Synthesis of a Dimeric Magnesium(I) Compound by an MgI/MgII Redox Reaction

The synthesis of dimeric magnesium(I) compounds of the general type RMgMgR (R=monoanionic substituent) is still a challenging synthetic task and limited to few examples with sterically demanding ligands with delocalized CN‐frameworks that all have been accessed by Na or K metal reduction of magnesium(II) halide precursors. Here we report on the synthesis of a novel diiminophosphinato magnesium(I) compound that has been synthesized by a facile redox reaction using a known magnesium(I) complex. The synthetic strategy may be applicable to other ligand systems and can help expand the class of low oxidation state magnesium complexes even if reductions with Na or K are unsuccessful. The new dimeric magnesium(I) complex has been structurally characterized and undergoes a C? C coupling reaction with tert‐butylisocyanate.     

Reversible M−M Bonding by Alkaline Earth Metals (Mg,Ca, Sr,Ba) in Graphite Intercalation Compounds

The alkaline earth metals (M=Mg, Ca, Sr, and Ba) exhibit a +2 oxidation state in nearly all known stable compounds, but M^I dimeric complexes with M−M bonding, [M₂(en)₂]²⁺, (en=ethylenediamine) of all these metals can be stabilized within the galleries of donor-type graphite intercalation compounds (GICs). These metals can also form GICs with more conventional metal (II) ion complexes, [M(en)₂]²⁺. Here, the facile interconversion between dimeric-M^I and monomeric-M^II intercalates upon the addition/removal of en are reported. Thermogravimetry, powder X-ray diffraction, and pair distribution function analysis of total scattering data support the presence of either [M₂(en)₂]²⁺ or [M(en)₂]²⁺ guests. This phase conversion requires coupling graphene and metal redox centers, with associated reversible M−M bond formation within graphene galleries. This chemistry allows the facile isolation of unusual oxidation states, reveals M⁰→M²⁺ reaction pathways, and present new opportunities in the design of hybrid conversion/intercalation materials for applications such as charge storage.     

A Schiff base expanded porphyrin macrocycle that acts as a versatile binucleating ligand for late first-row transition metals

The coordination chemistry of the Schiff base polypyrrolic octaaza macrocycle 1 toward late first-row transition metals was investigated. Binuclear complexes with the divalent cations Ni(II), Cu(II), and Zn(II) and with the monovalent cation Cu(I) were prepared and characterized. Air oxidation of the Cu(I) ions in the latter complex to their divalent oxidation state resulted in a change in the coordination mode relative to the macrocycle.     

Synthesis and characterization of volatile, thermally stable, reactive transition metal amidinates

A series of homoleptic metal amidinates of the general type [M(R-R'AMD)(n)](x) (R = (i)Pr, (t)Bu, R' = Me, (t)Bu) has been prepared and structurally characterized for the transition metals Ti, V, Mn, Fe, Co, Ni, Cu, Ag, and La. In oxidation state 3, monomeric structures were found for the metals Ti(III), V(III), and La(III). Bridging structures were observed for the metals in oxidation state 1. Cu(I) and Ag(I) are held in bridged dimers, and Ag(I) also formed a trimer that cocrystallized with the dimer. Metals in oxidation state 2 occurred in either monomeric or dimeric form. Metals with smaller ionic radii (Co, Ni) were monomeric. Larger metals (Fe, Mn) gave monomeric structures only with the bulkier tert-butyl-substituted amidinates, while the less bulky isopropyl-substituted amidinates formed dimers. The new compounds were found to have properties well-suited for use as precursors for atomic layer deposition (ALD) of thin films. They have high volatility, high thermal stability, and high and properly self-limited reactivity with molecular hydrogen, depositing pure metals, or water vapor, depositing metal oxides.     

Free Aluminylenes: An Emerging Class of Compounds

Aluminylenes (R−Al) are aluminium analogs of carbenes. In contrast to isolable carbenes, aluminylenes are extremely rare species. In the past years, pioneered by Schnöckel, Roesky and Power, a few free aluminylenes and their complexes have been reported. Such compounds have the aluminium atom in the oxidation state +I, which contrasts with classical organoaluminium derivatives that contain the element in the +III oxidation state. Aluminylenes, either in their free state or in the coordination sphere of a Lewis base, are capable of coordinating to transition metals and activating inert chemical bonds. Free aluminylenes are emerging as potent synthetic platforms for unusual aluminium species.     

Single-molecule precipitation of transition metal(I) chlorides in water clusters.

Metal ions in unusual oxidation states can be introduced into water clusters using a standard laser vaporization source. Such nanosolutions of a single ion in typically 50 water molecules are comparable to a 1 M bulk solution, and their chemistry can be studied in the ion trap of a Fourier transform ion cyclotron resonance mass spectrometer. We find that a strong acid like hydrogen chloride oxidizes the early transition metal vanadium to the more common +III state, while later first row transition metals retain their unusual +I oxidation state, and the binary metal chlorides M(I)Cl precipitate.     

