twin and five gig copper ports and half duplex

Anyone know if it's possible to set twin or five gig copper ports to half duplex? Cisco documentation says this:

"Gigabit Ethernet (10/100/1000-Mb/s) ports and multigigabit ethernet ports (2.5 Gb/s, 5Gb/s, 10 Gb/s) support all speed options and all duplex options (auto, half, and full). However, Gigabit Ethernet ports operating at 1000 Mb/s and above do not support half-duplex mode."

I figured that means if you set the speed to 100 on a five gig port you could then set the duplex to half. This is not the case in my testing however. We are running into problems where legacy equipment isn't compatible with the newer switches we are installing.

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Any advice would be appreciated.