Article pubs.acs.org/Organometallics
Fine Tuning of the Substituents on the N‑Geminal Phosphorus/ Silicon-Based Lewis Pairs for the Synthesis of Z‑Type Silyliminophosphoranylalkenes Jiancheng Li,† Yan Li,† Indu Purushothaman,‡ Susmita De,‡ Bin Li,† Hongping Zhu,*,† Pattiyil Parameswaran,*,‡ Qingsong Ye,§ and Weiping Liu§ †
State Key Laboratory of Physical Chemistry of Solid Surfaces, National Engineering Laboratory for Green Chemical Productions of Alcohols-Ethers-Esters, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People’s Republic of China ‡ Department of Chemistry, National Institute of Technology Calicut, NIT Campus PO, Kozhikode, Kerala 673601, India § State Key Laboratory for Platinum Group Metals, Kunming Institute of Precious Metals, Kunming, Yunnan 650106, People’s Republic of China S Supporting Information *
ABSTRACT: Reactions of the N-aryl(diphenylphosphanyl)aminosilane Ph2PN(Ar)SiCl3−nMen (Ar = 2,4,6-Me3C6H2, n = 0 (1a), 1 (2a), 2 (3a), 3 (4a); Ar = 2,6-iPr2C6H3, n = 0 (1b), 1 (2b), 2 (3b), 3 (4b)) with methyl propiolate and dimethyl acetylenedicarboxylate (DMAD) give two types of products, the zwitterionic heterocycles [Ph2PN(2,4,6-Me3C6H2)SiCl3](HCCCO 2 Me) (5c) and [Ph 2 PN(Ar)SiCl 3−n Me n ](MeO 2 CC CCO2Me) (Ar = 2,4,6-Me3C6H2, n = 0 (5a), 1 (6a), 2 (7a); Ar = 2,6iPr2C6H3, n = 0 (5b), 1 (6b), 2 (7b)) and (Z)-silyliminophosphoranylalkene ArNP(Ph2)C(CO2Me)C(CO2Me)SiMe3 (Ar = 2,4,6-Me3C6H2 (8a), 2,6-iPr2C6H3 (8b)). The reaction of Ph2PN(SiMe3)2 with DMAD gives only the acyclic alkene Me3SiNP(Ph2)(MeO2C)C C(CO2Me)SiMe3 (9), which is similar to 8a,b. In these reactions, compounds 1a−4a and 1b−4b behave as N-geminal P/Sibased Lewis pairs, which undergo a dipolar cycloaddition reaction with the alkyne. The theoretical calculations indicate that the reactions proceed through a concerted cycloaddition reaction mechanism. The stability of these heterocycles decreases as the number of the Me substituent on the pentacoordinated Si atom increases. When the Si center is substituted with three Me groups (4a,b), the heterocyclic intermediates undergo ring opening by Si−N bond cleavage and concomitant NP bond formation resulting in 8a,b. The formation of the acyclic (Z)-alkene (8a,b and 9) can be considered as a stepwise SN2 reaction at the silicon center.
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generated Cp2Zr(η2-C6H4) to silylphosphanylacetylenes (Chart 1 (III)).10 The synthesis of (Z)-silyl(phosphanyl)alkenes (Chart 1 (IV)) by the addition reaction of silylphosphine to the alkynes has also been reported.11 All of these reactions proceed through complex reaction pathways and usually yield a mixture of stereoisomers. Moreover, the detailed mechanisms of these reactions have not been well studied.12 The aforementioned reports also indicate that the precursors and their substituents play a significant role in controlling the reactions and stereochemistry of the products. Herein, we report the effective use of Naryl(diphenylphosphanyl)aminosilanes Ph2PN(Ar)SiCl3−nMen (Ar = 2,4,6-Me3C6H2, n = 0 (1a), 1 (2a), 2 (3a), 3 (4a); Ar = 2,6-iPr2C6H3, n = 0 (1b), 1 (2b), 2 (3b), 3 (4b)) as precursors for the reactions with methyl propiolate and dimethyl acetylenedicarboxylate (DMAD). In these reactions, two types of products, viz., the zwitterionic heterocycles
INTRODUCTION Vinylsilanes and vinylphosphines are important alkene derivatives, which have been widely utilized as synthetic intermediates, monomers, coupling agents, and/or ligands.1,2 These compounds can be conveniently prepared by hydrosilylation or hydrophosphination of the alkynes catalyzed by the transition metals.3 The addition of a Si−Si4 or P−P bond5 across a CC bond presents an effective route for the synthesis of the 1,2-disilylated or 1,2-diphosphinated alkenes among other reported pathways.6 In contrast, the synthesis of silyl- and phosphanyl-cosubstituted alkenes is limited, which is probably due to the lack of suitable materials and/or effective synthesis procedures. In 1998, Kazankova and co-workers reported the palladiumcatalyzed cross-coupling reaction of silylated vinyl halides with diphenylphosphine for the synthesis of silyl(phosphanyl)alkenes.7 The addition reactions have been proven to be an alternative route to such alkenes,: for example, additions of a phosphine to silylalkynes (Chart 1 (I)),8 silylcuprates to alkynylphosphine oxides (Chart 1 (II)),9 and the in situ © XXXX American Chemical Society
Received: December 16, 2014
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DOI: 10.1021/om501288t Organometallics XXXX, XXX, XXX−XXX
