Transition Metal Derivatives Research Articles

Synthesis of zinc dialkyls from zinc and alkyl bromides

Zinc dialkyls with linear radicals were prepared from zinc and alkyl bromides in the presence of stimulating systems based on a transition metal derivative and an organometallic compound capable of reducing the transition metal derivative under the reaction conditions.

Transition metal derivatives of peptide nucleic acid (PNA) oligomers-synthesis, characterization, and DNA binding.

This work describes the first automated solid-phase synthesis of metal derivatives of peptide nucleic acid (PNA) oligomers and their interaction with DNA and PNA. PNA constitutes a relatively young and very promising class of DNA analogues with excellent DNA and RNA binding properties. However, PNA lacks a suitable handle that would permit its sensitive detection on its own as well as when hybridized with complementary oligonucleotides. Metal complexes, on the other hand, offer high potential as markers for biomolecules. In this paper, we describe the synthesis of PNA heptamers (tggatcg-gly, where gly is a C-terminal glycine carboxylic acid amide) with two covalently attached metal complexes at the PNA N-terminus, namely a ferrocene carboxylic acid derivative and a tris(bipyridine)ruthenium(II) derivative. We show how all synthesis steps may be carried out with high yield on a DNA synthesizer, including attachment of the metal complexes. The conjugates were characterized by HPLC (>90% purity) and ESI-MS. Binding studies of the purified Ru-PNA heptamer to complementary DNA and PNA and comparison to the isosequential metal-free acetyl PNA heptamer proves that the attached metal complex has an influence on the stability (UV-T(m)) and structure (CD spectroscopy) of the conjugates, possibly by disruption of the nearby A:T base pair.

Synthesis and structure of {η 3-MeSi(CH 2SPh) 3}Cr(CO) 3: how long can a Cr(0)–S(thioether) bond length be?

The new tridentate thioether ligand MeSi(CH 2SPh) 3 has been prepared in good yield and its first transition metal derivative, the octahedral chromium tricarbonyl complex {η 3-MeSi(CH 2SPh) 3}Cr(CO) 3, has been synthesized and fully characterized. In agreement with the reduced basicity of arylthioethers and the expected lability of their metal complexes, the new complex exhibits the longest Cr(0)–S(thioether) bond distances observed to date.

Synthetic Approaches to Mixed-Metal Heteroleptic Derivatives of Late Transition Metals

The approach based on isomorphous substitution permitted preparation of (Co, Ni)4(acac)4(μ3–OMe)4(MeOH)4(I) via interaction of individual M4(acac)4(μ3–OMe)4(MeOH)4 in toluene/methanol media. The oxidation of I in air in solution in MeOH in the presence of NaOAc and aminoalcohols as catalysts gives Co2Ni2-(acac)4(μ3–OMe)4(OAc)2(II). The symmetrization reaction between a complex formed by a hard Pearson acid and a soft Pearson base and that formed by a soft acid and a hard base led to CuNi2(OCOC2H5)3(ORN)3-(RNOH)(III) and Ni(Ni0.25Cu0.75)2(μ3–OH)(μ2–OAc)(OAc)2(μ2, η2-ORN)3(η2-RNOH)(IV) RN = CH(CH3)-CH2NMe2 via interaction of Ni(ORN)2 with copper propionate and copper acetate hydrate respectively in hydrocarbon media.

Kinetic and UV−Visible Spectroscopic Studies of Hex-1-ene Polymerization Initiated by an α-Diimine-[N,N] Nickel Dibromide/MAO Catalytic System

A study of the elementary reactions involved in the catalytic activation process of α-diimine NiBr2 by methylaluminoxane (MAO), for α-olefins polymerization, was undertaken in toluene and chlorobenzene as solvents. The investigation is based on the comparative study of polymerization kinetics of hex-1-ene, UV−visible spectroscopic analysis of the catalytic system and structural analysis of the poly(hex-1-ene)s formed. Correlation between polymerization activities and changes in the UV−visible absorption spectrum of the transition metal derivative were found. Spectroscopic data have underlined the important role of the monomer in the stabilization process of the nickel-based active species. Partial polymerization orders with respect to MAO, nickel derivative and monomer were determined. Surprisingly, an apparently negative monomer order of the polymerization corresponding to a decrease of the polymerization rate with an increase of monomer concentration in the reacting medium was observed. A tentative inte...

