Second Comes First: Switching Elementary Steps in Palladium‐Catalyzed Cross‐Coupling Reactions

Abstract

The electron‐poor palladium(0) complex L3Pd (L=tris[3,5‐bis(trifluoromethyl)phenyl]phosphine) reacts with Grignard reagents RMgX and organolithium compounds RLi via transmetalation to furnish the anionic organopalladates [L2PdR]−, as shown by negative‐ion mode electrospray‐ionization mass spectrometry. These palladates undergo oxidative additions of organyl halides R′X (or related SN2‐type reactions) followed by further transmetalation. Gas‐phase fragmentation of the resulting heteroleptic palladate(II) complexes results in the reductive elimination of the cross‐coupling products RR′. This reaction sequence corresponds to a catalytic cycle, in which the order of the elementary steps of transmetalation and oxidative addition is switched relative to that of palladium‐catalyzed cross‐coupling reactions proceeding via neutral intermediates. An attractive feature of the palladate‐based catalytic system is its ability to mediate challenging alkyl–alkyl coupling reactions. However, the poor stability of the phosphine ligand L against decomposition reactions has so far prevented its successful use in practical applications.

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

“…3 Moreover, Mg/Zn-based heterobimetallic complexes are usually postulated as intermediates in the transmetalation steps of various catalytic reactions, 4 specifically for transition-metal catalysed Kumada 5 and Negishi coupling reactions. 6 However, their isolation and characterization are still difficult since these heterometallic complexes are extremely sensitive and prone to undergo Schlenk equilibria to generate dialkyl compounds and elemental metals, especially for Mg-based heterometallic complexes. As a result, the development of sterically hindered multidentate ligand stabilized organomagnesium and organozinc compounds as a new class of supporting ligands for transition metals is necessary.…”

Towards determining molecular structure with ESI-MS backed by computational methods: structures of subnanoclusters of Pd and Cu chlorides, ion dynamics in vacuum, and challenges to the methodology

“…4 Such an advantageous combination makes this analytic technique ideal for studies of systems that undergo time evolution as catalytic solutions. Other (colloid) solutions of organic and organometallic compounds, such as (nano)clusters and transition metal complexes, have been effectively studied with ESI-MS. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] However, the analysis of (colloid) solutions with ESI-MS is a tedious and time-consuming activity that requires expert knowledge. 3,21 Inefficient automation of spectral analysis significantly slows research on various complex catalytic systems based on transition metals.…”

“…4 Such an advantageous combination makes this analytic technique ideal for studies of systems that undergo time evolution as catalytic solutions. Other (colloid) solutions of organic and organometallic compounds, such as (nano)clusters and transition metal complexes, have been effectively studied with ESI-MS. 5–20…”

Synthesis and Reactivity of Triangular Heterometallic Complexes Containing Zn–Zn Bond

“…Heterometallic complexes predicated on the combination of transition metals (TMs) and main group metals have been of intense interest owing to their electronic properties and reaction modes. , Such a system enabled novel small-molecule activation and efficient catalytic applications as a result of heteronuclear metal–metal cooperative effects . Zinc-based heterometallic complexes have become a focus of application-oriented research due to their participation in the pivotal transmetalation steps of various catalytic reactions, such as Negishi coupling reactions. , To date, hundreds of heterometallic compounds containing Zn–TM bonds have been accessed and most of them were based on organozinc groups ZnR (R = cyclopentadienyl and its derivatives, alkyl, aryl, etc. ). , …”