Oxygen harvesting from carbon dioxide: simultaneous epoxidation and CO formation

Due to increasing concentrations in the atmosphere, carbon dioxide has, in recent times, been targeted for utilisation (Carbon Capture Utilisation and Storage, CCUS). In particular, the production of CO from CO₂ has been an area of intense interest, particularly since the CO can be utilized in Fischer–Tropsch synthesis. Herein we report that CO₂ can also be used as a source of atomic oxygen that is efficiently harvested and used as a waste-free terminal oxidant for the oxidation of alkenes to epoxides. Simultaneously, the process yields CO. Utilization of the atomic oxygen does not only generate a valuable product, but also prevents the recombination of O and CO, thus increasing the yield of CO for possible application in the synthesis of higher-order hydrocarbons.

Selective formation of atomic oxygen to form epoxides in a waste free process is reported. Simultaneously generating carbon monoxide from carbon dioxide for further use.     

Principles of melting in hybrid organic–inorganic perovskite and polymorphic ABX3 structures

Four novel dicyanamide-containing hybrid organic–inorganic ABX₃ structures are reported, and the thermal behaviour of a series of nine perovskite and non-perovskite [AB(N(CN)₂)₃] (A = (C₃H₇)₄N, (C₄H₉)₄N, (C₅H₁₁)₄N; B = Co, Fe, Mn) is analyzed. Structure–property relationships are investigated by varying both A-site organic and B-site transition metal cations. In particular, increasing the size of the A-site cation from (C₃H₇)₄N → (C₄H₉)₄N → (C₅H₁₁)₄N was observed to result in a decrease in T_m through an increase in ΔS_f. Consistent trends in T_m with metal replacement are observed with each A-site cation, with Co < Fe < Mn. The majority of the melts formed were found to recrystallise partially upon cooling, though glasses could be formed through a small degree of organic linker decomposition. Total scattering methods are used to provide a greater understanding of the melting mechanism.

Increasing the size of the A-site cation from (C₃H₇)₄N → (C₄H₉)₄N → (C₅H₁₁)₄N in hybrid organic–inorganic ABX₃ structures was observed to result in a decrease in T_m, through an increase in ΔS_f.     

Intermolecular CDC amination of remote and proximal unactivated Csp3–H bonds through intrinsic substrate reactivity – expanding towards a traceless directing group

An intermolecular radical based distal selectivity in appended alkyl chains has been developed. The selectivity is maximum when the distal carbon is γ to the appended group and decreases by moving from γ → δ → ε positions. In –COO– linked alkyl chains, the same distal γ-selectivity is observed irrespective of its origin, either from the alkyl carboxy acid or alkyl alcohol. The appended groups include esters, N–H protected amines, phthaloyl, sulfone, sulfinimide, nitrile, phosphite, phosphate and borate esters. In borate esters, boron serves as a traceless directing group, which is hitherto unprecedented for any remote C_sp³–H functionalization. The selectivity order follows the trend: 3° benzylic > 2° benzylic > 3° tertiary > α to keto > distal methylene (γ > δ > ε). Computations predicted the radical stability (thermodynamic factors) and the kinetic barriers as the factors responsible for such trends. Remarkably, this strategy eludes any designer catalysts, and the selectivity is due to the intrinsic substrate reactivity.

An intermolecular amination at the distal methylene carbon has been realized in an appended alkyl chain with electron withdrawing groups. Traceless remote C_sp³–H functionalization has been accomplished using borate esters.     

Ni single atoms on carbon nitride for visible-light-promoted full heterogeneous dual catalysis

Visible-light-driven organic transformations are of great interest in synthesizing valuable fine chemicals under mild conditions. The merger of heterogeneous photocatalysts and transition metal catalysts has recently drawn much attention due to its versatility for organic transformations. However, these semi-heterogenous systems suffered several drawbacks, such as transition metal agglomeration on the heterogeneous surface, hindering further applications. Here, we introduce heterogeneous single Ni atoms supported on carbon nitride (NiSAC/CN) for visible-light-driven C–N functionalization with a broad substrate scope. Compared to a semi-heterogeneous system, high activity and stability were observed due to metal–support interactions. Furthermore, through systematic experimental mechanistic studies, we demonstrate that the stabilized single Ni atoms on CN effectively change their redox states, leading to a complete photoredox cycle for C–N coupling.

