The chemistry of heterobimetallic sulfide clusters relevant to hydrodesulfurization and the structures of methylcyclopentadiene tantalum thiophenyl and cyclopentadiene niobium chloride(tetra carbon tetraphenyl).

Abstract

The reactivity of the cluster $\rm Cp\sp\prime\sb2Mo\sb2Co\sb2S\sb3(CO)\sb4$ (1) ($\rm Cp\sp\prime=C\sb5H\sb4CH\sb3$) was studied to gain an understanding of the catalyzed hydrodesulfurization process. Reaction with alkyl thiols was shown by NMR to proceed quantitatively to the cluster $\rm Cp\sp\prime\sb2Mo\sb2Co\sb2S\sb4(CO)\sb2$ (2) and the alkane, with no products of $\beta$-elimination. Carbonyl sulfide, isothiocyanates and episulfides also give cluster 2, along with CO, isocyanide and the alkene, respectively. The isothiocyanate products react further to give isocyanide substituted clusters of 2 (confirmed by independent syntheses from 2). Carbonyl substitution reactions of 1 were shown to occur by an associative mechanism with nucleophilic attack at a Co atom and cleavage of a Co-S bond. The trimethylphosphine intermediate, $\rm Cp\sp\prime\sb2Mo\sb2Co\sb2S\sb3(CO)\sb4(PMe\sb3$), was characterized by an X-ray structure determination. Carbonyl substitution reactions of 2 are also associative, but may go via Co-Co bond breaking. The phenylphosphine monoadduct of 1, in the presence of excess phenylphosphine at 80$\sp\circ$C, forms the phosphinidene cluster $\rm Cp\sp\prime\sb2Mo\sb2Co\sb2S\sb3(\mu\sb3$-PPh)(CO)$\sb2$, confirmed by an X-ray structure determination, and its monophenylphosphine adduct. The corresponding reaction with diphenylphosphine gives the cis and trans diadducts at 80$\sp\circ$C, but does not give a clean phosphinidene abstraction reaction (at 110$\sp\circ$C), however, some benzene is observed to form. The diphenylphosphinoethane (DPPE) adduct of 1, $\rm Cp\sp\prime\sb2Mo\sb2Co\sb2S\sb3(CO)\sb2$(DPPE), was also found to desulfurize thiols, and to form a phosphinidene cluster by reaction with phenylphosphine. Mechanisms are proposed for the phosphinidene abstraction and desulfurization reactions. An X-ray structure determination of $\rm Cp\sp\prime Ta(SPh)\sb4$, prepared from $\rm Cp\sp\prime TaCl\sb4$ and NaSPh in THF at low temperature, showed it to have a distorted four-legged piano stool structure. EHMO calculations on CpTa(SH)$\sb4$ confirmed the distortion to be largely electronic in nature. An X-ray structure determination of CpNbCl$\sb2(\eta\sp4$-$\rm C\sb4Ph\sb4$) (3), prepared in one reaction of CpNbCl$\sb4$ with PhCCPh and Al/HgCl$\sb2$, showed it to have a bent-sandwich metallocene structure. A comparison with CpMoCl$\sb2(\eta\sp4$-$\rm C\sb4Ph\sb4$) (4), suggests that the LUMO of 3 and HOMO of 4 is located in the MCl$\sb2$ plane, similar to that found for Cp$\sb2$ML$\sb2$ compounds.