36 for spectra of isoelectronic d7 Co11 species).It is less clear from the spectra in Figure 5 how the weak IR band on the side of the e mode is polarized. This uncertainty is completely removed by the difference spectra illustrated in Figure 6. These spectra, obtained by computer subtraction, show that this weak band, arrowed, is polarized in the same direction as the e mode and opposite to the a! mode. This supports our original assignment of this band to a matrix splitting of the e mode (qv). ConclusionsThese experiments have finally ended the search for the elusive Mn(CO)5 radical and it is clear that earlier attempts12 to synthesize Mn(CO)5 in matrices were unsuccessful.37 Mn(CO)5 has (35) Alexander,

The Pd(II)-catalyzed cyclocarbonylation of acetylenic alcohols to methylene lactones proceeds through carboalkoxypalladium intermediates, followed by intramolecular cis addition to the triple bond. Such intermediates have been independently synthesized, isolated, and found to undergo appropriate interconversions. A PdI2/Bu3P/CH3CN catalyst system gives rates first order in CO pressure, with the rate-determining step evidently being the uptake of CO by Pd. The use of an SnCl2 cocatalyst (PdCl2/2Ph3P/SnCI2/CH3CN) labilizes the coordination sphere of the palladium, dissociating Cland forming a cation which is a much faster cyclocarbonylation catalyst. The rate is now independent of CO pressure and first order in Pd and in substrate. The rate-determining step is coordination of the substrate, followed by rapid uptake of CO and completion of the cyclocarbonylation reaction. As the carboalkoxy intermediates also react intermolecularly with terminal acetylenes, yields in the catalytic cyclocarbonylation reaction improve substantially when it is run at concentrations below 0.3 M.

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bvans-2-Ethynyl substituted alcohols can be obtained by treatment of epoxides with ether-stabilised methyl ethynyl alanes; a cis analogue, obtained by oxidation and stereoselective reduction, has been converted into the corresponding cis ring-fused methylene lactone.