P-Based Frustrated Lewis Pairs in Dipolar

Article Cite This: Organometallics 2019, 38, 2839−2852

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P−H Functionalized Al/P-Based Frustrated Lewis Pairs in Dipolar Activation and Hydrophosphination: Reactions with CO2 and SO2 Niklas Aders, Lukas Keweloh, Damian Pleschka, Alexander Hepp, Marcus Layh, Friedhelm Rogel, and Werner Uhl* Institut für Anorganische und Analytische Chemie der Universität Münster, Corrensstraße 30, D-48149 Münster, Germany

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ABSTRACT: The P−H functionalized FLPs R(H)PC(AlBis2)C(H)CMe3 (1a, R = Bis; 1b, R = Mes; Bis = CH(SiMe3)2) combine the typical FLP properties based on Lewis acidic Al and basic P atoms with the reactivity of a P−H bond. They allow the coordination of substrates followed by hydrophosphination with the activated P−H group. Reactions of 1a with R′−NCS (R′ = Ph, CMe3) or of both FLPs with Et−N CCPh2 afforded five-membered AlCPCS/N heterocycles (4 and 5) via coordination of CS or CN bonds to the FLP backbone. Isomerization by a 1,3-H shift from P to N or C (6 and 7) was only achieved in the presence of an auxiliary base (DABCO; 1−5 mol %). (Z)-1a coordinated CO2 to yield the adduct 8, which features a five-membered AlCPCO heterocycle with an exocyclic CO bond. Addition of bases such as DABCO and DBU afforded by deprotonation of the P atom the compounds [Bis-PC(AlBis2)C(H)−CMe3(CO2)]−[HB]+ (9a, B = DABCO; 9b, B = DBU) that displayed hydrogen bonding between the ammonium ions and the exocyclic O atom of the FLP adducts in solution and the solid state. The stronger base n-BuLi afforded the dimeric Li compound 10, in which the Li cation was coordinated in a chelating manner to the oxygen atoms of one FLP adduct and additionally to the exocyclic O atom of the second adduct, resulting in a fourmembered Li2O2 heterocycle. The related reaction of (Z)-1a with DABCO(SO2)2 led in contrast to the elimination of BisH and formation of a SO2-bridged dimer that features a central (AlOSO)2 heterocycle with Al−O and S−O single bonds. The resulting unusual structural motifs may be derived from those of dialkylcarbamic or dialkylamidosulfinic acids with the N atoms replaced by P atoms.

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INTRODUCTION

such as Mes and Bis on P and two Bis substituents on Al to prevent Al−P interactions and a reduction of the FLP activity. The unusual reactivity of P−H FLPs was demonstrated in reactions with e.g. nitriles R−CN which for R = OR, NR2 resulted in formation of heterocycles and selective 1,3-H transfer from P to N to yield phosphaguanidines/phosphaiminocarbamates under mild conditions (3; Scheme 1).3d,4,5 Coordination of the nitriles to aluminum and the electronwithdrawing substituents increase the electrophilicity of the nitrile C atom and favor the attack of the P atom by ring closure. The H transfer may be viewed as the addition of the P−H group to the CN bond and corresponds to hydrophosphination,6,7 which is usually initiated thermally, by means of a radical starter, UV light, basic materials, or a range of catalysts based on e.g. alkaline-earth, transition, or lanthanide metals. Recently, B/P FLPs have also been applied as catalysts.7 In contrast, treatment of the P−H functionalized FLPs 1 with Ph−CN or Me3C−CN afforded the simple adducts 2 (Scheme 1), in which the nitrile group was coordinated in a terminal fashion to the Al atom, while the P−H group remained unchanged.4 The adduct of 1a with

Frustrated Lewis pairs (FLPs) based on main-group elements have coordinatively unsaturated Lewis acidic and basic centers and show a fascinating reactivity in stoichiometric and catalytic transformations.1 Most FLPs feature B and P atoms, but recently FLPs such as Mes2PC[Al(CMe3)2]CH−Ph2 with Al and P atoms bound to a vinyl group in a geminal position have gained considerable interest. They are easily accessible from alkynylphosphines and dialkylaluminum hydrides via hydroalumination, and the high Lewis acidity of Al atoms does not require the application of electron-withdrawing fluorinated substituents. These FLPs tolerate different groups bound to aluminum and allow a careful adjustment of steric and electronic properties. They have found wide application in the coordination and activation of small molecules and showed an exceptional reactivity toward multiple bonds, chalcogens, hydrogen halides, CsF, BX3, transition metals, and various other substrates.3 The simple synthetic procedure allowed the synthesis of P−H functionalized FLPs, R(H)PC(AlBis2) C(H)−CMe3 (1a,4 R = Bis = CH(SiMe3)2; 1b,5 R = Mes = 2,4,6-Me3C6H2), which combine the typical reactivity of an FLP with that of a hydrophosphination reagent.3d,4,5 The small H atoms attached to P necessitate the use of bulky substituents © 2019 American Chemical Society

Received: May 23, 2019 Published: July 10, 2019 2839

DOI: 10.1021/acs.organomet.9b00346 Organometallics 2019, 38, 2839−2852

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Organometallics

Scheme 2. cis/trans Rearrangement of Compound 1a4

Scheme 1. Hydrophosphination of Nitriles by P−H Functionalized FLPs 1a

in the course of our current investigations, and the crystal structure confirms the assignment based on NMR data (Figure 1). P and vinylic H atoms are cis to each other. The distance

a Legend: (i) +R′-CN. Abbreviations: Mes = 2,4,6-Me3C6H2, Bis = CH(SiMe3)2.

benzonitrile partially dissociated in solution at room temperature, and the FLP was completely recovered upon removal of all volatiles under vacuum.4 Dissociation was not observed for the analogous adducts of 1a with Me3C−CN4 or of 1b with Ph−CN.4 This difference reflects the basicity of the nitriles (Me3C−CN versus Ph−CN) and the greater steric demand of the Bis in comparison to the Mes substituents. The adduct of benzonitrile and the mesityl FLP 1b afforded quantitatively a five-membered heterocycle (3) by P−C bond formation and hydrophosphination upon warming to 50 °C (Scheme 1).5a Quantum chemical calculations suggested a mechanism which starts with ring closure by P−C bond formation followed by the formal 1,3-H transfer from P to the more basic N atom. A calculated high activation barrier precludes an intramolecular process.5a The unstable adduct of 1a did not rearrange even after prolonged stirring at room temperature or in the presence of a large excess of benzonitrile. Since the H transfer likely proceeds via an intermolecular mechanism, we anticipated that strong bases may help to catalyze hydrophosphination of a wide variety of substrates, for which the spontaneous H shift was not observed. This paper reports on reactions of the P−H FLPs 1 with heteronuclear multiple bonds and the hydrophosphination of various unreactive substrates by addition of a suitable catalyst.

Figure 1. Molecular structure and atomic numbering of compound (E)-1a (R enantiomer). Displacement ellipsoids are drawn at the 40% level. H atoms (except H1, H2) have been omitted. Selected bond lengths (Å) and angles (deg): Al1−C1 1.984(1), Al1−CSi2 1.968 (av), P1−C1 1.852(4), P1−C30 1.844(4), P1−H1 1.38(2), C1−C2 1.338(2); Al1−C1−P1 111.4(1).

RESULTS AND DISCUSSION Molecular Structure of (E)-1a. The starting compounds 1a,b are conveniently prepared in high yield by hydroalumination of R(H)P−CC−CMe3 with H−AlBis2.4,5 The concerted nature of these reactions leads to the selective formation of the kinetically favored cis products with Al and H on the same side of the resulting CC double bonds. Only relatively small substituents allow rearrangement to the thermodynamically favored trans products.8 Surprisingly, the cis product (Z)-1a was found to be the thermodynamically preferred isomer by 3.6 kcal/mol, as predicted by quantum chemical calculations.4 This result may depend on the bulk of the Bis substituents at Al and their steric interaction with the neighboring vinylic CMe3 groups in the trans form. Recently, we reported that cis/trans isomerization is achievable by UV irradiation.4 The trans isomer (E)-1a is metastable up to 70 °C in benzene (Scheme 2). Both isomers showed nearly identical NMR data with coupling constants of 1JPH = 204.3 (cis) and 209.0 Hz (trans) to the P-bound H atom. The major difference resulted for the 3JPH coupling constant to the vinylic H atoms, which in agreement with the Karplus relation9 was larger (33.0 Hz) for the cis (P and H trans) than for the trans isomer (23.5 Hz, P and H cis). Single crystals of (E)-1a were only obtained

between Al and P is at 3.18 Å shorter than that in the Z isomer (3.34 Å) but is still indicative of the frustration of the Al and P atoms. The distances between the P-bound H atom and Al differ considerably at 3.26 Å ((E)-1a) and 4.27 Å ((Z)-1a). The sum of the AlC 2 angles (358.5°) confirms the coordination number 3 at Al. Catalyzed Hydrogen Shift in a Nitrile Adduct. As discussed above, H migration in the FLP adducts seems to be an intermolecular process, and we hoped to catalyze this rearrangement by addition of a base. The choice of the auxiliary base is important, because its basicity should allow deprotonation of the P−H group, but it should not coordinate in a competitive reaction irreversibly to the proton or the Lewis acidic Al atom. We treated the equilibrium mixture of (Z)-1a, Ph−CN, and 2a (Scheme 3; cf. the Introduction) at −30 °C with catalytic quantities (5 mol %) of the nitrogen base DABCO (1,4-diazabicyclo[2.2.2]octane) and stirred the mixture for 12 h at room temperature. Quantitative hydrophosphination was achieved, and compound 3a was isolated after crystallization in 89% yield. The NMR parameters of 3a are similar to those of the related mesityl derivative.4 The newly formed N−H group showed a 1H NMR resonance at δ 8.74. The 3JPH coupling constant to the vinylic H atom

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single resonance for both Al−C−H groups in the 1H NMR spectrum. Catalyzed H Shift in Heterocumulene Adducts. In further experiments we explored the general applicability of the catalytic H transfer for various substrates. Treatment of compounds 1 with the heterocumulenes R′−NCS (R′ = Ph, CMe3) and EtNCCPh2 afforded in 76−95% yield the persistent adducts 4a and 5 in which the polar CX bonds (X = S, N) were coordinated to the Lewis basic and acidic centers of the FLPs (Scheme 4). (Z)-1a and Me3C−NCS yielded

Scheme 3. Reaction of (Z)-1a with PhCN and Formation of Compound 3a Catalyzed by DABCOa