Rhenium and technetium complexes with N-heterocyclic carbenes – A review

The coordination chemistry of technetium and rhenium with N-heterocyclic carbenes of the dimethylimidazol-2-ylidene and 1,2,4-triazol-5-ylidene types is reviewed. Compounds containing the metals in the oxidation states “+7”, “+5” and “+1” are introduced. General trends and differences in the chemical behaviour of the complexes, particularly between the different metal cores (oxo, nitrido, imido) of Tc(V) and Re(V) compounds, are discussed. The influence of electronic and steric factors for the stabilisation of the metal complexes is explored.     

Deprotonative metalation using ate compounds: synergy, synthesis, and structure building

Historically, single-metal organometallic species such as organolithium compounds have been the reagents of choice in synthetic organic chemistry for performing deprotonation reactions. Over the past few years, a complementary new class of metalating agents has started to emerge. Owing to a variable central metal (magnesium, zinc, or aluminum), variable ligands (both in their nature and number), and a variable second metallic center (an alkali metal such as lithium or sodium), "ate" complexes are highly versatile bases that exhibit a synergic chemistry which cannot be replicated by the homometallic magnesium, zinc, or aluminum compounds on their own. Deprotonation accomplished by using these organometallic ate complexes has opened up new perspectives in organic chemistry with unprecedented reactivities and sometimes unusual and unpredictable regioselectivities.     

Bulky guanidinates for the stabilization of low oxidation state metallacycles

This article summarizes the development of a new class of very bulky guanidinate ligands. These have been used to prepare unprecedented examples of heterocycles containing groups 2, 13, 14 or 15 elements in the +1 oxidation state. The ligands have also been harnessed in the preparation of the only examples of guanidinato, and/or closely related amidinato, complexes of iron(I), cobalt(I) and planar four-coordinate lanthanide(II) metals. Preliminary studies of the further chemistry of these very reactive complexes are also reviewed. Throughout, the tendency of the bulky guanidinate ligands to exhibit ligating and stabilizing properties more akin to those of bulky β-diketiminate ligands than less bulky amidinates or guanidinates, will be discussed.     

Topologically constrained manganese(III) and iron(III) complexes of two cross-bridged tetraazamacrocycles

A family of Mn3+ and Fe3+ complexes of 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (1) and 4,10-dimethyl-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane (2) has been prepared by the chemical oxidation of the divalent manganese and iron analogues. The ligands are ethylene cross-bridged tetraazamacrocycles derived from cylam and cyclen, respectively. The synthesis and characterization of these complexes, including X-ray crystal structure determinations, are described. The structural evidence demonstrates that the tetradentate ligands enforce distorted octahedral geometries on the metal ions, with two cis sites occupied by labile ligands. Magnetic measurements reveal that the complexes are high spin with typical magnetic moments. Cyclic voltammetry shows reversible redox processes for the Fe3+/Fe2+ couples of the iron(III) complexes, while Mn3+/Mn2+ and Mn4+/Mn3+ couples were observed for the complexes with manganese(III). The manganese chemistry of 1 was studied in depth. The dichloro manganese(III) cation of 1 undergoes facile ligand substitution reactions at the labile, monodentate sites, for example substituting azide for chloride ligands. Air oxidation of the dichloro complex of Mn (1)2+ in basic solution does not give the expected mu-oxo dimeric product common to manganese. Instead, an unusual manganese(III)-OH complex has been isolated from this reaction and structurally characterized. A similar reaction under slightly different conditions gives a putative MnIII(OH)2 complex that metathesizes to MnIII(OMe)2 upon recrystallization from methanol.     

The Quest for Mononuclear Gold(II) and Its Potential Role in Photocatalysis and Drug Action

The chemistry of gold strongly focuses on the ubiquitous oxidation states +I and +III. The intermediate oxidation state +II is generally avoided in mononuclear gold species. In recent years, gold(II) has been increasingly suggested as a key intermediate in artificial photosynthesis systems, with gold(III) moieties acting as electron acceptors, as well as in gold‐catalyzed photoredox catalysis and radical chemistry. This Minireview provides a concise summary of confirmed and characterized mononuclear open‐shell gold(II) complexes. Recent findings on structural motifs and reactivity patterns will be discussed. Exciting developments in the fields of photosynthesis, photocatalysis, and potential roles in medicinal chemistry will be outlined.     

M(CN)(2) Species (M = Be, Mg, Ca, Sr, Ba): Cyanides, Nitriles, or Neither?

