DOI: 10.1002/zaac.202200192 Adducts of Diaminophosphines with Organoboranes Tobias Dunaj,[a] Christoph M. Feil,[a] Martin Nieger,[b] and Dietrich Gudat*[a] Dedicated to our dear colleague Prof. Dr. Thomas Schleid on the occasion of his 65th birthday. Reactions of chlorodiaminophosphines (R2N)2PCl (R=Et, iPr) with organoborohydrides M[BR’nH4-n] (M=Na, Li; n=1–3; R’= alkyl, Ph, CN) proceed via H/Cl metathesis to furnish secondary phosphines and boranes which may either combine to afford isolable donor-acceptor adducts (R2N)2P(H)� BR’nH3-n, coexist without any sign of mutual interaction, or give rise to mixtures comprising both a labile phosphine borane and its constituents in a temperature dependent equilibrium. Stable phosphine complexes of BH2CN and BH2Ph react with KN(SiMe3)2 under PH- bond metalation to afford spectroscopically detectable diami- nophosphide boranes whose usability as nucleophilic building blocks is illustrated by trapping one specimen in a PC-bond formation reaction with an alkyl halide. The selectivity of the individual H/Cl-metathesis and electrophilic substitution steps as well as the thermal stability of the various reaction products depend subtly on the Lewis acidity of the borane fragment and on steric factors. Several complexes of (iPr2N)-substituted phosphines with cyano- and phenylborane were characterized by single-crystal XRD. Introduction Borane coordination is not only a well-recognized measure to protect non-tertiary phosphines against unwanted oxidation or quaternization with electrophiles,[1] but may also enhance their PH-acidity and thus facilitate phosphide formation.[2] We have recently shown that borane coordination can be used to overcome the notorious reluctance of secondary diaminophos- phines Ia and phosphonites IIa (Scheme 1) to undergo metal- ation at their PH-bond and enables the forthright generation of thermally stable – and in some cases even isolable – phosphide boranes Ib and IIb, respectively.[3][4] Such species, which had previously only been described as elusive intermediates,[5] make attractive synthetic tools that can serve, like the traditional PH- or P(SiR3)-substituted phosphides (IIIb, IVb), as nucleophilic building blocks for the synthesis of functional phosphines.[6] However, whereas the products formed by quenching IIIb/IVb with electrophiles retain nucleophilic character at phosphorus (implying that further derivatization requires as well electro- philic reagents), the substituents in Ib/IIb impose electrophilic character on the P-atom in a resulting phosphine and make Ib/ IIb reagents that can decorate an electrophilic substrate with an electrophilic R2P-fragment allowing for post-functionalization with nucleophiles.[3,4] In this respect, the reactivity of both classes of phosphide reagents can be considered as comple- mentary. Like the majority of known studies on the chemistry of phosphine boranes in general, our previous exploration of the metalation of O/N-substituted derivatives[3,4] focused on adducts with parent borane (BH3). Nonetheless, there is also a consid- erable body of reports on phosphine complexes of various organoboranes.[7] As the substituents on boron affect both the Lewis acidity and steric properties of a borane, their variation can be expected to offer a possibility for fine-tuning the acidifying effect on a bound phosphine. With this prospect in mind, we considered that adducts of hetero-substituted phosphines with organoboranes might make a further appeal- ing synthetic target. Herein, we report on our studies on the formation of the appropriate adducts of secondary diamino- phosphines and their metalation properties. [a] T. Dunaj, Dr. C. M. Feil, Prof. Dr. Dr. h.c. D. Gudat Institute of Inorganic Chemistry University of Stuttgart Pfaffenwaldring 55, 70550 Stuttgart, Germany E-mail: gudat@iac.uni-stuttgart.de [b] Dr. M. Nieger Department of Chemistry University of Helsinki P.O Box 55, 00014 Helsinki, Finland Supporting information for this article is available on the WWW under https://doi.org/10.1002/zaac.202200192 © 2022 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Scheme 1. Generic molecular structures of secondary diaminophos- phines Ia, phosphonites IIa, and known phosphide reagents Ib–IVb (R=alkyl, aryl; M= (alkali)metal). Journal of Inorganic and General Chemistry Zeitschrift für anorganische und allgemeine Chemie www.zaac.wiley-vch.de RESEARCH ARTICLE Z. Anorg. Allg. Chem. 2022, 648, e202200192 (1 of 7) © 2022 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH Wiley VCH Donnerstag, 01.12.2022 2223 / 258476 [S. 79/85] 1 http://orcid.org/0000-0001-5459-8480 http://orcid.org/0000-0003-1677-0109 http://orcid.org/0000-0002-9196-0466 