The structure of [Co3((eta)^5-C5H5)3((mu)3-S)((mu)3-CSMe)]^+, and the reactions of the metal cluster cations [{Co((eta)^5-C5H5)}2{Fe(CO)2(PPh3)}((mu)3-S)((mu)3-CSR)]^+ and [{Co((eta)^5-C5H5)}3((mu)3-S)((mu)3-CSR)]^+ (R=Me, Et) with nucleophiles

Co3((eta)^5-C5H5)3((mu)3-S)((mu)3-CSR)][I], [5]I (R=Me), [6]I (R=Et) are not dealkylated by treatment with [PhCH2NMe3]OH, NaOH, NaOMe or NaOEt in either CH2Cl2 or MeOH–EtOH solutions. [{Co((eta)^5-C5H5)}2{Fe(CO)2 (PPh3)}((mu)3-S)((mu)3-CSMe)][X], [3]X (X-=I- or [SO3CF3]-), is similarly not dealkylated but instead undergoes nucleophilic attack at coordinated CO to give zwitterionic [{Co((eta)^5-C5H5)}2{Fe(CO)(CONu)(PPh3)} ((mu)3-S)((mu)3-CSMe)] derivatives (7) (Nu^-=(a) OH^-, (b) MeO^-, or (c) EtO^-). Although they may be identified unambiguously by spectroscopy, they could not be isolated in the pure state as their formation is reversible and made completely so by addition of aqueous acids. [{Co((eta)^5-C5H5)}2{Fe(CO)2(PPh3)}((mu)3-S) ((mu)3-CSEt)][X], [4]X, undergoes partial dealkylation (ca. 20%) to [{Co((eta)^5-C5H5)}2{Fe(CO)2(PPh3)}((mu)3 -S)((mu)3-CS)] (1), but the principal reaction is CO attack to give [{Co((eta)^5-C5H5)}2{Fe(CO)(CONu)(PPh3)} ((mu)3-S)((mu)3-CSEt)] derivatives (8) (Nu^-=(a) OH^-, (b) MeO^-, or (c) EtO^-). The structure of [Co3((eta)5 -C5H5)3((mu)3-S)((mu)3-CSMe)][BPh4] has been determined by X-ray diffraction. It is concluded that the conversion of (mu)3-CS in [Co3((eta)^5-C5H5)3((mu)3-S)((mu)3-CS)] (2) to (mu)3-CSMe in [5]^+ greatly modifies the bonding between Co3S and CS fragments. The Co3 triangle is distorted from equilateral to isosceles and the C–S bond is lengthened to 1.714(5)/1.719(5) (angstrom) (c.f. 1.638(3) (angstrom) in 1 and 1.728(7) (angstrom) in [3a]+). This suggests that the positive charge is not localised on the (mu)3-CSMe moiety but has been delocalised into the cluster by backbonding which, consequently, renders the Me group less susceptible to nucleophilic attack. The (mu)3-CSEt ligand is more susceptible to nucleophilic attack, perhaps due to the possibility of elimination-type reaction pathways.