A Biomimetic Nickel Complex with a Reduced CO2 Ligand Generated by Formate Deprotonation and Its Behaviour towards CO2

Appropriation of group II metals: synthesis and characterisation of the first alkaline earth metal supported transition metal carbonite complexes

Nickel carbonite complexes supported by alkaline earth metals have been accessed via salt-metathesis of the corresponding alkali metal precursors. The new complexes undergo Schlenk-like exchange reactions in solution which have been investigated by NMR spectroscopy. Also their reactivity towards epoxides and carbon monoxide was studied.

Controlling the Activation at NiII -CO2 2- Moieties through Lewis Acid Interactions in the Second Coordination Sphere

Nickel complexes with a two-electron reduced CO2 ligand (CO2 2- , "carbonite") are investigated with regard to the influence alkali metal (AM) ions have as Lewis acids on the activation of the CO2 entity. For this purpose complexes with NiII (CO2 )AM (AM=Li, Na, K) moieties were accessed via deprotonation of nickel-formate compounds with (AM)N(i Pr)2 . It was found that not only the nature of the AM ions in vicinity to CO2 affect the activation, but also the number and the ligation of a given AM. To this end the effects of added (AM)N(R)2 , THF, open and closed polyethers as well as cryptands were systematically studied. In 14 cases the products were characterized by X-ray diffraction and correlations with the situation in solution were made. The more the AM ions get detached from the carbonite ligand, the lower is the degree of aggregation. At the same time the extent of CO2 activation is decreased as indicated by the structural and spectroscopic analysis and reactivity studies. Accompanying DFT studies showed that the coordinating AM Lewis acidic fragment withdraws only a small amount of charge from the carbonite moiety, but it also affects the internal charge equilibration between the LtBu Ni and carbonite moieties.

Cleavage of Carbon Dioxide C=O Bond Promoted by Nickel-Boron Cooperativity in a PBP-Ni Complex

The synthesis and characterization of (tBu PBP)Ni(OAc) (5) by insertion of carbon dioxide into the Ni-C bond of (tBu PBP)NiMe (1) is presented. An unexpected CO2 cleavage process involving the formation of new B-O and Ni-CO bonds leads to the generation of a butterfly-structured tetra-nickel cluster (tBu PBOP)2 Ni4 (μ-CO)2 (6). Mechanistic investigation of this reaction indicates a reductive scission of CO2 by O-atom transfer to the boron atom via a cooperative nickel-boron mechanism. The CO2 activation reaction produces a three-coordinate (tBu P2 BO)Ni-acyl intermediate (A) that leads to a (tBu P2 BO)-NiI complex (B) via a likely radical pathway. The NiI species is trapped by treatment with the radical trap (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) to give (tBu P2 BO)NiII (η2 -TEMPO) (7). Additionally, 13 C and 1 H NMR spectroscopy analysis using 13 C-enriched CO2 provides information about the species involved in the CO2 activation process.

Carbon Dioxide Chemically Responsive Switchable Gas Valves with Protonation-Induced Liquid Gating Self-Adaptive Systems

Carbon dioxide (CO₂ ) capture and storage technologies are promising to limit CO₂ emission from anthropogenic activities, to achieve carbon neutrality goals. CO₂ capture requires one to separate CO₂ from other gases, and therefore a gas flow system that exhibits discernible gating behaviors for CO₂ would be very useful. Here we propose a self-adaptive CO₂ gas valve composed of chemically responsive liquid gating systems. The transmembrane critical pressures of the liquid gate vary upon the presence of CO₂ , due to the superamphiphiles assembled by poly(propylene glycol) bis(2-aminopropyl ether) and oleic acid in gating liquids that are protonated specifically by CO₂ . It is shown that the valve can perform self-adaptive regulation for specific gases and different concentrations of CO₂ . This protonation-induced liquid gating mechanism opens a potential platform for applications of CO₂ separators, detectors, sensors and beyond.

Selective Transformation of Nickel-Bound Formate to CO or C-C Coupling Products Triggered by Deprotonation and Steered by Alkali-Metal Ions

The complexes [LtBu Ni(OCO-κ2 O,C)]M3 [N(SiMe3 )2 ]2 (M=Li, Na, K), synthesized by deprotonation of a nickel formate complex [LtBu NiOOCH] with the corresponding amides M[N(SiMe3 )2 ], feature a NiII -CO2 2- core surrounded by Lewis-acidic cations (M+ ) and the influence of the latter on the behavior and reactivity was studied. The results point to a decrease of CO2 activation within the series Li, Na, and K, which is also reflected in the reactivity with Me3 SiOTf leading to the liberation of CO and formation of a Ni-OSiMe3 complex. Furthermore, in case of K+ , the {[K3 [N(SiMe3 )2 ]2 }+ shell around the Ni-CO2 2- entity was shown to have a large impact on its stabilization and behavior. If the number of K[N(SiMe3 )2 ] equivalents used in the reaction with [LtBu NiOOCH] is decreased from 3 to 0.5, the deprotonated part of the precursor enters a complex reaction sequence with formation of [LtBu NiI (μ-OOCH)NiI LtBu ]K and [LtBu Ni(C2 O4 )NiLtBu ]. The same reaction at higher concentrations additionally led to the formation of a unique hexanuclear NiII complex containing both oxalate and mesoxalate ([O2 C-CO2 -CO2 ]4- ) ligands.

