Gerard A. Lawless

Lipophilic strontium and calcium alkyls, amides and phenoxides; X-ray structures of the crystalline square-planar [{trans-Sr(NR′2)2(µ-1,4-dioxane)}∞] and tetrahedral [CaR2(1,4-dioxane)2]; R′= SiMe3, R = CH(SiMe3)2]

Treatment of pyrophoric strontium powder in tetrahydrofuran with ArOH (Ar = C6H2But3-2,4,6) or HNR′2 at ambient temperature affords crystalline [Sr(OAr)2(THF)4] or [Sr(NR′2)2(THF)2]3, respectively, and 3 with 1,4-dioxane yields crystalline [{trans-Sr(NR′2)2(µ-1,4-dioxane)}∞]4; co-condensation of calcium vapour and RBr in THF at 77 K affords [CaR2(THF)3]5, which with 1,4-dioxane gives [CaR2(1,4-dioxane)2]6; X-ray structures reveal the alkaline earth metal environment to be square-planar for 4[Sr-N 2.449(7), Sr-O 2.533(9)A] but tetrahedral for 6[Ca-C 2.483(5), Ca-O 2.373(4)A] with dioxane as a bridging bidentate 4 or monodentate 6 ligand.

A study of the kinetics of polymerization of aniline using proton NMR spectroscopy

Abstract The polymerization of aniline has been studied by monitoring monomer depletion using proton NMR spectroscopy. For precipitation polymerization at 298 K using Na 2 S 2 O 8 as oxidant an induction period of several minutes was observed, followed by relatively rapid polyaniline formation. In contrast, much slower polymerization was found using KIO 3 as oxidant. In both cases there is a significant residual NMR signal, even though a stoichiometric amount of oxidant was used. This was attributed to soluble aniline oligomers rather than unreacted aniline monomer. At 278 K the rate of polymerization is markedly slower for both oxidants. No significant differences were observed between the rates of precipitation polymerization and dispersion polymerization using a reactive poly(ethylene oxide)-based stabilizer. Faster reactions were observed when aniline was polymerized in the presence of ultrafine 20 nm silica particles to form polyaniline-silica colloidal nanocomposites. Polymerization was slower when aniline was polymerized in the presence of surfactant micelles to form surfactant-stabilized polyaniline particles; this is probably due to the high viscosity of the reaction solution.

The synthesis and structure of the alkaline earth metal organic compounds [M(OAr)2(thf)n][M = Ca, n= 3 (1) or 0; M = Ba, n= 4] and [{Ca(NR2)(µNR2)(thf)}2], and the X-ray structure of (1)(Ar = C6H2But2-2,6-Me-4; R = SiMe3; thf - OC4H8)

Treatment of highly reactive, pyrophoric calcium or barium (obtained by co-condensation of the appropriate metal vapour and toluene) in tetrahydrofuran with (i) ArOH (Ca more reactive than Ba) affords the phenoxide [M(OAr)2(thf)n][M = Ca and n= 3 (1), or n= 0 after heating at 80°C and 10–2 Torr; M = Ba, n= 4], or (ii) R2NH (for M = Ca) yields [{Ca(NR2)(µ-NR2)(thf)}2][also obtained from (1)+ 2LiNR2 in n-C6H14; Ar = C6H2But2-2,6-Me-4; R = SiMe3)]; the X-ray structure of crystalline (1) shows a distorted trigonal bipyramidal Ca environment with the thf ligands in apical sites.

Crystalline binuclear cis- and trans-chlorotin(II) amides [Sn(µ-Cl)(NR2)]2, the cis-1a ⇌trans-1b isomerisation for [NR2= NCMe2(CH2)3CMe2], and the X-ray structures of 1a and of trans-[Sn(µ-Cl){N(SiMe3)2}]2

Crystalline binuclear chlorotin(II) amides [Sn(µ-Cl)(NR2)]2 have been X-ray characterised as cis-[NR2= [graphic omitted]Me2, 1a] and trans-(R = SiMe3, 2b) conformers [Cl–Sn–Cl′= 78.53(4)1a or 81.33(4)°2b, Sn–Cl–Sn′ 100.91(4)1a or 98.67(4)°2b, 2.74 1a or 2.67 A2b]; a solution of 1 in toluene undergoes rapid cis⇌trans exchange at ambient temperature, but distinct cis-1a and trans-1b forms coexist below 192 K (119Sn NMR spectroscopy and line-shape analysis) and evidence is presented for an intramolecular mechanism for this exchange.

