Molecular Catalysts with Diphosphine Ligands Containing Pendant Amines

Abstract

Pendant amines play an invaluable role in chemical reactivity, especially for molecular catalysts based on earth-abundant metals. As inspired by [FeFe]-hydrogenases, which contain a pendant amine positioned for cooperative bifunctionality, synthetic catalysts have been developed to emulate this multifunctionality through incorporation of a pendant amine in the second coordination sphere. Cyclic diphosphine ligands containing two amines serve as the basis for a class of catalysts that have been extensively studied and used to demonstrate the impact of a pendant base. These 1,5-diaza-3,7-diphosphacyclooctanes, now often referred to as “P2N2” ligands, have profound effects on the reactivity of many catalysts. The resulting [Ni­(PR 2NR′ 2)2]2+ complexes are electrocatalysts for both the oxidation and production of H2. Achieving the optimal benefit of the pendant amine requires that it has suitable basicity and is properly positioned relative to the metal center. In addition to the catalytic efficacy demonstrated with [Ni­(PR 2NR′ 2)2]2+ complexes for the oxidation and production of H2, catalysts with diphosphine ligands containing pendant amines have also been demonstrated for several metals for many different reactions, both in solution and immobilized on surfaces. The impact of pendant amines in catalyst design continues to expand.

Reductive 1,2-Arylation of Isatins

“…P 2 N 2 ligands have been extensively studied in organometallic chemistry For instance, cationic Ni­(II)–P 2 N 2 complexes have been isolated and found to be exceptional catalysts for electrocatalytic hydrogen splitting and hydrogen formation . However, their use in cross-coupling has been underdeveloped, and low-valent metal-P 2 N 2 complexes are less well studied .…”

Synthesis and anti-microbial activity of a new series of bis(diphosphine) rhenium(v) dioxo complexes

“…36 This reaction has been employed by our group, and others, for the facile synthesis of numerous hetero-functionalised di-(and tri-) phosphines from parent primary amines or ammonia. [37][38][39][40] Upon addition to a solution of a Re(V) precursor, the rapid formation of monocationic bis(diphosphine) complexes containing a trans-dioxo unit {Re V O 2 } + was observed (Fig. 1(b)).…”

A redox-active Mn(0) dicarbene metalloradical

“…There is ongoing interest in developing redox active transition metal complexes for applications in molecular electrocatalysis using Earth-abundant metals such as Ni, Fe, and Co. 1,2 An equally attractive metal is manganese and several groups have reported Mn I complexes that are electrocatalytically active for CO 2 reduction to CO [3][4][5][6] and H + to H 2 7 via intermediates with a formal Mn ÀI oxidation state. A key Mn 0 intermediate is typically proposed, however observing and chemically separating the mononuclear species has proven to be challenging because Mn 0 complexes readily dimerize to form a Mn-Mn bond, such as in Mn 2 (CO) 10 and [Mn(CO) 3 (tmbp)] 2 8 (tmbp = 4,4 0 5,5 0 -tetramethyl-2,2 0 biphosphinine).…”