β-Alkyl Elimination: Fundamental Principles and Some Applications

Abstract

This review describes organometallic compounds and materials that are capable of mediating a rarely encountered but fundamentally important reaction: β-alkyl elimination at the metal-Cα-Cβ-R moiety, in which an alkyl group attached to the Cβ atom is transferred to the metal or to a coordinated substrate. The objectives of this review are to provide a cohesive fundamental understanding of β-alkyl-elimination reactions and to highlight its applications in olefin polymerization, alkane hydrogenolysis, depolymerization of branched polymers, ring-opening polymerization of cycloalkanes, and other useful organic reactions. To provide a coherent understanding of the β-alkyl elimination reaction, special attention is given to conditions and strategies used to facilitate β-alkyl-elimination/transfer events in metal-catalyzed olefin polymerization, which provide the well-studied examples.

Ligand-promoted cobalt-catalyzed radical hydroamination of alkenes

“…The reaction of vinyl cyclopropane 28 afforded the ring-opening product 29 in 62% yield (Fig. 4b) via cleavage of the more substituted carbon-carbon bond 50 , which supported the radical promoted ring-opening pathway 51 . A deuterium-labeled experimental reaction of indene using PhSiD 3 was conducted to afford 30 in 89% yield with 94% D and 1/1 dr (Fig.…”

NNNO‐Heteroscorpionate nickel (II) and cobalt (II) complexes for ethylene oligomerization: the unprecedented formation of odd carbon number olefins

“…2). β-alkyl elimination, [65] as an alternative mechanism of chain termination. Cleavage of β-CH 3 gives products that differ by only one carbon atom, considering the case of ethylene oligomerization.…”

Silyl‐functionalized polyolefins via co‐polymerization of vinylsilanes with ethylene or propylene catalyzed by group IV metallocene complexes

“…With Cp′ 2 Zr ( I ), the polymer/oligomer produced has a similar random backbone as with Cp 2 Zr ( II ), but different unsaturated end groups: vinyl termination (85%) and vinylidene terminations (15%), formed via β‐Me elimination and β‐H elimination processes, respectively [Fig. (A)] . The resonances observed at 22.2–22.7, 23.2–24.0, and 25.6 ppm in the 13 C‐NMR spectrum suggest that an iso‐propyl group is the predominant saturated end group and only a small percentage of n ‐propyl end group (14.5 ppm) are present in the polymer.…”

“…4(A)]. 40 The resonances observed at 22.2-22.7, 23.2-24.0, and 25.6 ppm in the 13 C-NMR spectrum suggest that an iso-propyl group is the predominant saturated end group and only a small It is most likely formed by 1,2 insertion of 1 into MAMe (eq 18) rather than 2,1 insertion of 1 into the MAH bond, although the latter possibility cannot be ruled out (eq 19).…”