(Dialkylamino)dichloroboranes R2NBCl2 react with N,N'-bis(trimethylsilyl)sulfur diimide to give a novel class of compds., the eight-membered rings 3,7-bis(dialkylamino)-3H,7H-1l4,5l4,2,4,6,8,3,7-dithiatetrazadiborocines I [R = Pr (1a), CHMe2 (1b), and Bu (1c)]. The derivs. I have been synthesized and characterized. The x-ray structure anal. of 1b shows the mol. to have a boat-like configuration with two N:S:N functions connected via the BNR2 groups. Although the B atoms are linked to three N atoms, only the exocyclic nitrogen is engaged in p bond interactions with the boron. 1B reacts with W(CO)5(THF) to form a dinuclear complex which is also investigated by means of an x-ray structure anal. One W(CO)5 fragment is coordinated to a nitrogen atom of one N:S:N unit, whereas another W(CO)5 group is linked to the S atom of the second SN2 function. However, the original sulfur diimide has changed into a sulfur diamide group HNSNH. A similar change of a N:S:N unit happens on treatment of 1b with Cp(CO)3WH leading to II. As the X-ray structure anal. shows, in II again one sulfur diimide group retains its original character. The second SN2 unit has turned into a sulfur amide function, where one N atom binds the H atom of Cp(CO)3WH, the other one is linked to one of the CO ligands to form a carbonyl bridge between N and W. Among a series of other complexes only TiCl4 has addnl. been found to react with 1b to yield 1b.2TiCl4, the structure of which is still unknown.