Deck and coworkers previously showed that Me3Si substituents adjacent to group 4 metallocene dichlorides (M = Ti, Zr, Hf) are converted to corresponding BrMe2Si groups using BBr3, and that these BrMe2Si substituents are highly reactive to nucleophilic reagents such as water. The high reactivity of the Si-Br bonds suggested that these substituents could react with hydroxyl groups on the surface of partially dehydroxylated silica, forming covalently immobilized metallocene catalysts. This dissertation concerns the synthesis of electrophile-functionalized zirconocene dihalide complexes and the use of functionalized zirconocene dihalides as precursors to silica-supported metallocene olefin polymerization catalysts. Our first objective was to extend the metallocene "functionalization" chemistry to obtain substituents bearing more than one electrophilic bond. The reactivities of Me3Sn and Ph2MeSi substituents were explored in detail. (Me3Sn)2C5H4 combined with CpZrCl3 in toluene to afford (h5-Me3Sn-C5H4)CpZrCl2 (A). Reactions of A with electrophiles (E-X = Cl2B-Cl, I-Cl, and I-I) afforded (ï ¨5-XMe2Sn-C5H4)CpZrCl2 (and E-Me) cleanly. The reaction of A with BBr3 afforded either (ï ¨5-BrMe2Sn-C5H4)CpZrBr2 (25 ï °C, 10 min) or (ï ¨5-Br2MeSn-C5H4)CpZrBr2 (25 ï °C, 15 h). Ph2MeSi-C5H4Li combined with ZrCl4·2THF to afford (h5-Ph2MeSi-C5H4)2ZrCl2 (B). The reaction of B with BCl3 led to incomplete cleavage of the Ph-Si bonds, however treatment of B with BBr3 afforded (h5-Br2MeSi-C5H4)2ZrBr2 (C) efficiently. The Sn-X bonds of the stannylated metallocenes were however relatively unreactive toward water and were excluded as candidates precursors for supported metallocene catalysts. X-ray crystal structures of (h5-ClMe2Sn-C5H4)CpZrCl2·½toluene, (h5-Br2MeSn-C5H4)CpZrBr2·THF, B, and C were obtained. The functionalized metallocene C reacts with water to afford an oligosiloxane-supported zirconocene dibromide. Combinations of solution 1H NMR, solid state CPMAS 13C NMR, and solid state CPMAS 29Si NMR spectroscopy suggested a stereoregular structure in which the metallocene units have local Cs (meso) symmetry. Although only sparingly soluble, the oligomeric substance showed activity for homogeneous ethylene polymerization (toluene solution, MAO cocatalyst, Al:Zr = 5000, 50 ï °C) similar to Cp2ZrCl2. Supported metallocene olefin polymerization catalysts were prepared by combining a functionalized metallocene precursor (Cp2ZrBr2 bearing either BrMe2Si or Br2MeSi groups) and partially dehydroxylated silica. Ethylene polymerization activity of the resulting catalysts was examined as a function of the precursor structure (number of reactive "tethering" groups, one vs. two Si-Br bonds per tethering group) and the immobilization conditions (time, temperature, presence or absence of NEt3 promoter). The activities of the immobilized zirconocene catalysts decreased and the stabilities increased with increasing number of tethers. The immobilized catalyst prepared from (ï ¨5-Br2MeSi-C5H4)2ZrBr2, which is assumed to form two "double-tethers" to silica, was significantly more active than the catalyst prepared from [ï ¨5-1,3-(BrMe2Si)2C5H3]2ZrBr2, which is assumed to form four "single-tethers" to silica. Catalyst leaching was observed in all the immobilized zirconocene catalysts. The use of NEt3 in the immobilization reaction enabled more metallocene to be supported, but the resulting activity was lower. The dissertation also includes model studies on the immobilization reaction and the stability of the Si-O-Si bonds. The reaction of C with tBuMe2SiOH results in the formation of Si-O-Si bonds; addition of NEt3 results in further reaction to afford Si-O-Zr bonds. The reaction of Reaction of Me3Si-O-SiMe3 with MAO showed that Si-O-Si bonds can be cleaved under the conditions of our polymerization reactions. / Ph. D.