https://doi.org/10.1002/zaac.202200192 Results and Discussion Generation of diaminophosphine boranes. Elaborating on our earlier approach to access secondary diaminophosphine bor- anes by borohydride reduction of chlorophosphine precursors,[3] we investigated the reactions of 1a,b with selected substituted borohydrides. The reactions of both starting materials with Na[BH3CN] and Li[BH3Ph] (Scheme 2(a), (b)) proceeded with high selectivity to afford the expected diaminophosphine boranes 2a,b and 3a,b that were readily identified by multi- nuclear NMR spectroscopy. The presence of Lewis pairs with the targeted >PH� BH2-unit follows unmistakably from the multip- let structures of the 31P and 11B NMR signals arising from spin coupling of each nucleus with the adjacent proton(s) as well as mutual coupling with each other. Moreover, the 1H NMR spectra reveal coupling between B- and P-bound hydrogens via 3JHH (see Experimental Section). The magnitudes of the one-bond coupling constants (1JPB, 1JPH, 1JBH, see Table 1) in 3a,b roughly match those in the parent borane complexes (R2N)2P(H)BH3 4a,b (R= iPr, Et)[3] and increase further in 2a,b upon formal replacement of the phenyl group on boron by a more electron withdrawing cyano group. Work-up furnished 2a as a crystalline solid and 3a as a colorless oil that crystallized upon standing, and character- ization of both materials by single-crystal XRD studies con- firmed the molecular structures inferred from the NMR data (see further below). Whereas 2a proved thermally stable as a solid and in solution (a toluene solution showed no significant degeneration upon heating to 100 °C for 1 h), solid 3a was found to turn yellow and undergo slow decomposition (which also impeded obtaining a satisfactory elemental analysis) even at ambient temperature, but could be stored for a limited time at � 28 °C. Applying the same work-up scheme to N-ethylated phosphine borane 2b furnished only a crude product in the form of a yellowish oil that could not be freed from impurities. Even more extensive and faster decomposition occurred as well during the attempted purification of phenyl borane complex 3b which, although being rather stable in solution, remained up to now inaccessible in pure form. Action of alkyl borohydrides on 1a,b (Scheme 2(b), (c)) resulted likewise in hydride transfer from boron to phosphorus, but the reactions were mostly less selective (with Li[CyBH3], Li[Et3BH], Li[B(s-Bu)3H]) or even unselective (with Lithium-9- boratabicyclo[3.1.1]nonane) and gave generally labile adducts that were in dynamic equilibrium with their components (Scheme 2, (e)), or Lewis pairing was completely absent. While this behavior thwarted the isolation of well-defined products, 31P and 11B NMR studies still provided a clear picture of the ongoing processes. Regarding phosphine formation, we found that hydride transfer from Li[s-Bu3BH] to both 1a,b and from Li[CyBH3] to 1a proceeds with a comparable degree of selectivity as with cyano and phenyl borohydride. Action of Li[Et3BH] on 1a yielded a 93 :7 mixture of secondary phosphine (iPr2N)2PH (5a) [8] and a by-product identified as P-ethylated (iPr2N)2PEt. We attribute the formation of the latter to a competing ethyl transfer reaction between both reactants. Delineation of the Lewis pairing behavior of the phosphines formed was feasible from a closer analysis of 31P NMR chemical shifts and 1JPH coupling constants. The data for all borohydride reduction products derived from 1a match the values reported for 5a,[8] indicating that the phosphine and any boranes formed coexist in solution without significant mutual interaction. This hypothesis is in the case of the reactions of 1a with Li[R3BH] (R=Et, s-Bu) corroborated by the detection of the signals of the Scheme 2. Reaction of chlorophosphines 1a,b with borohydrides M[BHnR’4-n] (Cy=cyclohexyl). Table 1. 31P and 11B NMR data of phosphine boranes (R2N)2P(X)- borane. R X borane δ31P 1JPB [Hz] 1JPH [Hz] δ11B 1JBH [Hz] 2a iPr H BH2CN 32.2 99 435 � 36.1 104 2b Et H BH2CN 66.5 100 453 � 38.4 100 3a iPr H BH2Ph 42.0 67 407 � 25.2 99 3b Et H BH2Ph 77.7 70 423 � 25.9 95 4a[a] iPr H BH3 46.3 73 407 � 35.6 107 4b[b] Et H BH3 80.3 73 433 � 39.1 93 6[c] Et H BEt3 81.4 –[d] 410 � 8.9 –[d] 8a iPr K BH2CN 55.6 66 – � 35.1 92 8b Et K BH2CN 118.4 62 – � 36.0 95 9a iPr K BH2Ph 60.5 62 – � 17.8 81 9b Et K BH2Ph 135.5 51 – � 21.2 87 10a[a] iPr K BH3 53.4 64 – � 29.5 84 10b[b] Et K BH3 130.7 52 – � 32.3 85 [a] data from ref. [3b]. [b] data from ref. [3a]. [c] at � 90 °C. [d] obscured by line broadening effects. Journal of Inorganic and General Chemistry Zeitschrift für anorganische und allgemeine Chemie RESEARCH ARTICLE