Discrete Transition Metal Research Articles

Strong Photocurrent Response of Selenoarsenates With Different Transition Metal Complexes as Structure-Directing Agents.

Four selenoarsenates with different transition-metal complexes [Co(tren)2H]AsSe4 [tren = tris(2-aminoethyl)amine] (1); [Ni2(dien)4](As2Se5) (dien = diethylenetriamine) (2); [Zn(tren)]2(As2Se5) (3) and [Mn(tren)]2(As2Se5) (4) were solvothermally synthesized in a mixed solvent of organic amine and alcohol solution. The compounds 1-4 have pyramidal/tetrahedral structures (AsSe3/AsSe4), and contain transition metal (Co2+, Ni2+, Zn2+ and Mn2+) complex that form distinct zero-dimensional (0-D) clusters. Arsenic atoms form a tetrahedron in compounds 1 and 2; 1 consists of discrete tetrahedral (AsSe4) and transition metal complex [Co(tren)2]2+; 2 is composed of an anion [As2Se5]4- cluster and transition metal complex [Ni(dien)2]2+. In compounds 3 and 4, arsenic atom forms a pyramidal AsSe3 and the two pyramidal AsSe3 share a corner connection to form a dimer [As2Se5]4-; 3 is characterized as a cluster consisting of two unsaturated [Zn(tren)]2+ caiton linked by a dimer (As2Se5)4- linkage; in 4, unsaturated [Mn(tren)]2+ caiton is linked to two trigonal-bipyramidal [Mn(tren)]Se via dimer (As2Se5)4- to form [Mn(tren)]4[As4Se10] cluster. To our knowledge, [Zn(tren)]2(As2Se5) (3) is the first zinc selenoarsenate containing the (As2Se5)4- anion type. Furthermore, the Mn2+ ions adopt a trigonal-biyramidal (five-coordinate) and octahedral (six-coordinate) environment. Adding K2CO3/Cs2CO3 to the synthesis system is necessary and may act as a mineralizer. Several properties of compounds 1-4 have been characterized in our studies, in particular their strong photocurrent response characteristics under visible light irradiation.

N-Alkanes to n-alcohols: Formal primary C─H bond hydroxymethylation via quadruple relay catalysis.

Nature is able to synergistically combine multiple enzymes to conduct well-ordered biosynthetic transformations. Mimicking nature's multicatalysis in vitro may give rise to new chemical transformations via interplay of numerous molecular catalysts in one pot. The direct and selective conversion of abundant n-alkanes to valuable n-alcohols is a reaction with enormous potential applicability but has remained an unreached goal. Here, we show that a quadruple relay catalysis system involving three discrete transition metal catalysts enables selective synthesis of n-alcohols via n-alkane primary C─H bond hydroxymethylation. This one-pot multicatalysis system is composed of Ir-catalyzed alkane dehydrogenation, Rh-catalyzed olefin isomerization and hydroformylation, and Ru-catalyzed aldehyde hydrogenation. This system is further applied to synthesis of α,ω-diols from simple α-olefins through terminal-selective hydroxymethylation of silyl alkanes.

Synthesis and crystallographic characterisation of a homologous series of bis-tridentate phosphine oxide NP3O3 Fe(II), Co(II), Ni(II) and Cu(II) complexes

Despite the large numbers of mono- and bidentate phosphine oxide complexes, examples of well characterised discrete multidentate phosphine oxide transition metal complexes are relatively rare. Herein, we report the coordination chemistry of the triphosphine oxide ligand N{CH2P(O)Ph2}3 (NP3O3, 1) with a series of first row transition metals. Ligand 1 was found to form a series of bis-tridentate homoleptic complexes with Fe(II), Co(II), Ni(II) and Cu(II) salts of the type M(BF4)2·6H2O. The anion exchange reaction of BF4— for BPh4— aided in the crystallisation of three of the four complexes. X-Ray crystallographic analysis of this series: [Fe(N{CH2P(O)Ph2}3)2](BPh4)2 (2), [Co(N{CH2P(O)Ph2}3)2](BPh4)2 (3), [Ni(N{CH2P(O)Ph2}3)2](BPh4)2 (4) and [Cu(N{CH2P(O)Ph2}3)2](BF4)2 (5) confirmed either almost idealised octahedral or distorted octahedral structures and tridentate coordination of 1. Complex 5, Cu(II) d9, displayed a classic Jahn-Teller distortion showing a prominent elongation of the axial M–O bonds. All complexes were found to be paramagnetic which precluded NMR spectroscopy analysis. Magnetic susceptibility measurements on solid samples of the complexes confirmed their number of unpaired electrons and high spin states.

