Application of an indenyl molybdenum dicarbonyl complex in the isomerisation of alpha-pinene oxide to campholenic aldehyde

Abstract

The complex [{(eta(5)-Ind)Mo(CO)(2)(mu-CI)(2)] (1) has been tested for the industrially relevant catalytic isomerisation of CL-pinene oxide (PinOx) to campholenic aldehyde (CPA) in the liquid phase. PinOx conversion and CPA selectivity are strongly influenced by the solvent employed. Complete conversion of PinOx was achieved within 1 min at 55 degrees C or 30 min at 35 degrees C using 1,2-dichloroethane as solvent, giving CPA in 68% yield. Other products included trans-carveol, iso-pinocamphone and trans-pinocarveol. The stability of 1 under the reaction conditions used was investigated by using FT-IR spectroscopy and electrospray ionisation mass spectrometry (ESI-MS) to characterise recovered solids. In the presence of air/moisture 1 undergoes oxidative decarbonylation upon dissolution to give oxomolybdenum species that are proposed to include a tetranuclear oxomolybdenum(v) complex. Conversely, ESI-MS studies of 1 dissolved in dry acetonitrile show mononuclear species of the type [IndMo(CO)(2)(CH3CN)(n)](+) The crystal structure of the ring-slipped dicarbonyl complex [{(eta(5)-Ind)Mo(CO)(2)(mu-CI)(2)] (2) (obtained after dissolution of 1 in acetonitrile) is reported.