Z. Anorg. Allg. Chem. 2022, 648, e202200192 (2 of 7) © 2022 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH Wiley VCH Donnerstag, 01.12.2022 2223 / 258476 [S. 80/85] 1 respective boranes (δ11B 87.4 (Et3B), 85.6 (s-Bu3B)), and is also in accord with the identification of an oily residue obtained after reduction of 1a with Li[Et3BH] and removal of all insoluble and volatile components as crude 5a. Reduction of 1b with Li[s-Bu3BH] gave, according to the 31P and 11B NMR spectra, also a non-interacting mixture of the known secondary phosphine ((Et2N)2PH, 5b [8]) and the respec- tive tertiary borane. Formation of a secondary diaminophos- phine was likewise confirmed for the reaction of 1b with Li[Et3BH], but an observed 1JPH coupling constant of 274 Hz exceeds in this case perceptibly the value of 259 Hz reported[8] for 5b. Considering that 1JPH coupling constants in diamino- phosphine boranes are usually about twice as large as in the free phosphines (see the data for 2a,b–4a,b in the experimental and in ref [3]), we interpret our findings as a hint to the presence of a dynamic equilibrium between the separate components and a respective Lewis pair (5a/BEt3 and 6, Scheme 2). Confirmation of this hypothesis was obtained from VT NMR studies, which revealed a further numerical increase in 1JPH and a concomitant decline in δ11B with falling temperature (Figures 1, S22, S23) indicating that the molar fraction of 6 in the equilibrium increases upon cooling and approaches unity at temperatures between � 70 and � 90 °C. Similar thermally induced dissociation of Lewis pairs has also been observed in other cases.[9] Titration experiments indicated that adduct formation can also be promoted at ambient temperature by adding excess borane (see Figure S24). Finally, formation of a mixture of two room-temperature stable Lewis pairs as main products along with further by- products was observed for the reduction of 1b with Li[CyBH3]. Based on the multiplicities of the 11B NMR signals, we assign one major product as the expected adduct 7 (δ31P 78.8, δ11B � 26.7, doublet (1JPB=61 Hz) of triplets ( 1JBH=97 Hz)), while the second one is identified as known 4b[3] (δ31P 83.7, δ11B � 40.2, doublet (1JPB=66 Hz) of quartets ( 1JPB=100 Hz)). The origin of 4b is not yet understood in detail, but it may arise from similar transalkylation processes as had been observed during hydro- boration reactions with CyBH2. [10] The unselective formation and long-term instability of 4b (as evidenced by an eventual decay of the NMR signals at prolonged reaction times) prevented until now its isolation in pure form. Comparing the outcome of all our attempts on the synthesis of diaminophosphine boranes (R2N)2PH� B (R=Et, iPr) with both parent (B=BH3) and substituted borane acceptors (B=BH2CN, BH2Ph, B(alkyl)3), we note that the relative thermal stabilities of the adducts reveal a similar trend as the hydride affinities of the respective boranes,[11] which decrease in the order BH2CN@ BH3>BH2Ph@B(alkyl)3 and can be considered as a measure of declining Lewis-acidity. Varying Lewis-pairing behavior of a given acceptor towards different donors (5a, 5b, (Me2N)2PH [3]) indicates, however, that the stability of the adducts depends not only on the borane Lewis-acidity, but as well on the nucleophilicity of the phosphine and steric influences. Regard- ing this last aspect, it seems that a certain steric protection of the phosphorus atom seems to be needed for selective reactions while accruing steric bulk around boron obviously has a detrimental effect. Metalation studies. Metalation of phosphine boranes 2a,b and 3a,b was achieved by treatment with potassium hexameth- yl disilazide (KHMDS) in diethyl ether, which had previously been identified[3] as suitable approach to diaminophosphide boranes (Scheme 3). With the exception of 9b, which precipi- tated as a colorless solid from the reaction mixture and was separated in crude form after filtration, the high sensitivity of the metalation products impeded work-up and isolation, and 8a,b and 9a were only characterized in situ by NMR spectro- scopy. Evaluation of the 31P NMR spectra indicated that all products had formed with 86–99% selectivity.