  We investigate the half-filled Hubbard chain with additional nearest- and
next-nearest-neighbor spin exchange, J1 and J2, using bosonization and the
density-matrix renormalization group. For J2 = 0 we find a spin-density-wave
phase for all positive values of the Hubbard interaction U and the Heisenberg
exchange J1. A frustrating spin exchange J2 induces a bond-order-wave phase.
For some values of J1, J2 and U, we observe a spin-gapped metallic Luther-Emery
phase.
