Is there any ethical issue which prevents me from paying high quality authors monetary compensation, to agree to write papers with me?
I think the other answers are way too nice. As for myself, I have never heard of such a insulting / distorted idea about what a PHD is. Do you want to buy yourself a PHD? There are countless diploma mills for that, so you could hang a useless paper on your wall to claim you have a PHD without doing all the necessary work / research yourself. Do you want to buy yourself an academic career by hiring established professors to write papers for and with you? That is even more insulting. If that was the case, every rich kid could tell his / her dad. "I want a PHD for Christmas. Buy me some high impact authors to write papers with me. Pleaaase..".

It does not work that way. And the fact that you are at the beginning of your PHD and you are even considering this, is even more infuriating for people who have busted their behinds to get a PHD (and some of the people in Academia SE still do to this day). Reconsider why you want a PHD and what you want a PHD for. I am mostly sure you want it for the all the wrong reasons and not because you actually want to do research. In that case, you should probably spare yourself the agony, because without a passion for research your PHD road will be a long, rocky one.

UPDATE: In retrospect, the tone of my answer is pretty hostile. Still, the upvotes showed that my initial reaction to the OP's question also expressed an important part of the Academia SE community. In this sense, my answer might still be useful if it makes the OP reconsider his "thought" of hiring "high-impact" authors to write papers with him, since such an action will probably cause much more damage to him than my "harsh" words. 

Moreover, since we had a previous question about "Is it ethical to hire a programmer for ... my CS PHD" and now "Is it ethical to hire high-impact authors ... to write papers with me", I sincerely hope that in the future we do not get any other questions like "Is it ethical to hire a professor to write my PHD thesis if I still do the typesetting in Latex and all spell checking" or "Is it ethical to hire a professor to do my PHD defence, since I will still bring the pizza and the drinks".