number of researchers have demonstrated the importance of the secondary coordination sphere in controlling the properties of metal complexes, − systematic alteration of these secondary sphere interactions remains less developed, likely due to the nontrivial nature of such modifications. Several ligand families have been developed specifically to study the impact of changing the number (and/or type) of pendant hydrogen-bond donors on the properties of their metal complexes. − Borovik has shown that these alterations in the secondary coordination sphere can contribute to significant differences in reactivity. − However, variations in the secondary coordination sphere often directly impact the primary coordination sphere through steric or electronic interactions, complicating the interpretation of the resulting changes in reactivity. , …”

Examining the Generality of Metal–Ligand Cooperativity Across a Series of First-Row Transition Metals: Capture, Bond Activation, and Stabilization

“…With the series of N 2 H 4 templated species 2-M , we sought to investigate the redox requirements of the metal for N–N bond scission. − Investigation of the complexes by voltammetry (0.2 M [Bu 4 N]­[PF 6 ], THF) revealed reduction events ranging from −1.53 to −2.28 V (vs Fc/Fc + ) with 2-Co and 2-V the easiest and hardest to reduce, respectively (Figure C). The reductive waves of 2-Mn , 2-Fe , and 2-Co all show good reversibility at fast scan rates (>100 mV/s), while 2-V and 2-Zn are irreversible.…”