SYNTHESIS AND CHARACTERIZATION OF TUNGSTEN ALKENYL-CARBYNE AND ALKENYL-KETENYL COMPLEXES CONTAINING DITHIO LIGANDS - X-RAY CRYSTAL-STRUCTURE AND MO ANALYSES OF )(KAPPA(3)(S,C,S)-S2CPCY3)W-CCH=C(CH2)(3)CH2][BF4]

The reaction of [(dppe)(CO)(2)(MeCN)W=CCH=CCH2(CH2)(n)CH2CH2][BF4] (dp pe = 1,2-bis(diphenylphosphino)ethane; n = 1 (la), 4 (Ib)) with S2CPCy 3 in methanol for 10 min affords 2){kappa(S)-S2CPCy3}W=CCH=CCH2(CH2)(n )CH2CH2][BF4] (n = 1(2a), 4 (2b)). Similarly, the complexes (2){kappa( S)-S2P(OEt)(2)}W=CCH=CCH2(CH2)(n)CH2CH2] (n = 1(3a), 4 (3b)) have been prepared by the reaction with [NBu4][S2P(OEt)(2)]. When la and Ib are eacted with S2CPCy3 in methanol for 24 h, the complexes [(dppe){kappa (3)(S,C,S)-S2CPCy3} W=CCH=CCH2(CH2)(n)CH2CH2][BF4] (n = 1 (4a), 4 (4b) ) are formed. Moreover, when la and Ib are reacted with NaS2CNR2 (n = Me, Et), the ketenyl complexes [(dppe)(CO){kappa(2)(S,S)S2CNR2)W{kappa (2)(C, C)=C-(C=O)CH=CCH2(CH2)(n)CH2CH2}] are formed (R = Me, n = 1 (5a ), 4 (5b); R = Et, n = 1 (5c), 4 (5d)) subsequent to the coupling betw een the carbyne group and carbon monoxide. IR and H-1, P-31, and C-13 NMR data are reported for all of the species. The molecular structure of compound 4a, determined by X-ray diffraction methods, shows that th e S2CPCy3 ligand is bound to the metal in a pseudoallylic kappa(3)(S,C ,S) fashion. The metal coordination is completed by the W=C triple bon d of the alkenyl-carbyne group and by two additional W-P bonds. Since the metal center in 4a is formally a deficient 16-electron species and since the synthetic route has clearly indicated that an additional CO ligand is preferentially rejected by the metal, a reasonable interpre tation of the bonding has been sought by means of EHMO calculations. N ot only has the coexistence between the dithiocarboxylate and the carb yne ligands been elucidated, but also the strength of the W-S bonds is accounted for in comparison with the weaker W-S bonds observed in oth er saturated W complexes containing a kappa(3)(S,C,S) dithio ligand. F inally, qualitative theoretical considerations are presented for the d ifferent behavior of the dithiocarbamate ligand.