Matrix isolated metal carbonyl anions

Cocondensation at 20K of sodium atoms with transition metal carbonyls (e.g. Cr(CO)₆) diluted in argon gives IR spectroscopic evidence for carbonyl anions (e.g. Cr(CO)₅⁻).     

Insertion reactions of metal carbonyl anions with methyl formate in the gas phase as revealed by 13C- and D-labeling

School of Chemistry, University of New South Wales, Kensington, Australia Institute of Mass Spectrometry, University of Amsterdam, Nieuwe Achtergracht The gas-phase reactions of coordinatively unsaturated metal carbonyl anions (M(CO) _n ^? , M=Cr, Mn, Fe, Co; n=0-3 and Co(CO)_nNO^?, n=0-2) with unlabeled and D- and ¹³C-labeled methyl formate have been studied with Fourier transform ion cyclotron resonance mass spectrometry. The reactions proceed in most instances by loss of one or more CO molecules from the collision complex. In the reactions of the dicarbonyl and tricarbonyl anions with H¹³COOCH₃, part of the eliminated carbon monoxide molecules contain the label revealing the occurrence of initial insertion of the metal center into the bonds adjacent to the carbonyl function of the substrate with formation of five- or six-coordinate intermediates, respectively. In addition, the MnCCO) ₃ ^? , Fe(CO) ₂ ^? , and CoCCO) ₂ ^? ions react by the loss of methanol and a [C,H₂,O] neutral species. The D- and ¹³C-labeling show that methanol is expelled in a reductive elimination from a five- or six-coordinate species, whereas the [C,H₂,O] loss is a more complex process possibly involving the competing losses of formaldehyde and CO + H₂. In the reaction of Fe(CO) ₃ ^? with H ₁₃ ¹³ COOCH₃, a facile consecutive exchange of all three CO ligands of the reactant ion for ¹³CO is observed. This novel reaction appears to involve initial insertion into the H¹³CO—OCH₃-bond followed by facile hydrogen shifts from the formyl ligand to a CO Hgand prior to the loss of unlabeled methyl formate.     

Gas-phase reactivity of ruthenium carbonyl cluster anions

Partially-ligated anionic ruthenium carbonyl clusters react with alkenes, arenes, and alkanes in the gas phase; the products undergo extensive C-H activation and lose dihydrogen and carbon monoxide under collision-induced dissociation conditions. Triethylsilane and phenylsilane are also reactive towards the unsaturated clusters, and oxygen was shown to rapidly break down the cluster core by oxidative cleavage of the metal-metal bonds. These qualitative gas-phase reactivity studies were conducted using an easily-installed and inexpensive modification of a commercial electrospray ionization mass spectrometer. Interpretation of the large amounts of data generated in these studies is made relatively straightforward by employing energy-dependent electrospray ionization mass spectrometry (EDESI-MS).     

Bond strengths in cyclopentadienyl metal carbonyl anions

Energy-resolved collision-induced dissociation of metal cyclopentadienyl carbonyl anions CpM(CO)_x⁻(Cpc-C₅H₅, MV, Cr, Mn, Fe, Co) is used to determine metal–carbonyl bond energies in these systems. These bond energies are, in general, slightly stronger than those for the corresponding homoleptic metal carbonyl anions. The bond strength in CpCo(CO)₂⁻, a 19-electron complex, is notably weaker than most of the others. D[CpMn⁻-CO] is also weak; this is attributed to a mismatch in the electronic ground states of CpMn⁻ and CpMnCO⁻. D[CpCo⁻-CO], on the other hand, is substantially larger than the others, and is comparable to the bond energy measured in solution for CpMn(CO)₃.     

Activation of carbon disulphide by metal carbonyl anions: Formation of trithiocarbonate complexes

Trithiocarbonate complexes are formed when metal carbonyl anions are treated consecutively with carbon disulphide and a neutralising agent such as methyl iodide or Re(CO)₅ Br.     

Reactions of carbon dioxide with metal carbonyl anions

The reactivity of a series of metal carbonyl anions with CO₂ has been found to parallel their relative nucleophilicities. The highly nucleophilic species, C₅H₅Fe(CO)^?₂, reacts readily to give the dimer, (C₅H₅Fe(CO)₂)₂, and carbonate while Co(CO)^?₄ is unreactive. The reaction of ¹³CO₂ with C₅H₅Fe(CO)^?₂ results in the formation of the ¹³CO enriched dimer.     