The development of new strategies and associated reagents that enable previously inaccessible synthetic disconnections is largely attributing to the remarkable progress in exploring new chemical space for drug discovery and innovative complex molecule syntheses. In the Wengryniuk laboratory, we are devoted to discovering new synthetic methodologies that are based on umpolung or reverse polarity, strategies, enabled by Nitrogen-ligated (bis)cationic hypervalent iodine reagents (N-HVIs). I(III) N-HVIs represent an attractive new class of oxidant as they are environmentally benign, highly tunable, and have shown ability in enabling distinguished modes of reactivity. This dissertation focuses on demonstrating the synthetic utility of these N-HVI reagents towards C–O bond formation via a reverse polarity approach.In Chapter 1, a summary of the reactivity and characteristics of hypervalent iodine reagents is provided. Chapter 2 describes a mild and metal-free strategy for alcohol oxidation mediated by I(III) N-HVI reagents. This method demonstrates the first method for chemoselective oxidation of equatorial over axial alcohols and was the first in situ synthesis and application of N-HVIs for a simple one-pot procedure. Chapter 3 discusses a novel strategy for a dual C–H functionalization to access functionalized chroman scaffolds via an umpolung oxygen activation cyclization cascade. Computational studies in collaboration with Prof. Dean Tantillo (UC-Davis) along with experimental probes in our laboratory, support the formation of an umpoled oxygen intermediate as well as competitive direct and spirocyclization pathways for the key C–O bond forming event. The utility of the developed method is demonstrated through a downstream derivatization of the iodonium salt moiety to access C–H, C–X, and C–C substitution via established Pd-catalyzed cross couplings. Total synthesis of (±)-conicol natural product was performed in 8 steps and 23% overall yield, further demonstrating the synthetic utility of the developed method. Key synthetic steps include a smooth construction of the chroman core via N-HVI mediated C–H etherification of a pendant alcohol followed by a late-stage double bond installation. Overall, this dissertation summarizes the current state of research enabled by N-HVI reagents, with a focus on their utility in reverse polarity heteroatom activation strategies, and it serves as a practical guide for future development in the field. / Chemistry

Ultrahigh vacuum (UHV) surface science experiments were designed to study reaction kinetics and mechanisms of gas-phase NO₃ radicals with well-organized, highly characterized, organic thin films. The surface reactions were monitored in situ with reflection-absorption infrared spectroscopy (RAIRS). The oxidation states of surface-bound molecules were identified with X-ray photoelectron spectroscopy (XPS). Consumption of vinyl groups was observed concurrently with formation of organic nitrates in RAIRS. XPS spectra showed little oxidation of sulfur head groups. The observed rate constant was determined based on the consumption of carbon-carbon double bonds and the formation of organic nitrates. Using this rate constant, the initial reaction probability was determined to be (3 ± 1) X 10⁻³. This reaction probability is approximately two orders of magnitude higher than that for the reactions between the same surface and pure O₃, which is due to the higher electron affinity of NO₃ relative to O₃. These results led to the development of a proposed mechanism that involves electrophilic addition of NO₃ to the double bonds. Reactions between NO₃ and a methyl-terminated SAM were also monitored in situ with RAIRS. In the CH3-SAM studies, hydrogen abstraction was observed during NO3 exposure. The results presented in this thesis should help develop an understanding of the fundamental interfacial reaction dynamics of NO₃ radicals with organic surfaces. / Master of Science