Niobium and tantalum derivatives with bidentate nitrogen ligands as potential precursors to nitrides

Early transition metal derivatives with N-donors have attracted interest as precursors of nitrides, the latter being used as diffusion barriers for the ULSI technology. Potential precursors to niobium and tantalum nitrides have been synthesized in good yields and characterized. They are based on bidentate nitrogen donors namely amidinates, benzamidinates and diamido ligands. These have been reacted with niobium or tantalum derivatives namely penta and tetrachlorides, TaCl 3 (NEt 2 ) 2 . Disubstituted niobium(IV) and tantalum(V) species such as for instance NbCl 2 [RNCR'NR 2 ] 2 [R= Cy, N(SiMe 3 ) 2 ; R = SiMe 3 , R' = p-tolyl] have been obtained and structurally characterized, The more rigid o-dimethylphenylene diamido ligand lead to a volatile, air stable disubstituted Nb(V) species NbCl{N 2 (SiMe 3 ) 2 C 5 H 3 } 2 . However, π-stacking as shown by X-ray studies are responsible of quite low sublimation rates. Thus, volatility could be reached for some species, their properties, high solubility due to the trimethylsilylligands, their stability in solution is more suited for applications in wet MOCVD than conventional one.

Methyltris(pyrazolyl)silanes: new tripodal nitrogen-donor ligands

Two tridentate nitrogen-donor ligands, the methyltris(pyrazolyl)silanes MeSi(3,5-RR′pz) 3 (R=R′=Me; R=Bu t, R′=H), have been synthesized and the X-ray structure of the latter has been determined. The first transition metal derivatives of these ligands, the cationic copper(I) complexes [LCu(NCMe)] + (where L=MeSi(3,5-Me 2pz) 3 or MeSi(3-Bu tpz) 3), have been prepared and characterized analytically and spectroscopically.

New catalysts for olefin polymerization: from elementary processes to the synthesis of polyolefins

A general investigation of the elementary reactions involved in the activation processes of zirconocene and Ni-based derivatives by methylaluminoxane (MAO) was performed through the association of polymerization kinetics and spectroscopic investigation of the catalytic system. This study demonstrates the close correlation between polymerization activities and the changes in the UV/visible characteristic absorption bands of the transition metal derivative used as catalyst. Hex-1-ene was chosen as model monomer.

Transition Metal Derivatives of a ((Dimethylamino)ethyl)cyclopentadienyl Ligand. Synthesis and Structures of Amino-Containing Cyclopentadienyl Derivatives of Cobalt(I) and -(III) Including Water-Soluble Compounds.