The chemistry of metal carbonyl anions : III. Sodium-potassium alloy: An efficient reagent for the production of metal carbonyl anions

Reduction of several metal carbonyl dimers including Mn₂](CO)₁₀, [C₅H₅Fe(C0)₂]₂, Co₂(CO)₈, and [C₅H₅M(CO)₃]₂ (M = Cr, Mo and W) by sodium—potassium alloy (NaK) in tetrahydrofuran at room temperature provides a rapid and clean method for the production of the corresponding metal carbonyl anions in high yield. Isolation and characterization of [n-Bu₄N] [Fe(CO)₂C₅H₅] from the iron dimer reduction is described. Reductions of other carbonyls including M(CO)₆ (M = Cr, Mo and W) and Re₂(CO)₁₀ proceed more slowly than previously established methods and provide principally M₂(CO)₁₀^2? and Re(CO)₅₅^?. Methods for the preparation of Re(CO)₅^? are critically considered. The reaction of NaK with [C₅H₅NiCO]₂ is discussed in relation to previously reported results. Infrared solution spectra of a number of carbonyl anions in THF, obtained in a special infrared solution cell, are reported.     

Perspectives in the syntheses of novel organometallic compounds using metal carbonyl anions

The molecular structure of [(C₆H₅)₃P]₂Pt(C₅H₈) has been determined from three-dimensional X-ray diffraction data (R = 0.045 for 6033 reflections). The crystal belongs to the triclinic system, space group P$\text{1}$, with two formula units in a cell of dimensions: a = 18.557(2), b = 10.216(2), c = 9.647(2) Å, α = 98.29 (3), β = 73.44(2), and γ = 88.34(2)°.One of the olefinic bonds of dimethylallene, which has no adjacent methyl groups, is coordinated to the platinum atom: PtC(1) = 2.108(8), PtC(2) = 2.049(7) Å. The coordinated dimethylallene molecule is no longer linear, the C(1)C(2)C(3) angle being 140.8(8)°, which is significantly smaller than that found in [(C₆H₅)₃P]₂Pd(C₃H₄). The C(1)C(2) distance is 1.430(11) Å, whereas the uncoordinated bond distance is normal [C(2)C(3) = 1.316(11)Å].     

Hydration of alumina cluster anions in the gas phase

Hydration reactions of anionic aluminum oxide clusters were measured using a quadrupole ion trap secondary ion mass spectrometer, wherein the number of Lewis acid sites were determined. The extent of hydration varied irregularly as cluster size increased and indicated that the clusters possessed condensed structures where the majority of the Al atoms were fully coordinated, with a limited number of undercoordinated sites susceptible to hydrolysis. For maximally hydrated ions, the number of OH groups per Al decreased in an exponential fashion from 4.0 in Al(1) cluster to 1.4 in the Al(9) cluster, which was greater than that expected for a highly hydroxylated surface but less than that for solution phase alumina clusters.     

Rearrangement of aromatic sulfonate anions in the gas phase

Collisionally activated dissociation of deprotonated aromatic sulfonic acids in the gas phase causes rearrangement and fragmentation to produce the corresponding phenoxide ions. The mechanism for this reaction has been investigated and the results of this study favor initial intramolecular nucleophilic addition of a sulfonate oxygen atom to the aromatic ring, a process which is followed by heterolytic cleavage of the carbon–sulfur bond to rearomatize the ring. The product from this addition–elimination sequence is the anion of a sulfurous acid half-ester, which loses SO₂ to generate the corresponding phenoxide ion.     

Fragmentation of collisionally activated hydroxyphenoxide anions in the gas phase

Low-energy collisionally activated dissociation of O-deprotonated dihydroxybenzenes (catechol, resorcinol, hydroquinone) in the gas phase causes both fragmentation to form [C₆H₄O₂]^– ions by loss of the remaining oxygen-bound hydrogen atom and intramolecular hydrogen atom migration from O to C. The rearranged anions then undergo ring-cleavage reactions which are different in each case. Both catechol and hydroquinone produce fragments which are the result of the loss of two carbon atoms and both oxygen atoms but the proposed mechanisms are different. Resorcinol also produces a fragment which derives from the loss of carbon dioxide. For this process a mechanism is proposed which involves a 6-methylpyranone anion intermediate.     

Reactions of atomic metal anions in the gas phase: competition between electron transfer, proton abstraction and bond activation

Bare metal anions K(-), Rb(-), Cs(-), Fe(-), Co(-), Ni(-), Cu(-), and Ag(-), generated by electrospray ionization of the corresponding oxalate or tricarballylate solutions, were allowed to react with methyl and ethyl chloride, methyl bromide, nitromethane, and acetonitrile in the collision hexapole of a triple-quadrupole mass spectrometer. Observed reactions include (a) the formation of halide, nitride, and cyanide anions, which was shown to be likely due to the insertion of the metal into the C-X, C-N, and C-C bonds, (b) transfer of H(+) from the organic molecule, which is demonstrated to most likely be due to the simple transfer of a proton to form neutral metal hydride, and (c) in the case of nitromethane, direct electron transfer to form the nitromethane radical anion. Interestingly, Co(-) was the only metal anion to transfer an electron to acetonitrile. Differences in the reactions are related to the differences in electron affinity of the metals and the Δ(acid)H° of the metals and organic substrates. Density functional theory calculations at the B3-LYP/6-311++G(3df,2p)//B3-LYP/6-31+G(d) level of theory shed light on the relative energetics of these processes and the mechanisms by which they take place.     