Isolable iodosylarene and iodoxyarene adducts of Co and their O-atom transfer and C-H activation reactivity.

We report an unusual series of discrete iodosyl- and iodoxyarene adducts of Co. The formation of these adducts was confirmed by a suite of techniques including single crystal X-ray diffraction. The reactivity of these adducts with O-atom acceptors and an H-atom donor has been investigated with particular focus on elucidating mechanistic details. Detailed kinetic analysis allows for discrimination between proposed oxo and adduct mediated mechanisms. In particular, these reactions have been interrogated by competition experiments with isotopically labelled mixtures which shows that all of the studied adducts display a large KIE. These studies suggest different mechanisms may be relevant depending on subtle substituent changes in the adduct complexes. Reactivity data are consistent with the involvement of a transient oxo complex in one case, while the two other systems appear to react with substrates directly as iodosyl- or iodoxyarene adducts. These results support that reactivity typically ascribed to metal-oxo complexes, such as O-atom transfer and C-H activation, can also be mediated by discrete transition metal iodosyl- or iodoxyarene adducts that are frequent intermediates in the generation of oxo complexes. The influence of additional Lewis acids such as Sc3+ on the reactivity of these systems has also been investigated.

Three discrete transition metal complexes of N-hydroxy-1,8-naphthalimidato ligand: synthesis, structure and magnetic properties

The reactions of N-hydroxy-1,8-naphthalimide (HL) with Mn(OAc)2·4H2O, Co(NO3)2·6H2O and CoCl2·6H2O gave three new coordination compounds [Mn4(H2O)2L6(OH)(OAc)]·DMF·6H2O (1), [Co2(H2O)2L4]·2H2O (2) and [(CH3)2NH2][Co(L)2Cl] (3), the structures of which were determined. Compound 1 presents a parallelogram tetranuclear Mn4 skeleton, and compound 2 shows a dinuclear structure. However, compound 3 has a mononuclear structure with the Co(II) center five-coordinated in a square-pyramidal geometry. The discrete units of the three compounds are linked by hydrogen bonds and π···π stacking interactions to form three-dimensional supramolecular frameworks. The magnetic data of 1 and 2 were collected and simulated in the temperature range of 2.0–300 K. These studies revealed the presence of two kinds of intramolecular antiferromagnetic interactions between the Mn(II) atoms in 1, in contrast to intramolecular ferromagnetic interactions between the two Co(II) atoms in 2, which are associated with the structural features.

Four Discrete Transition Metal Complexes Involving Pyridyl-substituted Nitronyl Nitroxide: Syntheses, Crystal Structures, and Magnetic Properties

Four discrete metal-radical complexes, [Cu(p-MePh-COO)2(NITpPy)2] (1), [Ni(m-MePhCOO)2(NITpPy)2(H2O)2]·(CH3-OH)2 (2), [Mn(p-MePhCOO)2(NITpPy)2(H2O)2] (3), and [Mn(m-MePhCOO)2(NITpPy)2(H2O)2] (4) [NITpPy = 2-(4-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxide] were synthesized and characterized by elemental analyses, IR spectroscopy, PXRD, single-crystal X-ray diffraction, and magnetic susceptibility. For the four complexes, the crystal structural analyses indicate that the two radical ligands coordinated to the metal ions by the nitrogen atoms of the pyridine rings form three spin complexes, where toluates act as co-ligands. Weak antiferromagnetic interactions [JCu–Rad = –6.75 cm–1 (1), JCo–Rad = –4.15 cm–1 (2), JMn–Rad = –0.22 cm–1 (3), and JMn–Rad = –3.74 cm–1 (4)] were observed, spin polarization mechanism and orbital symmetry are used to explain the magnetic coupling in these complexes.

