Connect Sennheiser bluetooth headphones to MacBook Pro

Hi,

I am trying to connect my Sennheiser Momentum Wireless headphones to my MacBook Pro (Mid 2014, Sierra 10.12.6)

When opening the Bluetooth Preferences, the window remains empty and the wheel keeps spinning. The MacBook can't see the headphones. The BT on the headphones is on, my iPhone can see them and pair without problems.

When powered up, the headphone keeps saying "No device found"

I've already tried debugging the BT module on the MacBook - without success...

Any other idea?

Many thanks, Christian