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.