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Mohammad Aghazadeh Meshgi, Rainer Zitz, Małgorzata Walewska, Judith Baumgartner, Christoph Marschner
Most known silatrane chemistry is concerned with examples where the attached silatrane substituent atom is that of an element more electronegative than silicon. The current study features silylated silatranes with a range of electropositive elements attached to the silyl group. The resulting compounds show different degrees of electron density on the silatrane-substituted silicon atom. This directly affects the Si-N interaction of the silatrane which can be monitored either by (29)Si NMR spectroscopy or directly by single crystal XRD analysis of the Si-N distance...
April 10, 2017: Organometallics
Isabelle Chambrier, Dragoş-Adrian Roşca, Julio Fernandez-Cestau, David L Hughes, Peter H M Budzelaar, Manfred Bochmann
The gold(III) methoxide complex (C(∧)N(∧)C)AuOMe (1) reacts with tris(p-tolyl)phosphine in benzene at room temperature under O abstraction to give the methylgold product (C(∧)N(∧)C)AuMe (2) together with O=P(p-tol)3 ((C(∧)N(∧)C) = [2,6-(C6H3(t) Bu-4)2pyridine](2-)). Calculations show that this reaction is energetically favorable (ΔG = -32.3 kcal mol(-1)). The side products in this reaction, the Au(II) complex [Au(C(∧)N(∧)C)]2 (3) and the phosphorane (p-tol)3P(OMe)2, suggest that at least two reaction pathways may operate, including one involving (C(∧)N(∧)C)Au(•) radicals...
April 10, 2017: Organometallics
Mark K Rong, Koen van Duin, Tom van Dijk, Jeroen J M de Pater, Berth-Jan Deelman, Martin Nieger, A W Ehlers, J Chris Slootweg, Koop Lammertsma
Highly stable iminophosphanes, obtained from alkylating nitriles and reaction of the resulting nitrilium ions with secondary phosphanes, were explored as tunable P-monodentate and 1,3-P,N bidentate ligands in rhodium complexes. X-ray crystal structures are reported for both κ(1) and κ(2) complexes with the counterion in one of them being an unusual anionic coordination polymer of silver triflate. The iminophosphane-based ruthenium(II)-catalyzed hydration of benzonitrile in 1,2-dimethoxyethane (180 °C, 3 h) and water (100 °C, 24 h) and under solvent free conditions (180 °C, 3 h) results in all cases in the selective formation of benzamide with yields of up to 96%, thereby outperforming by far the reactions in which the common 2-pyridyldiphenylphosphane is used as the 1,3-P,N ligand...
March 13, 2017: Organometallics
Mohammad Aghazadeh Meshgi, Judith Baumgartner, Viatcheslav V Jouikov, Christoph Marschner
Several silatranyl -substituted oligosilanes were prepared starting from bis(trimethylsilyl)silatranylsilanide. Electrochemical and theoretical investigations of some oligosilanes revealed that electrooxidation occurs by formation of a short-lived cation radical. This species undergoes structural relaxation to form a pair of conformers, with endo and exo relationships with respect to the Si-N interaction. Reaction of a 1,4-disilatranyl-1,4-disilanide with 1,2-dichlorotetramethyldisilane gave a mixture of cis and trans diastereomers of a cyclohexasilane with the trans isomer showing a diminished Si-N distance...
January 23, 2017: Organometallics
Kristine Klimovica, Kristin Kirschbaum, Olafs Daugulis
Synthesis and full characterization of cationic isostructural "sandwich" diimine-coinage metal ethylene complexes are reported. Ethylene self-exchange kinetics proceeds by an associative exchange mechanism for Cu and Au complexes. The fastest ligand exchange was observed for Ag complex 8a. The upper limit of ΔG(‡), assuming associative ligand exchange, was found to be ca. 5.0 kcal/mol. Ethylene self-exchange in Cu complex 7b proceeds with ΔG298(‡) = 12.9 ± 0.1 kcal/mol, while the exchange is the slowest in Au complex 9, with ΔG298(‡) = 16...
September 12, 2016: Organometallics
Małgorzata Walewska, Johann Hlina, Judith Baumgartner, Thomas Müller, Christoph Marschner
In order to estimate the reactivity of disilylated germylene phosphine adducts, a cyclic version of this compound class was reacted with a number of different reagents. Reactions with the chalcogens sulfur, selenium, and tellurium led to dimers of the heavy ketone analogues. Reactions with water and ethyl bromide proceeded to give the respective oxidized germanol and germyl bromide. Two different reactions with alkynes were observed which led either to a germacyclopropene, by addition of tolane to the germylene, or to a silagermacyclobutene, likely formed by addition of the alkyne across a silagermene...
August 22, 2016: Organometallics
Yiu Fung Mui, Jacob Fernández-Gallardo, Benelita T Elie, Ahmed Gubran, Irene Maluenda, Mercedes Sanaú, Oscar Navarro, María Contel
We report on the synthesis, characterization, and stability studies of new titanocene complexes containing a methyl group and a carboxylate ligand (mba = -OC(O)-p-C6H4-S-) bound to gold(I)-N-heterocyclic carbene fragments through the thiolate group: [(η(5)-C5H5)2TiMe(μ-mba)Au(NHC)]. The cytotoxicities of the heterometallic compounds along with those of novel monometallic gold-N-heterocyclic carbene precursors [(NHC)Au(mbaH)] have been evaluated against renal, prostate, colon, and breast cancer cell lines...