The synthesis of monometallic cobalt(III) and -(I) complexes of ((dimethylamino)ethyl)cyclopentadienyl are reported. The presence of the basic amino group facilitates these synthesis using the corresponding cyclopentadiene complexes as starting material. A cobaltocenium green complex [{eta(5)-C(5)H(4)(CH(2))(2)N(H)Me(2)}(2)Co(III)](3+)(Cl(-))(3) (3) was obtained from C(5)H(5)(CH(2))(2)NMe(2) (1) or from its salt M[C(5)H(4)(CH(2))(2)NMe(2)] (M = Na, Li) (2) upon reaction with Co(II)Cl(2) in THF. The structure of the complex [{(eta(5)-C(5)H(4)(CH(2))(2)NMe(2))(eta(5)-C(5)H(4)(CH(2))(2)N(H)Me(2))}Co(I)(II)](PF(6))(2) (4), prepared from 3 by treatment with NH(4)PF(6) in aqueous solutions, was solved in the triclinic space group P&onemacr; with one molecule in the unit cell, the dimensions of which were a = 6.314(2) Å, b = 7.137(2) Å, c = 13.452(2) Å, alpha = 103.66(2) degrees, beta = 90.25(2) degrees, gamma = 92.89(2) degrees, and V = 588.2(3) Å(3). Adjacent molecules in the unit cell of 4 are hydrogen bonded via a H(+) through their -NMe(2) side chains. The reaction of Co(2)(CO)(8) with C(5)H(5)(CH(2))(2)NMe(2) (1) leads to the formation of [{eta(5)-C(5)H(4)(CH(2))(2)NMe(2)}Co(I)(CO)(2)] (5). Treatment of 5 with HBF(4) in ether solutions yielded [{eta(5)-C(5)H(4)(CH(2))(2)N(H)Me(2)}Co(I)(CO)(2)](+)BF(4)(-) (6). Oxidation of 5 with I(2) or Cl(2) gas yielded [{eta(5)-C(5)H(4)(CH(2))(2)NMe(2)}Co(III)I(2)] (7a) and [{eta(5)-C(5)H(4)(CH(2))(2)NMe(2)}Co(III)Cl(2)] (7b). Addition of HBF(4) to complex 7a resulted in the breaking of the Co(III)-NMe(2) bond, producing the dimeric complex [{(eta(5)-C(5)H(4)(CH(2))(2)N(H)Me(2))Co(III)I(2)}(2)](2+)(BF(4)(-))(2) (9). The bridged diiodo dimer 10, [{(eta(5)-C(5)H(4)(CH(2))(2)NMe(2))CoI}(2)](2+)(BF(4)(-))(2), on the other hand, could be obtained from complex 7a upon addition of AgBF(4) in CH(2)Cl(2).

Aggregative Activation in Connection with a Few Reactions Using Transition or Alkali Metal Derivatives as Intermediates

AbstractAggregative Activation principles are given. The first application described deals with the preparation of reducing agents used to perform couplings and carbonylations of aryl and hetaryl halides. The second application deals with the preparation of two kind of super bases: sodium amide and butyllithium containing complex bases. The arynic synthesis of indoles is given as an illustration of the use of the first kind of base while the metalation of pyridine derivatives exemplifies the use of the second. In this latter case, a new metalation radical mechanism is proposed.

On the Nature and Incidence of β-Agostic Interactions in Ethyl Derivatives of Early Transition Metals: Ethyltitanium Trichloride and Related Compounds

In light of the structures and spectroscopic properties of the ethyltitanium compounds EtTiCl 3 (1), and EtTiCl3(dmpe) (dmpe ) Me2PCH2CH2PMe2 )( 2), extensive DFT calculations have been carried out to explore the structures, energetics, potential energy surfaces, and spectroscopic properties not only of these but also of related ethyl derivatives of early transition metals, M. The analysis has sought to assess the true nature of so-called ‚-agostic interactions in these systems and how such interactions depend on the atomic number, coordination number, valence electron (VE) count, and net charge of M. The calculations reproduce well the experimentally determined properties of 1 and 2. Analysis of wave functions indicates that, where significant ‚-interactions occur, the M-CR bonding electrons are delocalized over the entire ethyl group, the marked reduction of the MCC valence angle allowing the metal atom to establish covalent bonding interactions with the ‚-C atom and, perhaps to a lesser extent, with its appended proximal H atom. A ‚-agostic alkyl group may be considered a two-electron ligand, and the main contribution to the stabilization arises from Ti‚‚‚C‚ bonding. Barriers to conformational change of the M-Et unit depend inter alia on the space available in the coordination sphere of the central M atom, with rearrangement of the ethyl group to accommodate significant ‚-interaction being opposed by interligand repulsion. Such interaction is found not in 1, but in its dmpe adduct 2 because the increase in coordination number is offset by elongation of the Ti-C and Ti-Cl bonds and by the extra pliability of the EtTiCl3 moiety resulting from complexation by the dmpe ligand.

