1998/02/10 by Arturo L. Casado, Pablo Espinet · 4 citations
Chemistry · #Catalytic Cross-Coupling Reactions #Organometallic Complex Synthesis and Catalysis #Coordination Chemistry and Organometallics
paper · doi:10.1021/om9709502
openalex publication_date 1998/02/10 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/26
The oxidative addition of RI to Pd(0) and further cis -to- trans isomerization, which are involved in the Stille reaction and other Pd-catalyzed syntheses, have been studied. C 6 Cl 2 F 3 I ( 1, C 6 Cl 2 F 3 = 3,5-dichlorotrifluorophenyl) adds to Pd(PPh 3 ) 4 in THF at room temperature giving cis -[Pd(C 6 Cl 2 F 3 )I(PPh 3 ) 2 ] ( 2 ), which could be isolated before isomerization to the more stable trans -[Pd(C 6 Cl 2 F 3 )I(PPh 3 ) 2 ] ( 3 ). A 19 F NMR kinetic study of the isomerization of 2 in THF at 322.6 K reveals a first-order law r iso = k iso [ 2 ], with k iso = f + g [ 2 ] 0 + ( h + i [ 2 ] 0 )/([PPh 3 ] + j ) ( f = (1.66 ± 0.03) × 10 - 4 s - 1, g = (2.5 ± 0.2) × 10 - 3 mol - 1 L s - 1, h = (1.3 ± 0.7) × 10 - 8 mol L - 1 s - 1, i = (4 ± 2) × 10 -7 s - 1, and j = (1.4 ± 0.7) × 10 - 5 mol L - 1 ). A four-pathway mechanism accounts for these results: Two are assigned to the associative replacements of PPh 3 coordinated to 2 by an iodide ligand of I−[Pd] (I−[Pd] = 2 or 3 ), both THF-assisted (coefficient h ) or direct (coefficient i ), leading to a monoiodide-bridged intermediate cis -Pd(C 6 Cl 2 F 3 )I(PPh 3 )(μ- I )-[Pd]. The later rearranges via terminal-for-bridging iodide exchange to trans -Pd(C 6 Cl 2 F 3 ) I (PPh 3 )(μ-I)]-[Pd], which is finally cleaved by PPh 3 yielding complex 3 . The other two concurrent pathways are assigned to the isomerization via two consecutive Berry pseudorotations in the pentacoordinated species derived from 2 by coordination of THF (coefficient f ) or I−[Pd] (coefficient g ). The apparent activation entropy associated with k iso is negative (Δ S ⧧ = −21 ± 3 J K - 1 mol - 1 ), in agreement with the proposed bimolecular mechanisms.