This is the latest diesel not come to the US.
Fans of diesels living in the US have been waiting a long time for any good news regarding a manufacturer bringing a new diesel engine stateside. All we hear are excuses for why it doesn't make financial sense to sell a particular diesel model in the US. Meanwhile, companies like Audi and BMW have launched tri-turbo and even quad-turbo diesel engines that are extremely impressive. However, none of these engines are destined for the US, and the latest calamity of this trend is the Mercedes C-Class.
In the US, the C-Class is currently offered with a 242-horsepower four cylinder turbo, a 362 hp six-cylinder twin-turbo, and the eight-cylinder twin-turbo AMG. The base four-cylinder is pretty efficient at 24/34 mpg, but likely not as good as the diesel. The C300d was expected to use Mercedes' 2.1-liter four-cylinder with AWD. This engine produces 195 hp and 369 lb-ft of torque in the E-Class and gets 27/38 mpg in a heavier car. It's important to note that this engine hasn't failed any emissions tests. Mercedes is simply placing priority on diesel versions of its GLS SUV, because the take rate for diesels in the SUV models is higher.
After Dieselgate, the certification process for diesel engines is much longer and more expensive in the US, and it has disrupted the company's plans for the C-Class diesel. The US is more stringent on allowing diesel engines to be sold, so we will probably continue to see cars like the C-Class forgo diesel variants in America.