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Advances Towards Transition Metal-Catalyzed C-H Activation & Cross-Couplings

Thesis Info

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Author

Soneela Asghar

Program

PhD

Institute

Lahore University of Management Sciences

City

Lahore

Province

Punjab

Country

Pakistan

Thesis Completing Year

2019

Thesis Completion Status

Completed

Subject

Chemistry

Language

English

Link

http://prr.hec.gov.pk/jspui/bitstream/123456789/11471/1/Soneela%20Asghar%20Chemistry%202019%20lums%20lhr.pdf

Added

2021-02-17 19:49:13

Modified

2024-03-24 20:25:49

ARI ID

1676725439775

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Synthetic approaches that harness metal-catalyzed pathways can provide facile alternatives to cumbersome conventional strategies. The dissertation reports advances made towards exploring novel catalytic processes and substrates for the formation of C–C (C–H activation, Suzuki-coupling), C–B (borylation) and C–N (amination) bonds. In order to improve the sustainability of the processes investigated, a conscious effort was made to move from precious metal- (palladium, iridium) catalyzed reactions towards the use of more earth abundant metals (cobalt, iron), with promising results. The sterically governed, iridium-catalyzed regioselective borylation of a novel class of substituted biaryls has been achieved. The biaryl pinacol esters obtained, have been demonstrated as enabling motifs for building C–O, C–Br and C–C bonds. The one-pot combination of a palladium-catalyzed Suzuki-Miyaura cross-coupling and a Buchwald-Hartwig amination has been employed to afford a series of substituted carbazoles. The protocol, using ortho-chloroboronic acids and ortho-bromoanilines, relies on readily available starting materials and mild conditions, whilst avoiding the formation of any isomers. The versatility of the reaction is demonstrated by the selective substitution at various points of the carbazole ring. An efficient synthetic route has been proposed for substituted cyclohexa-m-phenylenes, based on palladium- and iridium-catalyzed reactions leading to the functionalized terphenyls. These terphenyl synthons when reacted under Suzuki-Miyaura crosscoupling conditions, cyclise to cyclohexa-m-phenylenes. Cobalt has been shown as a promising alternative to palladium for the Suzuki-Miyaura cross-coupling of aryl halides. The developed protocol shows how readily accessed cobalt pre-catalysts in combination with NHC ligands can catalyze the cross-coupling of aryl chlorides and bromides with alkyllithium-activated arylboronic pinacolate esters. Preliminary mechanistic studies hint towards cobalt reduction to Co(0) during catalysis. The extended substrate scope demonstrates the efficacy of the process for various aryl halides without the aid of any directing group. Furthermore, novel derivatives of a neuro-protective drug edaravone, have been synthesized utilizing this protocol that echoes the broader range of applications of the study. Finally, the development of a small library of derivatives based on edaravone, has been achieved through an iron-catalyzed, substrate directed ortho-arylation procedure. The preliminary computational assessment predicts that these synthesized analogues can inhibit the human enzyme, monoamine oxidase-B, more strongly than the parent edaravone.
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ا یڈو رڈ ویسٹر مارک

