Create instance of user control to another user control via main windows

<Window x:Class="WpfApplication10.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <DockPanel LastChildFill="True">
        <ToolBar DockPanel.Dock="Top">
            <Button Content="UserControl1" Click="Button1_Click" />
            <Button Content="UserControl2" Click="Button2_Click" />
        </ToolBar>
        <ContentPresenter x:Name="workspacePlaceHolder" />
    </DockPanel>
</Window>

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void Button1_Click(object sender, RoutedEventArgs e)
    {
        this.workspacePlaceHolder.Content = new UserControl1();
    }

    private void Button2_Click(object sender, RoutedEventArgs e)
    {
        this.workspacePlaceHolder.Content = new UserControl2();
    }
}