Polyhydrides, phosphine-stabilized

Polyhydrides are complexes such as FeH4(PR3)3, with a H M ratio exceeding 3. Hydrogen is not as electronegative as carbon, and so the metal in a polyhydride is not as oxidized as in a polyalkyl. Polyhydrides therefore retain more of the properties of low-valent complexes than do polyalkyls. For example, many of them are 18e, and relatively soft ligands (in the vast majority of cases a phosphine or a cyclopentadienyl) are required to stabilize them. Rare examples of N-donor-stabilized polyhydrides are [TpReH ] and [BpReH7] (Tp = tris-pyrazolylborate (5J7) Bp = bis-pyrazolylmethane). ... 

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