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Synthesis, Characterization, and Catalytic Application of Mononuclear and Dendritic Cationic Cu I Iminopyridine‐Ligated Complexes in Aryl Iodide Hydroxylation
Author(s) -
Mketo Nomvano,
Jordaan Johan H. L.,
Jordaan Anine,
Swarts Andrew J.,
Mapolie Selwyn F.
Publication year - 2016
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201600417
Subject(s) - chemistry , hydroxylation , catalysis , cationic polymerization , iodide , aryl , medicinal chemistry , homogeneous catalysis , stereochemistry , polymer chemistry , organic chemistry , alkyl , enzyme
A series of mononuclear ( C1 – C4 ) and dendritic G1 ( DC1 – DC4 ) and G2 ( DC5 – DC8 ) cationic Cu I iminopyridine complexes of the general formula [Cu{(R‐C 5 H 3 N)CH=N( n Pr)‐κ 2 ‐ N , N } 2 ][BF 4 ] ( C1 : R = 6‐Me; C2 : R = H; C3 : R = 6‐Br; C4 : R = C 4 H 3 ) and [DAB‐G x ‐PPI‐(Cu{(R‐C 5 H 3 N)‐κ 2 ‐ N , N } y ) z ][BF 4 ] n [DAB: 1,4‐diaminobutane; PPI: poly(propyleneimine); for G1: x = 1, y = 4, z = 2, n = 2; for G2: x = 2, y = 8, z = 4, n = 4; DC1 / DC5 : R = 6‐Me; DC2 / DC6 : R = H; DC3 / DC7 : R = 6‐Br; DC4 / DC8 : R = C 4 H 3 ] have been prepared and characterized by a range of spectroscopic and analytical techniques. The mononuclear and dendritic complexes were found to be active catalysts for the hydroxylation of 4‐iodotoluene to p ‐cresol in DMSO/H 2 O mixtures. A positive dendritic effect on catalytic activity was observed. Furthermore, our catalyst system was found to be active for the hydroxylation of 4‐iodotoluene in neat water. The active catalyst could be recycled twice before catalyst deactivation was observed. HRTEM analysis revealed that catalyst deactivation arose as a result of metal agglomeration. A series of poisoning experiments provided evidence for the mediation of hydroxylation by a homogeneous active species for both classes of pre‐catalysts, and a radical‐trapping experiment in combination with our experimental observations provided evidence that the reaction proceeds through a similar mechanism to that reported for Cu‐catalyzed halide exchange.