Exchange interactions between spin 1 2 sites in piperazinium hexachlorodicuprate produce a frustrated bilayer antiferromagnet with a bond ordered singlet ground state. We report the field temperature phase diagram of this system as determined via high field susceptibility and neutron scattering experiments. There are two quantum critical points Hc1 7.5 T separates the singlet phase from a three dimensional, antiferromagnetically ordered state while Hc2 37 T marks the onset of a fully spin polarized state. The long range ordered phase is embedded in a gapless quasi two dimensional paramagnetic regime with short range transverse spin correlations. Close to the low field quantum critical point, a reentrant phase transition between long range order and the singlet phase indicates that weak interactions with lattice or nuclear spin degrees of freedom become important