Browsing by Subject "crystallography"
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Item Impact of the ligands on linear trimetal chains(Texas A&M University, 2004-09-30) Lei, PengIncreasing attention has been given to the preparation and study of compounds with linear chains of metal atoms surrounded by four ligands. The majority of linear trimetal complexes are supported by dpa, the anion of dipyridylamine, having the general formula M3(dpa)4X2, where X is typically a monoanion. It has been shown that the behavior of the trinuclear system is far more complicated than might have been expected. Specifically, both symmetrical and unsymmetrical chains can occur and the interpretation of the magnetic properties of certain compounds has been a challenging task. Present in this dissertation is the bulk of work completed on an exploration of syntheses and characterizations of linear trichromium and trinickel compounds with different types of tridentate ligands. These ligands include 2,6-bis(phenylamino)pyridine,H2BPAP, (the corresponding dianion of this is denoted by BPAP) and a set of five unsymmetrical formamidines with different organic substituents ranging from strong electron-donating groups, such as -OCH3, to electron-withdrawing groups, e.g., F. Ligands impact on the trimetal chain in various ways. In the case of the M3(BPAP)42- ions, there are no axial interactions because these anionic species do not attract electron donating ligands. Thus they have properties which are different from those of M3(dpa)4X2 molecules. Most notably, the Ni3(BPAP)42- ion is diamagnetic and all three nickel ions can be described as square-planar, low-spin NiII centers. ivWhen unsymmetrical formamidines are used to support linear trichromium chains with a Cl anion at each end, the separation between terminal chromium atoms is significantly longer (ca. 0.15 - 0.25) than those in trichromium compounds reported earlier. Moreover, the unsymmetrical formamidinates tend to support symmetrical trichromium chains, while the rest of the known tridentate ligands typically yield unsymmetrical Cr36+ chains. The synthesis and structural studies of trinickel compounds with unsymmetrical formamidines are also presented.Item Studies of Platinum Polyynyl Complexes: Elaboration of Novel "Click" Cycloadducts and Fluorous and Polygon Based Platinum Polyyndiyl Systems(2012-11-13) Clough, Melissa Catherine 1985-The major directions of this dissertation involve (1) the syntheses and characterization of molecular polygons incorporating sp1hybridized carbon linkers and L2Pt corners (L2 = cis-1,3-diphosphine), (2) the development of protected carbon chain complexes featuring fluorous phosphine ligands and (3) click reactions of metal terminal polyynyl complexes and further metallations of the resulting triazole rings. A brief overview is provided in Chapter I. Chapter II details the syntheses of molecular squares containing bidendate diphosphine ligands of the formula R2C(CH2PPh2)2 where R = Me, Et, n-Bu, n-Dec, Bn, and p-tolCH2 (general designation dppp*), in which the R2 groups are intended to circumvent the solubility issues encountered by others. Their syntheses involve double substitutions of the dimesylate compounds R2C(CH2OMs)2 using KPPh2. Building blocks of the formulae (dppp*)PtCl2 and (dppp*)Pt((C?C)2H)2 are synthesized and characterized, including one crystal structure of the latter. The target complexes are accessed by reactions of (dppp*)PtCl2 with (dppp*)Pt((C?C)2H)2 under Sonogashira type conditions. Six new squares of the formula [(R2C(CH2PPh2)2)Pt(C?C)2]4 are characterized including two crystal structures. Further topics include approaches to higher homologues and cyclocarbon synthesis. Chapter III focuses on carbon chain complexes bearing fluorous phosphine ligands of the formula P((CH2)mRfn)3 (Rfn = (CF2)n-1CF3; m/n = 2/8, 3/8, and 3/10). Precursors of the formula trans-(C6F5)((Rfn(CH2)m)3P)2PtCl are