Reactions of an Al–P-Based Frustrated Lewis Pair with Carbonyl

Article pubs.acs.org/Organometallics

Reactions of an Al−P-Based Frustrated Lewis Pair with Carbonyl Compounds: Dynamic Coordination of Benzaldehyde, Activation of Benzoyl Chloride, and Al−C Bond Cleavage with Benzamide Werner Uhl* and Christian Appelt Institut für Anorganische und Analytische Chemie der Universität Münster, Corrensstraße 30, D-48149 Münster, Germany S Supporting Information *

ABSTRACT: Treatment of the Al/P-based frustrated Lewis pair (FLP) Mes2PC(CHPh)Al(CMe3)2 (1) with benzaldehyde afforded the adduct 2 with a five-membered AlCPCO heterocycle. The carbonyl oxygen atom is bound to aluminum and the carbonyl carbon atom to phosphorus. 2 is dynamic in solution at room temperature, which results in a fast equilibration of the enantiomeric molecules by cleavage of the P−C and fast rotation about the Al−O bond. Benzoyl chloride and 1 yielded three products (3−5). Quinoid structures were formed by C−Cl bond activation, chlorine abstraction, and loss of aromaticity in the benzoyl phenyl group. Alkylation of the p-C atom by an AlCMe3 group completed the transformation and resulted concomitantly in the formation of derivatives with Al−Cl bonds. The complexes may be described as a ketene molecule coordinated to FLP 1. Benzamide reacted as a proton donor and gave cleavage of the Al−C bond to the vinylic carbon atom of 1. An alkenylphosphine, Mes2PC(H)C(H)CMe3, and a dinuclear amidate complex with two dialkylaluminum groups bridged by two chelating ligands were isolated.

■

INTRODUCTION The activation of small molecules by main-group-element compounds rather than traditional transition-metal complexes is the focus of current research interest. Particularly interesting and promising are frustrated Lewis pairs (FLPs), which have coordinatively unsaturated Lewis acidic and Lewis basic centers in single molecules or bimolecular systems.1 Quenching of the opposite functionalities by adduct formation is prevented by steric restrictions such as shielding by bulky substituents and rigid molecular backbones. In most cases FLPs based on B and P atoms were applied, in which the Lewis acidity of the boron atoms was enhanced by electron-withdrawing, fluorinated substituents. They were shown to activate or coordinate H2, CO2, NO, terminal alkynes, etc.1 Nitrogen, sulfur, or carbene carbon atoms were applied as alternative basic centers.1,2 In recent investigations it was impressively demonstrated that aluminum−phosphorus compounds are a powerful alternative class of FLPs. Al atoms have the advantage of an inherently high Lewis acidity that makes activation by fluorinated aromatic substituents unnecessary. Their reactivity was shown in the activation or coordination of terminal alkynes,3,4 CO2,3,5 or alkenes6 and in polymerization reactions.7 They are effective ion pair receptors8 and catalysts for the dehydrogenation of amine−boranes.9 We obtained a monomolecular Al/P-based FLP (1) in high yield by simple hydroalumination of an alkynylphosphine with di-tert-butylaluminum hydride.3 This compound is monomeric in the solid state with coordinatively unsaturated Al and P atoms. In this report we describe © XXXX American Chemical Society

reactions of 1 with three carbonyl compounds (benzaldehyde, benzoyl chloride, and benzamide) which gave three different types of products.

■

RESULTS AND DISCUSSION Reaction of 1 with Benzaldehyde. A solution of the Al/ P-based FLP 1 in toluene was treated with an equimolar quantity of neat benzaldehyde at room temperature (eq 1). The

color changed from yellow to red and back to yellow. The red color may indicate the formation of an unknown intermediate which could, however, not be identified by NMR spectroscopy. The reaction was complete after 3 h. Recrystallization from CH2Cl2 afforded yellow to orange crystals of compound 2 in 68% yield. The molecular structure (Figure 1) revealed that the expected adduct between 1 and benzaldehyde had formed in which the O atom is coordinated to Al and the P atom bonded Received: June 27, 2013

A

dx.doi.org/10.1021/om400620h | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

Figure 1. Molecular structure and atomic numbering scheme of compound 2. Displacement ellipsoids are drawn at the 40% level. Hydrogen atoms (except H1, arbitrary radius) are omitted for clarity. Important bond lengths (Å) and angles (deg): P(1)−C(8) = 1.938(2), C(8)−O(1) = 1.370(3), Al(1)−O(1) = 1.816(2); C(1)−P(1)−C(8) = 94.8(1), C(1)−Al(1)−O(1) = 91.38(8), P(1)−C(8)−O(1) = 109.8(2), C(8)−O(1)−Al(1) = 115.8(1).

carbonyl carbon atom resonated at δ 90.0 with a 1JP−C coupling constant of 38.2 Hz, which indicates a P−C interaction. Only recently have corresponding adducts of B/P-based FLPs been reported.13 They showed NMR parameters expected for chiral molecules at room temperature. A dynamic behavior was observed in a single case only when the sample was heated to +90 °C. This marked difference from 2 may depend on the acceptor strength of the Lewis acidic centers. The boron atoms in the B/P-based systems are activated by two electronwithdrawing pentafluorophenyl groups. The high polarizing effect of the B atoms may enhance the polarity of the carbonyl group and may favor the coordination of the P atom to the carbonyl C atom. These findings demonstrate impressively the importance of the variation of the donor and acceptor properties of the FLPs. The weakness of the P−C interaction in 2 leads to the spontaneous cleavage of the P−C bond in solution at room temperature. This behavior is important for secondary reactions and an activation of the aldehyde with a cooperative influence of the Lewis basic P atom. Reaction of 1 with Benzoyl Chloride. Benzoyl chloride was added to a solution of FLP 1 in toluene at room temperature. A mixture consisting of three compounds was formed (eq 3). Fractional crystallization from cyclopentane at