Scheme 4. Reaction of 1 with Heterocumulenes: Formation of the Cyclic Addition Products 4 and 5 and 1,3-H Shift

a

DABCO = 1,4-diazabicyclo[2.2.2]octane.

increased from 33.0 Hz ((Z)-1a) to 45.0 Hz, and the iminic C atom resonated at a low field (δ 205.2). The solid-state structure of 3a (Figure 2) compares well with that of the

Figure 2. Molecular structure and atomic numbering of compound 3a (S enantiomer). Displacement ellipsoids are drawn at the 40% level. H atoms (except H1, H2) have been omitted. Selected bond lengths (Å) and angles (deg): Al1−C1 2.032(2), Al1−CSi2 2.005 (av), Al1−N1 1.957(2), P1−C1 1.804(2), P1−C4 1.826(2), P1−C30 1.865(2), C1−C2 1.345(2), C4−N1 1.299(2); Al1−C1−P1 111.4(1).

adduct 4b, which in solution slowly rearranged to compound 6 via 1,3-H transfer from P to N. After 10 days the ratio of 4b to 6 was about 12:1 and after 1 month 4:1, but even after 1 year the reaction was still incomplete. A few single crystals of compound 4b were obtained from a 1:1 mixture of both isomers, but bulk quantities could not be isolated. Pure 6, in contrast, was obtained in 88% yield from the reaction mixture in n-pentane after 1 year. Addition of catalytic quantities of DABCO (1 mol %) to a mixture of (Z)-1a and Me3C−N CS led in an NMR experiment after 1 h at room temperature quantitatively to compound 6, while in the case of Ph−NCS even stoichiometric amounts of the base or heating did not result in H transfer. Compound (Z)-1b, in contrast, was previously shown to react with both isothiocyanates directly to give the analogues of 6.5b The different

mesityl compound.4 An almost planar PCAlNC heterocycle is formed, in which C1 shows the largest deviation from the plane (0.13 Å). Al−C (2.01 Å on average), Al−N (1.957(2) Å), and P−C bond lengths (1.83 Å on average) are in the typical ranges of four-coordinate Al and three-coordinate P atoms. The bond lengths of 1.299(2) and 1.345(2) Å for the endocyclic CN and the exocyclic CC bonds, respectively, correspond to standard values of the corresponding double bonds. The surrounding of the P atom is chiral; a fast inversion of the configuration may be derived from the observation of a 2841


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Organometallics reactivities of (Z)-1a and (Z)-1b toward both isothiocyanates are influenced by the basicity of the N atoms (Ph−NCS versus Me3C−NCS), the acidity of the P−H groups in the phosphonium groups of 4 (R2BisP(H)+ versus R2MesP(H)+), and the steric bulk of the substituents (Bis versus Mes and Me3C versus Ph), which may hinder autocatalytic H migration. Thermal activation of compounds 5 by heating to 100 °C was not successful. Catalytic quantities of DABCO (1 mol %) were therefore added to a solution of 5b in n-hexane, but complete conversion of 5b to the rearranged product 7 required 7 days at room temperature, as determined by NMR spectroscopy. With almost stoichiometric quantities of DABCO the reaction proceeded to completion in 14 h, and 7 was isolated in 77% yield. Compound 7 represents the unexpected product of the hydrophosphination of a CC double bond, but the reaction may proceed by H transfer to the basic N atom followed by enamine−imine tautomerism to yield the thermodynamically favored imine tautomer.10 The NMR spectra of 4 and 5 are characterized by low-field resonances in the 31P (δ −9.0 (4a), −12.0 (4b), −21.9 (5a), −34.9 (5b)) and 1H NMR spectra (PH: δ 7.11 (4a), 6.75 (4b), 7.65 (5a), 7.92 (5b)) relative to the starting materials (δ(31P) −74.0 ((Z)-1a), −80.8 ((Z)-1b); δ(1H, PH) 4.46 ((Z)-1a), 5.33 ((Z)-1b)) and the appearance of new resonances in the 13C NMR spectra at δ 135.7−167.8 for the endocyclic C atoms of the heterocumulene ligands with large 1 JPC coupling constants of 103.7−133.4 Hz. The increase of the coordination number at P results in a significant increase in 1 JPH (441 to 456 Hz), 2JPH (19.0 to 25.2 Hz, PCHSi2) and 3JPH (66.3 to 74.0 Hz, CCH) coupling constants in comparison to the starting materials (1JPH about 200 Hz, 2JPH = 1.2 Hz for (Z)-1a and 3JPH = 32 Hz). The observed large 3JPH coupling constants confirm the trans orientation of P and H atoms in the vinyl groups. The increase of the coordination number at the Al atoms leads to a characteristic downfield shift of the Al− C−H signals of the Bis substituents to about δ −0.7 in comparison to δ −0.10 and −0.50 in compounds 1. Ring closure results in four-coordinate P atoms with a chiral surrounding, and the atoms of the Bis substituents on Al and the Bis or Mes substituents on P become diastereotopic. The signals of the Ph substituents of the CCPh2 fragment of compounds 5 did not split but are significantly broadened. π delocalization and weakening of the CC bonds (see below) may allow rotation and equilibration of the phenyl groups. The hydrophosphination products 6 and 7 are characterized by a further downfield shift of the resonances in the 31P NMR spectra to δ 31.6 and 10.7, respectively. The migration of the H atom results in the disappearance of the P−H signals in the 1H NMR spectra, the appearance of low-field signals for NH (δ 7.08) and CHPh2 (δ 5.46) protons, and smaller 3JPH coupling constants to the vinylic H atom of about 48 Hz, which is consistent with a coordination number of 3 at P and a trans arrangement of P and H in the vinyl group. The endocyclic CS and CN groups show characteristic low-field shifts in the 13C NMR spectra at δ 217.0 and 200.8, respectively. The barrier of inversion at the P atoms of 6 and 7 is reduced, the diastereotopic H atoms in the Bis, Mes, and CPh2 substituents become equivalent, and only one set of signals was observed in the NMR spectra at room temperature. The signals for the CPh2 protons in 7 have a small line width in comparison to compounds 5. The molecular structures of 4a and 5b (Figures 3 and 4, respectively; 4b and 5a are similar) feature five-membered

Figure 3. Molecular structure and atomic numbering of 4a (S enantiomer). 4b is similar. Displacement ellipsoids are drawn at the 40% level. H atoms (except H1, H2) have been omitted. Selected bond lengths (Å) and angles (deg) (values for 4b in brackets): Al1− C1 2.043(1) [2.055(2)], Al1−CSi2 2.004 (av) [2.014 (av)], Al1−S1 2.359(1) [2.358(1)], P1−C1 1.762(1) [1.776(2)], P1−C30 1.794(1) [1.801(2)], P1−C40 1.830(1) [1.828(2)], P1−H1 1.27(2) [1.18(3)], C1−C2 1.348(2) [1.341(3)], C40−S1 1.728(1) [1.742(2)], C40− N1 1.281(1) [1.277(3)]; S1−Al1−C1 93.7(1) [93.3(1)], S1−C40− P1 119.3(1) [117.9(1)].

Figure 4. Molecular structure and atomic numbering of 5b (R enantiomer). 5a is similar. Displacement ellipsoids are drawn at the 40% level. H atoms (except H1, H2) have been omitted. Selected bond lengths (Å) and angles (deg) (values for 5a in brackets): Al1− C1 2.039(1) [2.046(2)], Al1−CSi2 2.020 (av) [2.024 (av)], Al1−N1 1.906(1) [1.917(2)], P1−C1 1.774(1) [1.782(2)], P1−C4 1.805(1) [P1−C30 1.818(2)], P1−C40 1.841(1) [1.850(2)], P1−H1 1.29(2) [1.29(3)], C1−C2 1.343(2) [1.345(3)], C40−N1 1.371(1) [1.366(2)], C40−C50 1.381(2) [1.395(3)]; N1−Al1−C1 90.3(1) [90.6(1)], C40−N1−Al1 122.4(1) [123.5(1)].

PC2AlX heterocycles (X = S, N) that are planar (5a; largest deviation from plane C40 at 0.014 Å) or adopt an envelope conformation with the S atoms (4) or the vinylic C atom (5b) above the plane of the remaining ring atoms (largest deviation from these planes: 4a: 0.04 Å for C1; 4b: 0.006 Å for C1, P1; 2842


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Organometallics 5b: 0.004 Å for C40, N1). The flap angles of the envelopes range from 16.8° (4a) to 27.7° (5b). The bulky substituents on the P atoms are perpendicular to the molecular plane, and one SiMe3 (Bis substituent) or Me group (Mes substituent) is located above the heterocycle. The smallest endocyclic bond angles were observed at the Al atoms (C1−Al1−S1 93.5°; C1−Al1−N1 90.4°) and the largest at C40 (4; P1−C40−S1 118.6°) or N1 (5; C40−N1−Al1 123.0°). The Al−S11 and Al−N bond lengths12 are at about 2.36 and 1.91 Å in the typical ranges. The exocyclic CN bonds in compounds 4 correspond at 1.279 Å to double bonds, while in compounds 5 the π-electron density is delocalized between the endocyclic C−N (1.369 Å) and the exocyclic C−C(Ph2) bonds (1.388 Å). The hydrophosphination products 6 and 7 (Figures 5 and 6, respectively) have five-membered heterocycles in a distorted

Figure 6. Molecular structure and atomic numbering of compound 7 (R enantiomer). Displacement ellipsoids are drawn at the 40% level. H atoms (except H1, H10, H20, and H50) and methyl groups of the SiMe3 substituents have been omitted. Selected bond lengths (Å) and angles (deg): Al1−C1 2.015(2), Al1−CSi2 2.014 (av), Al1−N1 2.004(2), P1−C1 1.795(2), P1−C4 1.840(2), P1−C40 1.846(2), C1−C2 1.345(2), C40−N1 1.299(2), C40−C50 1.531(2); P1−C1− Al1 106.0(1), C1−Al1−N1 89.5(1).