Variable coordination of redox-active TCNB in discrete and polymeric ferrocenylcopper(i) complexes: structures and spectroelectrochemical behaviour

1,2,4,5-Tetracyanobenzene (TCNB) was reacted with [Cu(dppf)(CH3CN)2](BF4) and [Cu(dchpf)(CH3CN)](BF4), dppf = 1,1'-bis(diphenylphosphino)ferrocene and dchpf = 1,1'-bis(dicyclohexylphosphino)ferrocene, to produce a heterotetranuclear metallamacrocycle 1, {[Cu(dppf)(μ-TCNB)](BF4)}2, and a heterooctanuclear complex 2, [{Cu(dchpf)}4(μ4-TCNB)](BF4)4. Complex 1 is the first example of a structurally characterised discrete transition metal complex of TCNB. Upon crystallisation attempts, compound 2 formed the structurally identified coordination polymer 3, {[Cu(dchpf)(μ-TCNB)]2(BF4)2}n. Structural and spectroscopic analyses confirmed the redox-innocent behaviour of TCNB in 1, 2 and 3. However, the soluble compounds 1 and 2 could be oxidised and reduced spectroelectrochemically (UV-vis, IR, and EPR). The oxidation occurs invariably at the ferrocene sites without notable splitting of redox potentials. Reduction involves the TCNB bridging ligands to produce radical complexes. As a variably bridging acceptor component of supramolecular structures the TCNB ligand thus adopts an intermediate position between the highly electron transfer-active TCNE, TCNQ and TCNQF4 systems and the numerous redox-innocent bridges.

Arylpalladium Phosphonate Complexes as Reactive Intermediates in Phosphorus−Carbon Bond Forming Reactions

Phosphorus−carbon bond formation from discrete transition metal complexes have been investigated through a combination of synthetic, spectroscopic, crystallographic, and computational methods. Reactive intermediates of the type (diphosphine)Pd(aryl)(P(O)(OEt)2) have been prepared, characterized, and studied as possible intermediates in metal-mediated coupling reactions. Several of the reactive intermediates were characterized crystallographically, and a discussion of the solid state structures is presented. In contrast to other carbon−heteroelement bond forming reactions, palladium complexes containing electron-donating substituents on the aromatic fragment exhibited faster rates of reductive elimination. Large bite angle diphosphine ligands induced rapid rates of elimination, while bipyridine and small bite angle diphosphine ligands resulted in much slower rates of elimination. An investigation of the effect of typical impurities on the elimination reaction was carried out. While excess diphosphine, pyridine, and acetonitrile had little effect on the observed rate, the addition of water slowed the phosphorus−carbon bond forming reaction. Coordination of water to the complex was observed spectroscopically and crystallographically. Computational studies were utilized to probe the reaction pathways for P−C bond formation via Pd catalysis.

The roles of the first and second coordination spheres in the design of molecular catalysts for H2production and oxidation

This tutorial review describes the development of discrete transition metal complexes as electrocatalysts for H2 formation and oxidation. The approach involves the study of thermodynamic properties of metal hydride intermediates and the design of ligands that incorporate proton relays. The work is inspired by structural features of the H2ase enzymes and should be of interest to researchers in the areas of biomimetic chemistry as well as catalyst design and hydrogen utilization.

