The stabilization of silicon(II) and germanium(II) dihydrides by an intramolecular Frustrated Lewis Pair (FLP) ligand, PB, i Pr 2 P(C 6 H 4)BCy 2 (Cy = cyclohexyl) is reported. The resulting hydride complexes [PB{SiH 2 }] and [PB{GeH 2 }] are indefinitely stable at room temperature, yet can deposit films of silicon and germanium, respectively, upon mild thermolysis in solution. Hallmarks of this work include: 1) the ability to recycle the FLP phosphine-borane ligand (PB) after element deposition, and 2) the single-source precursor [PB{SiH 2 }] deposits Si films at a record low temperature from solution (110 8C). The dialkylsilicon(II) adduct [PB{SiMe 2 }] was also prepared, and shown to release poly(dimethylsilane) [SiMe 2 ] n upon heating. Overall, this study introduces a "closed loop" deposition strategy for semiconductors that steers materials science away from the use of harsh reagents or high temperatures. Scheme 1. General concept of FLP-assisted semiconductor (E) and polymer [ER 2 ] n deposition (E = Si, Ge).

We studied 80 healthy ASA 1 patients (aged 20-52 yr) to determine if fentanyl affects sevoflurane requirements for achieving 50% probability of no movement in response to laryngoscopy and tracheal intubation (MAC-TI). Patients were allocated randomly to one of four fentanyl dose groups (0, 1, 2 and 4 micrograms kg-1). Patients in each group received sevoflurane at a pre-selected end-tidal concentration according to an 'up-down' technique. After steady state sevoflurane concentration had been maintained for at least 10 min, fentanyl was administered i.v. Tracheal intubation was performed 4 min after administration of fentanyl, and patients were assessed as moving or not moving. Heart rate (HR) and mean arterial pressure (MAP) were recorded before induction of anaesthesia, just before administration of fentanyl, just before laryngoscopy for intubation, and after intubation. The MAC-TI of sevoflurane was 3.55% (95% confidence intervals 3.32-3.78%), and this was reduced markedly to 2.07%, 1.45% and 1.37% by addition of fentanyl 1, 2 and 4 micrograms kg-1, with no significant difference in the reduction between 2 and 4 micrograms kg-1, showing a ceiling effect. Fentanyl attenuated haemodynamic responses (HR and MAP) to tracheal intubation in a dose-dependent manner, even with decreasing concomitant sevoflurane concentration. Fentanyl 4 micrograms kg-1 suppressed the changes in HR and MAP more effectively than fentanyl 1 or 2 micrograms kg-1 at sevoflurane concentrations close to MAC-TI.

MAC and MAC-BAR decreased similarly with increasing concentrations of fentanyl in plasma, showing an initial steep reduction followed by a ceiling effect. In the presence of N2O, MAC and MAC-BAR decreased similarly but did not exhibit a ceiling effect.

A stable cyclic dialkylgermylene (1) was synthesized by reductive dechlorination of the corresponding dichlorogermane (6) with sodium. Germylene 1 is monomeric both in solution and in the solid state, as observed by UV-vis spectroscopy and X-ray crystallography.

X-ray structural analyses of tetrakis (trialkylsilyl)digermenes have shown that the trialkylsilyl substituents enforce near-planar geometry around the GedGe bonds, in accordance with theoretical predictions. A remarkable temperature dependence of the UV-vis spectra of tetrakis(triisopropylsilyl)digermene in solution was observed, suggesting an equilibrium between two different structures around the GedGe bond.One of the most intriguing structural characteristics of the doubly bonded group 14 metal compounds dimetalenes (R 2 MdMR 2 ; M ) Si, Ge, Sn) 1 is deformation from planarity around the double bonds. Theoretical calculations have shown that the parent dimetalenes (H 2 MdMH 2 ) adopt trans-bent structures but the geometry is significantly affected by the electronic effects of the substituents; more electronegative and π-electrondonating substituents induce a larger bending deformation, while electropositive substituents favor a planar geometry. 2 However, it is difficult to detect the electronic effects of substituents on the geometry, because of the inevitable steric effects exerted by the bulky protecting groups. Although tetrasilyldimetalenes, (H 3 -Si) 2 MdM(SiH 3 ) 2 (M ) Si, Ge, Sn), have been predicted theoretically to be planar in the optimized geometry, 2a in a recent study of tetrakis(trialkylsilyl)disilenes 1ac 3 we have found that the tetrasilyldisilenes show two modes of deformation, bending and twisting, in the solid state, depending on the alkyl substituents of the silyl groups.We report herein the structure of novel tetrakis-(trialkylsilyl)digermenes, 2a-c, synthesized by reductive coupling of the corresponding bis(trialkylsilyl)dichlorogermanes by sodium in toluene at room temperature and isolated as thermally stable but airsensitive crystals. 4