We have a 25 month old that has "all of the sudden" become frustrated at times. Fortunatly, she really hasn't started hitting YET.
And you're absolutely right - it's because there's this communication gap. He's having trouble expressing himself and doesn't know what to do about it.
I've seen "super nanny" version of time outs where she has the parent sit the child in the "time out spot" and say, I'm putting you in time out because you hit, and that's not acceptable." Then after the child has been in time out for 2 minutes, the parent goes and tells the child, "Do you know why you're in time out?" or "You were put in time out because you hit your brother. That isn't nice. You need to say sorry to brother..." then give him a hug and a kiss. And just keep reaffirming "we need to be nice to little brother. He's little isn't he."
Our 2 and 5 year olds have trouble sharing sometimes. You can always tell when the 5 year old is trying to swipe something the 2 year old has because she'll just screach. We've tried to tell the 5 year old, "We know she's playing with your toy, but she doesn't understand that that's your toy because she's too little. Maybe if you tried to trade her another toy for it, she'll be okay."
Sometimes diversion works too. The "Hey, why don't you come over here and play with that." We've tried to tell our oldest that there are times that are better for her to play with her playdough than others...like when the youngest is asleep. Yours might be too young for that yet, but it could be that the 6 month old sleeps enough more than the 2 year old to tell him, "Hey, when brother goes to sleep we can play with that. I know you're frustrated and want to do it now, but brother will be asleep in just a few minutes, okay?"
I have noticed that boys are different than girls though - so I don't know if what's worked for me with my girls will work for you, but for whatever it's worth....