Nanosized (μ12-Pt)Pd164-xPtx(CO)72(PPh3)20(x≈ 7) Containing Pt-Centered Four-Shell 165-Atom Pd−Pt Core with Unprecedented Intershell Bridging Carbonyl Ligands: Comparative Analysis of Icosahedral Shell-Growth Patterns with Geometrically Related Pd145(CO)x(PEt3)30(x≈ 60) Containing Capped Three-Shell Pd145Core

Presented herein are the preparation and crystallographic/microanalytical/magnetic/spectroscopic characterization of the Pt-centered four-shell 165-atom Pd-Pt cluster, (mu(12)-Pt)Pd(164-x)Pt(x)(CO)(72)(PPh(3))(20) (x approximately 7), 1, that replaces the geometrically related capped three-shell icosahedral Pd(145) cluster, Pd(145)(CO)(x)(PEt(3))(30) (x approximately 60), 2, as the largest crystallographically determined discrete transition metal cluster with direct metal-metal bonding. A detailed comparison of their shell-growth patterns gives rise to important stereochemical implications concerning completely unexpected structural dissimilarities as well as similarities and provides new insight concerning possible synthetic approaches for generation of multi-shell metal clusters. 1 was reproducibly prepared in small yields (<10%) from the reaction of Pd(10)(CO)(12)(PPh(3))(6) with Pt(CO)(2)(PPh(3))(2). Its 165-atom metal-core geometry and 20 PPh(3) and 72 CO ligands were established from a low-temperature (100 K) CCD X-ray diffraction study. The well-determined crystal structure is attributed largely to 1 possessing cubic T(h) (2/m3) site symmetry, which is the highest crystallographic subgroup of the noncrystallographic pseudo-icosahedral I(h) (2/m35) symmetry. The "full" four-shell Pd-Pt anatomy of 1 consists of: (a) shell 1 with the centered (mu(12)-Pt) atom encapsulated by the 12-atom icosahedral Pt(x)Pd(12-x) cage, x = 1.2(3); (b) shell 2 with the 42-atom nu(2) icosahedral Pt(x)Pd(42-x) cage, x = 3.5(5); (c) shell 3 with the anti-Mackay 60-atom semi-regular rhombicosidodecahedral Pt(x)Pd(60-x) cage, x = 2.2(6); (d) shell 4 with the 50-atom nu(2) pentagonal dodecahedral Pd(50) cage. The total number of crystallographically estimated Pt atoms, 8 +/- 3, which was obtained from least-squares (Pt(x)/Pd(1-x))-occupancy analysis of the X-ray data that conclusively revealed the central atom to be pure Pt (occupancy factor, x = 1.00(3)), is fortuitously in agreement with that of 7.6(7) found from an X-ray Pt/Pd microanalysis (WDS spectrometer) on three crystals of 1. Our utilization of this site-occupancy (Pt(x)Pd(1-x))-analysis for shells 1-3 originated from the microanalytical results; otherwise, the presumed metal-core composition would have been (mu(12)-Pt)Pd(164). [Alternatively, the (mu(12)-Pt)M(164) core-geometry of 1 may be viewed as a pseudo-Ih Pt-centered six-shell successive nu(1) polyhedral system, each with radially equivalent vertex atoms: Pt@M(12)(icosahedron)@M(30)(icosidodecahedron)@M(12)(icosahedron)@M(60)(rhombicosidodecahedron)@M(30)(icosidodecahedron)@M(20)(pentagonal dodecahedron)]. Completely surprising structural dissimilarities between 1 and 2 are: (1) to date 1 is only reproducibly isolated as a heterometallic Pd-Pt cluster with a central Pt instead of Pd atom; (2) the 50 atoms comprising the outer fourth nu(2) pentagonal dodecahedral shell in 1 are less than the 60 atoms of the inner third shell in 1, in contradistinction to shell-by-shell growth processes in all other known shell-based structures; (3) the 10 fewer PR3 ligands in 1 necessitate larger bulky PPh(3) ligands to protect the Pd-Pt core-geometry; (4) the 72 CO ligands consist of six bridging COs within each of the 12 pentagons in shell 4 that are coordinated to intershell metal atoms. SQUID magnetometry measurements showed a single-crystal sample of 1 to be diamagnetic over the entire temperature range of 10-300 K.