Reactions of (Z)-1a with CO2 and SO2. We further investigated the reactivity of (Z)-1a toward SO2 or CO2. The activation and reduction of CO2 by FLPs is of particular interest and has recently been reviewed.13 A number of promising FLPs that reversibly bind CO2 have been developed on the basis of Lewis pairs including B/P,14 B/N,15 Al/P,2,16 Si/P,17 Sn/P,18 and Zr,Hf/P.19 Upon addition of suitable reductants, some of the adducts showed the stoichiometric or catalytic reduction of CO2. The reaction of an electron-rich phosphine with CO2 has also been reported.20 Exposing a solution of (Z)-1a in toluene at low temperature to an atmosphere of CO2 afforded adduct 8 in 82% yield after warming to room temperature (Scheme 5), while the reaction of 1b was unselective and no products were isolated. Further reactions of 8 with excess CO2, hydrogen transfer to an O atom, cis/trans isomerization of the vinyl group, or reversible release of CO2 were not observed even when solutions of 8 were heated to 100 °C. Instead, 8 slowly decomposed to an unknown product that did not feature a P−H bond, as evident from the absence of an NMR resonance with the typical large 1 JPH coupling constant. This behavior is in contrast to that of the related FLP Mes2PC(AltBu2)C(H)−Ph, which was fully recovered after heating of the adduct in the solid state to 135 °C.2a Compound 8 showed a 31P NMR resonance at δ −31.3 and 1 JPH (430.6 Hz), 2JPH (20.4 Hz), 3JPH (76.9 Hz), and 1JPC(O) coupling constants (117.6 Hz) to PH, PCHSi2, the vinylic H atom, and the inserted CO2 molecule, respectively, which are comparable to those of compounds 4 and 5 and indicative of a four-coordinate P atom. The chemical shifts of the P−H proton and the C atom of the CO2 ligand are at δ 6.64 and 164.5 similar to those of 4b, and we observe distinct signals for the diastereotopic H and C atoms of the CH(SiMe3)2 groups (3 × CH, 6 × SiMe3). The CO stretching vibration in the IR spectrum is at 1705 cm−1 similar to that of the CO2 adduct of

Figure 5. Molecular structure and atomic numbering of 6 (R enantiomer). Displacement ellipsoids are drawn at the 40% level. H atoms (except H1, H2) have been omitted. Selected bond lengths (Å) and angles (deg): Al1−C1 2.024(2), Al1-CSi2 2.007 (av), Al1−S1 2.373(1), P1−C1 1.800(2), P1−C40 1.873(2), P1−C40 1.852(2), C1−C2 1.349(2), C40−S1 1.694(2), C40−N1 1.327(2); P1−C1− Al1 116.1(1), C1−Al1−S1 91.3(1).

envelope conformation with the vinylic C or the P atom in the apical position and flap angles of 30.6 and 34.0°. The exocyclic bond C40−N1 (1.327(2) Å) in 6 is longer and the endocylic bond C40−S1 (1.694(2) Å) shorter than the respective bonds in compounds 4. They may indicate a higher degree of π delocalization. The Al−S bond is at 2.373(1) Å slightly longer than that in 4 and approaches the values of typical coordinative interactions.11 7 features an Al−N distance that is at 2.004(2) Å in the characteristic range of donor−acceptor bonds12 and significantly longer than in compounds 5. The C40−N1 distance of 1.299(2) Å corresponds to a double bond and the exocyclic C40−C50(H)Ph2 distance to a single bond (1.531(2) Å). Both values confirm the bonding situation shown in Scheme 4. 2843


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indicating a comparatively weak bond.21 The length of the exocyclic C40−O2 bond corresponds at 1.212(3) Å to a typical CO double bond, and the endocyclic bond C40−O1 is lengthened to 1.282(3) Å as a result of the coordination of the O atom to Al. O atoms are less basic than the N atoms of the substrates applied so far; therefore, an H shift from P to the terminal O atom of 8 seems to be unfavorable. Nevertheless, we added stoichiometric quantities of DABCO at room temperature to a solution of 8, which led to the immediate precipitation of 9a (Scheme 5). Characterization of 9a showed that DABCO has deprotonated the P−H group. The proton binds to an N atom of the base to yield an ammonium ion, which is connected to the terminal O atom of the CO2 group via an N−H···O bridge. The P atom is three-coordinate. DBU,22 which is used as a strong base in organic chemistry,23 behaved similarly and afforded the H-bonded adduct 9b in high yield. n-BuLi led also to deprotonation (Scheme 5) with formation of the Li compound 10, which has the Li cation bound to O atoms and is dimeric via Li−O bridges in the solid state. The uncoordinated FLPs 1 do not react with n-BuLi by deprotonation; these reactions clearly depend on the increased acidity of P−H groups with four-coordinate P atoms. The NMR spectra of 9 and 10 show the same trends as 6 and 7 with downfield-shifted 31P NMR signals (δ −11.1 (9a), −12.5 (9b), −12.6 (10)) and a decrease in 3JPH and 1JPC(O) coupling constants to about 42 and less than 9 Hz, respectively. The Bis substituents gave single sets of resonances (2 × CH, 3 × SiMe3) due to a fast inversion of configuration at the threecoordinate P atoms. Additional broad signals in the 1H NMR spectra of the adducts 9 (δ 13.08 (9a) and 12.06 (9b)) were assigned to the NH protons and may be compared to those of [DABCOH]Co(CO)424 and [DBUH]Cl.25 The downfield shifts suggest H bonding,26 and broad lines indicate dynamic behavior in solution. This is particularly evident for 9a, which shows only a single set of resonances for the H and C atoms of DABCO (δ(1H) 2.09 and δ(13C) 44.7), which is consistent with a fast exchange of the proton between both N atoms. The splitting of 1H NMR signals caused by a fixed proton was observed only upon cooling a solution in d8-toluene to 200 K (δ 1.96 (br and 1.74 (t, 3JHH = 7.7 Hz)). The Bis substituents gave three resonances for the CHSi2 and five peaks for the SiMe3 groups (the signals of two groups coincide), indicating that the inversion on P is slow at this temperature. The N−H stretching vibration could not be located unequivocally in the IR spectra of 9, but 9a showed several weak absorptions between 2000 and 2800 cm−1. Studies on ammonium salts have shown that, depending on the counterions and the substituents on the N atoms, the formation of H bridges leads to a red shift of νNH and to various, often broad bands below 2800 cm−1.27 The molecular structures of the adducts 9 (Figure 8) are similar and confirm deprotonation of the P−H group of 8, the coordination number of 3 at P (pyramidal surrounding), and the presence of an N−H···O hydrogen bond to the terminal O atom of the CO2 ligand. The five-membered AlOCPC heterocycles adopt an envelope conformation with the atoms Al, O1, C4, and P1 in a plane (largest deviation: 0.003 Å O1, C4 (9a); 0.017 Å O1 (9b)), the vinylic C atom in the apical position, and flap angles of about 44°. The Al−O bond lengths (1.858 Å) are similar to those of 4, 5, and 8, but the P−C(O) bond lengths are slightly shorter (1.838(2) Å (9a); 1.857(2) Å (9b)) and closer to those of 4 and 5. The C−O bond lengths

Scheme 5. Reaction of (Z)-1a with CO2: Deprotonation of the Adduct 8 with DABCO, DBU, or n-BuLia

a

DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene.

Mes2PC(AltBu2)C(H)−Ph (1707 cm−1).2a 8 crystallizes in the chiral space group P212121; the molecular structure of the S enantiomer is shown in Figure 7. It features an essentially

Figure 7. Molecular structure and atomic numbering scheme of the CO2 adduct 8 (S enantiomer). Displacement ellipsoids are drawn at the 40% level. H atoms (except H1, H2) have been omitted. Selected bond lengths (Å) and angles (deg): Al1−C1 2.057(2), Al1−CSi2 2.008 (av), Al1−O1 1.855(2), P1−C1 1.776(2), P1−C30 1.794(2), P1−C40 1.880(2), C1−C2 1.347(3), C40−O1 1.282(3), C40−O2 1.212(3); O1−C40−O2 128.7(2), P1−C40−O1 113.7(2).

planar AlCPCO heterocycle (largest deviation from plane: 0.06 Å for C1) with the Bis substituents on Al arranged perpendicular to the molecular plane (angle between planes 88.4°). The Al1−O1 distance is at 1.855(2) Å in the typical range of coordinative bonds and may be compared to that of the related adduct Mes2PC(AltBu2)C(H)-Ph·CO2 (1.859 Å).2a The distance P1−C40 to the carbonyl C atom is at 1.880(2) Å slightly longer than that in 4 and 5 (1.83−1.85 Å) but shorter than in Mes2PC(AltBu2)C(H)−Ph·CO2 (1.919 Å) or in the corresponding PhC(O)H adduct (1.938(2) Å), 2844


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Figure 8. Molecular structure and atomic numbering of compound 9a. 9b is similar. Displacement ellipsoids are drawn at the 40% level. H atoms (except H1, H2, H10, H20, H30) and methyl groups of the SiMe3 substituents have been omitted. Selected bond lengths (Å) and angles (deg) (values of 9b in brackets): Al1−C1 2.019(2) [2.027(2)], Al1−CSi2 1.996 (av) [2.011 (av)], Al1−O1 1.863(1) [1.852(1)], P1−C1 1.789(2) [1.796(2)], P1−C4(O) 1.838(2) [1.857(2)], P1− C30 1.860(2) [1.867(2)], C1−C2 1.340(3) [1.340(2)], C4−O1 1.290(2) [1.305(2)], C4−O2 1.250(2) [1.231(2)], N1−H1 0.88(3) [0.82(2)], O2−H1 1.74 [1.97], N1···O2 2.61 [2.79]; P1−C4−O1 117.3(1) [115.4(1)], O1−C4−O2 122.0(2) [122.7(2)], N1−H1− O2 168 [177].

Figure 9. Molecular structure and atomic numbering of 10. Displacement ellipsoids are drawn at the 40% level. H atoms (except H1, H10, H20, H30) and the CH3 groups of the SiMe3 substituents have been omitted. Selected bond lengths (Å) and angles (deg): Al1− C1 2.021(2), Al1−CSi2 2.001 (av), Al1−O1 1.898(2), P1−C1 1.792(2), P1−C4 1.828(3), P1−C30 1.862(2), C1−C2 1.332(3), C4−O1 1.306(3), C4−O2 1.245(3), O1−Li1′ 2.016(5), O2−Li1 1.847(5), O2−Li1′ 2.125(5); Li1′−O1−C4 90.7(2), O1−C4−O2 118.0(2), C4−O2−Li1 165.0(3), C4−O2−Li1′ 87.5(2), Li1′−O2− Li1 89.3(2), O1′−Li1−O2 151.3(3), O2−Li1−O2′ 87.7(2). Equivalent atoms by (′) −x + 2, y, −z + 3/2.