[12] The molecular structure as phosphides followed undeniably from the absence of the signal of a P-bound hydrogen atom in the 1H NMR spectra and the disappearance of the diagnostic 1JPH splitting in 31P NMR spectra. The appearance of the 11B NMR signal as doublets of triplets further confirm that the P� BH2R (R=CN, Ph) moieties remained intact. The increase in 31P NMR chemical shifts and numerical decrease in 1JPB coupling constants upon metalation is similar as for previously reported diaminophos- phide boranes (R2N)2P(BH3)K (10a,b, Table 1). [3] Diaminophosphine borane 6, although being unstable towards dissociation into its constituents 5b and BEt3 under ambient conditions, still forms the main phosphorus-containing constituent at low temperature or in the presence of an excess Figure 1. Temperature dependence of the observed values of δ11B (diamonds) and 1JPH (circles) for the equilibrium mixture 5b+BEt3/6 formed in situ upon reaction of equimolar amounts of 1b and Li[BEt3H] in Et2O. Scheme 3. Metalation of 2a,b/3a,b and ensuing alkylation of 8a. Journal of Inorganic and General Chemistry Zeitschrift für anorganische und allgemeine Chemie RESEARCH ARTICLE Z. Anorg. Allg. Chem. 2022, 648, e202200192 (3 of 7) © 2022 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH Wiley VCH Donnerstag, 01.12.2022 2223 / 258476 [S. 81/85] 1 borane, and might under these conditions in principle be also amenable to deprotonation. Performing the reaction of the equilibrium mixture of 5b/BEt3 and 6 with KHMDS at � 78 °C gave, however, no spectroscopic evidence for any phosphide formation. Identical behavior was also observed when the reaction was conducted in the presence of a 10-fold excess of BEt3 or at higher temperatures. We presume that the inert behavior of the secondary phosphine in these reactions is either due to the fact that the boost of PH-acidity induced by coordination of a noticeably weaker Lewis-acid than BH2CN, BH3 or BH2Ph is either insufficient for successful metalation, or that this reaction is inhibited by the steric demand of the substituents on boron. Having succeeded in deprotonation of 2a,b and 3a,b, we further investigated the coupling of the resulting phosphide boranes with selected electrophiles. Treatment of 8a with 2- iodopropane afforded the expected metathesis product 11 (Scheme 3), which was isolated in 65% yield after crystallization and characterized by NMR spectroscopy and a single crystal XRD study. NMR studies provided preliminary evidence that Me3SiCl and Ph2PCl might react similarly, but less selectively, and we could neither isolate nor unambiguously identify any products until now. The reactions of 8b and 9a,b with the same set of electrophiles were unselective and usually furnished mixtures of several phosphorus-containing species from which likewise no pure compounds could be isolated.[13] In total, it appears that organic substituents on the boron atom of a phosphide borane disfavor clean reactions with electrophiles, causing either less selective transformations as have been observed for adducts with parent borane (BH3), [3] or introducing additional complications during work-up. Moreover, our findings seem to confirm that not only the formation of stable donor-acceptor bonds but also a successful boost of PH- acidity upon borane coordination require boranes with suffi- ciently high Lewis-acidity. Finally, while a certain steric protection of the phosphorus atom seems to be needed for selective reactions, accruing steric bulk around boron obviously has a detrimental effect. Crystal structure studies. The crystals of phosphine boranes 2a, 3a and 11 (Figure 2) contain isolated molecules with the expected tetrahedral coordination at the phosphorus and boron atoms, with crystalline 11 being special due to the presence of two conformers with slightly different disposition of the NiPr2- moieties (Figure S1). The P� B distances in 2a (1.929(4) Å), 3a (1.934(5) Å), and 11 (1.955(5) and 1.964(5) Å) fall into the typical region of P� B dative bonds in diaminophosphine boranes (1.915�0.059 Å[14]). The substituents at all P� B bonds adopt a staggered conformation in which the non-hydrogen substituent on boron and one of the amino groups on phosphorus adopt a trans-periplanar orientation granting minimal steric interactions. The P� B bond lengthening in 11 is at first glance counter- intuitive if one considers that formal replacement of a P-bound hydrogen in 2a by an alkyl should render the phosphine a stronger donor. However, as this trend coincides with a parallel elongation of the P� N distances, we presume that both trends are sterically induced. That the variation of P� B distances in phosphine boranes is controlled by steric rather than electronic factors had been noted before.