Oxidation Products of
Calcium and Strontium Bis(diphenylphosphanide)
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Abstract
The tetrahydrofuran adducts [(thf)<sub>4</sub>M(PPh<sub>2</sub>)<sub>2</sub>] (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 MI<sub>2</sub> allow the synthesis
of [(thf)<sub>4</sub>Ca(OPPh<sub>2</sub>)<sub>2</sub>] (<b>1</b>), [(dmso)<sub>2</sub>Ca(O<sub>2</sub>PPh<sub>2</sub>)<sub>2</sub>] (<b>2</b>), [(thf)<sub>3</sub>Ca(O<sub>2</sub>PPh<sub>2</sub>)I]<sub>2</sub> (<b>3</b>), [(thf)<sub>3</sub>Ca(S<sub>2</sub>PPh<sub>2</sub>)<sub>2</sub>] (<b>4</b>), [(thf)<sub>2</sub>Ca(Se<sub>2</sub>PPh<sub>2</sub>)<sub>2</sub>] (<b>5</b>),
[(thf)<sub>3</sub>Sr(S<sub>2</sub>PPh<sub>2</sub>)<sub>2</sub>] (<b>6</b>), [(thf)<sub>3</sub>Sr(Se<sub>2</sub>PPh<sub>2</sub>)<sub>2</sub>] (<b>7</b>), and [(thf)<sub>2</sub>Ca(O<sub>2</sub>PPh<sub>2</sub>)(S<sub>2</sub>PPh<sub>2</sub>)]<sub>2</sub> (<b>8</b>), respectively. The diphenylphosphinite anion in <b>1</b> 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 <b>2</b>. The chain structure can also be
cut into smaller units by ligands which avoid bridging positions such
as iodide and diphenyldithiophosphinate (<b>3</b> and <b>8</b>, respectively). In general, diphenyldithio- and -diselenophosphinate
anions act as terminal ligands and allow the isolation of mononuclear
complexes <b>4</b> to <b>7</b>. In these molecules the
alkaline earth metals show coordination numbers of six (<b>5</b>) and seven (<b>4</b>, <b>6</b>, and <b>7</b>)
