Synthesis, characterization and reactions of some short chain alkoxycarbonyl molybdenum compounds [M][Mo(CO)5(COOR)] (M = PPN, Et4N and R = Me, Et, iPr) and [Ph4As]2[Mo(CO)4{(COOCH(CH3)2)2}]: X-ray structure of [Et4N]2[Mo4O13]

The short chain alkoxycarbonyl complexes of molybdenum, [PPN][Mo(CO)5(COOR)], [R = CH3, CH2CH3 and CH(CH3)2], have been synthesized by the addition of [Mo(CO)6] to a refluxing solution of [PPN][OR] in different alcohol solvents under a CO atmosphere. In the absence of CO, metal alkoxide complexes [Mo(CO)5(OR)]− (R = CH2CH3 and CH(CH3)2) were formed. These new alkoxycarbonyl complexes were characterized by IR, 1H and 13C NMR spectroscopy, melting point and elemental analysis. When the CH3CN solution of the compounds [PPN][Mo(CO)5(COOCH(CH3)2)] and [PPN][Mo(CO)5(OCH(CH3)2)] were exposed to UV light the compounds decomposed to form the cluster compound [PPN]2[Mo6O19]. The tetraethylammonium derivative, [Et4N][Mo(CO)5(COOCH3)], prepared from [Et4N][OCH3] and Mo(CO)6 in methanolic solution also decomposed in CH3CN to form the new dark brown crystalline molybdenum oxo-cluster [Et4N]2[Mo4O13]. The compound crystallizes in the monoclinic form with a space group of P 21/n. Addition of [Ph4As][OCH(CH3)2] to Mo(CO)6 in a ratio of 4:1 results in the formation of the bis(alkoxycarbonyl) complex, [Ph4As]2[Mo(CO)4{(COOCH(CH3)2)2}]. The reaction of the methoxycarbonyl complex, [PPN][Mo(CO)5(COOCH3)] with synthesis gas in methanol at 125 °C gave methyl formate, formic acid and Mo(CO)6. The same reaction as above in THF yielded methyl formate, methanol and formic acid.

Graphical abstractMo(CO)6 reacts with [PPN][OCH(CH3)2] to form [PPN][Mo(CO)5(COOCH(CH3)2)] which decomposes under UV light to form [PPN][Mo6O19] (1). When Mo(CO)6 reacts with [Et4N][OCH3] it formed [Et4N][Mo(CO)5(COOCH3)] which also decomposed to form [Et4N]2[Mo4O13] (2) under UV light in CH3CN. The [Mo(CO)5(COOCH3)]− intermediate played a significant role in the production of methyl formate from Mo(CO)6 and KOCH3.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Mo(CO)6 react with alkoxides to form alkoxycarbonyl complexes, [M][Mo(CO)5(COOR)]. ► [PPN][Mo(CO)5(COOCH(CH3)2)] under UV light forms [PPN]2[Mo6O19]. ► [PPN][Mo(CO)5(OCH(CH3)2)] under UV light also forms [PPN]2[Mo6O19]. ► [Et4N][Mo(CO)5(COOCH3)] under UV light forms the oxo cluster [Et4N]2[Mo4O13]. ► [PPN][Mo(CO)5(COOCH3)] under syngas (1:1) produced methyl formate.