Thunderbolt 1 connection

I have a 500GB Extreme SSD that I am trying to connect to a Late 2012 iMac with Thunderbolt 1 and USB 3 ports.  I tried hooking the drive with the Apple ThunderBolt/USB 3 dongle but the iMac doesn’t see it. I then tried the included USB C adapter to USB 2 and that did get recognized.  Not sure why it doesn’t the dongle setup.  I’d prefer it as it’s faster.  Any ideas? Comments?