OfficeTips Home || VBA Section || General Section || Download Section || Privacy Policy

You cannot achieve it thru the object model since the ViewType property is read-only when it applies to Panes object. But you can get around it making use of command bar control ID 6015 which toggles between thumbnails and outline view of the pane.
It  appears in the Tools | Customize | Commands | Categories: View, Commands: Show Outline.
 

' ---------------------------------------------------------------------
' Copyright ©1999-2018, Shyam Pillai, All Rights Reserved.
' ---------------------------------------------------------------------
' You are free to use this code within your own applications, add-ins,
' documents etc but you are expressly forbidden from selling or 
' otherwise distributing this source code without prior consent.
' This includes both posting free demo projects made from this
' code as well as reproducing the code in text or html format.

' You may include acknowledgement to the author and a link to this site.
' ----------------------------------------------------------------------

Sub SetSlideTab()
Dim oCmdButton As CommandBarButton
Set oCmdButton = CommandBars("Standard").Controls.Add(Id:=6015)
DoEvents
ActiveWindow.ViewType = ppViewNormal

If Not oCmdButton Is Nothing Then
    If ActiveWindow.Panes(1).ViewType = ppViewOutline Then
        oCmdButton.Execute
    End If
    oCmdButton.Delete
    Set oCmdButton = Nothing
End If
End Sub

Sub SetOutlineTab()
Dim oCmdButton As CommandBarButton
Set oCmdButton = CommandBars("Standard").Controls.Add(Id:=6015)
DoEvents
ActiveWindow.ViewType = ppViewNormal

If Not oCmdButton Is Nothing Then
    If ActiveWindow.Panes(1).ViewType = ppViewThumbnails Then
        oCmdButton.Execute
    End If
    oCmdButton.Delete
    Set oCmdButton = Nothing
End If
End Sub