Oxidation Products of Calcium and Strontium Bis(diphenylphosphanide)

The tetrahydrofuran adducts [(thf)4M­(PPh2)2] (M = Ca, Sr) are air sensitive and can easily be oxidized by chalcogens. Metalation of diphenylphosphane oxide, diphenylphosphinic acid, and diphenyldithiophosphinic acid as well as salt metathetical approaches of the potassium salts with MI2 allow the synthesis of [(thf)4Ca­(OPPh2)2] (1), [(dmso)2Ca­(O2PPh2)2] (2), [(thf)3Ca­(O2PPh2)­I]2 (3), [(thf)3Ca­(S2PPh2)2] (4), [(thf)2Ca­(Se2PPh2)2] (5), [(thf)3Sr­(S2PPh2)2] (6), [(thf)3Sr­(Se2PPh2)2] (7), and [(thf)2Ca­(O2PPh2)­(S2PPh2)]2 (8), respectively. The diphenylphosphinite anion in 1 contains a phosphorus atom in a trigonal pyramidal environment and binds terminally via the oxygen atom to calcium. The diphenylphosphinate anions act as bridging ligands leading to polymeric structures of calcium bis­(diphenylphosphinates). Therefore strong Lewis bases such as dimethylsulfoxide (dmso) are required to recrystallize this complex yielding chain-like 2. The chain structure can also be cut into smaller units by ligands which avoid bridging positions such as iodide and diphenyldithiophosphinate (3 and 8, respectively). In general, diphenyldithio- and -diselenophosphinate anions act as terminal ligands and allow the isolation of mononuclear complexes 4 to 7. In these molecules the alkaline earth metals show coordination numbers of six (5) and seven (4, 6, and 7).