Catalytic applications of cluster compounds: Synthesis, characterization, catalytic activity and solution dynamics of heavy main group-transition metal carbonyl clusters

Abstract

Alkylation of the compounds (PPN) $\sb2\lbrack$EFe$\rm\sb3(CO)\sb9\rbrack$ (E = S, Se, Te) was performed using methyl triflate and methyl iodide. The S-cluster yielded the novel compound (PPN) (Fe$\sb3$(CO)$\sb9$SMe), whereas the Se and Te-cluster alkylated at the Fe$\sb3$-base yielding (PPN) (MeFe$\sb3$(CO)$\sb9$E). For comparison, the clusters (PPN) $\sb2\lbrack$HE$\rm\{Fe(CO)\sb4\}\sb3\rbrack$ (E = Sb, As) were alkylated as well. Reaction of the Sb-cluster with MeI yielded (PPN) (MeSb(I)$\rm\{Fe(CO)\sb4\}\rbrack,$ whereas the reaction with EtI yielded (PPN) $\sb2\lbrack$ISb$\rm\{Fe(CO)\sb4\}\sb3\rbrack$ and ethane. The possibility of a radical chain reaction for the latter was ruled out by performing the reaction in the presence of a radical scavenger as well as in the dark. The compounds $\rm\lbrack Cat\rbrack\sb{2-x}\lbrack H\sb{x}M\sb3(CO)\sb9E\rbrack\ (cat=Et\sb4N\sp+,\ PPN\sp+;$ x = 0, 1; M = Fe, Ru; E = S, Se, Te) were shown to mediate the catalytic formation of methyl formate from methanol and CO. The reaction is pseudo first order in catalyst and the initial rate is independent of the pressure. NaAsO$\sb2$ reacts with Mo(CO)$\sb6$ in refluxing methanol or ethanol to form $\rm\lbrack Et\sb4N\rbrack\sb2\lbrack(OC)\sb5MoAsMo\sb3(CO)\sb9(\mu\sb3$-$\rm OR)\sb3Mo(CO)\sb3\rbrack$ (R=Me, Et). The compounds are electron rich, and extended Huckel calculations have shown that the extra electron pair resides in an a$\sb2$ orbital, equally delocalized over three molybdenum atoms. A $\sp{205}$Tl NMR study has been conducted on the following compounds with Tl-transition metal bonds: $\rm Tl\{CO(CO)\sb4\}\sb3,\ \lbrack BnMe\sb3N\rbrack\sb3\lbrack Tl\{Fe(CO)\sb4\}\sb3\rbrack,\ Tl\{M(CO)\sb3Cp\}\sb3$ (M = Cr, Mo, W), TlFp$\sb3,$ Fp = CpFe(CO)$\rm\sb2),\ \lbrack PPN\rbrack\sb2\lbrack Tl\sb2Fe\sb6(CO)\sb{24}\rbrack,\ \lbrack Et\sb4N\rbrack\sb2\lbrack Tl\sb2Fe\sb4(CO)\sb{16}\rbrack,\ \lbrack Et\sb4N\rbrack\lbrack LTl\{Fe(CO)\sb4\}\sb2\rbrack$ (L = bipy, en, phen, tmeda, dien), and $\rm\lbrack Et\sb4N\rbrack\sb4\lbrack Tl\sb4Fe\sb8(CO)\sb{30}\rbrack,$ as well as $\rm TlCo(CO)\sb4.$ The possibility of formation of carbonylate anion adducts was also investigated by $\sp{205}$Tl NMR. This technique was used to probe the dynamic behavior of the Tl-metal cluster complexes in solution, and it was shown that most larger Tl-Fe clusters dissociate into simpler fragments in solution.