Will a i3-6100 bottleneck a r9 380 2gb??

Probably it will; hard to say if it would be noticeable, which really depends on what kinds of games you play. Personally I'd think an i5 would be a better match for that card, and overall I am not a big fan of dual-core CPUs for gaming performance; they always seem to disappoint me somehow.
 


maybe you misread, but he said r9 380. thats very similar in architecture to an r9 280(x) and performance to a gtx 960. it may bottleneck slightly, but still isn't a bad choice.
 
you do realize that 280x and 380 are the same cards and 960 is about the same performance while a 970 is in 290/390 territory, if a 380 would be bottlenecked then all of them would, I would say depending on the game, best to go with i5 some of the newer titles would benefit from it, either way a i3 should be sufficient