Carbon monoxide is a key C1 feedstock for the industrial production of hydrocarbons, where it is used to make millions of tonnes of chemicals, fuels, and solvents per annum. Many transition metal complexes can coordinate CO, but the formation of new C−C bonds in well-defined compounds from the scission and subsequent coupling of two or more CO moieties at a transition metal centre remains a challenge. Herein, we report the use of low-coordinate iron(II) complexes for the selective scission and homologation of CO affording unusual squaraines and iron carboxylates at ambient temperature and pressure. A modification of the ligand framework allows for the isolation and structural characterisation of a proposed metallacyclic Fe(II) carbene intermediate. These results indicate that, with the appropriate choice of supporting ligands, it is possible to cleave and homologate carbon monoxide under mild conditions using an abundant and environmentally benign low-coordinate, first row transition metal.

A magnesium complex ( 1 ) featuring a bidentate aminopyridinato ligand is a remarkably selective catalyst for the dehydrocoupling of amine‐boranes. This reaction proceeds to completion with low catalyst loadings (1 mol %) under mild conditions (60 °C), exceeding previously reported s‐block systems in terms of selectivity, rate, and turnover number (TON). Mechanistic studies by in situ NMR analysis reveals the reaction to be first order in both catalyst and substrate. A reaction mechanism is proposed to account for these findings, with the high TON of the catalyst attributed to the bidentate nature of the ligand, which allows for reversible deprotonation of the substrate and regeneration of 1 as a stable resting state.

Here, we highlight the ability of peri-substitution chemistry to promote a series of unique P-P/P-As coupling reactions, which proceed with concomitant C-H bond formation. This dealkanative reactivity represents an interesting and unexpected expansion to the established family of main-group dehydrocoupling reactions. These transformations are exceptionally clean, proceeding essentially quantitatively at relatively low temperatures (70-140 °C), with 100% diastereoselectivity in the products. The reaction appears to be radical in nature, with the addition of small quantities of a radical initiator (azobis(isobutyronitrile)) increasing the rate dramatically, as well as altering the apparent order of reaction. DFT calculations suggest that the reaction involves dissociation of a phosphorus centered radical (stabilized by the peri-backbone) to the P-P coupled product and a free propyl radical, which carries the chain. This unusual reaction demonstrates the powerful effect that geometric constraints, in this case a rigid scaffold, can have on the reactivity of main group species, an area of research that is gaining increasing prominence in recent years.

In this Perspective, we will highlight selected examples of transition metal complexes with low coordination numbers whose high reactivity has been exploited in catalysis and the activation of small molecules featuring strong bonds (N2, CO2, and CO).

The fundamental synthetic building blocks FcPH2 and FcPCl2 are obtained in high yield and excellent purities via the fully regiospecific electrophilic monofunctionalisation of ferrocene with P4S10, thus replacing inconvenient tBuLi based procedures.

Coordination chemistry of an acenaphthene peri-backbone-supported phosphino-phosphonium chloride (1) was investigated, revealing three distinct modes of reactivity. The reaction of 1 with Mo(CO)4(nor) gives the Mo(0) complex [(1)Mo(CO)4Cl] (2), in which the ligand 1 exhibits monodentate coordination through the phosphine donor and the P-P bond is retained. PtCl2(cod) reacts with the chloride and triflate salts of 1 to form a mononuclear complex [(1Cl)PtCl2] (3) and a binuclear complex [((1Cl)PtCl)2][2TfO] (4), respectively. In both of these complexes, the platinum center adds across the P-P bond, and subsequent chloride transfer to the phosphenium center results in phosphine-chlorophosphine bidentate coordination. [((1)PdCl)2] (5) was isolated from the reaction of 1 and Pd2(dba)3 (dba = dibenzylideneacetone). Oxidative addition to palladium(0) results in a heteroleptic phosphine bridging phosphide coordination to the Pd(II) center. In addition, reaction of 1 with BH3·SMe2 leads to the bis(borane) adduct of the corresponding mixed tertiary/secondary phosphine (6), with BH3 acting as both a reducing agent and a Lewis acid. The new compounds were fully characterized, including X-ray diffraction. The ligand properties of 1 and related bonding issues are discussed with help of DFT computations.

Spectroscopic and computational investigation of the effects of para-substituted m-terphenyl lithium complexes reveals significant electronic differences at the metal centre.

Herein we report the synthesis of three heteroleptic first‐row transition metal(II) complexes containing carbazolido NNN pincer ligands and conversion to the corresponding metal(I)‐carbonyl complexes via a reductive carbonylation route. These complexes are precatalysts for the hydrophosphination of activated alkenes, affording a cobalt‐catalysed hydrophosphination process that solely and selectively yields the β addition (anti‐Markovnikov) product. The scope of this transformation has been investigated using a variety of activated alkenes. Isolation and characterisation of substrate‐coordinated intermediates reveal available coordination sites, which provide insight into the proposed catalytic cycle.magnified image