Dimethylgermylene (GeMe2) has been generated and studied by laser flash photolysis of 1,1-dimethyl- and 1,1,4-trimethyl-3-phenylgermacyclopent-3-ene (3a and 3b, respectively) in hexane solution, where it exhibits λmax = 470 nm and decays on the microsecond time scale with second-order kinetics. In the absence of scavengers the decay of GeMe2 is accompanied by the growth of absorptions due to tetramethyldigermene (Ge2Me4; λmax = 370 nm), which decays over the next ca. 100 μs. Absolute rate constants for reaction of GeMe2 with several reagents have been determined, including acetic acid, CCl4, oxygen, n-butyl- and triethylamine, a terminal alkene and alkyne, two dienes, and the group 14 trialkylmetallyl hydrides R3MH (M = Si, Ge, Sn; R = Et or n-Bu). The rate constants agree closely with gas-phase values for the same or similar substrates. The data are compared to those for reaction of GePh2 with the same set of reagents, showing GeMe2 to be significantly more reactive than its phenylated analogue in every case. Evidence of reversibility is obtained for the reactions with the alkene and dienes, which are thought to yield the corresponding three-membered germanocycles as primary products; the equilibrium constants for these reactions are also considerably higher than those for reaction of GePh2. Comparisons are also made with published data for SiMe2 in solution. Absolute rate constants for reaction of Ge2Me4 have also been measured or assigned upper limits and are compared to those for the tetraphenyl analogue (Ge2Ph4), providing the first quantitative assessment of the effects of substituents on the reactivity of the GeGe bond.

Laser flash photolysis techniques have been employed to study the reactivities of dimethylgermylene (GeMe2), diphenylgermylene (GePh2), and a series of ring-substituted diarylgermylenes (GeAr2) in methanol (MeOH) and tetrahydrofuran (THF) solution, where the germylenes exist as the corresponding Lewis acid−base complexes with the O-donor solvents. Dimerization to the corresponding digermene is a significant mode of decay in THF solution, particularly for the GeMe2−THF complex, though for the diaryl systems it is slowed dramatically compared to the situation in hexane solution. On the other hand, dimerization is undetectable in MeOH, where the GeAr2−MeOH complexes decay with pseudo-first-order kinetics at low laser intensities and lifetimes in the 20−50 μs range; the GeMe2−MeOH complex exhibits a lifetime of ca. 4 μs under similar conditions. Solvent kinetic isotope effects are consistent with solvent-catalyzed proton transfer to yield the corresponding alkoxyhydridogermane as the process responsible for the decay of the germylene−MeOH complexes. Their decay is accelerated by strong acids and bases such as methanesulfonic acid and sodium methoxide, respectively, which quench the GePh2−MeOH complex with rate constants of ca. 3 × 109 M−1 s−1 in each case. Kinetic isotope and substituent effects are consistent with rate-determining protonation at germanium in the reactions with acid, while the results for methoxide quenching are consistent with the formation of the corresponding Ar2(MeO)Ge− anion as a discrete intermediate, which has been detected in MeOH solution in one instance. Reaction of sodium methoxide with the germylene−THF complexes also proceeds rapidly and allows the detection of the corresponding Ar2(MeO)Ge− anions and determination of rate coefficients for their protonation by MeOH, for all four of the diaryl systems that were studied. The reactivity of the GeMe2−THF complex toward sodium methoxide, methanesulfonic and acetic acid, CCl4, oxygen, isoprene, and 4,4-dimethyl-1-pentene has also been examined.