The related reaction of (Z)-1a with excess SO2 was unselective and led to decomposition of the starting material, while the treatment with stoichiometric quantities of DABCO(SO2)230 afforded compound 11 in 63% yield (Scheme 6). SO2

are at 1.250(2)/1.231(2) Å and 1.290(2)/1.305(2) Å slightly longer than in 8, which may be attributed to the presence of O···H−N hydrogen bonds. The bond lengths and angles of the N−H···O bridges (O···HN 1.74 Å (9a), 1.97 Å (9b); N−H− O 168° (9a), 177° (9b)) are in the typical range of mediumstrong hydrogen bonds.28 Compound 10 is a dimer with a central four-membered Li2O2 heterocycle that is located on a 2-fold rotation axis (Figure 9). The five-membered AlOCPC heterocycle adopts a twist conformation with P1, C4, and O1 and the adjacent atoms O2 and Li1 in the molecular plane (largest deviation from plane: 0.027 Å for C4). Al1 and the vinylic C atom are above and below the plane. The Li atoms are bound to two O atoms of a carboxylate group in a chelating fashion (Li−O 2.016(5) and 2.125(5) Å), which is rare for lithium carboxylates,29 and to a third O atom of the second molecular half (Li−O 1.847(5) Å). The distances are in the normal range of Li−O groups.12 Relatively short contacts to methyl H atoms complete the coordination sphere of Li. A ladder-type structure results in which two five-membered and three four-membered heterocycles are fused by common edges. The P−C(O) bond length is at 1.828(3) Å significantly shorter and the C−O distances are at 1.245(3) and 1.306(3) Å longer than those in 8. The Al−O bond length (1.898(2) Å) is longer than in compounds 8 and 9, which may be attributed to the increased coordination number of the O atom by the coordination to lithium.

Scheme 6. Reaction of (Z)-1a with SO2a

a

R = CH(SiMe3)2.

adducts13 have been obtained for FLPs on the basis of P and B,14e,f,31 Si,17b Sn,18 or Zr/Hf.19b There is also an example for the addition of SO2 to a reactive phosphine without activation by a Lewis acid.32 However, the reaction of the P−H functionalized FLP (Z)-1a with SO2 is unique, because the activation of the P−H bond and the sensitivity of the Al−C bond toward protolysis results in release of H2C(SiMe3)2, as detected by NMR spectroscopy. The simple SO2 adduct may be considered as a reasonable intermediate but is expected to 2845


Article

Organometallics be sufficiently acidic to protonate an α-C atom of a Bis substituent with its comparatively high partial negative charge. This is the first example in which this type of reaction has been realized. 11 is dimeric in the solid state (see below) and in solution, as is evident from the high-field signal of the inner C−H proton of the Bis substituent on Al (δ −0.95), which confirms a four-coordinate Al atom.33 The low-field shift of the 31 P NMR signal (δ 96.6), the 1JPC(Si) coupling constant (61.9 Hz), and the 3JPH coupling constant to the vinylic H atom (36.4 Hz, P trans to H) are indicative of a three-coordinate P atom. 11 crystallizes as a centrosymmetric dimer (Figure 10) with an eight-membered Al2S2O4 heterocycle in a chair conforma-

distances close to 1.41 and 1.56 Å. The O atoms are coordinated to S and Al with angles of 149.3(1)° (O1) and 122.3(1)° (O2).

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CONCLUSION The recently obtained P−H functionalized Al/P based frustrated Lewis pairs (FLPs) coordinate substrates in the typical FLP fashion and frequently show the transfer of the Pbound H atom to the activated molecules by hydrophosphination. However, in several cases the simple FLP adducts were isolated without H transfer. The reactivity seems to depend on the strength of the phosphorus−substrate interaction, the acidity of the P−H group, and the basicity of the proton acceptor. Quantum chemical calculations suggested an intermolecular pathway for the H transfer, and catalytic quantities of the base DABCO indeed facilitated hydrophopsphination in the case of the inert FLP adducts with benzonitrile, tert-butyl isothiocyanate, or triphenylketenimine with H migration to an N or even a C atom. We studied two different FLPs (1a,b) with a mesityl (−I effect) or a bis(trimethylsilyl)methyl group (+I effect) attached to phosphorus. The H shift is slower or does not occur at all with the P−CH(SiMe3)2 compounds, which in comparison to the mesityl FLP are expected to have a lower acidity of the P− H group in the phosphonium intermediates. The transport of the H atom from P to N or C may proceed via an intermediate ammonium ion. A comparable catalytic H transfer from a P to a C atom by addition of DABCO has recently been used for the generation of [3H]-phosphaallenes from alkynylphosphines, R−P(H)−CC−R′.36 O atoms of neutral ligands are less basic and less suited to act as acceptors in H transfer. Nevertheless, the P−H FLP 1a showed a remarkable reactivity toward CO2 and SO2. The CO2 adduct was deprotonated by the bases DABCO, DBU, and nBuLi and afforded phosphines with three-coordinate P atoms and N−H···O hydrogen bridges or Li−O interactions. The resulting structures may be derived from that of N,Ndialkylcarbamic acids, R2N−CO2H,37 with the N atoms replaced by P atoms. With SO2 the increased acidity of the P−H group resulted in protolysis and cleavage of an Al−C bond to a CH(SiMe3)2 group. A dimeric compound with two SO2 ligands in bridging positions is formed. This compound represents a P analogue of dialkylamidosulfinic acids, R2N− SO2H, which are unstable and were generated as their Na salts.38 The interaction with the Lewis acidic Al atom may stabilize these unusual compounds. These results underscore the promising preparative potential of P−H functionalized FLPs. The catalyzed H transfer will allow hydrophosphination of further substrates, and more fascinating products with unusual constitutions are to be expected.

Figure 10. Molecular structure and atomic numbering of 11. Displacement ellipsoids are drawn at the 40% level. H atoms (except H2) have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Al1−C1 1.980(2), Al1−C10 1.962(2), Al1−O1 1.793(1), Al1−O2′ 1.827(1), P1−C1 1.821(2), P1−C30 1.872(2), P1−S1′ 2.230(1), C1−C2 1.344(2), S1−O1 1.533(1), S2−O2 1.546(1); Al1−O1−S1 149.3(1), S1−O2−Al1′ 122.3(1). Equivalent atoms by (′) −x + 1, −y + 1, −z + 1.

tion. This ring is annulated to two five-membered AlCPSO heterocycles, which feature an envelope conformation with the S atom in the apical position (largest deviation from plane of the atoms AlCPO 0.023 Å for C1; flap angle 23°). The Al atom is coordinated to two C (Al−C 1.971 Å on average) and two O atoms; one of its Bis substituents was removed. The P and S atoms are three-coordinate with a pyramidal surrounding (sum of angles 297.4 and 313.8°). The Al−O distances are at 1.793(1) and 1.827(1) Å shorter than those of compounds 8− 10. The P−S bond length is at 2.230(1) Å comparable to that in Mes(H)PC[B(C 6 F 5 ) 2 ]C(H)−CMe 3 ](PhNSO) (2.217(2) Å)14c but shorter than in related adducts with four-coordinate P atoms that typically feature distances ≥2.30 Å.17b,19,31 The S−O bond lengths are at 1.533(1) and 1.546(1) Å similar and in the range of single bonds as found in sulfuric acid esters34 or a sulfatodiboroxane35 that shows S−O

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EXPERIMENTAL SECTION

General Considerations. All procedures were carried out under an atmosphere of purified argon in dried solvents (n-hexane and npentane with LiAlH4; toluene with Na/benzophenone). NMR spectra were recorded in C6D6 or C4D8O at ambient probe temperature using the following Bruker instruments: Avance I (1H, 400.13 MHz; 13C, 100.60 MHz; 31P 161.98 MHz), Avance III (1H, 400.03 MHz; 13C, 100.59 MHz; 31P 161.93 MHz; 29Si 79.47 MHz; 15N 40.54 MHz; 7Li 155.47 MHz). Signals were referenced internally to residual solvent resonances (chemical shift data in δ). 13C NMR spectra were all proton-decoupled. Elemental analyses were determined by the microanalytic laboratory of the Westfälische Wilhelms Universität Münster. IR spectra were recorded as paraffin mulls between KBr or 2846