In this work, the first demonstration of heterogeneous photoredox C–N coupling is reported using Ni atoms on C₃N₄. Due to metal–support interactions, high activity and stability were observed during visible-light-driven C–N functionalization.     

Buffering the local pH via single-atomic Mn–N auxiliary sites to boost CO2 electroreduction

Electrocatalytic CO₂ reduction driven by renewable energy has become a promising approach to rebalance the carbon cycle. Atomically dispersed transition metals anchored on N-doped carbon supports (M-N-C) have been considered as the most attractive catalysts to catalyze CO₂ to CO. However, the sluggish kinetics of M-N-C limits the large-scale application of this type of catalyst. Here, it is found that the introduction of single atomic Mn–N auxiliary sites could effectively buffer the locally generated OH⁻ on the catalytic interface of the single-atomic Ni–N–C sites, thus accelerating proton-coupled electron transfer (PCET) steps to enhance the CO₂ electroreduction to CO. The constructed diatomic Ni/Mn–N–C catalysts show a CO faradaic efficiency of 96.6% and partial CO current density of 13.3 mA cm⁻² at −0.76 V vs. RHE, outperforming that of monometallic single-atomic Ni–N–C or Mn–N–C counterparts. The results suggest that constructing synergistic catalytic sites to regulate the surface local microenvironment might be an attractive strategy for boosting CO₂ electroreduction to value-added products.

An effective strategy is developed to regulate the local microenvironment of single atomic Ni–N–C sites for accelerating CO₂ to CO conversion. The Ni/Mn–N–C catalysts shows a CO faradaic efficiency of 96.6% due to the accelerated reaction kinetics.     

Ultrafast and long-time excited state kinetics of an NIR-emissive vanadium(iii) complex I: synthesis,spectroscopy and static quantum chemistry

In spite of intense, recent research efforts, luminescent transition metal complexes with Earth-abundant metals are still very rare owing to the small ligand field splitting of 3d transition metal complexes and the resulting non-emissive low-energy metal-centered states. Low-energy excited states decay efficiently non-radiatively, so that near-infrared emissive transition metal complexes with 3d transition metals are even more challenging. We report that the heteroleptic pseudo-octahedral d²-vanadium(iii) complex VCl₃(ddpd) (ddpd = N,N′-dimethyl-N,N′-dipyridine-2-yl-pyridine-2,6-diamine) shows near-infrared singlet → triplet spin–flip phosphorescence maxima at 1102, 1219 and 1256 nm with a lifetime of 0.5 μs at room temperature. Band splitting, ligand deuteration, excitation energy and temperature effects on the excited state dynamics will be discussed on slow and fast timescales using Raman, static and time-resolved photoluminescence, step-scan FTIR and fs-UV pump-vis probe spectroscopy as well as photolysis experiments in combination with static quantum chemical calculations. These results inform future design strategies for molecular materials of Earth-abundant metal ions exhibiting spin–flip luminescence and photoinduced metal–ligand bond homolysis.

Vanadium is an abundant and cheap metal but near-infrared luminescent vanadium complexes are extremely rare with largely unexplored photophysics and photochemistry. We delineate the photodynamics of VCl₃(ddpd) to infer novel design strategies.     

