The West Ham co-chairman has been discussing the 28-year-old forward.
However, West Ham's negotiating has resulted in a clause being in place to sign Emenike at the end of the loan shoudl they wish.
Indeed, Sullivan rues the fact the east London side had to deal with two different clubs to bring the Nigerian in.
But he also thanked club secretary Andrew Pincher for his help in clinching the move, as well as confirming West Ham have an option to buy the striker.
Sullivan told the West Ham site: "I am delighted to welcome Emmanuel Emenike to the club.
"We hope he will bring goals and we have an option to sign him at the end of the season.
"It took two weeks of tortuous negotiations and hard work by myself and our club secretary Andrew Pincher to get the player to the club. It was one of the most difficult deals we have ever done as we were dealing with two clubs not one."
Considering the amount of work the Hammers put in, Sullivan will no doubt be keen for Emenike to thrive at Upton Park.
Should he be able to stay fit, he might just prove crucial for West Ham.
The 28-year-old will be needed due to the club's other injury troubles and he clearly has the quality to succeed - it's just a matter of whether he can make the transition to the Premier League.