Pathways to Polynuclear Complexes with α-S,N-Substituted Alkynes as Bridging Ligands

Recently, alkyne complexes with terminal thiolate/amide substitution have been shown to act as S,N-chelate ligands in dinuclear complexes. In this study, the detailed synthesis and reactivity of W(II) alkyne complexes bearing different amino groups in the α-position are reported. The preparative scheme starts with cationic alkyne complexes [Tp′W(CO)2-η2-C,C′-C2Br(SR)]PF6 {Tp′ = hydridotris(3,5-dimethylpyrazolyl)borate, R = benzyl (Bn), C2H4SiMe3}, which are obtained by applying free bromo alkynes. Subsequent nucleophilic substitution of the bromine substituent led to unsymmetrical substituted alkyne complexes [Tp′W(CO)2-η2-C,C′-C2(SR)(NHBn)]PF6 with S,N substitution in the α position of the coordinated alkyne. Depending on the base used, deprotonation of the secondary amine resulted in either neutral iminoketenyl complexes [Tp′W(CO)2-η2-C,C′-C2(SR)(NBn)] or a zwitterionic PF5 adduct. Reductive removal of the benzyl protective group was primarily observed at the imine substituent, causing a side-on/end-on ...