Trimethylsilanolate-Promoted Activation of Alkynyl Trimethylsilanes: Hiyama-Type Sonogashira Cross-Coupling for the Synthesis of Arylene–Ethynylene-Linked Porphyrin Arrays

Abstract

To synthesize meso-ethynylene-conjugated porphyrin arrays, the Sonogashira cross-coupling reaction is straightforward to construct the C­(sp)–C­(sp2) bonds, but the reaction is often accompanied by side reactions such as the Glaser homocoupling. The rate-determining oxidative addition step results in the unexpected kinetic competition with the Glaser homocoupling, which is desired to be circumvented. We here propose two sets of improved strategies for the synthesis of arylene–ethynylene-linked porphyrin arrays from the meso-brominated porphyrin and alkynes. First, we explored the solvent-modulated approach employing dichloromethane as the reaction solvent to minimize the formation of the copper acetylide dimer as the intermediate for the Glaser homocoupling, while the scope of the approach is limited. Subsequently, we have developed the trimethylsilanolate-promoted Hiyama-type approach that activates alkynyl trimethylsilanes (TMSs) by use of potassium trimethylsilanolate under amine-free conditions. The latter approach is advantageous not only in skipping the preprotodesilylation of the TMS group but also in achieving an excellent isolated yield.

Metallic Lustrous Porphyrin Foil with an Exceptional Refractive Index

“…The Sonogashira cross-coupling reaction of meso-brominated porphyrin is often accompanied by the undesired oxidative Glaser homocoupling of terminal alkynes because of the slow oxidative addition of palladium to the meso-brominated porphyrin. 37 However, the sufficiently long polymer backbone of 1, comparable to the reported analogous polymer (M n = 2.45 × 10 4 ), 38 indicates only negligible consumption of 1,4-diethynylbenzene by the Glaser oxidative homocoupling in the stoichiometric reaction. This is consistent with no substantial signals of the butadiyne unit in the solid-state CP-MAS 13 C NMR spectrum (Figure S3C).…”

“…The Sonogashira polycondensation of 1 smoothly proceeded, and the molecular weight of the resultant polymer 1 reached M n = 4.5 × 10 4 (Figure S2). The Sonogashira cross-coupling reaction of meso -brominated porphyrin is often accompanied by the undesired oxidative Glaser homocoupling of terminal alkynes because of the slow oxidative addition of palladium to the meso -brominated porphyrin . However, the sufficiently long polymer backbone of 1 , comparable to the reported analogous polymer ( M n = 2.45 × 10 4 ), indicates only negligible consumption of 1,4-diethynylbenzene by the Glaser oxidative homocoupling in the stoichiometric reaction.…”

Synthesis and living crystallization-driven self-assembly of backbone asymmetric and symmetric π-conjugated oligo(p-phenylene ethynylene)-based block copolymers

“…Glaser coupling reactions of alkyne chain ends usually occur during a Sonogashira coupling reaction, giving an OPE with a diyne unit. 44,45 By taking advantage of this characteristic of Sonogashira coupling reaction, we synthesized S-OPE 7 -alkyne, D-OPE 7 -alkyne, S-OPE 8 -alkyne and D-OPE 8 -alkyne with an alkyne chain end (Scheme S1 †).…”