Incorporating Metal Clusters into Three-Dimensional Ln(III)−Cu(I) Coordination Frameworks through Linear Ligands

By using linear multifunctional ligands with different geometries, three novel three-dimensional (3D) Ln−M heterometallic coordination polymers, [Nd(H2O)2(CuI)2(nic)3]·H2O (1) (Hnic = nicotinic acid) and [LnCu(inic)2(ox)]·H2O [Ln = Nd (2), Eu (3); Hinic = isonicotinic acid, H2ox = oxalic acid], have been synthesized under hydrothermal conditions. Compound 1 exhibits a novel 3D coordination framework constructed by Cu4I4 clusters, Nd centers, and nic ligands. Our present work represents the first example of 3D Ln−M heterometallic coordination framework incorporating discrete cubane transition metal clusters covalently bonded to lanthanide centers through linear ligands. An unusual chemical rearrangement from Hinic to ox occurs in the formation of 2 and 3. Compounds 2 and 3 are isostructural and possess the first 3D coordination framework based on the linkage of two-dimensional layers constructed by tetranuclear Ln2Cu2 clusters and inic ligands. Furthermore, the luminescent properties of 3 were studied.

Researchers in This Field Still Have Many Challenges in Front of Them, but the Future is Indeed Very Bright

The cross-coupling reaction is old enough that even I, no longer a young scientist, learned about it in college. Indeed, the problem of coupling sp-based carbon nucleophiles and electrophiles was recognized as being important but difficult as long ago as 1941 by Kharasch, who found that coupling reactions of Grignard reagents worked better when traces of transition metals were present in the system. As it often happens in science, the seeds for the discovery of this excitingmodern synthetic tool lay dormant in the fertile soil of the scientific literature until the groups of Kochi, Corriu, and Kumada, among others, realized in 1971–1972 that discrete transition metal catalysts (Ag, Fe, Ni) can be devised to carry out these reactions in good yield and with some generality. Palladium rose to center stage more slowly a few years later, through thework ofMurahashi, followedbymanyothers. But Grignard reagents were not the only organometallic species in the world, and indeed not the most synthetically useful. Negishi and co-workersmust be credited with bringing more practical reagents into the menu of the synthetic organic chemist, i.e., Al, Zr and the now very popular Zn derivatives. Indeed, among practitioners, cross-coupling reactions involving organozinc reagents are now referred to as “Negishi couplings”. In 1968, even before the cross-coupling reactionmade it to the forefront of organic synthesis, Richard Heck had brought to light the reaction that now bears his name. His first entry into the field was a stunning series of seven consecutive papers with his name as the only author. The innumerable important observations contained in these early papers and those which soon followed transformed this unusual reaction into a general synthetic method. It has taken the synthetic community many years to realize the immense potential of theHeck reaction, and in the last 20 years countless refinements, extensions (e.g., enantioselective cyclizations), and applications have been reported. In 1975, Sonogashira found that alkynes could be coupled directly with carbon electrophiles, without preparing first an organometallic reagent, if both a Pd and aCu catalyst were used in tandem. The Sonogashira coupling is now a very popular synthetic tool in academia as well as in industry. In the late 1970s, tin derivativeswere shown to also undergo Pd-catalyzed coupling with a broad range of electrophiles, mainly through the work of Kosugi and Migita and Stille. These couplings are now referred to as the “Stille reaction”, and constitute an extremely important tool in the discovery of pharmaceuticals, the total synthesis of complex natural products, the synthesis of materials and devices, etc. It turned out to be more difficult to induce boron to undergo this reaction. I was a graduate student at the University of Alberta when I saw Akira Suzuki lecture for the first time. I was told by the organizers that Prof. Suzuki was going to disclose an important unpublished result. I listened carefully as he told us how he andNorio Miyaura had just found that organoboron compounds, easily available through a variety of synthetic means, can be made to cross-couple through the formation of “ate” complexes. The Suzuki reaction had been born. For us in the pharmaceutical industry, this is now the most practical way to cross-couple aromatics and heteroaromatics, and we have become quite skilled COMMENTARIES

ChemInform Abstract: Synthesis, Structure and Properties of [Cr2(PS4)4]6‐; the First Discrete Transition Metal Cluster from Thiophosphate Flux Reactions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis, structure and properties of [Cr2(PS4)4]6−; the first discrete transition metal cluster from thiophosphate flux reactions

The molecular cluster compound [Cr2(PS4)4]6– forms by the reaction of Cr metal with thiophosphate fluxes.

