连接到Exchange Online时，C＃的“哪里”子句不起作用

Question

我通过C＃连接到Exchange Online，可以毫无问题地运行Get-Mailbox命令。但是当我尝试

Get-Mailbox | Where LitigationHoldEnabled -eq $true

我遇到错误

  

术语“ where.exe”不能识别为cmdlet，函数，脚本文件或可运行程序的名称。检查名称的拼写，或者是否包含路径，请确认路径正确，然后重试。

该命令在PowerShell中运行良好。 我想念什么？

            PSCredential credential = new PSCredential("xxxxx@yyyyyyyy.de", secpassword);
            string connectionUri = "https://outlook.office365.com/powershell-liveid/";
            Runspace runspace = System.Management.Automation.Runspaces.RunspaceFactory.CreateRunspace( );
            PowerShell powershell = PowerShell.Create();
            PSCommand command = new PSCommand();
            command.AddCommand("New-PSSession");
            command.AddParameter("ConnectionUri", new Uri(connectionUri));
            command.AddParameter("ConfigurationName", "Microsoft.Exchange");
            command.AddParameter("Credential", credential);
            command.AddParameter("Authentication", "Basic");
            command.AddParameter("AllowRedirection", true);
            powershell.Commands = command;
            runspace.Open();
            powershell.Runspace = runspace;
            Collection<System.Management.Automation.PSObject> result = powershell.Invoke();
            if (powershell.Streams.Error.Count > 0 || result.Count != 1)
            {
                powershell.Dispose();
                runspace.Dispose();

            }
            command = new PSCommand();
            command.AddCommand("Invoke-Command");
            command.AddParameter("ScriptBlock", System.Management.Automation.ScriptBlock.Create("Get-Mailbox | Where-Object LitigationHoldEnabled - eq $true"));
            command.AddParameter("Session", result[0]);
            powershell.Commands = command;
            var Searches = powershell.Invoke();
        ....
            powershell.Dispose();
            runspace.Dispose();