to the carbonyl C atom. The five-membered AlCPCO heterocycle adopts a distorted-envelope conformation with the carbonyl carbon atom C(8) found 0.62 Å above the plane of the remaining four ring atoms (P(1)C(1)Al(1)O(1); maximum deviation of an atom 0.02 Å). The P(1)−C(1) distance is slightly shortened in comparison to the starting compound 1 (1.810(2) vs 1.822(3) Å). This may be caused by the higher positive charge at the phosphorus atom of 2. In contrast, the Al(1)−C(1) bond is considerably lengthened from 1.992(3) to 2.089(2) Å, reflecting the higher coordination number at aluminum (4 versus 3).10 The C−O bond length (1.370(3) Å) is intermediate between a C−O single and double bond.11 Particularly interesting for the behavior of compound 2 in solution is the relatively long endocyclic P−C distance including the carbonyl carbon atom C(8) (1.938(2) Å). It is longer than standard values for P−C single bonds (1.80 to 1.85 Å; cf. P(1)−C(1) above)12 and comparable to the corresponding P−C distance in the CO2 adduct of 1 (1.919 Å (av)).3 This observation may indicate a relatively weak P−C interaction. Indeed, the formation of the CO2 adduct proved to be reversible at elevated temperature and 1 was recovered quantitatively upon heating under reduced pressure.3 The carbon atom of 2 is chiral; the R form is shown in Figure 1, and its enantiomer is generated by the symmetry transformation of the space group. Molecular symmetry requires two different sets of resonances for the diastereotopic mesityl groups attached to phosphorus and the tert-butyl groups bound to aluminum. However, simple spectra were observed at room temperature indicating equivalent aryl and alkyl substituents. Only cooling of a solution of 2 in CH2Cl2 to −50 °C gave the expected set of split resonances. Compound 2 is obviously highly dynamic in solution and shows a fast equilibration of the substituents at room temperature. We assume that the relatively weak P− C(O) bond (see Figure 1) is cleaved. The benzaldehyde molecule is intermediately coordinated only to the Al atom. This allows fast rotation about the Al−O bond and fast exchange between both enantiomers (eq 2). At low temperature a racemic mixture between the R and S forms exists in solution. The activation barrier was estimated to be 54 kJ/mol from the coalescence temperature determined in 1H NMR spectra at variable temperatures and from the differences of the chemical shifts for the static molecules. The endocyclic

−20 °C afforded colorless crystals of the main component 3 in 20% yield as the first fraction. Concentration of the remaining solution gave compound 4 in 11% yield as an amorphous material. A third compound (5) was isolated in very small quantities in the following fraction. The integration of the B

dx.doi.org/10.1021/om400620h | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

resonances in the 31P NMR spectrum of the crude product showed the three products 3, 4 (both isomers, see below), and 5 in an approximate ratio of about 2:2:1. The molecular structure of 3 (Figure 2) consists of a fivemembered heterocycle in which the carbonyl group (C−O =

measured a crystal which contained a mixture of 3 and 4 and allowed an unambiguous assignment of the molecular structure of 4. It is in the most part identical with that of 3 with a ketene molecule coordinated to the FLP 1 via its carbonyl group, but the Al atom is bonded to a terminal Cl atom. The resulting Al(Cl)CMe3 group is disordered, with the chlorine atom alternatively above or below the molecular plane. This observation was extraordinarily important for the unambiguous assignment of the NMR spectra. There are two stereogenic centers in the molecule, the p-C atom of the C6 ring and the Al atom, which result in the formation of a pair of diastereomeric molecules. Accordingly, we detected two singlets in the 31P NMR spectrum (δ 11.0 and 11.3) and two resonances for the tert-butyl groups attached to the p-C atom C(84). The hydrogen atoms of the diasterotopic mesityl groups showed the expected splitting pattern for two distinct molecular species with four resonances for the o-methyl groups. The resonances of the Al-bonded tert-butyl groups and those of the vinylic hydrogen atoms coincided. The ratio between the diasteromeric molecules was 3:2. NMR experiments at temperatures up to 80 °C did expectedly not lead to coalescence or a change in signal intensities. The third compound (5) of the reaction mixture was only isolated in trace quantities as an amorphous solid. It is insoluble in hydrocarbons; NMR spectra were recorded with a dilute solution in CDCl3. A singlet (δ −7.8) was observed in the 31P {1H} NMR spectrum. The 1H NMR spectrum did not show a resonance for tert-butyl groups. Three singlets were observed for the o- and p-methyl substituents and the ring protons of the mesityl groups. The vinylic phenyl group showed the expected resonances. Particularly interesting was a doublet at δ 8.44 with a very large coupling constant of 492.2 Hz, which indicated a hydrogen atom directly bound to phosphorus. We assume that a zwitterionic Al/P compound, [Mes2P(H)C(CHPh)AlCl3], was formed in which both tertbutyl groups bonded to the Al atoms of 1 were replaced by chlorine atoms. The addition of HCl, which may be formed by dehydrochlorination of benzoyl chloride catalyzed by an FLP, gave 5 with a hydrogen atom bonded to phosphorus and a trichloroaluminate fragment. An HCl adduct of 1 was isolated in recent unpublished work. It shows NMR characteristics similar to those of 5 (with the exception of tert-butyl resonances). These results verify a highly fascinating and complicated reaction. Benzoyl chloride seems to react with the FLP 1 in the first step by coordination of its carbonyl group to the Al and P atoms. This results in the activation and cleavage of the C−Cl bond. The chloride anion is probably trapped by a second molecule of 1 to yield an adduct by Al−Cl bond formation. A mesomeric shift of π bonds leads to a quinoid structure in which the aromaticity in the phenyl group is lost and a cationic carbon atom resulted in a para position. This carbon atom is highly electrophilic and can accept a tert-butyl group from an Al atom. Al−C bond breakage is seemingly preferred to Al−Cl bond cleavage due to the high Al−Cl bond energy. This process of Cl capture by an Al atom and alkylation of the p-C atom is concomitantly a plausible source of the Al−Cl species, which upon reaction with a second equivalent of benzoyl chloride gives the chlorine compound 4 and so forth. This reaction is a true activation process and may be applicable to many similar transformations starting with carbonyl halides or related species. A similar formation of a quinoid structure has previously been observed by treatment of an amido di-tertbutyl zincate with benzophenone.16

Figure 2. Molecular structure and atomic numbering scheme of compound 3. Displacement ellipsoids are drawn at the 40% level. Hydrogen atoms (except those bound to the hexadiene ring, arbitrary radius) are omitted for clarity. Important bond lengths (Å) and angles (deg): P(1)−C(8) = 1.829(1), C(8)−O(1) = 1.336(1), O(1)−Al(1) = 1.824(1), C(8)−C(81) = 1.360(1); P(1)−C(1)−Al(1) = 106.49(6), C(8)−O(1)−Al(1) = 123.13(8), O(1)−Al(1)−C(1) = 89.46(5).