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Organometallics

562 vw, 532 vw, 511 s, 476 m ν(PC), ν(AlC), ν(AlS), δ(CC). Anal. Calcd for C34H73AlNPSSi6 (754.5): C, 54.1; H, 9.8; N, 1.9. Found: C, 53.9; H, 9.5; N, 1.8. Reaction of Compound (Z)-1a with Me3C−NCS: Synthesis of 4b and 6. Me3C−NCS (51 μL, 0.046 g, 0.40 mmol) was added at −30 °C to a solution of (Z)-1a (0.25 g, 0.41 mmol) in n-pentane (15 mL). The mixture was warmed to room temperature. The formation of compound 4b was accompanied by the rearrangement to compound 6. NMR spectra of the mixture showed the presence of both compounds. However, even after 1 year the rearrangement of 4b to 6 was not completed, but cooling a concentrated solution in n-pentane to −45 °C after this period yielded compound 6 as yellow crystals (0.26 g, 88%). An NMR experiment showed that in the presence of catalytic amounts of DABCO (1%) the conversion to compound 6 was quantitative after 1 h at room temperature. Characterization of 4b. 1H NMR (400 MHz, C6D6, 300 K): δ −0.70 and −0.68 (each s br, 1H, AlCH), 0.21 and 0.22 (each s, 9H, PCSiMe3), 0.23, 0.47, 0.475, and 0.476 (each s, 9H, AlCSiMe3), 0.88 (d, 2JPH = 20.0 Hz, 1H, PCH), 1.06 (s, 9H, CMe3), 1.54 (s, 9H, NCMe3), 6.75 (dd, 1JPH = 456.2 Hz, 4JHH = 1.0 Hz, 1H, PH), 7.42 (dd, 3JPH = 66.3 Hz, 4JHH = 1.0 Hz, 1H, CCH). 13C NMR (100 MHz, C6D6, 300 K): δ 2.0 (d, 3JPC = 2.5 Hz, PCSiMe3), 3.4 (d, 3JPC = 3.0 Hz, PCSiMe3), 4.2 and 4.4 (s br, AlCH), 5.1, 5.2, 6.1, and 6.3 (AlCSiMe3), 12.5 (d, 1JPC = 14.2 Hz, PCH), 28.8 (NCMe3), 30.0 (CC−CMe3), 39.2 (d, 3JPC = 12.0 Hz, CC-CMe3), 60.4 (d, 3JPC = 25.2 Hz, NCMe3), 132.3 (d br, PCAl), 163.0 (d, 1JPC = 133.4 Hz, PCN), 172.9 (d, 2JPC = 7.0 Hz, CCH). 29Si NMR (79 MHz, C6D6, 300 K): δ −3.2, −1.8, −1.7, and −1.1 (AlCSi), 3.5 (d, 2JPSi = 4.4 Hz, PCSi), 3.9 (d, 2JPSi = 8.7 Hz, PCSi). 31P NMR (162 MHz, C6D6, 300 K): δ −12.0. 15N NMR (41 MHz, C6D6, 300 K): δ ≈ 369 (d, HMBC, 2 JPN ≈ 80 Hz). Characterization of 6. Mp: 130 °C dec. 1H NMR (400 MHz, C6D6, 300 K): δ −0.67 (s br, 2H, AlCH), 0.16 (s, 18H, PCSiMe3), 0.44 and 0.47 (each s, 18H, AlCSiMe3), 1.24 (s, 9H, CC-CMe3), 1.32 (s, 9H, NCMe3), 1.45 (d, 2JPH = 9.0 Hz, 1H, PCH), 6.80 (d, 3JPH = 47.8 Hz, 1H, CCH), 7.08 (s, 1H, NH). 13C NMR (100 MHz, C6D6, 300 K): δ 3.0 (d, 3JPC = 3.9 Hz, PCSiMe3), 4.4 (s br, AlCH), 5.56 (AlCSiMe3), 5.61 (d, 5JPC = 2.3 Hz, AlCSiMe3), 17.5 (d, 1JPC = 59.5 Hz, PCH), 28.2 (d, 4JPC = 2.4 Hz, NCMe3), 31.7 (d, 4JPC = 2.0 Hz, CC−CMe3), 36.4 (d, 3JPC = 4.3 Hz, CC-CMe3), 60.0 (NCMe3), 147.4 (d, 1JPC = 54.0 Hz, PCAl), 155.5 (d, 2JPC = 5.2 Hz, CCH), 217.0 (d, 1JPC = 43.2 Hz, PCS). 29Si NMR (79 MHz, C6D6, 300 K): δ −1.9 and −1.8 (AlCSi), 3.0 (d, 2JPSi = 6.5 Hz, PCSi). 31 P NMR (162 MHz, C6D6, 300 K): δ 31.6. 15N NMR (41 MHz, C6D6, 300 K): δ ∼173. MS (20 eV, 353 K): m/z (%): 718 (2) [M − Me]+, 574 (100) [M − CH(SiMe3)2]+. IR (paraffin mull, KBr plates, cm−1): 3364 m ν(NH); 2951−2853 vs (paraffin); 1537 w, 1501 s ν(CN), ν(CC); 1458 vs, 1398 m, 1368 m (paraffin); 1252 s, 1240 s δ(CH3); 1192 m, 1045 w ν(CC); 1020 m, 1005 m δ(CHSi2); 978 m, 937 m, 922 w, 841 vs, 799 s, 775 s, 750 m ρ(CH3Si); 729 m (paraffin); 700 w, 667 s, 621 w, 608 w ν(SiC); 565 vw, 542 w, 509 m, 473 w ν(PC), ν(AlC), ν(AlS), δ(CC). Anal. Calcd for C32H77AlNPSSi6 (734.5): C, 52.3; H, 10.6; N, 1.9. Found: C, 52.0; H, 10.5; N, 1.8. Reaction of Compound (Z)-1a with EtNCCPh2: Synthesis of 5a. EtNCCPh2 (0.11 g, 0.50 mmol) was added at −90 °C to a solution of (Z)-1a (0.30 g, 0.49 mmol) in n-pentane (15 mL). The mixture was warmed to room temperature to yield a pale orange solution. It was concentrated and stored at −30 °C to yield orange crystals of compound 5a (0.32 g, 76%). Mp: 131 °C dec. 1H NMR (400 MHz, C6D6, 300 K): δ −1.00 and −0.54 (each s br, 1H, AlCH), −0.17 and 0.23 (each s, 9H, PCSiMe3), 0.39, 0.42, 0.49, and 0.50 (each s, 9H, AlCSiMe3), 0.85 (t, 3JHH = 6.7 Hz, 3H, NCH2Me), 1.07 (s, 9H, CMe3), 1.50 (d, 2JPH = 25.2 Hz, 1H, PCH), 2.97 (ddq, 2JHH = 13.8 Hz, 3JHH = 6.7 Hz, 4JPH = 2.1 Hz, 1H, NCH2), 3.57 (dq, 2JHH = 13.8 Hz, 3JHH = 6.7 Hz, NCH2), 6.97 and 6.99 (each m, 1H, p-H), 7.06 and 7.18 (each m, 2H, m-H), 7.49 (m, 2H, o-H), second o-H not assigned, 7.49 (d, 3JPH = 72.7 Hz, 1H, CCH), 7.65 (d, 1JPH = 441.0 Hz, 1H, PH). 13C NMR (100 MHz, C6D6, 300 K): δ 2.4 (d br, 3JPC =

CsI plates or as KBr pellets on a Shimadzu Prestige 21 spectrometer; electron impact mass spectra were obtained on a Finnigan MAT95 mass spectrometer. Commercially available Ph−CN, Ph−NC S, and Me3C−NCS were dried over molecular sieves; DABCO (1,4-diazabicyclo[2.2.2]octane), DBU (1,8-diazabicyclo[5.4.0]undec7-ene), DABCO(SO2)2, and n-BuLi were used as purchased. EtN CCPh2,39 (Me3Si)2HC−P(H)−C{Al[CH(SiMe3)2]2}CC(H)− CMe3 ((Z)-1a)4 and Mes−P(H)−C{Al[CH(SiMe3)2]2}CC(H)− CMe3 (1b)5 were synthesized according to literature procedures. The assignment of NMR spectra is based on HMBC, H,H-ROESY, HSQC, and DEPT135 data. Reaction of Compound (Z)-1a with Ph−CN: Synthesis of 3a. Treatment of a solution of (Z)-1a (0.19 g, 0.31 mmol) in npentane (20 mL) at −30 °C with Ph−CN (0.032 g, 0.31 mmol) afforded immediately the adduct (Me3Si)2HC−(H)P−C[Al{CH(SiMe3)2}2]C(H)−CMe3(NC−Ph), which was identified by NMR spectroscopy. Addition of DABCO (0.0017 g, 0.015 mmol) at room temperature yielded after stirring of the mixture for 16 h and cooling the concentrated solution to −30 °C compound 3a as orange crystals (0.20 g, 89%). Mp: 133 °C dec. 1H NMR (400 MHz, C6D6, 300 K): δ −0.75 (s br, 2H, AlCH), 0.08 (s, 18H, PCSiMe3), 0.35 and 0.44 (each s, 18H, AlCSiMe3), 1.04 (d, 2JPH = 9.4 Hz, 1H, PCH), 1.30 (s, 9H, CMe3), 6.90 (d, 3JPH = 45.0 Hz, 1H, CCH), 6.93 (d overlap, 3JHH = 7.6 Hz, 2H, m-H), 6.97 (m overlap, 1H, p-H), 7.62 (d, 3 JHH = 7.6 Hz, 2H, o-H), 8.74 (d br, 3JPH = 2.0 Hz, 1H, NH). 13C NMR (100 MHz, C6D6, 300 K): δ 3.1 (d, 3JPC = 4.2 Hz, PCSiMe3), 4.2 (s br, AlCH), 5.4 (AlCSiMe3), 5.6 (d, 5JPC = 1.8 Hz, AlCSiMe3), 15.7 (d, 1JPC = 50.8 Hz, PCH), 30.6 (d, 4JPC = 2.6 Hz, CMe3), 37.3 (d, 3 JPC = 4.2 Hz, CMe3), 127.1 (d, 3JPC = 11.9 Hz, o-C), 129.6 (d, 4JPC = 1.3 Hz, m-C), 132.5 (p-C), 139.6 (d, 2JPC = 17.9 Hz, ipso-C), 144.4 (d br, 1JPC ≈ 44 Hz, PCAl), 159.7 (d br, 2JPC = 9.0 Hz, CCH), 205.2 (d, 1JPC = 23.8 Hz, PCN). 29Si NMR (79 MHz, C6D6, 300 K): δ −2.1 and −1.9 (AlCSi), 4.1 (d, 2JPSi = 6.1 Hz, PCSi). 31P NMR (162 MHz, C6D6, 300 K): δ 16.1. MS (20 eV, 323 K): m/z (%): 721 (2) [M]+, 562 (100) [M − CH(SiMe3)2]+. IR (KBr pellet, cm−1): 3310 m ν(N−H); 3057 w, 2957 vs, 2897 vs, 2824 s, 2789 m ν(CH); 1915 vw, 1852 vw, 1821 vw, 1595 w, 1547 w, 1504 vs ν(CN), ν(CC), aryl; 1479 vs, 1443 m, 1423 m, 1396 w, 1350 vs, 1258 vs, 1250 vs δ(CH3); 1240 vs, 1207 s, 1074 w ν(CC); 1022 vs, 991 s δ(CHSi2); 934 vs, 910 vs, 820 vs, 806 vs, 775 vs, 748 vs ρ(CH3Si); 694 vs, 671 vs, 644 s, 617 s ν(SiC), aryl; 569 m, 523 s, 509 s, 473 m ν(PC), ν(AlC), ν(AlN), δ(CC). Anal. Calcd for C34H73AlNPSi6 (722.4): C, 56.5; H, 10.2; N, 1.9. Found: C, 56.6; H, 9.9; N, 1.9. Reaction of Compound (Z)-1a with Ph−NCS: Synthesis of 4a. Ph−NCS (0.042 g, 0.31 mmol) was added at −30 °C to a solution of (Z)-1a (0.19 g, 0.31 mmol) in n-pentane (20 mL). The mixture was warmed to room temperature, concentrated, and stored at −30 °C to yield yellow crystals of compound 4a (0.21 g, 90%). Mp: 167 °C (dec.). 1H NMR (400 MHz, C6D6, 300 K): δ −0.71 and −0.67 (each s br, 1H, AlCH), 0.20 and 0.24 (each s, 9H, PCSiMe3), 0.27, 0.34, 0.457, and 0.461 (each s, 9H, AlCSiMe3), 1.02 (d, 2JPH = 19.0 Hz, 1H, PCH), 1.09 (s, 9H, CMe3), 6.94 (t, 3JHH = 7.5 Hz, 1H, p-H), 7.11 (d, 1JPH = 453.7 Hz, 1H, PH), 7.23 (pseudo-t, 3JHH = 7.9 Hz, 2H, m-H), 7.50 (d, 3JHH = 7.8 Hz, 2H, o-H), 7.51 (d, 3JPH = 69.9 Hz, 1H, CCH). 13C NMR (100 MHz, C6D6, 300 K): δ 1.7 (d, 3JPC = 3.2 Hz, PCSiMe3), 3.3 (d, 3JPC = 3.2 Hz, PCSiMe3), 3.8 and 4.8 (each s br, AlCH), 5.1, 5.2, 5.8, and 6.2 (AlCSiMe3), 12.9 (d, 1JPC = 11.7 Hz, PCH), 30.3 (d, 5JPC = 1.2 Hz, CMe3), 38.8 (d, 3JPC = 12.1 Hz, CMe3), 121.9 (d, 4JPC = 1.1 Hz, o-C), 125.8 (p-C), 129.2 (m-C), 131.1 (br, PCAl), 150.1 (d, 3JPC = 28.2 Hz, ipso-C), 167.8 (d, 1JPC = 128.7 Hz, PCN), 173.3 (d, 2JPC = 7.2 Hz, CCH). 29Si NMR (79 MHz, C6D6, 300 K): δ −1.3, −1.6, −1.7, and −3.1 (AlCSi), 3.3 (d, 2 JPSi = 5.1 Hz, PCSi), 5.0 (d, 2JPSi = 8.4 Hz, PCSi). 31P NMR (162 MHz, C6D6, 300 K): δ −9.0. MS (20 eV, 363 K): m/z (%): 738 (2) [M − Me]+, 594 (100) [M − CH(SiMe3)2]+. IR (KBr pellet, cm−1): 3065 w, 2955 vs, 2897 vs, 2832 m, 2793 m ν(CH); 2417 w ν(PH); 1935 vw, 1871 vw, 1858 vw, 1587 m, 1549 vs ν(CN), ν(CC), aryl; 1481 m, 1414 w, 1404 w, 1364 m, 1244 vs δ(CH3); 1194 s, 1096 m ν(CC); 1001 vs δ(CHSi2); 928 vs, 916 vs, 868 vs, 835 vs, 816 vs, 773 vs, 750 sh ρ(CH3Si); 691 vs, 671 vs, 633 s ν(SiC), aryl; 581 vw, 2847