May 9, 2016: Organometallics
Andrew J Hoover, Mark Lazari, Hong Ren, Maruthi Kumar Narayanam, Jennifer M Murphy, R Michael van Dam, Jacob M Hooker, Tobias Ritter
Translation of new (18)F-fluorination reactions to produce radiotracers for human positron emission tomography (PET) imaging is rare because the chemistry must have useful scope and the process for (18)F-labeled tracer production must be robust and simple to execute. The application of transition metal mediators has enabled impactful (18)F-fluorination methods, but to date none of these reactions have been applied to produce a human-injectable PET tracer. In this article we present chemistry and process innovations that culminate in the first production from [(18)F]fluoride of human doses of [(18)F]5-fluorouracil, a PET tracer for cancer imaging in humans...
April 11, 2016: Organometallics
Noelia Casanova, Miguel A Esteruelas, Moisés Gulías, Carmen Larramona, José L Mascareñas, Enrique Oñate
The amide-directed synthesis of five-coordinate osmium alkylidene derivatives from alkynes is reported. These types of complexes, which have been elusive until now because of the tendency of osmium to give hydride alkylidyne species, are prepared by reaction of the dihydride OsH2Cl2(P(i)Pr3)2 (1) with terminal alkynes containing a distal amide group. Complex 1 reacts with N-phenylhex-5-ynamide and N-phenylhepta-6-ynamide to give OsCl2{=C(CH3)(CH2) n NH(CO)Ph}(P(i)Pr3)2 (n = 3 (2), 4 (3)). The relative position of carbonyl and NH groups in the organic substrates has no influence on the reaction...
January 25, 2016: Organometallics
Daniel L Crossley, Jessica Cid, Liam D Curless, Michael L Turner, Michael J Ingleson
The addition of AlCl3 to four-coordinate boranes of the general formula (C-N-chelate)BCl2 results in halide abstraction and formation of three-coordinate borenium cations of the general formula [(C-N-chelate)BCl](+). The latter react with both arylstannanes and arylsilanes by boro-destannylation and -desilylation, respectively, to form arylated boranes. Catalytic quantities of AlCl3 were sufficient to effect high-yielding arylation of (C-N-chelate)BCl2. Boro-destannylation is more rapid than boro-desilylation and leads to double arylation at the boron center, whereas in reactions with arylsilanes either single or double arylation occurs dependent on the nucleophilicity of the arylsilane and on the electrophilicity of the borenium cation...
December 28, 2015: Organometallics
Alexander F R Kilpatrick, Jennifer C Green, F Geoffrey N Cloke
Bonding in the bis(pentalene)dititanium "double-sandwich" species Ti2Pn2 (Pn = C8H6) and its interaction with other fragments have been investigated by density functional calculations and fragment analysis. Ti2Pn2 with C 2v symmetry has two metal-metal bonds and a low-lying metal-based empty orbital, all three frontier orbitals having a1 symmetry. The latter may be regarded as being derived by symmetric combinations of the classic three frontier orbitals of two bent bis(cyclopentadienyl) metal fragments. Electrochemical studies on Ti2Pn(†) 2 (Pn(†) = 1,4-{Si(i)Pr3}2C8H4) revealed a one-electron oxidation, and the formally mixed-valence Ti(II)-Ti(III) cationic complex [Ti2Pn(†) 2][B(C6F5)4] has been structurally characterized...
October 26, 2015: Organometallics
Alexander F R Kilpatrick, Jennifer C Green, F Geoffrey N Cloke
The reactivity of the bis(pentalene)dititanium double-sandwich compound Ti2Pn(†) 2 (1) (Pn(†) = 1,4-{Si(i)Pr3}2C8H4) with CO2 is investigated in detail using spectroscopic, X-ray crystallographic, and computational studies. When the CO2 reaction is performed at -78 °C, the 1:1 adduct 4 is formed, and low-temperature spectroscopic measurements are consistent with a CO2 molecule bound symmetrically to the two Ti centers in a μ:η(2),η(2) binding mode, a structure also indicated by theory. Upon warming to room temperature the coordinated CO2 is quantitatively reduced over a period of minutes to give the bis(oxo)-bridged dimer 2 and the dicarbonyl complex 3...
October 26, 2015: Organometallics
Behnaz Ghaffari, Britt A Vanchura, Ghayoor A Chotana, Richard J Staples, Daniel Holmes, Robert E Maleczka, Milton R Smith
Catalytic C-H borylation using the five-coordinate tris-boryl complex (dippe)Ir(Bpin)3 (5a, dippe = 1,2-bis(diisopropylphosphino)ethane) has been examined using (31)P{(1)H} and (1)H NMR spectroscopy. Compound 5a was shown to react rapidly and reversibly with HBpin to generate a six-coordinate borylene complex, (dippe)Ir(H)-(Bpin)2(BOCMe2CMe2OBpin) (6), whose structure was confirmed by X-ray crystallography. Under catalytic conditions, the H2 generated from C-H borylation converted compound 6 to a series of intermediates...
