Studies of Some Group VIII Metal Complexes Containing Nitrogen Or Oxygen Donor Ligands PDF Download

Author: Michael Frank Uttley
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Category : Oxidation-reduction reaction
Languages : en
Pages : 772

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Author: Peter Brandon Critchlow
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ISBN:
Category : Ligands
Languages : en
Pages : 532

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Author: William B. Beaulieu
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ISBN:
Category : Ligands
Languages : en
Pages : 146

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Author: 李富華
Publisher: Open Dissertation Press
ISBN: 9781374727731
Category :
Languages : en
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This dissertation, "Syntheses, Structures and Reactivity of the Group 6 and 7 Metal Complexes Containing Chelating Nitrogen Donor Ligands and Metal-ligand Multiple Bonds" by 李富華, Fu-wa, Lee, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled "SYNTHESES, STRUCTURES AND REACTIVITY OF THE GROUP 6 AND 7 METAL COMPLEXES CONTAINING CHELATING NITROGEN DONOR LIGANDS AND METAL-LIGAND MULTIPLE BONDS" submitted by Lee Fu Wa for the degree of Doctor of Philosophy at the University of Hong Kong in September, 1997. ____________________________________________________________________ [Cr(CRMe )Cl ] (CRMe =meso-2,3,7,11,12-pentamethyl-3,7,11,17- 3 2 3 2+ tetraazabicyclo[11.3.1]-heptadeca-1(17),13,15-triene), [Cr(CRMe )Cl(H O)], 3 2 2+ + [Cr(CRMe )Cl(CH CN)] and [Cr(CRMe )(N )(OH)] are prepared. Upon addition 3 3 3 3 2+ 2+ of PhI=O to solutions of [Cr(CRMe )Cl(CH CN)] and [Cr(CRMe )Cl(H O)] 3 3 3 2 respectively in CH CN, the UV-visible absorption spectra of the two mixtures show similar isosbestic spectral changes attributed to the formation of V 2+ [Cr (CRMe )Cl(O)] . Addition of PhP causes the immediate recovery of 3 3 2+ [Cr(CRMe )Cl(CH CN)] as the isosbestic changes are reversed. Irradiation of 3 3 [Cr(CRMe )(N )(OH)] in acetonitrile with UV-visible light gives an azide-free 3 3 product, the FAB-MS of which shows a molecular ion peak indicative of V + + ([Cr (CRMe )(N)]ClO ). The UV-visible spectra of [Cr(CRMe )Cl ], 3 4 3 2 2+ 2+ [Cr(CRMe )Cl(H O)] and [Cr(CRMe )Cl(CH CN)] measured in water are 3 2 3 3 3+ similar to that of [Cr(CRMe )(H O) ] . Results from the conductivity measurement 3 2 2 + 2+ show that in water, [Cr(CRMe )Cl ], [Cr(CRMe )Cl(H O)] and 3 2 3 2 2+ [Cr(CRMe )Cl(CH CN)] behave as 3:1 electrolytes. The species which exists in 3 3 3+ water is likely to be the di-aquo complex [Cr(CRMe )(H O) ] . 3 2 2 2+ 2+ [Cr(CRMe )Cl(H O)] and [Cr(CRMe )Cl(CH CN)] are both found to give a 3 2 3 3 reversible oxidation couple at +1.11 V vs. SCE in aqueous solutions at pH=1 which is assigned to Cr(III)/(IV). iii t + The bis(imido) complexes [(TACN)M(N Bu) Cl] (M=Cr, Mo; TACN=1,4,7-triazacyclononane) and their 1,4,7-trimethyl derivatives are prepared, the crystal structures of which reveal the trans influence of the imido group. These 0 +/0 d species display a quasi-reversible couple at potentials 0.86 - 1.20 V vs. Cp Fe in acetonitrile assignable to a imido ligand-centred oxidation. (Me TACN)Mo(CO), 1,4,7-Tri((S)-2-methylbutyl)-1,4,7-triazacyclononane 3 3 * * * (L ) and L Mo(CO) are synthesized. (Me TACN)Mo(CO) and L Mo(CO) show 3 3 3 3 +/0 reversible oxidation couples at -0.26 V and -0.24 V vs. Cp Fe in CH CN 2 3 I/0 respectively which are assigned to Mo . The comparable electronic effect of * Me TACN and L in this system is therefore implied. 2+ [(Me TACN) Mn (μ-O)(μ-OCOCH ) ] is prepared and found to mediate 3 2 2 3 2 aziridination of styrene, methylstyrene, cis- and trans-stilbene, 1,1-diphenylethene and norbornene by PhI=NTs in CH Cl at 25 C. The nitrene transfer to cis- and 2 2 trans-stilbene is found to be stereoselective to exclusively give the trans-aziridine product. + + [(Me TACN)(CO) M CPh] (M=Mo, W) and [(TACN)(CO) Mo CPh] 3 2 2 are prepared. [(Me TACN)(CO) M CPh] (M=Mo, W) exhibit a reversible 3 2 +/0 reduction couple at -2.15 V vs Fe Cp and an irreversible wave at 0.77 V vs +/0 Fe Cp, which are ascribed to a reduction centred at the phenyl ring and oxidation of the terminal CO respectively. Treatment of Cl(

