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Organometallics

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https://www.readbyqxmd.com/read/27642213/synthesis-and-properties-of-sandwich-diimine-coinage-metal-ethylene-complexes
#1
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 ΔG 298 (‡) = 12.9 ± 0.1 kcal/mol, while the exchange is the slowest in Au complex 9, with ΔG 298 (‡) = 16...
September 12, 2016: Organometallics
https://www.readbyqxmd.com/read/27570360/basic-reactivity-pattern-of-a-cyclic-disilylated-germylene
#2
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
https://www.readbyqxmd.com/read/27182101/titanocene-gold-complexes-containing-n-heterocyclic-carbene-ligands-inhibit-growth-of-prostate-renal-and-colon-cancers-in-vitro
#3
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
https://www.readbyqxmd.com/read/27087736/a-transmetalation-reaction-enables-the-synthesis-of-18-f-5-fluorouracil-from-18-f-fluoride-for-human-pet-imaging
#4
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
https://www.readbyqxmd.com/read/26877575/amide-directed-formation-of-five-coordinate-osmium-alkylidenes-from-alkynes
#5
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
https://www.readbyqxmd.com/read/27064894/facile-arylation-of-four-coordinate-boron-halides-by-borenium-cation-mediated-boro-desilylation-and-destannylation
#6
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
https://www.readbyqxmd.com/read/26538791/bonding-in-complexes-of-bis-pentalene-dititanium-ti2-c8h6-2
#7
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
https://www.readbyqxmd.com/read/26538790/the-reductive-activation-of-co2-across-a-ti-ti-double-bond-synthetic-structural-and-mechanistic-studies
#8
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
https://www.readbyqxmd.com/read/27056379/in-depth-assessment-of-the-palladium-catalyzed-fluorination-of-five-membered-heteroaryl-bromides
#9
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
https://www.readbyqxmd.com/read/26877574/selective-aromatic-c-h-hydroxylation-enabled-by-%C3%AE-6-coordination-to-iridium-iii
#10
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
https://www.readbyqxmd.com/read/26294806/halide-mediated-ortho-deprotonation-reactions-applied-to-the-synthesis-of-1-2-and-1-3-disubstituted-ferrocene-derivatives
#11
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
https://www.readbyqxmd.com/read/26294805/wagner-meerwein-type-rearrangements-of-germapolysilanes-a-stable-ion-study
#12
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
https://www.readbyqxmd.com/read/26294804/oligosilanylsilatranes
#13
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
https://www.readbyqxmd.com/read/26146438/promoting-c-c-bond-coupling-of-benzyne-and-methyl-ligands-in-electron-deficient-triphos-pt-ch3-complexes
#14
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
https://www.readbyqxmd.com/read/26146437/contrasting-anticancer-activity-of-half-sandwich-iridium-iii-complexes-bearing-functionally-diverse-2-phenylpyridine-ligands
#15
Adam J Millett, Abraha Habtemariam, Isolda Romero-Canelón, Guy J Clarkson, Peter J Sadler
We report the synthesis, characterization, and antiproliferative activity of 15 iridium(III) half-sandwich complexes of the type [(η(5)-Cp*)Ir(2-(R'-phenyl)-R-pyridine)Cl] bearing either an electron-donating (-OH, -CH2OH, -CH3) or electron-withdrawing (-F, -CHO, -NO2) group at various positions on the 2-phenylpyridine (2-PhPy) chelating ligand giving rise to six sets of structural isomers. The X-ray crystal structures of [(η(5)-Cp*)Ir(2-(2'-fluorophenyl)pyridine)Cl] (1) and [(η(5)-Cp*)Ir(2-(4'-fluorophenyl)pyridine)Cl] (2) exhibit the expected "piano-stool" configuration...
