Gradual Coordination and Reversible P–P Bond Activation of a P3-Unit with Transition Metal Carbony

Coordination of a stereochemically defined P3-chain to a series of transition metal carbonyls [M(CO)x]z− (M = Mn (x = 5, z = 1), Fe (x = 4, z = 2) or Co (x = 4, z = 1)) is explored using a 3]ferrocenophane scaffold. A gradual transition from 𝜼1-, 𝜼2- to 𝜼3-coordination is observed where in the 𝜼2-mode the terminal positions of the phosphorus chain are bridged. With an excess of cobalt carbonyl successive P–P bond activation and gradual separation of the central phosphorus atoms from the phosphorus chain has been observed. This process is reversible and with suitable reagents such as methyl lithium, the P3-unit is regenerated in stereospecific manner. The bonding situation and steps of the gradual P–P bond activation are investigated by DFT calculations as well as experimental methods (e.g., NMR spectroscopy, X-ray crystallography).