Quantitative aspects of 119Sn-CIDNP

Enhancement factors of the ¹¹⁹Sn-CIDNP signals observed in hexamethylditin — the recombination product of trimethyltin radicals — are determined. The enhanced absorption in the main ¹¹⁹Sn signal, which cannot be explained by Kaptein's rules based on a first order perturbation treatment of the radical pair theory, can be described by applying the high field approximation of the radical pair model if second order perturbation theory is used. The A/E type multiplet effect in the satellites arising from coupling with ¹¹⁷Sn nuclei which is in accordance with Kaptein's rules is not affected by the second order treatment. Pedersen's analytical expressions derived from the three-dimensional diffusion model describe the ¹¹⁹Sn-CIDNP effects using p = 0.32 and Λ = 1 or p = 0.5 and Λ = 0.56. During the photochemical decomposition of hexamethylditin and octamethyltritin, the main ¹¹⁹Sn signals show enhanced absorption. Enhancement factors found experimentally are compared with values calculated using the second order treatment. It follows that both compounds mainly decompose from triplet states.     

Triaryl-silyl, -germyl,and -stannyl radicals .MAr3 (M = Si,Ge, or Sn and Ar = 2,4,6-Me3C6H2) and .Ge(2,6-Me2C6H3)3: Synthesis and ESR studies

The triarylmetal-centred radicals ^.MAr₃ (M = Si, Ge, or Sn; Ar = 2,6-Me₂C₆H₃ or 2,4,6-Me₃C₆H₂) have been prepared from the appropriate triarylmetal chloride, MAr₃Cl, and an electron-rich olefin [R$\text{NCH}{}_2\text{CH}{}_2\text{NRC}$]₂ (R = Me or Et) under UV irradiation in toluene at low temperature. The triarylgermyl radicals are persistent (t$\text{1}\text{2}$ > 24 h, 20°C) whilst the analogous tin and silicon radicals are only stable under constant irradiation at temperatures below ?20°C; the ESR spectra of the germanium radicals and of ^.Si(2,4,6-Me³C₆H₂)₃ (which is the first triarylsilyl radical to be spectroscopically identified) show coincidental equivalence of all the proton couplings due to twisting of thearomatic rings into a “propeller” arrangement about the metal. The synthesis and characterisation of precursors to these radicals are also reported.     

Fluorocarbon derivatives of nitrogen. Part I. Some reactions of perfluoro-1-azacyclohexene

Controlled displacement of fluorine from perfluoro-1-azacyclo-hexene (I) by the nucleophilic reagents Me₂NH, Et₂NH, $\text{CH}{}_2\text{CH}{}_2\text{O(CH}{}_2\text{)}{}_2\text{N}$H, C₆Cl₅ONa, and (CF₃)₂NONa provides the derivatives (II) - (IV), respectively. The last of these can also be obtained by treatment of the parent compound (I) with mercury^II bistrifluoromethylnitroxide.     

Synthesis of monohydridohexamethylbenzeneruthenium(II) complexes containing group V donor ligands. Isomerism arising from cyclometallation of a tertiary phosphine at aliphatic and aromatic carbon atoms

The η-hexamethylbenzenehydridoruthenium(II) complexes RuHCl(η-C₆Me₆)L (L = PPh₃ (11), AsPh₃ (12), P(C₆H₄-p-F)₃ (14), P(C₆H₄-p-Me)₃ (15), P(C₆H₄-p-OMe)₃ (16), P-t-BuPh₂ (17), P-i-PrPh₂ (18), P-i-Pr₃ (19), PCy₃ (20) and P-t-BuMe₂ (21)) have been made by heating [RuCl₂(η-C₆Me₆)]₂, the ligand and sodium carbonate in propan-2-ol. The triarylphosphine complexes 11, 14 and 15 react with methyllithium to give aryl ortho-metallated hydridoruthenium(II) complexes such as $\text{RuH(}\text{o}\text{-C}{}_6\text{H}{}_4\text{P}$Ph₂)(η-C₆Me₆) (22) and 19 similarly gives the isopropyl cyclometallated complex $\text{RuH(CH}{}_2\text{CHMeP}$-i-Pr₂(η-C₆Me₆) (29) as a mixture of diastereomers. Reaction of 17 with methyllithium gives initially the t-butyl cyclometallated complex $\text{RuH(CH}{}_2\text{CMe}{}_2\text{P}$Ph₂)(η-C₆Me₆) (25) which isomerizes by a first order process (k$\text{0}\text{?}$.2 h^?1 in C₆D₆ or THF-d₈ at 50°C) to the aryl ortho-metallated complex $\text{RuH(}\text{o}\text{-C}{}_6\text{H}{}_4\text{P}$-t-BuPh)(η-C₆Me₆) (26). The similarly generated isopropyl cyclometallated complex $\text{RuH(CH}{}_2\text{CHMeP}$Ph₂)(η-C₆Me₆) (27) has not been isolated in a pure state owing to rapid isomerization to $\text{RuH(}\text{o}\text{-C}{}_6\text{H}{}_4\text{P}$-i-PrPh)(η-C₆Me₆) (28); both 27 and 28 exist as a pair of diastereomers. The formation of the cyclometallated complexes and the isomerizations are thought to involve intermediate 16-electron ruthenium(O) complexes Ru(η-C₆Me₆)L.     

