Applications of iron pincer complexes in hydrosilylation reactions

Due to its abundance, low cost and low toxicity, the first-row transition metal, iron is widely preferred as a catalyst in organic synthesis. The only drawback of lower selectivity due to high reactivity and low stability of the metal centre is tuned by using pincer ligands of different types. The different iron pincer complexes thus prepared are extensively used in catalyzing different types of organic reactions with great selectivity and functional group tolerance under moderate reaction conditions. In this review, we focus on the applications of iron pincer complexes in hydrosilylation reactions, especially the hydrosilylation of carbonyl derivatives and alkene/alkynes.

Iron pincer complexes are efficient in catalyzing various organic reactions with excellent selectivity and functional group tolerance at moderate reaction conditions. This review focuses on the applications of iron pincer complexes in hydrosilylation reactions.

Chemically robust and readily available quinoline-based PNN iron complexes: application in C-H borylation of arenes

Iron catalysts have been used for over a century to produce ammonia industrially. However, the use of iron catalysts generally remained quite limited until relatively recently, when the abundance and low toxicity of iron spurred the development of a variety of iron catalysts. Despite the fact that iron catalysts are being developed as alternatives to precious metal catalysts, their reactivities and stabilities are quite different because of their unique electronic structures. In this context, our group previously developed a new family of quinoline-based PNN pincer-type ligands for low- to mid-valent iron catalysts. These chemically robust PNN ligands provide air- and moisture-tolerant iron complexes, which exhibit excellent catalytic performances in the C-H borylation of arenes. This feature article summarises our recent work on PNN iron complexes, including their conception and design, as well as related reports on iron pincer complexes and iron-catalysed C-H borylation reactions.

Sterically Demanding 8-(Diphenylphosphino)quinoline Complexes of Group 10 Metal(II): Synthesis, Crystal Structures, and Properties in Solution

Several series of platinum(II), palladium(II), and nickel(II) complexes bearing 8-(diphenylphosphino)quinoline (PQ^H) or its 2-methyl or 2-phenyl derivatives (PQ^Me or PQ^Ph) were synthesized, and their crystal structures and behaviors in solution were investigated. Most of the complexes [M(PQ^R)₂]X₂ (M^II = Pt^II, Pd^II, or Ni^II; R = H, Me or Ph; X = monoanionic ions) characterized in this study have an approximately square-planar coordination geometry with two bidentate P,N-chelating or monodentate P-donating quinolylphosphine ligands in the cis(P,P) configuration. A large steric requirement from the Me or Ph substituent introduced at the 2-position of the quinoline ring gives the resulting complexes severe distortion. The Pt^II and Pd^II complex cations maintained the square-planar coordination geometry, but the M^II center was displaced from the chelating ligand plane. This bending of the chelate coordination makes the M-N(quinoline) bond weaker, as demonstrated by the longer M-N bonds. In accord with the bond weakening, the partial dissociation of the PQ^H or PQ^Me chelates by substitution with halide anions were observed using UV-vis spectroscopy and X-ray crystallography. In contrast, the PQ^Ph complexes were stable in solution toward the addition of halide anions; the intramolecular π-π stacking interaction between the coordinating quinolyl and the 2-substituted phenyl rings protects the M^II center from nucleophilic attack. In the corresponding Ni^II complexes, the steric congestion arising from the mutually cis-positioned PQ^R ligands resulted in a large tetrahedral distortion around the Ni^II center. However, the intramolecular π-π stacking interaction was still effective in the PQ^Ph complex, and this interaction can explain some unusual robustness and electrochemical properties of the Ni^II-PQ^Ph complex.

Synthesis of a Redox-Active NNP-Type Pincer Ligand and Its Application to Electrocatalytic CO2 Reduction With First-Row Transition Metal Complexes

We report the synthesis of a rigid phosphine-substituted, redox-active pincer ligand and its application to electrocatalytic CO₂ reduction with first-row transition metal complexes. The tridentate ligand was prepared by Stille coupling of 2,8-dibromoquinoline and 2-(tributylstannyl)pyridine, followed by a palladium-catalyzed cross-coupling with HPPh₂. Complexes were synthesized from a variety of metal precursors and characterized by NMR, high-resolution mass spectrometry, elemental analysis, and cyclic voltammetry. Formation of bis-chelated metal complexes, rather than mono-chelated complexes, was favored in all synthetic conditions explored. The complexes were assessed for their ability to mediate electrocatalytic CO₂ reduction, where the cobalt complex was found to have the best activity for CO₂-to-CO conversion in the presence of water as an added proton source.