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.

The first transition metal catalyzed hydrophosphination of isocyanates is presented. The use of low-coordinate iron(II) precatalysts leads to an unprecedented catalytic double insertion of isocyanates into the P-H bond of diphenylphosphine to yield phosphinodicarboxamides [Ph PC(=O)N(R)C(=O)N(H)R], a new family of derivatized organophosphorus compounds. This remarkable result can be attributed to the low-coordinate nature of the iron(II) centers whose inherent electron deficiency enables a Lewis-acid mechanism in which a combination of the steric pocket of the metal center and substrate size determines the reaction products and regioselectivity.

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Treatment of [Ph3EMe][I] with [Na{N(SiMe3)2}] affords the ylides [Ph3E=CH2] (E=As, 1As; P, 1P). For 1As this overcomes prior difficulties in the synthesis of this classical arsonium‐ylide that have historically impeded its wider study. The structure of 1As has now been determined, 45 years after it was first convincingly isolated, and compared to 1P, confirming the long‐proposed hypothesis of increasing pyramidalisation of the ylide‐carbon, highlighting the increasing dominance of E+−C− dipolar resonance form (sp3‐C) over the E=C ene π‐bonded form (sp2‐C), as group 15 is descended. The uranium(IV)–cyclometallate complex [U{N(CH2CH2NSiPri3)2(CH2CH2SiPri2CH(Me)CH2)}] reacts with 1As and 1P by α‐proton abstraction to give [U(TrenTIPS)(CHEPh3)] (TrenTIPS=N(CH2CH2NSiPri3)3; E=As, 2As; P, 2P), where 2As is an unprecedented structurally characterised arsonium‐carbene complex. The short U−C distances and obtuse U‐C‐E angles suggest significant U=C double bond character. A shorter U−C distance is found for 2As than 2P, consistent with increased uranium‐ and reduced pnictonium‐stabilisation of the carbene as group 15 is descended, which is supported by quantum chemical calculations.