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Organometallics
HCl acceptor. However, only the reaction with methyl propiolate succeeded, yielding a heterocyclic compound.15 Hence, we carried out the reaction of 1a with stoichiometric methyl propiolate in toluene at room temperature for 12 h; the heterocyclic compound 5c was formed in a good yield (84%) (Scheme 1I). In order to understand the nature of the reaction, we have further carried out the reaction of 1a,b with DMAD under conditions similar to those used for synthesizing 5c. The heterocyclic compounds 5a (83%) and 5b (89%), similar to 5c, were obtained as well (Scheme 1II). These reactions can be considered as a dipolar cycloaddition, which are comparable to the addition of the frustrated Lewis pairs (FLPs) P/B,16 S/B,17 N/B,18 and P/Al19 to the CC bond of alkynes. These neutral compounds 1a,b indeed behave as an N-geminal P/Si Lewis pair. However, they are different from the silylium ion/ phosphane FLPs which have been recently reported by Müller and co-workers.20 Compounds 5a−c were characterized by NMR (1H, 13C, 29 Si, and 31P), IR, and ESI-MS spectroscopy as well as by C,H,N elemental analysis. Compounds 5a,b were further confirmed by single-crystal X-ray crystallography. The 1H and 13 C NMR spectra show two sets of proton and carbon resonances for the MeO2CCCCO2Me moiety in both 5a and 5b. However, a clear assignment of these resonances to the P and Si atom bonded fragments is not easy. Therefore, we further performed 2D heteronuclear correlation experiments (1H,13C-HMBC). The C(P)CO2Me protons resonate at δ 3.52 ppm for 5a and 3.45 ppm for 5b, while the C(Si)CO2Me protons resonate at δ 3.97 ppm for 5a and 3.95 ppm for 5b. A similar assignment has been reported for MeO2C(Ph2P)CC(SiMe2tBu)CO2Me (δC(P)CO2Me 3.15 and δC(Si)CO2Me 3.70 ppm).11 The 1H,13C−COSY spectra show two very close 13C resonances at δ 52.7 and 52.9 ppm, which correspond to the respective C(P)CO2Me and C(Si)CO2Me in 5a, whereas the highly overlapped resonances at δ 52.8 ppm are observed for these two groups in 5b. On considering the HMBC correlation by the 3JCH and 4JCH couplings, we could identify the C(Si)CO2Me (at δ 189.5 and 168.6 ppm for 5a as well as 188.5 and 168.8 ppm for 5b) and C(P)CO2Me (at δ 113.4 and 160.9 ppm for 5a and 114.3 and 161.2 ppm for 5b) resonances (see Table S5 in the Supporting Information). The proton and carbon resonances for the HCCCO2Me moiety in 5c could be clearly assigned (for proton, δC(P)H 6.60 and δC(Si)CO2Me 3.70 ppm; for carbon, δC(Si)CO2Me 179.2, 168.3, and 52.4, δC(P)H 113.0 ppm; Table S5), where the data for the C(Si)CO2Me group are comparable to those in the respective 5a,b. The 31P and 29Si NMR spectra of 5a−c show similar phosphorus and silicon resonance data. However, all of these data are significantly different from those of the starting materials 1a,b (see Tables S4-1 and S4-2 in the Supporting Information). Note that the 31 P resonances of 5a−c are close to those of the PBC3 (δP 25.2 ppm)16a and PAlC3 ring (δP 24.2 ppm) compounds.19a X-ray crystallographic data clearly reveal that compounds 5a (Figure S1 in the Supporting Information) and 5b (Figure 1) are five-membered-ring compounds. The central C2PNSi ring is almost planar (deviation from the least-squares plane ΔP(1)N(1)Si(1)C(1)C(2) = 0.0466 for 5a and 0.0504 Å for 5b). The C−C bond in the ring shows typical double-bond character (1.339(4) Å in 5a and 1.339(6) Å in 5b). It is
Chart 1. Addition Reactions for the Synthesis of Silyl and Phosphanyl Cosubstituted Alkenes
[Ph2PN(2,4,6-Me3C6H2)SiCl3](HCCCO2Me) (5c) and [Ph2PN(Ar)SiCl3−nMen](MeO2CCCCO2Me) (Ar = 2,4,6Me3C6H2, n = 0 (5a), 1 (6a), 2 (7a); Ar = 2,6-iPr2C6H3, n = 0 (5b), 1 (6b), 2 (7b)) as well as (Z)-silyliminophosphoranylalkenes ArNP(Ph2)C(CO2Me)C(CO2Me)SiMe3 (Ar = 2,4,6-Me3C6H2 (8a), 2,6-iPr2C6H3 (8b)) were obtained (Scheme 1). Thus, compounds 1a−3a and 1b−3b can be Scheme 1. Reactions of 1a with Methyl Propiolate as well as of 1a−4a and 1b−4b with DMAD to Give Zwitterionic Heterocycles and (Z)-Silyliminophosphoranylalkenes
considered as N-geminal P/Si Lewis pairs, which undergo a dipolar cycloaddition toward the alkyne, in a manner similar to that of the frustrated Lewis pairs (FLPs).13 On the other hand, compounds 4a,b can also be considered as the P/Si Lewis pairs, which react with DMAD to form silyl and iminophosphoranyl cosubstituted alkenes through heterocyclic intermediates. Theoretical calculations were also performed to understand the reaction mechanisms in detail.
