0000000000297264
AUTHOR
Henri Brunner
Metallocenes of Nb and Ta with η2-Se2H, SeH, and Se Ligands – Crystal Structures of [Cp′2Ta(SeH)H2] and [Cp′2Ta(=Se)H·W(CO)5] (Cp′ =tBuC5H4)
The reactions of [Cp#2NbBH4] (1) [Cp# = C5Me5 (Cp*) or C5Me4Et] and [Cp′2TaH3] (Cp′ = tBuC5H4) with elemental selenium give complexes of the general composition [Cp2MSe2H]. These exist in three isomeric forms, A–C, depending on the metal and the chalcogen. [Cp#2NbSe2H] (2) incorporates the novel η2-Se2H ligand (C), which is labile when exposed to light. Solutions of 2(Cp*) can be converted into [Cp*2NbSe2H] (3), which exists in two isomeric forms A or B, along with [Cp*2NbSe3H] (4) and [Cp*2NbO2H] (5). [Cp′2Ta(η2-Se2)H] (6) is the only isomer found for the Ta system. Se abstraction by means of P(OEt)3 gives [Cp′2Ta(=Se)H] (7). Complex 7 can be reduced with Na/Hg and subsequently hydrolysed …
Investigation into the reactivity of oxoniobocene complexes [Cp*2Nb(O)R] (Cp*=η5-C5Me5; R=H, OH, OMe) towards heterocumulenes: formation of carbamato and thiocarbamato complexes and catalytic cyclization of PhNCO
Abstract The reaction of [Cp*2NbCl2] (Cp*=η5-C5Me5) with KOH or Ba(OH)2·8H2O in THF was investigated under slightly modified conditions. In addition to the known complex [Cp*2Nb(O)H] (1), the new compound [Cp*2Nb(O)OH] (2) was formed. The reaction of 2 with PhNCS gave yellow [Cp*2Nb(O){SC(O)NHPh}] (3), while PhNCO formed yellow [Cp*2Nb(O){OC(O)NHPh}] (4). Complexes 3 and 4 were analytically and spectroscopically characterized. X-ray diffraction analyses of both compounds show that they contain either η1-S-thiocarbamato (3) or η1-O-carbamato ligand (4) along with a terminal NbO group. The reaction of 1 with one equivalent of PhNCO mainly gave orange [Cp*2NbH{OC(O)NPh}] (5) along with so…
Syntheses and reactivity of oxo niobocene complexes Cp*2Nb(O)X (X=H, OCH3) and crystal structures of [Cp*2Nb(OH)F]BF4 and Cp*2Nb(O)OC(O)H (Cp*=η5-C5Me5)
Abstract Reaction of Cp*2NbCl2 (Cp*=η5-C5Me5) with KOH or Ba(OH)2·8H2O in THF forms the complexes Cp*2Nb(O)X (X=Cl: 2, H: 3). The ratio of 2 and 3 depends on the stoichiometry. If NaOMe is added or MeOH in solution Cp*2Nb(O)OMe 4 is formed in good yields. Reactivity studies with 3 and 4 show that the NbO as well as the Nb–X unit behave as chemically active sites. Protonation of 3 or 4 with HBF4 is followed by an attack of fluoride (from BF4− anion) to give [Cp*2Nb(OH)F]BF4 6 and [Cp*2NbF2]BF4 7. In contrast the reaction of 3 or 4 with HCO2H results in an exchange of X− by formate to give Cp*2Nb(O)OC(O)H 8. The crystal structures of 6 and 8 are reported. Electrochemical investigations of…
Coordinative Stabilization ofCyclo-Tetratellurium as[Te4{Cr(CO)5}4]: The First Organometallic Derivative of a Tellurium Allotrope
Structural Rearrangements in Triple-Decker-Like Complexes with Mixed Group 15/16 Ligands: Synthesis and Characterization of the Redox Couple [Cp2*Fe2As2Se2]/[Cp2*Fe2As2Se2]+ (Cp*=C5Me5)
The reaction of As4Se4 with stoichiometric amounts of [Cp*Fe2(CO)4] (Cp* = C5Me5) in boiling toluene forms [Cp2*Fe2As2Se2] (1) in good yield. X-ray crystallography shows 1 to have a triple-decker structure which comprises a tetraatomic mu,eta4:4-As2Se2 ligand. Density functional theory (DFT) and extended Huckel molecular orbital (EHMO) calculations confirm that the As2Se2 ligand behaves as a four-electron pi donor. Oxidation of 1 with equimolar amounts of [(C5H5)2Fe]PF6, Br2 and I2, respectively, gave compounds 2-4. According to X-ray crystallographic investigations that were carried out on 2 and 4, the oxidation state has a considerable influence on the structure of the Fe2As2Se2 core: sig…
Electrochemical and chemical reduction of niobocene dichlorides in the presence of carbon dioxide
Abstract The chemical and electrochemical reduction of the niobocene dichlorides [Nb(η5-C5H4SiMe3)2Cl2]1, [Nb(η5-C5Me5)2Cl2] 2 and [Nb(η5-C5Me4Et)2Cl2] 3, in the presence of carbon dioxide has been investigated. Formation of compounds of the type [Cp2Nb(CO2)] and [Cp2(∗)NbCl(CO2))] 1 has been established by means of IR, ESR and/or NMR spectroscopy. They contain a labile η2-CO2. The order of stability increases with the degree of substitution the Cp. Less stable intermediates in the reduction of the system [Cp2NbCl2]/CO2 are discussed on the basis of cyclovoltammetric and coulometric data.
