I am trying to a backup functionality before the deployment by creating folder with current dateTime, but I am facing error

Error:

= : The term ‘=’ is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or
if a path was included, verify that the path is correct and try again.
At line:1 char:6

• & { = Get-Date -Format ‘yyyy_MM_dd_HH_mm_ss’; = ‘D:CommonWebsites …

My pipeline code:

        - npm install --force
        - ng build --configuration prod
        - powershell -Command "& {Import-Module WebAdministration; Stop-WebSite -Name 'mysite.com'}"
        - powershell -Command "& {iisreset /stop}"           
        - powershell -Command "& {
              $dateString = Get-Date -Format 'yyyy_MM_dd_HH_mm_ss';
              $destinationPath = 'D:CommonWebsitescicdbackupsmysite-' + $dateString;                 
              Copy-Item -Path 'E:WebsitesCommonmysite' -Destination $destinationPath -Recurse -Force;
              Start-Sleep -Seconds 20;                  
          }"           
        - powershell -Command "Remove-Item -Path 'E:WebsitesCommonmysite' -Recurse -Force;"  

Everything works fine apart from backup step
Error occurs exactly at this line

- powershell -Command "& {
              $dateString = Get-Date -Format 'yyyy_MM_dd_HH_mm_ss';
              $destinationPath = 'D:CommonWebsitescicdbackupsmysite-' + $dateString;                 
              Copy-Item -Path 'E:WebsitesCommonmysite' -Destination $destinationPath -Recurse -Force;
              Start-Sleep -Seconds 20;                  
          }"