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When Are Tricoordinated Pd II Species Accessible? Stability Trends and Mechanistic Consequences
Author(s) -
Moncho Salvador,
Ujaque Gregori,
Lledós Agustí,
Espinet Pablo
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200800423
Subject(s) - steric effects , chemistry , agostic interaction , ligand (biochemistry) , intramolecular force , lone pair , tetrahydrofuran , stereochemistry , crystallography , medicinal chemistry , solvent , molecule , receptor , organic chemistry , biochemistry , metal
Abstract The ease of access to Pd II tricoordinated species (whether intermediates or transition states) in organometallic and catalytic reactions has been assessed with DFT methods to analyze the relative stability of tricoordinated [PdArXL] complexes versus their tetracoordinated derivatives formed by two most common processes of filling the fourth coordination site: solvent coordination (with tetrahydrofuran), or dimerization to give [Pd 2 Ar 2 (μ‐X) 2 L 2 ]. The effect of each ligand (L=PH 3 , PMe 3 , PPh 3, P t Bu 3 , 1‐AdP t Bu 2 ; Ar=C 6 F 5 , C 6 H 5 , C 6 H 4 OH, C 6 H 4 OCH 3 , C 6 H 4 NH 2 , C 6 H 2 (NH 2 ) 3 ; X=F, Cl, Br, I, OH, SH, NH 2 , PH 2 , CH 3 ) on these two processes has been systematically considered, and the results have been compared with the experimental information available. The trends observed, match the experimental results and suggest that: 1) the formation of bridged dimeric complexes is strongly preferred; 2) electronic effects are in general less important compared to steric effects; 3) when steric effects prevent formation of bridges and coordination of a fourth external ligand, intramolecular agostic interactions are established with CH groups of one ligand; 4) as an exception, for X=NR 2 true tricoordinated complexes, not showing agostic interactions, become stable. In the later case NR 2 seems to act as π‐donor with its lone pair to the empty orbital at the fourth coordination site of palladium, thus avoiding a true 14e configuration for the tricoordinated Pd II complex.