Not true. Ligers (lion/tiger mixes) exist. Years ago there was one named Shasta I used to visit with my kids at Hogle Zoo in Salt Lake City. They're not abundant but definitely exist.
I just reread your statement and maybe I misunderstood it. Are you saying leopards can't mate with either lions or tigers? Maybe so. But lions and tigers get it on productively.
Same here. The wild Bobcats will mate and have off-spring with the domesticated cats. My dad (Bless his soul), years ago, had some that were mixed.
Dang! Learned something new tonight. Just did a quick search and found there are actually Zorses (Zebra/Horse), Wholphins (False Killer Whale/Dolphin); Cama (Camel/Llama); and Cattalo (Cow/Bison).
Also discovered there's a something called a Dasshole which is a cross between a Democratic Senator and a Sphincter.