Current fossil fuels (Coal and Petroleum) based economy is not sustainable in the long run because of its dwindling resources, and increasing concerns of climate change due to excessive carbon dioxide (CO2) emission. To mitigate CO2 emission and climate change, scientists across the world have been looking for clean and sustainable energy sources. Among them hydrogen gas (H2) could be more promising because it is the most clean fuel and can be produced from cheap source (water) which is renewable and abundant. Nevertheless, the bottleneck for hydrogen economy is lying in the cost of hydrogen production from water. Still there are no any efficient systems developed which can deliver hydrogen from water in economically viable way. Meanwhile, recent research on old molecule ammonia-borane (H3N•BH3, AB) as hydrogen source has increased the hope towards the hydrogen economy, however, catalytic recycling (or efficient regeneration) of AB from the dehydrogenated product polyborazylene (PB or BNHx) is the biggest hurdle which prevents use of AB as practical hydrogen storage material. Therefore, it is imperative to understand the dehydrogenation pathways of ammonia-borane (or related amine-boranes) which lead to polymeric or oligomeric product(s). On the other hand, methane (CH4) is abundant (mostly untamed) but cleaner fuel than its higher hydrocarbon analogs. To develop highly efficient catalytic systems to transform CH4 into methanol (gas to liquid) is of paramount importance in the field of catalysis and it could revolutionize the petrochemical industry. Therefore, to activate CH4, it is crucial to understand its binding interaction with metal center of a molecular catalyst under homogenous condition. However, these interactions are too weak and hence σ–methane complexes are very elusive. In this context, σ-H2 and σ-borane complexes bear some similarities in σ-bond coordination (and four coordinated boranes are isoelectronic with methane) could be considered as good models to study σ-methane complexes. Studying the H−H and B−H bond activation in H2 and amine-boranes, respectively, would provide fundamental insights into methane activation and its subsequent functionalization. Moreover, the proposed methanol economy by Nobel laureate George Olah seems more promising because methanol can be produced from CH4 (CO2 as well). This in turn will gradually reduce the amount of two powerful greenhouse gases from the earth’s atmosphere. Thus, efficient and economic production of methanol from CH4 and CO2 is one of most challenging problems of today in the field of catalysis and regarded as the holy grails. Furthermore, very recently formic acid (HCOOH) is envisaged as a promising reversible hydrogen storage material because it releases H2 and CO2 in the presence of a suitable and efficient catalyst or vice versa under ambient conditions. Objective of the research work: Taking the account of the above facts, the research work in this thesis is mostly confined to utilize electrophilic Ru(II)-complexes for activation of small molecules such as ammonia-borane (H3N•BH3) [and related amine-borane (Me2HN•BH3)], hydrogen (H2), methane (CH4), formic acid (HCOOH) and carbon dioxide (CO2) and investigation of their mechanistic pathways using NMR spectroscopy under homogeneous conditions. Though these molecules are small, they have huge impacts on chemical industries (energy sector and chemical synthesis: drugs/natural products) and environment [CO2 and CH4 are potent green house gases] as well. However, they are relatively inert molecules, especially CH4 and CO2, and impose very tough challenges to activate and functionalize them into useful products under ambient conditions. The partial oxidation of the strong C−H bond in CH4 for its transformation into methanol under relatively mild condition using an organometallic catalyst is considered as a holy grail in the field of catalysis which is mentioned earlier. More importantly, to develop better and highly efficient homogeneous catalytic systems for the activation of these molecules, it is imperative to understand the mechanistic pathways using well defined homogeneous metal complexes. Thus, an understanding of the interaction of these inert molecules with metal center is obligatory. In this context, discovery of a σ-complex of H2 gave remarkable insights into H−H bond activation pathways and its implications in catalytic hydrogenation reactions. Subsequently, σ-borane complexes of amine-boranes were discovered and found to be relatively more stable because of stronger M−H−B interaction and hence act as good models to study the M−H−C interaction of elusive σ-methane complex. On the other hand, HCOOH, a promising hydrogen storage material and its efficient catalytic dehydrogenation/decarboxylation and CO2 hydrogenation back to HCOOH using well defined homogeneous catalysts could lead to a sustainable energy cycle. Therefore, it is quite significant to understand