October 12, 2015: Organometallics
Phillip J Milner, Yang Yang, Stephen L Buchwald
A thorough investigation of the challenging Pd-catalyzed fluorination of five-membered heteroaryl bromides is presented. Crystallographic studies and density functional theory (DFT) calculations suggest that the challenging step of this transformation is C-F reductive elimination of five-membered heteroaryl fluorides from Pd(II) complexes. On the basis of these studies, we have found that various heteroaryl bromides bearing phenyl groups in the ortho position can be effectively fluorinated under catalytic conditions...
October 12, 2015: Organometallics
Erica M D'Amato, Constanze N Neumann, Tobias Ritter
We report an aromatic C-H hydroxylation protocol in which the arene is activated through η (6)-coordination to an iridium(III) complex. η (6)-Coordination of the arene increases its electrophilicity and allows for high positional selectivity of hydroxylation at the site of least electron density. Through investigation of intermediate η (5)-cyclohexadienyl adducts and arene exchange reactions, we evaluate incorporation of arene π-activation into a catalytic cycle for C-H functionalization.
September 28, 2015: Organometallics
Afrooz Zirakzadeh, Alexander Herlein, Manuela A Groß, Kurt Mereiter, Yaping Wang, Walter Weissensteiner
The ortho-deprotonation of halide-substituted ferrocenes by treatment with lithium tetramethylpiperidide (LiTMP) has been investigated. Iodo-, bromo-, and chloro-substituted ferrocenes were easily deprotonated adjacent to the halide substituents. The synthetic applicability of this reaction was, however, limited by the fact that, depending on the temperature and the degree of halide substitution, scrambling of both iodo and bromo substituents at the ferrocene core took place. Iodoferrocenes could not be transformed selectively into ortho-substituted iodoferrocenes since, in the presence of LiTMP, the iodo substituents scrambled efficiently even at -78 °C, and this process had occurred before electrophiles had been added...
August 10, 2015: Organometallics
Lena Albers, Mohammad Aghazadeh Meshgi, Judith Baumgartner, Christoph Marschner, Thomas Müller
The rearrangement of tris(trimethylsilyl)silyltrimethylgermane 1 to give tetrakis(trimethylsilyl)germane 2 was investigated as a typical example for Lewis acid catalyzed Wagner-Meerwein-type rearrangements of polysilanes and polygermasilanes. Direct (29)Si NMR spectroscopic evidence is provided for several cationic intermediates during the reaction. The identity of these species was verified by independent synthesis and NMR characterization, and their transformation was followed by NMR spectroscopy.
August 10, 2015: Organometallics
Mohammad Aghazadeh Meshgi, Judith Baumgartner, Christoph Marschner
Oligosilanes with attached silatranyl units were obtained by reactions of potassium oligosilanides with a silatranyl triflate. Interaction between Si and N atoms was observed in the (29)Si NMR spectra (upfield-shifted SiO3 resonances) and in the solid-state structures (Si-N distances between 2.29 and 2.16 Å). The Si-N interaction can be "switched off" either by protonation of the nitrogen lone pair or by potassium silanide formation caused by trimethylsilyl group cleavage in the presence of potassium tert-butoxide...
August 10, 2015: Organometallics
Amy J Ruddlesden, Ryan E Mewis, Gary G R Green, Adrian C Whitwood, Simon B Duckett
A novel neutral iridium carbene complex Ir(κC,O-L1)(COD) (1) [where COD = cyclooctadiene and L1 = 3-(2-methylene-4-nitrophenolate)-1-(2,4,6-trimethylphenyl) imidazolylidene] with a pendant alkoxide ligand has been prepared and characterized. It contains a strong Ir-O bond and X-ray analysis reveals a distorted square planar structure. NMR spectroscopy reveals dynamic solution state behavior commensurate with rapid seven-membered ring flipping. In CD2Cl2 solution, under hydrogen at low temperature, this complex dominates although it exists in equilibrium with a reactive iridium dihydride cyclooctadiene complex...
June 22, 2015: Organometallics
Marzieh Dadkhah Aseman, Christina A Roselli, Michel R Gagné
In situ generated benzyne reacts at room temperature with (triphos)Pt-CH3 (+) to form a five-coordinate π-complex (2) that is isolable and stable in solution. Thermolysis of 2 at 60 °C generates (triphos)Pt(o-tolyl)(+) (3), which is the product of formal migratory insertion of CH3 (-) onto the coordinated benzyne. The reaction of 2 with the acid Ph2NH2 (+) yields toluene at room temperature over the course of 8 h, while the same reaction with 3 only proceeds to 40% conversion over 2 days. These data indicate that the protonolysis of 2 does not proceed by CH3 migration onto benzyne to form 3 followed by protodemetalation...
June 22, 2015: Organometallics
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