Reaktionen von Vanadium(V)- und Tantal(V)-Komplexen Mit Kinetisch Stabilisierten Phosphaalkinen. Einfache Synthese von 1,3,4-Thia- und 1,3,4-Selenadiphospholen / Reactions of Vanadium(V) and Tantalum(V)-Complexes with Kinetically Stabilized Phosphaalkynes. A Simple Synthesis of 1,3,4-Thia and 1,3,4-Selenadiphospholes

Abstract A simple synthetic pathway to the unknown 1,3,4-thiadiphospholes 3 and 1,3,4- selenadiphospholes 4 has been developed involving reactions of the azaphosphavanada(V)- cyclobutenes 2, generated in situ from the imidovanadium(V) complex tBuN = VCl3 and the phosphaalkynes 1a - d, with an excess of elemental sulfur or grey selenium, respectively. The reactions of the phosphaalkynes 1a,b with TaOCl3 or VOCl3 · DME furnish the 1,2-dichloro-phosphaalkenes 5a,b and 1,2,3,4-tetrachloro-3,4-di-tert-butyl-1,1-diphosphethane 7a. The metallacyclic species 2e - h with secondary or primary alkyl groups on the ring nitrogen atom are unstable and undergo quantitative conversion to the 1H-1,2,4-azadiphospholes 8, whereas in the presence of an excess of phenylacetylene the 1H-1,2-azaphospholes 9e - h, are formed selectively. A catalytic reaction course has been demonstrated for the cyclotrimerization of phenylacetylene and 2-butyne initiated by small amounts of TaSCl3. The syntheses of the vanadium(IV) complexes [tBuN = VCl2 · 2Py] and [tBuN = VCl2 · TMEDA] are also described starting from tBuN = VCl3 and phosphaalkene 12.