the mechanistic pathways of formic acid dehydrogenation/decarboxylation and carbon dioxide reduction to formic acid for the development of next generation efficient catalysts. Chapter highlights: Keeping all these in view, we carried out thorough studies on the activation of these small molecules by electrophilic Ru(II)-complexes. This thesis provides useful insights and perspective on the detailed investigation of mechanistic pathways for the activation of small molecules such as H3N•BH3 [and Me2HN•BH3], H2, CH4, HCOOH and CO2 using electrophilic Ru(II)-complexes under homogeneous conditions using NMR spectroscopy. In Chapter 1 we provide brief overview of small molecule activation using organometallic complexes. This chapter presents pertinent and latest results from literature on the significance of small molecule activation. Although there are several small molecules which need our attention, however, we have focused mainly on H3N•BH3 [and Me2HN•BH3], H2, CH4, HCOOH and CO2. In Chapter 2, we present detailed investigation of mechanistic pathways of B−H bond activation of H3N•BH3 and Me2HN•BH3 using electrophilic [RuCl(dppe)2][OTf] complex using NMR spectroscopy as a model for methane activation. In these reactions, using variable temperature (VT) 1H, 31P{1H} and 11B NMR spectroscopy we detected several intermediates en route to the final products at room temperature including a σ-borane complex. On the basis of elaborative studies using NMR spectroscopy, we have established the complete mechanistic pathways for dehydrogenation of H3N•BH3/Me2HN•BH3 and formation of B−H bond activated/cleaved products along with several Ru-hydride and Ru-(dihydrogen) complexes. Keeping the B−H bond activation of amine-boranes in view as a model for methane activation, we attempted to activate methane using [RuCl(dppe)2][OTf] complex. In addition, [Ru(OTf)(dppe)2][OTf] complex having better electrophilicity than [RuCl(dppe)2][OTf], was synthesized and characterized. The [Ru(OTf)(dppe)2][OTf] complex has highly labile triflate bound to Ru-metal and therefore its reactivity studies toward H2 and CH4 were carried out where H2 activation was successfully achieved, however, no any spectroscopic evidence was found for C−H bond activation of CH4. The Chapter 3 describes the synthesis and characterization of several Ru-Me complexes such as trans-[Ru(Me)Cl(dppe)2], [Ru(Me)(dppe)2][OTf], trans-[Ru(Me)(L)(dppe)2][OTf] (L = CH3CN, tBuNC, tBuCN, H2) with an aim to trap corresponding σ-methane intermediate at low temperature. However, interestingly, we observed spontaneous but gradual methane elimination and orthometalation of [Ru(Me)(dppe)2][OTf] complex at room temperature. We thoroughly investigated mechanistic details of methane elimination and orthometalation of [Ru(Me)(dppe)2][OTf] using VT NMR spectroscopy, NOESY and DFT calculations. Furthermore, H2 activation was confirmed unambiguously by [Ru(Me)(dppe)2][OTf] and Ru-orthometalated complexes using NMR spectroscopy under ambient conditions. An effort was also made to activate methane using Ruorthometalated complex in pressurized condition of methane in a pressure stable NMR tube. Moreover, preliminary studies on protonation reaction of [Ru(Me)(dppe)2][OTf] using VT NMR spectroscopy to trap σ-methane at low temperature was carried out which provided us some useful information on dynamics between proton and Ru-Me species. The Chapter 4 provides useful insights into the mechanistic pathways of dehydrogenation/decarboxylation of formic acid using [RuCl(dppe)2][OTf]. Catalytic dehydrogenation of HCOOH using [RuCl(dppe)2][OTf] was observed in presence of Hunig base (proton sponge). In addition, a complex [Ru(CF3COO)(dppe)2][OTf] was synthesized and characterized using NMR spectroscopy, and found to readily dehydrogenate HCOOH. Moreover, preliminary results on transfer hydrogenation of CO2 into formamide using [RuCl(dppe)2][OTf] as a precatalyst and tert-butyl amine-borane (tBuH2N•BH3) as secondary hydrogen source was confirmed using 13C NMR spectroscopy. The mechanisms were proposed for HCOOH dehydrogenation and transfer hydrogenation of CO2 based on our NMR spectroscopic studies. Furthermore, a few test reactions of transfer hydrogenation of selected alkenes such as cyclooctene, acrylonitrile, 1-hexene using [RuCl(dppe)2][OTf] as pre-catalyst and tert-butyl amine-borane (tBuH2N•BH3) as secondary hydrogen source showed quantitative conversion to hydrogenated products.

