Because you are creating dynamic sql (why in this case with a fixed name?) you need to add extra quotes to get quotes in the query, like this

SET @temp_xml1 = 'INSERT INTO XMLwithOpenXML(XMLData, LoadedDateTime)SELECT CONVERT(XML, BulkColumn) AS BulkColumn, GETDATE() FROM OPENROWSET(BULK ''' + 'c:\Desktop\11451.xml' + ''', SINGLE_BLOB) AS x'