public interface IProjectWindow 

{
  //Get the catalog pane
  IProjectWindow projectWindow = Project.GetCatalogPane();
  //or get the active catalog view...
  //ArcGIS.Desktop.Core.IProjectWindow projectWindow = Project.GetActiveCatalogWindow();

  //eg Find a toolbox in the project
  string gpName = "Interacting with Maps.tbx";
  var toolbox = Project.Current.GetItems<GeoprocessingProjectItem>().FirstOrDefault(tbx => tbx.Name == gpName);
  //Select it under Toolboxes
  projectWindow.SelectItemAsync(toolbox, true, true, null);//null selects it in the first container - optionally await
                                                           //Note: Project.Current.GetProjectItemContainer("GP") would get toolbox container...

  //assume toolbox is also under Folders container. Select it under Folders instead of Toolboxes
  var foldersContainer = Project.Current.ProjectItemContainers.First(c => c.Path == "FolderConnection");
  //We must specify the container because Folders comes second (after Toolboxes)
  projectWindow.SelectItemAsync(toolbox, true, true, foldersContainer);//optionally await

  //Find a map and select it
  var mapItem = Project.Current.GetItems<MapProjectItem>().FirstOrDefault(m => m.Name == "Map");
  //Map only occurs under "Maps" so the container need not be specified
  projectWindow.SelectItemAsync(mapItem, true, false, null);
}