Slaughter and May's best friend in Germany Hengeler Mueller is sitting across the table, advising seller Bayer.
Freshfields corporate partners Axel Epe and Barbara Keil in Munich are leading the team for Siemens, which includes partners Timothy Wilkins in New York and Claude Stansbury in Washington DC. A link-up between the US and Germany was key. Epe said: "The cooperation between our offices in Germany and the US proved very helpful to Siemens."
Hengeler M&A partners Matthias Hentzen, Christian Möller and Jochen Vetter are leading the deal for Bayer, a long-term client of the firm.
Möller said: "Bayer don't always retain the same law firm, but we do have a longstanding relationship with them."
Möller said the best friends network came into its own on the deal, which covered more than 40 jurisdictions. "It only took one phone call and one email - we lined up a team on Saturday and everyone was ready by Sunday. All except Kenya, who came through on Monday," he said.
Jones Day partner Phil Proger is advising Bayer on the US merger control aspects of the deal.
Shearman & Sterling is handling the employment aspects for Siemens. The firm is also working on Siemens' €16bn (£11.1bn) joint venture with Nokia to merge their network businesses.