June 8, 2015: Organometallics
https://www.readbyqxmd.com/read/26146436/gold-i-and-gold-iii-complexes-of-cyclic-alkyl-amino-carbenes
#16
Alexander S Romanov, Manfred Bochmann
The chemistry of Au(I) complexes with two types of cyclic (alkyl)(amino)carbene (CAAC) ligands has been explored, using the sterically less demanding dimethyl derivative (Me2)CAAC and the 2-adamantyl ligand (Ad)CAAC. The conversion of ((Ad)CAAC)AuCl into ((Ad)CAAC)AuOH by treatment with KOH is significantly accelerated by the addition of tBuOH. ((Ad)CAAC)AuOH is a convenient starting material for the high-yield syntheses of ((Ad)CAAC)AuX complexes by acid/base and C-H activation reactions (X = OAryl, CF3CO2, N(Tf)2, C2Ph, C6F5, C6HF4, C6H2F3, CH2C(O)C6H4OMe, CH(Ph)C(O)Ph, CH2SO2Ph), while the cationic complexes [((Ad)CAAC)AuL](+) (L = CO, CN (t) Bu) and ((Ad)CAAC)AuCN were obtained by chloride substitution from ((Ad)CAAC)AuCl...
June 8, 2015: Organometallics
https://www.readbyqxmd.com/read/26146435/reactivity-of-gold-hydrides-o2-insertion-into-the-au-h-bond
#17
Dragoş-Adrian Roşca, Julio Fernandez-Cestau, David L Hughes, Manfred Bochmann
Dioxygen reacts with the gold(I) hydride (IPr)AuH under insertion to give the hydroperoxide (IPr)AuOOH, a long-postulated reaction in gold catalysis and the first demonstration of O2 activation by Au-H in a well-defined system. Subsequent condensation gave the peroxide (IPr)Au-OO-Au(IPr) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). The reaction kinetics are reported, as well as the reactivity of Au(I) hydrides with radical scavengers.
June 8, 2015: Organometallics
https://www.readbyqxmd.com/read/25937692/metalated-oligosilanylstibines
#18
Rainer Zitz, Judith Baumgartner, Christoph Marschner
The reaction of a cyclic disilylated bromostibine with magnesium yields a rare example of a magnesium stibide that can be silylated with trimethylchlorosilane. Reaction of the thus-obtained trisilylated stibine with potassium tert-butoxide gives a potassium stibide in a clean reaction. Attempts to obtain an antimony-containing oligosilanide did not lead to the expected compound but to another potassium stibide, which presumably forms from the initially formed silanide by a 1,2-silyl shift. The synthetic potential of the obtained stibides to serve as building blocks could be shown by the preparation of stibylated zircono- and hafnocenes...
April 27, 2015: Organometallics
https://www.readbyqxmd.com/read/25937691/oligosilanylated-antimony-compounds
#19
Rainer Zitz, Karl Gatterer, Crispin R W Reinhold, Thomas Müller, Judith Baumgartner, Christoph Marschner
By reactions of magnesium oligosilanides with SbCl3, a number of oligosilanylated antimony compounds were obtained. When oligosilanyl dianions were used, either the expected cyclic disilylated halostibine was obtained or alternatively the formation of a distibine was observed. Deliberate formation of the distibine from the disilylated halostibine was achieved by reductive coupling with C8K. Computational studies of Sb-Sb bond energies, barriers of pyramidal inversion at Sb, and the conformational behavior of distibines provided insight for the understanding of the spectroscopic properties...
April 27, 2015: Organometallics
https://www.readbyqxmd.com/read/27642212/synthesis-structure-and-reactivity-of-co-ii-and-ni-ii-pcp-pincer-borohydride-complexes
#20
Sathiyamoorthy Murugesan, Berthold Stöger, Matthias Weil, Luis F Veiros, Karl Kirchner
The 15e square-planar complexes [Co(PCP(Me)-iPr)Cl] (2a) and [Co(PCP-tBu)Cl] (2b), respectively, react readily with NaBH4 to afford complexes [Co(PCP(Me)-iPr)(η(2)-BH4)] (4a) and [Co(PCP-tBu)(η(2)-BH4)] (4b) in high yields, as confirmed by IR spectroscopy, X-ray crystallography, and elemental analysis. The borohydride ligand is symmetrically bound to the cobalt center in η(2)-fashion. These compounds are paramagnetic with effective magnetic moments of 2.0(1) and 2.1(1) μB consistent with a d(7) low-spin system corresponding to one unpaired electron...
April 13, 2015: Organometallics
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