Organometallic motifs in the structures of solid state ternary carbides of the late transition metals

Solid state ternary transition metal carbides containing carbon, a middle to late transition metal (Re to Ni), and a highly electropositive multivalent metal such as lanthanide, yttrium, or thorium exhibit a number of structural motifs resembling those in metal carbonyls and other transition metal derivatives of strong -acceptor ligands. This paper presents models for the chemical bonding in the transition metal—carbon subnetworks of the ternary late transition metal carbides LnCoC (Ln=lanthanide), Ln₂ReC₂, Th₂NiC₂, Ln₂FeC₄, Ln₃MC₄ (M=Fe, Co, Ni, Ru, Rh, Os, Ir), Ln₄NiC₅, Ca₄Ni₃C₅, and Er₈Rh₅C₁₂. Carbide ligands present in such materials include terminal C^4– in Th₂NiC₂ and Y₂ReC₂, ₂-C^4– in YCoC or Y₂ReC₂ similar to the central allene carbon atom, 1,2-bridging C ₂ ^4– in Sc₃CoC₄ formally derived from ethylene, ₃-bridging C ₂ ^4– in LnMC₂ (M=Fe, Co, Ni, Ru) formally derived from ethylene, and 1,1-bridging C ₂ ^2– in Ln₂FeC₄ isoelectronic with ₂-CO group in metal carbonyls.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1358–1366, August, 1994.     

Metal complexes of allyl derivatives of C60 fullerene: molecular and electronic structure prediction from density functional calculations

The problem of existence of ³—-complexes of C₆₀ fullerene with transition metal atoms is discussed. The complexes C₆₀R₃Co(CO)₃ (R = H, F, Cl, Br), C₆₀H₃NiCp, and C₆₀H₃Fe(CO)Cp, where C₆₀R₃ is an allyl derivative of C₆₀ fullerene, were shown to be sufficiently stable. In these complexes the metal atoms are ³—-bound to the fullerene cage. In contrast to this, the metal atoms in the C₆₀H₃Li and C₆₀H₃FeCp complexes are ⁵—-coordinated to the carbon cage. Density functional calculations were carried out with the Perdew—Burke—Ernzerhof exchange-correlation potential (PBE). It was concluded that the type of bonding in the complexes of allyl derivatives of C₆₀ fullerene depends on the nature of the species attached. Among the systems studied, the maximum energy of the ³—-bond was obtained for the C₆₀H₃NiCp complex. The results obtained can be useful in the design of synthesis of new fullerene derivatives with the ³—-coordination of the transition metal atoms to the carbon cage.     

Arsolyl-supported intermetallic dative bonding

The first examples of late transition metal η⁵-arsolyls (L = CO, P(OMe)₃; R = Ph, Me, Et, SiMe₃; R′ = Ph, H, Me, Et, Me) serve as ditopic donors to extraneous metal centres (M = Pt^II, Au^I, Hg^II) through both conventional As → M and polar-covalent (dative) Co → M interactions.

Cobalt carbonyl reacts with arsoles to provide the first late transition metal η⁵-arsolyls. These serve as ditopic donors to extraneous metal centres (M = Pt^II, Au^I, Hg^II) through both conventional AsM and polar-covalent (dative) CoM interactions.     

ThC2@C82versus Th@C84: unexpected formation of triangular thorium carbide cluster inside fullerenes

Synthesis of the first thorium-containing clusterfullerenes, ThC₂@C_s(6)–C₈₂ and ThC₂@C₂(5)–C₈₂, is reported. These two novel actinide fullerene compounds were characterized by mass spectrometry, single-crystal X-ray diffraction crystallography, UV–vis–NIR spectroscopy, and theoretical calculations. Crystallographic studies reveal that the encapsulated ThC₂ clusters in both C_s(6)–C₈₂ and C₂(5)–C₈₂ feature a novel bonding structure with one thorium metal center connected by a C C unit, forming an isosceles triangular configuration, which has not been hitherto observed for endohedral fullerenes or for solid phase thorium carbides. Electronic structure calculations assign a formal electronic structure of [Th⁴⁺(C₂)²⁻]²⁺@[C₈₂]²⁻, with pronounced donation bonding from (C₂)²⁻ to Th⁴⁺, secondary backbonding from the fullerene to thorium and Th–C double bond character in both compounds. This work presents a new family of endohedral fullerenes, MC₂@C_2n−2, being unexpected isomers of MC_2n, and provides broader understanding of thorium bonding.

