Gradual Coordination and Reversible P-P Bond Activation of a P 3 -Unit with Transition Metal Carbonyls.

Coordination of a stereochemically defined P 3 -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 η 1 -, η 2 - to η 3 -coordination is observed where in the η 2 -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 P 3 -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).