Article

Organometallics

(400 MHz, C6D6, 300 K): δ −0.66 (s br, 2H, AlCH), 0.44 and 0.51 (each s, 18H, AlCSiMe3), 0.62 (t, 3JHH = 7.2 Hz, 3H, NCH2Me), 1.00 (s, 9H, CMe3), 1.94 (s, 3H, p-Me), 2.42 (s, 6H, o-Me), 3.82, (dq, 3JHH = 7.2 Hz, 4JPH = 4.0 Hz, 2H, NCH2), 5.46 (d, 3JPH = 9.3 Hz, 1H, CHPh2), 6.54 [d, 4JPH = 2.4 Hz, 2H, m-H(Mes)], 6.80 (d, 3JPH = 47.2 Hz, 1H, CCH), 6.96 [m overlap, 2H, p-H(Ph)], 6.97 [m overlap, 8H, m-H and o-H (Ph)]. 13C NMR (100 MHz, C6D6, 300 K): δ 3.6 (br, AlCH), 6.3 (d, 5JPC = 1.8 Hz, AlCSiMe3), 6.5 (AlCSiMe3), 15.9 (d, 4JPC = 6.1 Hz, NCH2Me), 21.0 (p-Me), 25.3 (d, 3JPC = 13.0 Hz, oMe), 29.3 (d, 4JPC = 2.5 Hz, CMe3), 37.0 (d, 3JPC = 5.5 Hz, CMe3), 48.9 (NCH2), 57.4 (d, 2JPC = 20.8 Hz, CHPh2), 127.6 (p-C(Ph)], 128.7 [m-C(Ph)], 129.5 [d, 3JPC = 5.1 Hz, m-C(Mes)], 130.0 [d, 4JPC = 0.9 Hz, o-C(Ph)], 131.0 [d, 1JPC = 18.7 Hz, ipso-C(Mes)], 138.6 [d, 3 JPC = 3.2 Hz, ipso-C(Ph)], 140 (HMBC, d, 1JPC ≈ 40 Hz, AlCP), 140.7 [d, 4JPC = 1.7 Hz, p-C(Mes)], 145.2 [d, 2JPC = 14.9 Hz, oC(Mes)], 157.7 (d, 2JPC = 5.2 Hz, CCH), 200.8 (d, 1JPC = 14.5 Hz, CN). 29Si NMR (79 MHz, C6D6, 300 K): δ −2.0. 31P NMR (162 MHz, C6D6, 300 K): δ 10.7. MS (20 eV, 323 K): m/z (%): 785 (2) [M − CH3 + H]+, 640 (100) [M − CH(SiMe3)2]+. IR (paraffin mull, KBr plates, cm−1): 1601 w, 1543 s, 1492 m ν(CC), ν(CN), aryl; 1460 s, 1377 m (paraffin); 1292 vw, 1244 s δ(CH3); 1194 vw, 1153 vw, 1086 w, 1061 w, 1031 w ν(CC), ν(CN); 1003 m δ(CHSi2); 937 w, 920 m, 839 vs, 785 s, 746 s, 735 s ρ(CH3Si); 729 m (paraffin); 710 m, 698 s, 669 m, 627 vw, 608 vw ν(SiC), aryl; 558 w, 548 vw, 525 m, 505 w, 473 w, 447 vw, 411 w ν(PC), ν(AlC), ν(AlN), δ(CC). Reaction of Compound (Z)-1a with CO2: Synthesis of 8. A solution of compound (Z)-1a (0.73 g, 1.18 mmol) in toluene (20 mL) was frozen with liquid nitrogen. The gas phase above the frozen material was removed under vacuum and replaced with CO2 (1 bar, dried with CaCO3). The frozen solution was slowly warmed to room temperature and vigorously stirred as soon as the frozen solid started to melt. Removal of all volatiles under vacuum, dissolution of the residue in n-pentane, and cooling the mixture to 0 °C yielded 8 as a colorless solid (0.64 g, 82%). Mp: 140 °C dec. 1H NMR (400 MHz, C6D6, 300 K): δ −0.85 and −0.79 (each s br, 1H, AlCH), 0.16 (d, 4 JPH = 0.6 Hz, 9H, PCSiMe3), 0.18 (s, 9H, PCSiMe3), 0.31, 0.38, 0.42, and 0.43 (each s, 9H, AlCSiMe3), 0.97 (d, 2JPH = 20.4 Hz, 1H, PCH), 0.99 (s, 9H, CMe3), 6.64 (dd, 1JPH = 430.6 Hz, 4JHH = 2.3 Hz, 1H, PH), 7.40 (dd, 3JPH = 76.9 Hz, 4JHH = 2.3 Hz, 1H, CCH). 13C NMR (100 MHz, C6D6, 300 K): δ 0.9 (d, 3JPC = 3.2 Hz, PCSiMe3), 2.5 (d, 3JPC = 3.9 Hz, PCSiMe3), 3.8 (s br, AlCH), 4.8, 5.2, 5.4, and 5.5 (AlCSiMe3), 10.3 (PCH), 30.1 (d, 4JPC = 1.6 Hz, CMe3), 38.6 (d, 3 JPC = 14.5 Hz, CMe3), 129.2 (d br, HMBC, 1JPC ≈ 24 Hz, PCAl), 164.5 (d, 1JPC = 117.6 Hz, PCO), 173.8 (d, 2JPC = 13.3 Hz, CCH). 29 Si NMR (79 MHz, C6D6, 300 K): δ −2.8, −2.0, −1.6, and −1.0 (AlCSi), 3.0 (d, 2JPSi = 3.9 Hz, PCSi), 5.9 (d, 2JPSi = 8.6 Hz, PCSi). 31 P NMR (162 MHz, C6D6, 300 K): δ −31.3. MS (20 eV, 353 K): m/ z (%): 618 (2) [M − CO2; (Z)-1a]+, 503 (4) [M − CH(SiMe3)2]+. IR (paraffin mull, KBr plates, cm−1): P−H not detected; 1705 m ν(CO); 1460 vs, 1377 vs (paraffin); 1258 m, 1244 m δ(CH3); 1092 w ν(CC); 1016 w δ(CHSi2); 935 w, 918 w, 843 s, 777 m ρ(CH3Si); 723 w (paraffin); 669 w, 645 vw ν(SiC); 525 w, 480 w, br ν(PC), ν(AlC), ν(AlO), δ(CC). Anal. Calcd for C28H68AlO2PSi6 (663.3): C, 50.7; H, 10.3. Found: C, 50.5; H, 10.0. Treatment of Compound 8 with DABCO: Synthesis of 9a. DABCO (0.04 g, 0.36 mmol) was added at room temperature to a solution of compound 8 (0.23 g, 0.35 mmol) in n-pentane (20 mL). A colorless solid precipitated, and the suspension was stirred for 12 h at room temperature. The precipitate was dissolved by adding n-pentane (10 mL). Cooling the solution to −30 °C afforded colorless crystals of 9a (0.23 g, 85%). Mp: 176 °C dec. 1H NMR (400 MHz, C6D6, 300 K): δ −0.77 (s br, 2H, AlCH), 0.42 (s, 18H, PCSiMe3), 0.46 and 0.56 (each s, 18H, AlCSiMe3), 1.06 (d, 2JPH = 5.3 Hz, 1H, PCH), 1.36 (s, 9H, CMe3), 2.09 (s, 12H, CH2 DABCO), 6.74 (d, 3JPH = 43.7 Hz, 1H, CCH), 13.08 (s br, 1H, NH). 13C NMR (100 MHz, C6D6, 300 K): δ 2.7 (d, 3JPC = 4.1 Hz, PCSiMe3), 3.4 (br, AlCH), 5.7 (AlCSiMe3), 5.9 (d, 5JPC = 2.2 Hz, AlCSiMe3), 14.3 (d, 1JPC = 54.5 Hz, PCH), 31.2 (d, 4JPC = 2.1 Hz, CMe3), 35.6 (d, 3JPC = 5.7 Hz, CMe3), 44.7 (CH2 DABCO), 149.8 (d br, HMBC, 1JPC ≈ 61 Hz, PCAl),

