Preparation and CO Insertion Reactions of Late Transition Metal (mu)-Imido/Amido Complexes PDF Download
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Author: Fei Peng
Publisher:
ISBN:
Category : Organometallic chemistry
Languages : en
Pages : 140
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Author: Fei Peng
Publisher:
ISBN:
Category : Organometallic chemistry
Languages : en
Pages : 140
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Author:
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ISBN:
Category :
Languages : en
Pages : 8
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The synthesis and reactions of late-transition-metal oxo and imido complexes was explored. The deprotonation of platinum(II) hydroxo complexes yielded new oxo complexes. Attempted deprotonation of Cp*Rh(III) hydroxo complexes did not give oxo complexes but complex mixtures probably resulting from reduction of the Rh(III) center. The reaction of Na/Hg with (Cp*RhCl2)2 gave the very reactive Rh(II) dimer, (Cp*RhCl)2. Rhodium(I) imido complexes with the bis(dimethylphosphino)methane ligand were prepared and found to be similar to the previously prepared bis(diphenylphosphino)methane complexes. Attempts to prepare bis(diphenylphosphino)methylamine, bis(diphenylphosphino)phenylamine, PMe{sub e} and NO analogues were not successful. Attempts to prepare Cp*Rh(III) imido complexes resulted in amido complexes and reduction. Rhodium (III) tris(3.5-dimethylpyrazoyl)borate analogues are reduction resistant but have not yet yielded imido complexes. The first imido complexes of Au were prepared by treating a Au oxo complex with amines or isocyanates. Dimeric Cp*Rh dioxygen and nitrosobenzene complexes were prepared by insertion into the Rh-Rh bond of (Cp*RhCl)2. The dioxygen complex activates a C-H bond of the Cp* ligand on treatment with PMe3. Imido and oxo complexes nitrene and oxygen atom transfer product in reactions with CO. A novel electrophilic ring addition was observed with sterically protected aryl imido complexes. 15 refs.
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Languages : en
Pages : 4
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A range of new phosphine Au(I) oxo complexes, [(LAu)3([mu]-O)], were prepared, testing the limits of the phosphine steric and electronic properties. Their reaction with reducing agents (hydrazines, CO and RNC) give a variety of new and known gold clusters in unprecedented high yields and establish the steric and electronic relationships between the phosphine and the nuclearity of the product Au cluster. The [L2Pt([mu]-O)]2 class of dioxo complexes has been expanded to include the first anionic oxo complex, ([(dppm-H)Pt([mu]-O)]2)Li2 and the first Pt imido complexes, [(L2Pt)2([mu]-O)([mu]-NR)] and [L2Pt([mu]-NR)]2. The previously observed Rh imido/amido A-frame chemistry has been extended to Ir. The p-MePh-imido complex has been characterized by X-ray diffraction and clearly shows the resonance delocalization of the nitrogen lone pair into the aryl ring which is responsible for the previously observed electrophilic ring addition and oxidative ring coupling reactions.
Author: Manoj K. Kolel-Veetil
Publisher:
ISBN:
Category : Metal complexes
Languages : en
Pages : 470
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Category : Aeronautics
Languages : en
Pages : 316
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Author: Pei Zhao
Publisher:
ISBN: 9781339544052
Category :
Languages : en
Pages :
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This dissertation focuses on the synthesis, characterization and reactivity study of terphenyl ligand stabilized bis([mu]-oxo) dimeric iron and cobalt complexes. The synthesis and characterization of low-coordinate cobalt alkyl and iron alkyl complexes are also described. In addition, it describes the preparation of the first monomeric homoleptic solvent-free bis(aryloxide) lanthanide complex. The solid state structures of new compounds were determined by single crystal X-ray crystallography. Magnetic properties of paramagnetic compounds were measured by superconducting quantum interference device (SQUID) or Evans' methods for solid state or solution phase, respectively. The new compounds were also characterized by UV-Visible spectroscopy. Furthermore, infrared spectroscopy, Mössbauer spectroscopy, electron paramagnetic resonance spectroscopy, mass spectrometry, cyclic voltammetry and elemental analysis were employed to characterize some of the compounds when applicable. In some cases, DFT calculations were applied to elucidate the bonding and energy