= Solution
The neutral product is \b[cis-$[\mathrm{NiCl_2(dppe)}]$], and the displaced material is \b[six <waters> per <nickel>]:
$$
\mathrm{NiCl_2\cdot6H_2O+dppe\longrightarrow[NiCl_2(dppe)]+6H_2O}.
$$
The two <phosphorus> donors of <dppe> chelate the same <metal>, forcing adjacent donor positions. The <diamagnetism> identifies a square-planar, paired $d^8$ Ni(II) centre rather than a tetrahedral high-spin $d^8$ centre. Its valence count is $8+4_{\rm P,P}+4_{\rm Cl,Cl}=16$ <electrons>. The reaction is <ligand substitution>, not reduction of Ni(II).
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