I am able to put the device in bootloader mode by pulling SWCLK high and then pulling RESET low. However, the chip ID message does not immediately appear. What's going on?
The chip ID indeed does not appear immediately. You should send one upper case 'U' (0x55) for the autobaud command, and then the ID will appear. See AN0003 section 1.2 for more information. Application Notes can be found on the Silicon Labs website: www.silabs.com/32bit-appnotes.