A terminal molybdenum carbide prepared by methylidyne deprotonation

The carbide anion [CMo{N(R)Ar}_3]– [R = C(CD_3)_2CH_3, Ar = C_6H_3Me_2-3,5], is obtained by deprotonation of the corresponding methylidyne compound, [HCMo{N(R)Ar}_3], and is characterized by X-ray diffraction as its {K(benzo-15-crown-5)_2}+ salt, thereby providing precedent for the carbon atom as a terminal substituent in transition-metal chemistry

Radical anionic versus neutral 2,2′-bipyridyl coordination in uranium complexes supported by amide and ketimide ligands

The synthesis and characterization of (bipy)₂U(N[t-Bu]Ar)₂ (1-(bipy)₂, bipy = 2,2′-bipyridyl, Ar = 3,5-C₆H₃Me₂), (bipy)U(N[1Ad]Ar)₃ (2-bipy), (bipy)₂U(NC[t-Bu]Mes)₃ (3-(bipy)2, Mes = 2,4,6-C₆H₂Me₃), and IU(bipy)(NC[t-Bu]Mes)₃ (3-I-bipy) are reported. X-ray crystallography studies indicate that bipy coordinates as a radical anion in 1-(bipy)₂ and 2-bipy, and as a neutral ligand in 3-I-bipy. In 3-(bipy)₂, one of the bipy ligands is best viewed as a radical anion, the other as a neutral ligand. The electronic structure assignments are supported by NMR spectroscopy studies of exchange experiments with 4,4′-dimethyl-2,2′-bipyridyl and also by optical spectroscopy. In all complexes, uranium was assigned a +4 formal oxidation state.National Science Foundation (U.S.) (Grant CHE-9988806

Tetraphosphabenzenes Obtained via a Triphosphacyclobutadiene Intermediate

An acyl triphosphirene ligand transfers an O atom to Nb to liberate the putative triphosphacyclobutadiene intermediate [RCP3{W(CO)5}2], which engages in [2+4]-cycloaddition reactions with an organic diene and a phosphaalkyne (see scheme; P orange, O red, W violet, C white). The latter reaction yields the Dewar isomer of a tetraphosphabenzene, which can be converted to a tetraphosphabenzvalene containing a Z-diphosphene.National Science Foundation (U.S.) (grant CHE-719157

Experimental and computational studies on the formation of cyanate from early metal terminal nitrido ligands and carbon monoxide

An important challenge in the artificial fixation of N[subscript 2] is to find atom efficient transformations that yield value-added products. Here we explore the coordination complex mediated conversion of ubiquitous species, CO and N[subscript 2], into isocyanate. We have conceptually split the process into three steps: (1) the six-electron splitting of dinitrogen into terminal metal nitrido ligands, (2) the reduction of the complex by two electrons with CO to form an isocyanate linkage, and (3) the one electron reduction of the metal isocyanate complex to regenerate the starting metal complex and release the product. These steps are explored separately in an attempt to understand the limitations of each step and what is required of a coordination complex in order to facilitate a catalytic cycle. The possibility of this cyanate cycle was explored with both Mo and V complexes which have previously been shown to perform select steps in the sequence. Experimental results demonstrate the feasibility of some of the steps and DFT calculations suggest that, although the reduction of the terminal metal nitride complex by carbon monoxide should be thermodynamically favorable, there is a large kinetic barrier associated with the change in spin state which can be avoided in the case of the V complexes by an initial binding of the CO to the metal center followed by rearrangement. This mandates certain minimal design principles for the metal complex: the metal center should be sterically accessible for CO binding and the ligands should not readily succumb to CO insertion reactions.National Science Foundation (U.S.) (CHE-1111357

An exploding N-isocyanide reagent formally composed of anthracene, dinitrogen and a carbon atom

Targeted as an example of a compound composed of a carbon atom together with two stable neutral leaving groups, 7-isocyano-7-azadibenzonorbornadiene, CN[subscript 2]A (1, A = C[subscript 14]H[subscript 10] or anthracene) has been synthesized and spectroscopically and structurally characterized. The terminal C atom of 1 can be transferred: mesityl nitrile oxide reacts with 1 to produce carbon monoxide, likely via intermediacy of the N-isocyanate OCN[subscript 2]A. Reaction of 1 with [RuCl[subscript 2](CO)(PCy[subscript 3])[subscript 2]] leads to [RuCl2(CO)(1)(PCy3)2] which decomposes unselectively: in the product mixture, the carbide complex [RuCl[subscript 2[](C)(PCy[subscript 3])[subscript 2]] was detected. Upon heating in the solid state or in solution, 1 decomposes to A, N2 and cyanogen (C2N2) as substantiated using molecular beam mass spectrometry, IR and NMR spectroscopy techniques.Alexander von Humboldt Foundation (Feodor Lynen Postdoctoral Fellowship

Uptake of one and two molecules of CO2 by the molybdate dianion: a soluble, molecular oxide model system for carbon dioxide fixation