The development of polymeric systems with tailored properties as nonviral gene carriers continues to be a challenging and exciting field of research. We report here the synthesis and characterization of biodegradable, temperature- and pH-sensitive carbohydrate-based cationic nanogels as effective gene delivery carriers to Hep G2 cells. The temperature-sensitive property of the nanogels allows their facile complexation of DNA, while the pH-sensitive property allows the degradation of nanogels followed by the release of plasmid in the endosome. The nanogels are synthesized via reversible addition-fragmentation chain transfer polymerization (RAFT) technique and are evaluated for their DNA condensation efficacy. The gene delivery efficacies of these nanogels are subsequently studied and it is found that these cationic glyconanogels can serve as potent gene delivery vectors in hepatocytes. It is found that the gene delivery efficacies of this system are similar to that of branched poly(ethyleneimine), which is used as a positive control. Moreover, these nanogels show desirable properties for systemic applications including low toxicity and degradation in acidic environment.

Photolysis of 1,3,4-trimethyl-1-phenylgermacyclopent-3-ene (5) in hydrocarbon solvents containing isoprene, methanol, or acetic acid affords 2,3-dimethyl-1,3-butadiene (DMB) and the expected trapping products of methyl phenylgermylene (GeMePh) in chemical yields exceeding 90%. The germylene has been detected in hexane solution by laser flash photolysis as a short-lived species (τ ~ 2 µs) exhibiting a UV-vis absorption spectrum centered at λmax = 490 nm. It decays with second-order kinetics and a rate constant close to the diffusion-controlled limit, with the concomitant growth of a second longer-lived transient (λmax = 420 nm) that is assigned to a mixture of (E)- and (Z)-1,2-dimethyl-1,2-diphenyldigermene (4). Absolute rate constants have been determined for the reactions of the germylene with primary and tertiary amines (n-BuNH2 and Et3N, respectively), acetic acid (AcOH), a terminal alkyne and alkene, isoprene, DMB, CCl4, and the group 14 hydrides Et3SiH and Bu3SnH. GeMePh is slightly more reactive than GePh2 towards all the reagents studied in this work; both are significantly less reactive than GeMe2 toward the same substrates. Absolute rate constants for the reactions of 4 have also been measured or assigned upper limits in every case and are compared to previously reported values for tetraphenyl- and tetramethyl-digermene with the same reagents.Key words: germylene, digermene, kinetics, laser flash photolysis, germirane, germirene, vinylgermirane, complex, UV–vis spectrum, insertion, addition.

Laser flash photolysis of 2-phenylheptamethyltrisilane (5d), 2,2-diphenylhexamethyltrisilane (5e), and phenyltris(trimethylsilyl)silane (5f) in hexane and acetonitrile solution affords strong, long-lived transient absorptions centered in the 440–470 nm range, which are assigned to the transient silenes formed via [1,3]-trimethylsilyl migration into the ortho-position of a phenyl ring on the basis of their UV–vis spectra and kinetic data for their reactions with methanol (MeOH), acetic acid (AcOH), acetone, 2,3-dimethyl-1,3-butadiene (DMB), carbon tetrachloride (CCl4), and oxygen. The silene derivatives are formed along with the corresponding silylenes (SiMePh, SiPh2, and Si(SiMe3)Ph, respectively) upon photolysis of these compounds in solution, and indeed, weak, short-lived transient absorptions assignable to the silylenes can also be detected in laser photolysis experiments with the three compounds in hexane, superimposed on the much more prominent absorptions due to the silenes. The silylene absorptions are quenched by MeOH and triethylsilane (Et3SiH) with absolute rate constants varying over the narrow ranges of (1.1–1.8) × 1010 (mol/L)–1 s–1 and (2.5–3.6) × 109 (mol/L)–1 s–1, respectively, in excellent agreement with previously reported values for SiPh2 and SiMe2 under the same conditions. The kinetic data obtained for the silenes are compared to previously reported data for the reactions of the same substrates with the related silenes (6a–6c) formed by photolysis of pentamethylphenyl-, 1,1,1,2-tetramethyl-2,2-diphenyl-, and 1,1,1-trimethyl-2,2,2-triphenyldisilane (5a–5c, respectively) under similar conditions. The comparison provides the first systematic, quantitative assessment of the stabilizing effects of trialkylsilyl substitution at the silenic silicon atom in silene derivatives.Key words: silene, silylene, trisilane, tetrasilane, kinetics.