Flexible Coordination of Carbodiphosphorane-based Pincer Ligands in Chromium(0) Carbonyl Complexes

A series of chromium(0) complexes was obtained by subsequent irradiation of [Cr(CO)6] in the presence of [(Ph2P-CH2-PPh2)CH]+. Depending on the reaction conditions and the duration of irradiation, it is possible to isolate complexes with different coordination modes of the potentially tridentate ligand. Initially, the coordination of the terminal PPh2-groups is observed in [(κ2P,P’-{Ph2P-CH2-PPh2}CH)Cr(CO)4]+ (2), followed by the formation of fac- and mer-[(κ3P,C,P’-{Ph2P-CH2-PPh2}CH)Cr(CO)3]+ (3). In the presence of base the neutral complex [(κ3P,C,P’-{Ph2P-CH2-PPh2}C)Cr(CO)3] (4) can be isolated, for which the net donor strength of the central CDP-group is compared by the C-O-stretching vibration. Finally, the utilization of reductants like potassium graphite leads the loss of hydrogen and generation of an anionic chromium(0) complex (5). Using quantum chemical methods the stability of possible isomers is explored.