Chemistry of CS2- and SCNPh-adducts of the pyramidal phosphinidene-bridged complex [Mo2Cp(μ–κ1:κ1,η5-PC5H4)(CO)2(η6-HMes*)(PMe3)]

Abstract

The title complex reacted readily with CS₂ and SCNPh to give the phosphinidene–cumulene adducts [Mo₂Cp{μ–κ¹_P:κ¹_S,η⁵-P(CS₂)C₅H₄}(CO)₂(η⁶-HMes*)(PMe₃)] and [Mo₂Cp{μ–κ¹_P:κ¹_S,η⁵-P(C(NPh)S)C₅H₄}(CO)₂(η⁶-HMes*)(PMe₃)] respectively (Mes* = 2,4,6-C₆H₂^tBu₃), as a result of the formal insertion of the CS bond of the heterocumulene into the metallocene Mo–P bond of the phosphinidene complex. The newly formed species bear a pyramidal P atom with a lone electron pair involved in fast inversion, and displayed strong nucleophilicity which enabled easy addition at the P site of carbon-based electrophiles and chalcogen atoms, while the uncoordinated S and N atoms were also competitive nucleophilic sites in these complexes. These air-sensitive materials readily added an O₂ molecule in the solid state, to give the corresponding derivatives [Mo₂Cp{μ–κ¹_O:κ¹_S,η⁵-OP(O)(C(X)S)C₅H₄}(CO)₂(η⁶-HMes*)(PMe₃)] (X = S, NPh), and the CS₂ adduct reacted selectively with S₈ in solution to give the sulfide derivative [Mo₂Cp{μ–κ¹_P:κ¹_S,η⁵-P(S)(CS₂)C₅H₄}(CO)₂(η⁶-HMes*)(PMe₃)], which was stabilized through methylation, thus yielding the cationic complex [Mo₂Cp{μ–κ¹_P:κ¹_S,η⁵-P(S)(C(SMe)S)C₅H₄}(CO)₂(η⁶-HMes*)(PMe₃)]⁺. The CS₂ adduct could be methylated selectively at either the P or CS sites, depending on the reagent used, to give respectively the cationic complexes [Mo₂Cp{μ–κ¹_P:κ¹_S,η⁵-PMe(CS₂)C₅H₄}(CO)₂(η⁶-HMes*)(PMe₃)]⁺ or [Mo₂Cp{μ–κ¹_P:κ¹_S,η⁵-P(C(SMe)S)C₅H₄}(CO)₂(η⁶-HMes*)(PMe₃)]⁺. Further methylation could be accomplished through reaction with [Me₃O]BF₄ to give the dipositive cation [Mo₂Cp{μ–κ¹_P:κ¹_S,η⁵-PMe(C(SMe)S)C₅H₄}(CO)₂(η⁶-HMes*)(PMe₃)]²⁺. In contrast, the SCNPh adduct was only methylated at the P site to yield the phosphanylthioformamidato complex [Mo₂Cp{μ–κ¹_P:κ¹_S,η⁵-PMe(C(NPh)S)C₅H₄}(CO)₂(η⁶-HMes*)(PMe₃)]⁺, but was readily protonated at the N site upon reaction with (NH₄)PF₆, to give the phosphanylthioformamide-like derivative [Mo₂Cp{μ–κ¹_P:κ¹_S,η⁵-P(C(NHPh)S)C₅H₄}(CO)₂(η⁶-HMes*)(PMe₃)]⁺. In the presence of Na(BAr′₄), this adduct was even able to displace chloride from the solvent (dichloromethane) to give the corresponding chloromethyl derivative [Mo₂Cp{μ–κ¹_P:κ¹_S,η⁵-P(CH₂Cl)(C(NPh)S)C₅H₄}(CO)₂(η⁶-HMes*)(PMe₃)]⁺. The structures of the new complexes were analyzed using spectroscopic, diffractometric and, in some cases, density functional theory methods.