levels of molecular orbitals in the complexes. In Chapter 2, The bis([mu]-oxo) dimeric complexes {Ar[superscript iPr8]OM([mu]-O)}2 (Ar [superscript iPr8] = -C6H-2,6-(C6H2-2,4,6-[superscript i]Pr3)2-3,5-[superscript i]Pr2; M = Fe or Co) were prepared by oxidation of the metal (I) half-sandwich complexes {Ar[superscript iPr8]M([eta]6-arene)} (arene = benzene or toluene; M = Fe or Co). The iron species {Ar[superscript iPr8]OFe([mu]-O)}2 was prepared by reacting {Ar[superscript iPr8]Fe([eta]6-benzene)} with N2O or O2 and the cobalt species {Ar[superscript iPr8]OCo([mu]-O)}2 was prepared by reacting {Ar[superscript iPr8]Co([eta]6-toluene)} with O2. Both {Ar[superscript iPr8]OFe([mu]-O)}2 and {Ar[superscript iPr8]OCo([mu]-O)}2 were characterized by X-ray crystallography, UV-vis spectroscopy, magnetic measurements and, in the case of the iron species, by Mössbauer spectroscopy. The solid-state structures of both compounds reveal unique M2([mu]-O)2 (M = Fe or Co) cores with formally three-coordinate metal ions. The Fe···Fe separation in {Ar[superscript iPr8]OFe([mu]-O)}2 bears a resemblance to that in the Fe2([mu]-O)2 diamond core proposed for the methane monooxygenase intermediate Q. The structural differences between {Ar[superscript iPr8]OFe([mu]-O)}2 and {Ar[superscript iPr8]OCo([mu]-O)}2 are reflected in rather differing magnetic behavior. Compound {Ar[superscript iPr8]OCo([mu]-O)}2 is thermally unstable and its decomposition at room temperature resulted in the oxidation of the Ar[superscript iPr8] ligand via oxygen insertion and addition to the central aryl ring of the terphenyl ligand to produce the 5,5'-peroxy-bis[4,6-[superscript i]Pr2-3,7-bis(2,4,6-iPr3-phenyl)oxepin-2(5H)-one]. The structure of the oxidized terphenyl species is closely related to that of a key intermediate proposed for the oxidation of benzene. In Chapter 3, the homoleptic, cobalt(I) alkyl [Co{C(SiMe2Ph)3}]2 was prepared by reacting CoCl2 with [Li{C(SiMe2Ph)3}(THF)] in a 1:2 ratio though the initial intent was to synthesize a dialkyl cobalt (II) complex. Attempts to synthesize the corresponding iron(I) species led to the iron(II) salt [Li(THF)4][Fe2([mu]-Cl)3{C(SiMe2Ph)3}2]. Both complexes were characterized by X-ray crystallography, UV-vis spectroscopy, and magnetic measurements. The structure of [Co{C(SiMe2Ph)3}]2 consists of dimeric units in which each cobalt(I) ion is [sigma]-bonded to the central carbon of the alkyl group -C(SiMe2Ph)3 and [pi]-bonded to one of the phenyl rings of the -C(SiMe2Ph)3 ligand attached to the other cobalt(I) ion in the dimer. The structure of [Li(THF)4][Fe2([mu]-Cl)3{C(SiMe2Ph)3}2] features three chlorides bridging two iron(II) ions. Each iron (II) ion is also [sigma]-bonded to the central carbon of a terminal -C(SiMe2Ph)3 anionic ligand. The magnetic properties of [Co{C(SiMe2Ph)3}]2 reveal the presence of two independent cobalt (I) ions with S = 1 and a significant zero-field splitting of D = 38.0(2) cm−1. The magnetic properties of [Li(THF)4][Fe2([mu]-Cl)3{C(SiMe2Ph)3}2] reveal extensive antiferromagnetic exchange coupling with J = -149(4) cm−1 and a large second-order Zeeman contribution to its molar magnetic susceptibility. Formation of the alkyl [Co{C(SiMe2Ph)3}]2 and the halide complex [Li(THF)4][Fe2([mu]-Cl)3{C(SiMe2Ph)3}2] under similar conditions is probably due to the fact that Co(II) is more readily reduced than Fe(II). Some other synthetic routes were also attempted to synthesize a dialkyl cobalt (II) complex and they are described in this chapter. Neither [Co(NPh2)2]2 nor cobaltocene reacts with [Li{C(SiMe2Ph)3}(THF)] to afford a dialkyl cobalt (II) complex. Metathesis reactions of cobalt halides with lithium salts of alkyl ligand HCPh2R (R = -Ph or -SiMe3) resulted in the reduction of cobalt (II) to cobalt metal and the coupling of ligands, which indicate that homolytic cleavage of the cobalt-carbon bond was probably involved in the metathesis reactions. Furthermore, in chapter 4, reaction of Sm[N(SiMe3)2]2(THF)2 with two equivalents of bulky aryloxide ligand HOAr[superscript iPr6] (Ar[superscript iPr6] = -C6H3-2,6-(C6H2-2,4,6-[superscript i]Pr3)2) afforded the first monomeric homoleptic solvent-free bis(aryloxide) lanthanide complex Sm(OAr[superscript iPr6])2. The complex was characterized by crystallography, UV-Visible spectrum, IR and magnetically by the Evans' method. The O-Sm-O angle is bent at 111.08(9)̊. The samarium ion in Sm(OAr[superscript iPr6])2 also shows weak interactions with the flanking aryl rings of the terphenyloxide ligands. The complex is paramagnetic at room temperature with magnetic moment of 3.51 [mu]B.
