N,N-Bis(diphenyl­phosphino)-1,2-dimethyl­propyl­amine

The diphenyl­phosphine groups in the title compound, C29H31NP2, are staggered relative to the PNP backbone. The N atom adopts an almost planar geometry with the two P atoms and the C atom attached to it, in order to accommodate the steric bulk of the phenyl groups and the alkyl group. Three C atoms of the 1,2-dimethylpropylamine group are disordered over two positions in a 9:1 ratio. The mol­ecules pack diagonally in the unit cell across the ac plane in a head-to-tail fashion

Samarium(II) iodide induced reactions: a case of make or break.

Chemistry has been defined by some as an art, by others as a science and people have gone as far as dismissing it as pure alchemy. Overall, however, one cannot help but come to the conclusion that chemistry is a unique blend of all three. The work contained within this manuscript is an attempt to delve deep into the mysteries of but one type of transformation - a ¡¥simple¡¦ cyclisation step in which one couples two different moieties to form a cyclobutane ring with the aid of SmI2. There are two opposing forces of nature which control the outcome of this reaction, namely elimination and cyclisation and it is the contest between these two driving forces that ultimately decides the fate of these transformations. This work was born from previous attempts in RAU¡¦s laboratories to synthesise chiral cyclobutane derivatives from carbohydrates as well as the apparent discrepancies in two independent scientists¡¦ publications on the effect of SmI2 on reactions utilising 1,4-diketones. Hoffmann from Germany had managed to form 1,2-cyclobutanediols from a pinacol reaction promoted by SmI2 while Ghosh in India had experienced fragmentation products under similar conditions. The information contained herein provides a bird¡¦s eye view of cyclisation vs. fragmentation in 1,4-disubstituted compounds as well as an insight into how one might avoid or exploit the particular reaction pathways. The effects of various moieties in a ¡§ƒ×¡¨ disposition to the ketone have been investigated to obtain a broader understanding of the scope of the cyclobutane ring formation. These findings also provide the information necessary for effecting cyclobutane ring closures within the realm of carbohydrate chemistry. One will learn that the ¡¥geminal¡¦ effect is not the only efficacious method for the coupling of a ketyl radical and an activated alkene to form a four-membered ring. The thesis concludes with a strategic route towards the synthesis of a potential antiviral compound containing the cyclobutane substructure, originating from the simple sugar D-ribose.Prof. D.B.G. William

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Carbon-bridged diphosphine ligands for chromium-catalysed ethylene tetramerisation and trimerisation reactions

The use of carbon-bridged diphosphine ligands in chromium-catalysed ethylene tri- and tetramerisation reactions has been investigated. Two- and three-carbon spacer ligands all showed activity for selective oligomerisation, with a structure-selectivity correlation between P-Cr-P bite angle and 1-octene: 1-hexene ratio evident. Activated chromium complexes of single carbon spacer diphosphines were also shown to be effective tetramerisation catalysts, provided that the ligand is innocent under the conditions of catalyst activation. A catalyst with the bis(diphenylphosphino)benzene ligand was found to be exceptionally active, although the combined 1-hexene and 1-octene selectivity was lower than with the best diphosphinoamine (PNP) ligands. The yield losses to by-products can to an extent be minimised by the use of high reaction temperatures and pressures. Unlike with the PNP-based systems, attempts to activate the Cr/bis(diphenylphosphino)benzene catalyst in situ from a chromium salt and free ligand resulted in low activity and high polymer formation. The effect of different phosphine substitution on catalyst selectivity was explored. Steric constraints around the catalytic centre (ortho-alkylphenyl phosphines) resulted in a shift towards 1-hexene formation, as with PNP catalysts. Additionally, the basicity of the phosphines appears to influence catalyst selectivity, with alkyl phosphines favouring trimerisation. An interplay between phosphine basicity and bridge structure is in evidence, however, as a catalyst containing a ligand with both basic phosphine atoms and a small bite angle was shown to be selective towards I-octene. (c) 2007 Elsevier B.V. All rights reserved.</p

Ethylene oligomerisation chromium catalysts with unsymmetrical PCNP ligands

Chromium(III) complexes of chelating diphosphines, with PNP or PCNCP backbones, are excellent catalysts for ethylene tetra- and/or trimerisations. A missing link within this ligand series are unsymmetric chelating diphosphines based on a PCNP scaffold. New bidentate PCNP ligands of the type Ph2PCH2N(R)PPh2 (R = 1-naphthyl or 5-quinoline groups, 2a–d) have been synthesised and shown to be extremely effective ligands for ethylene tri-/tetramerisations. Three representative tetracarbonyl Cr0 complexes bearing a single PN(R)P (5), PCN(R)P (6), or PCN(R)CP (7) diphosphine (R = 1-naphthyl) have been prepared from Cr(CO)4(η4-nbd) (nbd = norbornadiene). Furthermore we report a single crystal X-ray diffraction study of these compounds and discuss their structural parameters.</p