Molecular Calcium Phosphides and Mixed Phosphide Hydrides

[(BDI)Ca-μ-H]₂ (BDI = HC{(Me)CNDipp}₂, Dipp = 2,6-i-Pr₂C₆H₃), has been employed to synthesize diorganophosphido- and bis(trimethylsilyl)phosphidocalcium derivatives. Reaction with two equivalents of Ph₂PH yielded [(BDI)Ca-μ-PPh₂]₂, which displays two differentiated (μ₂-Ca-P-Ca versus Ca-P-C₆H₅···Ca) phosphide bridging modes in the solid state. Although this compound may be employed to synthesize the calcium phosphaguanidinate, [(BDI)Ca{CyNC(PPh₂)NCy}], by reaction with CyN═C=NCy and is a likely intermediate for the catalytic addition of Ph₂PH to unsaturated substrates, any enhancement in reactivity is only marginal in comparison to previous reports of previous calcium precatalysts. [(BDI)Ca-μ-H]₂ reacts incompletely with less acidic or more sterically encumbered phosphines. Selective replacement of a single hydride function and the generation of [(BDI)Ca(μ₂-H)(μ₂-PR₂)]₂ was, however, achieved by transmetalation with Hg(PR₂)₂ (R = t-Bu and SiMe₃). While the remaining hydride in these compounds was resistant to further reactions, a μ₂-H₂-Zn₂-bridged calcium zincate was identified as a minor product from treatment of [(BDI)Ca(μ₂-H)(μ₂-Pt-Bu₂)]₂ with ZnMe₂. In contrast, heating (40 °C) of [(BDI)Ca-μ-H]₂ with two equivalents of P(SiMe₃)₃ induced Me₃SiH elimination to provide [(BDI)Ca-μ-P(SiMe₃)₂]₂. This highly labile compound also presents two differentiated modes of phosphide bridging, via direct engagement of a single phosphide center with both calcium atoms as well as a combination of terminal Ca-P and Ca'···H₃CSi interactions.