By Guy Faulconbridge

MOSCOW (Reuters) -Oligarch Oleg Deripaska said Russia has weathered Western sanctions imposed over the invasion of Ukraine and cautioned that Western hopes of using such a 19th Century instrument to end the war or trigger regime change were doomed to failure.

President Vladimir Putin is girding the $2.1 trillion economy for a long Ukraine war and has repeatedly goaded the West for failing to cripple Russia, which is forecast to grow 2.8% this year and 2.3% next year.

Western hopes of stoking a swift Russian economic crisis have been proven to be wrong: the world's second largest oil exporter has no trouble selling its oil on global markets while trade is booming with China - and with some other countries.

"I was surprised that private business would be so flexible. I was more or less sure that up to 30 per cent of the economy would collapse, but it was way less," Deripaska, a 55-year-old tycoon, told the FT.

Deripaska said Russia's vast natural resource wealth made it too attractive for many - including China and other countries - to ever abandon, and that Western hopes of using sanctions to change Russia's leaders were doomed.

Since the Feb. 24 invasion of Ukraine, Deripaska himself has been sanctioned by Britain for his alleged ties to Putin. He has mounted a legal challenge against the sanctions.

"Believing that the sanctions will stop [the war] or create regime change or somehow make us closer to the end of the conflict . . . No. We need to have another solution," he was quoted by the FT as saying.

Deripaska, who studied physics at Moscow University, branched out into metals trading as the Soviet Union crumbled, making a fortune by buying up stakes in aluminium factories.

He founded RUSAL, which united the jewels of the Soviet aluminium industry into one holding, in 2000. He was ranked by the Russian version of Forbes this year as Russia's 54th richest man with a worth of $2.5 billion.

Deripaska still owns part of Rusal through his stake in its parent En+ Group.

He said he doubted sanctions, which he cast as a tool of the 19th Century, would work as a wonder weapon in a global world.

"I always doubted this Wunderwaffe [wonder-weapon], as Germans used to say, of the sanctions -- weaponising the financial system as a kind of tool to negotiate," said Deripaska.

"Yes, there is war spending and all this kind of subsidies and government support but still it's a surprisingly low slowdown [ . . .] The private economy found its way to operate and to do so successfully."

The United States in 2018 imposed sanctions on Deripaska and other influential Russians because it said they were profiting from a Russian state engaged in "malign activities" around the world.

The sanctions, an attempt to punish Moscow for alleged meddling in the 2016 U.S. election, were "groundless, ridiculous and absurd", Deripaska said at the time.

(Reporting by Guy FaulconbridgeEditing by Alexandra Hudson)