The "cyanide" salts of the group 2 (alkaline earth) metals exhibit remarkable structural variations: CN(-) binds to the metals via the carbon, via the nitrogen, and via bridged arrangements. The most stable geometries of the beryllium and the magnesium salts are linear (CNBeNC and NCMgCN, respectively), but CaC(2)N(2), SrC(2)N(2), and BaC(2)N(2) prefer twisted, bridged structures. However, several stationary points of the bridged complexes are close in energy, and considerable fluxionality is to be expected. These theoretical predictions (MP4SDTQ/6-311+G(2d)//MP2(fu)/6-31+G, Ca, Sr, Ba: 5s5p3d1f//5s5p3d basis sets and 10 valence electron pseudopotentials) invite experimental verification.     

Electrospray ionization studies of transition-metal complexes of 2-acetylbenzimidazolethiosemicarbazone using collision-induced dissociation and ion-molecule reactions

The complexes of transition-metal ions (M2+, where M = Fe, Co, Ni, Cu, Zn, Cd, and Hg) with 2-acetylbenzimidazolethiosemicarbazone (L) are studied under electrospray ionization (ESI) conditions. The ESI mass spectra of Fe and Co complexes showed the complex ions corresponding to [M+2L-2H]+, and those of Ni and Zn complexes showed [M+2L-H]+ ions, wherein the metal/ligand ratio is 1:2 and the oxidation state of the central metal ion is +3 in the case of Fe and Co and +2 in the case of Ni and Zn. The Cd and Cu complexes showed preferentially 1:1 complex ions, i.e., [M+L-H]+ or [M+L+Cl]+, whereas Hg formed both 1:1 and 1:2 complex ions. During formation of the above complex ions one or two ligands are deprotonated after keto-enol tautomerism, depending on the nature and oxidation state of central metal ion. The structures and coordination numbers of the metal ions in the complex ions were studied by their collision-induced dissociation spectra and ion-molecule reactions with acetonitrile or propylamine in the collision cell. Based on these results it is concluded that Fe, Co, Ni and Zn form stable octahedral complexes, whereas tetrahedral or square planar complexes are formed preferentially for other metals. In addition, the Cu complex showed a [2L+2Cu-3H]+ ion with a Cu-Cu bond.     

Generation of organo-alkaline earth metal complexes from non-polar unsaturated molecules and their synthetic applications

Organomagnesium compounds, represented by the Grignard reagents, are one of the most classical yet versatile carbanion species which have widely been utilized in synthetic chemistry. These reagents are typically prepared via oxidative addition of organic halides to magnesium metals, via halogen–magnesium exchange between halo(hetero)arenes and organomagnesium reagents or via deprotonative magnesiation of prefunctionalized (hetero)arenes. On the other hand, recent studies have demonstrated that the organo-alkaline earth metal complexes including those based on heavier alkaline earth metals such as calcium, strontium and barium could be generated from readily available non-polar unsaturated molecules such as alkenes, alkynes, 1,3-enynes and arenes through unique metallation processes. Nonetheless, the resulting organo-alkaline earth metal complexes could be further functionalized with a variety of electrophiles in various reaction modes. In particular, organocalcium, strontium and barium species have shown unprecedented reactivity in the downstream functionalization, which could not be observed in the reactivity of organomagnesium complexes. This perspective will focus on the newly emerging protocols for the generation of organo-alkaline earth metal complexes from non-polar unsaturated molecules and their applications in chemical synthesis and catalysis.

In this perspective, we highlight the recent development of metallation protocols of non-polar unsaturated molecules for the generation of organo-alkaline earth metal compounds and their applications in chemical synthesis and catalysis.     

Synthesis, spectroscopic characterization and ESR studies on electron transfer reactions of bis[N-(2,6-di-tert-butyl-1-hydroxyphenyl)salicylaldiminato]-copper(II) complexes with PbO2 and PPh3

New bis[N-(2,6-di-t-butyl-1-hydroxyphenyl)salicylideneminato]copper(II) complexes bearing HO and CH3O substituents on the salicyaldehyde moiety were prepared, and their spectroscopic properties, as well as redox reactivity towards PbO2 and PPh3, examined by ESR and UV spectroscopy. In the process of synthesis of HO complexes unlike CH3O the oxidative C-C coupling of coordinated salicylaldimine ligands does not takes place. The powder ESR spectra of CH3O substituted complexes unlike of HO analogues are typical of a triplet state Cu(II) dimers with a half-field forbidden (deltaM = +/- 2) transition and the allowed transitions (AM = +/- 1) dimeric form of the complexes at 300 and 113 K. The one-electron oxidation of 3-CH3O and all of the OH complexes with PbO2 to give indophenoxyl type secondary radicals which are significantly different from those observed for analogues Cl, Br and NO2 substituted chelates. The presented complexes unlike their electron-withdrawing analogues are readily reduced by PPh3 via intramolecular electron transfer from ligand to copper(II) to give various radical intermediates as well as Cu(I) radical ligand compounds. The analysis of ESR spectra all of the complexes and radical intermediates are presented.     

