T 0657/19 29-06-2023

The following abbreviations are used below:

AA alkylation agent

Bu butyl

Oct octyl

R alkyl

X halide

Admittance of D13

1. The opponent filed D13 after the expiry of the opposition period and raised a novelty objection to granted claim 1 on the basis of this document. It also pointed out that D13 could serve as the closest prior art if the subject-matter of claim 1 is considered novel.

2. The opposition division admitted D13 because it considered this document to be prima facie relevant for the assessment of patentability (see the decision under appeal, page 8, paragraph 2). In particular, the opposition division considered D13 to represent the closest prior art for the subject-matter of granted claim 1 (see point III. above).

3. On appeal, the patent proprietor requested that the opposition division's decision to admit D13 be overturned and that D13 be held inadmissible. The opponent requested that the opposition division's decision be confirmed.

4. The admittance of D13 by the opposition division was a discretionary decision. According to G 7/93 (point 2.6 of the Reasons), a board should only overrule the way in which a first-instance department exercised its discretion if it comes to the conclusion either that the first-instance department did not exercise its discretion in accordance with the right principles, or that it exercised its discretion in an unreasonable way, and thus exceeded the proper limits of its discretion.

4.1 In its decision, the opposition division considered the prima facie relevance of D13. This is considered a right principle within the meaning of G 7/93.

4.2 According to the patent proprietor, D13 was not more relevant than any of the documents cited in the notice of opposition. In particular, D13 was not prima facie relevant to the inventive step of granted claim 1. D13 concerned the production of (allyl)SnX3. This technical field/problem differed from that of the patent, which related to the production of RSnX3.

However, this argument does not suggest that the opposition division exercised its discretion in an unreasonable way. In the absence of such an argument, the opposition division's alleged substantive error in its discretionary decision is by no means tantamount to an unreasonable exercise of discretion. Notwithstanding the above, the board fully agrees with the opposition division's assessment of D13 as regards its prima facie relevance (see below), and therefore the admittance decision is not to be set aside for this reason alone.

5. In its communication pursuant to Article 15(1) RPBA 2020, the board had already set out the conclusions above. At the oral proceedings before the board, the patent proprietor refrained from making further submissions on these points. Therefore, at the oral proceedings the board saw no reason to deviate from its written preliminary opinion and decided that D13 would stay in the proceedings.

Main request (patent as granted) - inventive step (Article 56 EPC)

6. Claim 1 reads as follows:

"A process for producing monoalkyltin trihalide comprising:

(a) contacting dialkyltin dihalide with an

alkylation agent and, optionally, tin

tetrahalide, to form a tetraalkyltin mixture

comprising tetraalkyltin, trialkyltin halide,

and dialkyltin dihalide;

(b) reacting the tetraalkyltin mixture with tin

tetrahalide to form a monoalkyltin trihalide

mixture comprising monoalkyltin trihalide,

dialkyltin dihalide and optionally

trialkyltin halide;

(c) processing the monoalkyltin trihalide mixture

to separately recover the monoalkyltin

trihalide and a dialkyltin dihalide stream

comprising the dialkyltin dihalide and

optionally trialkyltin halide; and

(d) recycling at least a portion of the

dialkyltin dihalide stream recovered in step

(c) to the contacting step (a),

wherein the dialkyltin dihalide is re-alkylated in step (a) either alone or with the optional tin tetrahalide; and wherein the alkyl is a linear alkyl, a branched alkyl, or a cycloalkyl."

In the following, steps (a), (b), (c) and (d) are referred to as alkylation, redistribution, separation and recycling steps, respectively. Thus, claim 1 relates to a process for producing RSnX3, comprising the following steps (the reactions are only shown schematically, i.e. the stoichiometry on both sides of the reaction arrow is not balanced; educts/products which are only optional according to claim 1 have been omitted):

(a) an alkylation step:

R2SnX2 + AA --> R4Sn + R3SnX + R2SnX2

(b) a redistribution step:

R4Sn + R3SnX + R2SnX2 + SnX4 --> RSnX3 + R2SnX2

(c) a separation of RSnX3 from the RSnX3/R2SnX2

mixture resulting from step (b)

(d) recycling (some of) the R2SnX2 remaining from

step (c) by feeding it back into step (a)

