TEMPO coordination and reactivity in group 6; pseudo-pentagonal planar (η-TEMPO)CrX (X = Cl, TEMPO)

The exposure of CrCl 2 (THF) 2 to 1 equiv. of TEMPO and 1 equiv. [TEMPO]Na afforded (η 2 -O,N-TEMPO) 2 CrCl (1, 67%); addition of [TEMPO]Na to 1 yielded (η 2 -O,N-TEMPO) 2 Cr(TEMPO) ( 2 ). Both 1 and 2 exhibit pseudo-pentagonal planar (PPP) geometry, instead of myriad alternatives. Calculations and spectral studies suggest the solid-state geometry persists in solution. The quest for homoleptic Cr TEMPO species has led to the preparation of pseudo-pentagonal planar (η 2 -TEMPO) 2 CrX (X = Cl, TEMPO), with perturbations from TEMPO(−) lone pairs at roughly 0°, 90°, 135°, 225° and 270°.