AbstractSyntheses and Properties of Di‐tert‐butylphosphides [M(PtBu2)2]2 (M = Zn, Hg) and [Cu(PtBu2)]4The phosphides [M(PtBu2)2]2 (M = Zn, Hg) and [Cu(PtBu2)]4 are accessible from reaction of LiPtBu2 with ZnI2, HgCl2 and CuCl, respectively. [M(PtBu2)2]2 (M = Zn, Hg) are dimers in the solid state. X‐ray structural analyses of these phosphides reveal that [M(PtBu2)2]2 (M = Zn, Hg) contain four‐membered M2P2‐rings whereas [Cu(PtBu2)]4 features a planar eight‐membered Cu4P4‐ring. Degradation reaction of LiPtBu2(BH3) in the presence of HgCl2 results in the dimeric phosphanylborane BH3 adduct [tBu2PBH2(BH3)]2. X‐ray quality crystals of [tBu2PBH2(BH3)]2 (monoclinic, P21/n) are obtained from a pentane solution at 6 °C. According to the result of the X‐ray structural analysis, the O2‐oxidation product of [Hg(PtBu2)2]2, [Hg{OP(O)(tBu)OPtBu2}(μ‐OPtBu)]2, features in the solid state structure two five‐membered HgP2O2‐rings and a six‐membered Hg2P2O2‐ring. Herein the spiro‐connected Hg atoms are member of one five‐membered and of the six‐membered ring.