7. Closest prior art

D13 is a scientific paper which relates to the reaction of allylic halides with tin(II) halides to produce (allyl)SnX3 using platinum and palladium complexes. Although these studies form the core of D13, as argued by the patent proprietor, the disclosure of D13 is not limited thereto. Rather, the introductory part of D13 describes routes already taken to prepare structurally similar compounds, such as RSnX3, in particular (see page 10261, left column):

"Monoalkyltin trihalides, RSnX3, (X=Cl, Br, I; R=alkyl) find application as precursors for PVC stabilizers,**(1) as catalysts for polyurethane production and as precursors for the deposition of SnO2-coatings on glass.**(2) They are produced industrially by a redistribution reaction, which is controlled by the stoichiometry of the reactants and which usually involves X=Cl (Eq. (1)).**(3) For economic reasons, the R2SnX2 is converted in a subsequent step into the R4Sn starting material. Full conversion of R4Sn into 4 equiv. of RSnCl3 is only successful for allyl,**(4) vinyl**(5) and phenyltins**(6) or requires a catalyst in the case of alkyltins.**(7)

FORMULA/TABLE/GRAPHIC"

In its communication pursuant to Article 15(1) RPBA 2020 (point 31.1), the board agreed with the view of the opponent and the opposition division that this part of the disclosure of D13, which relates to the synthesis of RSnX3 but does not form part of the actual core of D13, can indeed be considered the closest prior art in the present case. This view was not challenged by the patent proprietor in the further course of the appeal proceedings.

8. Distinguishing feature

In its communication pursuant to Article 15(1) RPBA 2020 (point 27), the board had also explained that, and why, the subject-matter of claim 1 differed from the disclosure of D13 as quoted above, in particular equation (1), at most in that in alkylation step (a) a

"tetraalkyltin mixture comprising tetraalkyltin, trialkyltin halide, and dialkyltin dihalide"

was obtained and reacted in the redistribution step (b).

At the oral proceedings before the board, the patent proprietor did not dispute this but instead focused all of its arguments on the above-mentioned distinguishing feature. In favour of the patent proprietor, it is assumed in the following that the feature set out above is in fact a distinguishing feature.

9. Technical effects

9.1 Before the summons to oral proceedings was issued, the patent proprietor's constant position was that compared with the process of D13, the process according to claim 1 increased the efficiency of tin use when preparing RSnX3. In its last written submission before the oral proceedings, which was filed after the summons, and in fact at the oral proceedings themselves, the patent proprietor relied for the first time in the appeal proceedings on the following three technical effects in support of an inventive step:

- the improved purity of the RSnX3

- a reduced amount of the R3SnX

- a more economic process due to the use of a sub-stoichiometric amount of alkylation agent

As pointed out by the opponent, invoking these three effects constituted a change of the technical effect relied on by the patent proprietor. This was not disputed by the patent proprietor. Moreover, when questioned by the board, the patent proprietor was unable to cite passages from its earlier written submissions, prior to the summons, in which these effects were mentioned or alluded to. The patent proprietor's reliance on these effects thus constitutes an amendment to its appeal case.

Since this amendment was made after the summons, Article 13(2) RPBA 2020 applies, which stipulates that such an amendment shall, in principle, not be taken into account unless there are exceptional circumstances which have been justified with cogent reasons by the party concerned.

At the oral proceedings, the patent proprietor's representative stated that he had only recently taken over the case. However, a change of representative cannot be considered an exceptional circumstance justifying very late amendments to a party's appeal case (see T 2125/18, point 2.3 of the Reasons). Therefore, at the oral proceedings the board decided not to admit the patent proprietor's submissions based on the three effects mentioned above.

9.2 As set out above, before the summons to oral proceedings was issued, the patent proprietor's constant position was that compared with the process of D13, the process according to claim 1 increased the efficiency of tin use when preparing RSnX3. At the oral proceedings before the board, the patent proprietor clarified this to mean that compared with the process of D13, the process of claim 1 resulted in a higher yield of RSnX3. Whether this effect has actually been demonstrated and can therefore be taken into account in the formulation of the objective technical problem is assessed in the following.

9.3 With regard to the effect of a higher yield of RSnX3, the patent proprietor in its written submissions referred in a sweeping manner to tables 5 and 6 of the patent (see the statement of grounds of appeal, page 6, paragraph 4). However, it did so without explaining how this effect could be derived from these tables and, in particular, without establishing a link between this effect and an alleged distinguishing feature.