Transition metalcarbon bonds: XL. Palladium(II) complexes of [(dimethylamino)methyl]-ferrocene

C₅H₅FeC₅H₄CH₂NMe₂ reacts with sodium chloropalladate(II) in the presence of sodium acetate to give the internally metallated binuclear species [$\text{Pd}{}_2\text{X}{}_2\text{{C}{}_5\text{H}{}_5\text{FeC}{}_5\text{H}{}_3\text{CH}{}_2\text{N}$Me₂}₂] (X = Cl). The corresponding iodide was prepared as were mononuclear species [$\text{Pd(acac) {C}{}_5\text{H}{}_5\text{FeC}{}_5\text{H}{}_3\text{CH}{}_2\text{N}$Me₂}] and [$\text{Pd-{C}{}_5\text{H}{}_5\text{FeC}{}_5\text{H}{}_3\text{CH}{}_2\text{N}$Me₂}L] L = PMe₂Ph, AsMe₂Ph, P(OMe)₃ or PPh₃. ¹H NMR data are given.     

Primary radical termination in polymerization: Evaluation of the characteristic constant

Polymerization experiments with styrene in benzene at 60°, initiated by benzoyl peroxide, covering a wide range of concentration of both monomer and initiator are reported; the results cannot be explained in terms of the classical rate relationship with $\text{R}{}_{\mathrm{p}}\text{∝ [}\text{I}\text{]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{[}\text{M}\text{]}$. Deviations were reflected in unexpected orders of monomer up to [M]^1·4 and of initiator down to [I]^0·42 when the initiator concentration is increased and monomer concentration is decreased. Based on the concept of primary radical termination, an equation, viz.

$\text{ln}\text{R}\text{p}\text{2}\text{[I][M]}{}^2\text{=}\text{ln}\text{2f}{}_{\mathrm{k}}\text{k}{}_{\mathrm{d}}\text{k}\text{p}\text{2}\text{k}{}_{\mathrm{t}}\text{?2}\text{k}{}_{\mathrm{prt}}\text{k}{}_{\mathrm{i}}\text{k}{}_{\mathrm{p}}\text{×}\text{R}{}_{\mathrm{p}}\text{[M]}{}^2$

is proposed. Semi-log plots of R_p²/[I] [M]² vs R_p/[M]² show a wide range of linearity; the characteristic constant k_prt/k_ik_p and also f_k can be obtained from the slope and intercept, respectively, k_prt, k_i and k_p are, respectively, the rate constants of primary radical termination, initiation and propagation and f_k is the efficiency of initiation, defined as the fraction of radicals which come out of the solvent cage and take part in initiation, primary radical termination and primary radical recombination. The definition of f_k is thus differentiated from the conventional efficiency of initiation. Finally, we have derived an equation which allows determination of the classical efficiency of initiation as a function of [I]/[M]² and also allows a correction of R_p in handling the above equation by taking into account the small amount of monomer consumed in initiation.     

Standard Gibbs free energy of formation of SnO2 from high-temperature e.m.f. measurements

The thermodynamic equilibrium Sn(l) + O₂(g) = SnO₂(s) has been studied between 773 and 1380 K by e.m.f. measurements on cells involving a solid electrolyte, of the type:

$\text{Pt∥Ni(s), NiO(s)∥ZrO}{}_2\text{+ Y}{}_2\text{O}{}_3\text{∥Sn(1), SnO}{}_2\text{(s)∥Pt}$

     

Rate parameters for transfer reactions of some polymer radicals: in terms of Swain and Lupton's f and r and the unique positional weighting factors of Williams and Norrington

