AbstractIn order to study the properties of sulfur coordinated transition metal centers. [MoCl2dttd] (dttd2 = 2,3,8,9-dibenzo-1,4.7,10-tetrathiadecane(2-)) was reacted with NO in the presence of Zn. [Mo(NO)2dttd] was obtained whose X-ray structure analysis shows that Mo is coordinated pseudo-octahedrally by two trans thiolato S, two cis thioether S as well as two cis N atoms of nearly linear MoNO groups. With respect to its low v(NO) frequencies (1760/1665 cm -1) and quite normal bond lengths as well as angles [Mo(NO)2dttd] shows unexpectedly facile and rapid reactions with nucleophiles; with two equivalents of PR3 (PMe3, PEt3, PMePh2, PEtPh2, PPh3) it yields the corresponding phosphiniminato complexes [Mo(NO)(NPR3)dttd] and free phosphinoxides OPR3, respectively. Reaction mechanisms as well as the bonding situation in the [Mo(NPR3)] entity are discussed; on the basis of 95Mo and 14N NMR it is concluded that the conversion of NO into NPR3 ligands includes a reduction of N(+2) to N(-3) as well as an oxidation of (formal) Mo(+2) to Mo(+3). With H2O the [Mo(NO)(NPR3)dttd] complexes hydrolyze with loss of the NPR3 ligands and formation of binuclear [Mo(NO)dttd]2. The ease of hydrolysis depends on the substituents R: In THF [Mo(NO)(NPMe3)dttd] hydrolyzes at 20 °C within a few minutes, [Mo(NO)(NPPh3)dttd], however, needs the addition of cone. HCl.