First X‐Ray Structure Analyses of Rhodium(III) η¹‐Allyl Complexes and a Mechanism for Allylic Isomerization Reactions

Abstract

Metal-to-metal allyl transfer: Using the first structurally characterized rhodium eta(1)-allyl complexes it is shown that the sigma-bound allyl substituent can be transferred from the Rh(III) complex to a Rh(I) complex in a fast equilibrium. This process may account for the decrease in regioselectivity observed in allylic alkylation reactions in which complex 1 is used as a catalyst.

An NHC–Silyl–NHC Pincer Ligand for the Oxidative Addition of C−H, N−H, and O−H Bonds to Cobalt(I) Complexes

“…[12] Theo xidative addition of E À Hb onds (E = C, N, O) to low-valent transition-metal species is af undamental bondactivation step that is involved in many important catalytic transformations. [4] As for Group 9metals,such areactivity has (7), Co1-N1 1.790 (2), N1-N2 1.119 (3);N1-Co1-Si1 131.08 (8), N1-Co1-C1 95.60 (9), N1-Co1-C2 96.02 (10), C1-Co1-Si1 90.18 (7), C2-Co1-Si1 86.33 (7), C2-Co1-C1 167.13 (10).…”

“…The wide and successful application of phosphine-based pincer ligands [1] in organometallic chemistry and catalysis has stimulated great interest in their N-heterocyclic carbene (NHC) analogues, [2,3] which represent ac lass of strongly electron-donating pincer ligands,i deal for creating electronrich metal complexes.T he latter complexes are useful in the activation of inert bonds by oxidative addition. [4] Thus far, many NHC-based pincer ligands that feature versatile donor groups, [3] such as aryl anion, [5] pyridine, [3a,6] or amide [7] moieties,h ave been developed and applied in transitionmetal-catalyzed reactions.N otable examples include Chianeses(CC Ar C)Ir I pincer complex (C and C Ar denote NHC and aryl anion, respectively), which catalyzes the acceptorless dehydrogenation of cyclooctane with high initial rates, [5c] and Chiriksf ormal iron(0) and cobalt(I) complexes with CNC pincer ligands,w hich are among the most active transitionmetal catalysts for olefin hydrogenation. [6d,f] Along with these developments,ithas been envisioned that NHC-based pincer ligands containing ac entral silyl donor, abbreviated as [CSiC] À ,c ould be strong electron donors [3e] as silyl anions are among the strongest s-donors.…”

Rhodium‐Catalyzed Allylic Substitution Reactions with Indium(III) Organometallics

“…This yield was improved by using 70 mol-% of Ph 3 In (80 %, Table 3, entry 1). [17,18] In our reactions we believe that σ-π-σ isomerization could take place under the reaction conditions (80°C) and that this would favor the formation of the σ-allyl-Rh complex at the less hindered position. [17] As a continuation of this study, the reactions of substituted triarylindium reagents, such as the 4-methyl-, 2and 4-methoxy-, and 4-fluorophenyl systems, with 12 gave the corresponding α-substituted products 14-17 regioselectively in good yields (72-97 %, entries [2][3][4][5].…”

Asymmetric synthesis of N-allylic indoles via regio- and enantioselective allylation of aryl hydrazines

“…The oxidative addition step favours the formation of intermediate A because of the higher acidity of N–H bond of N 1 than N 2 . Hydrometalation of the less-substituted double bond could generate π-allyl-Rh (or δ-allyl-Rh) complex B (or B′ ) 42 43 44 45 , which could generate the desired branched N -allylic aryl hydrazine 1a via reductive elimination. The N -selectivity was determined within the oxidative addition step 46 .…”