[15] Conclusions Reactions of bis(dialkylamino)chlorophosphines with organo- borohydrides compare to those with parent borohydride in involving an initial Cl/H-metathesis step, but differ in that the resulting secondary phosphines and boranes may either coexist without mutually interacting or combine to form more or less stable donor-acceptor complexes. Highly stable adducts of this type derived from boranes whose electron accepting power matches (BH2Ph) or even exceeds (BH2CN) that of parent BH3 undergo metalation and post-functionalization of the newly formed PH-bond upon treatment with KHMDS and an electro- phile. While a certain steric protection of the phosphorus atom is obviously needed to render these reactions selective, accruing steric bulk around boron seems to reduce both adduct stabilities and the selectivity in post-functionalization steps. Since these obstacles render work-up procedures more tedious and less effective than for complexes with parent borane, using Figure 2. Representations of the molecular structures of 2a, 3a and one of the crystallographically independent molecules of 11 (from top to bottom) in the crystal. Hydrogen atoms, except those on boron and phosphorus atoms, were omitted for clarity and thermal ellipsoids were drawn at the 50% probability level. Selected distances and angles are listed in Table S2. Journal of Inorganic and General Chemistry Zeitschrift für anorganische und allgemeine Chemie RESEARCH ARTICLE Z. Anorg. Allg. Chem. 2022, 648, e202200192 (4 of 7) © 2022 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH Wiley VCH Donnerstag, 01.12.2022 2223 / 258476 [S. 82/85] 1 organoboranes instead of BH3 for PH-bond activation does not seem to offer any particular advantage, except in cases where the higher Lewis acidity of BH2CN compared to BH3 may assist in enforcing the derivatization of low reactive PH bonds. Experimental Section All manipulations were carried out under an atmosphere of inert argon inside glove boxes or by using standard vacuum line techniques. Solvents were dried by refluxing over Na (toluene) or NaK (Et2O, pentane) and distilled before use. NMR spectra were recorded on Bruker Avance 250 (1H 250.0 MHz, 11B 80.2 MHz, 13C 62.9 MHz, 31P 101.2 MHz) or Avance 400 (1H 400.1 MHz, 11B 128.4 MHz, 13C 100.5 MHz, 31P 161.9 MHz) instruments at 293 K if not stated otherwise. 1H Chemical shifts were referenced to TMS using the signals of the residual protons of the deuterated solvent (δ1H=7.15 (C6D6), 1.73 (THF-D8)) as secondary reference. Spectra of heteronuclei were referenced using the Ξ-scale[16] employing TMS (Ξ=25.145020 MHz, 13C), BF3·OEt2 (Ξ=32.083974 MHz, 11B) and 85% H3PO4 (Ξ=40.480747 MHz, 31P) as secondary references. Coupling constants involving boron nuclei refer to the isotope 11B if not stated otherwise. The 13C{1H} NMR signals of carbon atoms next to boron were mostly unidentifiable due to insufficient signal-to- noise ratio and signal broadening effects. Conversions and selectivities derived from NMR data are based on the evaluation of the relative integrals in 31P{1H} NMR spectra recorded with 30° excitation pulses and neglecting influences of different relaxation times. Elemental analyses were determined on a Thermo Micro Cube CHN analyzer. Phenyl and cyclohexyl borohydrides were prepared as reported elsewhere.[17] Diaminophosphine cyanoboranes 2a,b. A solution of the appro- priate chlorophosphine (1a: 1.50 g, 5.62 mmol, 1b: 137 mg, 0.65 mmol) in Et2O (5 ml) was added to a cooled (� 78 °C) suspension of Na[BH3CN] (0.42 g, 6.7 mmol/49 mg, 0.78 mmol) in Et2O (20 ml). The mixture was allowed to warm to ambient temperature and stirred for 12 h. Volatiles were then evaporated under reduced pressure and the solid residue extracted with three portions of pentane (20 ml). The extracts were combined and volatiles removed in vacuum to leave a colorless powder (2a) or yellow oil (2b), respectively. Recrystallization of 2a from pentane (5 ml) at � 28 °C furnished colorless crystals, whereas 2b could not be freed from impurities resulting from partial decomposition during work-up and was only characterized spectroscopically. 2a: Yield 1.14 g (4.21 mmol, 75%). – 1H NMR (C6D6): δ=6.53 (dt, 1 H, 1JPH=435 Hz, 3JHH=5.1 Hz, PH), 3.25 (d sept, 4 H, 3JPH=14.6 Hz, 3JHH=6.8 Hz, CH), 1.94 (br q, 2 H, 1JBH=104 Hz, BH2), 0.99 (d, 12 H, 3JHH=6.8 Hz, CH3), 0.84 (d, 12 H, 3JHH=6.8 Hz, CH3). – 11B NMR (C6D6): δ= � 36.1 (dt, 1JPB=99 Hz, 1JBH=104 Hz). – 13C{1H} NMR (C6D6): δ= 47.1 (d, CH, 2JPC=4.8 Hz), 22.5 (d, CH3, 3JPC=3.4 Hz), 22.4 (d, CH3, 3JPC=3.2 Hz). – 31P{1H} NMR (C6D6): δ=32.2 (q, 1JPB=99 Hz). – C13H31BN3P (271.20 g/mol), calcd. C 57.58 H 11.52 N 15.49, found C 56.92 H 11.67 N 15.15. The deviation in carbon content may arise from the presence of minor impurities visible in the 1H NMR spectrum. 