Molecular Calcium Phosphides and Mixed Phosphide Hydrides

[(BDI)CaH]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)CaPPh2]2, which displays two differentiated (μ2-Ca-P-Ca versus Ca-P-C-6H5···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 [(BDI)CaH(THF)]2. [(BDI)CaH]2 reacts incompletely with less acidic or more sterically encumbered phosphines. Selective replacement of a single hydride function and the generation of [(BDI)Ca(H)(PR2)]2 was, however, achieved by transmetallation with Hg(PR2)2 (R = t-Bu and SiMe3). While the remaining hydride in these compounds was resistant to further reactions, a H2-Zn2-bridged calcium zincate was identified as a minor product from treatment of [(BDI)Ca(H)(Pt-Bu2)]2 with ZnMe2. In contrast, heating (40 °C) of [(BDI)CaH]2 with two equivalents of P(SiMe3)3 induced Me3SiH elimination to provide [(BDI)CaP(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 Caʹ···H3CSi interactions.