Bismuth Meets Olefins: Ethylene Activation and Reversible Alkene Insertion into Bi─N Bonds

Abstract

Owing to its fundamental properties as the parent olefin, its outstanding industrial relevance, and the challenges associated with its activation, ethylene remains a benchmark substrate, especially in main group chemistry. Here we report the unprecedented activation of ethylene and related simple α-olefins by well-defined cationic bismuth complexes. The polarization of a substrate by a softly Lewis-acidic central atom and a nucleophilic functional group positioned in a constrained geometry is for the first time exploited in the activation of ethylene and related olefins by compounds of a heavy p-block element. Mechanistic investigations point toward a coordination-insertion-reaction mechanism. The bonding properties of the cationic bismuth species facilitate unprecedented reversible reactivity patterns and unusual characteristics in chemoselectivity.

Keywords: Bismuth; Cationic species; Ethylene activation; Reversibility; Small molecule activation.

Scheme 1

a) Reactions of 1‐R ethylene and simple α‐olefins to give insertion products 2‐R (n = 20 bar for R’ = H; n = ca. 100 equiv for the remaining cases). b) Side reaction of 1‐Ph to give compound A.^{[ 63 ].}

Figure 1

Molecular structure of compound a) 2‐Ph and b) 3‐iPr in the solid state. Displacement ellipsoids are shown at the 50% probability level, C atoms of pyridine ligands are shown as a wireframe. For 2‐Ph, a lattice‐bound C₆H₄F₂ molecule and for 2‐Ph and 3‐iPr, hydrogen atoms (except for those in C₂H₄) are omitted for clarity. Selected bond lengths [Å] for 2‐Ph: Bi1─C1 2.246(5), Bi1─C10 2.245(4), Bi1─N2 2.498(3), Bi1─N3 2.543(3), C1─C2 1.520(7), C2─N1 1.458(6). Selected bond angles for 2‐Ph (°): C1─Bi1─C10 91.58(2), N2─Bi1─N3 171.05(1). Selected bond lengths [Å] for 3‐iPr: Bi1─C1 2.247(2), Bi1─C10 2.228(2), Bi1─N2 2.576(2), Bi1─N3 2.491(2), C1─C2 1.526(3), C2─N1 1.484(3). Selected bond angles for 3‐iPr (°): C1─Bi1─C10 90.99(8), N2─Bi1─N3 172.07(7).

Figure 2

a) Calculated mechanism for the olefin insertion reaction with 1‐Ph. ∆G values are shown in italics blue font and ∆ H values are shown in black regular font, calculated with respect to reactant 1‐Ph‐py. The energies in the figure corresponds to R = H. For other olefins, see Table S5. Computed at ZORA‐BLYP‐D3(BJ)/TZP in pyridine. Diagram not in scale. b) VDD charges in TS‐1. c) Frontier orbitals of TS‐1 at an isovalue of 0.03.

Scheme 2

a) The isolated olefin insertion products 2‐Ph–6‐Ph eliminate the hydrocarbons CH₂═CHR’, showcasing reversible olefin insertion into Bi─N bonds. b) Olefin exchange reactions between 6‐Ph (R’ = Ph) and CH₂═CHR’ to give 3‐Ph–5‐Ph (R’ = nBu, nPr, C₄H₇).

Scheme 3

Competition reactions of 1‐Ph with 1‐hexene versus a range of carbonyl compounds. a) the formation of A with 24% spectroscopic yield was observed.