Past exam of the chemistry B course of the University of Cambridge 2022 Paper 2 B9 e Solution 2026-10-20
A reasonable product is sodium facial trimetaphosphate–molybdenum tricarbonyl, with the anionOne terminal O from each phosphorus binds Mo; the three O donors occupy one octahedral face, while the three carbonyls occupy the opposite face. The ring bridges remain P–O–P bridges and are not replaced by Mo–P bonds. Mo remains Mo(0), , and electrons. Overall,acetonitrile can transiently replace CO during heating, but it is not required in the final six-coordinate proposal. The same anion has been structurally characterized with a different counterion: that primary study independently supports the facial O/CO connectivity, without establishing identical solubility or yield for the sodium salt.[ref]
Synthesis and characterization of the trimetaphosphate molybdenum tricarbonyl anion [(P3O9)Mo(CO)3]3- as its tris(bis(triphenylphosphine)iminium) salt by Christopher R. Clough and others. pp. 195–196, Scheme 2 and Fig. 1; §4.3 for Mo(CO)6 in refluxing acetonitrile