Hadley S. Clayton

Review: active homogeneous reagents and catalysts in n-alkane activation

The development of selective, efficient, and direct routes for activation and functionalization of naturally abundant n-alkanes could lead to a new paradigm in materials and energy technologies. In this context, the use of homogeneous catalysts to functionalize C–H bonds of unactivated hydrocarbons is of particular interest from a scientific as well as an economic viewpoint. Despite the large body of work on stoichiometric C–H activation reactions produced over the last three decades, relatively few systems have been developed to allow catalytic functionalization of hydrocarbons. This review deals with homogeneous catalytic processes available in the literature for paraffin activation and functionalization. The key intermediates involved in catalytic systems are highlighted, providing important information in the design of new and efficient catalysts. Also, some of the key challenges and approaches to rational development of the next generation of organometallic catalysts will be highlighted.

Metallacycloalkanes – Synthesis, Structure and Reactivity of Medium to Large Ring Compounds

Publisher Summary This chapter discusses metallacyclopentane and larger rings containing only one transition metal. It focuses on the synthesis, structure, reactivity, and applications of metallacycles. The preparation of saturated five-membered metallacycles containing a group 4 transition metal has been extensively investigated and a number of synthetic routes are available for complexes of this type. Reactions of metallocene dichlorides with 1,4-dilithiobutane or the corresponding di-Grignard reagent represent the most common methods for preparation of these compounds. Although there are no reports of metallacyclohexane compounds for groups 5 or 6, there is a report of a group 7 rhenacyclohexane compound. The few reports can possibly be attributed to the fact that most of the routes to the metallacycles of this type make use of ethylene co-ordination, followed by coupling. There are no reported metallacycloheptane compounds of group 4 or group 5 transition metals. There is, however, a report of a chromacycloheptane 107.There are no reported metallacycloalkanes higher than metallacycloheptanes reported for the groups 4–7 and 9 transition metals.

Investigations on synthesis, thermolysis, and coordination chemistry of aminophosphine oxides

Some aminophosphine oxides (AmPOs), (R 1)(R 2)(R 3)P=O [R 1 = R 2 = R 3 = HNCH2CH=CH2; R 1 = R 2 = Ph, R 3 = HNCH2CH=CH2; R 1 = R 2 = R 3 = HNNMe2; R 1 = R 2 = Ph, R 3 = HNNMe2; R 1 = R 2 = R 3 = NC4H8O; R 1 = R 2=Ph, R 3 = NC4H8O], have been synthesized. The coordination chemistry of these AmPOs is studied with La(III), Th(IV), and U(VI) salts. The products are characterized by various analytical and spectroscopic techniques, and the thermal properties of the ligands and their complexes examined. The TGA data for these compounds show different decomposition temperatures, as well as thermal stability of the metal complexes. Comparisons are made among different ligands on their selective complexing ability towards some chosen metal salts. Mulliken population analysis shows that the basicity of P=O of ligand increases with an increase in the number of P-bonded amino groups.

Synthesis, structure, chemistry, and applications of tetravalent nickel complexes

This review provides an overview of the synthetic pathways, structures, and reactivity of various nickel(IV) complexes. The complexes are classified according to the various ligand types including sulfur, oxygen, nitrogen, and phosphorus donors. The main emphasis is on different ligand systems which stabilize Ni in higher oxidation state in the solid state and solution. The structural aspects of the complexes are briefly discussed. The possible applications of these nickel(IV) complexes are reviewed and future prospects are also highlighted.

Crystal structure of dibromido-carbonyl-(η6-p-cymene)osmium(II), C11H14Br2OOs

Abstract C11H14Br2OOs, monoclinic, P21/c (no. 14), a = 10.3844(5) Å, b = 6.7833(3) Å, c = 19.0379(9) Å, β = 102.143(2)°, V = 1311.03(11) Å3, Z = 4, Rgt(F) = 0.0258, wRref(F2) = 0.0582, T = 173(2) K.

Crystal structure of bromido(η6-1-isopropyl-4-methylbenzene)(7-oxocyclohepta-1,3,5-trien-1-olato-κ2O,O′)osmium

In the title compound, the central OsII ion is ligated by a hexahaptic η6 p-cymene ring, a Br− ligand and two O atoms of a chelating tropolonate group. The p-cymene ligand presents more than one conformation, giving rise to a discrete disorder, which was modelled with two different orientations with occupancy values of 0.561 (15) and 0.439 (15).

Crystal structure of dibromido μ-oxalato-κ2O,O′:κ2O′′,O′′′−η6-p-cymenediosmium(II), C22H28Br2O4Os2

Abstract C22H28Br2O4Os2, orthorhombic, Pbca (no. 61), a = 10.8433(5)Å, b = 11.8395(5) Å, c = 18.7871(8) Å, V = 2411.87(18) Å3, Z = 4, Rgt(F) = 0.0511, wRref(F2) = 0.1061, T = 173 K.

ENHANCING STUDENT PERFORMANCE IN FIRST YEAR CHEMISTRY THROUGH WEB -BASED LEARNING IN AN OPEN DISTANCE UNIVERSITY CONTEXT

This paper reports the results of a study to assess the impact of MasteringChemistry® on student performance in chemistry. The proprietary MasteringChemistry® is a web-based tutoring application and assessment system currently used in first year chemistry modules at the University of South Africa (Unisa). This web-based programme provides supplementary work, giving students practice with instructor-assigned problems. The system is able to coach students with feedback specific to their needs and with simpler problems upon request. The application also provides the individual student with immediate and specific feedback on incorrect or partially incorrect answers. There is great potential for web-based learning in an open distance-learning environment. In particular, in subjects such as chemistry where problem-solving strategies are intrinsic to the learning process, the internet could be an effective medium for teaching and learning. The rationale for this study was to explore new teaching strategies to increase the pass rate in chemistry. A profile of the student demographic, with data gathered from registration records, is presented. Data collection on student assessment occurred through the instructor diagnostic tools in the MasteringChemistry® application or with the assistance of the Unisa Examination Administration. Here we present preliminary results that indicate that most students who regularly accessed the material achieved better examination results than those who did not. This pilot study has led to improved and innovative formative assessment practices by the academic staff in the Chemistry Department at Unisa. It further formed an interesting and challenging learning experience for staff investigating web-based approaches directed at improvement of their assessment activities.Â

Theoretical and experimental studies on formation of diethylzinc-triphenylphosphine complex

GRAPHICAL ABSTRACT Abstract This work is mainly focused on understanding the complex-forming behavior of diethylzinc with neutral phosphine ligands such as triphenylphosphine (PPh3) to yield [Zn(PPh3)2Et2]. The complex formation in solution is observed in the presence of a large excess of diethylzinc, but leaving an insoluble solid on aging. The product formed in solution was analyzed by spectroscopic data. 31P-NMR was also used as a tool to observe this behavior, i.e., the disappearance of the chemical shift of PPh3 (δ -5.45) requires 14-fold excess of ZnEt2 in solution. The alkyl chains reduce the Lewis acidity on Zn and thereby the formation of phosphine adducts is restricted. Results obtained from orbital analyses calculations reveal that the LUMO appears to be asymmetrically distributed, and localized on one of the PPh3 ligands. The length of alkyl chains also influence the stability of [Zn(PPh3)2R2] and the longer chains on Zn impart less stability.