Structurally Defined Allyl Compounds of Main Group Metals: Coordination and Reactivity

Organometallic allyl compounds are important as allylation reagents in organic synthesis, as polymerization catalysts, and as volatile metal precursors in material science. Whereas the allyl chemistry of synthetically relevant transition metals such as palladium and of the lanthanoids is well‐established, that of main group metals has been lagging behind. Recent progress on allyl complexes of Groups 1, 2, and 12–16 now provides a more complete picture. This is based on a fundamental understanding of metal–allyl bonding interactions in solution and in the solid state. Furthermore, reactivity trends have been rationalized and new types of allyl‐specific reactivity patterns have been uncovered. Key features include 1) the exploitation of the different types of metal–allyl bonding (highly ionic to predominantly covalent), 2) the use of synergistic effects in heterobimetallic compounds, and 3) the adjustment of Lewis acidity by variation of the charge of allyl compounds.     

Preparation of L-asparagine complex of technetium-99m

Attempts have been made to employ magnesium oxide as the preconcentration agent for determination of trace metal sin seawater by neutron activation analysis. Hydrous magnesium oxide can efficienthy adsorb most cationic transition metals and rare earths in a simple water system. The adsorption behavior is believed to depend mainly from the association of the cationic species of the metals with MgO ₂ ^2– adsorbent. In seawater matrix some of the metal ions such as Hg²⁺, Ni²⁺, etc. may become inefficiently adsorbed owing to the formation of highly stable metal-chloro complexes with chloride ion. Usually the adsorption efficiencies of the metals can be recovered to be as high as the case in the simple water system if an acidified seawater (to pH1) is subjected to the adsorption experiment. In practice, a large volume of seawater (5 1) is stirred with a small amount of hydrous MgO (1 g). Thereafter, the trace metals adsorbed MgO is separated and taken to be neutron activated. The abundant sodium ion and ubiquitous bromide ion can be obviated by the adsorption process, thereby beneficial to the -spectrometry of the metals enriched on MgO.     

Metalloid group 14 cluster compounds: an introduction and perspectives to this novel group of cluster compounds

Metalloid cluster compounds of group 14 of the general formulae E(n)R(m) with n > m (E = Si, Ge, Sn and Pb, tetrel elements; R = ligand), where "naked" tetrel atoms are present as well as ligand-bound tetrel atoms, represent a novel class of cluster compounds in group 14 chemistry. Since the "naked" tetrel atoms in these clusters exhibit an oxidation state of 0, the average oxidation state of the tetrel atoms in such metalloid group 14 cluster compounds is between 0 and 1. Thus, these cluster compounds may be seen as intermediates on the way to the elemental state. Therefore, interesting properties maybe expected for these compounds which might complement results from nanotechnology. During the last years many different syntheses of such novel cluster compounds have been introduced, leading to several metalloid group 14 cluster compounds which exhibit new and unusual structure and bonding properties. In this tutorial review an account is given of the first steps in this novel field of group 14 chemistry. Special attention is focused on structural features and bonding properties.     

Reactions of perfluoroalkyl iodides with CC-multiple bonds induced by transition metal centers

Additions of perfluoroalkyl iodides R_FI to 1-alkenes can be catalyzed by transition metals, especially by noble metals such as ruthenium or platinum. Complexes of group VI–VIII metals in low oxidation states are even more effective and may also be employed for the addition of R_FI to alkynes. Heterogeneous metal catalysts facilitate the transfer of the perfluoroalkyl group from R_FI to aromatic ring systems.Iodo-perfluoroalkanes 1 belong to the most important intermediates in organofluorine chemistry [1]. The addition of 1 to alkenes according to

is known to be a radical process which can be initiated by means of heat, UV- or ?-radiation, electrocatalysis or by organic azo or peroxo compounds.     

Syntheses and structures of magnesium pyridine thiolates--model compounds for magnesium binding in photosystem I

Novel magnesium pyridine-2-thiolates were prepared by using alkane elimination chemistry. The resulting complexes display a metal coordination environment composed of sulfur/nitrogen bonding from the intramolecularly stabilized mercaptopyridine ligand, in addition to coordination by the oxygen centers from two THF donors. The compounds are well-suited model compounds for the magnesium centers in Photosystem I, in which magnesium, situated in the central chlorophyll ligand, is bound to sulfur from a nearby methionine residue. All compounds were characterized by (1)H, (13)C NMR, and IR spectroscopy, in addition to Xray crystallography.