Calcium-mediated hydroboration of alkenes: "trojan horse" or "true" catalysis?
Harder S, Spielmann J (2012)
Publication Type: Journal article, Original article
Publication year: 2012
Journal
Original Authors: Harder S., Spielmann J.
Publisher: Elsevier
Book Volume: 698
Pages Range: 7-14
DOI: 10.1016/j.jorganchem.2011.09.025
Abstract
The hydroboration of 1,1-diphenylethylene (DPE) with catecholborane (HBcat) proceeds at 100 °C. For conversion at room temperature three different organocalcium catalysts have been investigated: the calcium hydride complex [DIPPnacnacCaH·(THF)] (1, DIPPnacnac = CH{(CMe)(2,6-iPr C H N)} ), Ca[2-Me N-α-Me Si-benzyl) ·(THF) (2) and DIPPnacnacCa(H-BBN)·(THF) (3, BBN = 9-borabicyclo[3.3.1.]nonane). Although up to 96% conversion of DPE is found, the product of the reaction is not the expected Ph CHCH Bcat but (Ph CHCH ) B is formed instead. Organocalcium compounds catalyze the decomposition of HBcat to B (cat) and BH (or B H ) and the latter is involved in hydroboration of DPE. The calcium-catalyzed decomposition of HBcat was investigated with B NMR and the signals were assigned to the following species: B (cat) , B(cat) , HBcat, BH (THF), BH and B H . A tentative mechanism for the formation of these species was proposed. The intermediate DIPPnacnacCa(BH )·(THF) (5) was independently prepared by reaction of 1 and BH (Me S) and was structurally characterized by X-ray diffraction. Stoichiometric reaction of 1 with pinacolborane (HBpin) gave a trimeric complex [DIPPnacnacCa(H Bpin)] (6) which was structurally characterized by X-ray diffraction. This complex does not react with DPE, also not at elevated temperatures. The possible equilibrium between 6 and 1/HBpin is therefore fully at the side of 6. As 6 is unstable in the presence of HBpin, no further catalytic conversions have been investigated. © 2011 Elsevier B.V. All rights reserved.
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APA:
Harder, S., & Spielmann, J. (2012). Calcium-mediated hydroboration of alkenes: "trojan horse" or "true" catalysis? Journal of Organometallic Chemistry, 698, 7-14. https://doi.org/10.1016/j.jorganchem.2011.09.025
MLA:
Harder, Sjoerd, and Jan Spielmann. "Calcium-mediated hydroboration of alkenes: "trojan horse" or "true" catalysis?" Journal of Organometallic Chemistry 698 (2012): 7-14.
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