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New Designs Of Rigid Pincer Complexes With Pxp Ligands And Late Transition Metals And Sp3 C F Bond Activation With Silylium And Alumenium Species
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Book Synopsis New Designs of Rigid Pincer Complexes with PXP Ligands and Late Transition Metals and Sp3 C-F Bond Activation with Silylium and Alumenium Species by : Weixing Gu
Download or read book New Designs of Rigid Pincer Complexes with PXP Ligands and Late Transition Metals and Sp3 C-F Bond Activation with Silylium and Alumenium Species written by Weixing Gu and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this dissertation, catalytic C-F bond activation mediated by alumenium and silylium species, improved methods for the synthesis of highly chlorinated carboranes and dodecaborates, new type of P2Si= pincer silylene Pt complexes and PBP pincer Rh complexes are presented. In Chapter II, the design and synthesis of P2Si= and PBP ligand precursors is described. BrC6H4PR2 is shown to be a useful building block for PXP type of ligands with o-arylene backbone. RLi reagents displayed high chemoselectivity towards electrophiles, such as Si(OEt)4 and BX3 (X = Hal). In Chapter III, new chlorination methods to synthesize [HCB11Cl11]- and [B12Cl12]2- are presented. [HCB11Cl11]- was obtained via reactions of Cs[HCB11H11] with SbCl5 or via reactions of Cs[HCB11H11] with Cl2 in acetic acid and triflic acid. Heating Cs2[B12H12] in mixtures of SO2Cl2 and MeCN led to the isolation of Cs2[B12Cl12] in high yield. In Chapter IV, Et2Al[HCB11H5Br6] or Ph3C[HCB11H5Br6] were shown to be robust catalysts for sp3 C-F bond activation with trialkylaluminum as the stoichiometric reagent. Trialkylaluminum compounds were also shown to be able to be used as 0́clean-up0́+ reagent for the C-F bond activation reactions, which led to ultra high TON for the catalytic reactions. In Chapter V, a series of (TPB)M complexes (M = Ni, Pd, Pt) were synthesized and characterized by multinuclear NMR spectroscopy and X-ray crystallography. The resulting metal complexes displayed strong dative M-->B interaction and unusual tetrahedral geometry for four-coordinate 16 species, due to the cage structure of the ligand. In Chapter VI, (PSiHP)PtCl was synthesized via the reaction of the ligand precursor and Pt(COD)Cl2, which was used to obtain a series of (PSiHP)PtX complexes(X= I, OTf, Me, Ph, Mes). After hydride abstraction by Ph3C[HCB11Cl11], the X ligand (X= I, OTf, Me, Ph) migrated from the Pt center to silicon center to give a cationic pincer silyl species. The migration was not observed when mesityl was used as the X ligand, which resulted in the first known pincer complex with central silylene donor. Our approaches towards PNP pincer boryl Rh complexes were summarized in Chapter VII. (PBPhP)Rh pivalate complex underwent C-Ph bond activation to yield the pivalate-bridging Rh borane complex.
Book Synopsis The Chemistry of Pincer Compounds by : David Morales-Morales
Download or read book The Chemistry of Pincer Compounds written by David Morales-Morales and published by Elsevier. This book was released on 2011-08-11 with total page 467 pages. Available in PDF, EPUB and Kindle. Book excerpt: Pincer complexes are formed by the binding of a chemical structure to a metal atom with at least one carbon-metal bond. Usually the metal atom has three bonds to a chemical backbone, enclosing the atom like a pincer. The resulting structure protects the metal atom and gives it unique properties.The last decade has witnessed the continuous growth in the development of pincer complexes. These species have passed from being curiosity compounds to chemical chameleons able to perform a wide variety of applications. Their unique metal bound structures provide some of the most active catalysts yet known for organic transformations involving the activation of bonds. The Chemistry of Pincer Compounds details use of pincer compounds including homogeneous catalysis, enantioselective organic transformations, the activation of strong bonds, the biological importance of pincer compounds as potential therapeutic or pharmaceutical agents, dendrimeric and supported materials. * Describes the chemistry and applications of this important class of organometallic and coordination compounds* Covers the areas in which pincer complexes have had an impact* Includes information on more recent and interesting pincer compounds not just those that are well-known