Synthesis, reactivity and structures of ruthenium carbonyl clusters with telluride and hydride ligands
The reaction of [Cp* 2 Nb(Te 2 H)] ( 1 ) (Cp*=C 5 Me 5 ) with [Ru 3 (CO) 12 ] in boiling toluene gave [Ru 3 (μ 2 -H) 2 (CO) 9 (μ 3 -Te)] ( 2 ), [Ru 6 (μ 3 -H)(CO) 15 (μ 3 -Te) 3 ][Cp* 2 Nb(CO) 2 ] ( 3 ) and [Ru 5 (μ 2 -H)(CO) 14 (μ 4 -Te)][Cp* 2 Nb(CO) 2 ] ( 4 ) along with already known [Ru 4 (CO) 11 (μ 4 -Te) 2 ] ( 5 ). Complexes 2 – 4 were analytically and spectroscopically characterized and X-ray diffraction analyses of 3 and 4 were carried out. The anion of 3 is built up of a triangular hexametallic core of C 3 v symmetry, in which the central Ru 3 triangle, being bridged by a μ 3 -H ligand, is composed of three corner-linked Ru 3 Te tetrahedra. The main structural feature of the anion …
Mu,eta2:2-SbS: an antimony-containing heterodiatomic ligand from group 15 and 16 elements.
Preparative and Electrochemical Investigations on the Electron Sponge Behavior of Cobalt Telluride Clusters: CO Substitution in[Co11Te7(CO)10]n− Ions (n=1, 2) by PMe2Ph and Crystal Structure of[Co11Te7(CO)5(PMe2Ph)5]
The reaction of the cluster salts [Cp* 2 Nb(CO) 2 ] n [Co 1 1 Te 7 (CO) 1 0 ] (Cp* = C 5 Me 5 ; n = 1, 2) with excess PMe 2 Ph gave the neutral, dark brown clusters [Co 1 1 Te 7 (CO) 6 (PMe 2 Ph) 4 ] (5) and [Co 1 1 Te 7 (CO) 5 (PMe 2 Ph) 5 ] (6) with 147 metal valence electrons. The new compounds were characterized by IR spectroscopy, elemental analyses, and mass spectrometry. The molecular structure of 6 was determined by X+ray crystallography. Like its precursor anion, it consists of a pentagonal-prismatic [Co 1 1 Te 7 ] core, but with a ligand sphere composed of five CO and five PMe 2 Ph ligands. Detailed electrochemical studies of both reactions reveal that a stepwise substitution of C…
Bis(η-tert-butylcyclopentadienyl)hydridoniobium Ditelluride, a Convenient Reagent for the Synthesis of Polynuclear Metal Telluride Complexes
Metal Telluride Clusters Composed of Niobocene Carbonyl, Telluride, and Cobalt Carbonyl Units: Syntheses, Structures, and Reactivity
Abstract: The reaction of [Cp#2NbTe2H] (1#; Cp# = Cp* (C5Me5) or Cp(x) (C5Me4Et)) with two equivalents of [Co2(CO)8] gives a series of cobalt carbonyl telluride clusters that contain different types of niobocene carbonyl fragments. At 0 degrees C, [Cp#2NbTe2CO3(CO)7] (2#) and [Co4Te2(CO)10] (3) are formed which disappear at higher temperatures: in boiling toluene a mixture of [cat2][Co9Te6(CO)8] (5#) (cat= [Cp#2Nb(CO)2]+) and [cat2][Co11Te7(CO)10] (6#) is formed along with [cat][Co(CO)4] (4#). Complexes 6# transform into [cat][Co11Te7(CO)10] (7#) upon interaction with HPF6 or wet SiO2. The molecular structures of 2(Cp(x)), 4(Cp(x)), 5(Cp*), 6(Cp*) and 7(Cp*) have been determined by X-ray cr…
Preparative, structural, and electrochemical investigations on peralkylated niobocene dichlorides and difluorides
