We describe the synthesis and characterization of three platinum­(II) ω-alkenyl complexes of stoichiometry Pt­[CH2CMe2(CH2) x CHCH2]2 where x is 0, 1, or 2, as well as some related platinum­(II) compounds formed as byproducts during their synthesis. The ω-alkenyl ligands in all three complexes, cis-bis­(η1,η2-2,2-dimethylbut-3-en-1-yl)­platinum (2), cis-bis­(η1,η2-2,2-dimethylpent-4-en-1-yl)platinum (3), and cis-bis­(η1,η2-2,2-dimethylhex-5-en-1-yl)­platinum (4), bind to Pt by means of a Pt–alkyl sigma bond at one end of the ligand chain and a Pt–olefin pi interaction at the other; the olefins reversibly decomplex from the Pt centers in solution. The good volatility of 3 (10 mTorr at 20 °C), its ability to be stored for long periods without decomposition, and its stability toward air and moisture make it an attractive platinum chemical vapor deposition (CVD) precursor. CVD of thin films from 3 shows no nucleation delay on several different substrates (SiO2/Si, Al2O3, and VN) and gives films that are unusually smooth. At 330 °C in the absence of a reactive gas, the precursor deposits platinum containing 50% carbon, but in the presence of a remote oxygen plasma, the amount of carbon is reduced to below the Rutherford backscattering spectroscopy (RBS) detection limit without affecting the film smoothness. Under hot wall CVD conditions at 250 °C in the absence of a co-reactant, 72% of the carbon atoms in 3 are released as hydrogenated products (largely 4,4-dimethylpentenes), 22% are released as dehydrogenated products (all of which are the result of skeletal rearrangements), and 6% remain in the film. Some conclusions about the CVD mechanism are drawn from this product distribution.

Abstract. The giant panda (Ailuropoda melanoleuca) was taken to the brink of extinction in the 1980s through a combination of deforestation, large-scale loss of bamboo in the core of its range, poaching, and zoo collection, causing over 1000 deaths from the 1950s. It was thought that the drastic population decline was likely to impose a severe impact on population viability. Here, based on temporal genotyping of individuals, we show that this rapid decline did not significantly reduce the overall effective population size and genetic variation of this species, or of the two focal populations (Minshan and Qionglai ) that declined the most. These results are contrary to previously assumptions, probably because the population decline has not produced the expected negative impact due to the short time scale involved (at most 10 generations), or because previous surveys underestimated the population size at the time of decline. However, if present-day habitat fragmentation and limited migration of giant pandas remains, we predict a loss of genetic diversity across the giant pandas' range in the near future. Thus, our findings highlight the substantial resilience of this species when facing demographic and environmental stochasticity, but key conservation strategies, such as enhancing habitat connectivity and habitat restoration should be immediately implemented to retain the extant genetic variation and maintain long-term evolutionary potential of this endangered species.

The compound cis-bis­(η1,η2-2,2-dimethylpent-4-en-1-yl)­platinum, Pt­[CH2CMe2CH2CHCH2]2 (3), is a recently discovered chemical vapor deposition (CVD) precursor for the deposition of highly smooth platinum thin films without nucleation delays on a variety of substrates. This paper describes detailed mechanistic studies of the pathway by which 3 reacts upon being heated in solution. In various solvents between 90 and 130 °C, 3 decomposes to generate ∼1 equiv of 4,4-dimethylpentenes by addition of a hydrogen atom to the pentenyl ligands in 3. The “extra” hydrogen atoms arise by dehydrogenation of other pentenyl ligands; some of these dehydrogenated ligands are released as methyl-substituted methylenecyclobutanes and cyclobutenes. A combination of isotope labeling and kinetic studies suggests that 3 decomposes by C–H activation of both allylic and olefinic C–H bonds to give transient platinum hydride intermediates, followed by reductive elimination steps to form the pentene products, but that the exact mechanism is solvent-dependent. In C6F6, solvent association occurs before C–H bond activation, and the rate-determining step for thermolysis is most likely the formation of a Pt σ complex. In hydrocarbon solvents, the solvent is little involved before C–H bond activation, and the rate-determining step is most likely the formation of a Pt σ complex only for γ-C–H and ε-C–H bond activation, but cleavage or formation of a C–H bond for δ-C–H bond activation. A comparison of the thermolysis reactions under CVD conditions and in solution suggests that the high smoothness of the CVD-grown films is due in part to rapid nucleation (which is a consequence of the availability of low-barrier CC bond dissociation pathways) and in part to the formation of carbon-containing species that passivate the Pt surface.

MgO thin films are deposited by chemical vapor deposition from the precursor magnesium N,N-dimethylaminodiboranate, Mg(H3BNMe2BH3)2, and water at a substrate temperature of 270–350 °C. Highly conformal coatings with 98% step coverage in trenches of aspect ratio 9 are obtained at a substrate temperature of 270 °C and a growth rate of 7.5 nm/min, most notably through the use of a forward-directed flux, in which some of the precursor molecules travel ballistically down the recessed feature, strike the bottom, and are scattered there to create a virtual source. The deposition conditions can also be adjusted to afford a growth rate up to 200 nm/min with reduced conformality. Most of the films have a dense and column-free microstructure with low surface roughness; the film density, measured by a combination of Rutherford backscattering spectrometry and scanning electron microscopy, is 82%–86% of bulk. Films grown on Si substrates have good adhesion and a low coefficient of friction (∼0.1) in nanoscratch measurements. The refractive index of the films is slightly lower than that of bulk MgO, consistent with the reduced physical densities. Depending on the growth conditions, the C content in the films varies between 0.7 and 6 at. %, and the B content ranges from 1 to 16 at. %. B in the film is present in the B2O3 chemical state; after subtracting the O content in B2O3, the O/Mg ratio = 1.02 in the MgO matrix. A film grown at a temperature of 270 °C and a growth rate of 6 nm/min has a dielectric constant of 9.5 and a breakdown strength of 6 MV/cm.