An experimental and theoretical investigation of the carbon dioxide insertion process into the tungsten-nitrogen bond of an anionic W(0) complex

Sustainable synthesis of CO2-derived polycarbonates from d-xylose

Synthetic transformation of d-xylose into a four-membered cyclic ether allows for reactions with CO2 leading to linear polycarbonates by either ring-opening copolymerisation directly or by isolation of a six-membered cyclic carbonate followed by ring-opening polymerisation.

Carbon dioxide and related heterocumulenes at zinc and lithium cations: bioinspired reactions and principles

This Perspective starts with the discussion of the properties of an interesting metalloenzyme (carbonic anhydrase, CA) that performs extremely successfully the activation of carbon dioxide. Conclusions from that are important for many synthetic procedures and include experimental and theoretical investigation (DFT calculations) of such metal mediated processes in the condensed and in the gas phase in which the zinc cation plays a dominant role. This is extended to the bio-analogue activation of further heterocumulenes such as COS, an important atmospheric trace gas, and CS(2). Novel metal complexes which serve as useful catalysts for the reactions (copolymerisations and cyclisation) of CO(2) and oxiranes are discussed subject to the inclusion of recently published DFT calculations. We continue with the discussion of the very general aspect of the insertion of CO(2) into metal-nitrogen bonds (formation of carbamates). This again is closely related to many biological or bio-analogue processes. We describe the synthesis and mechanistic aspects of characteristic metal carbamates of a wide variety of metals and include a discussion of the mechanistic aspects, especially for the formation of Mg(2+) and Li(+) carbamates and the formation of related cyclic products after addition of the heterocumulenes CO(2), Ph-NCO or CS(2) to novel ligands, the 4H-pyridin-1-ides which finally result in the formation of e.g. 1,3-thiazole-5(2H)-thiones.

Evidence for unimolecular CO2 elimination in C-N bond metathesis reactions of basic carbamatozinc complexes Zn4O(O2CAm)6(Am=N-diethylamino, N-piperidyl, N-pyrrolidyl)

The tetranuclear basic zinc carbamates Zn4O(O2CAm)6(1, Am =N-diethylamino; 2, Am =N-piperidyl; 3, Am =N-pyrrolidyl) were shown by transient FTIR spectroscopy to undergo C-N bond metathesis reactions that result in exchange of the carboxyl group with bulk carbon dioxide and exchange of the amino group with bulk secondary amine (transamination). The net rate for CO2 exchange was measured by monitoring the uptake of 13CO2 and the concomitant release of 12CO2. This revealed a CO2-dependent and CO2-independent component to the CO2 exchange process. The CO2-dependent process was interpreted in terms of preassociation of the incoming CO2 with the complex prior to the N-CO2 bond cleavage process while the CO2-independent process was interpreted in terms of a unimolecular elimination of CO2 from the complex. The transamination reaction gave rates that are independent of the concentration of the incoming amine. Furthermore, the transamination rate for each complex was within a factor of four of the CO2-independent CO2 exchange rate for that complex. These data were interpreted in terms of a common rate-limiting process for CO2 exchange and transamination that involves unimolecular elimination of CO2. Rate-limiting unimolecular dissociation of intact carbamato ligands was eliminated as a possible pathway by showing that ligand exchange dynamics is rapid relative to the overall rate of C-N bond metathesis. The ability of these metal carbamate complexes to undergo facile C-N bond metathesis reactions of this type has implications in heterocumulene metathesis and CO2 fixation chemistry.

Reaction of (mu-oxo)diiron(III) core with CO2 in N-methylimidazole: formation of mono(mu-carboxylato)(mu-oxo)diiron(III) complexes with N-methylimidazole as ligands

Several iron(III) complexes with N-methylimidazole (N-MeIm) as the ligand have been synthesized by using N-MeIm as the solvent. Under anaerobic conditions, [Fe(N-MeIm)(6)](ClO(4))(3) (1) reacts with stoichiometric amounts of water in N-MeIm to afford the (mu-oxo)diiron(III) complex, [Fe(2)(mu-O)(N-MeIm)(10)](ClO(4))(4) (3). Exposure of a solution of 3 in N-MeIm to stoichiometric and excess CO(2) gives rise to the (mu-oxo)(mu-carboxylato)diiron(III) species [Fe(2)(mu-O)(mu-HCO(2))(N-MeIm)(8)](ClO(4))(3) (4) and the methyl carbonate complex [Fe(2)(mu-O)(mu-CH(3)OCO(2))(N-MeIm)(8)](ClO(4))(3) (5), respectively. Formation of the formato-bridged complex 4 upon fixation of CO(2) by 3 in N-MeIm is unprecedentated. Methyl transfer from N-MeIm to a bicarbonato-bridged (mu-oxo)diiron(III) intermediate appears to give rise to 5. Complex 3 is a good starting material for the synthesis of (mu-oxo)mono(mu-carboxylato)diiron(III) species [Fe(2)(mu-O)(mu-RCO(2))(N-MeIm)(8)](ClO(4))(3) (where R = H (4), CH(3) (6), or C(6)H(5) (7)); addition of the respective carboxylate ligand in stoichiometric amount to a solution of 3 in N-MeIm affords these complexes in high yields. Attempts to add a third bridge to complexes 4, 6, and 7 to form the (mu-oxo)bis(mu-carboxylato)diiron(III) species result in the isolation of the previously known triiron(III) mu-eta(3)-oxo clusters [[Fe(mu-RCO(2))(2)(N-MeIm)](3)O](ClO(4)) (8). The structures of 3, 4, 6, and 7 allow one, for the first time, to inspect the various features of the [Fe(2)(mu-O)(mu-RCO(2))](3+) moiety with no strain from the ligand framework.