Electron transfer within β-diketiminato nickel bromide and cobaltocene redox couples activating CO2

Reduction of β-diketiminato nickel(ii) complexes (LtBuNiII) to the corresponding nickel(i) compounds does not require alkali metal compounds but can also be performed with the milder cobaltocenes. LtBuNiBr and Cp2Co have rather similar redox potentials, so that the equilibrium with the corresponding electron transfer compound [LtBuNiIBr][Cp2CoIII] (ETC) clearly lies on the side of the starting materials. Still, the ETC portion can be used to activate CO2 yielding a mononuclear nickel(ii) carbonate complex and ETC can be isolated almost quantitatively from the solutions through crystallisation. The more negative reduction potential of Cp*2Co shifts the equilibrium formed with LtBuNiBr strongly towards the ETC and accordingly the reaction of such solutions with CO2 is much faster.

Cp2Ti(κ2-tBuNCNtBu): A Complex with an Unusual κ2 Coordination Mode of a Heterocumulene Featuring a Free Carbene

Although there are myriad binding modes of heterocumulenes to metal centers, the monometallic κ2-ECE (E = O, S, NR) coordination mode has not been reported. Herein, the synthesis, isolation, and physical characterization of Cp2Ti(κ2-tBuNCNtBu) (3) (Cp = cyclopentadienyl, tBu = tert-butyl), a strained 4-membered metallacycle bearing a free carbene, is described. Computational (DFT, CASSCF, QT-AIM, ELF) and solid-state CP-MAS 13C NMR spectroscopic analysis indicate that 3 is best described as a free carbene with partial Ti-Cβ bonding that results from Ti-N π-bonding mixing with N-C-N σ-bonding of the bent N-C-N framework. Reactivity studies of 3 corroborate its carbene-like nature: protonation with [LutH]I results in the formation of a Ti-formamidinate (4), while oxidation with S8 yields a Ti-thioureate (5). Additionally, a related bridged dititanamidocarbene, (Cp2Ti)2(μ-η1,η1-CyNCNCy) (10) (Cy = cyclohexyl) is reported. Taken together, this work suggests that the 2-electron reduction of heterocumulene moieties can allow access to unusual free carbene coordination geometries given the proper stabilizing coordination environment from the reducing transition metal fragment.

Deprotonation of a formato ligand by a cis-coordinated carbyne ligand within a bis(phenolate) tungsten complex

Deprotonation of a formato ligand by a cis-coordinated propylidyne ligand in a tungsten(vi) complex [(OSSO)W([triple bond, length as m-dash]CEt)(OCHO)] (3) that contains a tetradentate bis(phenolato) ligand (OSSO = {1,4-dithiabutanediyl-2,2'-bis(4,6-di-tert-butyl-phenolato)}) gave the dioxo complex [(OSSO)WO2] (4) along with CO, ethylene and propylene as major products of decomposition.

Synthesis and reactivity of a nickel(ii) thioperoxide complex: demonstration of sulfide-mediated N2O reduction

The “masked” terminal nickel sulfide [K(18-crown-6)][L^tBuNi^II(S)] mediates the reduction of N₂O by CO, via the thioperoxide complex [K(18-crown-6)][L^tBuNi^II(η²-SO)].

The thiohyponitrite ([SNNO]^2–) complex, [K(18-crown-6)][L^tBuNi^II(κ²-SNNO)] (L^tBu = {(2,6-ⁱPr₂C₆H₃)NC(^tBu)}₂CH), extrudes N₂ under mild heating to yield [K(18-crown-6)][L^tBuNi^II(η²-SO)] (1), along with minor products [K(18-crown-6)][L^tBuNi^II(η²-OSSO)] (2) and [K(18-crown-6)][L^tBuNi^II(η²-S₂)] (3). Subsequent reaction of 1 with carbon monoxide (CO) results in the formation of [K(18-crown-6)][L^tBuNi^II(η²-SCO)] (4), [K(18-crown-6)][L^tBuNi^II(S,O:κ²-SCO₂)] (5), [K(18-crown-6)][L^tBuNi^II(κ²-CO₃)] (6), carbonyl sulfide (COS) (7), and [K(18-crown-6)][L^tBuNi^II(S₂CO)] (8). To rationalize the formation of these products we propose that 1 first reacts with CO to form [K(18-crown-6)][L^tBuNi^II(S)] (I) and CO₂, via O-atom abstraction. Subsequently, complex I reacts with CO or CO₂ to form 4 and 5, respectively. Similarly, the formation of complex 6 and COS can be rationalized by the reaction of 1 with CO₂ to form a putative Ni(ii) monothiopercarbonate, [K(18-crown-6)][L^tBuNi^II(κ²-SOCO₂)] (11). The Ni(ii) monothiopercarbonate subsequently transfers a S-atom to CO to form COS and [K(18-crown-6)][L^tBuNi^II(κ²-CO₃)] (6). Finally, the formation of 8 can be rationalized by the reaction of COS with I. Critically, the observation of complexes 4 and 5 in the reaction mixture reveals the stepwise conversion of [K(18-crown-6)][L^tBuNi^II(κ²-SNNO)] to 1 and then I, which represents the formal reduction of N₂O by CO.