1.336(1) Å) is coordinated by di-tert-butylaluminum and dimesitylphosphinyl groups of the FLP (Al−O = 1.824(1); P−C = 1.792(1) Å). The most interesting feature is that the aromaticity of the phenyl ring is lost. A typical cyclohexadiene system is formed instead with two short (1.335 Å(av); CC) and four long C−C distances (1.455 Å (av), C(ortho)−C(ipso); 1.499 Å (av), C(meta)−C(para)). The quinoid π-electronic system is completed by an exocyclic CC double bond (1.360(2) Å) between the carbonyl C atom C(8) and the ipsoC atom of the C6 ring C(81). The p-C atom of the ring C(84) is sp3-hybridized. It represents a stereogenic center and is bonded to a terminal hydrogen atom and a tert-butyl group. A chlorine atom is not present. Compound 3 may be described as a unique adduct of a ketene, R2CCO, in which the carbonyl group is coordinated to the acceptor and donor functions of the FLP 1. This is a stimulating observation which will influence further investigations. In comparison to bond lengths observed typically for ketenes (CC, 1.298−1.314 Å; CO, 1.147−1.166 Å)14 the bond lengths in 3 are lengthened. They are, however, similar to bond parameters detected for some transition-metal complexes.15 The NMR spectroscopic data confirm the molecular structure. Singlets in the 1H NMR spectrum in a 2:1 intensity ratio were observed for the tert-butyl groups at Al and at the p-C atom C(84) of the C6 ring (δ 1.21 and 0.81), and four doublets resulted for the vinylic hydrogen atoms of the C6 ring. The E configuration of the terminal alkenyl group attached to P and Al was conserved, as is evident from the 3JP−H coupling constant of 38.9 Hz between phosphorus and the vinylic hydrogen atom.3 In contrast, relatively complicated spectra resulted for the second product of this reaction (4). We were not able to generate single crystals of 4 for a crystal structure determination. However, in one instance we fortuitously C

dx.doi.org/10.1021/om400620h | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

Reaction of 1 with Benzoyl Amide. Neat benzamide was treated with a toluene solution of FLP 1 at room temperature. Two compounds were selectively formed (6 and 7; eq 4). After

C−N bond lengths (1.278(2) and 1.305(2) Å) are in accordance with a delocalized π system that is characteristic of amidate groups.18 Dialkylaluminum amidates are known in the literature.18 They are usually obtained by the treatment of trialkylaluminum compounds with carboxylic acid amids and form monomeric, dimeric, or trimeric molecular structures depending on the steric shielding by the alkyl groups.

■

CONCLUSION Different types of reactions were observed upon treatment of the Al/P-based FLP 1 with carbonyl compounds. Benzaldehyde gave an adduct (2) which showed a unique dynamic behavior in solution, probably caused by cleavage of the relatively weak P− C bond to the carbonyl C atom. This behavior is different from that reported for a B/P-based adduct and underscores the importance of the balanced variation of the acceptor and donor properties of FLPs for their application in specific transformations. Chloride abstraction from benzoyl chloride gave by mesomeric charge distribution and alkylation of its p-C atom two complexes of the FLP with a ketene (3 and 4). Finally, benzamide resulted in protolysis of the FLP and cleavage of the bond between the vinylic C atom and aluminum. These three different types of reactions are highly stimulating for further investigations. Nonprotic carboxylic acid derivatives such as alkylated amides or esters may show a reactivity similar to that of benzoyl chloride with the formation of ketene complexes. Alternatively, labile complexes analogous to 2 may result. Similar compounds may be formed with benzophenone or mixed alkyl aryl ketones. An activation of the carbonyl compounds by the interaction with the Lewis acidic Al atom and the cooperative influence of the lone pair at phosphorus may favor secondary reactions such as hydrogenation and hydrosilylation. As a consequence further systematic investigations into the reactivity of FLP 1 toward carbonyl compounds seem to be highly promising and may open access to a wide range of interesting secondary processes.

evaporation of all volatiles compound 6 was extracted from the residue with n-hexane and after removal of the solvent isolated as a spectroscopically pure yellowish oil. The remaining solid was dissolved at 50 °C in 1,2-difluorobenzene, and compound 7 crystallized from this solution upon cooling to room temperature in 44% yield. Benzamide reacted as a proton donor and caused the cleavage of the C(sp2)−Al bond between the vinylic C atom of the FLP 1 and the dialkylaluminum group. The first cleavage product is the alkenylphosphine 6, in which the P atom is bound to a CC double bond and both vinylic hydrogen atoms adopt a trans arrangement (E configuration; ABX spin system; δ 6.64 and 7.34, 3JHH = 16.8 Hz, 2JPH = 10.3 Hz; 3JPH = 23.5 Hz). The corresponding diphenylalkenylphosphine has been described in the literature17 and has quite similar NMR spectroscopic data. 7 is dimeric, with the metal atoms brdged by two benzamidate ligands. The N−H proton was found in the 1H NMR spectrum as a broad resonance at δ 7.68; the carbonyl C atom resonated at δ(13C) 178.1. The molecular structure of the centrosymmetric dimer is depicted in Figure 3. It has an eight-membered C2N2O2Al2 heterocycle in a chair conformation. The endocyclic C−O and

■

EXPERIMENTAL SECTION

All procedures were carried out under an atmosphere of purified argon in dried solvents (THF with Na/benzophenone). Mes2PC( CHPh)Al(CMe3)2 (1) was obtained according to a literature procedure.3 Commercially available benzaldehyde and benzoyl chloride were purified by vacuum distillation and stored over molecular sieves (4 Å); benzamide was dried in vacuo. The assignment of the NMR spectra is based on HMBC, HSQC, ROESY, and DEPT135 data. Reaction of 1 with Benzaldehyde: Synthesis of 2. A solution of the FLP 1 (0.510 g, 1.00 mmol) in 20 mL of toluene was treated with benzaldehyde (0.10 mL, 0.106 g, 1.00 mmol) at room temperature. The color changed from yellow to red for a few minutes and then back to yellow. The mixture was stirred for 3 h. All volatiles were removed in vacuo. The residue was recrystallized from dichloromethane (20/5 °C) to afford yellow-orange crystals of 2. Yield: 0.422 g (68%). Mp (argon, sealed capillary): 178 °C dec. Anal. Calcd for C41H52OAlP (618.8): C, 79.6; H, 8.5. Found: C, 79.1; H, 8.4. 31P{1H} NMR (C6D6, 162 MHz, 298 K): δ 31.7 (s). 31P{1H} NMR (C6D6, 162 MHz, 220 K): δ 31.3 (s). 1H NMR (C6D6, 200 MHz, 298 K): δ 1.41 (18 H, s, Al(CMe3)2), 1.93 (6 H, s, p-CH3), 2.10 (12 H, s, o-CH3), 6.53 (4 H, d, 4JHP = 3.2 Hz, m-HMes), 6.87 (1 H, d, 2 JHP = 10.7 Hz, Ph−CH-O), 6.98 (2 H, m, m-Hbenzyl), 7.00 (1 H, m, pHbenzyl), 7.08 (1 H, m, p-HvinylPh), 7.22 (2 H, m, m-HvinylPh), 7.41 (2 H, m, o-Hbenzyl), 7.64 (2 H, pseudo-d, 3JHH = 7.3 Hz, o-HvinylPh), 7.91 (1 H, d, 3JHP = 37.5 Hz, P−CC−H). 1H NMR (C6D6, 200 MHz, 220 K): δ 1.50 and 1.52 (each 9 H, s, Al(CMe3)2), mesityl I: 1.93 (3 H, s, p-CH3), 1.99 (6 H, s, o-CH3), 6.44 (2 H, d, 4JHP = 2.0 Hz, m-HMes),