Dibenzotetraaza[14]annulenes: versatile ligands for transition and main group metal chemistry

This article presents an overview of the chemistry of metal complexes of dibenzotetraaza[14]annulene ligands and highlights most of the recent developments. The title tetraazamacrocycles are related to the porphyrins but have a smaller N4 coordination cavity ‘hole size’ and typically possess a non-planar, saddle-shaped conformation. The similarity of the dibenzotetraaza[14]annulenes to the porphyrins means that these synthetic macrocycles are of bioinorganic relevance, while their distinctive individual characteristics make them interesting ligands in their own right. In early transition metal chemistry, for example, the dibenzotetraaza[14]annulenes have been studied as potential alternatives to the ubiquitous bis(η-cyclopentadienyl) ligand set, while later transition metal derivatives can mimic certain biological systems and act as precursors to electroactive polymeric films. The dibenzotetraaza[14]annulenes have also recently allowed advances in structural and reactivity studies of main group organometallic and coordination compounds, including the stabilisation of new metal–chalcogenide multiple bonds.

Heterobimetallische Komplexe mit 2-(Dimethylaminomethyl)ferrocenyl-Liganden

Heterobimetallic Complexes Containing 2-(Dimethylaminomethyl)ferrocenyl Ligands The chemistry of heterobimetallic complexes containing the 2-(dimethylaminomethyl)ferrocenyl ligand is reviewed, including main group element, transition metal, and f-element derivatives. An overview on synthetic methods and molecular structures is given.

New transition-metal derivatives of the fullerene C60

The new compounds [M(NO)(PPh3)2(η2-C60)] (M = Co 1 or Rh 2), [RuX(NO)(PPh3)2(η2-C60)] (X = Cl 3 or H 4), [Re2H8(PMe3)4(η2: η2′-C60)] 5 and [TaH(η-C5H5)2(η2-C60)] have been prepared and characterised. Crystal structures have been determined for 3 and 5 and show typical η2 co-ordination of C60 in the former, but a rare example of η4 co-ordination in the latter. The soluble adducts 1, 2, 4, 5 and [M(CO)4(η2-C60)] (M = Ru 7 or Fe 8) have been electrochemically reversibly reduced up to the dianion and to the trianion for 4. The E° values are shifted to slightly less negative values than for C60 itself in consonance with the reduction in the number of fullerene double bonds. Addition of the electrophiles I2, maleic anhydride or PPh3 to 1 or 2 easily regenerated free C60. The presence of an isobenzofuran side chain in C60(C20H14O) prevents attack by the incoming metal centre Fe(CO)4 at adjacent double bonds and results in inequivalency of the remaining double bonds and a mixture of regioisomeric products. However, the isobenzofuran side chain may be displaced by Pd(PPh3)2 or [Co(η-C5H5)2] resulting in the formation of [Pd(PPh3)2(η2-C60)] or [Co(η-C5H5)2]+[C60]–.

Reactivity of a Cyclopentadienyl Containing Heterobimetallic Alkoxide

The synthesis of the new heteroleptic heterotrimetallic cluster, [(C5H5)Sn(μ-OBut)2Ge(OBut)Mo(CO)5] (1) has been achieved by a thermally induced CO substitution of the transition metal derivative, Mo(CO)6, by the basic germanium atom of the cyclopentadienyl heterobimetallic alkoxide, [(C5H5)Sn(μ-OBut)2Ge(OBut)]. The microanalysis, molecular weight (monomer in benzene), IR and multinuclear NMR data and X-ray diffraction study is consistent with the formulation of 1. The Sn atom has a trigonal pyramidal coordination environment formed by a aysmmterically π-bonded terminal C5H5 ring and two symmetrically bridged tert-butoxy groups. The four-coordinate Ge atom lies at the centre of a distorted tetrahedron and is terminally attached to a tert-butoxy group and a Mo(CO)55− fragment.

