H2 and carbon-heteroatom bond activation mediated by polarized heterobimetallic complexes

Abstract

The field of heterobimetallic chemistry has rapidly expanded over the last decade. In addition to their interesting structural features, heterobimetallic structures have been found to facilitate a range of stoichiometric bond activations and catalytic processes. The accompanying review summarizes advances in this area since January of 2010. The review encompasses well-characterized heterobimetallic complexes, with a particular focus on mechanistic details surrounding their reactivity applications.

Keywords: Bond activation; Catalysis; Heterobimetallic; Metalloligand.

Fig. 1.

Two general methods of bimetallic bond activation.

Fig. 2.

Computationally supported proposed catalytic cycle for alkene hydrogenation by 1 with plausible short circuit loop shown in blue.

Fig. 3.

Activation of H₂ by 2a-b.

Fig. 4.

Hydrogenation of styrene by 2b.

Fig. 5.

Ru-Ag heterobimetallic complex.

Fig. 6.

Synthesis of Pt-Al heterobimetallic complex 4.

Fig. 7.

Activation of H₂ by 4.

Fig. 8.

General hydrogen activation and hydrogenolysis reaction.

Fig. 9.

Considered mechanisms for reaction of Ir-Al and Rh-Al heterobimetallics with H₂.

Fig. 10.

General H₂ activation and H/D exchange reaction.

Fig. 11.

Ni-Group 13 olefin hydrogenation catalysts.

Fig. 12.

Heterobimetallic Ni-Lu catalysts 8, 9, 10.

Fig. 13.

Synthetic routes for preparation of heterobimetallics 11–13.

Fig. 14.

Proposed catalytic cycles for (E)-selective semihydrogenation of DPA catalyzed by 11 (A) and 12–13 (B).

Fig. 15.

Reaction of terminal alkynes with 14.

Fig. 16.

Reaction of trimethylsilylacetylene with 15.

Fig. 17.

H/D exchange of fluorobenzene catalyzed by 17.

Fig. 18.

Fe-Cu arene C–H borylation catalyst.

Fig. 19.

Proposed catalytic cycle for para-selective pyridine alkenylation.

Fig. 20.

Proposed catalytic cycle for C-4-selective alkylation of pyridine.

Fig. 21.

Plausible catalytic cycle for dehydrogenative [4 + 2] cycloaddition of formamides with alkynes.

Fig. 22.

Asymmetric hydrocarbamoylation reaction catalyzed by 18; note, 18 assembled from Ni and Al in solution.

Fig. 23.

Proposed catalytic cycle for asymmetric hydrocarbamoylation of alkenes catalyzed by 18.

Fig. 24.

Overall para-selective alkylation reaction mediated by Ni/Al catalysis.

Fig. 25.

Overall para-selective alkylation reaction mediated by Ni/Al catalysis.

Fig. 26.

Plausible mechanism for para-selective alkylation of sulfonylarenes.

Fig. 27.

General reaction for meta-selective C–H borylation of pyridines and benzamides.

Fig. 28.

General alkyne hydrocarbofunctionalization reaction.

Fig. 29.

Oxidative addition of CO₂ by Zr-Co heterobimetallic complex 19.

Fig. 30.

Functionalization of oxo bridging ligand.

Fig. 31.

Stoichiometric reactions of 14.

Fig. 32.

Proposed catalytic cycle for hydrosilylation of ketones using heterobimetallic Zr/Co complex 14.

Fig. 33.

Generation of 23 and 24 via thermolysis of 22.

Fig. 34.

Reaction of 23 with phenylsilane.

Fig. 35.

Synthesis of heterobimetallic complexes 25–29 from 14.

Fig. 36.

Ti-Co heterobimetallic 30.

Fig. 37.

Reaction of 30 with benzophenone.

Fig. 38.

Proposed reaction pathway of McMurry reaction mediated by 30.

Fig. 39.

Heterobimetallic Cu-M catalysts. L = IPr or IMes, [M] = W, Mo, or Fe.

Fig. 40.

Proposed mechanism for Cu-M catalyzed hydroboration: (a) catalyst activation, followed by autotandem (b) CO₂ hydroboration, and (c) CO₂-assisted formate decarbonylation. E = B(pin) for the first turnover and then H throughout. L = IPr or IMes, [M] = Fp, Wp, or Mp, pin = pinacolate.

Fig. 41.

Reaction of 33 with ArNCO.

Fig. 42.

Possible mechanism for reaction of 33 with ArNCO.

Fig. 43.

Catalytically active species for 35.

Fig. 44.

DFT-calculated mechanism for CO₂ hydrogenation to formate by the Co-Ga catalyst, [35b-H₂].

Fig. 45.

Catalytic scheme for CO₂ hydrogenation to formate by NiGaL (36).

Fig. 46.

Most energetically favorable catalytic cycle for CO₂ hydrogenation catalyzed by 36.

Fig. 47.

Two Verkade’s bases (Vkd_Me and Vkd_iPr) and the pK_a values of their conjugate acids in CH₃CN.

Fig. 48.

Hydrosilylation of CO₂ catalyzed by 37.

Fig. 49.

Plausible mechanism of indene formation reaction catalyzed by 38.

Fig. 50.

Plausible mechanism of the nucleophilic substitution of allylic alcohols catalyzed by 38.

Fig. 51.

Proposed Pd-Sc heterobimetallic complex for nitrile hydration.

Fig. 52.

AFCR of indoles and 1,3,5-trimethyoxybenzene with N-sulfonyl aldimines catalyzed by 38.

Fig. 53.

Reaction of 4 with thiobenzophenone compared to ketone.

Fig. 54.

Two possible mechanisms for reaction of 33 with ArNCS.

Fig. 55.

Proposed mechanism for synthesis of 44 via oxidative addition of MeI to 43.

Fig. 56.

Oxidative addition of CH₃I by 14.

Fig. 57.

Proposed catalytic cycle of Kumada coupling reaction via 14-trunc (left) compared to monometallic complex 47 (right); note that 14 was truncated in authors’ calculations.

Fig. 58.

Metal-Rh paddlewheel complexes 48 and 48′.

Fig. 59.

Carbene insertion into C–Cl bond catalyzed by 48.

Fig. 60.

Decomposition of ethyl diazoacetate by 48 and 48′.

Fig. 61.

C–F bond activation by 49.

Fig. 62.

Proposed catalytic cycle for magnesiation of aryl fluorides by 49.

Fig. 63.

Overall hydrodefluorination reaction catalyzed by 52.

Fig. 64.

Proposed cycle for hydrodefluorination catalyzed by 52; note, 52 is truncated in the cycle for clarity.

Fig. 65.

Overall C–F activation reaction of pentafluoropyridine facilitated by 58a-b.

Fig. 66.

C–H and C–F activation of fluorinated aromatics facilitated by 58a-b.

Fig. 67.

C–F activation of 2,3,5,6-tetrafluoropyridine and pentafluoropyridine facilitated by 58a-b.