The first thorium-containing cluster fullerenes, ThC₂@C_s(6)–C₈₂ and ThC₂@C₂(5)–C₈₂, were synthesized and characterized. ThC₂ clusters in both C₈₂ cages feature a novel bonding structure with thorium metal and C C forming an isosceles triangular configuration.     

Catalytic Reduction of CN−, CO,and CO2 by Nitrogenase Cofactors in Lanthanide‐Driven Reactions

Nitrogenase cofactors can be extracted into an organic solvent to catalyze the reduction of cyanide (CN⁻), carbon monoxide (CO), and carbon dioxide (CO₂) without using adenosine triphosphate (ATP), when samarium(II) iodide (SmI₂) and 2,6‐lutidinium triflate (Lut‐H) are employed as a reductant and a proton source, respectively. Driven by SmI₂, the cofactors catalytically reduce CN⁻ or CO to C₁–C₄ hydrocarbons, and CO₂ to CO and C₁–C₃ hydrocarbons. The C C coupling from CO₂ indicates a unique Fischer–Tropsch‐like reaction with an atypical carbonaceous substrate, whereas the catalytic turnover of CN⁻, CO, and CO₂ by isolated cofactors suggests the possibility to develop nitrogenase‐based electrocatalysts for the production of hydrocarbons from these carbon‐containing compounds.     

Catalytic Reduction of CN−, CO,and CO2 by Nitrogenase Cofactors in Lanthanide‐Driven Reactions

Nitrogenase cofactors can be extracted into an organic solvent to catalyze the reduction of cyanide (CN^?), carbon monoxide (CO), and carbon dioxide (CO₂) without using adenosine triphosphate (ATP), when samarium(II) iodide (SmI₂) and 2,6‐lutidinium triflate (Lut‐H) are employed as a reductant and a proton source, respectively. Driven by SmI₂, the cofactors catalytically reduce CN^? or CO to C₁–C₄ hydrocarbons, and CO₂ to CO and C₁–C₃ hydrocarbons. The C? C coupling from CO₂ indicates a unique Fischer–Tropsch‐like reaction with an atypical carbonaceous substrate, whereas the catalytic turnover of CN^?, CO, and CO₂ by isolated cofactors suggests the possibility to develop nitrogenase‐based electrocatalysts for the production of hydrocarbons from these carbon‐containing compounds.     

CO reductive oligomerization by a divalent thulium complex and CO2-induced functionalization

The divalent thulium complex [Tm(Cp^ttt)₂] (Cp^ttt = 1,2,4-tris(tert-butyl)cyclopentadienyl) reacts with CO to afford selective CO reductive dimerization and trimerization into ethynediolate (C₂) and ketenecarboxylate (C₃) complexes, respectively. DFT calculations were performed to shed light on the elementary steps of CO homologation and support a stepwise chain growth. The attempted decoordination of the ethynediolate fragment by treatment with Me₃SiI led to dimerization and rearrangement into a 3,4-dihydroxyfuran-2-one complex. Investigation of the reactivity of the C₂ and C₃ complexes towards other electrophiles led to unusual functionalization reactions: while the reaction of the ketenecarboxylate C₃ complex with electrophiles yielded new multicarbon oxygenated complexes, the addition of CO₂ to the ethynediolate C₂ complex resulted in the formation of a very reactive intermediate, allowing C–H activation of aromatic solvents. This original intermolecular reactivity corresponds to an unprecedented functionalization of CO-derived ligands, which is induced by CO₂.

The divalent thulium complex [Tm(Cp^ttt)₂] activates CO to form reductive CO dimerization or trimerization products. These complexes further react with electrophiles, including CO₂, yielding multicarbon oxygenates and original C–H activation products.     

