How to dynamically generate query with OPENXML and convert columns in BASE64 to binary

DECLARE @XmlDocument XML;
SET @XmlDocument = (select TOP 1 * FROM BRO.Dialogs FOR XML AUTO, BINARY BASE64, ROOT('root'));

declare @SQL varchar(max), @SQL2 varchar(max), @SQL3 varchar(max);
select @SQL = coalesce(@SQL + ','+ space(1),' ') + quotename(COLUMN_NAME),
       @SQL2 = coalesce(@SQL2 + ',' + space(1),' ') + (CASE WHEN DATA_TYPE = 'binary'
               THEN  'dbo.f_Base64ToBinary(' + COLUMN_NAME + ')'
               ELSE COLUMN_NAME END),
       @SQL3 = coalesce(@SQL3 + ',' + space(1),' ') + (CASE WHEN DATA_TYPE = 'binary'
               THEN  COLUMN_NAME + ' ' + 'VARCHAR(max)'
               WHEN CHARACTER_MAXIMUM_LENGTH IS NOT NULL THEN COLUMN_NAME + ' ' + DATA_TYPE +'(' + CAST(CHARACTER_MAXIMUM_LENGTH AS VARCHAR(20)) + ')'
               ELSE COLUMN_NAME + ' ' + DATA_TYPE END)
  from INFORMATION_SCHEMA.COLUMNS
  where TABLE_SCHEMA = 'BRO' AND TABLE_NAME = 'Dialogs'
  and COLUMNPROPERTY(object_id(TABLE_SCHEMA + '.' +TABLE_NAME), COLUMN_NAME, 'IsIdentity') <> 1
  ORDER BY ORDINAL_POSITION;
  --SELECT @SQL, @SQL2, @SQL3;           

  declare @var_query nvarchar(max)
  SET @var_query = '
  DECLARE @DocHandle int;
  DECLARE @XmlDocument XML;
  SET @XmlDocument = ''' +CAST(@XmlDocument AS NVARCHAR(max)) + ''';
  -- Create an internal representation of the XML document.
  EXEC sp_xml_preparedocument @DocHandle OUTPUT, @XmlDocument;
  SELECT  '+ @SQL2+ '
  FROM OPENXML (@DocHandle, ''/root/BRO.Dialogs'',1)
  WITH ( '+ @SQL3 +' );'
  --SELECT @var_query          

  exec dbo.sp_executesql @statement = @var_query 


CREATE FUNCTION [dbo].[f_BinaryToBase64]
(
  @bin VARBINARY(MAX)
)
RETURNS VARCHAR(MAX)
AS
BEGIN
	DECLARE @Base64 VARCHAR(MAX)
   
	SET @Base64 = CAST(N'' AS XML).value('xs:base64Binary(xs:hexBinary(sql:variable("@bin")))', 'VARCHAR(MAX)')
   
	RETURN @Base64
END
		
		
		
		
		
		
CREATE FUNCTION [dbo].[f_Base64ToBinary]
(
	@Base64 VARCHAR(MAX)
)
RETURNS VARBINARY(MAX)
AS
BEGIN
	DECLARE @Bin VARBINARY(MAX)
   
  
	SET @Bin = CAST(N'' AS XML).value('xs:base64Binary(sql:variable("@Base64"))', 'VARBINARY(MAX)')
 
	RETURN @Bin
END