Synthesis and characterization of tungsten alkenyl-carbyne and alkenyl-ketenyl complexes containing dithio ligands. X-ray crystal structure and MO analyses of [(dppe){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] (dppe = 1,2-bis(diphenylphosphino)ethane; n = 1 (la), 4 (Ib)) with S2CPCy3 in methanol for 10 min affords [(dppe)(CO)(2){kappa(S)-S2CPCy3}W=CCH=CCH2(CH2)(n)CH2CH2][BF4] (n = 1(2a), 4 (2b)). Similarly, the complexes [(dppe)(CO)(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 between 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 the 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 bond 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 interpretation of the bonding has been sought by means of EHMO calculations. Not only has the coexistence between the dithiocarboxylate and the carbyne 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 other saturated W complexes containing a kappa(3)(S,C,S) dithio ligand. Finally, qualitative theoretical considerations are presented for the different behavior of the dithiocarbamate ligand.