Global Tax 50 2015: Marissa Mayer

Marissa Mayer is a new entry this year

$19 billion. That is what one analyst estimated could have been the tax cost of Yahoo's spin-off of its $31 billion stake in Alibaba, the Chinese e-commerce company. No doubt Marissa Mayer, the chief executive officer of Yahoo, would prefer if she did not grab so many headlines. It would allow her to get on with the job of securing the future of one of the pioneering companies of the early internet. But she is in this list because, for what seemed like the whole of 2015, analysts and the business media discussed her plans for the Alibaba transaction. When the Internal Revenue Service declined to state categorically that it would treat the transaction as tax-free, it was back to the drawing board for Mayer and her tax advisers, believed to be Skadden Arps Slate Meagher & Flom, and they came up with a structure called a reverse spin, which will see the company's core internet business, including a large stake in Yahoo Japan being spun off and the Alibaba stake retained. The transaction is expected to take most of 2016 to complete.

The now-shelved Alibaba deal was another example of the increasing trend for tax to be front-and-centre of the biggest corporate transactions. For example, Pfizer's takeover of Allergan hinged on how to achieve the tax inversion that would allow the new company to become tax resident in Ireland, where the corporate tax rate is 12.5%, rather than the US, where it is more than 20 percentage points higher. And GE said tax was a "catalyst" in its decision earlier this year to move its headquarters from Stamford, Connecticut to Boston, Massachussetts.