Organometallic structural units in solid state ternary transition metal carbides

Solid state ternary transition metal carbides containing carbon, a transition metal (Cr to Ni and their heavier congeners), and a highly electropositive multivalent metal such as a lanthanide (Ln), Sc, Y, or Th, exhibit a number of structural features resembling those in metal carbonyls and other transition metal derivatives of π-acceptor hydrocarbon ligands. Complete ionization of the electropositive metal to the stable ions Ln3+, Sc3+, Y3+, and Th4+ leads to a negatively charged transition metalȁcarbon subnetwork, which may be regarded as an organometallic net. Many such carbides contain discrete C2 units with C=C distances in the range 1.32 to 1.47 Å suggestive of double bonding and the C24ȡ tetra-anion obtained by the complete deprotonation of ethylene. Thus the carbides Ln2FeC4, Sc3CoC4, and Ln3MC4 (M = Fe, Co, Ni, Ru, Rh, Os, Ir) may be considered to contain 1,1-μ2-C24ȡ, 1,2-μ2-C24ȡ and μ3-C24ȡ ligands respectively. Other ternary transition metal carbides contain C22ȡ ligands in [M]=C=C units derived by complete deprotonation of a terminal vinylidene ligand, [M]=C=CH2. Such terminal deprotonated vinylidene ligands are isoelectronic and isostructural with terminal metal carbonyl groups and are found in trigonal M(C2)3 units isoelectronic with M(CO)3 units with the transition metal in very low formal oxidation states (e.g. Mn(ȁV) of Mn(C2)311ȡ in Ln3Mn2C6 isoelectronic with Mn(CO)35ȡ and Ni(ȁII) of Ni(C2)38ȡ in Eu3.16NiC6 isoelectronic with Ni(CO)32ȡ). The carbide ScCrC2 contains a C2 pair with a longer C-C distance of 1.60 Å, suggesting a C-C single bond and the C26ȡ anion obtained by complete deprotonation of ethane. Examples of C1 ligands found in the solid state ternary transition metal carbides include terminal C4ȡ in Th2NiC2, Y2ReC2, and Ln12M5C15 (M = Mn, Re) and μ2(=C=)4ȡ in YCoC and Y2ReC2.

Transition-Metal Derivatives of a Functionalized Cyclopentadienyl Ligand. 15. Synthesis and Structures of Amino Cyclopentadienyl Derivatives of Rhodium(I) and Rhodium(III) Including Water-Soluble Compounds.

The synthesis of monometallic rhodium(III) and rhodium(I) derivatives of dialkylamino-functionalized cyclopentadienyl using the corresponding cyclopentadiene as starting material is facilitated by the presence of the basic amino group. This procedure affords the chloro salts of the substituted rhodicinium cation [(eta(5)-C(5)H(4)(CH(2))(2)NMe(2)H)(2)Rh(III)](3+) ([1][Cl](3)) from the reaction of the [2-(dimethylamino)ethyl]cyclopentadiene with Na(3)Rh(III)Cl(6). 12H(2)O. Similarly the cationic half-sandwich complexes [(eta(5)-C(5)H(4)(CH(2))(n)()NMe(2)H)Rh(I)(cod)](+) (n = 2, [2][Cl], n = 3, [5][Cl]) are obtained from the reaction of the corresponding dialkylamino cyclopentadiene with [RhCl(cod)](2). These types of cationic complexes, 1, 2, and 5, bear pendant ammonium groups. The most classical procedure, starting from the lithium or more efficiently from the sodium cyclopentadienide salt, was used to synthesize neutral complexes [(eta(5)-C(5)H(4)(CH(2))(n)()NMe(2))Rh(I)(cod)] (n = 2, 3; n = 3, 4). The structure of the chloride bis(hexafluorophosphate) salt, [(eta(5)-C(5)H(4)(CH(2))(2)NMe(2)H)(2)Rh(III)](3+)(Cl(-))(PF(6)(-))(2), ([1][Cl][PF(6)](2)) was solved in the triclinic space group P&onemacr; with one molecule in the unit cell, the dimensions of which are a = 6.617(2) Å, b= 7.436(2) Å, c = 13.965(3) Å, alpha = 76.39(2) degrees, beta = 82.31(3) degrees, gamma = 87.26(2) degrees, and V = 661.8(3) Å(3). The noncentrosymmetric character of this solid is attributed to the chloride ion. The tetrafluoroborate salt [(eta(5)-C(5)H(4)(CH(2))(2)NMe(2)H)Rh(I)(cod)](+)(BF(4)(-)) ([2][BF(4)]) crystallizes in the tetragonal space group P4(2)/n with eight molecules in the unit cell, the dimensions of which are a= 21.183(2) Å, b = 21.179(3) Å, c= 8.324(2) Å, and V = 3734(1) Å(3). Least squares refinement leads to values for the conventional R index of [1][Cl][PF(6)](2) (0.0484 for 2191 reflections used) and of [2][BF(4)] (0.0525 for 1083 reflections used); in both cases I > 3sigma(I). As expected, compounds like [2][Cl](3,) [1][Cl][PF(6)](2), [2][Cl], [2][BF(4)], [5][Cl], and [5][BF(4)] are soluble in water.

