Qatar’s Emir Sheikh Tamim bin Hamad Al Thani says he has discussed purchasing Russia’s state-of-the-art S-400 missile defense system with President Vladimir Putin.

AVA- “There is no agreement. It’s true that we discussed it, we talked about it,” Emir Sheikh Tamim bin Hamad Al Thani said at a press conference in Paris after talks with French President Emmanuel Macron.
“I don’t want to go into details,” he, however, said.
The monarch last met Putin in Moscow in March and is set to hold talks with him again during the latter stages of the World Cup in Russia.
Saudi Arabia - which is engaged in an intense diplomatic rift with Qatar since last year - has also signed a contract with Moscow to buy the surface-to-air missile system. The two sides signed the contract during a visit to Moscow by Saudi King Salman in March 2017.
Last month, the French daily Le Monde cited King Salman as conveying his “profound concern” in a letter to President Macron over the prospect of Qatar’s buying S-400 missile system. He had even warned that Riyadh “would be ready to take all necessary measures - including military action - to eliminate this defense system" if Qatar purchased it. 
This was seen as a threat of war by Qatar. In response, Qatar's Ambassador to Moscow Fahad bin Mohammed al-Attiyah was quoted by media as saying that the world did not live in an "era of the law of the jungle based on threats."
Last June, Saudi Arabia, Egypt, Bahrain, and the United Arab Emirates abruptly cut diplomatic ties with Qatar and imposed an economic embargo on the country, accusing it of supporting terrorism, a claim Doha strongly rejected.
The four later presented Qatar with a list of 13 demands for it to meet before ending the blockade, including reducing its relations with Iran, closing a Turkish military base in Qatar and shutting down its Al Jazeera television.
Doha rejected those demands as an attack on its sovereignty and interference in its domestic affairs.