Synthesis and characterization of BIAN derivativesAs already described in our previous work27, BIANs have shown to interact with alkyl magnesium solutions and have the potential to lower their viscosities. In contrast to the past study, this time a solution of butyl octyl magnesium (BOMAG) in heptane was used as this is the commercially available product unlike the toluene solution used previously and it has a higher concentration of the alkyl magnesium compound, in this case 35% by weight. To better understand the influence of the substituents present on the basic BIAN structure, we have synthesized a series of derivatives where the type and position of the residues have been varied. As not all desired aniline moieties necessary for the synthesis were commercially available, or, in some rare cases, were simply too expensive to justify an industrial application, not all isomers were synthesized in the course of this study.Figure 1 shows the general reaction scheme for the synthesis of BIANs and their hydrogenated analogues (R-BIAN-H4) as well as a list of compounds used.Fig. 1General synthesis route for the manufacture of R-BIAN-Zn complexes, R-BIANs and their hydrogenated analogues (R-BIAN-H4).The reaction pathway to the BIANs proceeds via a zinc complex, which is typically not isolated. In our study we have isolated these compounds to test them for their viscosity reducing potential as well as to investigate the influence of a pre-existing complex. An additional bonus of using these compounds would be that the synthesis route is shortened by one step and thus the production costs lower.The second group of compounds that is newly introduced in this work are hydrogenated BIANs (R-BIAN-H4). As we have previously described27, an important step in the viscosity reduction mechanism of BIANs is the formation of a complex between Mg and the C=N double bonds. During this complexation one alkyl residue is transferred onto the carbon atom of one C=N double bond and an NH group is thus formed. As those isolated reaction products have then successfully been used for further viscosity reduction and afterwards could again be isolated without further permanent chemical modification, the idea behind this approach was to investigate if a double bond is even necessary at all. Also, the influence of different substituents, e.g., alkyl groups of different bulkiness (methyl, isopropyl and tert-butyl), an aromatic substituent, chlorine, and one alkylamino group in terms of their ability to reduce the viscosity of BOMAG solutions was tested. Substituent positions screened were ortho and para, as well as combinations thereof.Characterization of the synthesized BIAN derivatives was carried out by using NMR spectroscopy as well as mass spectrometry. In both cases hydrolysis of certain compounds due to contact with acidic solvents was observed, in the case of NMR the use of freshly percolated chloroform could solve all issues. For HPLC–MS analyses an acidic mobile phase was necessary, thus, decomposition could not be prevented in all cases. In the cases where no intact BIAN could be detected and for all Zn-complexes solvent free MALDI-ToF MS analysis was applied. All data on the synthetized substances including NMR and m/z vales can be found in the SI (Figs. S1–S82).In Fig. 2 the 1H-NMR spectra of 2-iPr-BIAN, its Zn-complex and the hydrogenated moiety are displayed. Comparing the BIAN to the Zn-complex it can be seen that most signals are identical but shifted to a lower field in the Zn-complex, and the methyl groups of the isopropyl units are split into two signals (Fig. 2a,b). While the BIAN shows the expected doublet at 1.1 ppm (12 protons), the Zn-complex has a triplet at 1.3 ppm and an unsymmetrical quartet around 1 ppm (6 + 6 protons). This splitting suggests that the chemical surrounding is changed by the coordination of the ZnCl2, hence the symmetrical complex suggested in Scheme 1 must be seen as a simplification.Fig. 21H-NMR of 2-iPr-BIAN, the corresponding Zn-complex and hydrogenated BIAN. CDCl3 @ 7.26 ppm, H2O @ 1.6 ppm, CH3COOH @ 2.1 ppm.Upon hydrogenation we see that the newly formed CH is visible at 5.6 ppm and the NH at 4.6 ppm (Fig. 2c), the identity of the latter one being confirmed by the lack of coupling in the HSQC spectrum (SI Fig. S41). Again, the methyl groups of the isopropyl