The data shown in tables 5 and 6 concern the increase in the (cumulative) yield of RSnX3 over several cycles attributable to the recycling of R2SnX2. Since the process in D13 also involves the recycling of R2SnX2 (see the dashed arrow in equation (1) in the passage quoted from D13 above), this effect must also be implicitly achieved by the process of D13. However, a technical effect attributable to the present distinguishing feature cannot be deduced from tables 5 and 6.

9.4 Indeed, with regard to the effect of a higher yield of RSnX3, the patent proprietor no longer relied on tables 5 and 6 at the oral proceedings before the board. Instead, the patent proprietor referred to example 3, and more specifically to tables 2 to 4, of the application as filed.

9.4.1 Example 3 describes the synthesis of OctSnCl3 according to the process of claim 1. In a first cycle, a commercially available sample of Oct4Sn is reacted with SnCl4. The desired product, OctSnCl3, is isolated by distillation. The Oct2SnCl2-rich distillation residue is reacted with OctMgCl to give a mixture comprising Oct4Sn, Oct3SnCl and, if applicable, Oct2SnCl2 ("Oct4Sn-mixture"). Using this Oct4Sn-mixture, the process is then repeated for a total of four cycles. The series of cycles is completed with a partial fifth cycle to convert the Oct2SnCl2-rich distillation residue of the fourth cycle back to an Oct4Sn-mixture. Table 2 gives the composition of the Oct4Sn-mixture used as the starting material in each cycle (as noted above, in the first cycle, a commercial grade of Oct4Sn was used; unlike tables 3 and 4 (see below), table 2 shows five cycles due to the partial fifth cycle).

Table 2:

FORMULA/TABLE/GRAPHIC

Table 3 summarises the results of the redistribution reaction using the Oct4Sn-mixtures from table 2 and SnCl4.

Table 3:

FORMULA/TABLE/GRAPHIC

Lastly, table 4 summarises the results of the distillation of OctSnCl3 from the OctSnCl3/Oct2SnCl2 mixtures from table 3.

Table 4:

FORMULA/TABLE/GRAPHIC

9.4.2 The patent proprietor essentially argued as follows:

The Oct4Sn-mixture of the second cycle contained Oct4Sn and Oct3SnCl but not Oct2SnCl2; by contrast, that of the third cycle contained all three tin species, i.e. Oct4Sn, Oct3SnCl and Oct2SnCl2 (see the composition of the product mixture for cycles 2 and 3 in table 2 above). Therefore, only the Oct4Sn-mixture of the third cycle was a "tetraalkyltin mixture comprising tetraalkyltin, trialkyltin halide and dialkyltin dihalide" as stipulated in claim 1. As could be seen from table 2, the alkylation reaction at the beginning of the third cycle gave a higher yield on tin than in the second cycle (98.6% vs. 96.4%). Furthermore, table 4 showed that the Oct4Sn-mixture of cycle 3 gave a higher yield of OctSnCl3 after distillation than the Oct4Sn-mixture of cycle 2 (83% vs. 75%). These results showed the advantages of the process of claim 1 over that of D13 and, in particular, that the distinguishing feature of claim 1 over D13 was linked to a higher yield of OctSnCl3/RSnX3.

9.4.3 The board does not find the patent proprietor's arguments convincing for the following reasons:

- The yields on tin given in table 2 for the second and third cycles (96.4% vs. 98.6%, respectively) correspond to the yield on tin after the alkylation step, i.e. the step that brings about the distinguishing feature. These yields can only be due to the alkylation reaction itself or to the components used for this. However, any change in the yield on tin derivable from table 2 is not an effect attributable to the present distinguishing feature, since such an effect, if any, could only become apparent in the further subsequent steps of the process. The patent proprietor's reference to the yields given in table 2 is therefore not relevant in the present case.