Migratory insertion of isocyanide into a ketenyl–tungsten bond as key step in cyclization reactions

Treatment of the side-on tungsten alkyne complex of ethinylethyl ether [Tp*W(CO)₂(η²-C,C′-HCCOCH₂CH₃)]⁺ {Tp* = hydridotris(3,4,5-trimethylpyrazolyl)borate} (2a) with n-Bu₄NI afforded the end-on ketenyl complex [Tp*W(CO)₂(κ¹-HCCO)] (4a). This formal 16 ve complex bearing the prototype of a ketenyl ligand is surprisingly stable and converts only under activation by UV light or heat to form a dinuclear complex [Tp*₂W₂(CO)₄(μ-CCH₂)] (6). The ketenyl ligand in complex 4a underwent a metal template controlled cyclization reaction upon addition of isocyanides. The oxametallacycles [Tp*W(CO)₂{κ²-C,O-C(NHXy)C(H)C(Nu)O}] {Nu = OMe (7), OEt (8), N(i-Pr)₂ (9), OH (10), O_1/2 (11)} were formed by coordination of Xy-NC (Xy = 2,6-dimethylphenyl) at 4a and subsequent migratory insertion (MI) into the W-ketenyl bond. The resulting intermediate is susceptible to addition reactions with protic nucleophiles. Compounds 2a-PF₆, 4a/b, and 7–11 were fully characterized including XRD analysis. The cyclization mechanism has been confirmed both experimentally and by DFT calculations. In cyclic voltammetry, complexes 7–9 are characterized by a reversible W(ii)/W(iii) redox process. The dinuclear complex 11 however shows two separated redox events. Based on cyclic voltammetry measurements with different conducting electrolytes and IR spectroelectrochemical (SEC) measurements the W(ii)/W(iii) mixed valent complex 11⁺ is assigned to class II in terms of the Robin-Day classification.

The prototype ketenyl ligand is bound end-on despite a formal 16 valence electron count at the metal. This situation opens a reaction pathway for a multicomponent cyclization centred on the migration of the ketenyl ligand.     

Towards new coordination modes of 1,2,3-triazolylidene: controlled by the nature of the 1st metalation in a heteroditopic bis-NHC ligand

An unusual effect of the nature of the first metal coordination of a heteroditopic N-heterocyclic carbene ligand (L2) towards the coordination behavior of 1,2,3-tzNHC is explored. The first metal coordination at the ImNHC site (complexes 3 and 4) was noted to substantially influence the electronics of the 1,2,3-triazolium moiety leading to an unprecedented chemistry of this MIC donor. Along this line, the Rh^III/Ir^III-orthometalation in complexes 4 makes the triazolium C₄–H more downfield shifted than C₅–H, whereas a reverse trend, although to a lesser extent, is observed in the case of the non-chelated Pd^II-coordination. This difference in behavior assisted us to achieve the selective activation of triazole C₄/C₅ positions, not observed before, as supported by the isolation of the homo- and hetero-bimetallic complexes, 5, 6 and 7–9via C₅- and C₄-metalation, respectively. Furthermore, the %V_bur calculations eliminate any considerable steric influence and the DFT studies strongly support the selectivity observed during bimetalation.

The nature of the first metal coordination electronically influences the 1,2,3-triazolium moiety in [L2-H₂]Br₂, which leads to the unprecedented selective activation of triazole C₄/C₅ positions as supported by the isolation of several bimetallic complexes.     

Scaffold-based [Fe]-hydrogenase model: H2 activation initiates Fe(0)-hydride extrusion and non-biomimetic hydride transfer

