DEHYDRATION REACTION OF 2-METHYL-3-BUTYN-2-OL IN THE PRESENCE OF FE-3(CO)(12), SPECTROSCOPIC CHARACTERIZATION OF 2 CLOSO AND NIDO PENTAGONAL BIPYRAMIDAL COMPLEXES AND CRYSTAL-STRUCTURE OF THE ALLENYLIDENE CLUSTER FE-3(CO)(9)(MU(3),ETA(2)-C=C=CME(2))

The reaction of 3-methyl-2-butyn-3-ol (MBO) with Fe-3(CO)(12) gives lo w yields of Fe-3(CO)(9)(mu-CO)(C=C=CMe(2)), 1, and considerable yields of the close and nide pentagonal bipyramidal complexes Fe-3(CO)6(mu-C O)(2)[RC(CH)(2)CR'], 2, and Fe-2(CO)(6)RC(CH)(2)CR'], 3, R = C(Me)(2)O H, R' = C(Me) = CH2, in only one isomer each. The formation of 1 requi res the dehydration of MBO with loss of the OH and of the terminal alk yne hydrogen; the complex is a rare example of an allenylidene-substit uted cluster and, to our knowledge, the first formed upon dehydration of a propargyl alcohol in non-ionic conditions. Its structure has been confirmed by an X-ray diffraction study. The formation of 2 and 3 occ urs via dehydration of only one ligand molecule with loss of the OH an d of one of the methyl hydrogens. Complexes 2 and 3 have been characte rized by elemental analyses, NMR spectroscopy and CI-mass spectrometry .