Figure 3. Molecular structure and atomic numbering scheme of compound 7. Displacement ellipsoids are drawn at the 40% level. Hydrogen atoms (except H1, arbitrary radius) are omitted for clarity. Important bond lengths (Å) and angles (deg): Al(1)−N(1) = 1.923(2), Al(1)−O(1)′ = 1.792(1), N(1)−C(1) = 1.305(2), C(1)− O(1) = 1.278(2); N(1)−Al(1)−O(1)′ = 106.53(7), Al(1)−N(1)− C(1) = 133.2(1), N(1)−C(1)−O(1) = 120.2(2), C(1)−O(1)−Al(1)′ = 147.2(1). Transformation for symmetry equivalent atoms: −x + 1, −y, −z. D

dx.doi.org/10.1021/om400620h | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

1726 vw, 1694 vw, 1601 s, 1553 m ν(CC), ν(CO), phenyl; 1466 vs, 1452 vs, 1404 w, 1375 vs (paraffin); 1340 w, 1306 w δ(CH3); 1233 w, 1198 vw, 1167 m, 1119 w, 1070 s, 1055 s, 1005 w, 955 vw, 928 w, 889 w, 849 m, 808 m, 758 m ν(CC), ν(CO); 721 vs (paraffin); 696 m, 644 w, 610 w, 586 vw, 557 m, 530 w, 470 m, 420 vw, 395 w, 361 m, 338 vw δ(CC), ν(AlC), ν(AlO), ν(PC). MS (EI, 20 eV, 373 K): m/z (%) 617 (100), 618 (45), 619 (10) [M+ − CMe3], 560 (12), 561 (5) [M+ − 2 CMe3], 503 (21), 504 (7) [M+ − 3 CMe3], 161 (11) [(pCMe3)C6H5(CO) − H], 105 (17) [C6H5(CO)+]. Characterization of 4. Yield: 0.065 g (11%). Mp (argon, sealed capillary): >115 °C dec. Anal. Calcd for C41H51OAlPCl (653.3): C, 75.4; H, 7.9. Found: C, 74.9; H, 8.0. Data for the f irst diastereomer (main component (60%)) are as follows. 31P{1H} NMR (C6D6, 162 MHz, 298 K): δ 11.0 (s). 1H NMR (C6D6, 200 MHz, 298 K): δ 0.82 (9 H, s, CMe3, hexadiene), 1.25 (9 H, s, AlCMe3), Mesityl I: 1.91 (3 H, s, p-CH3), 2.41 (6 H, s, o-CH3), 6.63 (2 H, m, m-HMes), mesityl II: 1.97 (3 H, s, p-CH3), 2.28 (6 H, s, o-CH3), 6.65 (2 H, m, m-HMes), hexadiene: 2.67 (1 H, s br, CHCMe3), 5.48 (1 H, m, CH CHCHCMe3) and 6.23 (1 H, d, 3JHH = 10.3 Hz, CHCHCHCMe3), 5.82 (1 H, m, CHCHCHCMe3) and 7.55 (1 H, d, 3JHH = 10.6 Hz, CHCHCHCMe3), 7.04 (1 H, m, p-HPh), 7.18 (2 H, m, m-HPh), 7.55 (1 H, d, 3JHP = 35.0 Hz, PCCH), 7.69 (2 H, m, o-HPh). 13 C{1H} NMR (C6D6, 101 MHz, 298 K): δ 15.8 (s br, AlCMe3) and 30.4 (s, AlCMe3), mesityl I: 20.9 (s, p-CH3), 24.5 (d, 3JCP =5.0 Hz, oCH3), 120.3 (d, 1JCP = 72.4 Hz, ipso-CMes), 132.7 (d, 3JCP = 10.0 Hz, m-CMes), 143.4 (s, p-CMes), 144.5 (d, 2JCP = 10.0 Hz, o-CMes), mesityl II: 20.9 (s, p-CH3), 24.6 (d, 3JCP = 5.0 Hz, o-CH3), 119.0 (d, 1JCP = 61.0 Hz, ipso-CMes), 132.6 (d, 3JCP = 10.0 Hz, m-CMes), 143.4 (s, pCMes), 144.9 (d, 2JCP = 10.0 Hz, o-CMes), 27.5 (s, CH-CMe3) and 35.6 (d, 6JCP = 2 Hz, CH-CMe3), hexadiene: 49.8 (s, CHCHCHCMe3), 122.8 (d, 3JCP = 10.0 Hz, CHCHCHCMe3) and 128.9 (s, CH CHCHCMe3), 125.3 (d, 3JCP = 10.0 Hz, CHCHCHCMe3) and 129.2 (s, CHCHCHCMe3), 125.6 (d, 2JCP = 30.3 Hz, C-CH CHCHCMe3), 128.8 (s, o-CPh), 129.2 (s, m-CPh), 129.9 (s, p-CPh), 134.9 (s br, PCCH), 140.0 (d, 3JCP = 31.7 Hz, ipso-CPh), 141.0 (d, 1 JCP = 92.9 Hz, PCO), 156.2 (d, 2JCP = 2.7 Hz, PCCH). Data for the second diastereomer, minor component (40%) are as follows. 31P{1H} NMR (C6D6, 162 MHz, 298 K): δ 11.3 (s). 1H NMR (C6D6, 200 MHz, 298 K): δ 0.78 (9 H, s, CHCMe3), 1.25 (9 H, s, AlCMe3), mesityl I: 2.40 (6 H, s, o-CH3), 6.63 (2 H, m, m-HMes), mesityl II: 1.93 (6 H, s, p-CH3), 2.41 (6 H, s, o-CH3), 6.65 (2 H, m, m-HMes), 2.67 (1 H, s br, CHCMe3), 5.48 (1 H, m, CHCHCHCMe3) and 6.23 (1 H, d, 3JHH = 10.3 Hz, CHCHCHCMe3), 5.82 (1 H, m, CH CHCHCMe3) and 7.55 (1 H, d, 3JHH = 10.6 Hz, CHCHCHCMe3), 7.04 (1 H, m, p-HPh), 7.18 (2 H, m, m-HPh), 7.55 (1 H, d, 3JHP = 35.0 Hz, PCCH), 7.69 (2 H, m, o-HPh). 13C NMR (C6D6, 101 MHz, 298 K): δ 15.8 (s br, AlCMe3) and 30.4 (s, AlCMe3), mesityl I: 20.9 (s, pCH3), 24.4 (d, 3JCP =5.0 Hz, o-CH3), 119.9 (d, 1JCP = 71.0 Hz, ipsoCMes), 132.7 (d, 3JCP = 10.0 Hz, m-CMes), 143.3 (s, p-CMes), 144.6 (d, 2 JCP = 10.0 Hz, o-CMes), mesityl II: 20.9 (s, p-CH3), 24.7 (d, 3JCP = 5.0 Hz, o-CH3), 119.5 (d, 1JCP = 63.0 Hz, ipso-CMes), 132.6 (d, 3JCP = 10.0 Hz, m-CMes), 143.3 (s, p-CMes), 144.9 (d, 2JCP = 10.0 Hz, o-CMes), 27.4 (s, CHCMe3) and 35.7 (d, 6JCP = 2.0 Hz, CHCMe3), hexadiene: 49.9 (s, CHCHCHCMe3), 122.9 (d, 3JCP = 10.0 Hz, CHCHCHCMe3) and 128.9 (s, CHCHCHCMe3), 125.2 (d, 3JCP = 10.0 Hz, CH CHCHCMe3) and 129.2 (s, CHCHCHCMe3), 125.6 (d, 2JCP = 30.3 Hz, CCHCHCHCMe3), 128.8 (s, o-CPh), 129.2 (s, m-CPh), 129.9 (s, p-CPh), 134.9 (s br, PCCH), 139.8 (d, 3JCP = 31.8 Hz, ipsoCPh), 141.1 (d, 1JCP = 93.9 Hz, PCO), 156.4 (d, 2JCP = 2.7 Hz, PC CH). IR (paraffin, CsI, cm−1, mixture of diastereomers): 1950 vw, 1883 vw, 1697 vw, 1645 w, 1603 m, 1553 m ν(CC), phenyl; 1466 m, 1433 w, 1371 m (paraffin); 1354 w, 1289 w, 1250 vw δ(CH3); 1213 w, 1171 m, 1148 m, 1055 m, 1028 m, 974 vw, 922 m, 893 w, 855 s, 812 w, 787 vw, 743 m ν(CO), ν(CC); 721 s (paraffin); 692 m, 648 s, 623 vw, 606 w, 554 w, 511 vw, 480 w, 465 w, 426 vw δ(CC), ν(AlC), ν(AlO), ν(PC),ν(AlCl). MS (EI, 20 eV, 323 K, mixture of diastereomers): m/z (%) 618 (81), 619 (36), 620 (8) [M+ - Cl + H], 596 (10), 597 (4), 598 (4), 599 (1) [M+ − butene], 561 (10), 562 (5), 563 (1) [M+ − Cl − butene], 504 (19), 505 (6), 506(1) [M+ − Cl