2b: Yield 51 mg of crude product. – 1H NMR (C6D6): δ=5.89 (dt, 1 H, 1JPH=453 Hz, 3JHH=5 Hz, PH), 2.61 (ddq, 4 H, 2JHH=15.3 Hz, 3JHH= 7.4 Hz, 3JPH=3.0 Hz, CH2), 2.52 (ddq, 4 H, 2JHH=15.3 Hz, 3JHH=7.3 Hz, 3JPH=4.6 Hz CH2), 0.71 (t, 12 H, CH3, 3JHH=7.4 Hz), signal from BH2CN not identified. – 11B NMR (C6D6): δ= � 38.4 (q, 1JPB� 1JBH�100 Hz). – 13C{1H} NMR (C6D6): δ=41.3 (d, 2JPC=3.1 Hz, CH2), 13.6 (d, 3JPC= 2.5 Hz, CH3). – 31P{1H} NMR (C6D6): δ=66.5 (q, 1JPB=100 Hz). Diaminophosphine phenylboranes 3a,b. A solution of the appro- priate chlorophosphine (1a: 150 mg, 0.56 mmol, 1b: 164 mg, 0.78 mmol) in Et2O (5 ml) was added to a cooled (� 78 °C) suspension of Li[BH3Ph] (61 mg, 0.62 mmol/85 mg, 0.86 mmol) in Et2O (20 ml). The mixture was allowed to warm to ambient temperature and stirred for 12 h. Volatiles were then evaporated under reduced pressure and the solid residue extracted with pentane (30 ml). The extracts were combined and volatiles removed in vacuum to leave the crude product as colorless oil, which in the case of 3a eventually solidified to produce a crystalline material. Both products decayed slowly (3a) or rapidly (3b) to produce yellowish, gummy materials when stored in substance whereas solutions in inert solvents proved to be reasonably stable as long as air and moisture were excluded. 3a: Yield 152 mg (0.47 mmol, 84%) of crude product. – 1H NMR (C6D6): δ=7.53 (br m, 2 H, o-H), 7.30 (m, 2 H, m-H), 7.16 (m, 1 H, p- H), 6.73 (dt, 1 H, 1JPH=407 Hz, 3JHH=6.5 Hz, PH), 3.37 (d sept, 4 H, 3JHH=6.8 Hz, 3JPH=14.0 Hz, CH), 2.7 (br, 2 H, BH2), 0.94 (d, 12 H, 3JHH=6.8 Hz, CH3) 0.89 (d, 12 H, 3JHH=6.8 Hz, CH3). – 11B NMR (C6D6): δ= � 23.2 (dt, 1JPB=67 Hz, 1JBH=99 Hz). – 13C{1H} NMR (C6D6): δ= 147.4 (br, i-C), 136.1 (d, 3JPC=10.1 Hz, o-C), 127.2 (d, 4JPC=3.0 Hz, m- C), 124.5 (d, 5JPC=4.5 Hz, p-C), 47.0 (d, 2JPC=4.5 Hz, CH), 22.9 (d, 3JPC=2.3 Hz, CH3), 22.5 (d, 3JPC=2.3 Hz, CH3). – 31P{1H} NMR (C6D6): δ=42.0 (m). 3b: Yield not determined. – 1H NMR (C6D6): δ=7.74 (br m, 2 H, o-H), 7.34 (m, 2 H, m-H), 7.20 (m, 1 H, p-H), 6.09 (dt, 1 H, 1JPH=423 Hz, 3JHH=5.7 Hz), 2.76 (ddq, 8 H, 2JHH=14.4 Hz, 3JHH=7.1 Hz, 3JPH= 9.3 Hz, CH2), 2.78 (br, 2 H, BH2), 2.65 (ddq, 8 H, 2JHH=14.4 Hz, 3JHH= 7.1 Hz, 3JPH=11.0 Hz, CH2), 0.69 (t, 12 H, 3JHH=7.1 Hz, CH3). – 11B NMR (C6D6): δ= � 25.9 (dt, 1JPB=70 Hz, 1JBH=95 Hz). – 13C{1H} NMR (C6D6): δ=146.6 (br, i-C), 136.3 (d, 3JPC=9.0 Hz, o-C), 127.2 (d, 4JPC= 3.0 Hz, m-C), 124.7 (d, 5JPC=4.5 Hz, p-C), 41.5 (d, 2JPC=2.3 Hz, CH2), 13.7 (d, 3JPC=2.4 Hz, CH3) – 31P{1H} NMR (C6D6): δ=77.7 (m). Reactions of diaminochlorophosphines with trialkylborohydrides. In a typical procedure, Li[BHEt3] (3.78 ml of a 1 M soln in Et2O, 3.78 mmol) was added to a cooled (-78 °C) solution of 1b (404 mg, 1.92 mmol) in Et2O (8.1 ml). The mixture was allowed to warm to room temperature and solid precipitates were removed by filtration. The filtrate analyzed using 31P and 11B NMR spectroscopy. For the study of donor/acceptor equilibria, aliquots (4×2 ml, 1× 0.1 ml) of the aforementioned filtrate were transferred to five separate flasks. Defined portions of Et3B (0.38/1.52/3.43/8.50 ml of a 1 M solution adding up to 1/4/9/500 equivalents) were added to flask #2 to #5, respectively. The content of the first flask was analyzed by 31P and 11B VT-NMR spectroscopy and the remaining solutions by 31P NMR spectroscopy at ambient temperature (see Figures S22–S24). Potassium diaminophosphide boranes 8a,b and 9a. The appro- priate crude diaminophosphine borane (2a: 25 mg, 90 μmol, 2b: 25 mg, 11 μmol, 3a: 25 mg, 80 μmol) and KHMDS (20 mg, 10 μmol/ 26 mg, 13 μmol/25 mg, 85 μmol) were dissolved in Et2O (5 ml). The resulting solution was stirred for 15 min. Volatiles were evaporated under reduced pressure. The residue was dissolved in THF-d8 (8a,b) or C6D6 (9a) and the resulting mixture of metalated diaminophos- phine borane and residual HN(SiMe3)2 characterized NMR spectro- scopically. 8a: conversion >99% (by 31P NMR); 1H NMR (THF-D8): δ=3.48(d sept, 4 H, 3JPH=9.4 Hz, 3JHH=6.7 Hz, CH), 1.12 (d, 12 H, 3JHH=6.7 Hz, CH3), 1.04 (m, 12 H, 3JHH=6.7 Hz, CH3), 0.85–1-3 (br, 2H, BH2). – 11B NMR (THF-D8): δ= � 35.1 (dt, 1JPB=66 Hz, 1JBH=92 Hz). – 13C{1H} NMR (THF-D8): δ=47.3 (d, 2JPC=5 Hz), 24.1 (s, CH3), 24.0 (s, CH3). – 31P{1H} NMR (THF-D8): δ=55.6 (m). Journal of Inorganic and General Chemistry Zeitschrift für anorganische und allgemeine Chemie RESEARCH ARTICLE Z. Anorg. Allg. Chem. 2022, 648, e202200192 (5 of 7) © 2022 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH Wiley VCH Donnerstag, 01.12.2022 2223 / 258476 [S. 83/85] 1 8b: conversion >86% (by 31P NMR); 1H NMR (THF-D8): δ=3.11 (ddq, 4 H, 2JHH=13.2 Hz, 3JHH=7.1 Hz, 3JPH=9.7 Hz, CH2), 2.98 (ddq, 4 H, 2JHH=13.2 Hz, 3JHH=7.1 Hz, 3JPH=9.9 Hz, CH2), 0.95 (dt, 12 H, 3JHH=7.1 Hz, 4JPH=1.2 Hz, CH3), 0.5-1.0 (br, 2 H, BH2). – 11B NMR (THF-D8): δ= � 36.0 (dq, 1JPB=62 Hz, 1JBH=95 Hz). – 13C{1H} NMR (THF-D8): δ=45.0 (d, 2JPC=8.0 Hz, CH2), 14.4 (d, 3JPC=4.0 Hz, CH3). – 31P{1H} NMR (THF-D8): δ=118.4 (m). 