- Table 4 does show a higher yield of OctSnCl3 after distillation for the third cycle (83%) as compared to the second cycle (75%), i.e. a higher yield of OctSnCl3 for a cycle starting from an Oct4Sn-mixture according to claim 1 (third cycle) compared to a cycle starting from a mixture which is not in accordance with claim 1 (second cycle). At the same time, however, as set out by the board at the oral proceedings, the yield of OctSnCl3 reported for the fourth cycle - and this cycle also starts from an Oct4Sn-mixture according to claim 1 (see the composition of the product mixture for cycle 4 in table 2 above) - is as low as the yield reported for the second cycle (75% in both cases). Therefore, when comparing the fourth cycle with the second cycle, no improvement in the yield of OctSnCl3 can be seen. Against this background, the board is not convinced that the present distinguishing feature results in a higher yield of OctSnCl3/RSnX3.

In this context, the patent proprietor argued that the "tetraalkyltin mixture comprising tetraalkyltin, trialkyltin halide, and dialkyltin dihalide" according to claim 1 was the result of using a sub-stoichiometric amount of alkylation agent. Since the application as filed did not give details for the alkylation agent used to prepare the Oct4Sn-mixture used for the fourth cycle, the data given for this cycle in table 4 could not refute the patent proprietor's conclusion based on a comparison of the second and third cycles. This reasoning cannot be accepted. First and foremost, the lack of details in experimental data cannot be to the advantage of a patent proprietor if these details are relevant for the recognition of an inventive step. Notwithstanding this, the use of sub-stoichiometric amounts of the alkylation agent is not a feature of claim 1, but the composition of the R4Sn mixture in relation to the tin species that must be present is. Moreover, with respect to the presence of these tin species, the Oct4Sn-mixture used for the fourth cycle meets the requirements of claim 1. These arguments cannot therefore change the conclusion drawn above.

10. Objective technical problem

It follows that the effect linked to the distinguishing feature, which the patent proprietor invoked in support of an inventive step, cannot be accepted. Consequently, the objective technical problem must be formulated as being to provide an alternative process for producing RSnX3.

11. Obviousness

From their common general knowledge (see D4, page 41, first paragraph), the skilled person understands that a redistribution reaction forming BuSnCl3 and Bu2SnCl2 can be carried out not only between SnCl4 and Bu4Sn, but also between SnCl4 and a mixture of Bu4Sn and Bu3SnCl. D2 (example 2) further discloses that the reaction of Bu2SnCl2 with an alkylation agent under selected conditions results in a mixture containing small amounts of Bu2SnCl2 in addition to Bu4Sn and Bu3SnCl. The board is not aware of any reason, and the patent proprietor did not present any reasons of its own in this respect, as to why the skilled person would have regarded the Bu4Sn/Bu3SnCl mixture obtained according to D2, with only a very small content of Bu2SnCl2, as being unsuitable for being reacted with SnCl4 in a redistribution reaction as suggested in D4. Small amounts of Bu2SnCl2 in the mixture used in the redistribution reaction also seem unproblematic, if only because the redistribution reaction between Bu4Sn, Bu3SnCl and SnCl4 produces Bu2SnCl2 anyway. The fact that the mixture of D2 contains less Bu4Sn than Bu3SnCl is not relevant in the present case, contrary to the patent proprietor's argument based thereon, since claim 1 is not limited in any way with regard to the ratio of R4Sn and R3SnCl.

Thus, at least for the process according to D13, in which the alkyl group is butyl and the halide is chlorine, an obvious alternative process is suggested to the skilled person, in which Bu2SnCl2 is first subjected to an alkylation reaction according to D2 to obtain a mixture of Bu4Sn, Bu3SnCl and Bu2SnCl2, and in which this mixture is then subjected to redistribution with SnCl4 to obtain BuSnCl3 and Bu2SnCl2. This obvious alternative to the process of D13 falls within the scope of the subject-matter of claim 1, which is not limited with respect to its alkyl groups and halide atoms. Thus, the subject-matter of claim 1 of the main request is not based on an inventive step and the main request is not allowable.

Auxiliary request 1 - inventive step (Article 56 EPC)

12. Claim 1 of auxiliary request 1 differs from claim 1 of the main request only in that step (b) reads as follows (emphasis added):

"(b) reacting the tetraalkyltin mixture with tin

tetrahalide, wherein no catalyst is

included, to form a monoalkyltin trihalide

mixture comprising monoalkyltin trihalide,

dialkyltin dihalide and optionally

trialkyltin halide"

Thus, the process of claim 1 of auxiliary request 1 further requires that the redistribution step be conducted without a catalyst.

