SAO PAULO (Reuters) -Brazilian businessman Nelson Tanure has begun talks with the banks that will be key to his bid for petrochemical firm Braskem ( BAK ) , he told Reuters, as he aims to clinch a deal this year and give oil giant Petrobras a larger role in operations.

Braskem ( BAK ) is Latin America's largest petrochemical firm, and its controlling shareholder Novonor has been exploring a sale for years as it looks to exit bankruptcy protection and turn the page on a vast corruption scandal.

Tanure is the latest bidder trying to unlock a stalemate between Novonor, the banks holding Braskem ( BAK ) shares as collateral and state-run Petrobras, which is an influential shareholder and key supplier of the firm.

In his first public comments since revealing his Braskem ( BAK ) bid last month, Tanure said he began courting engineering group Novonor, formerly known as Odebrecht, after the Abu Dhabi National Oil Company's offer to buy its Braskem ( BAK ) stake collapsed over a year ago.

"After Adnoc withdrew their offer, I began confidential discussions with (Novonor) in absolute secrecy," Tanure wrote in response to questions.

Novonor would remain a shareholder in the proposed deal, Tanure said, with the latest proposal reducing its stake from 38.3% to around 3.5%, adding: "I would not make an agreement if they did not remain involved."

Tanure said the deal is still under discussion. Novonor confirmed the talks in May, but declined to comment on details provided by Tanure.

During the corruption scandal a decade ago, Novonor used its Braskem ( BAK ) stake as collateral for some 15 billion reais ($2.7 billion) in bank loans. The shares' value has fallen with profit margins in petrochemical markets and now covers less than a quarter of that debt.

Despite Tanure's progress with Novonor, its creditors view his offer with skepticism as they have their own plans for Braskem ( BAK ), according to two people familiar with the matter.

State development bank BNDES and other major banks have proposed pooling the shares pledged as collateral into a private equity fund that would make investments to turn the company around before selling the shares, Reuters reported in November.

BNDES President Aloizio Mercadante confirmed talks with Petrobras and other banks to resolve the standoff at the time. On Tuesday, the bank declined to comment on Tanure's competing proposal to Novonor.

"The success of this acquisition necessarily depends on alignment with (the banks)," Tanure said, although he pushed back at the idea that the lenders effectively control Braskem ( BAK ).

"It's important to clarify that the shares still belong to the Novonor group. They are merely pledged to banks as collateral for loans."

The Rio de Janeiro-based businessman, who has a track record of investing in companies undergoing contentious restructuring, is a major shareholder in power firm Light and oil company Prio.

If he can clinch the deal for Braskem ( BAK ), Tanure sees a larger role for Petrobras, which has a right of first refusal for Novonor's stake under their shareholder agreement.

"I believe their presence in (Braskem's ( BAK )) operations is small and needs to be expanded," Tanure said. "We must acknowledge that Petrobras has seniority and management expertise in oil companies comparable to the best in the world."

Petrobras declined to comment. Last week, Petrobras CEO Magda Chambriard said Braskem ( BAK ) was a very important asset, but its current management was "not what we want." Asked by Reuters about Tanure's offer, she said: "We can only applaud. We want a solution."

Tanure said his ambitions for Braskem ( BAK ) include transforming its Camaçari complex in Bahia state into a hub for sustainable innovation and "green" petrochemicals with lower emissions.

($1 = 5.5626 reais)