2-Phosphanyl-substituted imidazolium salts 2-PR2(4,5-Cl-Im)[OTf] (9a,b[OTf]) (4,5-Cl-Im = 4,5-dichloro-1,3-bis(2,6-di-isopropylphenyl)-imidazolium) (a: R = Cy, b: R = Ph) are prepared from the reaction of R2PCl (R = Cy, Ph) with NHC 8 (4,5-dichloro-1,3-bis(2,6-di-isopropylphenyl)-imidazolin-2-ylidene) in the presence of Me3SiOTf. 5-Phospanyl-substituted imidazolium salts 5-PR2(2,4-Cl-Im)[OTf] (10a,b[OTf]) are obtained in quantitative yield when a slight excess of the NHC 8 is used. 5-Phosphonio-substituted imidazolium salts 5-PR2Me(2,4-Cl-Im)[OTf]2 (14a,b[OTf]2) and 5-PR2F(2,4-Cl-Im)[OTf]2 (16a,b[OTf]2) result from methylation reaction or oxidation of 10a,b[OTf] with XeF2 and subsequent fluoride abstraction. According to our quantum chemical studies the Cl1 atom at the 2-position at the imidazolium ring of dication 14b2+ carries a slightly positive charge and is therefore accessible for nucleophilic attack. Accordingly, the reaction of 14a,b[OTf]2 and 16a,b[OTf]2 with R3P (R = Cy, Ph) affords cationic 5-phosphonio-substituted NHCs 5-PR2Me(4-Cl-NHC)[OTf] (17a,b[OTf]) and 5-PR2F(4-Cl-NHC)[OTf] (18a,b[OTf]) via a SN2(Cl)-type reaction. A series of transition metal complexes such as [AuCl(5-PPh2Me(4-Cl-NHC))][OTf] (19[OTf]), [CuBr(5-PPh2Me(4-Cl-NHC))][OTf] (20[OTf]), [AuCl(5-PPh2F(4-Cl-NHC))[OTf] (21[OTf]) and [RhCl(cod)(5-PPh2Me(4-Cl-NHC))][OTf] (23[OTf]) are prepared to prove the coordination abilities of carbenes 17b[OTf] and 18b[OTf]. The isolation of a rare example of a tricationic bis-carbene silver complex [Ag(5-PPh2Me(4-Cl-NHC))2][OTf]3 (22[OTf]3) is achieved by reacting 14b[OTf] with Cy3P in the presence of AgOTf. NHC 17b[OTf] represents a very effective dehydrocoupling reagent for secondary (R2PH, R = Ph, Cy, iBu) and primary (RPH2, R = Ph, Cy) phosphanes to give diphosphanes of type R4P2 (R = Ph, Cy, iBu) and oligophosphanes R4P4, R5P5 (R = Ph, Cy), respectively. Methylation of 17b+ and subsequent deprotonation reaction with LDA affords the cationic NHO (N-heterocyclic olefin) 35+ of which the gold complex 36+ is readily accessible via the reaction with AuCl(tht).

Au cours de nos différents travaux sur les réactions de cyclisations électrophiles diastéréosélectives 5-endo d’hydroxamates insaturés par l’hexafluorophosphate de bromo biscollidine (HBB). Nous avons constaté la formation d’imidates cycliques et nous avons mis en évidence un réarrangement lactames-imidates. Une fragmentation de type Beckman aboutissant à la formation d’une famille de cyano énones, anisi qu’une nouvelle formation d’imidates a été étudiée.Dans l’introduction générale, nous avons rapporté différents exemples d’halolactonisations électrophiles 5-endo et 5-exo, énantio et diastériosélectives rapportés dans la littérature, ainsi que les facteurs influençant la régio et la diastereoselectivité de ces cyclisations.Dans le premier chapitre, après un rappel bibliographique sur les différentes synthèses de lactames à partir de différents substrats par cyclisation électrophile, nous avons présenté nos propres travaux.Le traitement d’hydroxamates β, γ−éthyléniques γ-disubstitués avec de l’hexafluorophosphate de bromo bis(sym-collidine) dans du dichlorométhane aboutit à la formation de lactames et d’imidates cycliques. On a pu confirmer par des études RMN, l’existence d’un réarrangement lactame-imidate cyclique.Dans une deuxième partie, nous avons étudié la diastereosélectivité de la cyclisation. A cet effet, des hydroxamates optiquement actifs ont été synthétisés via la méthodologie développée par Evans. Dans tous les cas, un seul produit, un bromo-imidate cyclique optiquement actif est obtenu.Dans le deuxième chapitre, l’étude de la réaction de cyclisation des hydroxamates β, γ−éthyléniques γ-monosubstitués avec HBB, nous a permis de mettre en évidence une fragmentation