Trivalent boron nucleophile as a new tool in organic synthesis: reactivity and asymmetric induction

Abstract

Boron compounds have been traditionally regarded as "Lewis acids" preferring to accept electrons rather than donate them in the course of their reactions but current examples of unusual reactivity between tricoordinated boranes and electrophilic sites suggest a new conceptual context for the boryl moieties, based on their nucleophilic character which can be enhanced depending on the substituents on boron.

Synthesis of a Tri(gold)boride Complex (Cy3P)B[AuP(o-Tol)3]3

“…Owing to the strongly reduced hydridic character of hydrogen atoms in phosphine boranes [20], the -BH 2 -group in Cy 3 PBH 2 SiMe 3 could finally allow complete auration. The favorable 3 : 3 stoichiometric relation of suitable functions in Cy 3 PBH 2 SiMe 3 on the one hand, and in reagents of the type [(LAu) 3 O] + on the other hand, appeared to offer the right conditions for the envisaged metathesis. It should be noted that similar effects have now been demonstrated for carbene-boranes [1].…”

“…FAB-MS (from 4-nitrobenzyl alcohol) gave the molecular ion [M] + at m/z = 1796.0 (12.5 % relative intensity), followed by the fragments m/z = 1491.6 (9.1), 1295. 3 ], and a single broad resonance at δ (B) = − 20.5 ppm, respectively. These spectra confirm the presence of the two sorts of PR 3 units, the equivalence of the three [P(o-Tol) 3 ] ligands, and the absence of BF 4 − anions.…”

“…3 ], and a single broad resonance at δ (B) = − 20.5 ppm, respectively. These spectra confirm the presence of the two sorts of PR 3 units, the equivalence of the three [P(o-Tol) 3 ] ligands, and the absence of BF 4 − anions. Some complementary analytical and spectroscopic data for 3b, c are given in the Experimental Section (for 3a, see ref.…”

“…Owing to the C 3v symmetry, the dihedral angle H-P-B-Au of 60.0 • indicates a perfectly staggered conformation, and the dihedral angle H-P-(Au)-B-P shows that there is no distortion away from an eclipsed conformation of the units under consideration. 3 PAu] + , the relation to simple phosphine-boranes R 3 PBH 3 is also obvious [9].…”

“…

A tri(gold)boride of the formula B [AuP(o-Tol) 3 ] 3 (2) is generated in the reaction of the silylated phosphine borane Cy 3 PBH 2 SiMe 3 with the tri(gold)oxonium tetrafluoroborate [(o-Tol)

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