residue are split, but in this case symmetrical as expected due to the loss of planarity. The isomer formed in this reaction is predominantly the cis isomer.As already stated above, when running HPLC–MS experiments it was not possible to avoid the contact with acids completely as the gradient used was composed to acetonitrile and water, each containing 0.1% formic acid. By using this gradient, we could observe three different types of results. In some cases, the BIAN formation was reversed and the corresponding aniline derivative and acenaphthoquinone were completely reformed (Fig. 3a). In other cases, partial hydrolysis took place and while aniline as well as acenaphthoquinone were formed besides a compound with only one aniline moiety cleaved off, to various extents the intact BIAN derivative was found from which the exact mass could be retrieved (Fig. 3b). The cases where no decomposition took place are rare and typically have one or two bulky groups in the ortho position(s) (Fig. 3c), indicating a steric hindrance of the hydrolysis (see Table 1). The Zn-complexes were all together not stable in the acidic solvent and behaved exactly the same as their corresponding BIAN analogues. The hydrogenated R-BIAN-H4s, on the other side, where all stable under the chosen conditions and only yielded peaks for intact moieties, sometimes two peaks with identical mass were observed indicating the formation of a second diastereomer (Fig. 3d)35. A correlation between the hydrolytic stability of the BIAN derivatives and the viscosity reduction behaviour could not be found.Fig. 3HPLC–MS chromatograms of 2-iPr-BIAN compounds showing different hydrolysis behaviour; (a) completely instable 4-iPr-BIAN; (b) partially stable 2-iPr-BIAN; (c) fully stable 2,6-iPr-BIAN; and (d) the fully stable 2-iPr-BIAN-H4.Table 1 Hydrolysis stability of the various BIAN derivatives as observed by HPLC–MS analysis.To successfully obtain the molecular weights of the Zn-complexes and the unstable BIANs, MALDI mass spectra were recorded. By using this technique all the Zn-complexes could be identified as their BIAN-ZnCl+ ions, rather than the typically expected proton or alkali adducts (see SI Sect. 1). The BIANs were identified as Na+ and K+ adducts, the first ones were used for the determination of the molecular weights. Besides those alkali adducts, a protonated, but dehydrogenated (MH+-H2) ion was detected for all species, except for the 2,4,6-trichloro derivative, where dehydrochlorination was observed instead.Viscosity reduction effect of BIAN derivatives on alkyl magnesium compoundsThe starting material, 35% BOMAG in heptane, has a viscosity of 137.8 ± 3.0 mPa s (average of five measurements, Table 2). At first, unmodified and unsubstituted BIAN was measured as benchmark, which already reduces the viscosity of the BOMAG solution to 39 mPa s. When trying to repeat this experiment with the Zn complex and the hydrogenated BIAN a first problem arose, which is the solubility of the BIAN derivatives in the BOMAG-heptane solution. Both derivatives were only poorly soluble, and a large amount of the modifier remained undissolved (Table 2). Nevertheless, in those cases where the compounds were not completely soluble, the saturated solutions were used for the viscosity measurements. Despite this problem, the Zn complex showed a reduction of the viscosity to 66 mPa s. The hydrogenated BIAN (H-BIAN-H4) did not show any influence at all, and the viscosity remained constant at 140 mPa s. In general, all BIANs showed good solubility (except for the naphthyl and 2,4,6-trichloro derivative, which proved to be insoluble in all three modifications), in case of the hydrogenated products the ortho substituted products are better soluble than the para substituted ones, again with one exception which are the tert-butyl derivatives. For the Zn-complexes, no trend could be found.