mesityl II: 1.90 (3 H, s, p-CH3), 2.11 (6 H, s, o-CH3), 6.37 (2 H, d, 4 JHP = 2.7 Hz, m-HMes), 6.85 (1 H, d, 2JHP = 10.7 Hz, Ph−CH-O), 6.95 (2 H, m, m-Hbenzyl), 7.00 (1 H, m, p-Hbenzyl), 7.05 (1 H, m, p-HvinylPh), 7.17 (2 H, m, m-HvinylPh), 7.38 (2 H, m, o-Hbenzyl), 7.64 (2 H, pseudod, 3JHH = 7.3 Hz, o-HvinylPh), 7.87 (1 H, d, 3JHP = 37.0 Hz, PCCH). 13 C{1H} NMR (C6D6, 101 MHz, 298 K): δ 17.2 (s br, Al(CMe3)2), 20.7 (s, p-CH3), 25.5 (d, 3JCP = 2.5 Hz, o-CH3), 33.1 (s, Al(CMe3)2), 90.0 (d, 1JCP = 38.2 Hz, PCOAl), 125.2 (d, 1JCP = 47.8 Hz, ipso-CMes), 127.8 (d, 4JCP = 10.1 Hz, m-Cbenzyl), 128.0 (s, p-Cbenzyl), 128.4 (s, oCbenzyl), 128.5 (d, 4JCP = 1 Hz, o-CvinylPh), 129.1 (s, m-CvinylPh), 129.7 (s, p-CvinylPh), 131.6 (d, 3JCP = 9.7 Hz, m-CMes), 141.1 (s, ipso-Cbenzyl), 141.3 (d, 3JCP = 32.1 Hz, ipso-CvinylPh), 141.8 (d, 4JCP = 2.9 Hz, p-CMes), 142.7 (d, 2JCP = 7.9 Hz, o-CMes), 145.8 (s br, PCCH), 158.2 (d, 2JCP = 4.6 Hz, PCCH). 13C{1H} NMR (C6D6, 101 MHz, 220 K): δ 16.9 and 17.9 (each s br Al(CMe3)2), 32.8 and 33.4 (each s, Al(CMe3)2), mesityl I: 20.7 (s, p-CH3), 25.8 (d, 3JCP = 2.8 Hz, o-CH3), 124.2 (d, 1 JCP = 47.7 Hz, ipso-CMes), 131.8 (d, 3JCP = 9.4 Hz, m-CMes), 141.5 (d, 4 JCP = 2.9 Hz, p-CMes), 142.1 (d, 2JCP = 7.6 Hz, o-CMes), mesityl II: 20.7 (s, p-CH3), 25.5 (d, 3JCP = 2.1 Hz, o-CH3), 124.7 (d, 1JCP = 44.0 Hz, ipso-CMes), 131.0 (d, 3JCP = 10.3 Hz, m-CMes), 141.7 (d, 4JCP = 2.9 Hz, p-CMes), 142.2 (d, 2JCP = 8.0 Hz, o-CMes), 89.5 (d, 1JCP = 38.3 Hz, PCOAl), 127.7 (br m-Cbenzyl), 128.2 (s, p-Cbenzyl), 128.3 (s, o-Cbenzyl), 128.3 (br, o-CvinylPh), 129.1 (s, m-CvinylPh), 129.7 (s, p-CvinylPh), 140.6 (s, ipso-Cbenzyl), 141.1 (d, 3JCP = 31.7 Hz, ipso-CvinylPh), 144.6 (d, 3JCP = 12.8 Hz, PCCH), 157.9 (d, 2JCP = 3.1 Hz, PCCH). IR (paraffin, CsI, cm−1): 1603 s, 1557 m, 1532 s ν(CC), ν(CO), phenyl; 1487 s, 1352 m (paraffin); 1310 w, 1290 m, 1242 m δ(CH3); 1175 w, 1155 m, 1113 m, 1070 m, 1036 w, 1028 m, 1001 m, 926 vs, 889 m, 860 vs, 849 vs, 808 vs ν(CC), ν(CO); 783 vs, 772 vs, 748 vs ν(CC); 721 vs (parraffin); 708 vs, 689 vs, 654 s, 600 s, 584 s, 569 s, 525 m, 490 vs, 446 s, 434 vs, 407 s, 397 m, 372 m, 341 w δ(CC), ν(AlC), ν(AlO), ν(PC). MS (EI, 20 eV, 353 K): m/z (%) 512 (19) [M+ − PhC(H)O], 455 (80) [M+ − PhC(H)O − CMe3], 399 (34) [M+ − CMe3 − butene − PhC(H)O], 372 (48) [M+ − PhC(H)O − Al(CMe3)2 + H], 106 (15) [PhC(H)O]. [α]D20 (589 nm, CH2Cl2): −0.57°. Reaction of 1 with Benzoyl Chloride: Synthesis of Compounds 3−5. A solution of the FLP 1 (0.455 g, 0.89 mmol) in 10 mL of toluene was treated with benzoyl chloride (0.10 mL, 0.125 g, 0.89 mmol) at room temperature. The color changed from yellow to dark red. The mixture was stirred for 12 h. All volatiles were removed in vacuo. The residue was extracted with cyclopentane. The resulting suspension was filtered (the solid shows a complicated NMR spectrum with resonances of unknown components), and the filtrate was cooled to −20 °C. Compounds 3 and 4 were obtained in different fractions and purified by repeated recrystallization. 5 was isolated in small quantities as the third fraction. Characterization of 3. Yield: 0.121 g (20%). Mp (argon, sealed capillary): >118 °C dec. Anal. Calcd for C45H60OAlP (674.9): C, 80.1; H, 9.0. Found: C, 79.5; H, 8.9. 31P{1H} NMR (C6D6, 162 MHz, 298 K): δ 10.3 (s). 1H NMR (C6D6, 200 MHz, 298 K): δ 0.81 (9 H, s, CMe3, hexadiene), 1.21 (18 H, s, Al(CMe3)2), mesityl I: 1.93 (3 H, s, p-CH3), 1.94 (6 H, s br, o-CH3), mesityl II: 1.95 (3 H, s, p-CH3), 2.75 (6 H, m, o-CH3), 2.70 (1 H, s br, CH-CMe3), 5.44 (1 H, dd, 3JHH = 10.5 Hz, 3JHH = 3.5 Hz, CHCHCHCMe3) and 6.37 (1 H, d, 3JHH = 10.5 Hz, CHCHCHCMe3), 5.84 (1 H, s br, CHCHCHCMe3) and 7.63 (1 H, s br, CHCHCHCMe3), 6.65 (4 H, s br, m-HMes), 7.08 (1 H, pseudo-t, 3JHH = 7.2 Hz, p-HPh), 7.22 (2 H, pseudo-t, 3JHH = 7.5 Hz, m-HPh), 7.55 (2 H, pseudo-d, 3JHH = 7.7 Hz, o-HPh), 7.59 (1 H, d, 3JHP = 38.9 Hz, P−CC-H). 13C{1H} NMR (C6D6, 101 MHz, 298 K; the resonances of the mesityl groups overlap): δ 17.0 (s br, Al(CMe3)2), 20.8 (s, p-CH3), 24.6 (s br, o-CH3), 27.4 (s, CHCMe3), 32.2 (s, Al(CMe3)2), 35.7 (s, CHCMe3), 49.9 (s, CHCHCH), 118.9 and 120.3 (s br, ipso-C Mes), 122.9 (s br, CHCHCHCMe3) and 127.7 (s, CHCHCHCMe3), 125.2 (s br, O(P)CC), 125.7 (d, 3JCP = 10.4 Hz, CHCHCHCMe3) and 128.5 (s, CHCHCHCMe3), 128.2 (s, o-CPh), 129.2 (s, m-CPh), 129.5 (s, p-CPh), 132.7 (s br, mCMes), 138.1 (s br, PCCH), 140.4 (d, 3JCP = 34.2 Hz, ipso-CPh), 143.0 (s br, P-C-O), 143.1 (s, p-CMes), 144.5 (s br, o-CMes), 156.2 (d, 2 JCP = 3.3 Hz, PCCH). IR (paraffin, CsI, cm−1): 1954 vw, 1883 vw, E

