Pacman Compounds: From Energy Transfer to Cooperative Catalysis

Abstract

In this Concept article we present the syntheses and application of homo and heterodinuclear "Pacman" compounds. This architecture implies that two metal coordination fragments are brought in close vicinity to each other via a covalent linkage to either support energy transfer between the two units or cooperative transformation of a substrate. Nature has shown that the combination of metal fragments, in particular two different metals, can dramatically improve the efficiency of small molecule activation. We exemplify this strategy for the activation of water, dioxygen and carbon dioxide. Furthermore, we present artificial systems in which a positive effect on the catalytic performance because of the combination of two (different) metal centers could be observed. Thus, Pacman-type compounds are very well suited as structural and functional models for their biological counterparts.

Syntheses and solid-state structures of two cofacial (bis)dipyrrin dichromium complexes in different charge states

“…Bimetallic Pacman complexes are of interest as catalysts for small-molecule activation and bond functionalization (Cowie et al, 2020), and have been employed in water reduction and dioxygen activation (Devoille & Love, 2011;Rosenthal & Nocera, 2007b). Lang & Schwalbe (2017) have provided a recent review of Pacman compounds and their applications. Whereas all equatorial metal coordination sites are occupied in porphyrin Pacman compounds, the related Pacman dipyrrin framework occupies two cis coordination sites per metal, potentially allowing for both axial and equatorial chemistry.…”

Diiron Complexes with a Bridging Functionalized Allylidene Ligand: Synthesis, Structural Aspects, and Cytotoxicity

“…The anticancer properties of diiron complexes, however, have been largely unexplored. Nevertheless, a diiron frame has been shown to supply unique cooperative effects in terms of chemical reactivity and offers wide possibilities to design and modify the nature of bridging-coordinated ligands, thus allowing the introduction of the most suitable functional groups to gain full control of the fundamental properties for a metal-based drug (e.g., water solubility, lipophilicity, stability, redox potential, etc.). In addition, it should be noted that only a few iron carbonyl compounds have been investigated for their anticancer behavior so far. , …”

Constructing Organometallic Architectures from Aminoalkylidyne Diiron Complexes

“…I would say that this fruitful chemistry held some prophetical character, since it relied on key concepts that have been more clearly focused later on. In principle, a dinuclear complex is the most simple metal system offering the opportunity for cooperative effects and multisite coordination modes, thus giving rise to reactivity patterns not commonly observed with mononuclear species . In this sense, it is impressive that diiron units are present in nature in some enzymes, and in particular [FeFe]‐hydrogenases are actually based on an organometallic core, comprising carbonyl and cyanide ligands .…”