Table 2 Viscosity of BOMAG solutions modified using 2.5 mol% of the different additives and their solubility in the BOMAG heptane solution.All synthesized BIANs, Zn-complexes and BIAN-H4 have been tested and the measured viscosities are listed in Table 2. As shown in Table 2 not all derivatives were completely soluble but no trend regarding the substituent position can be observed. For example, while the hydrogenated 2-iPr is completely soluble and the 4-iPr not, it is the other way round for the hydrogenated 2-tBu and 4-tBu. The BIANs are all, except for the 2,4,6-Cl, easily soluble while the Zn derivatives are in general only poorly soluble, indicating an interaction of the BOMAG solution with Zn.A selection of the viscosities achieved using different BIAN derivatives can be seen in Fig. 4. 2,4,6-Cl-BIAN is an absolute outlier, which, despite being only poorly soluble, increases the viscosity of the solution to 230 mPa s. A possible reason may be that the compound is not pure, which is suggested by NMR and HPLC data. Such a rise in viscosity has otherwise only been observed for the hydrogenated naphthyl-BIAN (174 mPa s) and N,N-dimethylamino-BIAN (172 mPa s), the latter one also despite being completely soluble. A general trend is that a substituent in position 4 shows a better viscosity reduction behavior than the same substituent in position 2, which is most likely due to the steric hindrance in the latter derivatives, as has already been seen in their increased stability against hydrolysis. The viscosity of the para-derivatives shows a rather similar value of 29–36 mPa s, which is on the better side of all tested compounds. The 2,6-Me-BIAN has a very poor performance, while the other 2,6 derivatives give good results, even a bit better than the corresponding molecules with a single ortho substitution. The 2,4,6 derivatives, which were only available for methyl and chloro substituents, show very low ability to reduce the viscosity of BOMAG solutions, chlorine even increasing its viscosity as mentioned above.Fig. 4Viscosity of the BIAN modified BOMAG solutions. First column shows the unsubstituted BIAN as reference. The column for 2,4,6-Cl-BIAN is cropped at 120 mPa s (would have a viscosity of 230 mPa s) for better visibility of all other compounds. Numbers written in the columns are the absolute values as listed in Table 2.When looking at the Zn complexes (Fig. 5) it can first of all be noticed that the unsubstituted H-Zn is clearly worse than its BIAN analogue (66 vs 39 mPa s), which might be due to its lower solubility (see Table 2), but also an interaction of the Zn with BOMAG. In contrast to the BIANs the viscosities of the ortho-isomers are a bit lower than that of the para-isomers, 2-tBu-Zn being an outlier most likely due to its limited solubility. 2,6 and 2,4,6 isomers show the least capability to interact and break the BOMAG chains, especially the 2,6-Cl-Zn and 2,4,6-Cl-Zn compounds, but again, those derivatives could not be dissolved at 2.5 mol% and were thus tested as saturated solutions.Fig. 5Viscosity of the R-Zn complex modified BOMAG solutions. First column shows the unsubstituted H-Zn as reference. The columns for 2,4-Cl-Zn and 2,4,6-Cl-Zn are cropped at 120 mPa s for better visibility of all other compounds. Numbers written in the columns are the absolute values as listed in Table 2.The most interesting results were, however, obtained with the hydrogenated BIANs. H-BIAN-H4 (without substituents) does not show any effect on the viscosity of the BOMAG solution, the change in color, which is a first indication of complexation, is also not very pronounced (Table 3). The para-isomers of hydrogenated substituted BIANs all together show a very poor viscosity reduction behavior, also the 2,4,6-Cl-BIAN-H4 derivative is rather ineffective (Fig. 6). When the substituent is located in the ortho position, excellent viscosity reduction behavior is observed and a trend can be seen that the larger the alkyl substituent, the better the value. This latter observation is different from the trend in BIANs and Zn complexes, where the methyl substituent works best (see Figs. 4, 5). A reason for this might be that the reaction mechanism of the latter compounds starts with the addition of an alkyl residue to the double bond and a steric hindrance would have a negative effect on this step.
