Syntheses, Structures and Reactivity of the Group 6 and 7 Metal Complexes Containing Chelating Nitrogen Donor Ligands and Metal-Ligand Multiple Bonds PDF Download

Author: 李富華
Publisher: Open Dissertation Press
ISBN: 9781374727731
Category :
Languages : en
Pages :

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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: Fu-wa Lee
Publisher:
ISBN:
Category : Ligands
Languages : en
Pages : 504

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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.

Author: William A. Nugent
Publisher: Wiley-Interscience
ISBN:
Category : Science
Languages : en
Pages : 360

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The only comprehensive one-volume text/reference on metal-ligand multiple bonds. Stresses the unified nature of the field and includes handy new tabulations of data. The flow within each subtopic is oxygen to nitrogen to carbon. Coverage is up-to-date--virtually every subtopic leads to interesting questions for future research. Presents information otherwise scattered through hundreds of publications.

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: Meg E. Fasulo
Publisher:
ISBN:
Category :
Languages : en
Pages : 120

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The ruthenium triflate complex Cp*(PiPr3)RuOTf (1) was generated from the reaction of Cp*(PiPr3)RuCl with Me3SiOTf in dibutyl ether. Complex 1 reacted with primary and secondary silanes to produce a family of Ru(IV) silyl dihydride complexes of the type Cp*(PiPr3)Ru(H)2(SiRR'OTf) (3 - 12). Structural analyses of complexes 8 (R = R' = Ph) and 12 (R = R' = fluorenyl) revealed the presence of a tetrahedral silicon center and a four-legged piano stool geometry about ruthenium. Anion abstraction from Cp*(PiPr3)Ru(H)2(SiHROTf) by [Et3Si*toluene][B(C6F5)4] afforded hydrogen-substituted cationic ruthenium silylene complexes [Cp*(PiPr3)Ru(H)2(=SiHR)][B(C6F5)4] (R = Mes (13), R = Si(SiMe3) (14)) that display a significant Ru - H ... Si interaction, as indicated by relatively large 2JSiH coupling constants (2JSiH = 58.2 Hz (13), 2JSiH = 37.1 Hz (14)). The syntheses of secondary silylene complexes [Cp*(PiPr3)Ru(H)2(=SiRR')][B(C6F5)4] (R = R' = Ph (15); R = Ph, R' = Me (16), R = R' = fluorenyl (17)) were also achieved by anion abstraction with [Et3Si*toluene][B(C6F5)4]. Complexes 15 - 17 do not display strong Ru - H ... Si secondary interactions, as indicated by very small 2JSiH coupling constant values. The cationic ruthenium silylene complex [Cp*(PiPr3)Ru(H)2(SiHMes)] [CB11H6Br6], a catalyst for olefin hydrosilations with primary silanes, was isolated and characterized by X-ray crystallography. Relatively strong interactions between the silylene Si atom and Ru-H hydride ligands appear to reflect a highly electrophilic silicon center. Kinetic and mechanistic studies on hydrosilations with this catalyst reveal a fast, initial addition of the Si-H bond of the silylene complex to the olefin. Subsequent migration of a hydride ligand to silicon produces a 16-electron intermediate, which can be trapped by olefin, resulting in inhibition of catalysis, or intercepted by the silane substrate. The latter reaction pathway, involving oxidative addition of the Si-H bond and a somewhat concomitant loss of product, is the rate-determining step in the catalytic cycle. Reactions of the cationic ruthenium silylene complexes [Cp*(PiPr3)Ru(H)2(=SiRR')][B(C6F5)4] (R = Mes, R' = H, 1; R = R' =Ph, 2) with alkenes, alkynes, ketones, and Lewis bases were explored. Addition of 1-hexene, 3,3-dimethylbut-1-ene, styrene, and cyclopentene to 1 afforded the disubstituted silylene products [Cp*(PiPr3)Ru(H)2(=SiMesR)][B(C6F5)4] (R = Hex, 3; R = CH2CH2tBu, 4; R = CH2CH2Ph, 5; R = C5H9, 6). Analogous reactions with 2-butyne and 3,3-dimethylbut-1-yne yielded the vinyl-substituted silylene complexes [Cp*(PiPr3)Ru(H)2(=Si(CR=CHR')Mes)][B(C6F)4] (R = R' = Me, 7; R = H, R' = tBu, 8). Complex 1 undergoes reactions with ketones to give the heteroatom-substituted silylene complexes [Cp*(PiPr3)Ru(H)2(=Si(OCHPhR)Mes)][B(C6F)4] (R = Ph, 9; R = Me, 10). Interestingly, complexes 3 - 8 display a weak interaction between the hydride ligands and the silicon center, while 9 and 10 exhibit a relatively large interaction (as determined by 2JSiH values). The reaction of isocyanates with 1 resulted in the silyl complexes [Cp*(PiPr3)Ru(H)2(Si(Mes)[n2-O(CH)(NC6H4R)][B(C6F5)4] (R = H, 11; R = CF3, 12), and an intermediate in this transformation is