Book Synopsis PNP Pincer Ligands and Their Late Transition Metal Complexes in the Context of Strong Bond Activation and Catalysis by : Lei Fan
Download or read book PNP Pincer Ligands and Their Late Transition Metal Complexes in the Context of Strong Bond Activation and Catalysis written by Lei Fan and published by . This book was released on 2006 with total page 236 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Unconventional Pincer Ligands and Their Transition Metal Complexes by : Caitlin McQueen
Download or read book Unconventional Pincer Ligands and Their Transition Metal Complexes written by Caitlin McQueen and published by . This book was released on 2013 with total page 404 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis describes investigations into unconventional pincer systems incorporating non-classical central donor groups. Direct reaction of 1,3-bis(diphenylphosphinomethyl)-2,3-dihydro-1H-1,3,2-benzodiazaborole (dppBH) with metal complexes and subsequent ligand manipulations have provided novel ruthenium and, for the first time, osmium boryl pincer complexes. The boryl complexes thus prepared have been observed to undergo various subsequent reactions involving the chloride and triphenylphosphine co-ligands to give new complexes. Further reactions of dppBH with complexes dichlorotris(triphenylphosphine)ruthenium(II) and -osmium(II) resulted in the first examples of sigma-borane pincer complexes, which represent intercepted intermediates in the B-H activation process, affording rare structural data for an osmium sigma-borane complex. The B-H bond of the ruthenium complex could be readily cleaved upon ligand manipulation, such as substitution of triphenylphosphine with the pi-acidic carbonyl and isocyanide ligands, which gave the disubstituted boryl complexes via spontaneous loss of HCl. Attempts to isolate a 1,8-diaminonaphthalene-based borane analogue of dppBH proved unsuccessful, though the compound 1,3 bis(diphenylphosphinomethyl)-2,3-dihydroperimidine (PhDHP) was obtained as a side-product in one case. Further investigations into this compound resulted in the development of a convenient one-pot synthesis, which could be extended to the cyclohexyl analogue 1,3 bis(dicyclohexylphosphinomethyl)-2,3-dihydroperimidine (CyDHP). These compounds were observed to react with various platinum group metal complexes to give novel N-heterocyclic carbene (NHC) pincer complexes via double geminal C-H activation of the central methylene group, providing the first examples of perimidine-based NHC inclusion as the central equatorial group of a pincer system. Reactions of dihydroperimidines with group 8 complexes dichlorotris(triphenylphosphine)ruthenium(II) and -osmium(II) have thus provided the novel pincer NHC complexes. However, reactions of PhDHP with dichlorotris(triphenylphosphine)ruthenium and CyDHP with less electron-rich ruthenium precursors instead gave asymmetric PNP coordinated complexes, in which C-H activation had not occurred, though this could be induced thermally in one case. Reactions of PhDHP and CyDHP with chlorotris(triphenylphosphine)rhodium(I) gave 16-electron chloro rhodium(I) NHC pincer complexes, and their reactivity was investigated via co-ligand manipulations and a preliminary catalytic study. The latter revealed that, while this complex was not particularly efficient for most of the reactions investigated, in some cases simple modifications of the co-ligands could substantially improve catalytic activity. Reactions of the pro-ligands with iridium precursors instead favoured the formation of coordinatively saturated complexes. The reaction of CyDHP with chlorobis(cyclooctene)iridium(I) dimer resulted in a dihydrido chloro iridium(III) NHC pincer complex, while reaction with chlorocarbonylbis(triphenylphosphine)iridium(I) instead afforded a sigma perimidinyl hydrido complex, resulting from oxidative addition of only one C-H bond to the metal centre. This was subsequently shown to readily form an NHC complex upon hydride abstraction. It became apparent that, upon reaction of the dihydroperimidine pro-ligands with metal complexes, carbene formation occurs more readily for electron-rich systems, otherwise resulting in either single or no C-H activation. These observations have provided some insight into the mechanism of NHC formation via chelate-assisted C-H activation of these precursors.