Table 3 Colour of the solid BIAN derivatives and their colour change when interacting with BOMAG (35% in heptane). Furthermore, the colour gradient during the quenching with water and the finally achieved colour in heptane are described.Fig. 6Viscosity of the hydrogenated BIAN modified BOMAG solutions. First column shows the unsubstituted H-BIAN-H4 as reference. Numbers written in the columns are the absolute values as listed in Table 2.When a second substituent is added in position 6 the viscosity values of around 25 mPa s can be obtained, even the 2,4,6-Me-BIAN-H4 substituted derivative performs very well. This is comparable to the best values obtained with previously published modifiers such as bis-trimethylsilylcarbodiimide (25 mPa s), dicyclohexylcarbodiimide (41.2 mPa s), or the commercially used triethyl aluminium (20.4 mPa s)20. Based on these results we conclude that for hydrogenated BIANs a steric hindrance is key to the successful reduction of the viscosity of BOMAG solutions.To better summarize the individual trends of BIANs, Zn complexes and BIAN-H4 compounds, we have selected all compounds where substituents in ortho- and para-positions were available and grouped them together in Fig. 7. Here, the strong difference between the ortho- and para-isomers of the hydrogenated BIANs is clearly visible, with the ortho-isomers being the most effective ones. But also Zn complexes and BIANs show a trend, although less pronounced. The trend within the Zn complexes is similar to the one in hydrogenated BIANs: the ortho-isomer is resulting in lower viscosity than the para-isomer, with the only exception of the 4-tBu substituted derivative that is less soluble than the ortho-isomer. The BIANs on the other hand show the opposite trend where all para-isomers show a better performance than the ortho-isomers.Fig. 7Viscosity trends of ortho- and para-substituted BIAN derivatives. Numbers written in the columns are the absolute values as listed in Table 2.A fast way to see if any interaction between BOMAG and BIAN takes place, is the change of the solution’s colour (Table 3). While the BOMAG solution is colourless, the BIAN derivatives are typically intensely coloured. When a complex is formed in solution it is indicated by a distinctive change in coloration. The BIAN compounds, especially with alkyl groups, are reddish violet in the interaction with BOMAG, whereas the Zn-complexes are mostly red in the beginning and after some minutes change to a violet colour as well. This shows the exchange of zinc with magnesium. The behaviour of chlorine substituted BIANs and their Zn derivatives is somehow different as their colour is always red. The colour of the BOMAG modified with BIAN-H4 on the other hand differs completely. Here a yellowish colour is usually recognizable, only in very rare cases, such as with 2-iPr and 4-tBu, an intense blue respectively orange coloration was observed. During the careful quenching with water a colour gradient from the initial colour to pink to brown to green and finally yellow was seen for the majority of the hydrogenated derivatives.Quenching of inert solutionsA first approach to gain insight into the mechanisms is the isolation of the BIAN derivatives after aqueous workup of the inert BOMAG-BIAN solutions. For BIANs it has already been shown that they undergo alkylation on the carbon atom of one of the C=N bonds27. As expected, all BIANs were isolated as butyl or octyl substituted derivatives (SI Fig. S83) and the structures could be identified with HPLC–MS (exact masses are listed in the SI in Table S1) as well as 1H-NMR (SI Sect. 3). The latter showed newly formed NH signals, which have unequivocally been assigned by HSQC experiments (SI Fig. S90), where no correlation of the proton signal to any carbon is found. In the case of all BIANs and their corresponding Zn-complexes the quenched products are identical, as shown in Fig. 7 for the 2-iPr derivatives, and consist of a mixture of C-octyl and C-butyl BIAN as confirmed by HPLC–MS (see SI Table S1). Zn or chlorine residues could not be found in the quenched products, they are obviously transferred into the aqueous phase during quenching. A clear and quantitative assignment of the alkyl substituent from the NMR spectra could, however, not be done as those signals are obscured by other peaks in the alkyl range. Despite drying the quenched products under high vacuum for at least 12 h, we were not able to remove those impurities. Analysis of several samples with GC–MS revealed that a mixture of higher hydrocarbons and 1-octanol are present, which are derived from the industrial synthesis of the BOMAG solutions in heptane. Those impurities have not been found in our previous study27, because in this case BOMAG was supplied in a toluene solution