Gradual Coordination and Reversible P–P Bond Activation of a P₃‐Unit with Transition Metal Carbonyls

Abstract 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).