In quantum mechanics, we work with linear operators on Hilbert spaces $\mathscr{H}$.
Suppose I have two bounded ones, defined on the same space $A, B: \mathscr{H}\to\mathscr{H}$.
It seems to me there is an ambiguity on the way to deal with the derivative.
On one way, the operator $AB$ is usually interpreted as the composition $(A\circ B)f:=A(B(f))$ for every test function $f$ on $\mathscr{H}$.
If so, the derivative $D$ operator on $AB$ should act as follows
$$
D[AB]f = D[(A\circ B)f]= D[A(Bf)]D(B(f))
$$
On the other way, the following right examples treat $AB$ as if it were literally a product of operators instead of a composition. In other words, the preferred way to compute the derivative is the Leibniz rule
$$
D[AB]= AD[B]+BD[A]
$$
$1^{\rm{st}}$ example, by E. Pisanty:
The exponential of an operator $\hat A(t)$ does not obey the differential equation
$$ \frac{d}{ dt}e^{\hat A(t)} \stackrel{?}{=} \frac{d \hat{A}}{ dt} e^{\hat A(t)} $$
that one might naively hope to satisfy.
To see why this does not work, consider the series expansion of the exponential
\begin{align*}
\frac{d}{dt}e^{\hat A(t)}
& = \frac{d}{dt}\sum_{n=0}^\infty \frac{1}{n!} = \sum_{n=0}^\infty \frac{1}{n!} \frac{d}{dt} \hat A^n(t),
\end{align*}
When we apply the product rule, we get the individual derivatives of each of the operators in the product, at their place within the product
\begin{equation*}
\frac{d}{dt} \hat A^n(t)
=
\frac{d\hat A}{dt} \hat A^{n-1}(t)
+\hat A(t)\frac{d\hat A}{dt} \hat A^{n-2}(t)
+ \ \dots \
+\hat A^{n-2}(t)\frac{d\hat A}{dt} \hat A(t)
+\hat A^{n-1}(t)\frac{d\hat A}{dt}
\end{equation*}
This can simplify to just $n\frac{ d\hat A}{dt} \hat A^{n-1}(t)$, in which case $\frac{d}{dt}e^{\hat A(t)}
= \frac{d \hat A}{dt} \sum_{n=1}^\infty \frac{\hat A^{n-1}(t)}{(n-1)!} = \frac{d\hat A}{dt}e^{\hat{A}(t)}$, but only under the condition that $\hat A(t)$ commute with its derivative
$$ \left[\frac{ d\hat A}{ dt} , \hat A(t)\right] \stackrel{?}{=} 0 $$
In this case, $A^n$ is seen as a product of $A$ with itself $n$ times, instead of $A \circ A \circ \dots \circ A$ $n$ times.
$2^{\rm{nd}}$ example, by Wikipedia:
The expectation value of an observable $A$, which is a Hermitian linear operator, for a given Schrödinger state $\vert\psi(t)\rangle$, is given by
${\displaystyle \langle A\rangle _{t}=\langle \psi (t)|A|\psi (t)\rangle .}$
In the Schrödinger picture, the state $\vert\psi(t)\rangle$ at time $t$ is related to the state $\vert\psi(0)\rangle$ at time $0$ by a unitary time-evolution operator $U(t)$: ${\displaystyle |\psi (t)\rangle =U(t)|\psi (0)\rangle .}$
In the Heisenberg picture, all state vectors are considered to remain constant at their initial values $\vert \psi(t)\rangle$, whereas operators evolve with time according to
${\displaystyle A(t):=U^{\dagger }(t)AU(t)\,.}$
The Schrödinger equation for the time-evolution operator is
$${\displaystyle {\frac {d}{dt}}U(t)=-{\frac {iH}{\hbar }}U(t)}$$
where $H$ is the Hamiltonian and $\hbar$ is the reduced Planck constant.
It now follows that
$${\displaystyle {\begin{aligned}{\frac {d}{dt}}A(t)&={\frac {i}{\hbar }}U^{\dagger }(t)HAU(t)+U^{\dagger }(t)\left({\frac {\partial A}{\partial t}}\right)U(t)+{\frac {i}{\hbar }}U^{\dagger }(t)A(-H)U(t)\\&={\frac {i}{\hbar }}U^{\dagger }(t)HU(t)U^{\dagger }(t)AU(t)+U^{\dagger }(t)\left({\frac {\partial A}{\partial t}}\right)U(t)-{\frac {i}{\hbar }}U^{\dagger }(t)AU(t)U^{\dagger }(t)HU(t)\\&={\frac {i}{\hbar }}\left(H(t)A(t)-A(t)H(t)\right)+U^{\dagger }(t)\left({\frac {\partial A}{\partial t}}\right)U(t),\end{aligned}}}$$
where differentiation was carried out according to the product rule.
I really don't understand
Best Answer
On top of what @Raskolnikov pointed out in their comment, I believe there is another problem here: you seem to be mixing the derivative of a Hilbert space operator $A:\mathcal H\to\mathcal H$ and the derivative of objects $f:\mathbb R\to\mathcal B(\mathcal H)$ which map into the space of (bounded linear) Hilbert space operators.
${}^\text{footnote 1}$: If $\rho_0$ is a pure state $|\psi_0\rangle\langle\psi_0|$, then this reduces to the Schrödinger equation with solution $\psi(t)=e^{-\frac{i}\hbar tH}\psi_0$.