Issue 6, 2020

Reactions of carbene-stabilized borenium cations

Abstract

In this paper we probe the reactivity of the borenium cations [C3H2(NCH2C6H4)(NCH2Ph)BH][B(C6F5)4] 2 and [C3H2(NCH2C6H4)2B][B(C6F5)4] 3. The reactions of 2 with cyclohexene or 3,3-dimethyl-1-butene gave the alkyl-aryl borenium salts [PhCH2(CHN)2CCH2C6H4BR][B(C6F5)4] (R = Cy 4, CH2CH2tBu 5) while the corresponding reactions with diphenylacetylene, 1-hexyne and 1-phenyl-1-propyne gave the aryl–alkenyl borenium cation salts [PhCH2(CHN)2CCH2C6H4BC(R1)C(H)R2][B(C6F5)4] (R1 = R2 = Ph 6, R1 = H, R2 = C4H97, R1 = Me, R2 = Ph 8a, R1 = Ph, R2 = Me 8b). In contrast, the reaction of 2 with ethynyldiphenylphosphane or 2-vinylpyridine lead to the formation of the adducts, [PhCH2(CHN)2CCH2C6H4B(H)P(Ph2)CCH][B(C6F5)4] 9, [PhCH2(CHN)2CCH2C6H4B(H)NC5H4C(H)CH2][B(C6F5)4] 10, respectively, while the more bulky donor H2C[double bond, length as m-dash]C(Ph)PMes2 gave 1,2-hydroboration of the phosphinoalkene affording [PhCH2(CHN)2CCH2C6H4BCH2CH(Ph)PMes2][B(C6F5)4] 11. In another vein of reactivity, one or two equivalents of the FLP, PtBu3/B(C6F5)3 is shown to react with 3 to give the zwitterionic borenium-borate species [C2H2(NCH(BC(CHNCH2C6H4)2)C6H4)(NCH(B(C6F5)3)C6H4)CB] 12 and the anionic bis-borate species[tBu3PH][C2H2(NCH(B(C6F5)3)2C6H4)2CB] 13. The implications of these findings are discussed.

Graphical abstract: Reactions of carbene-stabilized borenium cations

Supplementary files

Article information

Article type
Paper
Submitted
12 Dec 2019
Accepted
13 Jan 2020
First published
14 Jan 2020

Dalton Trans., 2020,49, 1839-1846

Reactions of carbene-stabilized borenium cations

J. Lam, L. L. Cao, J. M. Farrell and Douglas. W. Stephan, Dalton Trans., 2020, 49, 1839 DOI: 10.1039/C9DT04731J

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