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RESULTS AND DISCUSSION We have recently shown that the reaction of Ph2PN(Ar)SiCl3 with in situ generated LiCCR resulted in the compounds Ph2PCCR and [ArNSi(CCR)]2,3 (Ar = aryl and R = alkyl, aryl) by P−N bond cleavage, rather than the anticipated product Ph2PN(Ar)Si(CCR)3 formed via a routine LiCl elimination.14 In order to synthesize the latter species, we attempted the reaction of Ph2PN(2,4,6-Me3C6H2)SiCl3 (1a) with several terminal alkynes in the presence of NEt3 as the B
DOI: 10.1021/om501288t Organometallics XXXX, XXX, XXX−XXX
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Organometallics
heterocycles [Ph2PN(Ar)SiCl3−nMen](MeO2CCCCO2Me) (Ar = 2,4,6-Me3C6H2, n = 1 (6a, 84%), 2 (7a, 92%); Ar = 2,6-iPr2C6H3, n = 1 (6b, 89%), 2 (7b, 83%)) in good yields, which are similar to 5a−c. This implies that the SiCl2Me group in 2a,b and SiClMe2 group in 3a,b exhibit Lewis acidic character similar to that of the SiCl3 group. Interestingly, the acyclic alkene compounds (Z)-ArNP(Ph2)C(CO2Me) C(CO2Me)SiMe3 (Ar = 2,4,6-Me3C6H2 (8a, 85%), 2,6iPr2C6H3 (8b, 85%)) were resulted from the reactions of 4a,b with DMAD (Scheme 1II), in which the SiMe3 and P(Ph2)NAr groups were formed in a cis fashion across the CC bond. This suggests that the formation of 8a,b might have proceeded through an initial dipolar cycloaddition reaction followed by ring opening through Si−N bond cleavage and concomitant NP bond formation (Scheme 2). We tried
Figure 1. X-ray crystal structures of 5b (left) and 8b (right) with thermal ellipsoids at the 50% probability level.
noteworthy that the P−N bond (1.668(2) Å in 5a and 1.658(3) Å in 5b) becomes slightly shorter while the Si−N bond (1.797(2) Å in 5a and 1.783(2) Å in 5b) is longer in comparison to those in the precursor 1b (P−N, 1.759(2) Å; Si−N, 1.700(2) Å).14 The P−CCC bond length is 1.783(3) Å and is comparable to those of the P−CPh bond length (1.792(3)−1.799(3) Å). However, the Si−CCC bond (1.970(3) Å) is slightly longer than that of the Si−CMe bond in 6a (1.905(2) Å; vide infra). The P atom in these products is tetracoordinated with a tetrahedral geometry. The Si center is pentacoordinated, adopting a trigonal-bipyramidal geometry, where N(1)Cl(2)Cl(3) forms the trigonal equatorial plane (ΔN(1)Si(1)Cl(2)Cl(3) = 0.0079 Å) and the C(2) and Cl(1) atoms are at the axial positions (Figure S1). Similar structural features are observed in 5b (C(1)−C(2), 1.339(6) Å; P(1)−N(1), 1.658(3) Å; Si(1)−N(1), 1.783(2) Å; P(1)−C(1), 1.789(2) Å; Si(1)−C(2), 1.969(4) Å; ΔN(1)Si(1)Cl(1)Cl(3) = 0.0178 Å) as well. Hence, compounds 5a,b can be considered as zwitterionic heterocycles having a formal positive charge on the P atom and a formal negative charge on the Si center. This structural pattern is similar to those for the PBC 3 and PAlC 3 heterocycles.16a,19a Note that the phosphonium-containing cyclic compounds are well-known;16,19 however, the cyclic silanion-type species are rare and are usually considered as intermediates.21 Note that the strong Lewis acidic silylium ion and the Lewis base phosphane in the silylium ion/phosphane FLPs have been used for the activation of H2 and CO2.20 The formation of 5a− c indicates the Lewis acidic reactivity of the SiCl3 group toward the activated alkynes.15 The enhanced Lewis acidity of the silicon polyhalides has been well documented.22 Thus, we were intrigued whether such a dipolar cycloaddition could be tuned by altering the SiCl3 group to SiCl2Me, SiClMe2, and even the SiMe3 group. Therefore, we synthesized the compounds Ph2PN(Ar)SiCl3−nMen (Ar = 2,4,6-Me3C6H2, n = 1 (2a), 2 (3a), 3 (4a); Ar = 2,6-iPr2C6H3, n = 1 (2b), 2 (3b), 3 (4b)) by using a method similar to that used for the synthesis of 1a,b (Scheme S1 in the Supporting Information). Compounds 2a−4a and 2b−4b were characterized by multinuclear NMR (1H, 13C, 29Si, and 31P) and C,H,N elemental analysis. The 31P NMR spectra of these compounds show resonances (see Table S4-1 in the Supporting Information) close to those of 1a,b.14 However, the 29Si NMR spectra show the silicon resonances with a significant variation (see Table S4-1), indicating the effect of the different silyl groups. We subsequently carried out the reactions of 2a−4a and 2b− 4b with DMAD. The reactions of 2a,b and 3a,b gave the
Scheme 2. Mechanism for the Formation of the Zwitterionic Heterocycle and (Z)-Silyliminophosphoranylalkene
to isolate the heterocyclic intermediates [Ph2PN(Ar)SiMe3](MeO2CCCCO2Me) (Ar = 2,4,6-Me3C6H2 (8a′), 2,6iPr2C6H3 (8b′)) by controlling the reaction temperature and/ or time but failed. This indicates that the electronic property of the substituents on the Si center plays a significant role in stabilizing the pentacoordinated Si center and thereby controlling the reactivity. Since the Lewis acidity of the SiMe3 group is weaker than that of the SiCl3, SiCl2Me, and SiClMe2 groups, the as-formed heterocycles (8a′,b′) are not stable. Nonetheless, this is a very interesting result, which shows a novel route for the synthesis of the silyl and iminophosphoranyl cosubstituted alkenes. Compounds 6a−8a and 6b−8b were characterized by multinuclear NMR (1H, 13C, 29Si, and 31P), IR, and ESI-MS spectroscopy together with 1H,13C-HMBC spectroscopy. The structures of 6a and 6b−8b were further determined by X-ray crystallographic studies. The 29Si NMR resonance signals for the heterocycles 6a,b and 7a,b changed dramatically because of variation of the silyl groups (see Table S4-2 in the Supporting Information). The 31P resonances appear to be less shifted in comparison to the 29Si NMR resonances. However, these data are significantly different from those of the ring-opened alkenes 8a,b. Notably, the 31P resonances of 8a,b are observed at a much higher field (δP −22.00 ppm for 8a and −22.49 ppm for 8b). These data are comparable to those of the NP bond substituted alkene tBuNP(Ph2)C(R′)CH(CO2Me) (δP −8.5 ppm for R′ = H and −10.0 ppm for R′ = Ph)23 but differ from those of (Z)-Ph2PC(R)C(CO2Me)SiMe2tBu (δP 6.8 ppm for R = CO2Me and 4.1 ppm for R = Ph).11b The crystal structures of compounds 6a,b and 7b with selected bond lengths and angles are shown in Figures S2−S4 in the Supporting Information. These structures are similar to those of 5a,b, having the zwitterionic planar C2PNSi ring (ΔC2PNSi = 0.0525 for 6a, 0.0354 for 6b, and 0.0487 Å for 7b), in which the P atom is tetracoordinated and the Si atom is pentacoordinated. It is interesting to note that the C−Si and N−Si bond lengths gradually increase from 5a,b to 6b and then to 7b, while the other bond lengths change only very little (see C
DOI: 10.1021/om501288t Organometallics XXXX, XXX, XXX−XXX
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Organometallics Table S3 in the Supporting Information). The change of the silyl group from the SiCl3 to SiCl2Me and then to SiClMe2 results in a gradual decrease of the Lewis acidity at the Si center, thereby weakening the interactions between the Si atom and its adjacent C and N atoms. The structure of 8b is shown in Figure 1, featuring a Z-type alkene configuration. The C(1)− C(2) bond length is 1.347(2) Å, which indicates the CC double bond nature. The N(1)−P(1) bond length is 1.544(2) Å and is significantly shorter than those in 1b, 5a, and 5b−7b (1.651(2)−1.759(2) Å). This bond length is close to that of