Synthesis and structure of crystalline [K{Sn(CH2But)3}(η-C6H5Me)3] and the first NMR spectral observation of 119Sn–39K coupling

Treatment of [Sn2(CH2But)6] with K in tetrahydrofuran (thf) at 25 °C affords crystalline [K{Sn(CH2But)3}(thf)2]1, which with toluene gives [K{Sn(CH2But)3}(η6-C6H5Me)3]2, the X-ray structure of 2 at 295 K revealing that potassium is in a distorted tetrahedral environment (taking each of the η6-toluene molecules as occupying a single site), with l(K–Sn) 3.548(3)A and l(K–C) ranging from 3.21 to 3.72 A; a solid state 1l9Sn cross-polarisation magic angle spinning (CP-MAS) NMR spectral study of 2 provides the first observation of direct 119Sn–39K coupling.

Crystal structure of [Li(tmen)2][Li{C(SiMe3)3}2]. A multinuclear magnetic resonance study of tris(trimethylsilyl)methyllithium–tetrahydrofuran(1/2) and –N,N,N′,N′-tetramethylethylenediamine (1/1)(tmen)

A single-crystal X-ray study of (Me3Si)3CLi·tmen (tmen =N,N,N′,N′-tetramethylethylenediamine) shows that it crystallises with the ionic structure [Li(tmen)2][Li{C(SiMe3)3}2] but that the anions pack with different orientations from those in crystalline [Li(thf)4][Li{C(SiMe3)3}2](thf = tetrahydrofuran). The 1H, 7Li, 13C and 29Si NMR spectra of (Me3Si)3CLi·2thf and (Me3Si)3CLi·tmen in thf and toluene, and 7Li, 13C and 29Si NMR spectra of the solids are described. Spectra obtained from solutions below ca. 25 °C show the presence of ion pairs [Li(thf)4][Li{C(SiMe3)3}2] or [Li(tmen)2][Li{C(SiMe3)3}2], together with further species which appear to be different in thf and toluene. Spectra from solutions at higher temperatures show inter-species exchange on the NMR timescale.

Synthesis, structure and reactivity of [Yb(η-C5Me5){Si(SiMe3)3}(thf)2]

The reaction of [Yb(η-C5Me5)2(OEt2)] with 1 equiv. of [Li{Si(SiMe3)3}(thf)3] in toluene affords [Yb(η-C5Me5){Si(SiMe3)3}(thf)2]1 in high yield; a single-crystal X-ray analysis and multinuclear 171Yb and 29Si NMR spectroscopic data for 1 are reported.

Synthesis and structural characterisation of bis(trimethylsilyl)amidotin(II) triflate [{Sn(NR2)(μ-η2-∞ (R=SiMe3, −OTf=−OSO2CF3)

Abstract The amidotin(II) triflate [{Sn(NR 2 ){μ-η 2 - OTf)} 2 ] ∞ ( 1 ) has been prepared in high yield by two methods: from Sn(NR 2 ) 2 +HOTf, or from [Sn(NR 2 )(μ-Cl)] 2 +2AgOTf (R=SiMe 3 , − OTf= − OSO 2 CF 3 ). The triflate ligand in the crystalline compound 1 binds to two tin atoms in an O , O ′-bridging fashion (av. SnO 2.395(4) A) and uses its third oxygen atom to bind more loosely to a tin atom of a neighbouring dinuclear tin unit [av. SnO″ 2.832(4) A]. Multinuclear [ 1 H-, 13 C-, 19 F- and 119 Sn- ( δ −78.0 in PhMeC 6 D 6 at 298 K)] NMR and 119 Sn Mossbauer (I.S. 3.37, Q.S. 3.75 mm s −1 ) spectral data are reported.

First example of a conducting polymer synthesised in supercritical fluids

Polypyrrole is synthesisedvia thermal decarboxylation of a precursor monomer, pyrrole-2-carboxylic acid, using ferric salts in both supercritical carbon dioxide and supercritical fluoroform; pressed pellet conductivities were as high as 2×10–2 S cm–1 and scanning electron microscopy studies revealed an unusual non-spherical morphology.

[{Yb6[η-C5Me4(SiMe2But)]6I8}{Li(thf)4}2]: the spontaneous self-assembly of a hexanuclear ytterbium(II) octaiododianion

Reaction of 1 equiv. of LiCps[Cps= C5Me4(SiMe2But)] with YbI2 affords the novel half-sandwich polyatomic species [{Yb6(η-Cps)6I8}{Li(thf)4}2] 1; the molecular structures and solid- and solution-state 171Yb NMR data for 1 and, for comparison, the dimeric half sandwich derivatives [{Yb(η-C5Me5)(µ-I)Ln}2](L = thf, n= 2, 2; L = dme, n= 1,3) are presented.