Book Synopsis Synthesis of Pincer-type NHC Ligands with Phosphorus Functionalities and Their Ag(I), Cu(I) and Ir(I/III) Organometallic Complexes by : Xianghao Liu
Download or read book Synthesis of Pincer-type NHC Ligands with Phosphorus Functionalities and Their Ag(I), Cu(I) and Ir(I/III) Organometallic Complexes written by Xianghao Liu and published by . This book was released on 2011 with total page 166 pages. Available in PDF, EPUB and Kindle. Book excerpt: Although the first metal complexes with the cyclometalated PCP pincer ligands (Figure 1a) were reported about 30 years ago, it is still a hot and fast developing topic covering all aspects of chemistry: mechanistic, structural, catalytic, synthetic, theoretical, and coordination studies. Pincer-based metal complexes possess a unique balance of stability and reactivity that can be controlled by systematic ligand modifications and variation of the metal centre.Numerous metal complexes with related pincer-type NHC ligands (Figure 1b) have been reported and well characterized (with e.g. CCC or CNC donor sets). Largely because the NHC ligands have a lesser tendency to dissociate from the metal centre than phosphines, their complexes exhibit advantages over phosphine metal complexes, such as improved air and thermal stability, which are highly desirable in e.g. organometallic chemistry and homogeneous catalysis. The aim of this thesis was to design and synthesize partial/full NHC analogues to the PCP framework, which may result in CCP, CCOP and CCC pincer ligands. Among the transition metals, silver and iridium are at the focus of our work because (i) NHC ligands bound to Ag(I) can generally be transferred to another metal and (ii) Ir complexes are good candidates for the challenging Csp3-H bond activation and hydrogen transfer reactions. Three different types of ligand precursors have been successfully synthesized: 1) bis-imidazolium salts with a methylene bridge connecting the aromatic ring to each of the two imidazole rings; 2) hybrid phosphino-imidazolium salts with a methylene bridge connecting the aromatic ring to the imidazole ring and to the phosphine group; 3) hybrid phosphinito-imidazolium salts where the corresponding oxygen and nitrogen atoms, respectively, are directly connected to the aromatic ring. The corresponding metal carbene complexes were prepared in situ from these imidazolium precursors in the presence of the weak base Cs2CO3 and isolated.The bis-NHC ligandTwo mutually meta positions of the aromatic ring were blocked with methyl groups to avoid possible ortho-C-H activation on the ring so that only pincer-type complexes would form if metalation was to occur on the aromatic ring. The bromides in the imidazolium dibromide salt were replaced with non-coordinating counterions PF6 to suppress their high hygroscopic character.An initial coordination chemistry study was performed by reaction of 1 with Ag2O as a weak base. However, owing to possible H-bonding between the NCHN units and a fluorine atom of PF6, Ag2O was not able to deprotonate the imidazolium to generate the silver NHC complex. However, the corresponding Cu(I) complex was obtained by treating the imidazolium salt with [Cu(NCMe)4]PF6 and Cs2CO3 in MeCN at 60 _C. Surprisingly, a transmetalation reaction between 4 and AgOTF afforded the desired Ag(I) complex 5. This reaction is particularly noteworthy since carbene transmetalation reactions always feature the opposite reaction (from Ag to Cu).The short distances observed by X-ray diffraction for 4 and 5 between the metal and the aromatic rings led us to examine whether these d10 metal centers are better described as T/Y-shaped tri-coordinated or linearly di-coordinated, and the results of detailed DFT calculations suggested the absence of a chemical bond between the Cu(I) or Ag(I) center and parts of the aromatic ring. The proximity observed experimentally between the aromatic carbon and the metals thus results from the combined effects of a chelating ligand structure and the metal preferred coordination geometry.In the cases of iridium complexes, the nature of the metal precursors played an important role. In complex 7, the cod ligand was preferably chelated to the Ir center and the two bridging CNHC^CH^CNHC ligands connect the Ir(I) centres in such a way that each metal is bonded to two mutually cis carbene donors, resulting in a dicationic 20-membered dimetallacycle. While cyclooctene (coe) is more labile than 1,5-cyclooctadiene (cod), it was easily replaced by the solvent molecule MeCN which coordinates to the Ir center through its nitrogen in complex 6. The requirement for shorter reacting times (compared with the reaction using [Ir(cod)(μ-Cl)]2) also showed the higher lability of the complex resulting from a more weakly bound coe ligand compared to cod. Unlike the situation found in the figure-of-eight complex 7, the aromatic ring was metalated, resulting in the formation of an Ir-C and an Ir-H bond. Mixtures of solvents were used to increase the solubility of the ligand (soluble in MeCN) and [Ir(coe)2(μ-Cl)]2 (soluble in THF). It is worth mentioning that MeCN seemed to have stabilized the pincer-type Ir(III) hydride because when bis-imidazolium dibromide, which is soluble in THF, was treated under the same conditions but in the absence of MeCN, only decomposition of the Ir precursor was observed.Hybrid phosphino-NHC ligandIn order to limit possible problems associated with the sensitivity of uncoordinated phosphine groups, we introduced the P-donor moiety in the final step of the preparation. Diethyl ether was used as the solvent in the first step to precipitate the mono-substituted derivative, thus preventing further substitution eventhough 1,3-bis(chloromethyl)benzene was present in large excess. [...].