observed. Complex 2 was subjected to various Lewis bases to yield the base-stabilized silylene complexes [Cp*(PiPr3)Ru(H)2(SiPh2*L)][B(C6F)4] (L = DMAP, 13; L = Ph2CO, 14; L = PhCONH2, 15; L = NHMePh, 16, L = tBuSONH2, 18) and the reaction of 1 with NHMePh gave [Cp*(PiPr3)Ru(H)2(SiHMes*NHMePh)][B(C6F)4]. The cationic germylene complex [Cp*(PiPr3)Ru(H)2(=GeMes2)][OTf] (1) was synthesized from the reaction of Cp*(PiPr3)RuOTf with H2GeMes2, and addition of DMAP to 1 yielded the neutral germylene complex [Cp*(PiPr3)Ru(H)(=GeMes2) (2). The reaction of H3GeTrip and Cp*(PiPr3)RuCl gave the germyl complex Cp*(PiPr3)Ru(H)2(GeHTripCl) (3), which undergoes a reaction with Li(Et2O)2[B(C6F5)4] to afford the cationic H-substituted germylene complex [Cp*(PiPr3)Ru(H)2(=GeHTrip)][B(C6F5)4] (4). Addition of 1-hexene, 3,3-dimethylbut-1-ene, styrene, and allyl chloride to 4 afforded the disubstituted germylene products [Cp*(PiPr3)Ru(H)2(=GeTripR)][B(C6F5)4] (R = Hex, 5; R = CH2CH2Ph, 6; R = CH2CH2tBu, 7; R = CH2CH2CH2Cl, 8). Analogous reactions with 2-butyne and 3,3-dimethylbut-1-yne yielded the vinyl-substituted germylene complexes [Cp*(PiPr3)Ru(H)2(=Ge(CR=CHR')Trip)][B(C6F)4] (R = H, R' = tBu, 9; R = R' = Me, 10). New di(phosphine)-supported rhodium and iridium silyl complexes were synthesized. Reactions of the di(t-butylphosphino)ethane complex (dtbpe)Rh(CH2Ph) with Ph2SiH2 and Et2SiH2 resulted in isolation of (dtbpe)Rh(H)2(SiBnPh2) (1, Bn = CH2Ph) and (dtbpe)Rh(H)2(SiBnEt2) (2), respectively. Both 1 and 2 display strong interactions between the rhodium hydride ligands and the silyl ligand, as indicated by large 2JSiH values (44.4 and 52.1 Hz). The reaction of (dtbpm)Rh(CH2Ph) (dtbpm = di(t-butylphosphino)methane) with Mes2SiH2 gave the pseudo-three-coordinate Rh complex (dtbpm)Rh(SiHMes2) (3), which is stabilized in the solid state by agostic interactions between the rhodium center and two C - H bonds of a methyl substituent of a mesityl group. The analogous germanium compound (dtbpm)Rh(GeHMes2) (4) is also accessible. Complex 3 readily undergoes reactions with diphenylacetylene, phenylacetylene, and 2-butyne to give the silaallyl complexes (dtbpm)Rh[Si(CPh=CHPh)Mes2] (5), (dtbpm)Rh[Si(CH=CHPh)Mes2] (7), and (dtbpm)Rh(Si(CMe=CHMe)Mes2) (8) via net insertions into the Si - H bond. The germaallyl complexes (dtbpm)Rh[Ge(CPh=CHPh)Mes2] (6) and (dtbpm)Rh[Ge(CMe=CHMe)Mes2] (9) were synthesized under identical conditions starting from 4. The reaction of (dtbpm)Rh(CH2Ph) with 1 equiv of TripPhSiH2 yielded (dtbpm)Rh(H)2[5,7-diisopropyl-3-methyl-1-phenyl-2,3-dihydro-1H-silaindenyl-kSi] (11), and catalytic investigations indicate that both (dtbpm)Rh(CH2Ph) and 11 are competent catalysts for the conversion of TripPhSiH2 to 5,7-diisopropyl-3-methyl-1-phenyl-2,3-dihydro-1H-silaindole. A dtbpm-supported Ir complex, [(dtbpm)IrCl]€2, was used to access the dinuclear bridging silylene complexes [(dtbpm)IrH](SiPh2)(Cl)2[(dtbpm)IrH] (12) and [(dtbpm)IrH](SiMesCl)( -Cl)(H)[(dtbpm)IrH] (13). The reaction of [(dtbpm)IrCl]2 with a sterically bulky primary silane, (dmp)SiH3 (dmp = 2,6-dimesitylphenyl), allowed isolation of the mononuclear complex (dtbpm)Ir(H)4(10-chloro-1-mesityl-5,7-dimethyl-9,10-dihydrosilaphenanthrene-Si) (14), in which the dmp substituent has undergone C-H activation. The dichloride complex Cp*(Am)WCl2 (1, Am = [(iPrN)2CMe]- ) reacted with the primary silanes PhSiH3, (p-tolyl)SiH3, (3,5-xylyl)SiH3, and (C6F5)SiH3 to produce the W(VI) (silyl)trihydrides Cp*(Am)W(H)3(SiHPhCl) (2), Cp*(Am)W(H)3(SiHTolylCl) (3), Cp*(Am)W(H)3(SiHXylylCl) (4), and Cp*(Am)W(H)3[SiH(C6F5)Cl] (5). In an analogous manner, 1 reacted with PhSiH2Cl to give Cp*(Am)W(H)3(SiPhCl2) (6). Complex 6 can alternatively be quantitatively produced from the reaction of 2 with Ph3CCl. NMR spectroscopic studies and X-ray crystallography reveal an interligand H ... Si interaction between one W - H and the chlorosilyl group, which is further supported by DFT calculations. Complexes of Ru(II) containing the pincer ligand [-N(2-PPh2-4-Me-C6H3)2] (PNPPh) were prepared. The complex (PNPPhH)RuCl2 (1) was treated with 2 equiv AgOTf to produce the triflate complex (PNPPhH)Ru(OTf)2 (2). Complex 1 was also treated with an excess of NaBH4 to give a bimetallic complex [(PNPPh)RuH3]2 (3). A number of methods, including X-ray crystallography, NMR spectroscopy, and computational studies, were used to probe the structure of 3. Addition of Lewis bases to 3 resulted in octahedral complexes containing a hydride ligand trans to a dihydrogen ligand.