Author: Hui Shan
Publisher:
ISBN:
Category : Organometallic chemistry
Languages : en
Pages : 412
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Rhodium/gold (1a, 1b) and iridium/gold (2) [mu] 4 -oxo complexes with diene ligands have been synthesized from reactions between [(AuPPh 3) 3 ([mu]-O)]BF 4 and [(diene)MCl] 2 (M = Rh, diene = NBD, COD; M = Ir, diene = COD). A family of platinum/gold [mu] 3 -oxo complexes with COD ligand (3a-3g), [(1,5-COD)Pt([mu]-OAuL)] 2 (BF 4) 2 (L = PPh 3, PPh 2 Pr i, PPh 2 Et, P(o-toly) 3, P(p-toly) 3, P(p-MeOPh) 3, P(p-CF 3 Ph) 3), and a gold free platinum [mu] 3 -oxo/hydroxo complex, [(1,5-COD) 4 Pt 4 ([mu] 3 -O) 2 ([mu]-OH)](BF 4) 3 (5) are also prepared from the novel oxo/halide exchange synthetic route. The structural and chemical properties of these new compounds have been studied. One of the special properties of 5 is its unique ability of reacting with unactivated olefins (e.g. ethylene, tetramethylethylene, and cyclooctadiene) to give oxidized organic products or intermediate adducts. The mechanism of olefin insertion into M-O bond is favored in the attempted rationalization of the formation of the diverse products observed in the reactions. A whole family of complexes (13a-13f), [(AuL) 6 N 2](BF 4) 2 (L = PPh 2 Pr i, PPh 2 Et, PPh 2 Me, P(p-toly) 3, P(p-MeOPh) 3, P(p-CF 3 Ph) 3), which contains dinitrogen bonding simultaneously to six metal atoms is synthesized and characterized. These compounds are studied as structural models for the coordination of dinitrogen at the center of the nitrogenase Fe-Mo cofactor cluster. The existence of our compound supports the idea that the bond order of dinitrogen is reduced from 3 to 1 on initial coordination to the inside of the cluster. The chemical properties of these new hydrazido complexes have been studied. One of the special properties of 13 is their unique ability of being reduced and protonated to generate ammonia. This reactivity makes them suitable chemical model for the reduction of dinitrogen at the active site of nitrogenase. Considerable experimental work has been devoted to the understanding of the protonation process of complex 13a, [(AuPPh 2 Pr i) 6 N 2](BF 4) 2 . Two partially protonated species, [(AuPPh 2 Pr i) 5 HN 2] 2+ and [(AuPPh 2 Pr i) 4 H 2 N 2] 2+, are determined and considered to be key intermediates in the generation of ammonia. Preliminary kinetic studies have been carried out, which led to the proposal that the formation of [(AuPPh 2 Pr i) 5 HN 2] 2+ species occur through an associate process involving the formation of a highly reactive hyper-coordinated complex, [(AuPPr i Ph 2) 6 N 2 H] 3+ [double dagger], in the transition-state.
Author: Michael Sean Driver
Publisher:
ISBN:
Category :
Languages : en
Pages : 426
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Author:
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Category :
Languages : en
Pages :
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Examples of late transition metal complexes with amido, alkoxo and sulfido ligands are relatively rare in part due to enhanced reactivity based on nucleophilicity and basicity of the heteroatomic ligand (X). The highly nucleophilic and basic character of formally anionic X ligands coordinated to metal centers with low oxidation states is attributable to the disruption of ligand-to-metal pi-bonding. Examples of common reactivity for these systems include nucleophilic addition reactions, insertions of unsaturated substrates, acid/base chemistry with acidic C-H bonds and C-H activation reactions with aromatic substrates. In addition to fundamental reactivity studies, these complexes also offer opportunities for incorporation into catalytic processes. Late transition metal complexes with non-dative X ligands have been implicated in several C-X bond forming reactions and have been demonstrated to activate non-polar substrates. Thus, in order to advance the understanding of these reactive systems and to exploit the prospects for synthetic applications toward small molecule transformations, further study is warranted. Presented herein is the study of (IPr)Cu(NR2), (IPr)Cu(OR) and (IPr)Cu(SR) {IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene} complexes in the catalytic hydroamination of electron-deficient olefins toward regioselective formation of C-N, C-O and C-S bonds. The substrate scope encompasses alkyl and aryl amines, including primary and secondary variants, as well as alcohols and thiols. Olefins with cyano, acyl, and ester functionalities and vinylarenes are reactive. In a demonstration of potential application, the hydroamination of p-nitrostyrene with N-methylbenzylamine by (IPr)Cu(NHPh) provides a straight-forward single-step route to an anti-arrhythmic agent. Mechanistic studies are consistent with a reaction pathway that involves intermolecular nucleophilic addition of the Cu-amido to free olefin. In an effort to obtain more active catalyst systems that.
Author: Robert H. Crabtree
Publisher: John Wiley & Sons
ISBN: 0471718750
Category : Science
Languages : en
Pages : 600
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Fully updated and expanded to reflect recent advances, this Fourth Edition of the classic text provides students and professional chemists with an excellent introduction to the principles and general properties of organometallic compounds, as well as including practical information on reaction mechanisms and detailed descriptions of contemporary applications.