the NP bond found in tBuNP(Ph2)C(Ph)CH(CO2Et) (1.525(4) Å).23 To further understand the reaction mechanism, we have performed quantum mechanical calculations at the M06/def2TZVPP//BP86/def2-SVP level of theory.24−28 We explored the mechanism for the reactions of 1a−4a with DMAD (Scheme 2), which gave the heterocycles (5a−7a) and acyclic alkene (8a). We have also calculated the hypothetical heterocycle (8a′) formed from 4a and DMAD as well as the acyclic alkenes (5a′−7a′) formed from 1a−3a and DMAD (Figure S6 in the Supporting Information). The overall energetics for the formation of the cyclic products 5a−7a is more exothermic as compared to the acyclic products 5a′−7a′ (Figure 2 and Table S6 in the Supporting Information). On the
Scheme 3. Schematic Representations of (a) P(1)−C(1) Bond Formation by the Donation of a Lone Pair of Electrons of the P Atom in 1a−4a to the Empty π*-MO of DMAD and (b) Si(1)−C(2) Bond Formation by Donation of Electrons from the C(1)−C(2) π-MO of DMAD to the Si−X σ*-MO
of DMAD, which has a major coefficient on the central carbon atoms C(1) and C(2), to the antibonding Si(1)−Cl/Si(1)− CMe σ*-MO of 1a−4a (Scheme 3b). The transfer of the lone pair of electrons from the P atom of 1a−4a to the π*-LUMO of DMAD leads to the P(1)−C(1) bond formation. The subsequent formation of the Si(1)−C(2) bond is analogous to a nucleophile attack in the SN2 reaction. Here, the nucleophilic center, C(2) (π-MO), attacks the tetracoordinated Si(1) center from the opposite side of the more electronegative atom: viz., the opposite side of the Si(1)−Cl bond in 1a−3a and the Si(1)−CMe bond in 4a. This results in the distortedtrigonal-bipyramidal geometry at the Si(1) center in 5a−7a and 8a′. The energy levels of the Si(1)−Cl σ*-MO in 1a−3a and Si(1)−CMe σ*-MO in 4a are 2.84, 3.41, 3.62, and 6.50 eV, respectively. This indicates that the Lewis acidity of the silicon atom decreases as the number of electronegative substituents decreases, which is in turn reflected in the decreasing exothermicity for the formation of the heterocycles. The significant elongation of the Si(1)−C(2) bond, when the SiCl3 group in 5a (2.004 Å) changes to the SiMe3 group in 8a′ (2.218 Å), also supports the reduction in the exothermicity. The formation of the acyclic alkenes 5a′−7a′ and 8a from the heterocycles by the N(1)−Si(1) bond cleavage (5a′TS2− 7a′TS2 and 8aTS2, Figure 2 and Figure S6 in the Supporting Information) can be considered as the second step of a SN2type reaction at the Si center. Here, in contrast to the normal SN2 reaction, the leaving group is on the same side as that of the incoming nucleophile. This results in the Z-type alkene, which is supported by the experimental isolation of 8a,b. Moreover, the formation of the acyclic alkene 8a is thermodynamically as well as kinetically favorable among the four reactants (Figure 2). Therefore, the progressive substitution of the electronegative Cl ligand by Me decreases the Lewis acidic character of the Si center and in turn destabilizes the pentacoordinated silicon in the heterocycles (5a−7a and 8a′) and in the limiting case leads to the cleavage of the Si(1)− N(1) bond to form 8a. We further performed the reaction of Ph2PN(SiMe3)230 with DMAD and isolated the expected alkene (Z)-Me3SiN P(Ph2)C(CO2Me)C(CO2Me)SiMe3 (9, 78%, Scheme 4). However, no reaction occurred when Me3SiN(2,6-iPrC6H3)SiMe331 was used as a precursor that does not have the phosphanyl Lewis base group. Obviously, the P/Si Lewis pairs
Figure 2. Reaction energy profile for the formation of the heterocycles (5a−7a and 8a′) and acyclic (Z)-alkenes (5a′−7a′ and 8a) at the M06/def2-TZVPP//BP86/def2-SVP level of theory.
