Nitrogen fixation, the six-electron/six-proton reduction of N2, to give NH3, is one of the most challenging and important chemical transformations. Notwithstanding the barriers associated with this reaction, significant progress has been made in developing molecular complexes that reduce N2 into its bioavailable form, NH3. This progress is driven by the dual aims of better understanding biological nitrogenases and improving upon industrial nitrogen fixation. In this review, we highlight both mechanistic understanding of nitrogen fixation that has been developed, as well as advances in yields, efficiencies, and rates that make molecular alternatives to nitrogen fixation increasingly appealing. We begin with a historical discussion of N2 functionalization chemistry that traverses a timeline of events leading up to the discovery of the first bona fide molecular catalyst system and follow with a comprehensive overview of d-block compounds that have been targeted as catalysts up to and including 2019. We end with a summary of lessons learned from this significant research effort and last offer a discussion of key remaining challenges in the field.

Catalytic N2-to-NH3 (or -N2H4) Conversion by Well-Defined Molecular Coordination Complexes.

Platinum compounds represent one of the great success stories of metals in medicine. Following the serendipitous discovery of the anticancer activity of cisplatin by Rosenberg, a large number of cisplatin variants have been prepared and tested for their ability to kill cancer cells and inhibit tumor growth. These efforts continue today with increased realization that new strategies are needed to overcome issues of toxicity and resistance inherent to treatment by the approved platinum anticancer agents. One approach has been the use of so-called “non-traditional” platinum(II) and platinum(IV) compounds that violate the structure–activity relationships that governed platinum drug-development research for many years. Another is the use of specialized drug-delivery strategies. Here we describe recent developments from our laboratory involving monofunctional platinum(II) complexes together with a historical account of the manner by which we came to investigate these compounds and their relationship to previous...

Monofunctional and Higher-Valent Platinum Anticancer Agents

Synthesis and reactivity of iron–dinitrogen complexes bearing anionic methyl- and phenyl-substituted pyrrole-based PNP-type pincer ligands toward catalytic nitrogen fixation

From the reaction of [{Ln(SO2)n(AsF6)3}x] (Ln = La or Sm) with acetonitrile the complexes [Ln(MeCN)9][AsF6]3 have been prepared. The crystal structures of [Ln(MeCN)9][AsF6]3·nMeCN (Ln = La, n = l; Ln = Sm, n = 3) show a nine-co-ordinate lanthanoid with a tricapped trigonal prismatic arrangement of N donor atoms. By reaction of LnCl3 with AlCl3 in acetonitrile the complexes [Ln(MeCN)n][AlCl4]3 (Ln = Pr, n = 9; Ln = Yb, n = 8) have been synthesized, and they have also been prepared very simply by the reaction of the lanthanoid metal, AlCl3, and C2Cl6 in acetonitrile. The crystal structure of [Pr(MeCN)9][AlCl4]3·MeCN shows nine-co-ordinate praseodymium also with a tricapped trigonal prismatic arrangement of N donor atoms, whilst [Yb(MeCN)8][AlCl4]3 has square dodecahedral YbN8 eight-co-ordination.

Syntheses and structures of some homoleptic acetonitrile lanthanoid(III) complexes

This study focused on the synthesis and characterization of a range of low-valent, high-spin iron(II) complexes supported by a carbazole-based PNP pincer-type ligand. The addition of the lithiated ...

Synthesis, Characterization, and Reactivity of a High-Spin Iron(II) Hydrido Complex Supported by a PNP Pincer Ligand and Its Application as a Homogenous Catalyst for the Hydrogenation of Alkenes

The pyrrolyl-based iron pincer compounds [(tBuPNP)FeCl] (1), [(tBuPNP)FeN2] (2), and [(tBuPNP)Fe(CO)2] (3) were prepared and structurally characterized. In addition, their electronic ground states were probed by various techniques including solid-state magnetic susceptibility and zero-field 57Fe Mossbauer and X-band electron paramagnetic resonance spectroscopy. While the iron(II) starting material 1 adopts an intermediate-spin (S = 1) state, the iron(I) reduction products 2 and 3 exhibit a low-spin (S = 1/2) ground state. Consistent with an intermediate-spin configuration for 1, the zero-field 57Fe Mossbauer spectrum shows a characteristically large quadrupole splitting (ΔEQ ≈ 3.7 mm s–1), and the solid-state magnetic susceptibility data show pronounced zero-field splitting (|D| ≈ 37 cm–1). The effective magnetic moments observed for the iron(I) species 2 and 3 are larger than expected from the spin-only value and indicate an incompletely quenched orbital angular momentum and the presence of spin–orbit co...

https://pubs.acs.org/doi/pdf/10.1021/acs.inorgchem.7b01078

Synthesis and Electronic Ground-State Properties of Pyrrolyl-Based Iron Pincer Complexes: Revisited

Pyrrolyl-based pincer complexes of iron – Synthesis and electronic structure

Synthesis of selected transition metal and main group compounds with synthetic applications

https://onlinelibrary.wiley.com/doi/pdf/10.1002/zaac.202100080

Nico Ehrlich

Papers

Synthesis and Electronic Ground-State Properties of Pyrrolyl-Based Iron Pincer Complexes: Revisited

Pyrrolyl-based pincer complexes of iron – Synthesis and electronic structure

Synthesis of selected transition metal and main group compounds with synthetic applications

Pyrrole‐based pincer ligands containing iminophosphorane moieties and their coordination chemistry with group 1 metals and magnesium