13. There was disagreement between the parties as to whether the use of a catalyst in the redistribution step in equation (1) of D13 was envisaged in the introductory part of this document quoted above. According to the patent proprietor, particularly the last sentence of the above quote from D13 ("Full conversion of R4Sn into 4 equiv. of RSnCl3 is only successful for allyl,**(4) vinyl**(5) and phenyltins**(6) or requires a catalyst in the case of alkyltins.**(7)", emphasis added) clearly indicated that a catalyst was used in equation (1).

14. In its communication pursuant to Article 15(1) RPBA 2020, the board came to the conclusion by analysing only the content of D13 that the use of a catalyst was not envisaged in the redistribution step in equation (1). This was because, from a logical point of view, the sentence highlighted by the patent proprietor could not refer to equation (1) since the stoichiometry of this equation did not allow a full conversion of R4Sn to RSnX3. Furthermore, the interpretation of the reaction equation as written, namely without a catalyst, was entirely consistent with the rest of D13, in which a catalyst is very much mentioned in the case of a different reaction equation. Based on its analysis, the board concluded that the additional feature in claim 1 of auxiliary request 1 was not an additional distinguishing feature. This was not contested by the patent proprietor in the further course of the appeal proceedings. At the oral proceedings, therefore, the board saw no reason to deviate from its written preliminary opinion.

15. In view of the above, the board cannot follow the conclusion of the opposition division in the decision under appeal that the entirety of D13 concerned only catalysed reactions and was therefore not suitable as the closest prior art for the subject-matter of claim 1 of auxiliary request 1. Rather, as with the main request, there is no apparent reason as to why D13 does not also constitute the closest prior art for the subject-matter of claim 1 of auxiliary request 1. The analysis of the inventive step of auxiliary request 1 is thus completely analogous to that of the main request and therefore auxiliary request 1 is not allowable.

Auxiliary requests 2 and 3

16. As pointed out by the opponent and then again by the board in its communication pursuant to Article 15(1) RPBA 2020, the patent proprietor did not provide any arguments as to why the amendments made in claim 1 of auxiliary requests 2 and 3 provide a further distinction from the cited prior art. At the oral proceedings before the board, the patent proprietor refrained from providing any reasoning in this respect.

The board does not see any reason why these amendments provide a further distinction from D13 either. The board has therefore concluded that the amendments made in claim 1 of auxiliary requests 2 and 3 do not further distinguish the subject-matter thereof from D13. Thus, claim 1 of auxiliary requests 2 and 3 does not involve an inventive step for the same reasons as those set out above for claim 1 of the main request and of auxiliary request 1.

Further points

17. There were opposing requests from both parties with regard to the (non-)admittance of D14. As it was concluded that this document was not relevant to the present decision, there was no need to decide on these requests at the oral proceedings before the board.

18. Before the opposition division, the opponent submitted its very first novelty objection based on D13, arguing that this document disclosed a "tetraalkyltin mixture" as stipulated in granted claim 1. This was after the expiry of the opposition period. The opposition division decided not only to admit D13 but also to introduce novelty as a new ground for opposition. The opponent pursued this novelty objection on appeal and filed experimental data and the further documents D15 to D20 in support thereof with its statement of grounds of appeal.

At the oral proceedings, the board decided to overturn the opposition division's decision to admit novelty as a new ground for opposition, and therefore this ground was not to be part of the appeal proceedings. The board also decided not to admit D15 to D19, the part of D20 relating to the tetraalkyltin mixture or the experimental data filed with the opponent's statement of grounds of appeal.

As the final decision is to revoke the patent, and does not adversely affect the opponent, the reasons for these decisions do not have to be provided.

19. D21 and the part of D20 relating to the use of a catalyst had been filed by the opponent in support of its argument that no catalyst was needed for the redistribution reaction in equation (1) of D13. In the board's reasoning above, which is in the opponent's favour, the board has not taken into account D21 or the part in D20 relating to the use of a catalyst. Consequently, there was no need to decide at the oral proceedings before the board on the admittance of D21 or the part of D20 relating to this issue.

20. As the patent proprietor's requests for the admittance of D22, D23 and the experimental data filed with the letter of 15 June 2023 were only subject to the admittance of D15 to D21 and the opponent's experimental evidence filed with its statement of grounds of appeal, there was no need to decide on these requests from the patent proprietor at the oral proceedings before the board.