3.1 Hz, PCSiMe3), 2.4 and 3.6 (s br, AlCH), 3.9 (d br, 3JPC = 3.1 Hz, PCSiMe3), 6.6, 6.7, 6.78, and 6.81 (AlCSiMe3), 13.0 (d, 1JPC = 18.8 Hz, PCH), 14.0 (NCH2Me), 30.1 (d, 4JPC = 1.0 Hz, CMe3), 39.4 (d, 3 JPC = 11.9 Hz, CMe3), 45.2 (d, 3JPC = 10.0 Hz, NCH2), 115.9 (d, 2JPC = 22.6 Hz, CPh2), 125.5 and 126.8 (p-C), 127.4 (s br, AlCP), 127.4 and 129.4 (m-C), 131.1 and 134.4 (o-C), 143.3 (d, 1JPC = 103.7 Hz, CCPh2), 144.9 (d, 3JPC = 4.7 Hz, ipso-C), 145.3 (d, 3JPC = 15.6 Hz, ipso-C), 172.8 (d, 2JPC = 10.4 Hz, CCH). 29Si NMR (79 MHz, C6D6, 300 K): δ −2.37, −2.35, −2.2, and −1.9 (AlCSi), 2.2 (d, 2JPSi = 4.2 Hz, PCSi), 4.1 (d, 2JPSi = 6.5 Hz, PCSi). 31P NMR (162 MHz, C6D6, 300 K): δ −21.9. MS (20 eV, 443 K): m/z (%): 681 (6) [M + H − CH(SiMe3)2]+. IR (paraffin mull, KBr plates, cm−1): P−H not detected; 1578 w, 1558 w, 1487 m ν(CC), aryl; 1458 s, 1377 s (paraffin); 1308 vw, 1294 w, 1256 m, 1242 s δ(CH3); 1132 w, 1123 w, 1072 w ν(CC), ν(CN); 1022 w, 995 w δ(CHSi2); 935 w, 839 vs, 775 m, 754 m ρ(CH3Si); 723 m (paraffin); 704 m, 664 m, 636 vw, 622 vw ν(SiC), aryl; 584 vw, 530 vw, 500 w, 485 vw, 439 vw ν(PC), ν(AlC), ν(AlN), δ(CC). Anal. Calcd for C43H83AlNPSi6 (840.6): C, 61.4; H, 10.0; N, 1.7. Found: C, 61.5; H, 9.9; N, 1.9. Reaction of Compound 1b with EtNCCPh2: Synthesis of 5b. EtNCCPh2 (0.11 g, 0.50 mmol) was added at −90 °C to a solution of (Z)-1a (0.29 g, 0.50 mmol) in n-pentane (15 mL). The mixture was warmed to room temperature to yield an orange solution. Concentration of the solution and cooling to −30 °C afforded yellow crystals of 5b (0.38 g, 95%). Mp: 120 °C dec. 1H NMR (400 MHz, C7D8, 260 K): δ −0.84 and −0.52 (each s br, 1H, AlCH), 0.42, 0.47, 0.48, and 0.55 (each s, 9H, AlCSiMe3), 0.81 (s, 9H, CMe3), 0.90 (t, 3 JHH = 6.7 Hz, 3H, NCH2Me), 1.78 (s, 3H, p-Me), 1.94 and 2.52 (each s, 3H, o-Me), 3.10 (ddq, 2JHH = 14.0 Hz, 3JHH = 6.7 Hz, 4JPH = 3.7 Hz, 1H, NCH2), 3.57 (dq, 2JHH = 14.0 Hz, 3JHH = 6.7 Hz, 1H, NCH2), 6.00 [d, 4JPH = 3.3 Hz, 1H, m-H(Mes)], 6.12 [d, 3JHH = 8.0 Hz, o-H(Pha)], 6.20 [s, 1H, m-H(Mes)], 6.33 [pseudo-t, 3JHH = 7.9 Hz, 1H, m-H(Pha)], 6.62 [s, 1H, o-H(Phb)], 6.72 [t, 3JHH = 7.4 Hz, 1H, p-H(Pha)], 6.94 [m, 1H, m-H(Ph2)], 6.98 [m, 2H, m-H and p-H (Phb)], 7.18 [d, 3JHH = 6.8 Hz, 1H, o-H(Pha)], 7.34 [m, 1H, mH(Phb)], 7.50 (d, 3JPH = 74.0 Hz, 1H, CCH), 7.53 [d, 3JHH = 7.8 Hz, 1H, o-H(Phb)], 7.92 (d, 1JPH = 445.0 Hz, 1H, PH). 13C NMR (100 MHz, C7D8, 260 K): δ 2.4 and 3.4 (br, AlCH), 5.0, 5.9, 6.2, and 6.5 (AlCSiMe3), 14.0 (s, NCH2Me), 20.8 (p-Me), 22.7 (d, 3JPC = 7.4 Hz, o-Me), 24.3 (d, 3JPC = 6.7 Hz, o-Me), 29.4 (CMe3), 38.2 (d, 3JPC = 13.0 Hz, CMe3), 44.8 (d, 3JPC = 9.2 Hz, NCH2), 120.9 (d, 2JPC = 26.1 Hz, CPh2), 121.1 [d, 1JPC = 64.6 Hz, ipso-C(Mes)], 125.6 [p-C(Phb)], 126.3 [p-C(Pha)], 127.0 [m-C(Phb)], 127.8 [m-C(Pha) coincide], 128.3 [m-C(Phb)], 130.1 [d, 3JPC = 10.3 Hz, m-C(Mes)], 130.2 [oC(Phb)], 130.5 [d, 3JPC = 9.3 Hz, m-C(Mes)], 130.7 [o-C(Pha)], 131.0 [o-C(Phb)], 131.5 [o-C(Pha)], 135.7 (d, 1JPC = 108.0 Hz, C CPh2), 140.9 [d, 2JPC = 6.8 Hz, o-C(Mes)], 142.3 [d, 4JPC = 2.9 Hz, pC(Mes)], 142.5 [d, 2JPC = 10.3 Hz, o-C(Mes)], 143.3 [d, 3JPC = 16.9 Hz, ipso-C(Phb)], 144.8 [d, 3JPC = 5.4 Hz, ipso-C(Pha)], 169.9 (d, 2JPC = 10.0 Hz, CCH), AlCP not observed. 29Si NMR (79 MHz, C7D8, 260 K): δ −3.4, −2.6, −2.5, and −2.1. 31P NMR (162 MHz, C7D8, 260 K): δ −34.9. MS (20 eV, 413 K): m/z (%): 640 (21) [M − CH(SiMe3)2]+, 563 (9) [M − CH(SiMe3)2 − Ph]+. IR (paraffin mull, KBr plates, cm−1): 2419 vw ν(PH); 1940 vw, 1883 vw, 1802 vw, 1732 vw, 1676 vw, 1634 w, 1609 m, 1589 m, 1553 w, 1506 s ν(CC), aryl; 1487 s, 1464 vs, 1377 s (paraffin); 1368 sh, 1294 m, 1242 vs δ(CH3); 1200 w, 1179 w, 1155 w, 1138 m, 1072 m, 1034 m, 1022 m ν(CC), ν(CN); 1013 m, 999 m δ(CHSi2); 949 w, 912 s, 841 vs, 779 vs, 760 s ρ(CH3Si); 723 m (paraffin); 698 m, 679 s, 665 s, 629 m, 608 w ν(SiC), aryl; 583 m, 550 w, 511 s, 483 w, 460 w, 438 w ν(PC), ν(AlC), ν(AlN), δ(CC). Anal. Calcd for C45H75AlNPSi4 (800.4): C, 67.5; H, 9.4; N, 1.7. Found: C, 67.6; H, 9.3; N, 2.0. Rearrangement of 5b: Synthesis of 7. DABCO (0.045 g, 0.40 mmol) was added at room temperature to a solution of compound 5b (0.34 g, 0.42 mmol) in n-hexane (15 mL). The mixture was stirred overnight. Removal of all volatiles under vacuum, extraction of the residue with n-pentane, concentration of the solution, and cooling to −30 °C yielded colorless crystals of compound 7 (0.26 g, 77%). Microanalysis of 7 failed (carbon value 2% too low); the purity of 7 was confirmed by NMR spectroscopy. Mp: 190 °C dec. 1H NMR 2848


Article

Organometallics

m, 424 w ν(PC), ν(AlC), ν(AlO), δ(CC). Anal. Calcd for C28H67AlLiO2PSi6 (669.3): C, 50.2; H, 10.1. Found: C, 50.4; H, 10.4. Reaction of 1a with DABCO(SO2)2: Synthesis of 11. Solid DABCO(SO2)2 (0.063 g, 0.26 mmol) was added at −78 °C to a solution of (Z)-1a (0.323 g, 0.52 mmol) in n-pentane (15 mL). The mixture was warmed to room temperature and stirred for 1 h. All volatiles were removed under vacuum, and the residue was extracted with n-pentane. Filtration, concentration of the filtrate, and cooling to −30 °C yielded colorless crystals of 11 (0.17 g, 63%). Mp: 175 °C dec. 1H NMR (400 MHz, C6D6, 300 K): δ −0.95 (s br, 1H, AlCH), 0.25 (s, 18H, PCSiMe3), 0.39 and 0.40 (each s, 9H, AlCSiMe3), 0.88 (d overlap, 2JPH = 5.8 Hz, 1H, PCH), 1.37 (s, 9H, CMe3), 7.22 (d, 3 JPH = 36.4 Hz, 1H, CCH). 13C NMR (100 MHz, C6D6, 300 K): δ 1.8 (br, AlCH), 3.0 (d, 3JPC = 6.3 Hz, PCSiMe3), 3.3 (d, 3JPC = 2.6 Hz, PCSiMe3), 4.4 (AlCSiMe3), 4.7 (d, 5JPC = 1.2 Hz, AlCSiMe3), 14.2 (d, 1 JPC = 61.9 Hz, PCH), 30.8 (d, 4JPC = 8.7 Hz, CMe3), 40.0 (d, 3JPC = 1.1 Hz, CMe3), 139 (d br, HMBC, 1JPC ≈ 53 Hz, PCAl), 170.4 (d, 2 JPC = 19.5 Hz, CCH). 29Si NMR (79 MHz, C6D6, 300 K): δ −1.7 and −0.6 (AlCSi), 1.9 (d, 2JPSi = 11.2 Hz, PCSi), 2.0 (d, 2JPSi = 8.6 Hz, PCSi). 31P NMR (162 MHz, C6D6, 300 K): δ 96.6. MS (20 eV, 453 K): m/z (%): 1044 (3) [M2]+, 1029 (5) [M2 − Me]+, 971 (6) [M2 − SiMe3]+, 885 (25) [M2 − CH(SiMe3)2]+. IR (paraffin mull, KBr plates, cm−1): 1651 vw, 1557 w ν(CC); 1460 s, 1377 m, 1364 w (paraffin); 1246 s δ(CH3); 1198 vw ν(CC); 1013 s, br δ(CHSi2); 972 m, 924 m, 843 vs, 781 m, 750 m, 725 m ρ(CH3Si); 673 m, 637 vw ν(SiC); 557 w, 529 w, 469 vw ν(PC), ν(PS), ν(AlC), ν(AlO), δ(CC). Anal. Calcd for C20H48AlO2PSSi4 (523.0): C, 45.9; H, 9.3. Found: C, 46.1; H, 9.2. X-ray Crystallography. Crystals suitable for X-ray crystallography were obtained from n-pentane (−30 °C; (E)-1a, 3a, 4a, 5a,b, 9a, 6, 10, 11), n-hexane (−30 °C; 7), or toluene (0 °C; 8). 4b was obtained from a 1:1 mixture of 4b and 6 in n-pentane at −30 °C. Intensity data were collected on a D8-Venture diffractometer with monochromated Mo Kα radiation. The collection method involved ω scans. Data reduction was carried out using the program SAINT+.40 The crystal structures were solved by Direct Methods using SHELXTL.41,42 Nonhydrogen atoms were first refined isotropically followed by anisotropic refinement by full-matrix least-squares calculation based on F2 using SHELXTL.41,42 H atoms directly bound to N or P in compounds (E)-1a, 3a, 4a,b, 5a,b, 8, and 9a,b were refined isotropically; all other H atoms were positioned geometrically and allowed to ride on the respective parent atoms. The P−H group of compound (E)-1a, one SiMe3 group of 10, two SiMe3 groups of 5a, one CH group (6), one CH(SiMe2)2 group of 8, and two CH(SiMe3)2 groups of 7 were disordered and refined on split positions. The molecules of 10 reside on 2-fold rotation axes. The crystals of 10 incorporated one molecule of n-pentane per dimer, which was disordered across a 2-fold rotation axis. The structure of 3a featured two voids which were occupied by approximately 1.5 molecules of disordered n-pentane molecules. They were treated using the SQUEEZE program.43