other hand, the formation of the acyclic product 8a is more exothermic than that of the cyclic product 8a′ by 6.1 kcal/mol. This is indeed in good agreement with the experimental observation that the acyclic products 8a,b are obtained when the SiMe3 group is attached at the N center. The formation of heterocycles 5a−7a and 8a′ proceeds through a concerted cycloaddition pathway, where P(1)−C(1) and Si(1)−C(2) bonds are formed via asynchronous transition states (Figure 2). This is indicated by the geometries of the transition states (5aTS1−7aTS1 and 8a′TS1) where the P(1)− C(1) bond formation occurs prior to the Si(1)−C(2) bond formation (Figure S6 in the Supporting Information). The EDA-NOCV analysis29 on transition states (Table S7 in the Supporting Information) indicates that the concerted cycloaddition process arises from the transfer of a lone pair of electrons from the P atom of 1a−4a to the π*-LUMO of DMAD (Scheme 3a) as well as the donation from the HOMO D
DOI: 10.1021/om501288t Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
solution containing 2,4,6-Me3C6H2NHLi was cooled to −78 °C, and to it was added neat PPh2PCl (1.13 mL, 6 mmol). The mixture reacted from −78 °C to room temperature over 12 h to give 2,4,6Me3C6H2NH(PPh2). Without isolation, the suspension containing 2,4,6-Me3C6H2NH(PPh2) was cooled again to −78 °C, and to it was added nBuLi (2.5 mL, 2.4 M solution in n-hexane, 6 mmol). By reacting from −78 °C to room temperature within 10 h, the lithium salt 2,4,6-Me3C6H2N(PPh2)Li was formed. This suspension was again cooled to −78 °C, and to it was added neat SiCl3Me (0.71 mL, 6 mmol) subsequently. The mixture reacted on natural warming to room temperature for 12 h. All of the insoluble solids were filtered off, and the filtrate was evaporated to dryness under reduced pressure. The oil obtained was extracted with n-hexane (10 mL). When the extract was kept at −20 °C for 1 day, an off-white solid of 2a was obtained. Yield: 2.1 g, 81%. Mp: 86 °C. 1H NMR (400 MHz, CDCl3, 298 K, ppm): δ 0.80 (s, 3 H, SiCl2Me), 1.63 (s, 6 H, o-Me), 2.30 (s, 3 H, pMe), 6.60 (s, 2 H, C6H2), 6.97−7.08 (m), 7.66−7.72 (m) (10 H, C6H5). 13C NMR (100 MHz, CDCl3, 298 K, ppm): δ 6.6 (d, JPC = 6.6 Hz, SiCl2Me), 19.7, 21.0 (o-Me and p-Me), 128.1 (d, JPC = 8.8 Hz), 129.6, 130.1, 135.1, 135.4, 135.8 (d, JPC = 8.4 Hz), 136.0, 137.9, 138.0 (d, JPC = 3.5 Hz) (C6H2 and C6H5). 31P{1H} NMR (162 MHz, CDCl3, 298 K, ppm): δ 42.0 (PPh2). 29Si NMR (79 MHz, CDCl3, 298 K, ppm): δ −1.4 (d, JPSi = 38.2 Hz, SiCl2Me). ESI-MS: m/z (%) 432.2 (6, [M + H]+). IR (KBr plate, cm−1): ν 3053, 2962, 1601, 1468, 1429, 1253, 1197, 1074, 966, 938, 864, 847, 802, 741, 695, 531, 494. Anal. Calcd for C22H24Cl2NPSi (Mr = 432.40): C, 61.11; H, 5.59; N, 3.24. Found: C, 61.38; H, 5.75; N, 3.04. Ph2PN(2,6-iPr2C6H3)SiCl2Me (2b). The synthetic procedure of 2b with the same scale was similar to that of 2a, in which 2,6iPr2C6H3NH2 (1.13 mL, 6 mmol) was used instead of 2,4,6Me3C6H2NH2. Compound 2b was obtained as an off-white solid. Yield: 2.2 g, 77%. Mp: 71 °C. 1H NMR (400 MHz, CDCl3, 298 K, ppm): δ 0.48 (d, 3JHH = 6.8 Hz, 6 H, CHMe2), 0.76 (s, 3 H, SiCl2Me), 1.10 (d, 3JHH = 6.8 Hz, 6 H, CHMe2), 3.16 (sept, 2 H, 3JHH = 6.8 Hz, CHMe2), 7.02−7.05 (m), 7.17−7.21 (m), 7.30−7.38 (m), 7.55−7.60 (m) (13 H, C6H3 and C6H5). 13C NMR (100 MHz, CDCl3, 298 K, ppm): δ 8.2 (d, JPC = 4.0 Hz, SiCl2Me), 23.7, 25.5, 28.0 (CHMe2), 124.7, 127.2, 128.4 (d, JPC = 8.0 Hz), 130.0, 135.3 (d, JPC = 25.0 Hz), 136.2 (d, JPC = 20.0 Hz), 139.6 (d, JPC = 3.3 Hz), 147.9 (C6H3 and C6H5). 