Derivatization of an Alkylideneborane with B═C Bond Cleavage.

We present the synthesis, structural characterization, and reactivity of alkylideneborane 2, supported by π-donating N-heterocyclic imino and σ-donating N-heterocyclic carbene (NHC) ligands. The incorporation of these ligands effectively weakens the B═C bond strength, leading to enhanced reactivity. Consequently, selective cleavage of the B═C bond can be achieved using pyridine-N-oxide, sulfur, and selenium, resulting in the formation of 1,3-dioxa-2,4-diboretane 3, thioxoborane 4, and selenoborane 5, respectively. Furthermore, intriguing B═C bond insertions with CO2 and CS2 are observed, affording zwitterionic borenium/fluorenide 6 and dithiaboretane 7. The former species 6 is readily converted to transient oxoborane and imidazolium enolate, showcasing the bora-Wittig reaction of alkylideneborane. This investigation highlights the potential of alkylideneborane as a versatile building block for synthesizing novel organoboron compounds through unconventional transformations.

Crystalline Neutral Diboron Analogues of Cyclopropanes.

Although Schleyer's computations in 1979 predicted that the ground state of the parent diborirane features a planar-tetracoordinate carbon atom (anti van't Hoff-Le Bel geometry), this work demonstrates that substitution of C coupled with N-heterocyclic carbene (NHC) coordination provides access to isolable diborirane derivatives 3 and 4 with van't Hoff-Le Bel geometry. Species 3 and 4 are isoelectronic with cyclopropane and the highly strained B2 C rings feature 2c-2e bent σ bonds. Consequently, the B-B and B-C bonds in 3 are cleaved in the presence of hydride, proton, and chalcogens. The former two reactions gave NHC-coordinated fluorenyldihydridoborane 5 and dichlorofluorenylborane 6, respectively, whereas the latter transformations afforded novel thiaborirane 8 and selenaborirane 9. In addition, transfer hydrogenation of 3 with ammonia borane (H3 N⋅BH3 ) led to the formation of (µ-hydrido)diborane 7 via selective cleavage of the B-B bond. These reactivities show potential for their future application in organic synthesis.

[Dynamic changes of vegetation net primary productivity in permafrost zone of Northeast China in 1982-2009 in response to global change].

As one of the high-latitude cold regions, the permafrost zone of Northeast China (PZNC) is more sensitive to global change. Based on the AVHRR GIMMS NDVI and MODIS NDVI, and by using CASA model, this paper simulated the net primary productivity (NPP) in the PZNC from 1982 to 2009. In 1982-2009, the mean annual air temperature, annual solar radiation and sunshine duration, and atmospheric CO2 concentration and its annual increasing rate in the PZNC increased significantly while the annual precipitation had a significant decrease, and the annual NPP showed an up-and-down trend, with the turning point in 1998. The annual NPP had a high spatial heterogeneity, with an average of 623 g C X m(-2). Comparing with air temperature, the precipitation in growth season was the main factor affecting the NPP. Land use change altered land cover, and thus, the spatiotemporal characteristics of NPP. A significant positive correlation was observed between the NPP and atmospheric CO2 concentration. The impact of permafrost degradation on NPP differed with regional environment. The NPP had a significant positive correlation with the mean annual ground temperature, but a negative correlation with the annual maximum permafrost depth.