Tetrahedral [MoO4][superscript 2−] readily binds CO[subscript 2] at room temperature to produce a robust monocarbonate complex, [MoO[subscript 3](κ[superscript 2]-CO[subscript 3])][superscript 2−], that does not release CO[subscript 2] even at modestly elevated temperatures (up to 56 °C in solution and 70 °C in the solid state). In the presence of excess carbon dioxide, a second molecule of CO[subscript 2] binds to afford a pseudo-octahedral dioxo dicarbonate complex, [MoO[subscript 2](κ[superscript 2]-CO[subscript 3])[subscript 2][superscript 2−], the first structurally characterized transition-metal dicarbonate complex derived from CO[subscript 2]. The monocarbonate [MoO[subscript 3](κ[superscript 2]-CO[subscript 3])][superscript 2−] reacts with triethylsilane in acetonitrile under an atmosphere of CO[subscript 2] to produce formate (69% isolated yield) together with silylated molybdate (quantitative conversion to [MoO[subscript 3](OSiEt[subscript 3])][superscript −], 50% isolated yield) after 22 hours at 85 °C. This system thus illustrates both the reversible binding of CO[subscript 2] by a simple transition-metal oxoanion and the ability of the latter molecular metal oxide to facilitate chemical CO[subscript 2] reduction.Saudi Basic Industries CorporationSpain. Ministerio de Educación, Cultura y DeporteSpain. Ministerio de Economía y Competitividad (CTQ2012-36966)National Science Foundation (U.S.) (CHE-1111357)National Science Foundation (U.S.) (CHE- 0946721

Rationalizing the Different Products in the Reaction of N\u3csub\u3e2\u3c/sub\u3e with Three-coordinate MoL\u3csub\u3e3\u3c/sub\u3e Complexes

The reaction of N2 with three-coordinate MoL3 complexes is known to give rise to different products, N–MoL3, L3Mo–N–MoL3 or Mo2L6, depending on the nature of the ligand L. The energetics of the different reaction pathways are compared for L = NH2, NMe2, N(iPr)Ar and N(tBu)Ar (Ar = 3,5-C6H3Me2) using density functional methods in order to rationalize the experimental results. Overall, the exothermicity of each reaction pathway decreases as the ligand size increases, largely due to the increased steric crowding in the products compared to reactants. In the absence of steric strain, the formation of the metal–metal bonded dimer, Mo2L6, is the most exothermic pathway but this reaction shows the greatest sensitivity to ligand size varying from significantly exothermic, −403 kJ mol−1 for L = NMe2, to endothermic, +78 kJ mol−1 for L = N(tBu)Ar. For all four ligands, formation of N–MoL3via cleavage of the N2 bridged dimer intermediate, L3Mo–N–N–MoL3, is strongly exothermic. However, in the presence of excess reactant MoL3, formation of the single atom-bridged complex L3Mo–N–MoL3 from N–MoL3 + MoL3 is both thermodynamically and kinetically favoured for L = NMe2 and N(iPr)Ar, in agreement with experiment. In the case of L = N(tBu)Ar, the greater steric bulk of the tBu group results in a much less exothermic reaction and a calculated barrier of 66 kJ mol−1 to formation of the L3Mo–N–MoL3 dimer. Consequently, for this ligand, the energetically and kinetically favoured product, consistent with the experimental data, is the nitride complex L3Mo–N

Facile synthesis of mononuclear early transition-metal complexes of κ3cyclo-tetrametaphosphate ([P4O12]4−) and cyclo-trimetaphosphate ([P3O9]3−)

We herein report the preparation of several mononuclear-metaphosphate complexes using simple techniques and mild conditions with yields ranging from 56% to 78%. Treatment of cyclo-tetrametaphosphate ([TBA]4[P4O12]·5H2O, TBA = tetra-n-butylammonium) with various metal sources including (CH3CN)3Mo(CO)3, (CH3CN)2Mo(CO)2(η3-C3H5)Cl, MoO2Cl2(OSMe2)2, and VOF3, leads to the clean and rapid formation of [TBA]4[(P4O12)Mo(CO)3]·2H2O, [TBA]3[(P4O12)Mo(CO)2(η3-C3H5)], [TBA]3[(P4O12)MoO2Cl] and [TBA]3[(P4O12)VOF2]·Et2O salts in isolated yields of 69, 56, 68, and 56% respectively. NMR spectroscopy, NMR simulations and single crystal X-ray studies reveal that the [P4O12]4− anion behaves as a tridentate ligand wherein one of the metaphosphate groups is not directly bound to the metal. cyclo-Trimetaphosphate-metal complexes were prepared using a similar procedure i.e., treatment of [PPN]3[P3O9]·H2O (PPN = bis(triphenylphosphine)iminium) with the metal sources (CH3CN)2Mo(CO)2(η3-C3H5)Cl, MoO2Cl2(OSMe2)2, MoOCl3, VOF3, WOCl4, and WO2Cl2(CH3CN)2 to produce the corresponding salts, [PPN]2[(P3O9)Mo(CO)2(η3-C3H5)], [PPN]2[(P3O9)MoO2Cl], [PPN]2[(P3O9)MoOCl2], [PPN]2[(P3O9)VOF2]·2CH2Cl2, and [PPN]2[(P3O9)WO2Cl] in isolated yields of 78, 56, 75, 59, and 77% respectively. NMR spectroscopy, NMR simulations and single-crystal X-ray studies indicate that the trianionic ligand [P3O9]3− in these complexes also has κ3 connectivity.Eni S.p.A. (Firm)Eni-MIT Solar Frontiers Center (Program

Methine (CH) Transfer via a Chlorine Atom Abstraction/Benzene-Elimination Strategy: Molybdenum Methylidyne Synthesis and Elaboration to a Phosphaisocyanide Complex

Methine (CH) transfer to an open coordination site was achieved in one pot by titanium(III) abstraction of Cl from 7-chloronorbornadiene, radical capture by Mo, and benzene extrusion. This efficient Mo methylidyne synthesis permitted elaboration to an anionic phosphaisocyanide derivative upon deprotonation, functionalization with dichlorophenylphosphine, and ultimate reduction