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.

Author: Edwin C. Constable
Publisher: Wiley-VCH
ISBN:
Category : Science
Languages : en
Pages : 332

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Edwin C. Constable Metals and Ligand Reactivity An Introduction to the Organic Chemistry of Metal Complexes New, revised and expanded edition This book is a highly readable introduction to the reactions of coordinated ligands, which have become a useful tool in organic synthesis. Bridging the gap between the traditional fields, this text presents the basic concepts of ligand reactivity as well as synthetic applications of these reactions. Topics covered include Principles of metal-ligand interaction Reactions of coordinated ligands with nucleophiles and electrophiles Oxidation and reduction of coordinated ligands Cyclic and encapsulating ligands, template effects and supramolecular chemistry Carefully selected examples, lucidly designed figures and schemes as well as numerous study problems make this book an ideal guide for students and practitioners of organic synthesis. References to further reading are also included.

Author: Harold Roger Powell
Publisher:
ISBN:
Category :
Languages : en
Pages : 376

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Author: Mark Stradiotto
Publisher: John Wiley & Sons
ISBN: 1118839773
Category : Science
Languages : en
Pages : 448

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The design of ancillary ligands used to modify the structural and reactivity properties of metal complexes has evolved into a rapidly expanding sub-discipline in inorganic and organometallic chemistry. Ancillary ligand design has figured directly in the discovery of new bonding motifs and stoichiometric reactivity, as well as in the development of new catalytic protocols that have had widespread positive impact on chemical synthesis on benchtop and industrial scales. Ligand Design in Metal Chemistry presents a collection of cutting-edge contributions from leaders in the field of ligand design, encompassing a broad spectrum of ancillary ligand classes and reactivity applications. Topics covered include: Key concepts in ligand design Redox non-innocent ligands Ligands for selective alkene metathesis Ligands in cross-coupling Ligand design in polymerization Ligand design in modern lanthanide chemistry Cooperative metal-ligand reactivity P,N Ligands for enantioselective hydrogenation Spiro-cyclic ligands in asymmetric catalysis This book will be a valuable reference for academic researchers and industry practitioners working in the field of ligand design, as well as those who work in the many areas in which the impact of ancillary ligand design has proven significant, for example synthetic organic chemistry, catalysis, medicinal chemistry, polymer science and materials chemistry.