Oxidationsreaktionen von Molybdän- und wolframcarbonyl-carbinkomplexen. Koordination der W≠C-Einheit an palladium(0) aktiviert carbonyl- und schützt carbinliganden bei der synthese von wolfram(VI)-chlorocarbinkomplexen

Abstract

Carbonyl carbyne complexes [L R(CO) 2M ≠ C-p-tol], M = Mo, W, containing the tripodal oxygen ligands L R − = [(C 5H 5)Co{P(O)R 2} 3] −], R = OMe, OEt, O-i-Pr, are oxidised by dioxygen, sulfur, bromine and iodine with concomitant splitting of the metal carbon bond. The reaction with iodine leads to highly labile complexes, probably of the composition [L R(CO)I 2Mo ≠ C-p-tol], R = OEt, O-i-Pr. The reaction with bromine yields the paramagnetic Mo(V) complex [L O-i-PrMoBr 4]. Sulfure is inserted in the tungsten-carbon bond to give the dithiocarboxylate complex [L OMe(CO) 2(S 2C-p-tol)]. Oxidation in moist air leads to the oxo-bridged ditungsten(VI) complex [{L OMe(O) 2W} 2O]. In order to test the stability of tungsten(VI) carbyne compounds bearing the oxygen ligands L R −, the complexes [L RBr 2W ≠ C-p-tol], R = OMe, OEt, O-i-Pr have been prepared from the known high valent carbyne complex mer-[Br 3(dme)W ≠ C-p-tol] and the sodium salts NaL R. Allylpalladium chloride reacts with the carbyne complexes [L OMe(CO) 2M ≠ C-p-tol] to yield palladium(0) complexes [{L OMe(CO) 2M ≠ Mo, W, in which the M ≠ C unit is coordinated to palladium like an alkyne. Additional allylpalladium chloride and hexachloroethane in boiling THF oxidise the palladium-tungste n complex [{ L OMe(CO) 2W ⇹ C-p-tol} 2Pd ] to yield the chloro-carbyne complex [L OMeCl 2W ≠ C-p-tol] that is not coordinated to palladium is completely inert towards hexachloroethane under these reaction conditions.