synthesized and characterized, including one crystal structure, which reveals phase separation of the fluorous and non-fluorous domains. Reactions with butadiyne give trans-(C6F5)((Rfn(CH2)m)3P)2Pt(C?C)2H. Oxidative homocouplings afford the target complexes trans,trans-(C6F5)((Rfn(CH2)m)3P)2Pt(C?C)4(C6F5)(P((CH2)mRfn)3)2Pt. Cyclic voltammetry indicates irreversible oxidations of the title compounds, in contrast to partially reversible oxidations of non-fluorous analogues. Chapter IV focuses on multimetallic complexes achieved by click reactions in metal coordination spheres. The copper catalyzed click reaction between trans-(C6F5)(p-tol3P)2Pt(C?C)2H (1) and (?5-C5H4N3)Re(CO)3 affords the bimetallic 1,2,3-triazole trans-C6F5)(p1tol3P)2PtC?CC=CHN((?51C5H4)Re(CO)3)N=N. Further reactions with Re(CO)5OTf and Re(CO)5Br give trimetallated adducts, which represent the first species of this type. An alternative route to a trimetallic complex involves the twofold cycloaddition of the diazide (?5-C5H4N3)2Fe and 1, giving (?5-C5H4NN=N-C(trans-(C?C)Pt(Pp-tol3)2(C6F5)=CH)2Fe. The crystal structures of the di and trimetallic complexes are compared, but attempts to achieve a fourth metallation involving the =CH groups are unsuccessful. However, when the triazolium salt [trans-(C6F5)(p-tol3P)2PtC?CC=CHN(CH2C6H5)N=N(Me)]+ I? is treated with Ag2O and [Rh(COD)Cl]2, a =CRh adduct is obtained. The success of =CH metallation is correlated to the 1H NMR chemical shift, indicative of an electronic effect.Item Synthesis and Characterization of Novel Pincer Ligands and Triarylaminium Oxidants(2014-12-15) Davidson, Jillian JordanDiarylamido-based tridentate pincer ligands have become an important archetype in transition-metal chemistry and their reactivity has been widely explored. The diarylamido backbone offers rigidity and can be easily tuned to change the steric and electronic properties of the ligand. Motivated by previous successes, efforts were made to expand the scope of pincer ligands developed within the Ozerov group, which historically have been limited to C2V symmetric ligands bearing either two phosphine donor arms or two imine donor arms. New ligands synthesized for this purpose include CS symmetric ligands PNP and PNN ligands. In an effort to categorize pincer ligands commonly employed in the Ozerov group we set out to compare the redox properties of the ligands and their donor ability towards a metal center. This was a two part endeavor where we (a) obtained cyclic voltammograms for (pincer)MCl compounds of Group 10 metals and (b) measured the IR stretching frequencies of (pincer)RhCO compounds. Our underlying assumptions were that the cyclic voltammograms report on how easy it is to oxidize the ligand (approximates the electron-richness of the ligand) and that the IR stretching frequencies give insight into the ?electron-richness? of the metal center (a reflection on the basicity of the pincer ligand). The results of this study suggest that changes to the ligand framework directly affect the level of conjugation and in turn affect the redox potentials and the ?(CO) values in a nearly linear fashion. The more electron-rich a ligand is, (due to direct conjugation from donor substituents on the diarylamido-backbone and from the influence of the donor arms) the more readily it is oxidized and the stronger donor it becomes. Chemical oxidations have become a rising field of interest. Triarylaminium oxidants are advantageous since they boast modest oxidation potentials and generate chemically neutral amines upon reduction. Our goal was to expand the scope of triarylaminium oxidants bearing non-coordinating carborane anions. A series of oxidizing triarylaminium radical cations were synthesized and isolated as [NAr3]^+[CRB11Cl11]^? salts (R = H, CH3). These salts were prepared by treatment of a neutral amine, Me3SiX (X = OTf, Cl), and Na[CRB11Cl11] (R = H, CH3) with half an equivalent of PhI(OAc)2.