مارک، ایڈورڈ ویسٹر
ایڈورڈ ویسٹر مارک کا انتقال
ایڈورڈ ویسٹر مارک نے جو ایک عرصہ تک لندن یونیورسٹی میں عمرانیات کا پروفیسر تھا، گزشتہ اکتوبر میں انتقال کیا، وہ ایک عمیق النظر فلسفی اور بین الاقوامی شہرت کا مالک تھا، اوائل زندگی میں اس کو خیال پیدا ہوا کہ اخلاقی خیالات اور مذہبی اعتقادات میں گہرا تعلق ہے، چنانچہ اس نقطہ نظر سے اس نے یورپ کے علاوہ دوسری قوموں کے روایات اور اعتقادات کا مطالعہ کرنا چاہا اور اس کے لئے مراکش کو منتخب کیا، اور وہاں جاکر چار سال تک مقیم رہا، یہاں اس نے نہ صرف انسانیاتی معلومات جمع کئے، بلکہ وہاں کے لوگوں طرز زندگی و غور و فکر سے بھی واقفیت حاصل کرکے ان کے رسم و رواج کو آسانی سے سمجھا جو تمدن کے مختلف دور میں پیدا ہوتے رہے، یہاں کی تحقیقات اس نے اپنی مشہور کتاب ’’اخلاقی تخیلات کی ابتدا اور نشوونما‘‘ (The origin and development of moral ideas) میں قلمبند کی جو دو جلدوں میں ۱۹۰۶؁ء اور ۱۹۰۸؁ء میں شائع ہوئی تھی، یہ کتاب بہت اہم اور بلند پایہ سمجھی جاتی ہے اور اخلاقیات پر ایک فلسفیانہ مقالہ یا اخلاقی خیالات کی تاریخ کہی جاسکتی ہے، اس کتاب کی خوبی یہ ہے کہ اس میں تحلیلی اور تاریخی تجزیوں میں امتزاج پیدا کرکے یہ دکھایا گیا ہے کہ اخلاقی پسندیدگی اور ناپسندیدگی کی ابتدا معاشرتی تکدر اور تشکر سے ہوتی ہے، ڈاکٹر ویسٹر مارک کی اور دوسری تصنیفات یہ ہیں، مراکش میں انسانی شادی، رسم اور اعتقاد کی تاریخ، (۲)اخلاقی اضافیت، (۳)عیسائی مذہب اور اخلاق۔
(’’ص ۔ ع‘‘، دسمبر ۱۹۳۹ء)

 

CERVICOGENIC HEADACHE AMONG DENTISTS WORKING IN LAHORE MEDICAL AND DENTAL COLLEGE

Background and Aim: Headache is a very common condition worldwide. Cervicogenic headache is a secondary type of headache. Dentistry requires both, the concentration and precision and dentists have to work in constricted zones for extended period of time so it is important to evaluate headache among dental population. The objective of this study was to screen Cervicogenic headache among dentists working in Lahore Medical and Dental College, Lahore. Methodology: The Descriptive Cross-sectional study, of 6 months duration, was conducted on 125 dentists. The data was collected from Lahore Medical and Dental College, Lahore.  Non-Probability convenience sampling technique was used. Dentists working for at least 2 years and more than 5 hours daily, with the known cases of headache were included and those who were diagnosed with any other condition that cause headache like acute sinusitis, High blood pressure etc. were excluded. Data was collected by using cervical Flexion Rotation test whose validity is 0.81. Data was entered by using Statistical package for Social Sciences (SPSS) version 21 and the same software was used for data analysis. Results: The findings showed that, out of 125 dentists, 36.8% (n=46) were male and 63.2% (n=79) were female and cervical flexion rotation test was positive in 30.4% (n=38) dentists. Conclusion: This study concluded that cervicogenic headache is present in 30.4% dentists working in Lahore Medical and Dental College.

Synthesis and Characterization of Mg and Ge Doped Cu0. 5Tl0. 5 Ba2can-1Cuno2n+4-Δ N = 3, 4, 5 Superconductors

