Unusual Me−O Bond Cleavage in a Metalated Crown-Ether: X-ray Molecular Structure of (5-Methoxy-4,6-dimethyl-1,3-xylylene-2-one)-15 Crown-4 Complex of Pentamethylcyclopentadienyl Iridium

The reaction of [(C5Me5)Ir(Solvent)3][BF4]2 (1) with (2,5-dimethoxy-4,6-dimethyl-1,3-xylylene)-15 crown-4 (2) affords the metalated crown-ether complex [(η5-C5Me5)Ir(η6-C18H28O6)][BF4]2 (3) in 88% yield. Complex 3 undergoes a facile MeO bond cleavage to give the related semiquinone form of the metalated crown-ether [(η5-C5Me5)Ir(η5-C17H25O6)][BF4] (4). A single-crystal X-ray structure determination of complex 4 is reported. Complex 4 crystallizes in the monoclinic space group P21/m with a = 8.187(5) Å, b = 17.193(4) Å, and c = 10.900(3) Å, α = 90°, β = 109.68(1)°, γ = 90°, and Z = 2. The structure provides us with valuable information about the nature of the η5-semiquinone form of the metalated crown-ether and reveals that, surprisingly, the MeO unit close to the crown chain is the one that undergoes hydrolysis. A rationale consistent with the experimental results is advanced.