We report the synthesis and reactivity of a model of [Fe]-hydrogenase derived from an anthracene-based scaffold that includes the endogenous, organometallic acyl(methylene) donor. In comparison to other non-scaffolded acyl-containing complexes, the complex described herein retains molecularly well-defined chemistry upon addition of multiple equivalents of exogenous base. Clean deprotonation of the acyl(methylene) C–H bond with a phenolate base results in the formation of a dimeric motif that contains a new Fe–C(methine) bond resulting from coordination of the deprotonated methylene unit to an adjacent iron center. This effective second carbanion in the ligand framework was demonstrated to drive heterolytic H₂ activation across the Fe(ii) center. However, this process results in reductive elimination and liberation of the ligand to extrude a lower-valent Fe–carbonyl complex. Through a series of isotopic labelling experiments, structural characterization (XRD, XAS), and spectroscopic characterization (IR, NMR, EXAFS), a mechanistic pathway is presented for H₂/hydride-induced loss of the organometallic acyl unit (i.e. pyCH₂–C O → pyCH₃+C O). The known reduced hydride species [HFe(CO)₄]⁻ and [HFe₃(CO)₁₁]⁻ have been observed as products by ¹H/²H NMR and IR spectroscopies, as well as independent syntheses of PNP[HFe(CO)₄]. The former species (i.e. [HFe(CO)₄]⁻) is deduced to be the actual hydride transfer agent in the hydride transfer reaction (nominally catalyzed by the title compound) to a biomimetic substrate ([^TolIm](BAr^F) = fluorinated imidazolium as hydride acceptor). This work provides mechanistic insight into the reasons for lack of functional biomimetic behavior (hydride transfer) in acyl(methylene)pyridine based mimics of [Fe]-hydrogenase.

We report the synthesis and reactivity of a model of [Fe]-hydrogenase derived from an anthracene-based scaffold that includes the endogenous, organometallic acyl(methylene) donor.     

Spatial disposition of square-planar mononuclear nodes in metal–organic frameworks for C2H2/CO2 separation

The efficient separation of acetylene (C₂H₂) from its mixture with carbon dioxide (CO₂) remains a challenging industrial process due to their close molecular sizes/shapes and similar physical properties. Herein, we report a microporous metal–organic framework (JNU-4) with square-planar mononuclear copper(ii) centers as nodes and tetrahedral organic linkers as spacers, allowing for two accessible binding sites per metal center for C₂H₂ molecules. Consequently, JNU-4 exhibits excellent C₂H₂ adsorption capacity, particularly at 298 K and 0.5 bar (200 cm³ g⁻¹). Detailed computational studies confirm that C₂H₂ molecules are indeed predominantly located in close proximity to the square-planar copper centers on both sides. Breakthrough experiments demonstrate that JNU-4 is capable of efficiently separating C₂H₂ from a 50 : 50 C₂H₂/CO₂ mixture over a broad range of flow rates, affording by far the largest C₂H₂ capture capacity (160 cm³ g⁻¹) and fuel-grade C₂H₂ production (105 cm³ g⁻¹, ≥98% purity) upon desorption. Simply by maximizing accessible open metal sites on mononuclear metal centers, this work presents a promising strategy to improve the C₂H₂ adsorption capacity and address the challenging C₂H₂/CO₂ separation.

C₂H₂/CO₂ separation is a challenging industrial process. We report a microporous MOF (JNU-4a) with square-planar mononuclear copper(ii) centers, allowing for a record high C₂H₂ capture capacity from an equimolar C₂H₂/CO₂ mixture.     

Metal triangles as building blocks in metal cluster chemistry

Many trinuclear metal clusters have structures based on isolated metal triangles with either single bonds (e.g.,M ₃(CO)₁₂ whereM = Fe, Ru, Os) or double bonds (e.g., Re₃ Cl ₁₂ ^3– ) along each edge of the triangle. Individual metal triangles can be joined in the following ways to form more complicated triangulated networks: (1) Bridging an edge of a triangle with a new vertex to give rafts in which adjacent triangles share edges; (2) Bridging a vertex of a triangle with a new edge to give bowties in which adjacent triangles share vertices; (3) Capping a triangular face with a new vertex to give a chain of tetrahedra in which adjacent tetrahedra share faces. Such triangulated metal networks are particularly common in osmium carbonyl chemistry and in mixed osmium/platinum carbonyl derivatives. Platinum triangles of the type Pt₃L₆ are analogous to cyclopropenyl rings and can form sandwiches with one or two mercury atoms in the center such as the mercuric derivative Hg[Pt.₃(µ₂-2,6-Me₂C₆H₃NC)₃] (2,6-Me₂C₆H₃NC)₃]₂ and the mercurous derivative Hg₂[Pt₃(µ₂-CO)₃L₃]₂. Platinum triangles can also be stacked in the absence of filling to give [Pt₃(µ₂-CO)₃(CO)₃] _n ^2– (n=2, 3, 4, 5, 6, 10). Metal triangles also form the faces of metal deltahera of which the octahedron, bicapped square antiprism, and icosahedron are found in globally delocalized transition metal clusters.This article is dedicated to Prof. L. F. Dahl in recognition of his many seminal contributions to metal cluster chemistry.     

