Basicity of transiton metal carbonyl complexes : XIII. Reactions of the π-cyclopentadienyl complexes of molybdenum and tungsten with aprotic acids

The aprotic acids HgCl₂ and SnX₄ (X  Cl, Br) react with the π-complexes C₅H₅M(CO)(NO)(L) (II, M  Mo W; L  PPh₃) by attack at the metal center. With HgCl₂ complexes II yield stable neutral 1:1 adducts CpM(CO)(NO)(L)HgCl₂(III). In the case of SnCl₄, complexes II initially produce the ionic 1:2 adducts CpM(CO)(NO)(L)(SnCl₃)]⁺SnCl₅^-(IV) which, as a result of oxidative elimination of CO, turn into the neutral complexes CpM(NO)(L)(SnCl₃)(Cl)(V). In reactions of II with SnBr₄ the corresponding CpM(NO)(L)(SnB₃)(Br) complexes are formed directly. The formation of III–V is accompanied by a considerable increase of the frequencies ν(CO) and ν(NO). The structures of the complexes IV (M  Mo) and V (M  Mo) have been established by an X-ray structure analysis.