CP(dagger)2NbCl2 (CP(dagger) = 175-C5Me4Et) (1b) was synthesized from NbCl5 and a slight excess of Cp(dagger)Li and NaBH4. Its electrochemical (2 e-, E1/2 = -1.6 V) and chemical reduction (2 equiv of Na/Hg) was studied showing that peralkylation of the Cp ligand facilitates two-electron reduction compared to less substituted CP2NbHal2 derivatives. The reduced solutions of CP*2NbCl2 (CP* = C5Me5) (1a) and of lb were shown by means of EPR spectroscopy to contain two new paramagnetic species 1A,B for which bent niobocene (A(Nb) = 100 G) and fulvene-like structures (A(Nb) = 55 G) are proposed. The high reduction potential of these species led in their reaction with HPF6 to the first stable difl…
Synthesis and characterisation of [(C5Me4R)2NbS2]2M complexes (M = Fe, Co; R = Me, Et) : organometallic tetrathiometalates with niobocene ligands
Abstract Irradiation of Cp 2 ∗ Nb(η 2 S 2 )H (Cp ∗ = C 5 Me 5 ) 1a in the presence of Fe(CO) 5 gives the CO-free complex [Cp 2 ∗ NbS 2 ] 2 Fe 2a . The core of 2a contains an FeS 4 tetrahedron which is ligated by two niobocene ligands as shown by X-ray diffraction analysis. In the reaction of 1a or Cp 2 x Nb(η 2 S 2 )H (CP x = C 5 Me 4 Et) 1b with Co 2 (CO) 8 , compounds 3a and 3b of the same type are formed. Electrochemical studies of 2a and 3a,b show that they undergo three reversible 1e − steps. The oxidation of 3b exerts a considerable influence on its absorption spectrum. A qualitative EHMO analysis is in agreement with a strong delocalisation of electron density over the whole NbS 2 …
Metallocene sulfide chemistry of niobium and tantalum: new insights into the formation of niobium-polysulfido complexes and synthesis, structure, and reactivity of Cp2'Ta(.eta.2-S2)H (Cp' = tert-BuC5H4)
The previously described reaction of Cp'2NbH3 (Cp' = t-BuC5H4) with S8 was investigated with regard to the kinetic stabilization of as yet elusive intermediates during the formation of the polysulfide complex Cp'4Nb2S9 (1). Therefore, the permethylated complex Cp*2NbS3H (2; Cp* = C5Me5) and the Ta complex Cp'2TaS2H (3) were synthesized in a related reaction and structurally investigated. Despite the problematic localization of the hydride atom during X-ray crystallographic studies, the molecules can be described in a proper manner: Characteristic of 2 and 3 are M(eta(2)-S2) cores to which either an SH (2) or a H (3) ligand is attached. Complex 3 is the first known tantalocene sulfide. It re…
Syntheses and properties of tetrathio- and tetraseleno metalates [(C5Me4R)2NbE2]2M (E=S, Se; M=Cr, Mo; R=Me, Et) with peripheric niobocene ligands
Abstract Reactions of Cp*2Nb(η2-S2)H 1 (Cp*=C5Me5 (a), C5Me4Et (b)) and Cp*2Nb(η2-Se2H) 3 with 0.5 equivalents of M(CO)6 (M=Cr, Mo) in boiling toluene give the CO free complexes [Cp*2NbE2]2M 4–7. X-ray diffraction analyses have been carried out for the Mo complexes 5a (E=S) and 7a (E=Se) showing that the structures contain ME4 tetrahedral cores with two attached niobocene ligands thus forming a nearly linear trimetallic unit. Absorption spectra and electrochemical studies of complexes 4–7 are described. Characteristic of the novel CrSe4 chromophor are four reversible one electron redox steps. Chemical oxidation of 4a and 5a with [(C5H5)2Fe]PF6 gives the salts {[Cp*2NbS2]2M}PF6 (M=Cr, Mo) 10…