Francis S. Mair

Alkaline earth diazapentadienyl compounds: Structure of [Ba2{(C6H11)NC(Me)CHC(Me)N(C6H11)}(3){(SiMe3)2N}]

Three different bonding modes in one molecule! The diazapentadienyl ligands in the title compound 1 adopt η1 ,η1 -N,N-chelating plus η5 -terminal, η1 η1 -N,N chelating plus η5 -bridging, and novel η1 -N plus η3 -1-aza-allyl bonding modes. R=cyclohexyl.

Calixarene-facilitated transfer of alkali metal ions across the polarised liquid–liquid interface

The transfer of sodium and potassium ions across the water–1,2-dichloroethane interface by the neutral ionophore tetraethyl-p-tert-butyl calix[4]arene tetraacetate has been investigated using voltammetric methods. The electrochemical data has been used to determine the stoichiometry of the metal: ligand complex and the appropriate association constants between the metal ions and the ligand in the organic phase. This data is correlated with structural studies, including the crystal structure of the Na+-calixarene complex, which is reported for the first time.

2-Substituted icosahedral monocarbon carboranes. Part 1. Synthesis via boron insertion

New 2-substituted icosahedral monocarbon carboranes have been synthesised by functionalised boron insertion. The compounds [NBun4][2-Ph-closo-1-CB11H11]1, [PPh4][2-(p-MeC6H4)-closo-1-CB11H11]2, [N(CH2Ph)Me3][2-F-closo-1-CB11H11]3, 2-Me3N-closo-1-CB11H114 and [PPh4][2-Cl(CH2)4O-closo-1-CB11H11]5 were characterised by 1H, 11B and 11B–11B correlation NMR spectroscopy. The crystal structure of 5 shows a cage distortion that is postulated to result from π interaction of the substituent with the cluster. Crystal data: triclinic, space group P, a= 10.672(2), b= 11.047(2), c= 14.203(3)A, α= 75.97(2), β= 87.84(2), γ= 83.22(2)°, Z= 2. Final R= 0.042 for 3951 reflections with I > 2σ(I).

The first structurally characterised early main-group metal diazallyl complex; synthesis and crystal structure of LiCPh(NPh)2·NMe[(CH2)2NMe2]2

n-Butyllithium reacts with a solution of PhNC(Ph)NHPh (N,N′-diphenylbenzamidine) and NMe[(CH2)2NMe2]2(pmdeta) to give the complex LiCPh(NPh)2·pmdeta, which is monomeric in the solid state with a five-co-ordinate litium cation bound to a tridentate pmdeta ligand and a bidentate amidinide anion (diazaallyl system, chelating), in which the two N–C bond lengths of 1.336(4) and 1.335(4)A suggest almost uniform delocalisation along the NCN unit.

Mixed aggregation between lithium diisopropylamide and lithium chloride: NMR, solid-state structure and ab initio calculations

Abstract An improved synthesis of (Pr i 2 NLi) 2 LiCl(Me 2 NCH 2 CH 2 me 2 ) 2 ( 1 ) is presented. The structural characterisation of 1 by single crystal X-ray diffraction (C 24 H 60 ClLi 3 N 6 , M =489.1, monoclinic P2 1 /n, a=9.126(3), b=17.538(6), c=20.470(7) A , β=98.02(4)°, V=3244.2(19) A , Z=4) revcaled a three-runged LiN, ClLi, LiN ladder molecular structure. Cryoscopy in benzene indicated that 1 remained substantially undissociated in that solvent. Multinuclear variable temperature NMR in toluene revealed fluxionality; a mechanism of fluxion in arene solution involving rupture of an R 2 NLi bond followed by pseudorotation of all external ligands around a chloride fulcrum is proposed. Semi-empirical (MNDO) and ab initio (HF/6–31G ∗ ) calculational studies of the simplified model (LiNH 2 ) 2 LiCl gave six-membered ring minimum energy geometries. While coordination of four water molecules to the model resulted in only modest changes to the six-membered ring structure at MNDO level, coordination of four dimethyl ehher molecules led to a preference for the three-runged ladder structure as predicted by SCF calculations using a 6–31g ∗ basis.

