Super-flexible coordination: the metal matters

Herein, we report a unique tripodal system, a tin-chelated trisphosphine oxide scorpionate ligand that coordinates to hard metal atoms through the oxygen atoms and, upon full skeletal rearrangement, to soft metals through the phosphorus atoms. The reactions of the previously reported potassium salt [κ$^3$O-Sn(P(O)Ph$_2$)$_3$K] with rare-earth complexes based on the cyclooctatetraenediide ligand yielded the compounds [κ$^3$O-Sn(P(O)Ph$_2$)$_3$Ln$^{III}$(η$^8$-Cot)] (Ln = Y, Ce, Tb, Er; Cot = C$_8$H$_8$$^{2−}$) and [κ$^3$O-Sn(P(O)Ph$_2$)$_3$Ln$^{III}$(η$^8$-Cot$^{TIPS}$)] (Ln = Y, Dy, Er; Cot$^{TIPS}$ = 1,4-(iPr$_3$Si)$_2$C$_8$H$_6$$^{2−}$), in which the trivalent lanthanide ions are coordinated by the oxygen atoms, analogous to the potassium ions in the starting material. The reactions of the potassium salt and transition metal chlorides led to the isolation of the compounds [κ$^3$P-Sn(P(O)Ph$_2$)$_3$MCl] (M = Co, Fe). Interestingly, an in situ ligand rearrangement was observed for the transition metals, whereby the arrangement of the P(O)Ph$_2$ groups inverted. This results in a coordination of the oxygen atoms to the tin atom, while the phosphorus atoms bind to the d-metal ions. ... mehrQuantum chemical calculations were performed to rationalize this observation.