You have to complete the path to the folder. If it is on the same level as Inbox then

Sub ChangeViewtoFolderDatenbank()
    Dim ns As Outlook.NameSpace
    Dim Exp As Outlook.Explorer
    Dim folder1 As Folder
    Set ns = Application.GetNamespace("MAPI")
    Set Exp = Application.ActiveExplorer
    Set folder1 = ns.GetDefaultFolder(olFolderInbox).Parent.folders.Item("Datenbank")
    Set Exp.CurrentFolder = folder1
End Sub