Different series of polycrystalline superconductor, Cu0.5Tl0.5Ba2Ca4-xMgxCu5O14-δ (x = 0, 1, 2 and 3), (Cu0.5Tl0.5)Ba2Ca2Cu3-yGeyO10-d (y = 0, 0.5, 0.75 and 1.0) and (Cu0.5Tl0.5)Ba2Ca3(Cu4-yGey)O12-d (y = 0, 0.3, 0.6 and 0.9) have been synthesized by solid-state reaction method. The structure and physical properties were investigated by powder X-ray diffraction (XRD), resistivity, ac-susceptibility and Fourier transform infrared absorption spectroscopy (FTIR). X-ray diffraction scans of polycrystalline samples of Cu0.5Tl0.5Ba2Ca4-xMgxCu5O14-δ (x = 0, 1, 2 and 3) samples show tetragonal structure following P4/mmm space group. The dominant phase in x = 0 sample is CuTl- 1234 while the remaining all Mg doped samples show the projected CuTl-1245 phase with a small inclusion of impurity phases. It suggests that the presence of Mg plays a very vital role in synthesis of five planar CuTl-1245 compounds. With the partial substitution of Ca with Mg in the samples, the CuO2 planes become uniformly doped due to improved inter-planer coupling which results in the enhancement of Tc (R = 0) as well as the magnitude of diamagnetism. Further superconducting properties of the samples have been enhanced by carrying out annealing experiments in nitrogen air and oxygen atmospheres. The enhanced superconductivity in different annealing environments have been attributed to the optimization of carrier density in the OPs and the IPs. Oxygen annealed samples show the best superconductivity among all, which have been attributed to the optimization of carrier concentration in the CuO2 planes and improved weak link behavior due to the intercalation of the oxygen in the unit cell and at the intra-grain and inter-grain sites. Superconductivity in the Cu0.5Tl0.5Ba2Ca2Mg2Cu5O14-d superconductor has been optimized by varying both time and temperature during the air annealing experiments by attaining Tc ~ 132 K. In (Cu0.5Tl0.5)Ba2Ca2Cu3-yGeyO10-d (y = 0, 0.5, 0.75 and 1.0) samples, synthesized at 860oC, y = 0 and 0.5 show the CuTl-1223 tetragonal phase but y = 0.75 and 1.0 develop CuTl-1234 as the dominant phase. It indicates that the substitution of Ge lowers the synthesis temperature and for single phase sample, temperature less than 860oC seems more plausible. Four planar Ge doped (Cu0.5Tl0.5)Ba2Ca3(Cu4-yGey)O12-d (y = 0, 0.3, 0.6 0.9) superconductors were prepared at 870oC rather than 880oC and investigated for their superconducting properties. X-ray diffraction scans of the samples confirm the CuTl-1234 phase. Increased Ge substitution at the Cu planar sites has been found to suppress the superconducting properties of the samples. Possible causes include the impurity scattering and the carrier depletion due the replacement of Cu2+ ions with Ge4+ ions. The superconductivity has been restored by carrier doping through annealing processes. FTIR analysis has also been conducted and the role Ge in the variations of different phonon modes has been discussed. Also the effect of oxygen annealing on these phonon modes have been observed and analyzed. The fluctuation induced conductivity of Cu0.5Tl0.5Ba2Ca4−xMgxCu5O14−δ (x = 1, 2) and Cu0.5Tl0.5Ba2Ca2Cu2M1O10-d (M =Si, Sn, Ge) superconductor samples has been done. FIC data of the as-prepared Cu0.5Tl0.5Ba2Ca4−xMgxCu5O14−δ (x = 1) sample does not fit with 2D, 3D AL equations, but for x = 2 and the oxygen annealed samples seem to fit well with 2DAL, 3D AL equations with two distinct cross over temperatures. In the samples the interlayer coupling strength J is found to increase with increased Mg content and oxygen post annealing. Higher concentration of Mg seems to lower the anisotropy along the c-axis and thus improves the inter-planer coupling. It results in 2D to 3D cross over of the conductivity and enhancement of the interlayer coupling strength J. The 2D to 3D cross over and higher J values in post annealed samples can be attributed to the change in the carrier concentration in the CuO2 planes, and improved weak link behavior, brought about by the intercalation of the oxygen in the charge reservoir layer. The excess- conductivity data of Cu0.5Tl0.5Ba2Ca2Cu2M1O10-d (M = Si, Sn and Ge) samples also shows two cross over temperatures and three distinct exponents. Si and Sn doped samples with almost same critical temperature have not shown much diversity in different parameters such as room temperature resistivity, transition width, a (rN 0 K) etc. Similarly not much difference is seen in the dimensionality exponents and the corresponding temperature ranges. The Ge doped sample with lower critical temperature has shown different FIC parameters with large transition width. Ge doped sample has shown higher 3D character; in this sample 2D fluctuations are found in very small temperature range. Here a possible link between the confinement of the 2D fluctuations to a narrow temperature window and the lower critical temperature of the Ge doped sample can be conjectured but not claimed.