Coordination compounds involving stable radicals represent a promising avenue toward the design of new magnetic materials. In this respect, a series of new metalverdazyl radical complexes has been prepared and their magnetic properties reported. These systems can be envisioned as model systems designed to help elucidate the fundamental electronic interactions between one paramagnetic metal ion and one verdazyl radical that lead to magnetic exchange. A new chelating verdazyl diradical has also been prepared and fully characterised. The electronic ground state of this diradical species has been established through magnetic and variable temperature electron paramagnetic resonance (VT-EPR) studies. In an effort to expand the metal-radical model systems beyond simple 1:1 metal:radical complexes, this verdazyl diradical was employed as a ligand to prepare a succession of first row transition metal complexes. The magnetic properties of the resulting coordination compounds have been studied in an effort to understand how the nature of the metal-diradical magnetic exchange changes with the metal used. In addition to the wide-spread interest in the magnetic properties of stable organic radicals, there is a growing awareness of the redox properties of this class of compounds. Electrochemical and spectroelectrochemical techniques were utilised to probe the redox properties of a verdazyl diradical and a structurally similar verdazyl monoradical. Coordination compounds involving the redox-inert metal zinc were also prepared and their redox properties investigated. While the addition of zinc to the verdazyl diradical had no significant impact on the magnetic properties of the diradical, there is a distinct difference between the redox properties of the diradical itself and its zinc complex. Coordination to zinc also affected the redox properties of the verdazyl monoradical, although to a lesser extent than what was observed for the diradical. / Graduate / 0485

Proefschrift Universiteit van Amsterdam. / Met bibliogr., lit. opg. - Met samenvatting in het Nederlands.

München, Techn. University, Diss., 2007.

Zugl.: München, Techn. Universiẗat, Diss., 2008.

Berlin, Techn. Univ., Diss., 2000. / Computerdatei im Fernzugriff.

University, Diss., 2008--Bayreuth.

Thesis (Ph.D.)--University of Florida, 2003. / Title from title page of source document. Includes vita. Includes bibliographical references.

University, Diss., 2004--Tübingen.

A serieso f chiral biaryl cyclic monophosphoniteli gands of type RP(OAr)2 (R = Ph, Me, t-Bu, o-anisyl and Cy; (OAr)2 = 1,1'-binaphthyl-2,2'-diyl, 9,9'- biphenanthryl- 10,1 0'-diyl) have been prepared. The ligands have been synthesised by reaction of the dichlorophosphine precursor with the corresponding biphenol (HOAr)2. Chiral biaryl diphosphonite ligand (ArO)2PCH2CH2(OAr)2 derived from binaphthol has also been prepared. Platinum(II), palladium(II) and rhodium(I) complexes of these ligands are described and the X-ray crystal structures of five of these complexes are reported and discussed.T he electronic propertieso f the phosphonitesa re betweent hose of phosphite and phosphine, and this is reflected in their coordination chemistry. The new chiral biaryl monophosphites of type (Ar'O)P(OAr)2 have been synthesised straightforwardly by condensation of a phenol and the corresponding chlorophosphites in the presence of NEt3. Preliminary studies of their coordination chemistry with platinum(II) and rhodium(I) have been carried out. The twist on the seven membered P(OCCCCO) ring leads to a deshielding of the 31P signal for the biaryl ligands and in the complexes studied here. The asymmetric hydrogenation of a-enamides with rhodium(I) complexes of the phosphonites and diphosphonites as catalysts is discussed. The ligands have been screened in the asymmetric hydrogenation of two substrates: methyl-2-acetamido acrylate and methyl-(Z)-2-acetamido cinnamate. Monodentate phosphonite systems show, in some cases, higher enantioselectivity (up to 92% ee) than the analogous bidentate. The results presented here challenge the long-accepted wisdom that chelating ligands are necessary to achieve high enantioselectivities in asymmetric hydrogenation. NMR studies and X-ray crystallographic data show that the asymmetric ligand profile caused by the biaryl units in these phosphonites has three consequences: (i) rotation about the M-P bond in monodentate phosphonites is inhibited; (ii) a different rotamer for the monodentate from that in the chelate analogues is favoured; (iii) the favoured rotamer in the monodentate causes more effective chiral induction in the hydrogenation catalyses. The generality of these new concepts has been probed with some preliminary catalytic studiesw ith monodentatep hosphitel igands. The phosphonite ligands have also been tested in the copper(I) catalysed 1,4- addition of diethylzinc to enones and nitro-olefins in an attempt to extend their potential use in asymmetric catalysis. The phosphonite ligands show moderate to high ee's for the ethyl transfer to enones (cyclic and acyclic). The monophosphonite ligands induce higher enantioselectivity for acyclic enones: ee's up to 82% are the highest obtained with a monodentate phosphonite ligand in asymmetric 1,4-addition of diethylzinc to chalcone.

No description available.