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

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).