9a: conversion 90% (by 1H NMR); 1H NMR (C6D6): δ=7.48 (br m, 2 H, o-H), 7.18 (m, 2 H, m-H), 7.01 (t, 1 H, p-H, 3JHH=7.2 Hz), 3.69 (d sept, 4 H, 3JHH=6.7 Hz, 3JPH 8.6 Hz, CH), 1.7 (br q, 1JBH=81 Hz, BH2), 1.42 (d, 12 H, 3JHH=6.7 Hz, CH3), 1.15 (d, 12 H, 3JHH=6.7 Hz, CH3). – 11B NMR (C6D6): δ= � 17.8 (dq, 1JPB=62 Hz, 1JBH=81 Hz). – 13C NMR (1H,13C gs-HSQC, C6D6) δ=135.1 (o-C), 127.8 (m-C), 124.1 (p-C), 48.6 (d, 2JPC=4 Hz, CH), 24.9 (d, 3JPC=6.2 Hz, CH3), 24.5 (d, 3JPC=5.4 Hz, CH3). – 31P{1H} NMR (C6D6): δ=60.5 (q, 1JPB=62 Hz). Potassium bis(diethylamino)phosphide borane 9b. A solution of 1b (149 mg, 0.71 mmol) in Et2O (5 ml) was added to a cooled (-78 °C) suspension of Li[BH3Ph] (76 mg, 0.78 mmol) in Et2O (10 ml). The mixture was allowed to warm to ambient temperature and stirred for 1 h. Volatiles were removed under reduced pressure and the residue right away extracted with pentane. Volatiles were evaporated once more and the residual yellowish oil immediately dissolved in Et2O (5 ml). Addition of a solution of K[N(SiMe3)2] in Et2O (5 ml) produced a colorless precipitate which was allowed to settle. The supernatant solution was decanted off and the residue washed with Et2O (10 ml) and pentane (10 ml) to afford crude 9b (75 mg, 0.25 mmol, 35%) as a highly air and moisture sensitive, colorless solid. 1H NMR (THF-D8): δ=7.42 (br s, 2 H, o-H), 6.90 (m, 2 H, m-H), 6.74 (m, 1 H, p-H) 3.20 (ddq, 4 H, 2JHH=13.2 Hz, 3JHH=7.0 Hz, 3JPH= 6.2 Hz, CH2), 3.08 (ddq, 4 H, 2JHH=13.2 Hz, 3JHH=7.0 Hz, 3JPH=7.5 Hz, CH2), 1.87 (br q, 1JBH=87 Hz, BH2), 0.92 (t, 12 H, 3JHH=7.0 Hz, CH3). – 11B NMR (THF-D8): δ= � 21.2 (dq, 1JPB=51 Hz, 1JBH=87 Hz). – 13C{1H} NMR (THF-D8): δ=135.5 (d, 3JPC=9.9 Hz, o-C), 125.7 (br m, m-C), 121.3 (d, 5JPC=2.7 Hz, p-C), 45.5 (br m, CH2), 14.5 (d, 3JPC=3.8 Hz, CH3). – 31P{1H} NMR (THF-D8): δ=135.5 (q, 1JPB=51 Hz). – C14H27BKN2P (304.27 g/mol), calcd. C 55.27 H 8.94 N 9.21, found C 54.56 H 9.01 N 8.73. Bis(diisopropylamino)isopropylphosphine borane 11. 2a (29 mg, 0.11 mmol) and KHMDS (23 mg, 0.12 mmol) were dissolved in Et2O (10 ml). The solution was stirred for 15 min, 2-iodopropane (11 μl, 19 mg, 0.12 mmol was added, and stirring was continued for 12 h. Volatiles were then removed under reduced pressure and the residue extracted with pentane (10 ml). Volatiles were evaporated once more and the residual colorless solid dissolved in a minimum volume of a mixture of pentane and toluene (approx. 1 :1). Storage at � 28 °C furnished colorless crystals of 11 (yield 22 mg, 70 μmol, 65%). The purity of the product was established by NMR spectroscopy. 1H NMR (C6D6): δ=3.49 (d sept, 4 H, 3JHH=6.9 Hz, 3JPH=11.4 Hz, NCH), 1.9 (br q, 2 H, 1JBH=100 Hz, BH2), 1.79 (d sept, 1 H, 3JPH= 17.9 Hz, 3JHH=7.1 Hz, PCH), 1.15 (dd, 6 H, 3JPH=16.6 Hz, 3JHH=6.8 Hz, PCCH3), 1.12 (d, 12 H, 3JHH=6.9 Hz, NCCH3), 1.08 (d, 12 H, 3JHH= 6.9 Hz, NCCH3). – 11B NMR (C6D6): δ= � 37.6 (dq, 1JPB=109 Hz, 1JBH= 100 Hz). – 13C{1H} NMR (C6D6): δ=48.5 (d, 2JPC=3.6 Hz, NCH), 25.2 (d, 1JPC=58.3 Hz, PCH), 24.8 (d, 3JPC=2.5 Hz, NCCH3), 24.4 (d, 3JPC= 2.9 Hz, NCCH3), 18.0 (d, 2JPC=2.9 Hz, PCCH3). – 31P{1H} NMR (C6D6): δ=89.0 (m). Crystallographic studies. X-ray diffraction data were collected on a Bruker Kappa Apex II Duo diffractometer equipped with an APEX II CCD-detector and a KRYO-FLEX cooling device with Mo-Ka radiation (l=0.71073 Å) at 130(2) K. The structures were solved with direct methods (SHELXS-2014[18]) and refined with a full-matrix least squares scheme on F2 (SHELXL-2014[18]). Semi-empirical absorption corrections were applied. Non-hydrogen atoms were refined anisotropically and hydrogen atoms except those bound to phosphorus and boron using a riding model. Further details on the refinement are given in the supporting information (Table S1), the cif-files, and the incorporated res-files. CCDC-2171774 to CCDC- 2171776 contain the crystallographic data for this paper, which can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data request/cif. Acknowledgements The authors gratefully acknowledge financial support from German Research Foundation (DFG) grant no Gu415-18/1 and thank B. Förtsch for elemental analyses and Dr. W. Frey (Institut für Organische Chemie) for collecting the X-ray data sets. Open Access funding enabled and organized by Projekt DEAL. Conflict of Interest The authors declare no conflict of interest. Data Availability Statement The data that support the findings of this study are available from the corresponding author upon reasonable request. Keywords: Phosphines · Phosphorus nitrogen compounds · Boranes · Alkali metals · Nucleophiles [1] For a recent review, see: A. Staubitz, A. P. M. Robertson, M. E. Sloan, I. Manners, Chem. Rev. 2010, 110, 4023–4078. [2] M. Hurtado, M. Yánez, R. Herrero, A. Guerrero, J. Z. Dávalos, J.