Ian J. Munslow

SYNTHESIS OF A HIGHLY STRAINED URANACYCLE : MOLECULAR STRUCTURES OF ORGANOMETALLIC PRODUCTS ARISING FROM REDUCTION, OXIDATION AND PROTONOLYSIS

Abstract The reaction of [U(NN′ 3 )I] [NN′ 3 =N(CH 2 CH 2 NSiMe 2 Bu t ) 3 ] with Group 1 and 2 metal alkyls gives, via metalation of a methylsilyl group, a highly strained metallacycle [U( bit -NN′ 3 )] in high yield. The molecular structure of this compound shows that it has an unusually long UC bond (ca. 2.75 A) and additional CH⋯M agostic interactions. On exposure of the complex in solution to 2 H 2 the methylsilyl groups and the metallacyclic UCH 2 Si group are deuterated, leaving the tert -butyl and methylene groups intact. The analogous thorium metallacycle is prepared from the reactions of [Th(NN′ 3 )Cl], or by attempted reduction of [Th(NN′ 3 )I] with potassium metal in pentane. Attempted reduction of [U(NN′ 3 )I] in a similar manner in toluene gave a high yield of a fascinating dimeric metallacyclic anion {[K(η 6 -C 6 H 5 Me)][U( bit -NN′ 3 )]} 2 , which was characterised by X-ray crystallography. The authenticity of this compound as U(III) is established by near-IR spectroscopy, and also by its production from the reaction of the neutral uranacycle [U( bit -NN′ 3 )] with potassium. A mechanism for the formation of the anion is postulated. Its reaction with benzyl chloride led to oxidation to the parent uranacycle. Oxidation of [U( bit -NN′ 3 )] with air or oxide sources leads to formation of an oxo-bridged dimer with intermonomer metalated methylsilyl groups and pentavalent uranium centres. Reactions of [U( bit -NN′ 3 )] with a range of acids HX occur rapidly, reprotonating the previously metalated methylsilyl group and forming complexes [U(NN′ 3 )X]. For example, lutidinium hydrochloride, diethylamine and tert -butanol gave [(NN′ 3 )UCl], [(NN′ 3 )U(NEt 2 )] and [(NN′ 3 )U(OBu t )], respectively. Reactions with carbon acids were also successful. For example, β-hydropyridines gave η 2 -dehydropyridyl complexes. One of these, [U(NN′ 3 )(η 2 -NC 5 H 4 )], is shown in the first X-ray crystallographic study of such an actinide complex to contain an essentially planar U(η 2 -NC 5 H 4 ) unit. Monosubstituted alkynes react with the uranacycle in a similar manner to give η 1 -alkynyls. The molecular structure of one example shows that the UCC unit is bent (156°) in contrast to other structurally characterised non-bridging alkynyls of the f-elements.

Biaryl-bridged Schiff base complexes of zirconium alkyls: synthesis structure and stability

Abstract Three substituted salicylaldimine derivatives H2L1–3 of 2,2′-diamino-6,6′-dimethylbiphenyl give, under appropriate conditions, isolable alkyls of zirconium [ZrL1–3R2] (R=CH2Ph, CH2But). Two molecular structures confirm their cis-α geometry (C2-symmetric with cis alkyl ligands). They decompose via 1,2-migratory insertion of an alkyl group to imine, followed in some instances by a second similar reaction. The dimeric molecular structure of one such doubly-inserted product is presented. The kinetics of decomposition by this process are studied briefly, and it is noted that the rate increases with increased steric demand of the salicylaldimine unit.

Stereoselective catalytic tishchenko reduction of β-hydroxyketones using scandium triflate

Abstract A number of aliphatic and aromatic β-hydroxyketones were reduced to 1,3-diol monoesters by aldehydes in the presence of a catalytic amount of scandium triflate. Chiral substrates were reduced with high 1,3-anti diastereoselectivity.

Efficient predetermination of chirality-at-zirconium

Only one of eight possible diastereomers of the organometallic chiral-at-metal complex [ZrL2(CH2Ph)2] (L = a bidentate, chiral non-racemic pyrdine alcoholate) is observed by NMR spectroscopy in the slow exchange regime.

Zirconium catalysed enantioselective hydroamination/cyclisation

A chiral zirconium alkyl cation catalyses the cyclisation of certain aminoalkenes with enantioselectivity up to 82%, the highest thus far observed for such a process.

Structure and reactions of a metallacyclic complex containing a remarkably long uranium–carbon bond

The intramolecular metalation of a β-silyl methyl group in [U{N(CH2CH2NSiMe2But)3}(CH2Ph)] occurs rapidly, despite the conformational demands of the triamidoamine ligand, to produce a highly strained metallacycle (U–C ca. 2.75 A); this complex reacts cleanly with a range of carbon and other acids to give, for example, an alkynyl with a bent (156°) U–CC unit.

Aminooxazolinate; a chiral amidinate analogue

High levels of diastereoselection with respect to chirality-at-metal are achieved at equilibrium for complexes containing a new and available range of diazaallyl ligands.

Bidentate carbenoid ester coordination in ruthenium(II) Schiff-base complexes leading to excellent levels of diastereo- and enantioselectivity in catalytic alkene cyclopropanation.

Exceptionally high stereoselectivity (ee < or = 98%, dr < or = 99:1) in the cyclopropanation of alkenes with ethyl diazoacetate using a non-planar ruthenium(II) Schiff-base precatalyst is a result of eta 2C,O binding of the carbenoid ester intermediate, according to DFT calculations.

Arylaminopyridinato complexes of zirconium

A range of 2-arylaminopyridines (HL) are synthesised readily from bromopyridines and amines using palladium-catalysed amination. Protonolysis reactions of these proligands with ZrX(4)(X = NMe(2), CH(2)Ph, CH(2)Bu(t)) yield zirconium complexes of the type [ML(n)X(4-n)], several of which have been characterised by X-ray crystallography. Control of metal/ligand stoichiometry and structure is pursued by investigation of the effects on substitution patterns of the pyridine and aryl rings. Some distinct patterns emerged; (i) the 6-methyl position on the pyridine appears to be particularly important with regards to control of stoichiometry, although there are co-ligand effects; (ii) structures of the metal alkyl derivatives [Zr(n)(CH(2)R)(4-n)] are dominated by aromatic pi-pi stacking, even when bulky arene substituents are employed at. This leads to the complexes adopting a C(2v)-symmetric core; (iii) the amides [Zr(2)(NMe(2))(2)] have structures for which aromatic pi-pi stacking is unfeasible, and correspondingly C(2)-symmetric or similar structures are adopted. All the structural data presented is consistent with a trans influence order at zirconium Me(2)N > RCH(2) > py.

A Novel Molecular Mechanics Strategy for Transition Metals Bound to Biological Molecules

Transition metals bound to biological molecules are frequently associated with unusual ligand sets and low symmetry coordination environments [1]. Additional complications arise for certain species, such as the d9 Cu(II) ion, where the electronic effects from the d-electrons already result in highly variable and ‘plastic’ coordination even in simple complexes. These features pose serious problems for conventional molecular modelling [2].