Rate parameters of the reaction of phenols, deuterated phenols and nitrobenzenes with polyvinylacetate radicals and of aromatic thiols with polymethylmethacrylate radicals have been correlated with Swain and Lupton's substituent constants (F_k and R_k) and Williams and Norrington's unique positional weighting factors (f_j and r_j) by the following equation: $\text{P}{}_{\mathrm{i}}\text{= α}{}_{\mathrm{i}}\text{?}{}_{\mathrm{j}}\text{F}{}_{\mathrm{k}}\text{+ β}{}_{\mathrm{i}}\text{r}{}_{\mathrm{j}}\text{R}{}_{\mathrm{k}}\text{+ e}{}_{\mathrm{i}}\text{+ P}{}^0{}_{\mathrm{i}}$where P_i's are the rate parameters, P⁰_i being that for a standard reference state. The correlations were found to be quite satisfactory. The sign and magnitude, and the ratio of the reaction dependent parameters α_i and β_i throw light on the nature of the transition state and the relative contributions of the mesomeric and inductive effects. The present studies also show that the mesomeric effect of meta-substituents is significantly greater than reported by earlier workers.     

Gibbs' free energy of formation of magnesium stannate

The thermodynamic properties of the spinel Mg₂SnO₄ have been determined by emf measurements on the solid oxide galvanic cell,

$\text{Pt,W,MgO}\text{+}\text{Mg}{}_2\text{SnO}{}_4\text{+}\text{Sn}\text{Y}{}_2\text{O}{}_3\text{?}\text{ThO}{}_2\text{Sn}\text{+}\text{SnO}{}_2\text{,}\text{W,Pt}$

in the temperature range 600 to 1000°C. The Gibbs' free energy of formation of Mg₂SnO₄ from the component oxides can be expressed as

$\text{2}\text{MgO}\text{(r.s)+}\text{SnO}{}_2\text{(}\text{rut}\text{)→}\text{Mg}{}_2\text{SnO}{}_4\text{(}\text{sp}\text{)}$

,

$\text{ΔG°=1420?2.96T (±100)}\text{cal mole}{}^{\mathrm{?1}}$

These values are in good agreement with the information obtained by Jackson et al. [Earth Planet. Sci. Lett.24, 203 (1974)] on the high pressure decomposition of magnesium stannate into component oxides at different temperatures. The thermodynamic data suggest that the spinel phase is entropy stabilized, and would be unstable below 207 (±25)°C at atmospheric pressure. Based on the information obtained in this study and trends in the stability of aluminate and chromite spinels, it can be deduced that the stannates of nickel and copper(II) are unstable.     

Kinetics and mechanism of solid-state reaction between bismuth(III) oxide and molybdenum(VI) oxide

The mechanism of the following solid-state reactions between bismuth(III) oxide and molybdenum(VI) oxide was investigated within the temperature range 400–650°C.

$\text{(i)}\text{Bi}{}_2\text{O}{}_3\text{+ MoO}{}_3\text{→ Bi}{}_2\text{MoO}{}_6\text{, (ii)}\text{Bi}{}_2\text{O}{}_3\text{+ 2MoO}{}_3\text{→ Bi}{}_2\text{MO}{}_2\text{O}{}_9\text{, (iii)}\text{Bi}{}_2\text{O}{}_3\text{+ 3MoO}{}_3\text{→ Bi}{}_2\text{(MOO}{}_4\text{)}{}_3\text{, (iv)}\text{Bi}{}_2\text{MoO}{}_6\text{+ MoO}{}_3\text{→ Bi}{}_2\text{MO}{}_2\text{O}{}_9\text{, (v)}\text{Bi}{}_2\text{Mo}{}_2\text{O}{}_9\text{+ MoO}{}_3\text{→ Bi}{}_2\text{(MoO}{}_{\mathrm{2)3}}\text{.}$

Two types of experiments, capillary and particle size, were performed to ascertain whether MoO₃ diffuses into Bi₂O₃ or vice versa. These show that molybdenum trioxide diffuses into bismuth oxide grains. If α is the fraction of molybdenum trioxide reacted, the kinetics in all five cases are found to be governed by the equation αⁿ = kt throughout the temperature range, where n and k are constants at a given temperature and t is the time. Both n and k are temperature dependent. The characteristic feature of these reactions is that they proceed to completion. Results are also fitted by the relation $\text{α = k}{}_2\text{t}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{? k}{}_3\text{t}$, where k₂ and k₃ are constants, which shows that the reactions occur by bulk diffusion through grain boundary contacts. The number of grain boundary contact points decreases with time in the course of reaction.