Article 13(2) RPBA 2020, sufficiency of disclosure

The appeal of the opponent (hereinafter appellant) lies from the decision of the opposition division to reject the opposition against European patent 2 421 876.
Granted claim 1 concerns a method for preparing a bidentate phosphite of structure I, by contacting a phosphorochloridite of structure II with a bisaryl compound, in the presence of a tertiary organic amine.
According to claim 1, the contacting step is carried out inter alia by controlling the feeding such that a first mole ratio is at least 2.0 during all stages of the contacting step, wherein the first mole ratio is defined as moles of phosphorochloridite in the reaction mixture divided by moles of bisaryl compound fed to the reaction mixture. A second mole ratio is also defined in the claim.
The interpretation of the expression "moles of bisaryl compound fed to the reaction mixture" in the first mole ratio was not a matter of dispute in written appeal proceedings. It was considered to be clear to the skilled person that this expression referred to the total amount of bisaryl which had been fed to the reaction mixture up to any given point in the contacting step, i.e. it was a dynamic amount which increased as the contacting step proceeded.
At oral proceedings, the respondent submitted that the expression "moles of bisaryl compound fed to the reaction mixture" in the first mole ratio was to be interpreted as referring to the amount of bisaryl compound that had not yet reacted in the reaction mixture, i.e. the amount of bisaryl compound present in the reaction mixture and available for reaction.
Subsequent to the respondent's submissions, the board raised the issue of admittance of the respondent's new interpretation of claim 1 into the proceedings.
According to Article 13(2) RPBA 2020, any amendment to a party's appeal case made after notification of a summons to oral proceedings shall, in principle, not be taken into account unless there are exceptional circumstances, which have been justified with cogent reasons by the party concerned.
The interpretation of the first mole ratio adopted by the board in its communication pursuant to Article 15(1) RPBA was the same as that proposed by the appellant with the statement of grounds of appeal. Hence, this interpretation was not new. Consequently, the admittance of the respondent's new interpretation at oral proceedings cannot be justified by any new objections or unexpected developments raised for the first time with the board's communication. Hence, no exceptional circumstances in the sense of Article 13(2) RPBA 2020 are present.
In view of these considerations, the board decided not to admit the respondent's new claim interpretation into the appeal proceedings pursuant to Article 13(2) RPBA.
The appellant submitted that the subject-matter of contested claim 1 was not sufficiently disclosed.
The board agrees. The examples of the patent provide no guidance to the skilled person on how to carry out the claimed method. Furthermore, it is not possible to carry out the characterising feature of claim 1 .
The board acknowledges that as a rule in inter partes proceedings the burden of proof to prove insufficiency of disclosure lies with the opponent (here appellant) first. However, when the patent does not give any information at all as to how a feature of the invention can be put into practice, such as in the present case, only a weak presumption exists that the invention is sufficiently disclosed.
In view of the above considerations, and taking into account this very weak presumption, the appellant has discharged its initial burden of proof.
The sole main request (patent as granted) is not allowable. The patent is revoked.