31P{1H} NMR (162 MHz, CDCl3, 298 K, ppm): δ 53.9 (PPh2). 29Si NMR (79 MHz, CDCl3, 298 K, ppm): δ −2.2 (d, JPSi = 20.2 Hz, SiCl2Me). ESI-MS: m/z (%) 474.3 (100, [M + H]+). IR (KBr plate, cm−1): ν 3051, 2961, 1581, 1551, 1482, 1459, 1438, 1379, 1257, 1171, 1090, 950, 861, 797, 743, 696, 541, 509, 486. Anal. Calcd for C25H30Cl2NPSi (Mr = 474.48): C, 63.28; H, 6.37; N, 2.95. Found: C, 63.22; H, 6.59; N, 2.83. Ph2PN(2,4,6-Me3C6H2)SiClMe2 (3a). The synthetic procedure of 3a with the same scale was similar to that of 2a, in which SiCl2Me2 (0.73 mL, 6 mmol) was used instead of SiCl3Me. Compound 3a was obtained as an off-white solid. Yield: 2.4 g, 87%. Mp: 96 °C. 1H NMR (400 MHz, CDCl3, 298 K, ppm): δ 0.42 (s, 6 H, SiClMe2), 1.46 (s, 6 H, o-Me), 2.15 (s, 3 H, p-Me), 6.60 (s, 2 H, C6H2), 7.16−7.21 (m), 7.25−7.30 (m), 7.41−7.46 (m) (10 H, C6H5). 13C NMR (100 MHz, CDCl3, 298 K, ppm): δ 4.2 (d, JPC = 9.0 Hz, SiClMe2), 19.8, 20.9 (oMe and p-Me), 127.9 (d, JPC = 8.5 Hz), 129.6 (d, JPC = 24.4 Hz), 135.1 (d, JPC = 26.4 Hz), 137.2 (d, JPC = 16.4 Hz), 137.6, 139.6 (d, JPC = 5.1 Hz) (C6H2 and C6H5). 31P{1H} NMR (162 MHz, CDCl3, 298 K, ppm): δ 42.9 (PPh2). 29Si NMR (79 MHz, CDCl3, 298 K, ppm): δ 15.7 (d, JPSi = 32.4 Hz, SiClMe2). ESI-MS: m/z (%) 411.6 (11, [M + H]+). IR (KBr plate, cm−1): ν 3040, 2956, 2922, 1477, 1432, 1378, 1251, 1203, 1150, 1091, 931, 875, 824, 785, 748, 727, 702, 676, 565, 490, 476. Anal. Calcd for C23H27ClNPSi (Mr = 411.98): C, 67.05; H, 6.61; N, 3.40. Found: C, 66.85; H, 6.78; N, 3.19. Ph2PN(2,6-iPr2C6H3)SiClMe2 (3b). The synthetic procedure of 3b with the same scale was similar to that of 2a, in which 2,6iPr2C6H3NH2 (1.13 mL, 6 mmol) and SiCl2Me2 (0.73 mL, 6 mmol) were used instead of the respective 2,4,6-Me3C6H2NH2 and SiCl3Me. Compound 3b was obtained as an off-white solid. Yield: 2.2 g, 81%. Mp: 78 °C. 1H NMR (400 MHz, CDCl3, 298 K, ppm): δ 0.36 (s, 6 H, SiClMe2), 0.52 (d, 3JHH = 6.8 Hz, 6 H, CHMe2), 1.10 (d, 3JHH = 6.8
Scheme 4. Reaction of Ph2PN(SiMe3)2 with DMAD to Give 9 and X-ray Crystal Structure of 9 with Thermal Ellipsoids at the 50% Probability Level
1a−4a and 1b−4b and Ph2PN(SiMe3)2 are crucial for the reaction with DMAD and methyl propiolate. Compound 9 has been characterized by multinuclear NMR (1H, 13C, 29Si, and 31 P) spectroscopy and X-ray crystallography, which indicates spectral and structural characteristics similar to those of 8a,b (Tables S4 and S5 in the Supporting Information).
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CONCLUSION In summary, we have shown that N-aryl(diphenylphosphanyl)aminosilanes Ph2PN(Ar)SiCl3−nMen (Ar = 2,4,6-Me3C6H2 or 2,6-iPr2C6H3, n = 0−3) and Ph2PN(SiMe3)2 represent a new class of N-geminal P/Si Lewis pairs, which can undergo a dipolar cycloaddition reaction with DMAD or methyl propiolate. The fine tuning of the silyl group by alternating the Cl and Me substituents results in either zwitterionic heterocycles (5a−7a, 5b−7b, and 5c) or (Z)-silyliminophosphoranylalkenes (8a,b and 9). The formation of the former resembles the dipolar cycloaddition of the P/B, S/B, N/B, and P/Al FLPs to the alkynes.16−19 The formation of the latter proceeds through an initial cycloaddition followed by ring opening, exhibiting a novel pathway for the preparation of silyl and iminophosphoranyl cosubstituted alkenes. Theoretical calculations indicate that the heterocycles are formed by a concerted cycloaddition mechanism. The formation of the (Z)silyliminophosphoranylalkene can be considered as a stepwise SN2 reaction at the Si center.
