Lewis acid promoted activation of inert chemical bonds is central to catalysis. The presence of a highly electrophilic central atom having minimum interactions with anions and solvent molecules is a requisite for a reactive Lewis acid. This requirement for a strong Lewis acid is met with by designing a reactive cation of a heavy element, bismuth, bearing the tridentate trispyrazolylborate ligand. The coordination sphere of the electrophilic bismuth dication is stabilized by very weak interactions with the halogen atoms of the weakly nucleophilic tetrakis(pentafluorophenyl)borate anion, chlorobenzene, and ortho‐dichlorobenzene in the solid state. The high electrophilicity at bismuth is demonstrated by the ability of the dication to efficiently catalyze the addition of Si–H to olefins.
Bismuth compounds are gaining importancea s potential alternatives to transition-metal complexes and electrond eficient lighter p-block compounds in homogeneous catalysis. Computationalanalysiso nt he two-coordinate [(Me 2 NC 6 H 4)Bi] 2 + possessing three electrophilics ites is experimentally evidencedb yt he isolation of [{Me 2 NC 6 H 4 }Bi{OP(NMe 2) 3 } 3 ][B(3,5-C 6 H 3 Cl 2) 4 ] 2 .T hese observationsl ed us to generate dicationic organobismuth catalyst, [(Me 2 NC 6 H 4)Bi(L) 3 ] 2 + (L = aldehyde/ketone), evidenced by NMR spectroscopy in solution and by single-crystal Xray diffraction in the solids tate. It efficiently catalyzes hydrosilylation of aldehydes and ketones resulting in silyl ethers as the only products in high yields. Our investigations support ac arbonyl activation mechanism at the bismuth center followed by SiÀHa ddition. Scheme1.Synthetic route for the preparation of 1-3 and generation of the active catalyst in CH 2 Cl 2 .
Investigations on the boundaries between the neutral and cationic models of (Mesityl)2EX (E = Sb, Bi and X = Cl―, OTf―) have facilitated reversing the Lewis acidity from bismuth to...
Invited for the cover of this issue is Ajay Venugopal from the Indian Institute of Science Education and Research Thiruvananthapuram. The cover image shows dication [TpMe2Bi]2+ catalyzing olefin hydrosilylation under mild conditions.
Compounds of heavy main group elements possessing polarized primary bonds exhibit trans‐influence. The extent of secondary interactions at the electrophilic sites trans to the primary bonds provides an understanding on the Lewis acidity exhibited by the main group element center, thus forming the basis for designing Lewis acid catalysts. Hydridotris(3,5‐dimethylpyrazolyl)borate(TpMe2), a C3v symmetric tridentate σ‐donor ligand, offers an opportunity to explore trans‐influence in Bi(III) compounds in the presence of donor ligands with varying nucleophilicity. We have examined a series of TpMe2Bi species by accessing five new moieties [TpMe2BiCl3]–, (TpMe2)2Bi+, TpMe2BiCl(OTf), TpMe2Bi(OTf)2 and [TpMe2Bi(solvent)3]2+ in addition to the recently reported TpMe2BiCl2, TpMe2Bi2+, [TpMe2Bi]2[Bi3Cl13] and K[TpMe2Bi(OTf)3]. Analysis of structures by X‐ray crystallographic studies and computational analysis on TpMe2Bi species establish the variation of trans‐influence and demonstrate a continuum in bonding of TpMe2 to bismuth correlating with the degree of nucleophilicity of the trans‐ligands.
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