The reaction of [LAlH2 ] (L=HC(CMeNAr)2 , Ar=2,6-iPr2 C6 H3 ) with MeOTf (Tf=SO2 CF3 ) resulted in the formation of [LAlH(OTf)] (1) in high yield. The triflate substituent in 1 increases the positive charge at the aluminum center, which implies that 1 has a strong Lewis acidic character. The excellent catalytic activity of 1 for the hydroboration of organic compounds with carbonyl groups was investigated. Furthermore, it was shown that 1 effectively initiates the addition reaction of trimethylsilyl cyanide (TMSCN) to both aldehydes and ketones. Quantum mechanical calculations were carried out to explore the reaction mechanism.
The well-defined aluminum dihydride LAlH2 (L = HC(CMeNAr)2, Ar = 2,6-Et2C6H3) (1) operates in catalysis like a transition metal complex. The catalytic activity of 1 for hydroboration of terminal alkynes was investigated. Furthermore, catalyst 1 effectively initiated the dehydrocoupling of boranes with amines, thiols, and phenols, respectively, to form compounds with B-E bonds (E = N, S, O) under elimination of H2. Quantum mechanical calculations indicate that hydroboration and dehydrocoupling reactions occur via three consecutive cycloaddition reactions involving the activation of the X-H (X = Al, B, C, and O) σ-bonds.
Over the past few decades, β-diketiminate ligands have been widely used in coordination chemistry and are capable of stabilizing various metal complexes in multiple oxidation states. Recently, the chemistry of aluminum and gallium in their +1 oxidation state has rapidly emerged. NacNacM(I) (M = Al, Ga; NacNac = β-diketiminate ligand) shows a two coordinate metal center comparable with singlet carbene-like species.The metal center also possesses a formally vacant p-orbital. In this article we present an overview of the last 10 years for aluminum(I) and gallium(I) stabilized by β-diketiminate ligands that have been widely explored in bond breaking and forming species. Scheme 2 Carbon chain growth by sequential reactions of CO and CO 2 with [W(CO) 6 ] and 1. Scheme 3 Syntheses of [2.2.1] metallobicycle 7 and reversible CO insertion. Scheme 17 Syntheses of IDipp-(69 and 70) and Me2 cAAC-stabilized stibinidenes (71 and 72). Scheme 18 Syntheses of complexes 73 and 74. Perspective Dalton Transactions 1358 | Dalton Trans., 2020, 49, 1351-1364 This journal is
Land cover classification of very high resolution (VHR) imagery over urban areas is an extremely challenging task. Impervious land covers such as buildings, roads, and parking lots are spectrally too similar to be separated using only the spectral information of VHR imagery. Additional information, therefore, is required for separating such land covers by the classifier. One source of additional information is the vector data, which are available in archives for many urban areas. Further, the object-based approach provides a more effective way to incorporate vector data into the classification process as the misregistration between different layers is less problematic in object-based compared to pixel-based image analysis. In this research, a hierarchical rule-based object-based classification framework was developed based on a small subset of QuickBird (QB) imagery coupled with a layer of height points called Spot Height (SH) to classify a complex urban environment. In the rule-set, different spectral, morphological, contextual, class-related, and thematic layer features were employed. To assess the general applicability of the rule-set, the same classification framework and a similar one using slightly different thresholds applied to larger subsets of QB and IKONOS (IK), respectively. Results show an overall accuracy of 92% and 86% and a Kappa coefficient of 0.88 and 0.80 for the QB and IK Test image, respectively. The average producers' accuracies for impervious land cover types were also 82% and 74.5% for QB and IK.
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