Organic Reactions Enabled by Catalytically Active Metal–Metal Bonds Conner M. Farley, Christopher Uyeda  Trends in Chemistry  DOI: 10.1016/j.trechm.2019.04.002 Copyright © 2019 Elsevier Inc. Terms and Conditions

Figure 1 Metal–Ligand and Metal–Metal Interactions: Orthogonal Tools for Controlling the Electronic Structure of Transition Metals. (A) Effect of metal–ligand and metal–metal interactions on the electronic structure of transition-metal catalysts. (B) Metal–metal bonds can serve as single site or multisite catalysts. Trends in Chemistry DOI: (10.1016/j.trechm.2019.04.002) Copyright © 2019 Elsevier Inc. Terms and Conditions

Figure 2 Diverse Roles of Pd(I) and Ni(I) Dimers in Cross-Coupling Reactions. (A) Pd exhibits a propensity to form metal–metal-bonded dimers in the +1 oxidation state. (B) Pd(I) dimers as off-cycle resting states or catalyst decomposition products in cross-coupling reactions [15,20,22]. (C) Pd(I) dimers as catalytic intermediates in transhalogenation reactions [32]. (D) Development of catalytic aryl halide trifluoromethylthiolation [34], and trifluoromethylselenolation reactions [33]. Trends in Chemistry DOI: (10.1016/j.trechm.2019.04.002) Copyright © 2019 Elsevier Inc. Terms and Conditions

Figure 3 Bimetallic Cooperativity Enables Catalytic C–H Borylations with Base Metals. (A) Arene C–H borylations using Ir catalysts [38]. (B) From stoichiometric to catalytic C–H borylations using base-metal catalysts [40]. (C) Photoinduced catalytic C–H borylations using heterobimetallic Fe/Cu catalysts [36]. Trends in Chemistry DOI: (10.1016/j.trechm.2019.04.002) Copyright © 2019 Elsevier Inc. Terms and Conditions

Figure 4 Dinuclear Active Sites Mediate Vinylidene Transfer Reactions to Alkenes and Dienes. (A) Designing catalytic vinylidene transfer reactions by suppressing the competing Fritsch–Buttenberg–Wiechell (FBW) rearrangement. (B) Dinuclear stabilization of vinyl ligands and a proposed Ni2-bound vinylidenoid. (C) Stoichiometric methylenecyclopropanation using a 1,1-dichloroalkene. (D) Catalytic reductive [2 + 1]-cycloadditions of alkenes [44] and [4 + 1]-cycloadditions of 1,3-dienes [56]. Trends in Chemistry DOI: (10.1016/j.trechm.2019.04.002) Copyright © 2019 Elsevier Inc. Terms and Conditions

Figure 5 An Ru–Ru Bond Facilitates Ligand Exchange in Propargylic Substitution Reactions. (A) Ru2 catalysts for the substitution reactions of propargylic alcohols [57]. (B) Ru–Ru interaction facilitates ligand substitution by stabilizing the low-coordinate state [62]. (C) Catalytic asymmetric propargylic substitutions using chiral Ru2 catalysts [63]. Abbreviation: ee, enantiomeric excess. Trends in Chemistry DOI: (10.1016/j.trechm.2019.04.002) Copyright © 2019 Elsevier Inc. Terms and Conditions

Figure 6 Selective C–H Insertion Reactions Using Rh2 Catalysts. (A) Formation of Rh2 carbene complexes using Rh2 tetracarboxylate catalysts. (B) Rh2 carbenes are highly reactive due to three-centered σ- and π-bonding interactions [9,75]. (C) Regioselective and stereoselective C–H insertion reactions using chiral Rh2 catalysts [76,77]. Abbreviations: ee, enantiomeric excess; LUMO, lowest unoccupied molecular orbital; rr, regiomeric ratio. Trends in Chemistry DOI: (10.1016/j.trechm.2019.04.002) Copyright © 2019 Elsevier Inc. Terms and Conditions