Is it permissible for an employee who stole from his company, as compensation for work-related exhaustion, to donate the stolen amount on behalf of the company's shareholders, knowing that he does not possess the full amount?

The money taken surreptitiously must be returned to its owners, for the Prophet, peace and blessings be upon him, said: "The hand is responsible for what it takes until it returns it." If one is unable to return all of it, then let him return what he can and strive to return the rest. In the event of complete despair of returning it, it is permissible to give it as charity on behalf of its owners. As for extra work, you have the right to demand payment for it or to refrain from doing it, and the company has no right to obligate you to it except with your consent. If you repent to Allah and return what you took, then your repentance is sound.