Formation and infrared spectroscopic characterization of carbon suboxide complexes TM-η1 -C3 O2 and the inserted ketenylidene complexes OCTMCCO (TM=Cu, Ag, Au) in solid neon

The reactions of coinage metal atoms Cu, Ag and Au with carbon suboxide (C₃ O₂ ) are studied by matrix isolation infrared spectroscopy. The weakly bound complexes TM-η¹ -C₃ O₂ (TM=Cu, Ag, Au), in which the carbon suboxide ligand binds to the metal center in the monohapto fashion are formed as initial reaction products. The complexes subsequently isomerize to the inserted products OCTMCCO upon visible light (λ = 400-500 nm) excitation. The analysis of the electronic structure using modern quantum chemistry methods suggests that the linear OCTMCCO complexes are best described by the bonding interactions between the TM⁺ cation in the electronic singlet ground state and the [OC…CCO]^- ligands in the doublet state forming two TM⁺  ← ligands σ donation and two TM⁺  → ligands π backdonation bonding components. In addition, the CuCCO, AgCCO and AuCCO complexes are also formed, which are predicted to be bent.

Trimerisation of carbon suboxide at a di-titanium centre to form a pyrone ring system

Bis(pentalene)dititanium Ti₂(μ:η⁵,η⁵-Pn^†)₂ trimerises carbon suboxide (O Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O) to form [{Ti₂(μ:η⁵,η⁵-Pn^†)₂}{μ-C₉O₆}], which contains a 4-pyrone core, via the monoadduct [Ti₂(μ:η⁵,η⁵-Pn^†)₂ (η²-C₃O₂)].

The reaction of the syn-bimetallic bis(pentalene)dititanium complex Ti₂(μ:η⁵,η⁵-Pn^†)₂ (Pn^† = C₈H₄(1,4-SiⁱPr₃)₂) 1 with carbon suboxide (O Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O, C₃O₂) results in trimerisation of the latter and formation of the structurally characterised complex [{Ti₂(μ:η⁵,η⁵-Pn^†)₂}{μ-C₉O₆}]. The trimeric bridging C₉O₆ unit in the latter contains a 4-pyrone core, a key feature of both the hexamer and octamer of carbon suboxide which are formed in the body from trace amounts of C₃O₂ and are, for example, potent inhibitors of Na⁺/K⁺-ATP-ase. The mechanism of this reaction has been studied in detail by DFT computational studies, which also suggest that the reaction proceeds via the initial formation of a mono-adduct of 1 with C₃O₂. Indeed, the carefully controlled reaction of 1 with C₃O₂ affords [Ti₂(μ:η⁵,η⁵-Pn^†)₂ (η²-C₃O₂)], as the first structurally authenticated complex of carbon suboxide.

Activation of carbon suboxide (C3O2) by U(iii) to form a cyclobutane-1,3-dione ring

[U(η⁵-C₅H₄SiMe₃)₃] reductively couples three C₃O₂ molecules to form a tetranuclear complex with a central cyclobutane-1,3-dione ring, via an intermediate bridging ketene complex.

Heavier Carbon Subchalcogenides as C3 Sources for Tungsten-Capped Cumulenes: A Theoretical Study

Heavier carbon subchalcogenides C₃E₂ (E = S, Se) can bind to transition metals through either a C═C or a C═E double bond. These two binding modes on a reactive tungsten (PMe₃)₄WCl₂ site have been explored by density functional theory methods (M06-L/DZP+Lanl2DZ). The important step controlling the reaction direction is the initial binding of the C₃E₂ ligand. Of particular significance is the M═C═C═C═E fragment resulting from the C═E coordination mode. This fragment can bind to additional C₃E₂ molecules or bridge to other metals. Ultimately C₃E₂ serves as a source of C₃ units for building C_3n carbon sp-hybridized allotropes.