# Molecular Calcium Phosphides and Mixed Phosphide Hydrides

## TL;DR

This paper explores the synthesis and reactivity of calcium phosphide and phosphide hydride compounds using a specific calcium complex.

## Contribution

The study introduces new calcium phosphide derivatives and their unique bridging modes and reactivity patterns.

## Key findings

- The compound [(BDI)Ca-μ-PPh2]2 exhibits two distinct phosphide bridging modes in the solid state.
- Transmetalation with Hg(PR2)2 selectively replaces a single hydride function in [(BDI)Ca-μ-H]2.
- Heating [(BDI)Ca-μ-H]2 with P(SiMe3)3 produces a highly labile calcium phosphide derivative with unique bridging interactions.

## Abstract

[(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.