Just as drug group AstraZeneca (AZN) did last year, when Pfizer (US:PFE) launched a similarly motivated bid, Syngenta has tried to shore up support among investors with heady pledges of growth. In half-year results last week management said the company's product pipeline could be worth up to $3.6bn (£2.3bn).
Management know they are on the hook. But the bigger losers from inversion deals are the US tax authorities. The US Treasury took action last September to clamp down on the practice, with some initial effect - AbbVie (US:ABVV) called off its $54bn takeover of Shire (SHP). But the number of inversions has since crept back up as corporate advisers have found ways around the new rules. Steris (US:STE) bought Synergy Health last autumn, and - away from the healthcare sector - US networking equipment group Arris (US:ARRS) announced the acquisition of UK set-top box maker Pace (PIC) in April.
The root problem for the US government is that its tax rate is so much higher than the European average. The federal tax is 35 per cent and state taxes come on top. Chancellor George Osborne reduced the UK corporate tax rate to 19 per cent in this month's budget. The rate for most companies in Ireland - another common source of takeover targets - is just 12.5 per cent.
A related problem is that the US taxes the global earnings of its multinationals, whereas most countries tax only domestic earnings. At least, that's the theory. In practice US multinationals keep their foreign earnings abroad so that they are not taxed. Apple's (US:AAPL) third-quarter results last week revealed that its cash pile had swelled to $203bn, of which almost 90 per cent is held offshore.
Politicians in Washington talk of the need for comprehensive reform, but so far they have been unable to agree what it should look like. The Wall Street Journal reported last week that an "ambitious overhaul" of the way the US taxes worldwide earnings was on the cards, but many congressmen, particularly Democrats, remain wary of exempting foreign profits altogether. Bill Dodwell, head of tax policy at Deloitte, reckons major reform is unlikely under Barack Obama, who - for all the mounting election fever - does not leave the White House for nearly a year and a half.
More likely is a quick political fix whereby companies are offered the chance, for a limited period, to bring home their vast overseas cash piles at a much lower tax rate than normal. This would please both Republicans, who want lower taxes, and Democrats, who want money to improve America's highways. Companies would also welcome the chance to access their cash more cheaply.
I can offer painful personal testimony to the need for road improvements in the US. I have just returned from a holiday in Washington DC, where a pothole was partly to blame for a cycling accident in which I broke my collarbone.
The idea of linking infrastructure investment to a one-off tax windfall seems odd from a European viewpoint, and certainly the mooted deal does not solve the underlying problem of why those cash reserves build up. But bipartisan agreement is a commodity in such scarce supply in Washington that any deal may be celebrated as a great success.
The same revenue-raising wheeze has been tried before. In 2004 George W Bush signed the American Jobs Creation Act, which allowed groups to bring money home during 2005 at a tax cost of just 5.25 per cent. The total repatriated was about $300bn - five times the average for the previous five years - of which Pfizer alone accounted for $37bn. The Act failed to create jobs, according to economic post mortems, but it did, for a while, fund Bush's infamous tax cuts.
If the trick is repeated, one likely financial consequence is a surge in the dollar as money is converted from foreign currencies. More speculatively, there could also be an impact on government bonds if, unlike last time, securities are sold to fund jobs or capital investments.
But the deal would do nothing to alter the incentives for US companies to emigrate. That will require far-reaching reform, which looks as far from the grasp of Washington legislators as ever. Tax inversions will continue to line the pockets of European investors for a few years to come.
