A rigid anilido bipyridyl ligand has been designed for use in an organoscandium-based carbon dioxide hydrosilation catalyst. Ligand attachment by alkane elimination results in metalation of an aryl C-H bond in a 3,5-di-tert-butylphenyl group installed on the pyridyl unit, thus rendering the ligand tetradentate. Insertion of CO2 into the newly formed Sc-C bond leads to a κ(1) carboxylate which, when treated with the borane B(C6F5)3, becomes hemilabile. In addition to activating the catalyst, the k(1) carboxylate effectively sequesters free B(C6F5)3 and the ensemble is able to effectively hydrosilate CO2, in the presence of excess Et3SiH, almost exclusively to R3SiOCH2OSiR3. A maximum turnover number of about 3400 (conversion of silane) is observed. Mechanistic experiments suggest that the sequestration of free B(C6F5)3 by the hemilabile carboxylate contributes to the selectivity observed and prevents over reduction to methane.

The reaction of D m (D = Me 2 SiO, m = 3-6) with silver hexafluoroantimonate in liquid SO 2 affords a mixture of AgD n SbF 6 (n = 6-8) complexes. Upon the addition of CH 3 CN, Ag + -directed ring transformations are effected, which allows for the isolation of neat D n (n = 6-8). The AgD n + cations are rare examples of Lewis acid donor complexes of siliconWe recently reported the preparation of Li + -cyclodimethylsiloxane host-guest cations directly from their components [1] and provided rare examples of silicon ethers behaving as Lewis bases as shown in Equation (1 ) with large anions, no other examples of a metal-cation-siloxane adduct have been reported. Metal-cation-siloxane salt formation is favored by large anions, which minimizes the unfavorable lattice-energy changes. Therefore, the question as to whether the formation of the complexes could be extended to the use of commercially available salts with smaller anions as the starting materials remains. The Ag + cation is regarded as a soft Lewis acid [3] and has a low affinity to oxygen donor ligands.[4] Nevertheless, we report below the first examples of the transition-metal-cation-siloxane SbF 6 -salts of AgD n + (n = 6-8) formed by the reactions of D m (m = 3-6) with AgSbF 6 in liquid SO 2 . Unlike the Li[Al] case, transformation of the siloxane rings occur with Ag + acting as a template for the formation of the most thermodynamically stable metal-cation-cyclodimethylsiloxane complex. The formation of macrocyclic ethers by the reaction of AgAsF 6 with (CH 2 O) 3 or ethylene oxide was described by Roesky and his coworkers.[5] However, no similar ring transformation reactions of cyclodimethylsiloxanes under mild conditions have been previously reported.[6] Ring-opening polymerization of D m (m = 3-6) has been widely investigated, and these results are also of interest in this context. [a]

The reactions of two highly air- and moisture-sensitive scandium bis­(alkyls) supported by a bulky β-diketiminato (nacnac) ligand with carbon dioxide are described. [κ2-ArNC­( t Bu)­CHC­( t Bu)­NAr]­ScR2 (Ar = 2,6- i Pr2C6H3; R = CH3, 1a; R = CH2SiMe3, 1b) react rapidly with CO2 to give mixtures of mono- and bis­(carboxylato) insertion products 2a/2b and 3a/3b depending on the stoichiometry and conditions of the reaction. Compound 2a (R = CH3) is a dimeric complex with bridging acetato groups, as determined by X-ray crystallography. These compounds were characterized by NMR spectroscopy, and 3a could be isolated in pure form. Treatment of these compounds with excess CO2 resulted in addition to the central carbon of the Sc­(nacnac) six-membered ring and displacement of the nitrogen donors to yield dimeric scandium carboxylates 4a/4b; compound 4b was characterized by X-ray crystallography. Reactions of the nacnac scandium cations formed upon abstraction of one or two methides from 1a using B­(C6F5)3 with CO2 were also explored. Although the products were qualitatively more thermally robust, eventually ligand displacement occurred in these cationic acetato complexes as well. Nevertheless, insertion products were characterizable in solution using NMR spectroscopy. Overall, this study shows the facility with which CO2 is taken up by scandium alkyls but that the nacnac ligand framework is too reactive to support chemistry aimed at catalytic conversion of CO2 into other products.

A rigid anilido bipyridyl ligand has been designed for use in an organoscandium-based carbon dioxide hydrosilation catalyst. Ligand attachment by alkane elimination results in metalation of an aryl CÀH bond in a 3,5-di-tertbutylphenyl group installed on the pyridyl unit, thus rendering the ligand tetradentate. Insertion of CO 2 into the newly formed Sc À C bond leads to a k 1 carboxylate which, when treated with the borane B(C 6 F 5 ) 3 , becomes hemilabile. In addition to activating the catalyst, the k 1 carboxylate effectively sequesters free B(C 6 F 5 ) 3 and the ensemble is able to effectively hydrosilate CO 2 , in the presence of excess Et 3 SiH, almost exclusively to R 3 SiOCH 2 OSiR 3 . A maximum turnover number of about 3400 (conversion of silane) is observed. Mechanistic experiments suggest that the sequestration of free B(C 6 F 5 ) 3 by the hemilabile carboxylate contributes to the selectivity observed and prevents over reduction to methane.Carbon dioxide (CO 2 ) is a cheap, readily available source of

A convenient method for the preparation of strongly Lewis acidic tris-perfluoro-tert-butoxyborane B(OR) (1), (OR = OC(CF)) was developed, and its X-ray structure was determined. 1 was used as a precursor, guided by density functional theory (DFT) calculations and volume-based thermodynamics, for the synthesis of [NEt][NCB(OR)] (3) and [NMe][FB(OR)] (5) and the novel large and weakly coordinating anion salts [Li 15-Crown-5][B(OR)] (2) and [NEt][CN{B(OR)}] (4). The stability of [B(OR)] was compared with that of some related known weakly coordinating anions by appropriate DFT calculations.