de type Beckmann. Cette dernière est améliorée par réaction des produits de cyclisation avec de la triethylamine. On a généralisé cette fragmentation en l’appliquant à différents substrats.Enfin, dans le troisième chapitre, après une étude bibliographique sur la synthèse d’imidates et leurs utilités en synthèse organique, on a synthétisé des imidates β, γéthyléniques, afin de les utiliser comme substrats dans la réaction de cyclisation éléctrophile utilisant HBB. Dans ce cas aussi, la formation d’imines cycliques est constatée. / This work deals with the 5-endo halogeno electrophilic cyclization reactions of β,γ-ethylenic hydroxamates to give halolactames and halo cyclic iminolactones.In the first chapter, the reaction of γ-disubstituted β,γ-unsaturated hydroxamates with bis(collidine)bromine(I) hexafluorophosphate is studied. This type of reaction led mainly to the formation of bromo cyclic imidates, which were the thermodynamic products. Unsaturated cyclic imidates were then obtained by reaction with triethylamine. A lactame-iminolactone rearrangement was obtained during those reactions. In a next step we decided to study the diastereoselectivity of the reaction, using optically actif hydroxamates. In the second chapter, we decided to study the reaction of bis(collidine)bromine(I) hexafluorophosphate with γ-aryl β,γ-unsaturated hydroxamates, the corresponding bromo cyclic imidates were also obtained. However, by reaction with triethylamine, these compounds led with good yields, to the formation of 3-cyano-2-propen-1-ones by a Beckmann type fragmentation reaction. In the third chapter, the reaction of γ-mono and disubstituted β,γ-unsaturated imidates with bis(collidine)bromine(I) hexafluorophosphate is studied. The results that we obtained were not sufficient enough to understand the electrophilic cyclization mechanism of these types of substrates.

The synthesis, photophysical and electronic properties of a series of novel boron containing fused and ladder type donor-acceptor (D-A) oligomers and polymers are reported. The synthesis was achieved through coordination of the basic functionality of the ubiquitous benzothiadiazole acceptor unit onto a boron Lewis acid followed by an electrophilic aromatic borylation resulting in the formation of fused and ladder type structures (termed borylative fusion). The novel C,N-chelated borane structures disclosed herein are a new member of a large family of tetra-coordinate organoboron compounds that are used for the construction of highly emissive materials. Upon borylation large bathochromic shifts in the absorption and fluorescence spectra were observed, DFT and cyclic voltammetry demonstrate that this is a result of a significant reduction of the LUMO energy levels whist the HOMO energy levels remains relatively unperturbed. These large bathochromic shifts lead to materials that show far red/NIR emission in the solid state with absolute quantum yields of up to 44%. Furthermore, the frontier molecular orbital energy levels of these fused structures can be modulated through judicious selection of the exocyclic boron substituents. These novel borocycles also proved stable to a range of cross-coupling conditions which facilitated further modulation of the frontier molecular orbitals and emissive properties. Borylative fusion was also applicable to D-A conjugated polymers, this represents a facile post-polymerisation functionalisation that is an effective method of modulating the photophysical properties of D-A conjugated polymers. Solution processed OLEDs with far red/NIR electroluminescence (EL) were fabricated from these materials. These devices showed good external quantum efficiency values (EQE) for the far red/NIR region of the electromagnetic spectrum (EQE > 0.4 % for maximum EL > 700 nm).

