Promoting the Hydrosilylation of Benzaldehyde by Using a Dicationic Antimony‐Based Lewis Acid: Evidence for the Double Electrophilic Activation of the Carbonyl Substrate

Abstract

The concomitant activation of carbonyl substrates by two Lewis acids has been investigated by using [1,2-(Ph2 MeSb)2 C6 H4 ](2+) ([1](2+) ), an antimony-based bidentate Lewis acid obtained by methylation of the corresponding distibine. Unlike the simple stibonium cation [Ph3 MeSb](+) , dication [1](2+) efficiently catalyzes the hydrosilylation of benzaldehyde under mild conditions. The catalytic activity of this dication is correlated to its ability to doubly activate the carbonyl functionality of the organic substrate. This view is supported by the isolation of [1-μ2 -DMF][OTf]2 , an adduct, in which the DMF oxygen atom bridges the two antimony centers.

Electrophilic Organobismuth Dication Catalyzes Carbonyl Hydrosilylation

“…The progress of PhCHO hydrosilylation was monitored by 1 H NMR spectroscopy and the reaction completed within an hour. PhCH 2 OSiEt 3 was observed as the only product with a yield of 98 % with respect to PhCHO (Scheme ) corresponding to a TOF of 49 h −1 , ten times more than the activity observed in [1,2‐(Ph 2 MeSb) 2 C 6 H 4 ][BF 4 ] 2 (TOF=4.2 h −1 ) . Using the same synthetic procedure, we successfully performed hydrosilylation of ortho ‐phthalaldehyde and terephthalaldehyde and observed the corresponding silyl ethers in high yields (Scheme ).…”

Antimony(v) cations for the selective catalytic transformation of aldehydes into symmetric ethers, α,β-unsaturated aldehydes, and 1,3,5-trioxanes

“…[4] + to catalyze the reductive coupling of aldehydes ( 7 Interestingly, when 5 mol% of [2] + was used as a catalyst, we did not observe the expected hydrosylilated species, benzyloxytriethylsilane (Ph-CH 2 -O-SiEt 3, 5, vide infra), but instead found that dibenzyl ether (L 8 ) along with the symmetric siloxane ((Et 3 Si) 2 O) were the only products (Scheme 2). We have extended this reactivity to include a wide substrate scope including aliphatic, aromatic, and haloaromatic aldehydes (Table 1).…”

Nitrenium Salts in Lewis Acid Catalysis

“…Traditional examples of main-group Lewis acid catalysts involve group 13 and 14 elements as the central locus of reactivity,a stheyf eature al ow-lying orbital for substrate activation. [1] Over the last decade there has been increasing interest in studying pnictogens,o ften considered Lewis basic given the availability of an energetically accessible lone pair, in this unconventional role.T his work has been expanded to include compounds of phosphorus, [2][3][4][5][6][7][8][9][10][11] arsenic, [12] antimony, [13][14][15][16][17][18][19][20] and bismuth. [21][22][23] By contrast, the reactivity of nitrogen-containing compounds as Lewis acids has been investigated to am uch lesser extent, largely due to the dearth of such species.C hloramines,n itrenes,d iazocarboxylates,azides,and diazonium salts have been shown to possess N-centered electrophilic behavior.…”