Author: Alexander Rothenberger
Publisher:
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Category :
Languages : en
Pages :

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Author: Vesa Hietapelto
Publisher:
ISBN: 9789514251863
Category :
Languages : en
Pages : 61

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Author:
Publisher: Academic Press
ISBN: 0080580181
Category : Science
Languages : en
Pages : 525

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Advances in Organometallic Chemistry

Author: Jelena Jenter
Publisher: Cuvillier Verlag
ISBN: 3736933428
Category : Science
Languages : en
Pages : 134

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Bis(phosphinimino)methanide rare earth metal bisborohydrides, as illustrated in Scheme I, were successfully synthesized by salt metathesis reactions of [K{CH(PPh2NSiMe3)2}] with [Ln(BH4)3(THF)n] (Ln = Sc (n = 2); Ln = La, Nd, Lu (n = 3)) or in the case of yttrium by the reaction of [{(Me3SiNPPh2)2CH}YCl2]2 with NaBH4. Interestingly, the BH4- anions are ?3-coordinated in the solid state structures of 3, 4, 6 and 7, while for the scandium complex 5 two different conformational polymorphs were identified, in which either both BH4- groups are ?3-coordinated or one BH4- anion shows an ?2-coordination mode. Furthermore, complexes 3, 6 and 7 showed high activities in the ring-opening polymerization (ROP) of e-caprolactone (CL). At 0 °C, the molar mass distribution reached the narrowest values ever obtained for the ROP of CL initiated by a rare earth metal borohydride species. In collaboration with N. Meyer, rare earth metal chlorides and borohydrides of the 2,5-bis{N-(2,6-diisopropylphenyl)iminomethyl}pyrrolyl ligand were synthesized, as shown in Scheme II. The reaction of [(DIP2pyr)K] (10) with anhydrous neodymium trichloride afforded [(DIP2pyr)NdCl2(THF)]2 (12) which is dimeric in the solid state. Excitingly, the reaction of [(DIP2pyr)K] (10) with [Ln(BH4)3(THF)n] (Ln = Sc (n = 2); Ln = La, Nd, Lu (n = 3)) depends on the ionic radii of the center metals. For the larger rare earth metals lanthanum and neodymium, the expected products [(DIP2pyr)Ln(BH4)2(THF)2] (Ln = La (13), Nd (14)) were obtained; while for the smaller rare earth metals scandium and lutetium, an unusual redox reaction of a BH4- anion with one of the Schiff-base functions of the ligand was observed and the products [{DIP2pyr*-BH3}Ln(BH4)(THF)2] (Ln = Sc (15), Lu (16)) were formed (Scheme II). Moreover, the two neodymium containing complexes 12 and 14 were investigated as Ziegler-Natta catalysts for the polymerization of 1,3-butadiene to form poly-cis-1,4-butadiene, by using various cocatalyst mixtures. Very high activities and good selectivities