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

Recently, alkyne complexes with terminal thiolate/amide substitution have been shown to act as ,-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)-η-,'-CBr(SR)]PF {Tp' = hydridotris(3,5-dimethylpyrazolyl)borate, R = benzyl (Bn), CHSiMe}, which are obtained by applying free bromo alkynes. Subsequent nucleophilic substitution of the bromine substituent led to unsymmetrical substituted alkyne complexes [Tp'W(CO)-η-,'-C(SR)(NHBn)]PF with , 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)-η-,'-C(SR)(NBn)] or a zwitterionic PF adduct. Reductive removal of the benzyl protective group was primarily observed at the imine substituent, causing a side-on/end-on rearrangement to the cyanide substituted carbene complex K[Tp'W(CO)-η-C(CN)(SBn)]. The reversibility of the rearrangement was proven with HBF/EtO, because double protonation led to [Tp'W(CO)-η-,'-C(SR)(NH)]BF exhibiting an unprecedented primary amine substitution at the coordinated alkyne. The reaction sequence starting with the thiol SCHSiMe derivative leading to the desired [Tp'W(CO)-η-,'-CS(NHBn)] with a terminal S atom as well as the bonding situation in those complexes is discussed based on full spectroscopic characterization including X-ray structure analyses. Finally, a trinuclear complex assembled by homoleptic coordination of Pd(II) by two anionic ,-chelates [Tp'W(CO)-η-,'-CS(NBn)] is presented.