Addition of proton and boron trifluoride at terminal and bridging cyano-ligands in dinuclear manganese compounds

Abstract

The addition of HBF₄·Et₂O to dichloromethane solutions of [Mn₂H(CN)(CO)₅(dppm)₂] and of [Mn₂H(µ-η²-CN)(CO)₄(dppm)₂](dppm = Ph₂PCH₂PPh₂) leads to complexes containing terminal and η²-bridging HNC respectively. The terminal cyano-ligand protonates more readily and the product was isolated as [Mn₂H(CNH)(CO)₅(dppm)₂][BPh₄]. Protonation of the µ-η²-CN ligand (confirmed by ¹⁵N n.m.r. spectroscopy) lowers the rate of the ‘windshield-wiper’ oscillation of the ligand between the manganese atoms and apparently destabilises the compound since above –20 °C uptake of CO (scavenged from solution) gives [Mn₂H(CNH)(CO)₅(dppm)₂]⁺. The addition of BF₃ produces the corresponding CNBF₃ compounds. Spectroscopic analysis was assisted by ¹³C and ¹⁵N enrichment at the cyanide ligand.