- L. M. Abboud, B. Khater, J.-C. Guillemin, Chem. Eur. J. 2009, 15, 4622–4629. [3] a) M. Blum, J. Kappler, S. H. Schlindwein, M. Nieger, D. Gudat, Dalton Trans. 2018, 47, 112–119; b) D. Gudat, M. Blum, T. Dunaj, J. A. Knöller, C. M. Feil, M. Nieger, Chem. Eur. J. 2020, 26, 15190–15199. [4] T. D. Hettich, R. Rudolf, C. M. Feil, N. Birchall, M. Nieger, D. Gudat, Chem. Eur. J. 2021, 27, 5412–5416. [5] a) A. Longeau, P. Knochel, Tetrahedron Lett. 1996, 37, 6099– 6102; b) Y. Belabassi, M. I. Antczak, J. Tellez, J.-L. Montchamp, Tetrahedron 2008, 64, 9181–9190; c) R. Higashida, N. Oka, T. Kawanaka, T. Wada, Chem. Commun. 2009, 2466–2468. [6] See: a) M. Stankevič, K. M. Pietrusiewicz, in Science of Synthesis, Vol 31.42 update 2013/2 (Ed. C. A. Ramsden), Thieme, Stuttgart, 2013, pp. 329–380; b) E. Hey-Hawkins, A. A. Karasik, in Science of Synthesis, Vol 42.4 (Ed. F. Mathey), Thieme, Stuttgart 2008, pp. 71–108; c) D. Gudat, in Science of Synthesis, Vol 42.6 (Ed. F. Mathey), Thieme, Stuttgart, 2008, pp. 155–220. [7] Selected reviews: a) B. Carboni, L. Monnier, Tetrahedron 1999, 55, 1197–1248; b) D. Gabel, M. B. El-Zaria, in Science of Synthesis, vol 6 (Eds.: D. E. Kaufmann, D. S. Matteson, E. Schaumann, M. Regitz), Thieme, Stuttgart, 2004, pp. 541–561; c) A. C. Gaumont, B. Carboni, in Science of Synthesis, vol 6 (Eds.: Journal of Inorganic and General Chemistry Zeitschrift für anorganische und allgemeine Chemie RESEARCH ARTICLE Z. Anorg. Allg. Chem. 2022, 648, e202200192 (6 of 7) © 2022 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH Wiley VCH Donnerstag, 01.12.2022 2223 / 258476 [S. 84/85] 1 http://www.ccdc.cam.ac.uk/data_request/cif https://doi.org/10.1021/cr100105a https://doi.org/10.1002/chem.200802307 https://doi.org/10.1002/chem.200802307 https://doi.org/10.1039/C7DT04110A https://doi.org/10.1002/chem.202005437 https://doi.org/10.1016/0040-4039(96)01296-8 https://doi.org/10.1016/0040-4039(96)01296-8 https://doi.org/10.1016/j.tet.2008.07.054 https://doi.org/10.1039/b901045a https://doi.org/10.1016/S0040-4020(98)01103-X https://doi.org/10.1016/S0040-4020(98)01103-X D. E. Kaufmann, D. S. Matteson, E. Schaumann, M. Regitz), Thieme, Stuttgart, 2004, pp. 485–512. [8] R. B. King, N. D. Sadanani, P. M. Sundaram, Phosphorus Sulfur Relat. Elem. 1983, 18, 125–128. [9] See for example: a) P. Spies, G. Kehr, K. Bergander, B. Wibbeling, R. Fröhlich, G. Erker, Dalton Trans. 2009, 1534–1541; b) K. V. Axenov, C. M. Mömming, G. Kehr, R. Fröhlich, G. Erker, Chem. Eur. J. 2010, 16, 14069–14073. [10] A. Andreou, M. Leskes, P. G. Jambrina, G. J. Tustin, C. P. Grey, E. Rostac, O. A. Scherman, Chem. Sci. 2015, 6, 6262–6269. [11] a) D. B. Workman, R. R. Squires, Inorg. Chem. 1988, 27, 1846– 1848; b) R. Vianello, Z. B. Maksić, Inorg. Chem. 2005, 44, 1095– 1102; c) M. Méndez, A. Cedillo, Comp. Theor. Chem. 2013, 1011, 44–56. [12] By-products were either unreacted secondary phosphine boranes resulting from incomplete metalation or decomposi- tion of the metalating agent, or unknown new products that could not be conclusively identified. [13] T. Dunaj, D. Gudat, unpublished results. [14] Results of a query in the CSD database for borane complexes of diaminophosphines. [15] O. Puntigam, D. Förster, N. A. Giffin, S. Burck, J. Bender, F. Ehret, A. D. Hendsbee, M. Nieger, J. D. Masuda, Dietrich Gudat, Eur. J. Inorg. Chem. 2013, 2041–2050. [16] R. H. Harris, E. D. Becher, S. M. Cabral de Menezes, R. Good- fellow, P. Granger, Concepts Magn. Reson. 2002, 14, 326–346. [17] B. Singaram, T. E. Cole, H. C. Brown, Organometallics 1984, 3, 774–777. [18] a) G. M. Sheldrick, Acta Cryst. 2015, C71, 3–8; b) G. M. Sheldrick, Acta Cryst. 2008, A64, 112–122. Manuscript received: June 8, 2022 Revised manuscript received: March 11, 2022 Accepted manuscript online: July 4, 2022 Journal of Inorganic and General Chemistry Zeitschrift für anorganische und allgemeine Chemie RESEARCH ARTICLE Z. Anorg. Allg. Chem. 2022, 648, e202200192 (7 of 7) © 2022 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH Wiley VCH Donnerstag, 01.12.2022 2223 / 258476 [S. 85/85] 1 https://doi.org/10.1080/03086648308075983 https://doi.org/10.1080/03086648308075983 https://doi.org/10.1039/b815832k https://doi.org/10.1002/chem.201001814 https://doi.org/10.1039/C4SC02729A https://doi.org/10.1021/ic00284a003 https://doi.org/10.1021/ic00284a003 https://doi.org/10.1021/ic048647y https://doi.org/10.1021/ic048647y https://doi.org/10.1016/j.comptc.2013.02.007 https://doi.org/10.1016/j.comptc.2013.02.007 https://doi.org/10.1002/ejic.201201471 https://doi.org/10.1002/cmr.10035 https://doi.org/10.1021/om00083a022 https://doi.org/10.1021/om00083a022