Synthesis and structures of organometallic derivatives of 1,2,3,4,5,6,7,8-octamethyl-1,5-dihydro-s-indacene

A new fused-ring compound 1,2,3,4,5,6,7,8-octamethyl-1,5-dihydro-s-indacene (H2L1) has been synthesized from p-xylene. Three transition-metal derivatives [Mn(η5-HL1)(CO)3], [Rh(η5-HL1)(η-C5Me5)]+[SbF6]− and [Cr(η6-H2L1)(CO)3] have been characterised: spectroscopic and crystallographic data for these compounds show the ligand system is strongly electron donating. Although H2L1 is readily deprotonated to the monoanion by potassium metal or potassium hydride, surprisingly we have been unable to form (L1)2. The crystal structure of [K]+[HL1]−·18-crown-6 reveals the potassium ion to be sandwiched between the crown ether (1,4,7,10,13,16-hexaoxacyclooctadecane) and the (HL1)− anion.

Synthesis and structures of organometallic derivatives of 1,2,3,4,5,6,7,8-octamethyl-1,5-dihydro-s-indacene

A new fused-ring compound 1,2,3,4,5,6,7,8-octamethyl-1,5-dihydro-s-indacene (H2L1) has been synthesized from p-xylene. Three transition-metal derivatives [Mn(η5-HL1)(CO)3], [Rh(η5-HL1)(η-C5Me5)]+[SbF6]− and [Cr(η6-H2L1)(CO)3] have been characterised: spectroscopic and crystallographic data for these compounds show the ligand system is strongly electron donating. Although H2L1 is readily deprotonated to the monoanion by potassium metal or potassium hydride, surprisingly we have been unable to form (L1)2. The crystal structure of [K]+[HL1]−·18-crown-6 reveals the potassium ion to be sandwiched between the crown ether (1,4,7,10,13,16-hexaoxacyclooctadecane) and the (HL1)− anion.

Reactivity of a Cyclopentadienyl Containing Heterobimetallic Alkoxide

The synthesis of the new heteroleptic heterotrimetallic cluster, [(C5H5)Sn(μ-OBut)2Ge(OBut)Mo(CO)5] (1) has been achieved by a thermally induced CO substitution of the transition metal derivative, Mo(CO)6, by the basic germanium atom of the cyclopentadienyl heterobimetallic alkoxide, [(C5H5)Sn(μ-OBut)2Ge(OBut)]. The microanalysis, molecular weight (monomer in benzene), IR and multinuclear NMR data and X-ray diffraction study is consistent with the formulation of 1. The Sn atom has a trigonal pyramidal coordination environment formed by a aysmmterically π-bonded terminal C5H5 ring and two symmetrically bridged tert-butoxy groups. The four-coordinate Ge atom lies at the centre of a distorted tetrahedron and is terminally attached to a tert-butoxy group and a Mo(CO)55− fragment.