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Sulfination by Using Pd‐PEPPSI Complexes: Studies into Precatalyst Activation, Cationic and Solvent Effects and the Role of Butoxide Base
Author(s) -
Sayah Mahmoud,
Lough Alan J.,
Organ Michael G.
Publication year - 2013
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.201203142
Subject(s) - chemistry , sulfide , catalytic cycle , cationic polymerization , catalysis , salt (chemistry) , solvent , medicinal chemistry , toluene , base (topology) , polymer chemistry , inorganic chemistry , organic chemistry , mathematical analysis , mathematics
The activation of PEPPSI precatalysts has been systematically studied in Pd‐catalysed sulfination. Under the reactions conditions of the sulfide and KO t Bu in toluene, the first thing that happens is exchange of the two chlorides on the PEPPSI precatalyst with the corresponding sulfides, creating the first resting state; it is via this complex that all Pd enters the catalytic cycle. However, it is also from this same complex that a tri‐Pd complex forms, which is a more persistent resting state. Under standard reaction conditions, this complex is catalytically inactive. However, if additional pyridine or a smaller base (i.e., KOEt) is added, this complex is broken down, presumably initially back to the first resting state and it is again capable of entering the catalytic cycle and completing the sulfination. Of note, once the tri‐Pd complex forms, one equivalent of Pd is lost to the transformation. Related to this, the nature of the cation of the sulfide salt and solvent dielectric is very important to the success of this transformation. That is, the less soluble the salt the better the performance, which can be attributed to lowering sulfide concentration to avoid the movement of the Pd‐NHC complex into the above described off‐cycle sulfinated resting states.