Bimetallic Catalysis Involving Dipalladium(I) and Diruthenium(I) Complexes

Abstract

Dipalladium(I) and diruthenium(I) compounds bridged by two [{(5,7-dimethyl-1,8-naphthyridin-2-yl)amino}carbonyl]ferrocene (L) ligands have been synthesized. The X-ray structures of [Pd(2)L(2)][BF(4)](2) (1) and [Ru(2)L(2)(CO)(4)][BF(4)](2) (2) reveal dinuclear structures with short metal-metal distances. In both of these structures, naphthyridine bridges the dimetal unit, and the site trans to the metal-metal bond is occupied by weakly coordinating oxygen from the amido fragment. The catalytic utilities of these bimetallic compounds are evaluated. Compound 1 is an excellent catalyst for phosphine-free, Suzuki cross-coupling reactions of aryl bromides with arylboronic acids and provides high yields in short reaction times. Compound 1 is also found to be catalytically active for aryl chlorides, although the corresponding yields are lower. A bimetallic mechanism is proposed, which involves the oxidative addition of aryl bromide across the Pd-Pd bond and the bimetallic reductive elimination of the product. Compound 1 is also an efficient catalyst for the Heck cross-coupling of aryl bromides with styrenes. The mechanism for aldehyde olefination with ethyl diazoacetate (EDA) and PPh(3), catalyzed by 2, has been fully elucidated. It is demonstrated that 2 catalyzes the formation of phosphorane utilizing EDA and PPh(3), which subsequently reacts with aldehyde to produce a new olefin and phosphine oxide. The efficacy of bimetallic complexes in catalytic organic transformations is illustrated in this work.

Amide‐Functionalized Naphthyridines on a RhII–RhII Platform: Effect of Steric Crowding, Hemilability, and Hydrogen‐Bonding Interactions on the Structural Diversity and Catalytic Activity of Dirhodium(II) Complexes

“…The carbonyl oxygen atom binds at the axial site and allows substrate coordination during the catalytic cycle. This type of hemilabile behavior of amide‐functionalized naphthyridine has been reported earlier for Pd I –Pd I and Ru I –Ru 1 platforms by our group 17…”

“…Furthermore, the bridging carboxylate units render a planar structure that involve the {Rh 2 } unit and NP ring, which is evident from the dihedral angles of f= 1.3(1) and 1.1(1)8 for N1-Rh1-Rh2-N2 in 1 and 5, respectively. This finding is unlike the Ru I ÀRu I complex [Ru 2 (L 1 H) 2 (CO) 4 (BF 4 ) 2 ], [17] in which the NP rings significantly deviate from planarity due to permitted rotation around the RuÀRu bond (the corresponding angles are f= 33.0(2) and 33.6(2)8 for N1-Ru1-Ru2-N2 and N4-Ru2-Ru1-N5, respectively; Figure 8). Therefore, the orthomethyl groups in the Ru I ÀRu I complex remain away from the axial sites of the {Ru 2 } core and allow the incorporation of the second L 1 H ligand.…”

“…This type of hemilabile behavior of amidefunctionalized naphthyridine has been reported earlier for Pd I -Pd I and Ru I -Ru 1 platforms by our group. [17] Herein, we demonstrate the effect of steric crowding, hemilability, and hydrogen-bonding functionalities of L 1 H and L 2 H ligands to control the structures and catalytic activities of dirhodium(II) compounds (Scheme 2).…”

Redox Reactions in Palladium Catalysis: On the Accelerating and/or Inhibiting Effects of Copper and Silver Salt Additives in Cross‐Coupling Chemistry Involving Electron‐rich Phosphine Ligands

“…Our results suggest the possibility of alternative cycles involving bimetallic Pd I [26] over the currently accepted co-existing, synergistic catalytic cycles involving Pd 0 /Pd II and Cu. In the same process, Cu I or Ag I cubanes are formed, which in turn effect the activity of the dinuclear Pd I complexes.…”

Contrasting Reactivity of 2-Mesityl-1,8-Naphthyridine (Mes-NP) with Singly-Bonded [RhII–RhII] and [RuI–RuI] Compounds

“…[1] The flexibility and adaptability are the key attributes of NP ligands which make them suitable for use in bimetallic catalysis. [2][3][4] We explored NP-R (2-(2-R)-1,8-naphthyridine) ligands in our pursuit of dimetallic chemistry. [5][6][7] Covalent attachment of a donor group, for example, the thiazolyl at 2-position of the NP (tz-NP), provides a tridentate ligand that bridges the dimetal unit and simultaneously binds one axial site, as illustrated in Fig.…”