Ligand substitution reactions in group 6 metal carbonyl complexes of a novel bicyclic ditertiary phosphine ether

Article abstract of DOI:10.1021/om00040a022

The complexes fac-(1-P,P′,O)M(CO)₃, where M = Mo or W and 1 is cis-1,5-bis((diphenylphosphino)-methyl)-3-oxabicyclo[3.3.0]octane, were found to react with the ligands L = acetonitrile, piperidine, pyridine, and P(OCH₂)₃CCH₃ to yield two diastereomers of fac-(1-P,P′)M(CO)₃(L) in each case. ¹H and ¹³C NMR spectroscopic data suggest that the major isomer in each product is that in which the added ligand occupies the site originally occupied by the ether oxygen of 1 and that the minor isomer contains the new ligand in the position trans to this site. Carbon monoxide reacts with the complexes fac-(1-P,P′,O)M(CO)₃ (M = Mo, W) to yield (1-P,P′)M(CO)₄. Using ¹³CO, these reactions stereoselectively yield two diastereomers of fac-(1-P,P′)M(CO)₃(¹³CO) in ratios of approximately 5:1 and 7:1 for M = Mo and W, respectively. A scheme involving the isomerization of diastereomeric five-coordinate square-pyramidal intermediates is discussed. The N-donor complexes fac-(1-P,P′)M(CO)₃L, where M = Mo and W and L = acetonitrile, pyridine, and piperidine, were observed by infrared and ¹H and ³¹P NMR spectroscopy to partially dissociate in solution, equilibrating with free L and fac-(1-P,P′,O)M(CO)₃. This equilibrium was further substantiated by monitoring the exchange reaction between free and coordinated CD₃CN in the presence of fac-(1-P,-P′)Mo(CO)₃(NCCH₃) using ²H NMR spectroscopy.