thanks for the responses here and @TrevorH I did --enablerepo=epel-testing and it worked, MATE desktop installed without the usual atril package error, however the resultant desktop has no menu. This centos 7 install is on a vps and I'm viewing it with vnc from a windows pc. Here is a screenshot of the desktop I end up with:
this screenshot also shows a right-click on the desktop, all I get is a home folder and and a trash icon. There's no way to access anything.
To install this desktop I used these commands:
# yum groups install "Server with GUI" -y
# yum groups install --enablerepo=epel-testing "MATE Desktop" -y
thanks for any further ideas