were observed for 12. The 2,5-bis{N-(2,6-diisopropylphenyl)iminomethyl}pyrrolyl ligand was successfully introduced into the coordination chemistry of the divalent lanthanides and the alkaline earth metals. As shown in Scheme III, salt metathesis reactions of [(DIP2pyr)K] (10) with either anhydrous lanthanide diiodides or alkaline earth metal diiodides afforded the corresponding heteroleptic iodo complexes [(DIP2pyr)LnI(THF)3] (Ln = Sm (19), Eu (20), Yb (21)) or [(DIP2pyr)MI(THF)n] (M = Ca (24), Sr (22) (n = 3); Ba (23) (n = 4)). Surprisingly, all complexes 19-24 are monomeric in the solid state, independently from the ionic radii of their center metals. Instead of forming dimers, the coordination sphere of each metal center is satisfied by additionally coordinated THF molecules, which is a very rare structural motif in the chemistry of the larger divalent lanthanides and alkaline earth metals. While the (DIP2pyr)- ligands in 19-23 are ?3-coordinated in the solid state, for the calcium complex 24 an ?2-coordination mode was observed (Scheme III). Interestingly, the calcium complex 24 and the analogous ytterbium compound 21 show different structures in the solid state. In order to obtain catalytically active species, [(DIP2pyr)M{N(SiMe3)2}(THF)2] (M = Ca (25), Sr (26)) were prepared by the reaction of [(DIP2pyr)MI(THF)3] (M = Ca (24), Sr (22)) with [K{N(SiMe3)2}] (Scheme IV). Compounds 25 and 26 were investigated for the intramolecular hydroamination of aminoalkenes and one aminoalkyne. Unfortunately, both catalysts exhibit a limited reaction scope, caused by the formation of undesired side products by alkene isomerization and imine-enamine tautomerism. However, both compounds are active catalysts and show high yields and short reaction times. The highest activities were observed for the calcium complex 25 and can be compared to the results obtained with the ß-diketiminato calcium amide [{(DIPNC(Me))2CH}Ca{N(SiMe3)2}(THF)] as a catalyst. Finally, imidazolin-2-imide and cyclopentadienyl-imidazolin-2-imine rare earth metal alkyl complexes, synthesized by M. Tamm et al., were investigated for the intramolecular hydroamination of non-activated aminoalkenes and one aminoalkyne. Both compounds showed high selectivities and activities, and although they cannot compete with the metallocene analogues, the imidazolin-2-imide complexes are new and interesting examples for catalytically active post-metallocenes.

Author: Phunrawie Sroisuwan
Publisher:
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Category :
Languages : en
Pages :

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Author: Bikimi Ayiya
Publisher:
ISBN:
Category : Heterocyclic compounds
Languages : en
Pages : 279

