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 ofpentamethylcyclopentadienyl 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 co mplex [(eta(5)-C5Me5)Ir(eta(6)-C18H28O6)][BF4](2) (3) in 88% yield. Complex 3 undergoes a facile Me-O bond cleavage to give the related semiquinone fo rm of the metalated crown-ether [(eta(5)-C5Me5)Ir(eta(5)-C17H25O6)][BF4] (4 ) A single-crystal X-ray structure determination of complex 4 is reported. Complex 4 crystallizes in the monoclinic space group P2(1)/m with a = 8.187 (5) Angstrom, b = 17.193(4) Angstrom, and c = 10.900(3) Angstrom, alpha = 9 0 degrees, beta = 109.68(1)degrees, gamma = 90 degrees, and Z = 2. The stru cture provides us with valuable information about the nature of the eta(5)- semiquinone form of the metalated crown-ether and reveals that, surprisingl y, the Me-O unit close to the crown chain is the one that undergoes hydroly sis. A rationale consistent with the experimental results is advanced.