page_title: Heterobimetallic catalysis
section_title: With preformed heterobimetallic catalysts
hierarchical_section_title: Heterobimetallic catalysis / With preformed heterobimetallic catalysts
caption_attribution_description: English: IPrCuFp borylation system developed by Mankad
context_page_description: Heterobimetallic catalysis is an approach to catalysis that employs two different metals to promote a chemical reaction. Included in this definition are cases where: 1 each metal activates a different substrate, 2 both metals interact with the same substrate, and 3 only one metal directly interacts with the substrate, while the second metal interacts with the first.
context_section_description: Catalyst systems in which both metal centers are contained in the same complex are also known (e.g. Shibasaki catalysts); further examples are provided below.
  Ion-paired combinations of early and late transition metal complexes can simultaneously interact with a substrate as both Lewis acid and Lewis base. For example, carbonylative ring expansion of epoxides (Scheme 4) is accomplished by Lewis acid activation by cationic complexes of Crᴵᴵᴵ, Tiᴵᴵᴵ or Alᴵᴵᴵ with simultaneous ring opening by the [Co(CO)₄]⁻ counterion. Carbonylation of the resultant alkylcobalt followed by lactonization releases the product.
  A heterobimetallic bond-breaking process is also employed in the IPrCuFp-catalyzed C-H borylation system developed by Mankad (Scheme 5).  Bimetallic cleavage of the B-H bond in pinacolborane generates a copper hydride (IPrCu-H) and an iron boryl [(pin)B-Fp], the latter of which borylates unactivated arenes upon UV irradiation. Bimetallic reductive elimination of H₂ from the combination of H-Fp and IPrCu-H restarts the catalytic cycle. The incorporation of copper into the catalyst is essential; C-H borylation using (pin)B-Fp alone is stoichiometric in iron due to dimerization of the HFp byproduct.
  Heterobimetallic catalysts containing persistent M¹-M² bonds exhibit altered reactivity due to interaction of the two different metal centers. For example, allylic amination catalyzed by the binuclear complex [Cl₂Ti(NᵗBuPPh₂)₂-/Pd(η³-CH₂C(CH₃)CH₂)]⁺ is exceptionally rapid. DFT studies suggest that a Pd→Ti dative interaction accelerates the typically slow reductive elimination step by withdrawing electron density from Pd in the transition state (Scheme 6).
caption: Scheme 5: UV-promoted C-H borylation of arenes catalyzed by IPrCuFp