Coinage metal aluminyl complexes: probing regiochemistry and mechanism in the insertion and reduction of carbon dioxide

The synthesis of coinage metal aluminyl complexes, featuring M–Al covalent bonds, is reported via a salt metathesis approach employing an anionic Al(i) (‘aluminyl’) nucleophile and group 11 electrophiles. This approach allows access to both bimetallic (1 : 1) systems of the type (^tBu₃P)MAl(NON) (M = Cu, Ag, Au; NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) and a 2 : 1 di(aluminyl)cuprate system, K[Cu{Al(NON)}₂]. The bimetallic complexes readily insert heteroallenes (CO₂, carbodiimides) into the unsupported M–Al bonds to give systems containing a M(CE₂)Al bridging unit (E = O, NR), with the μ-κ¹(C):κ²(E,E′) mode of heteroallene binding being demonstrated crystallographically for carbodiimide insertion in the cases of all three metals, Cu, Ag and Au. The regiochemistry of these processes, leading to the formation of M–C bonds, is rationalized computationally, and is consistent with addition of CO₂ across the M–Al covalent bond with the group 11 metal acting as the nucleophilic partner and Al as the electrophile. While the products of carbodiimide insertion are stable to further reaction, their CO₂ analogues have the potential to react further, depending on the identity of the group 11 metal. (^tBu₃P)Au(CO)₂Al(NON) is inert to further reaction, but its silver counterpart reacts slowly with CO₂ to give the corresponding carbonate complex (and CO), and the copper system proceeds rapidly to the carbonate even at low temperatures. Experimental and quantum chemical investigations of the mechanism of the CO₂ to CO/carbonate transformation are consistent with rate-determining extrusion of CO from the initially-formed M(CO)₂Al fragment to give a bimetallic oxide that rapidly assimilates a second molecule of CO₂. The calculated energetic barriers for the most feasible CO extrusion step (ΔG^‡ = 26.6, 33.1, 44.5 kcal mol⁻¹ for M = Cu, Ag and Au, respectively) are consistent not only with the observed experimental labilities of the respective M(CO)₂Al motifs, but also with the opposing trends in M–C (increasing) and M–O bond strengths (decreasing) on transitioning from Cu to Au.

The differential reactivity of copper, silver and gold aluminyl compounds towards CO₂ and other heteroallenes are probed by experimental and quantum chemical methods.     

Synthesis of Pt–Mo/Carbon Nanocomposites from Single-Source Molecular Precursors: A (1:1) PtMo/C PEMFC Anode Catalyst Exhibiting CO Tolerance*

Reactive, thermal degradation of py₂Pt[MoCp(CO)₃]₂, (Me)(cod)PtMoCp(CO)₃, or [BPh₄]/Vulcan carbon powder composites affords Pt–Mo/carbon nanocomposites containing metal nanoparticles of approximate compositions, PtMo₂, PtMo, or Pt₃Mo, widely dispersed on the carbon support. Total metal loadings range from 29–58 wt%. When tested as an anode electrocatalyst in a PEM fuel cell using either pure H₂ or H₂ containing 100 ppm CO as a fuel, the PtMo/carbon nanocomposite exhibits CO tolerance.Dedicated to F. A. Cotton on the occasion of his 75th birthday.