The phrase "deep negotiations" is correct and commonly used in written English.
It can be used when describing intense, thorough, or detailed discussions or talks between parties. Example: "After weeks of deep negotiations, the two companies finally reached a compromise on the terms of the merger."
Late last night, the agent for Brown, Marvin Demoff, was in deep negotiations with the team.
Ramphele was in deep negotiations with the DA about a year and half ago.
He called the summit meeting a "significant milestone, and at this point, the last one, in intensive and deep negotiations".
As Lagarde puts it: There has been some speculation that Mario Draghi and I are in deep negotiations over Spain..
He said: "In negotiations to sell, our main priority was to discover whether the buyer is capable of meeting the financial requirements before getting into deep negotiations.
The summit was a significant milestone and, at this point, the last one, in intensive and deep negotiations to achieve a framework agreement and a final status arrangement with the Palestinians.
Neither the Brooklyn Public Library nor the Theater for a New Audience nor WNYC, the public radio station, with which he is now in deep negotiation, satisfies the grand vision.
The stopgap deal, which would last six months, would buy time for deeper negotiations aimed at a more enduring settlement to the decade-long deadlock.
Kerry had hoped to announce a temporary truce between Israel and Hamas on Friday, envisaging a week-long cease-fire that would begin as the Muslim holiday of Eid al-Fitr begins over the weekend and allow time for deeper negotiations that might address Israeli security concerns and loosen Israeli and Egyptian prohibitions on Gazans' travel and trade.
Although Sexton was deep into negotiations with the Chinese government, he immediately offered Chen a fellowship.
The President said the United States is already deep into negotiations for their release.
