Boeing kicked off the Dubai Airshow by announcing the first big sales news of the five-day event.
Emirates has ordered 40 Boeing 787 Dreamliners in a deal worth about $15bn (£11.3bn) at list prices.
He had been expected to announce a big order for the Airbus A380 superjumbo at the media briefing.
Airbus desperately needs more orders for the A380, the biggest passenger aircraft in the skies.
The Franco-German company and Emirates were understood to be in intense final negotiations to have an announcement ready for this week’s show.
Emirates, the largest airline in the Middle East, is already the biggest customer for Boeing’s 777, with 165 in service and another 164 on order.
Sheikh Ahmed said Sunday’s order raises the cost of its purchase of Boeing aircraft to $90bn. Some of the new 787s will be used to replace older planes, while others will be used to expand the airline’s network.