Redox-induced κ ² –κ ³ isomerisation in rhodium hydrotris(3,5-dimethylpyrazolyl)borate chemistry: the stabilisation of square-pyramidal rhodium( II )

One-electron oxidation of the square-planar, 16-electron complex [Rh(CO)(PPh3)(κ2-Tp′)] with [FeCp2][PF6] gives the square-pyramidal RhII complex [Rh(CO)(PPh3)(κ3-Tp′)][PF6] in which the third pyrazolyl group of Tp′ is N-bound in the axial position by a three-electron two-centre bond (Rh–Naxial 0.13 Å longer than Rh–Nbasal).