How can I batch rename text files to be the first word in each text file?

I need to rename a few thousand text files to be the first word in the text file plus the file extension (.txt) using the terminal. All the files are in a single directory, and are currently named int the pattern "xx0001.txt' through 'xx9999.txt'. The first word in each file is of this pattern: '##221251', so maybe my issue comes from needing to comment out the pound signs. I've tried: rename File.ReadAllText('*.txt').split(' ') Which throws the error: zsh: no matches found: File.ReadAllText(*.txt).split( ) Thanks in advance for your help. I'm a true novice.