Dinuclear Ti(IV), Zr(IV), and Ce(IV) oxo and peroxo complexes containing the imidodiphosphinate ligand [N(i-Pr2PO)(2)](-) have been synthesized and structurally characterized. Treatment of Ti(O-i-Pr)(2)Cl-2 with KN(i-Pr2PO)(2) afforded the Ti(IV) di-mu-oxo complex [Ti{N(i-Pr2PO)(2)}(2)](2)(mu-O)(2) (1) that reacted with 35% H2O2 to give the peroxo complex Ti[N(i-Pr2PO)(2)](2)(eta(2)-O-2) (2). Treatment of HN(i-Pr2PO)(2) with Zr(O-t-Bu)(4) and Ce-2(O-i-Pr)(8)(i-PrOH)(2) afforded the di-mu-peroxo-bridged dimers [M{N(i-Pr2PO)(2)}(2)](2)(mu-O-2)(2) [M = Zr (3), Ce (4)] 4 was also obtained from the reaction of Ce[N(i-Pr2PO)(2)](3) with 35% H2O2. Treatment of (Et4N)(2)[CeCl6] with 3 equiv of KN(i-Pr2PO)(2) afforded Ce[N(i-Pr2PO)(2)](3)Cl (5). Reaction of (Et4N)(2)[CeCl6] with 2 equiv of KN(i-Pr2PO)(2) in acetonitrile, followed by treatment with Ag2O, afforded the mu-oxo-bridged complex [Ce{N(i-Pr2PO)(2)}Cl](2)[mu-N(i-Pr2PO)(2)](2)(mu-O) (6). 6 undergoes ligand redistribution in CH2Cl2 in air to give 5. The solid-state structures of [K-2{N(i-Pr2PO)(2)}(2)(H2O)(8)](n) and complexes 1-6 have been determined.