and exchanging the solvents must have led to a cleaner product. The octanol is also confirmed by 1H-NMR, where many quenched BIANs show a triplet at around 3.7 ppm that can be assigned to the CH2-group of a primary alcohol (Fig. 8, SI Sect. 3). The NMR of the quenched BOMAG without any BIAN can be also seen in the SI Fig. S84.Fig. 81H-NMR spectra of the quenched 2-iPr-BIAN (red) and the Zn-complex (black) being essentially similar. R = H or C4; Octanol @ 3.6 ppm.For the quenched para-substituted products, the HPLC–MS measurement shows other signals in addition to the butyl and octyl signals (Table S2). Figure 9a shows the HPLC–MS of pure 2-iPr-BIAN before and after quenching, where only two signals are observed, the structure with one butyl residue (36.2 min) and an octyl residue (51.4 min). These two signals can also be identified in the quenched 4-iPr-BIAN (butyl residue at 34.8 min and octyl residue at 47.2 min), but additionally some smaller fragments indicating, again, a lower hydrolytic stability of the para isomers (Fig. 9b).Fig. 9Chromatograms of the initial BIAN derivatives (black) and the reaction products after quenching (red). (a) 2-iPr-BIAN and (b) 4-iPr-BIAN.The situation with hydrogenated BIANs is of course different, as there are no more C=N double bonds available to undergo alkylation. Indeed, the hydrogenated BIANs could be regained without any structural change as could be proven by NMR as well as HPLC–MS analysis (Figs. 10, 11). HPLC–MS analysis also revealed that, in contrast to many of the BIANs and Zn complexes, the hydrogenated compounds do not undergo hydrolysis in the slightly acidic mobile phase. This behaviour sets them apart from the other derivatives as due to the lack of a chemical reaction and increased stability there is no permanent alteration of the BOMAG solution and, except for the 4-substituted derivatives, their interaction with the BOMAG chains is so strong that only small amounts are needed to reduce the viscosity of the solutions appropriately.Fig. 101H-NMR spectra the hydrogenated 2-iPr-BIAN-H4 and the isolated quenched product, again being similar.Fig. 11Chromatograms of the hydrogenated 2-iPr-BIAN-H4 (a) and the isolated quenched product (b).Investigation of the interaction with BOMAG under inert conditionsTo understand the actual interaction of the BIAN derivatives with the BOMAG chains and how they are able to reduce the solution’s viscosity, we have further focused on two analytical approaches. One is recording NMR spectra of inert solutions, and the other one is to observe the change of FTIR spectra of BIAN-BOMAG solutions under inert conditions and while gradually reacting with moisture until fully converted. In both cases inert conditions were obtained by shielding the solutions with argon. As a simplification, the following chapter only discusses the results for the isopropyl BIAN derivatives and in case of the FTIR experiments the unsubstituted BIAN as reference.FTIR analysisTo eliminate all effects and signals from the substituents we first investigated the unsubstituted BIAN. The hydrogenated form shows only a small number of well-defined bands under inert conditions, which are the aliphatic CH bonds at 2800–3000 cm−1, and the aromatic CH bonds at 1600, a broad (or double) at 1450, and one at 1380 cm−1 (Fig. 12a).Fig. 12FTIR spectra of inert unsubstituted BIAN derivatives in BOMAG solutions and their changes during the reaction with moisture. (a) Hydrogenated BIAN, (b) BIAN, (c) Zn-complex, (d) enlargement of the 1600 cm−1 region of BIAN.With the ongoing reaction with moisture a major change can be ascribed to the formation of Mg(OH)2 leading to broad bands at 3400, 1645, and 1414 cm−1. Those, together with aliphatic CH bands at 2800–3000 cm−1 are also the only ones seen, if pure BOMAG is left to react with moisture (SI Fig. S101).The other change that can be observed is the evolving of the secondary NH bands at 3376 and 3408 cm−1, along with a slightly better visibility of the aromatic CH bands at around 3050 cm−1. The 1600 cm−1 band remains unchanged and the final product shows an identical spectrum as the original hydrogenated BIAN.When comparing the inert spectra of the Zn-complex to the BIAN (Fig. 12b–d), the only difference, besides some minor changes in intensities, is that the C=N band shifts from 1640 to 1653 