Trump made the comments while being interviewed behind closed doors Thursday by members and staff of the Senate Judiciary Committee.
On Wednesday, the day before the meeting, Trump Jr.'s legal team released a statement saying that they "look forward to a professional and productive meeting and appreciate the opportunity to assist the committee".
The Senate panel's leaders, Sens.
"As will become clear, I did not collude with any foreign government and do not know of anyone who did", the statement said, promising to "set forth the sum and substance" of what happened at that meeting.
Trump also said the meeting with Russian lawyer Natalia Veselnitskaya and others in Trump Tower in NY provided no meaningful information.
The investigation into alleged Russian interference in 2016 election is gaining steam as Donald Trump Jr.is set to meet with the Senate Judiciary Committee Thursday during a closed-door session.
"It seems like there's not a week that doesn't go by that another undisclosed meeting doesn't come up or another relationship", Senator Mark Warner of Virginia, the top intelligence committee Democrat, said in an interview as lawmakers returned to Washington.
"We owe all the rest of the Congress and we owe the American public a full-fledged, thorough investigation", Warner said.
Senate aides anticipate a lengthy interview. Trump has repeatedly denied having any dealings with Russian Federation, but emails between a business associate and one of his lawyers showed that his company was pursuing a Trump Tower in Moscow while he was running for president.
In the initial email to arrange the meeting, Goldstone wrote that a client of his "offered to provide the Trump campaign with some official documents and information that would incriminate Hillary and her dealings with Russian Federation and would be very useful to your father".
Grassley's panel is investigating a number of issues linked to the Russian interference campaign, including "attempts to influence US elections" and whether there have been any violations of foreign lobbying laws.
The letter was signed by the committee chairman, Rep. Devin Nunes, R-Calif., who stepped back from the Russian Federation investigation this year after he was criticized for being too close to the White House.
"If you just take the number of new stories that have appeared in the public press that have to be validated or debunked that just have arisen" during the August recess, "that in itself is months of work", the Democratic senator said.
The intelligence committees have already spoken with Kushner and Manafort.