dx.doi.org/10.1021/om400620h | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

− butene − butyl], 119 (11) [Mesityl+], 105 (17) [C6H5(CO)+], 57 (9) [CMe3+]. NMR Data of 5. 31P{1H} NMR (CDCl3, 162 MHz, 298 K): δ −7.8 (s). 1H NMR (CDCl3, 200 MHz, 298 K): δ 2.36 (6 H, s, p-CH3), 2.39 (12 H, s, o-CH3), 7.03 (4 H, d, 4JPH = 4.5 Hz, m-HMes), 7.40 (3 H, m, m- and p-HPh), 7.73 (2 H, m, o-HPh), 8.44 (1 H, d, 1JPH = 492.2 Hz, PH). Reaction of 1 with Benzamide: Synthesis of Compounds 6 and 7. Neat benzamide (0.222 g, 1.83 mmol) was thoroughly dried in vacuo and subsequently treated with a solution of the FLP 1 (0.940 g, 1.83 mmol) in 20 mL of toluene at room temperature. The mixture was stirred for 12 h. All volatiles were removed under vacuum, and the residue was treated with n-hexane. The solution was separated from the remaining solid material by decantation. The white solid residue was extracted three times with n-hexane. The solvent was removed in vacuo, and compound 7 remained as a yellow oil, which could not be recrystallized. NMR spectroscopic characterization showed it to be analytically pure. The white solid, which was insoluble in n-hexane, was dissolved in 1,2-difluorobenzene at +50 °C. Slow cooling to room temperature gave colorless crystals of the amidate 6. Characterization of 6. Yield: 0.193 g (28%). Mp (argon, sealed capillary): 80 °C. Anal. Calcd for C26H29P (372.5): C, 83.8; H, 7.9. Found: C, 83.3; H, 7.9. 31P{1H} NMR (C6D6, 162 MHz, 298 K): δ −23.5 (s). 1H NMR (C6D6, 200 MHz, 298 K): δ 2.10 (6 H, s, p-CH3), 2.42 (12 H, s, o-CH3), 6.64 (1 H, dd, 2JHP = 10.3 Hz, 3JHH = 16.8 Hz, PC(H)CH)), 6.73 (2 H, d, 4JHP = 1.9 Hz. m-HMes), 6.98 (1 H, pseudo-t, 3JHH = 7.0 Hz, p-HPh), 7.04 (2 H, pseudo-t, 3JHH = 7.3 Hz, mHPh), 7.13 (2 H, pseudo-d, 3JHH = 7.4 Hz, o-HPh), 7.34 (1 H, dd, 3JHP = 23.5 Hz, 3JHH = 16.8 Hz, PC(H)CH). 13C NMR (C6D6, 101 MHz, 298 K): δ 21.0 (s, p-CH3), 23.3 (d, 3JCP = 14.5 Hz, o-CH3), 126.8 (s, oCPh), 127.6 (s, p-CPh), 127.8 (s, PCCH), 128.9 (s, m-CPh), 130.4 (d, 3 JCP = 3.4 Hz, m-CMes), 131.7 (d, 1JCP = 17.5 Hz, ipso-CMes), 135.7 (d, 1 JCP = 21.4 Hz, PCCH), 138.2 (s, p-CMes), 138.2 (d, 3JCP = 8.5 Hz, ipso-CPh), 142.6 (d, 2JCP = 14.8 Hz, o-CMes). IR (paraffin, CsI, cm−1): 1937 vw, 1883 vw, 1869 vw, 1796 vw, 1603 m, 1568 w, 1558 w ν(C C), phenyl; 1452 vs, 1375 vs (paraffin); 1290 vw δ(CH3); 1240 vw, 1169 vw, 1155 w, 1072 vw, 1028 w, 1016 vw, 970 w, 928 vw, 887 vw, 849 m, 816 vw, 785 vw, 739 m ν(CC); 721 s (paraffin); 689 w δ(phenyl); 623 w, 604 vw, 555 m, 494 vw, 440 w, 411 w ν(PC). MS (EI, 20 eV, 323 K): m/z (%) 372 (40), 373 (11) [M+], 357 (15), 358 (4) [M+ − CH3], 281 (100), 282 (20) [M+ − C6H5CH2], 253 (9), 254 (5) [M+ − mesityl], 119 (5) [mesityl+]. Characterization of 7. Yield: 0.210 g (44%). Mp (argon, sealed capillary): 220 °C. Anal. Calcd for C30H48N2O2Al2 (522.7): C, 68.9; H, 9.3; N, 5.4. Found: C, 69.2; H, 9.2; N, 5.2. 1H NMR (d8-THF, 200 MHz, 298 K): δ 0.89 (36 H, s, Al(CMe3)2), 7.52 (4 H, m, m-HPh), 7.60 (2 H, m, p-HPh), 7.68 (2 H, s, AlN(H)CO), 7.93 (4 H, m, o-HPh). 13 C NMR (d8-THF, 101 MHz, 298 K): δ 15.9 (s br, Al(CMe3)2), 31.0 (s, Al(CMe3)2), 128.9 (s, o-CPh), 129.5 (s, m-CPh), 133.4 (s, p-CPh), 135.6 (s, ipso-CPh), 178.1 (s, N(H)-CO). IR (paraffin, CsI, cm−1): 3375 vs δ(NH); 2951 vs−2853 vs (paraffin); 1981 vw, 1958 vw, 1913 vw, 1892 vw, 1802 vw, 1605 vs, 1571 vs, 1516 s ν(CC), ν(CO), phenyl; 1504 s, 1356 m (paraffin); 1337 m, 1302 m, 1250 vs δ(CH3); 1188 m, 1173 vw, 1152 s, 1096 w, 1067 w, 1028 s, 1001 vs, 970 w, 937 s, 849 m, 814 vs ν(CC), ν(CN); 735 vs (parraffin); 708 vs, 677 vs, 615 vs, 596 vs, 567 vs, 532 vs, 442 m, 413 vs, 397 vs, 370 s, 351 vs δ(CC), ν(AlC), ν(AlO), ν(AlN), phenyl. MS (EI, 20 eV, 373 K): m/z (%) 465 (24) [M+ − CMe3], 372 (71) [M+ − CMe3 − Ph − Me − H], 357 (13) [M+ − CMe3 − Ph − 2 Me − H], 281 (100) [M+ − CMe3 − 2 Ph − 2 Me]. Crystal Structure Determinations. Single crystals were obtained by recrystallization from cyclopentane (2, 5 °C; 3, −20 °C) or from 1,2-difluorobenzene (7, room temperature). The crystallographic data were collected with a Bruker APEX diffractometer. The structures were solved by direct methods and refined with the program SHELXL9719 by a full-matrix least-squares method based on F2. Hydrogen atoms were positioned geometrically and allowed to ride on their respective parent atoms. Compound 3 crystallizes with a cyclopentane molecule per formula unit. The solvent molecule was disordered and refined on split positions (0.58:0.42). A tert-butyl group of 7 (C4) was

