1 research outputs found
Regiospecific Acylation of Cycloplatinated Complexes: Scope, Limitations, and Mechanistic Implications
A series of platinum
complexes based on the tridentate cyclometalating
ligand derivatives 6-arylamino-2,2′-bipyridine, 6-phenoxy-2,2′-bipyridine,
6-phenylthio-2,2′-bipyridine, 6-benzyl-2,2′-bipyridine,
and 6-benzoyl-2,2′-bipyridine were synthesized, and their acylation
reactions were studied. Acylation of platinum complexes based on 6-(4-R-phenylamino)-2,2′-bipyridine
derivatives (R = CH<sub>3</sub>O, CH<sub>3</sub>, Cl, COOEt) tolerates
both electron-donating and electron-withdrawing substituents on the
aryl ring that are para to the amino group. However, platinum complexes
based on 6-(3-R′-phenylamino)-2,2′-bipyridine (R′
= CH<sub>3</sub>, Cl, Br) did not undergo the acylation reaction under
the same conditions. Interestingly, the acylation of the platinum
complexes based on 6-(3-fluorophenylamino)-2,2′-bipyridine
proceeded smoothly, and the results indicate that the acylation is
regiospecific and occurs at the metalated carbon. Complexes based
on 6-phenoxy-2,2′-bipyridine, 6-phenylthio-2,2′-bipyridine,
and 6-benzyl-2,2′-bipyridine are also regioselectively acylated.
A cyclometalated platinum complex based on 6-benzoyl-2,2′-bipyridine,
where the benzene is more electron deficient than those in other cyclometalated
platinum complexes, failed to undergo the acylation reaction. The
acylation can be carried out in acetic acid, 1,2-dichloroethane, benzonitrile,
and acetonitrile. Other acyl halides such as benzoyl chloride and
crotonyl chloride are also effective acylating reagents. On the basis
of the fact that the reaction is discouraged by the electron deficiency
of the phenyl ring and contrasting results of the acylation of platinum
complexes based on 6-(3-R′-phenylamino)-2,2′-bipyridine
(R′ = CH<sub>3</sub>, F, Cl, Br), an unprecedented electrophilic
addition–platinum migration–rearomatization cascade
mechanism is proposed for the regiospecific acylation reaction