cm−1 due to complexation, as already described in literature40,41,42,43. The shift is attributed to the complex of the nitrogen lone pair with a cation, in this case Zn, under inert conditions. After the reaction with moisture this band is finally shifted to 1656 cm−1, which indicates that the interaction with Zn is only weak compared to Mg. Another obvious difference is that the BIAN shows an NH band at ~ 3300 cm−1 (this is most likely obscured by the very intense OH band in the Zn-complex). There are also two new bands evolving in the BIAN sample: one at 1500 cm−1 and the other at 1317 cm−1. The same is seen in the Zn complex but here the bands are again obscured by the Mg(OH)2 bands. The reaction products obtained after quenching the viscosity testing solutions have been analysed with FTIR spectroscopy as well and found to be identical to the ones of the final stages in the online quenching experiments.In the next step we look at the hydrogenated BIANs with one isopropyl group attached. If this group is in the ortho position, the viscosity of the BOMAG solution is lowered dramatically, while when in the para position one of the higher values is found for hydrogenated BIANs, being in the same range as the unsubstituted BIAN. As we already know from the HPLC and NMR analyses, the hydrogenated BIAN species do not undergo any permanent reaction and after quenching can be isolated again in their native state. In this context the most obvious observation is, that, just like with the unsubstituted BIAN, in the inert spectra no NH bonds can be seen but they evolve during the reaction with water (Fig. 13). In the case of 4-iPr-BIAN-H4 a band can be seen at 3384 cm−1, 2-iPr-BIAN-H4 has two bands at 3412 and 3436 cm−1. For comparison, the hydrogenated 2,6-iPr-BIAN-H427 also shows two bands but shifted to lower wavenumbers (3340 and 3358 cm−1).Fig. 13FTIR spectra of (a) 2-iPr-BIAN-H4 and (b) 4-iPr-BIAN-H4-BOMAG mixtures under inert conditions and their changes during the reaction with moisture.In the fingerprint region, again a change in the aromatic CH band at around 1600 cm−1 is observed. The ortho isomer changes from a single band at 1595 into two bands at 1600 and 1580 cm−1 and the para isomer shows just a shift from 1607 to 1613 cm−1.An interpretation of the obtained results is that free BIANs form an intermediary complex with the Mg alkyl compounds under inert conditions as shown by the shift of the C=N band. When the Zn-complex is used, an exchange to Mg is seen as well as a reaction pathway identical to the free BIAN, both leading to singly alkylated BIANs. In contrast, the reaction pathway of the hydrogenated BIANs must be different, as no C=N double bond is present. Here, the inert IR measurements reveal that the amino group cannot be seen under inert conditions, thus the complexation with Mg must involve both amino groups. After the reaction with moisture the complex is destroyed and the initial hydrogenated BIANs are formed again.NMR analysisBefore looking at the spectra of the inert mixtures we look again at the quenched BIAN derivatives. As already known from previous experiments27, BIANs undergo addition of an alkyl group to the carbon of the C=N bond. Depending on the magnesium alkyl used, those alkyl residues may vary, in our case a mixture of butyl and octyl groups. As mentioned before, isolation of the quenched products was not straightforward, as some high boiling byproducts from the BOMAG synthesis process remain and obscure some signals in the alkyl region. In the case of all BIANs and their corresponding Zn-complexes the quenched products are identical, as shown in Fig. 8 for the 2-iPr derivatives and consist of a mixture of C-octyl and C-butyl BIAN as confirmed by HPLC–MS (Fig. 8). The hydrogenated 2-iPr-BIAN is not permanently changed by the BOMAG solution as can be seen by comparing the NMR spectra before and after the reaction (Fig. 10), the only difference being the alkyl signals due to the BOMAG impurities, which have been identified with GC–MS. Again, this structure was confirmed by HPLC–MS analysis (Fig. 11).Interpretation of the NMR spectra under inert condition seems to be quite an impossible task, but as in the FTIR experiments, we recorded the spectra several times at different stages of reaction with moisture (Figs. 14, 16). Figure 14 shows the