Cubic group 13 heterosiloxanes with four Co₃(CO)₉C cluster units as substituents: novel soluble model compounds for synthetic zeolites showing catalytic activity in hydroformylation reactions

Abstract

The reactions between the cobalt carbonyl anchored silanetriol Co₃(CO)₉CSi(OH)₃ (1) and EMe₃ (E = Al, Ga and In) in THF result in the formation of the respective group 13 heterosiloxanes [Co₃(CO)₉CSiO₃E.THF]₄ (Al (2); Ga (3); In (4)) in good yields. The new heterosiloxanes have been extensively characterized by means of their analytical and spectroscopic (mass, IR, and NMR) data. Additionally, the molecular structure of the Al complex 2 has been determined by X-ray diffraction studies. The compound contains a cubic Al₄O₁₂Si₄ core with four Co₃(CO)₉C cluster units anchored on each of the silicon atoms at the alternating corners of the cube. Interestingly, there are three different types of Co₃(CO)₉C cluster units within the same molecule based on the mode of coordination of the CO ligands. In order to test the utility of these compounds in catalytic conversions, hydroformylation reactions involving 1-hexene as substrate have been carried out at 120 °C under a H₂/CO initial pressure of 70 bar. A series of solution studies of the catalytic mixture (such as time-dependent IR, NMR, and MS) have been carried out in order to identify the catalytic active species in the process. The Al- and Ga-containing heterosiloxanes show a better hydroformylation activity compared to the In analogue. The regioselectivity of the hydroformylation reactions with 2 is found to be over 60%. The hydroformylation presumably proceeds via the decomposition of Co₃(CO)₉C cluster fragments into Co₂(CO)₈ units in the case of catalysts 2 and 3.