disordered (split positions 0.52:0.48). Further details of the crystal structure determinations are available from the Cambridge Crystallographic Data Center on quoting the depository numbers CCDC947420 (2), -947422 (3), and -947421 (7).

■

ASSOCIATED CONTENT

S Supporting Information *

CIF files giving crystal data for compounds 2, 3, and 7. This material is available free of charge via the Internet at http:// pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*W.U.: fax, +49-251-8336660; e-mail, [email protected]. Notes

The authors declare no competing financial interest. Biographies

Werner Uhl was born in Lich, Germany, in 1953. He completed his Diploma degree at the University of Karlsruhe in 1977. He started his Ph.D. research on the synthesis of compounds with P−C multiple bonds in the group of Prof. Becker at the University of Karlsruhe, moved with this group to the University of Marburg, and finished the Ph.D. in Karlsruhe in 1980. Afterward he worked in industry for two years (NUKEM GmbH, Hanau, Germany). His own research activities started at the University of Stuttgart (Stuttgart, Germany) and were finished with the Habilitation in 1989. In 1992 he accepted a position as a full professor of Inorganic Chemistry at the University of Oldenburg, moved to the University of Marburg in 1999, and has been a full professor at the University of Münster since 2004. He is a recipient of the Alfred-Stock-Memorial-Award of the German Chemical Society (2012). His research interests are directed toward organometallic chemistry of the heavier group 13 elements. He reported on the synthesis of compounds with the elements in unusually low oxidation states having E−E single bonds or element clusters and on their unprecedented chemical reactivity. The unique structural chemistry of element hydrazides was investigated, and a systematic study into the generation of alkylelement peroxides provided an interesting insight into the chemistry of these highly reactive compounds. Investigations into hydroalumination and hydrogallation (after the development of facile procedures for the synthesis of dialkylgallium hydrides) gave a consistent understanding of the mechanisms and resulted in the isolation of carbaalane clusters, carbocations, or frustrated Lewis pairs based on aluminium and phosphorus. F

dx.doi.org/10.1021/om400620h | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