spectra of the hydrogenated 2-iPr-BIAN-H4-BOMAG mixture starting under inert conditions, over the course of the reaction and finally the quenched product. The most obvious change is how complex the aromatic region is split up in the inert BOMAG solution, which does not allow any clean interpretation and strongly suggests the presence of multiple structures instead of a single reaction intermediate. The NH proton is seen from the beginning and does not shift very much from its starting position at 4.6 ppm until fully quenched. This is interesting in context with the FTIR spectra, where the NH bands became visible only when the sample was fully quenched. Another signal that is always clearly identifiable is the multiplet from the CH proton of the isopropyl group at 2.48 ppm, which does shift to 2.6 ppm in the quenched product. A quantitative comparison of those two signals to the combined aromatic protons and the ring CH proton reveals some interesting results. When using the isopropyl CH signal as an internal reference, the abundance of the NH signal is always slightly below 1 (as expected from such an acidic proton) but rather constant, while the total integral of the aromatic protons equals 62 in the inert state and goes gradually down to 25, until finally reaching 10 in the quenched product. The latter one is very close to the theoretical composition of 8:1:1 of the hydrogenated 2-iPr-BIAN-H4, the difference can be explained because in our case all impurities have been included into the integral. While we cannot give a proper interpretation of this behavior so far, it supports the findings of FTIR experiments that also suggest a change in the aromatic CH bands. The ratio of NH signal to isopropyl CH signal is almost constant, which suggests that the structural integrity of the BIAN molecule is kept. Interaction of the BOMAG chains must thus mostly interfere with the aromatic structure of the BIAN, which we consider rather unlikely, or form complexes with the NH and isopropyl CH in an equimolar ratio.Fig. 141H-NMR spectra of the hydrogenated 2-isopropyl-BIAN with BOMAG under inert conditions (bottom), during the reaction with moisture (middle three) and the quenched product (top).A comparison of the HSQC spectra of the quenched and inert solution of the hydrogenated 2-isopropyl BIAN gives a little more insight into the inert status (Fig. 15). The alkyl region below 2 ppm in the 1H spectra correlates well with 13C signals below 40 ppm. Whilst the quenched product shows only one multiplet at 2.6/27 ppm, in the inert spectrum a series of peaks can be found with a 13C shift of around 28 ppm, but in this case spread from 2.5 to 4 ppm in the 1H dimension. A similar situation is seen with the hydrogenated carbon atom next to the nitrogen: while there is only one clean signal at 5.6/59 ppm in the quenched product, there are at least 6 major peaks with the same 13C shift in the inert spectrum. The 1H shift of these signals now spreads between 5.4 and 6.4 ppm. Those latter signals now also interfere with some protons in the 1H NMR spectrum that start at 6.1 ppm but have a 13C shift of 120 ppm, thus identifying them as aromatic. Neither the BIAN (except for the well-defined NH and neighboring CH) nor the pure BOMAG solution show signals in this range, thus they must arise from the complexation of the two, indicating that not only one but several species are formed when hydrogenated BIANs interact with the BOMAG solution.Fig. 15HSQC spectra of the quenched hydrogenated 2-isopropyl BIAN and the inert mixture with BOMAG.The situation gets even more complex when looking at the inert spectra of 2-isopropyl BIAN BOMAG mixtures and their reaction with moisture (Fig. 16). Both, the NH and the isopropyl CH cannot be clearly seen in the inert spectrum but are formed in course of the reaction. The trends that can be observed are: the NH band is shifting to a higher field, as is the adjacent CH signal. This is also seen for the isopropyl CH but to a much lesser extent.Fig. 161H-NMR spectra of the isopropyl-BIAN with BOMAG under inert conditions (bottom), during the reaction with moisture (middle two) and the quenched product (top).
Structural and spectroscopic characterization of N1,N2-diphenylacenapthylene-1,2-diimines and the influence of substituents on the viscosity of alkyl magnesium solutions
