Synthesis and Reactivity of N-Heterocyclic PSiP Pincer Iron and Cobalt Complexes and Catalytic Application of Cobalt Hydride in Kumada Coupling Reactions

Abstract

The new N-heterocyclic σ-silyl pincer ligand HSiMe­(NCH2PPh2)2C6H4 (1) was designed. A series of tridentate silyl pincer Fe and Co complexes were prepared. Most of them were formed by chelate-assisted Si–H activation. The typical iron hydrido complex FeH­(PMe3)2(SiMe­(NCH2PPh2)2C6H4) (2) was obtained by Si–H activation of compound 1 with Fe­(PMe3)4. The combination of compound 1 with CoMe­(PMe3)4 afforded the Co­(I) complex Co­(PMe3)2(SiMe­(NCH2PPh2)2C6H4) (3). The Co­(III) complex CoHCl­(PMe3)­(SiMe­(NCH2PPh2)2C6H4) (5) was generated by the reaction of complex 1 with CoCl­(PMe3)3 or the combination of complex 3 with HCl. However, when complex 3 was treated with MeI, the Co­(II) complex CoI­(PMe3)­(SiMe­(NCH2PPh2)2C6H4) (4), rather than the Co­(III) complex, was isolated. The catalytic performance of complex 5 for Kumada coupling reactions was explored. With a catalyst loading of 5 mol %, complex 5 displayed efficient catalytic activity for Kumada cross-coupling reactions of aryl chlorides and aryl bromides with Grignard reagents. This catalytic reaction mechanism is proposed and partially experimentally verified.

Three‐Component Domino Knoevenagel/Vinylogous Michael Reaction: Entry to Challenging o‐Terphenyls

“…Intramolecular cyclization and subsequent aromatization of α,α‐dicyanoolefin‐comprising motifs towards polysubstituted m ‐terphenyls in the presence of a base was reported by Xue, Deng, and co‐authors . Instead, for synthesis of sterically more demanding o ‐terphenyls, classical synthetic approaches, for example, Kumada coupling or Suzuki coupling, are commonly employed. Substituted o ‐terphenyls are important intermediate compounds for the synthesis of polyaromatic hydrocarbons (PAHs) for the fabrication of organic light‐emitting diodes (OLEDs), and are subunits of synthetic anti‐inflammatory and anticoagulant pharmaceuticals .…”

“…Instead, for synthesis of sterically more demanding o ‐terphenyls, classical synthetic approaches, for example, Kumada coupling or Suzuki coupling, are commonly employed. Substituted o ‐terphenyls are important intermediate compounds for the synthesis of polyaromatic hydrocarbons (PAHs) for the fabrication of organic light‐emitting diodes (OLEDs), and are subunits of synthetic anti‐inflammatory and anticoagulant pharmaceuticals . Therefore, the development of new convenient and sustainable synthetic methods towards o ‐terphenyls is highly desirable.…”

Synthesis of a Silyl Cobalt Hydride and Its Catalytic Performance in Kumada Coupling Reactions

“…Our results indicate that the synthesiso f5 as ac helate complex is easier than that of our [PSiP]-pincer cobalt hydride. [11] With similarc atalytic efficiency for Kumada reactions, the catalytic loading (2 %) of 5 is lower than that (5 %) of [PSiP]-pincer cobalt hydride.…”

“…We reported that a[ PSiP]-pincer silyl hydrido cobalt chloride could catalyze Kumadacoupling reactions. [11] Complex 5 is ahydrido silyl [P,Si]-chelate Co III chloride with aC o ÀHa nd aC o ÀCl bond.T his structure was assumedt ob eu nstable under certain conditions, andc ould be ap otential catalyst. Encouraged by these results, as eries of Kumada coupling reactionsc atalyzed by complex 5 were studied.…”

“…The hydrido cobalt(III) complex [PSiP]Co(H)(Cl)(PMe 3 )w as found to be an excellent catalyst for Kumada couplingr eactions under mild conditions. [11] Although the syntheses of the silyl bidentate transitionmetal complexes are easier than those of tridentatecomplexes, reports on the former are very few. [12][13][14][15][16] Because silyl bidentate ligandsc an form only one chelate ring, their transition-metal complexes are less stable, but more reactive.…”