Synthesis and isomerism of Cr and Mn phosphonioallene complexes

Earlier, we have discovered the UV-promoted four-component reaction between (arene)chromium and cyclopentadienylmanganese tricarbonyl complexes, propargyl alcohol, PPh3, and HBF4 to afford isomeric terminal and internal phosphonioallene complexes. The present study revealed additional details for this reaction and was extended either to similar manganese and chromium complexes, or to propargyl alcohol derivatives (НС≡ССМе2ОН, DC≡CCH2OMe). In particular, the use of d1-propargyl methyl ether allowed us to exclude possible isomerization of propargylphosphonium to allenylphosphonium in the coordination sphere. The photolysis of CpMn(CO)3 and Cp∗Mn(CO)3 in the presence of propargyl alcohols afforded η2-alkyne complexes, which were then reacted in situ with acid and PPh3 under dark conditions. With unsubstituted propargyl alcohols, the terminal anti-isomer was the only product in both cases, while the internal isomer is exclusively produced in the reactions of both Cr and Mn complexes with 2-methylbut-3-yn-2-ol. Issues related to the isomeric ratio are discussed and the data obtained are compared with those for similar known metal complexes. The obtained compounds were characterized by IR, 1H, 31P, and 13C NMR spectroscopy and the structures of complexes IX and XIII were confirmed by X-ray diffraction.