[2+2]-Cycloaddukte PH-funktioneller Phosphenium-Komplexe mit Alkylisothiocyanaten: Darstellung von C5R5(OC)2M–P(H)(t-Bu)–C(NR′)–S (R=H, Me; M=Mo, W; R′=Me, Et, t-Bu) und Reaktion unter Beanspruchung der PH-Funktion: Phosphenium-Übergangsmetallkomplexe, 3

The phosphenium complex C5Me5(OC)2WP(H)t-Bu (2c) reacts with the alkylisothiocyanates RNCS (R=Me, Et, t-Bu) (3a–c) via [2+2]-cycloaddition to form the PH-functionalized phosphametallacycles C5Me5(OC)2 (R=Me, Et, t-Bu) (4a–c). In the case of the Cp-substituted phosphenium complexes Cp(OC)2MP(H)t-Bu (M=Mo, W) (2a,b) additional insertion of the isothiocyanate into the PH bond occurs yielding the cycloadducts Cp(OC)2 (M=Mo, W; R=Me, Et, t-Bu) (5a–c) with high diastereoselectivity. The analogous C5Me5-substituted compounds C5Me5(OC)2 (R=Me, t-Bu) (5d,e) are only obtained by treatment of 2c with a large excess of 3a,c. Insertion is realized as a separate step for 4c and EtNCS (3b) leading to the formation of isomeric C5Me5(OC)2 [R1=Et, R2=t-Bu (6a); R1=t-Bu, R2=Et (6b)]. The structure of 5d is characterized by X-ray diffraction analysis.