The behaviour of β-triketimine cobalt complexes in the polymerization of isoprene

Four new β-triketimine cobalt complexes [(LCo-μ-Br)2][BArF]2 where L = N,N′,N′′-triaryl-β-diketimine were synthesised and then characterized by single-crystal X-ray diffraction, MALDI-MS and elemental analysis. In combination with three previously reported, they provided a series of seven subtly different complexes which were screened for activity in the catalysis of isoprene polymerization: the structure of the ligand (L) had strong effects on activity and stereoselectivity. The produced polyisoprene contained a mixture of cis-1,4, trans-1,4 and 3,4-enchained monomers; 4,1-errors followed 3,4 errors. The highest percentage of cis-1,4 content (80%) was obtained with complex 5 where two electron-withdrawing fluorine substituents occupied the 2- and 6-positions of two of the imino-aryl rings. This polymer was obtained in 98.5% conversion. Both cis-1,4 content and activity decreased when electron donor substituents were present on the aryl rings, so that complex 1, with three methyl substituents in positions 2, 4 and 6 gave the lowest cis-1,4 content (73.6%), with a conversion of only 58.5%, under identical conditions. The temperature of the polymerization, the type of aluminium co-catalyst used, and the Al/Co ratio strongly affected the activity and microstructure of the polyisoprene produced. Ethylaluminiumsesquichloride was the most active of a range of organoaluminiums screened. A kinetic study using complex 6 as catalyst demonstrated that the polymerization was first-order in monomer, and that approximately 12% of cobalt formed active centers. The combination of high molecular weight (>105) with moderately high activity at conveniently accessible temperatures to give predominantly cis-1,4-polyisoprene but with 3,4 units to promote efficient crosslinking is potentially attractive, and has not previously been attained with 3d elements.

Borane and alane reductions of bulky N,N′-diaryl-1,3-diimines: Structural characterization of products and intermediates in the diastereoselective synthesis of 1,3-diamines

Two new C2-symmetric diazaborinanes were prepared by diastereoselective intramolecular dihydroboration of bulky 1,3-diamines, the remarkably stable l-[HB(2,6-Pri2-C6H3NCHMe)2CMe2], from which it was not possible to isolate free diimine, and the less bulky l-[HB(2-Pri-C6H4NCHMe)2CMe2], which yielded l-(2-Pri-C6H4NHCHMe)2CMe2 on acid work up. The BH3 reductions were highly diastereoselective for l-products (de > 95%). Use of AlCl3/LiAlH4 mixtures in diethyl ether gave lower (de ≈ 75%) and opposite selectivity, yielding predominantly u-(2,6-Pri2-C6H3NHCHMe)2CMe2 upon work up, via a u-[H2Al(2,6-Pri2-C6H3)NHCHMeCMe2CHMeN(2,6-Pri2-C6H3)] intermediate in a two-step reduction. All products were characterized crystallographically.

Structural studies of lithiated enaminones: the 1-oxa-5-azapentadienyllithium fluxional heterocubane [(PriNCMeCHCMeOLi)4] and its dimeric hexamethylphosphoric triamide complex [{PriNCMeCHCMeOLi·OP(NMe2)3}2]

Lithiation of 4-isopropylaminopent-3-en-2-one in hexane gave a 1-oxa-5-azapentadienyl compound [(PriNCMeCHCMeOLi)4] 1, which comprises a tetrameric aggregate of Li4 and O4 interpenetrating tetrahedra in which chelating terminal nitrogens undergo a fluxional process around each face of the Li4 tetrahedron in toluene solution. Addition of hexamethylphosphoric triamide (hmpa) produced a dimeric complex 2 in which oxygen bridges are retained. The crystal structures of both compounds were determined. Bond lengths indicate that an iminoenolate form of the ligand predominates, irrespective of aggregation state. The data are used to rationalise the selectivity of dimetallations of enaminones.

Reversible C–C bond formation: solid state structure of the aldol-like addition product of adamantanone to a 1,5-diazapentadienyllithium, and its solution state retro-aldol dissociation

Analysis of crystals of the lithium complex of the tripodal ligand formed upon addition of adamantanone to a 1,5 diazapentadienyllithium complex reveals a long C-C bond which ruptures upon dissolution in non-co-ordinating solvents.

A 3:1 mixed aggregate of diphenylamidolithium with lithium chloride:crystal structure of [(Ph2NLi)3LiCl·3tmen] (tmen = N,N,N′,N′-tetramethylethylenediamine)

Demonstrating a new structural type in mixed aggregate chemistry, a 3:1 mixture of Ph2NLi and LiCl with 3 equiv. of N,N,N′,N′-tetramethylethylenediamine exists in toluene and in the solid state as a Ph2NLi/LiCl mixed ‘dimer’ and a (Ph2NLi)2 homodimer linked only by a Li–Cl coordinate bond, as determined by NMR spectroscopy and X-ray crystallography.