Lammertsma, K.; Uhl, W. Dalton Trans. 2012, 41, 9033−9045. (c) Boudreau, J.; Courtemanche, M. A.; Fontaine, F. G. Chem. Commun. 2011, 11131−11133. (6) Ménard, G.; Stephan, D. W. Angew. Chem. 2012, 124, 4485− 4488; Angew. Chem., Int. Ed. 2012, 51, 4409−4412. (7) (a) Zhang, Y.; Miyake, G. M.; Chen, E. Y. X. Angew. Chem. 2010, 122, 10356−10360; Angew. Chem., Int. Ed. 2010, 49, 10158−10162. (8) Appelt, C.; Slootweg, J. C.; Lammertsma, K.; Uhl, W. Angew. Chem. 2012, 124, 6013−6016; Angew. Chem., Int. Ed. 2012, 51, 5911− 5914. (9) Appelt, C.; Slootweg, J. C.; Lammertsma, K.; Uhl, W. Angew. Chem. 2013, 125, 4350−4353; Angew. Chem., Int. Ed. 2013, 52, 4256− 4259. (10) (a) Uhl, W.; Rösener, C.; Layh, M.; Hepp, A. Z. Anorg. Allg. Chem. 2012, 638, 1746−1754. (b) Uhl, W.; Heller, D.; Kösters, J.; Würthwein, E.-U.; Ghavtadze, N. Eur. J. Inorg. Chem. 2012, 1359− 1368. (c) Uhl, W.; Heller, D.; Rohling, M.; Kösters, J. Inorg. Chim. Acta 2011, 374, 359−365. (11) March, J. Advanced Organic Chemistry; Wiley: New York, 1985; p 19. (12) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1−S19. (13) (a) Mömming, C. M.; Kehr, G.; Wibbeling, B.; Fröhlich, R.; Erker, G. Dalton Trans. 2010, 39, 7556−7564. (b) Rosorius, C.; Kehr, G.; Fröhlich, R.; Grimme, S.; Erker, G. Organometallics 2011, 30, 4211−4219. (c) Stute, A.; Kehr, G.; Daniluc, C.; Fröhlich, R.; Erker, G. Dalton Trans. 2013, 42, 4487−4499. (14) (a) Frey, J.; Rappoport, Z. J. Am. Chem. Soc. 1996, 118, 5169− 5181. (b) McAllister, M. A.; Tidwell, T. T. J. Am. Chem. Soc. 1992, 114, 5362−5368. (15) (a) Grotjahn, D. B.; Collins, L. S. B.; Wolpert, M.; Bikzhanova, G. A.; Lo, H. C.; Caombs, D.; Hubbard, J. L. J. Am. Chem. Soc. 2001, 123, 8260−8270. (b) Bristow, G. S.; Hitchcock, P. B.; Lappert, M. F. Chem. Commun. 1982, 462−464. (16) Hevia, E.; Honeyman, G. W.; Kennedy, A. R.; Mulvey, R. E. J. Am. Chem. Soc. 2005, 127, 131906−13107. (17) Taillefer, M.; Cristau, H. J.; Fruchier, A.; Vicente, V. J. Organomet. Chem. 2001, 624, 307−315. (18) (a) Kai, Y.; Yasuoka, N.; Kasai, N. J. Organomet. Chem. 1971, 32, 165−179. (b) Huang, B.-H.; Yu, T.-L.; Huang, Y.-L.; Ko, B.-T.; Lin, C.-C. Inorg. Chem. 2002, 41, 2987−2994. (c) Fawcett, J.; Solan, G. A. Acta Crystallogr. 2005, 61, 1210−1211. (d) Huang, Y.-L.; Huang, B.H.; Ko, B.-T.; Lin, C.-C. Dalton Trans. 2001, 1359−1365. (19) (a) SHELXTL-Plus, REL. 4.1; Siemens Analytical X-ray Instruments, Madison, WI, 1990. (b) Sheldrick, G. M. SHELXL-97, Program for the Refinement of Structures; Universität Göttingen, Göttingen, Germany, 1997.

Christian Appelt was born in Wolfenbüttel, Germany. He studied chemistry at the University of Münster and completed his Diploma degree in 2010. After a short time of only two years he finished his Ph.D. thesis in 2012 with the best possible result. His research in the Uhl group was directed toward the chemical properties of an Al−Pbased frustrated Lewis pair. He observed adduct formation with carbon dioxide and alkali-metal hydrides, an unprecedented phase transfer catalytic process for a hydride transfer reaction, and a very effective catalytic dehydrogenation reaction with dimethylamine− borane. Another aspect of his research is described in this article. He now has a position in the chemical industry.

■

ACKNOWLEDGMENTS We are grateful to the Deutsche Forschungsgemeinschaft for generous financial support.

■

REFERENCES

(1) (a) Stephan, D. W.; Erker, G. Angew. Chem. 2010, 122, 50−81; Angew. Chem., Int. Ed. 2010, 49, 46−76. (b) Sajid, M.; Stute, A.; Cardenas, A. J. P.; Culotta, B. J.; Hepperle, J. A. M.; Warren, T. H.; Schirmer, B.; Grimme, S.; Studer, A.; Daniliuc, C. G.; Fröhlich, R.; Petersen, J. L.; Kehr, G.; Erker, G. J. Am. Chem. Soc. 2012, 134, 10156−10168. (c) Otten, E.; Neu, R. C.; Stephan, D, W. J. Am. Chem. Soc. 2009, 131, 9918−9919. (d) Neu, R. C.; Otten, E.; Stephan, D. W. Angew. Chem. 2009, 121, 9889−9892; Angew. Chem., Int. Ed. 2009, 48, 9709−9712. (2) (a) Holschumacher, D.; Bannenberg, T.; Hrib, C. G.; Jones, P. G.; Tamm, M. Angew. Chem. 2008, 120, 7538−7542; Angew. Chem., Int. Ed. 2008, 47, 7428−7432. (b) Sumerin, V.; Schulz, F.; Nieger, M.; Leskelä, M.; Repo, T.; Rieger, B. Angew. Chem. 2008, 120, 6090−6092; Angew. Chem., Int. Ed. 2008, 47, 6001−6003. (c) Sumerin, V.; Schulz, F.; Atsumi, M.; Wang, C.; Nieger, M.; Leskelä, M.; Repo, T.; Pyykkö, Rieger, P. B. J. Am. Chem. Soc. 2008, 130, 14117−14119. (d) Geier, S. J.; Stephan, D. W. J. Am. Chem. Soc. 2009, 131, 3476−3477. (e) Geier, S. J.; Gille, A. L.; Gilbert, T. M.; Stephan, D. W. Inorg. Chem. 2009, 48, 10466−10474. (f) Chase, P. A.; Welch, G. C.; Jurca, T.; Stephan, D. W. Angew. Chem. 2007, 119, 9283−9296; Angew. Chem., Int. Ed. 2007, 46, 8050−8053. (g) Chase, P. A.; Stephan, D. W. Angew. Chem. 2008, 120, 7543−7547; Angew. Chem., Int. Ed. 2008, 47, 7433−7437. (h) Alcarazo, M.; Gomez, C.; Holle, S.; Goddard, R. Angew. Chem. 2010, 122, 5924−5927; Angew. Chem., Int. Ed. 2010, 49, 5788−5791. (3) Appelt, C.; Westenberg, H.; Bertini, F.; Ehlers, A. W.; Slootweg, J. C.; Lammertsma, K.; Uhl, W. Angew. Chem. 2011, 123, 4011−4014; Angew. Chem., Int. Ed. 2011, 50, 3925−3928. (4) (a) Dureen, M. A.; Stephan, D. W. J. Am. Chem. Soc. 2009, 131, 8396−8397. (b) Dureen, M. A.; Brown, C. C.; Stephan, D. W. Organometallics 2010, 29, 6594−6607. (5) (a) Menard, G.; Stephan, D. W. J. Am. Chem. Soc. 2010, 132, 1796−1797. (b) Menard, G.; Stephan, D. W. Angew. Chem. 2011, 123, 8546−8549; Angew. Chem., Int. Ed. 2010, 50, 8396−8399. See also: Roters, S.; Appelt, C.; Westenberg, H.; Hepp, A.; Slootweg, J. C.; G

dx.doi.org/10.1021/om400620h | Organometallics XXXX, XXX, XXX−XXX