Treatment of the iridacyclopentadiene complex ( 1, R = CO 2 CH 3 ) with silver tetrafluoroborate, followed by addition of a terminal alkyne (ethyne, ethyl ethnynyl ether, methyl propargyl ether), yields iridium(III) aryl-hydride complexes ( 6 -H, R 1 = H; 6 -OEt, R 1 = OCH 2 CH 3; 6 -CH 2 OMe, R 1 = CH 2 OCH 3 ). The structure of 6 -OEt was established by X-ray crystallographic analysis. Treatment of 6 -H with either HCl or carbon monoxide results in demetalation to give tetramethyl 1,2,3,4-benzenetetracarboxylate [C 6 (CO 2 Me) 4 H 2 ]. When 3-butyn-2-ol and propargyl alcohol are employed as substrates, a similar reaction occurs with 1 /AgBF 4 to produce the phthalimidyl complexes ( 7 -H, R 1 = H; 7 -Me, R 1 = CH 3 ). The lactone ring in 7 is generated from an intramolecular transesterification of the hydroxyl with an adjacent methyl ester. In all cases these products are attributed to tandem cycloaromatization and orthometalation processes.
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O’Connor et al. (2001) studied this question.