Gas phase reactivity of thermal metal clusters

Reaction kinetics of metal cluster ions under well defined thermal conditions were studied using a flow tube reactor in combination with laser vaporization. Aluminum anions and cations were reacted with oxygen, and several species which are predicted jellium shell closings, were found to have special stability. Metal alloy cluster anions comprised of Al, V and Nb were also seen to react with oxygen. Alloy clusters with an even number of electrons reacted more slowly than odd electron species, and certain clusters appeared to be exceptionally unreactive. Copper cation clusters were observed to associate with carbon monoxide with reactivities that approach bulk behavior at surprisingly small cluster size. These reactions demonstrate how the rate of reaction changes with cluster size.     

Structure and reactivity of benzoylnitrene radical anion in the gas phase

The open-shell benzoylnitrene radical anion, readily generated by electron ionization of benzoylazide, undergoes unique chemical reactivity with radical reagents and Lewis acids in the gas phase. Reaction with nitric oxide, NO, proceeds by loss of N2 and formation of benzoate ion. This novel reaction is also observed to occur with phenylnitrene anion, forming phenoxide. Similar reactivity was observed in the reaction between benzoylnitrene radical anion and NO2, forming benzoate ion and nitrous oxide. Electronic structure calculations indicate that the reaction has a high-energy barrier that is overcome by the energy released by bond formation. Benzoylnitrene radical anion also transfers oxygen anion to NO and NO2 as well as to CS2 and SO2. In contrast, phenylnitrene anion reacts with carbon disulfide by C+ or CS+ abstraction, forming S- or S2-. Electronic structure calculations indicate that benzoylnitrene in the ground state resembles a slightly polarized benzoate anion, but with a free radical localized on the nitrogen.     

Formation of tungstate-containing cluster ions by polyoxotungstate anions under matrix-assisted laser desorption/ionization conditions in the gas phase

The gas-phase studies of transition-metal oxides continue to attract interest as such oxides are being used as catalysts in various oxidation processes. In this paper, singly negatively charged heteropolyoxotungstate and isopolyoxotungstate ion clusters were produced from Keggin-type polyoxotungstates by matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (MALDI-FTICR MS). It was found that the ion series [(PO(3))(WO(3))(n)](-), [(WO(3))(n)](-) and [(OH)(WO(3))(n)](-) were the main fragment ions in the mass spectra and the matrix greatly influenced the resulting cluster ion abundances. [(PO(3))(WO(3))(3)](-), [(WO(3))(3)](-) and [(OH)(WO(3))(4)](-) were the most intense ions in each series when 2-(4-hydroxyphenylazo)benzoic acid was the matrix, whereas [(PO(3))(WO(3))(4)](-), [(WO(3))(6)](-) and [(OH)(WO(3))(4)](-) were the most intense when dithranol (DIT) was the matrix. In addition, a new kind of hybrid ion [W(2)C(14)H(7)O(8)](-) was produced through the reaction of DIT and [(OH)(WO(3))](-) in the plume of the gas phase. These results highlight the utility of the MALDI-FT method for obtaining novel ion clusters and also show the stability of these clusters.     

Fragmentation of transition metal carbonyl cluster anions: structural insights from mass spectrometry

The anionic clusters [HOs(5)(CO)(15)](-), [PtRu(5)C(CO)(15)](2-), [Os(10)C(CO)(24)](2-), [Os(17)(CO)(36)](2-), [Os(20)(CO)(40)](3-), [Co(6)C(CO)(15)](2-), [Pt(3)Ru(10)C(2)(CO)(32)](2-) and [Pd(6)Ru(6)(CO)(24)](2-) have been analysed by energy-dependent electrospray ionisation mass spectrometry (EDESI-MS). Three main features have emerged. Firstly, carbonyl ligands are fragmented from clusters with compact metal cores in an orderly fashion, with each of the ions generated by CO loss having approximately equal intensity. Secondly, electron autodetachment takes place in multiply charged anionic clusters, but only after elimination of a large proportion of their carbonyl ligands. Thirdly, clusters with open metal cores do not undergo CO loss in an orderly fashion, but certain peaks are considerably less intense. The appearance of these low-intensity peaks is believed to signify polyhedral core rearrangements, with open clusters folding to form more compact geometries. In some cases, the gas-phase transformations observed by EDESI-MS mirror those that are known to take place in solution.