Troubleshooting "Unexpected argument" error when running defaults write
There are backs lashes (\) in your path that should probably be forward slashes (/). You also use curly quotes (‘ and ’), which are weird at best. Try using straight quotes ('), although in that case straight double quotes (") should do as well:

defaults write com.apple.screencapture location '/Users/tommy/Google Drive/Sync/iMac/iMac Screenshots'