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This thesis describes the design and syntheses of metal complexes that contain chelating ligands with different combinations of pyridinylidene amide (PYA), amidate, and remote-N-heterocyclic carbene (rNHC) or a mesoionic-remote-N-heterocyclic carbene (m-rNHC) donor functions. Although ligands with amidate donors are relatively well known, metal complexes of ligands containing the other donors are relatively unexplored. All these groups exhibit strong donating properties. It was expected that suitable metal complexes of these new ligands could show interesting catalytic activity in reactions such as transfer hydrogenation. In Chapter 1, an overview of the chemistry and existing synthetic routes to a range of different pyridine derived ligands are given. The coordination chemistry and applications of these classes of ligands are briefly discussed and the motivation for this work is outlined at the end. In Chapter 2, the syntheses of two new palladium(II) NC’N-tridentate pincer complexes ([Pd(L)(LPPy{Me}3)]OTf), L= Cl, OAc) that features both rNHC and two PYA donors are described. The tricationic pro-ligand [H2LPPy{Me}3][OTf]3, bearing two pendant alkylated 4-pyridyl arms at the 3,5-positions of the head group pyridine was metallated with Pd(OAc)2 or [PdCl2(PhCN)2] by heating with NaOAc in situ. The two complexes were stable in air and moisture, but sparingly soluble in common solvents and this precluded further studies. The smaller related bidentate pro-ligands [LmPy{Me}2]OTf and [LPPy{Me}2]OTf, were synthesised and on metallation by heating in the presence of acetate afforded [RhCl(LmPy{Me}2)Cp*]OTf and [RhCl(LPPy{Me}2)Cp*]OTf. X-ray crystallography and NMR studies of these complexes confirmed coordination occurred through PYA and rNHC donors. In Chapters 3 and 4, the syntheses of the sets of pro-ligands [HLp1-6{Bz}]Cl and [HLm1-6{Bz}]Clis described. The compounds within each set differ in that they have different substituents (e.g. Ph, Me, OMe, Naphthyl, Cl and NO2) in the para-position of the aryl ring attached to the insipient amidate nitrogen donor. On metallation, these pro-ligands coordinate as bidentate ligands with amidate and rNHC donors (in the case of [HLm1-6{Bz}]Cl) or amidate and m-rNHC donors (in the case of [HLp1-6{Bz}]Cl). Metallation of the pro-ligands using [IrCp*Cl2]2as the metal substrate gives the sets of neutral complexes [IrCl(Lm1-6{Bz})Cp*] and [IrCl(Lp1-6{Bz})Cp*]. The corresponding cationic complexes [Ir(Lx1-6{Bz})(L)Cp*]OTf(L= DMSO, CO, Py, x= m, p) were prepared by Ag+ promoted exchange of the chloride ligands in [IrCl(Lx1-6{Bz})Cp*] (x= m, p) with DMSO, CO or pyridine. Comparison of the molecular structures of both the neutral and cationic forms of all the complexes obtained via single-crystal XRD suggests that the complexes with the rNHC donors ([IrCl(Lm1-6{Bz})Cp*], [Ir(Lm1-6{Bz})(L)Cp*]OTf(L= DMSO, CO, Py) all exhibit a similar pattern of C–C bond lengths within the pyridinium ring of the rNHC donor with some 2,5-diene character. In contrast, the complexes with m-rNHC donors ([IrCl(Lp1-6{Bz})Cp*], [Ir(Lp1-6{Bz})(L)Cp*]OTf(L= DMSO, CO) the C–C bond lengths in the corresponding rings are nearly equal suggesting a more pronounced aromatic character in these cases. On treatment of the pro-ligands [HLm1-2{Bz}]Cl with RuCl3.xH2Othe complexes [RuCl(Lm2,3{Bz})(PPh3)2(CO)]Cl were obtained. Unlike the iridium complexes formed with the same pro-ligands, the donor groups in these complexes were the carbon of a rNHC and the oxygen of the unchanged carboxamide group. The catalytic activities of the complexes [Ir(Lx1-6{Bz})(L)Cp*]OTf(L = DMSO, x= m,p) and [RuCl(Lm2,3{Bz})(PPh3)2(CO)]Cl were tested in both transfer hydrogenation and dehydrogenation. The results of these studies are described in Chapter 5. Notably, it was found that the iridium mesoionic-rNHC-containing complexes with methoxy substituents were the most active in the dehydrogenation of benzyl alcohol to benzaldehyde, achieving 99.9% conversion under 12 h. In transfer hydrogenation using isopropanol as the hydrogen source, the same mesoionic-rNHC-containing iridium complexes with OMe substituents were also the best iridium catalysts. Complete conversion of benzaldehyde to benzyl alcohol with 2 mol% catalyst loading occurred in 8 min. However, the ruthenium complexes displayed exceptionally good transfer hydrogenation catalytic activity reaching 99.9% conversion within3 min at 1 mol% catalyst loading, with TOF 1700 h-1. It was proposed that the hemilabilenature of the O-bound carboxamide group, the ancillary ligands and trans-influence alongside the donor strength of the rNHC group were important factors for the high activity displayed by the Ru(II) complexes. Finally, the thesis conclusion is outlined in this chapter.