= Solution
The trityl cation acts as an <electrophile> and removes one <metal>-bound methyl by <methyl abstraction>. The balanced conversion is
$$
\mathrm{Cp_2ZrMe_2}+[\mathrm{Ph_3C}]^+[\mathrm{B(C_6F_5)_4}]^-
\longrightarrow[\mathrm{Cp_2ZrMe}]^+[\mathrm{B(C_6F_5)_4}]^-+\mathrm{Ph_3CMe}.
$$
Thus \b[$C=[\mathrm{Cp_2ZrMe}]^+[\mathrm{B(C_6F_5)_4}]^-$ and $D=\mathrm{Ph_3CMe}$], 1,1,1-triphenylethane. Transfer is formally of $\mathrm{Me^-}$ to <carbon>, not transfer of a <hydride> or a methyl radical. <zirconium> remains Zr(IV), $d^0$. Ionic <electron counting> changes from $12+4=16$ in the dimethyl to $12+2=14$ at the cation, creating an accessible coordination site. The borate is a <weakly coordinating anion>, although ion pairing can still occur in solution.
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