Multiple deprotonation of a ferraborane. Evidence for the formation of a discrete transition metal boride

Multiple deprotonation of a ferraborane. Evidence for the formation of a discrete transition metal boride

Mechanism of phase transitions affecting intramolecular electron transfer in trinuclear mixed-valence transition-metal compounds

Intramolecular electron delocalization in discrete mixed-valence transition metal complexes in the condensed phase depends not only on the electronic structure of a single complex but also sensitively on the details of the packing arrangement [D. N. Hendrickson, S. M. Oh, T.-Y. Dong, T. Kambara, M. J. Cohn, and M. F. Moore, Comments Inorg. Chem. 4, 329 (1985)]. The problem of how the cooperative properties of mixed-valence complexes in the solid state depend on the electron localization and/or delocalization in a single complex is studied theoretically. A phenomenological intermolecular interaction which depends on the sense and the magnitude of molecular distortion arising from the electron localization is introduced. A theoretical model is developed based on molecular field theory in order to show what types of phase transitions relating to the electron delocalization are possible in the trinuclear mixed-valence compounds and how the electronic structure of constituent molecules determines the type of phase transition. There are three types of phase transitions: (1) Order–disorder transition with respect to the alignment of the sense of molecular distortion associated with the electron localization; (2) static localization–delocalization transition, where the molecular distortion disappears above the transition temperature and electrons are coherently delocalized on three transition metal ions; (3) dynamical localization–delocalization transition in which the delocalization comes from fast electron transfer between three transition-metal ions and the molecular structure is changed from a static distortion to a dynamical distortion. The theoretical model is used to explain the observed temperature dependencies of heat capacity and Mössbauer spectra for the trinuclear mixed-valence complex [Fe3O(O2CCH3)6(py)3](py), where (py) is pyridine [S. M. Oh. T. Kambara, D. N. Hendrickson, M. Sorai, K. Kaji, S. E. Woehler, and R. J. Wittebort, J. Am. Chem. Soc. 107, 5540 (1985); M. Sorai, K. Kaji, D. N. Hendrickson, and S. M. Oh, ibid. 108, 702 (1986)]. The first-order phase transition at ∼112 K is assigned as an order–disorder transition and the higher-order transition at ∼190 K is assigned as a dynamical localization–delocalization transition.

Reactions at the metal vertex of a monometal metallacarborane cluster. Chemistry of [closo-3,3-(PPh3)2-3-HSO4-3,1,2-RhC2B9H11] and [closo-3-PPh3-3,3-NO3-3,1,2-RhC2B9H11

Abstract : Reaction of (closo-3,3-(PPh3)2-3-(H)-3,1,2-RhC2B9H11)(1) with sulfuric or nitric acid affords (closo-3,3-(PPh3)2-3-(HSO4)-3,1,2-RhC2B9H11)(2) or (closo-3-(PPh3)-3,3-(NO3)-3,1,2-RhC2B9H11)(3), respectively. Compound (3) can also be prepared from nitric acid and the dimeric metallocarborane ((closo-Rh(PPh3)(C2B9H11))2) or from NO2/N2O4 and (1). Complexes (2) and (3) have been used to prepared other new metallocarboranes. The reactions of these new metallocarboranes described herein are representative of interconversions carried out at a discrete transition metal vertex of a cluster species.

Spectroscopic investigation on the molecular and electronic structure of [Mo 3S 13] 2−, a discrete binary transition metal sulfur cluster

The only known discrete transition metal sulfur cluster [Mo 3S 13] 2− has been investigated spectroscopically (XPS, UV/VIS, IR and Raman) and by a cyclovoltammetric study. It turns out that the cluster consists of three Mo atoms with the oxidation state +IV and six S 2− 2 ligands. A simplified MO treatment of the metal system in [Mo 3S 13] 2− explains the diamagnetism of the compound, as well as the single bond character of the MoMo bonds. The two absorption bands in the visible region are due to a transition within the Mo 3 metal system and the charge transfer transitions π * v(S 2− 2) → d(Mo).