Formation of Zn–Zn and Zn–Pd Bonded Complexes by Reactions of Terminal Zinc Hydrides with Pd(II) Species

Abstract

Divalent palladium-induced homocoupling of terminal zinc hydrides to zinc−zinc bonded complexes was achieved herein. Reactions of zinc hydrides [LZnH] (L = CH 3 C(2,6-i Pr 2 C 6 H 3 N)CHC(CH 3 )(N(CH 2 ) n CH 2 PPh 2 ); 1a: n = 1; 1b: n = 2) with 0.5 equiv of allyl(cyclopentadienyl)palladium(II) afforded heterotrinuclear [Zn 2 Pd] complexes 3 containing direct Zn−Zn and Zn−Pd bonds, with concomitant elimination of propylene and cyclopentadiene. Complexes 3 were also accessed by the reactions of zinc hydrides 1 with allylpalladium(II) chloride with release of propylene and hydrogen chloride. Treatment of zinc hydrides 1 with 1 equiv of allyl(cyclopentadienyl)palladium(II) gave Zn−Pd bonded complex 5 by elimination of propylene, which can be transformed into heterotrinuclear complex 3 by further reaction with one additional molar equivalent of zinc hydrides. Heterobimetallic Zn−Pd complex 5b was found to be an effective catalyst in the hydrosilylation of benzaldehyde and its derivatives. Reaction of 5b with silane reagent Ph 2 SiH 2 produced [Pd 2 Si 2 H 2 ] complex 8 with cleavage of the Pd−Zn bond, which served as an initiating species in the catalytic reaction. Complexes 4b, 5, and 8 in this study were characterized by X-ray diffraction.

Zinc Complexes with an Ethylene-Bridged Bis(β-diketiminate) Ligand: Syntheses, Structures, and Applications as Catalysts in the Borylation of Aryl Iodides

“…The chemistry of zinc complexes has undergone a remarkable renaissance in the past decade. − The renewed interest toward these compounds has mainly arisen from their attractive reactivities − and potential applications in a broad range of reactions, including the hydroboration of alkynes, , the Strecker reaction, the Barbier reaction, the aminophenol oxidation reaction, the C–S cross-coupling reaction, the hydrosilylation of N-heterocycles, the copolymerization of epoxides and CO 2 , − and so forth. , Zinc is an inexpensive, biocompatible, less toxic and earth-abundant metal, which makes it particularly appealing to replace toxic and/or noble-metal complexes in catalytic transformations. Thus, the synthesis of zinc complexes with high catalytic activity is of great importance.…”

Nickel(0)-Induced β-H Elimination of Magnesium Alkyls: Formation and Reactivity of Heterometallic Hydrides

“…In our previous work, we designed and synthesized a new type of tridentate β-diketiminato ligand with a pendent phosphine group [CH 3 C­(2,6- i Pr 2 C 6 H 3 N)­CHC­(CH 3 )­(NCH 2 CH 2 PPh 2 )], which could stabilize a series of highly reactive rare-earth metal complexes . Remarkably, treatment of NNP ligand-based zinc hydrides with a palladium-based TM complex resulted in dehydrocoupling to afford a η 2 -dizinc-bonded complex of palladium . We proposed that such a tridentate NNP ligand plays a critical role in the formation of the metal–metal bonded complex.…”

Synthesis and reactivity of heterometallic complexes containing Mg- or Zn-metalloligands

“…Subsequently, we found that a palladium( ii ) reagent, allyl(cyclopentadienyl)-palladium, also enabled the formation of the [Zn 2 Pd] complex 39b from zinc hydride 38b (Scheme 12). 36 Mechanistic studies revealed that the Zn–Pd bonded complex 41 was initially generated by the elimination of propylene, which could be transformed into 39b by further reaction with one molar equivalent of zinc hydride with the release of cyclopentadiene.…”

“…On the other hand, cooperative activation of Lewis acidic metalloligands and transition metals was also mentioned. 27,30,36,37 To date, the stoichiometric reactions of heterometallic complexes with a variety of small molecules have been extensively studied and they exhibit versatile reactivities. In contrast, catalytic reactions based on Mg/Zn-based heterometallic complexes are far less developed.…”

“…In the same year, our group showed that the heterobimetallic Zn–Pd complex 41 was an effective catalyst for the hydrosilylation of benzaldehyde and its derivatives (Scheme 30). 36 In contrast, the catalytic reactivity dropped significantly when using the palladium precursor, (η 3 -C 3 H 5 )Pd(η 5 -Cp), as a catalyst under the same conditions, thus demonstrating the importance of the Zn-metalloligand for efficient catalysis. To gain more insights into the bimetallic Zn–Pd catalysis, a stoichiometric reaction between 41 and the silane reagent Ph 2 SiH 2 was conducted and complex 85 was obtained with the cleavage of the Pd–Zn bond, which served as an initiating species in the catalytic reaction.…”