The electron-transfer rate from methylene-bridged molecular adsorbates to SnO 2 semiconductor nanocrystalline film was systematically investigated for short bridge lengths. The synthesized sensitizers were the homologues of Re(CO) 3 Cl(dcbpy) [dcbpy ) 4,4′-dicarboxy-2,2′-bipyridine] (ReCnA) with methylene units (CH 2 ) n (n ) 1-5) inserted between the bipyridine rings and the carboxylate anchoring groups. Use of femtosecond infrared spectroscopy provided the time resolution necessary to study the ultrafast electron transfer that occurs over these very short bridges. Electron injection is unambiguously observed by signals arising from both the injected electron and the CO stretching mode of the oxidized molecule. All dyes exhibited nonexponential electron injection. The kinetic traces for the different spacers can be superimposed on each other by scaling their time axes, which allows a quantitative comparison of these nonexponential injection rates. This comparison revealed an exponential decrease of injection rate with bridge length for 3 e n e 5 with a decay constant (β) of 1.0 per CH 2 unit. Deviation from the exponential dependence was observed for n ) 1 or 2. The applicability of the time-scaling method also implies a rate distribution that is nominally independent of bridge length for all of the investigated samples.

Microwave irradiation of alkynyl allenes affords an intramolecular [2 + 2] cycloaddition reaction. This cycloaddition provides an efficient route to bicyclomethylenecyclobutenes. The reaction occurs with complete regioselectivity for the distal double bond of the allene for the selective formation of a variety of hetero- and carbocyclic substrates. Bicyclo[4.2.0]octadienes and bicyclo[5.2.0]nonadienes have been prepared in high yield. [reaction: see text]

Salt-induced soil degradation is common in farmlands and limits the growth and development of numerous crop plants in the world. In this study, we isolated salt-tolerant bacteria from the rhizosphere of Tamarix chinensis, Suaeda salsa and Zoysia sinica, which are common wild plants grown on a saline-alkaline land, to test these bacteria's efficiency in alleviating salt stress in tomato plants. We screened out seven strains (TF1-7) that are efficient in reducing salt stress in tomato seedlings. The sequence data of 16S rRNA genes showed that these strains belong to Arthrobacter and Bacillus megaterium. All strains could hydrolyze casein and solubilize phosphate, and showed at least one plant growth promotion (PGP)-related gene, indicating their potential in promoting plant growth. The Arthrobacter strains TF1 and TF7 and the Bacillus megaterium strain TF2 and TF3 could produce indole acetic acid under salt stress, further demonstrating their PGP potential. Tomato seed germination, seedling length, vigor index, and plant fresh and dry weight were enhanced by inoculation of Arthrobacter and B. megaterium strains under salt stress. Our results demonstrated that salt-tolerant bacteria isolated from the rhizosphere of wild plants grown on saline-alkaline lands could be used for alleviating salt stress in crop plants.

Investigations of a Rh(I)-catalyzed cyclocarbonylation reaction reveal its general synthetic utility for accessing highly functionalized tricyclic [6-7-5] linear and angular ring systems from allene-ynes. Three types of allene-ynes were prepared and subjected to Rh(I)-catalyzed cyclocarbonylation conditions. For three series of allene-ynes, the [6-7-5] ring systems were afforded in varying yields depending on the substrate structure. One series of allene-ynes afforded the [6-6-5] ring system possessing an alpha-alkylidene cyclopentenone as a result of a selective reaction with the proximal double bond of the allene.

A Rh(I)-catalyzed carbocyclization reaction of alleneynones affords functionalized 2-alkylidene-3-vinylcyclohexenones and 2-alkylidene-3-vinylcyclopentenones. The scope, limitations, and utility of this triene-forming protocol have been examined and the results reported within.Selective and concise entry into molecular complexity via carbocyclization reactions of unsaturated carbon-carbon bonds is an important area in organometallic chemistry. 1 Recently, it was demonstrated that Rh(I)-catalyzed cycloisomerization reactions of allenes lead to trienyl-containing carbocycles, 2 heterocycles, 2 d-and e-lactams, 3 and d-lactones. 4 Combining these functional motifs with a cross-conjugated trienyl moiety provides functionally dense substructures and if chemical reactivity can be controlled, a means of gaining rapid access to molecular complexity.Using cross-conjugated trienes in complexity generating reactions requires novel approaches to controlling doublebond selectivity. 5 It was this control element that led us to consider the carbocyclization reactions of alkynones 6 because the resulting trienones would possess double bonds that are sterically biased and electronically differentiated by the carbonyl group. In this Letter we report on the assembly of the allene-ynones and their participation in Rh(I)-catalyzed carbocylization reactions to produce trienones. Selective reactions of the double bonds of the trienones were briefly investigated and also reported on.Allene-ynones 3a-j 7 were conveniently prepared by addition of the corresponding lithium acetylides 2a-j to amide 1 (Scheme 1). Compound 3k, possessing a terminal alkynone, was obtained by removal of the TMS group from 3e. 7c Subjecting allene-ynone 3e to the standard reaction protocol developed in our group for the Rh(I)-catalyzed cycloisomerization reaction {10 mol% [Rh(CO) 2 Cl] 2 , r.t.} afforded a 10% yield of 4e. Reasoning that alkynone 3e was either more reactive and/or trienone 4e less stable, the reaction was performed at 0°C using only 3 mol% of catalyst. 8 To our delight, trienone 4e was obtained in 95% yield after only five minutes at 0°C (entry 5, Table 1). Scheme 1 Formation of allenyl alkynones 3a-kNext, the scope and limitations of this reaction were examined by varying the substituents on the alkyne. These variations had a significant impact on the rate and yields of these cycloisomerization reactions. For example, if R 1 = Me (3a) or a TBS-protected propanol 3b, conversion to 4a or 4b required 90 minutes (entries 1 and 2, Table 1). Interestingly, shortening the tether between the protected alcohol and the alkyne from three to two methylene units dramatically reduces the reaction time to ca. 20 minutes (entries 3 and 4, Table 1). 9 Alternatively, placing an aromatic ring on the alkyne terminus slows the reaction, requiring that substrate 3g be heated to 50°C and 8 mol% of Rh(I) catalyst to effect the formation of trienone 4g. An electron-withdrawing or electron-donating group on the para-position of the aryl ring had a negligible effect on...