151.0 (CCH), 198.6 (d, 1JPC = 6.0 Hz, PCO). 29Si NMR (79 MHz, C6D6, 300 K): δ −1.9 and −1.5 (AlCSi), 2.4 (d, 2JPSi = 4.7 Hz, PCSi). 31 P NMR (162 MHz, C6D6, 300 K): δ −11.1. MS (20 eV, 353 K): m/ z (%): 603 (3) [M − DABCO − CO2 − Me; 1a − Me]+. IR (KBr pellet, cm−1): 2945 vs, 2896 vs, 2863 sh, 2820 m ν(CH); 2637 vw, 2591 w, 2475 w, 2329 vw, 2151 vw ν(NH); 2070 vw, 2028 vw, 1947 w, 1906 w, 1848 vw, 1700 vw, 1684 vw, 1654 vw, 1559 vs, 1544 vs, 1506 s ν(CO), ν(CC); 1463 vs, 1438 vs, 1405 vs, 1395 vs, 1345 vs, 1320 s, 1285 vs, 1254 vs, 1239 vs δ(CH3); 1200 m, 1177 m, 1054 s ν(CC), ν(CN); 1013 vs, 990 vs δ(CHSi2); 923 s, 909 s, 849 vs, 826 vs, 805 vs, 778 vs, 751 s, 718 s ρ(CH3Si); 670 vs, 633 m, 612 w ν(SiC); 591 vs, 556 m, 525 vs, 459 m ν(PC), ν(AlC), ν(AlO), δ(CC). Anal. Calcd for C34H80AlN2O2PSi6 (775.5): C, 52.7; H, 10.4; N, 3.6. Found: C, 51.9; H, 10.2; N, 3.5. Reaction of Compound 8 with DBU: Synthesis of 9b. DBU (0.095 g, 0.63 mmol) was added at room temperature to a solution of compound 8 (0.41 g, 0.62 mmol) in n-pentane (20 mL). The mixture was stirred for 12 h. Compound 9b precipitated as a colorless solid, which was isolated by filtration and dried under vacuum (0.51 g, 100%). Mp: 178 °C dec. 1H NMR (400 MHz, C6D6, 300 K): δ −0.76 (s br, 2H, AlCH), 0.50 (s, 18H, PCSiMe3), 0.51 and 0.59 (each s, 18H, AlCSiMe3), 0.72 (m, 2H, 3-H DBU), 0.95 (pseudo-quint, 3JHH = 5.8 Hz, 2H, 10-H DBU), 1.01 (pseudo-quint, 3JHH = 5.9 Hz, 2H, 4-H DBU), 1.11 (d, 2JPH = 5.3 Hz, 1H, PCH), 1.29 (pseudo-quint, 3JHH = 6.4 Hz, 2H, 5-H DBU), 1.41 (s, 9H, CMe3), 1.98 (t, 3JHH = 6.0 Hz, 2H, 11-H DBU), 2.15 (m, 2H, 2-H DBU), 2.28 (m, 2H, 6-H DBU), 2.94 (t, 3JHH = 5.8 Hz, 2H, 9-H DBU), 6.74 (d, 3JPH = 42.4 Hz, 1H, CCH), 12.06 (s br, 1H, NH). 13C NMR (100 MHz, C6D6, 300 K): δ 2.7 (d, 3JPC = 4.0 Hz, PCSiMe3), 3.5 (br, AlCH), 5.6 (AlCSiMe3), 5.9 (d, 5JPC = 2.0 Hz, AlCSiMe3), 14.2 (d, 1JPC = 55.0 Hz, PCH), 19.1 (10-C DBU), 24.0 (5-C DBU), 26.4 (3-C DBU), 28.7 (4-C DBU), 31.4 (d, 4JPC = 2.0 Hz, CMe3), 32.0 (6-C DBU), 35.5 (d, 3JPC = 5.6 Hz, CMe3), 38.1 (9-C DBU), 47.6 (11-C DBU), 53.3 (2-C DBU), 149.6 (CCH), 151.3 (d br, 1JPC ≈ 62 Hz, PCAl), 165.5 (7-C DBU), 195.7 (d, 1JPC = 8.5 Hz, PCO). 29Si NMR (79 MHz, C6D6, 300 K): δ −2.0 and −1.4 (AlCSi), 2.2 (d, 2JPSi = 4.8 Hz, PCSi). 31P NMR (162 MHz, C6D6, 300 K): δ −12.5. MS (20 eV, 393 K): m/z (%): 618 (1) [M − DBU − CO2; 1a]+. IR (KBr pellet, cm−1): 3094 w, 3034 w, 2951 vs, 2895 vs, 2862 s, 2806 s, 2700 w ν(CH); 1647 vs ν(CN); 1574 vs ν(CO), ν(CC); 1466 w, 1443 w, 1414 w, 1389 w, 1358 w, 1323 s, 1238 vs δ(CH3); 1203 m, 1109 w, 1051 w ν(CC) ν(CN); 1011 s, 982 m δ(CHSi2); 922 s, 903 s, 847 vs, 779 vs, 752 s ρ(CH3Si); 718 m, 671 s, 631 w, 613 vw ν(SiC); 559 w, 530 s, 507 w, 426 w ν(PC), ν(AlC), ν(AlO), δ(CC). Anal. Calcd for C37H84AlN2O2PSi6 (815.6): C, 54.5; H, 10.4; N, 3.4. Found: C, 54.2; H, 10.6; N, 3.4. Reaction of Compound 8 with BuLi: Synthesis of 10. n-BuLi (0.39 mL, 0.62 mmol, 1.6 M in n-hexane) was added at −78 °C to a solution of 8 (0.41 g, 0.62 mmol) in n-pentane (20 mL). The mixture was warmed to room temperature and stirred for 12 h. Concentration of the solution and cooling to −30 °C yielded colorless crystals of 10. A second crop of crystals was isolated from the mother liquor (combined yield 0.26 g, 63%). Mp: 200 °C dec. 1H NMR (400 MHz, d8-THF, 300 K): δ −1.22 (s br, 2H, AlCH), 0.07 and 0.10 (each s, 18H, AlCSiMe3), 0.19 (s, 18H, PCSiMe3), 0.80 (d, 2JPH = 6.0 Hz, 1H, PCH), 1.11 (s, 9H, CMe3), 6.34 (d, 3JPH = 41.2 Hz, 1H, CCH). 13 C NMR (100 MHz, d8-THF, 300 K): δ 2.9 (d, 3JPC = 4.0 Hz, PCSiMe3), 3.7 (br, AlCH), 5.5 (d, 5JPC = 1.0 Hz, AlCSiMe3), 5.8 (d, 5 JPC = 1.7 Hz, AlCSiMe3) 14.3 (d, 1JPC = 53.5 Hz, PCH), 31.4 (d, 4JPC = 2.4 Hz, CMe3), 36.1 (d, 3JPC = 4.5 Hz, CMe3), 151.1 (CCH), 152.2 (br, PCAl), 195.5 (s br, PCO). 29Si NMR (79 MHz, d8-THF, 300 K): δ −2.5 and −2.0 (AlCSi), 2.1 (d, 2JPSi = 5.5 Hz, PCSi). 31P NMR (162 MHz, d8-THF, 300 K): δ −12.6. 7Li NMR (155 MHz, d8THF, 300 K): δ −0.11. MS (20 eV, 393 K): m/z (%): 618 (2) [M − CO2 − Li; 1a]+. IR (KBr pellet, cm−1): 2957 vs, 2897 vs, 2816 w ν(CH); 1923 vw, 1709 vw, 1665 vw, 1558 s, 1510 vs, 1472 w ν(C O), ν(CC); 1460 w, 1420 vw, 1400 vw, 1391 vw, 1360 m, 1258 vs, 1242 vs δ(CH3); 1198 m, 1061 w ν(CC); 1007 vs, 984 s δ(CHSi2); 934 vs, 922 vs, 870 vs, 858 vs, 843 vs, 831 vs, 779 vs, 748 vs, 718 m ρ(CH3Si); 673 vs, 638 w, 623 vw, 610 vw ν(SiC); 559 w, 521 vs, 471

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.9b00346. NMR spectra of all compounds (PDF) Accession Codes

CCDC 1917217−1917229 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambrdge Crystallographic Data Centre, 12 Union Road, Cambrdge CB2 1EZ, UK; fax: +44 1223 336033. 2849


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Organometallics

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AUTHOR INFORMATION

Corresponding Author

*E-mail for W.U.: [email protected]. ORCID

Alexander Hepp: 0000-0003-1288-925X Werner Uhl: 0000-0002-7178-5517 Notes

The authors declare no competing financial interest.

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REFERENCES

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P-Based Frustrated Lewis Pairs in Dipolar

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