Chapter 1 presents a mini-review of the prominent theoretical models which are employed in the prediction of the outcome of organic chemical reactions. The chapter covers the most widely used empirical and semi-empirical models, as well as some more recently developed models. Most have a common theme in that they were developed using electrophilic aromatic substitution as a model reaction. Chapter 2 describes the development of a predictive model based on the average local ionisation energy. The model is shown to be of use in predicting both the regioselectivity and relative reactivity of a wide range of molecules in electrophilic aromatic substitution reactions. An attempt is made to expand the model beyond electrophilic aromatic substitution to various other electrophilic reactions. Chapter 3 details the investigation into the predicted enhancement of reactivity of aromatic rings. Calculations of electrostatic surface potential surfaces show that the proximity of an electron rich atom to an aromatic ring increases the electron density of the ring. Analysis of the local ionisation energy surfaces of these molecules suggests that the reactivity of these rings towards electrophiles is also increased. Preliminary studies on model systems using NMR spectroscopy aim to determine whether this effect can be observed experimentally. Chapter 4 introduces a method for applying the average local ionisation energy to nucleophilic reactions. The ability of the model to predict the regiochemical outcome and relative reaction rates of various molecules is examined in a variety of reaction types, including nucleophilic aromatic substitution. Chapter 5 reports studies into the polarisation-induced cooperative effects that exist between hydrogen bonding groups. The cooperative effect has been measured quantitatively in some simple hydroxybenzene derivatives. An improved understanding of this effect, developed using small molecule models, should lead to an improved ability to predict the extent of this effect in larger systems.

No description available.

2-Phosphanyl-substituted imidazolium salts 2-PR2(4,5-Cl-Im)[OTf] (9a,b[OTf]) (4,5-Cl-Im = 4,5-dichloro-1,3-bis(2,6-di-isopropylphenyl)-imidazolium) (a: R = Cy, b: R = Ph) are prepared from the reaction of R2PCl (R = Cy, Ph) with NHC 8 (4,5-dichloro-1,3-bis(2,6-di-isopropylphenyl)-imidazolin-2-ylidene) in the presence of Me3SiOTf. 5-Phospanyl-substituted imidazolium salts 5-PR2(2,4-Cl-Im)[OTf] (10a,b[OTf]) are obtained in quantitative yield when a slight excess of the NHC 8 is used. 5-Phosphonio-substituted imidazolium salts 5-PR2Me(2,4-Cl-Im)[OTf]2 (14a,b[OTf]2) and 5-PR2F(2,4-Cl-Im)[OTf]2 (16a,b[OTf]2) result from methylation reaction or oxidation of 10a,b[OTf] with XeF2 and subsequent fluoride abstraction. According to our quantum chemical studies the Cl1 atom at the 2-position at the imidazolium ring of dication 14b2+ carries a slightly positive charge and is therefore accessible for nucleophilic attack. Accordingly, the reaction of 14a,b[OTf]2 and 16a,b[OTf]2 with R3P (R = Cy, Ph) affords cationic 5-phosphonio-substituted NHCs 5-PR2Me(4-Cl-NHC)[OTf] (17a,b[OTf]) and 5-PR2F(4-Cl-NHC)[OTf] (18a,b[OTf]) via a SN2(Cl)-type reaction. A series of transition metal complexes such as [AuCl(5-PPh2Me(4-Cl-NHC))][OTf] (19[OTf]), [CuBr(5-PPh2Me(4-Cl-NHC))][OTf] (20[OTf]), [AuCl(5-PPh2F(4-Cl-NHC))[OTf] (21[OTf]) and [RhCl(cod)(5-PPh2Me(4-Cl-NHC))][OTf] (23[OTf]) are prepared to prove the coordination abilities of carbenes 17b[OTf] and 18b[OTf]. The isolation of a rare example of a tricationic bis-carbene silver complex [Ag(5-PPh2Me(4-Cl-NHC))2][OTf]3 (22[OTf]3) is achieved by reacting 14b[OTf] with Cy3P in the presence of AgOTf. NHC 17b[OTf] represents a very effective dehydrocoupling reagent for secondary (R2PH, R = Ph, Cy, iBu) and primary (RPH2, R = Ph, Cy) phosphanes to give diphosphanes of type R4P2 (R = Ph, Cy, iBu) and oligophosphanes R4P4, R5P5 (R = Ph, Cy), respectively. Methylation of 17b+ and subsequent deprotonation reaction with LDA affords the cationic NHO (N-heterocyclic olefin) 35+ of which the gold complex 36+ is readily accessible via the reaction with AuCl(tht).