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EXPERIMENTAL SECTION
Materials and Methods. All manipulations were carried out under a dry argon or nitrogen atmosphere by using Schlenk line and glovebox techniques. The organic solvents toluene, n-hexane, diethyl ether, and tetrahydrofuran were dried by refluxing with sodium/ potassium benzophenone under N2 prior to use. The NMR (1H, 13C, 29 Si, and 31P) spectra were recorded on Bruker Avance II 400 spectrometer. Infrared spectra were obtained on a Nicolet FT-IR 330 spectrometer. ESI mass spectra were measured on an Esquire HCT spectrometer. Melting points of compound in a sealed glass tube were measured by using a Büchi 540 instrument. Elemental analysis was performed on a Thermo Quest Italia SPA EA 1110 instrument. Commercial reagents were purchased from Aldrich, J&K, or Alfa-Aesar Chemical Co. and used as received. The compounds Ph2PN(2,4,6Me3C6H2)SiCl3 (1a), Ph2PN(2,6-iPr2C6H3)SiCl3 (1b),14 Ph2PN(SiMe3)2,30 and 2,6-iPr2C6H3N(SiMe3)231 were prepared according to the literature. The general synthesis of compounds 2a−4a and 2b−4b was carried out in a manner similar to that of 1a (or 1b)14 outlined in Scheme S1 in the Supporting Information. Ph2PN(2,4,6-Me3C6H2)SiCl2Me (2a). At −78 °C, nBuLi (2.5 mL, 2.4 M solution in n-hexane, 6 mmol) was added dropwise to a solution of 2,4,6-Me3C6H2NH2 (0.84 mL, 6 mmol) in diethyl ether (60 mL). By warming naturally to room temperature and stirring for an additional 10 h, the lithium salt 2,4,6-Me3C6H2NHLi was formed. The E
DOI: 10.1021/om501288t Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics Hz, 6 H, CHMe2), 3.26 (sept, 2 H, 3JHH = 6.8 Hz, CHMe2), 7.02−7.04 (m), 7.13−7.18 (m), 7.30−7.33 (m), 7.56−7.61 (m) (13 H, C6H3 and C6H5). 13C NMR (100 MHz, CDCl3, 298 K, ppm): δ 5.2 (d, JPC = 4.0 Hz, SiClMe2), 24.1, 25.3, 28.7 (CHMe2), 124.6, 126.7, 128.2 (d, JPC = 7.6 Hz), 129.6, 135.1 (d, JPC = 24.8 Hz), 137.7 (d, JPC = 21.3 Hz), 141.3 (d, JPC = 3.7 Hz), 147.8 (C6H3 and C6H5). 31P{1H} NMR (162 MHz, CDCl3, 298 K, ppm): δ 55.4 (PPh2). 29Si NMR (79 MHz, CDCl3, 298 K, ppm): δ 14.5 (d, JPSi = 13.2 Hz, SiClMe2). ESI-MS: m/ z (%) 453.9 (13, [M + H]+). IR (KBr plate, cm−1): ν 3048, 2965, 2923, 2863, 1584, 1477, 1462, 1435, 1388, 1260, 1168, 1093, 1049, 1043, 1028, 936, 884, 830, 797, 752, 704, 666, 539, 474. Anal. Calcd for C26H33ClNPSi (Mr = 454.06): C, 68.77; H, 7.33; N, 3.08. Found: C, 68.87; H, 7.53; N, 2.93. Ph2PN(2,4,6-Me3C6H2)SiMe3 (4a). The synthetic procedure of 4a with the same scale was similar to that of 2a, in which SiClMe3 (0.76 mL, 6 mmol) was used instead of SiCl3Me. Compound 4a was obtained as an off-white solid. Yield: 2.1 g, 91%. Mp: 78 °C. 1H NMR (400 MHz, CDCl3, 298 K, ppm): δ 0.35 (s, 9 H, SiMe3), 1.64 (s, 6 H, o-Me), 2.32 (s, 3 H, p-Me), 6.78 (s, 2 H, C6H2), 7.30−7.41 (m), 7.55− 7.61 (m) (10 H, C6H5). 13C NMR (100 MHz, CDCl3, 298 K, ppm): δ 2.3 (d, JPC = 8.2 Hz, SiMe3), 19.9, 20.9 (o-Me and p-Me), 127.8 (d, JPC = 8.4 Hz), 129.2 (d, JPC = 11.7 Hz), 134.0, 134.9 (d, JPC = 26.3 Hz), 137.6, 138.9 (d, JPC = 16.9 Hz), 141.2 (d, JPC = 6.9 Hz) (C6H2 and C6H5). 31P{1H} NMR (162 MHz, CDCl3, 298 K, ppm): δ 40.7 (PPh2). 29Si NMR (79 MHz, CDCl3, 298 K, ppm): δ 9.4 (d, JPSi = 32.2 Hz, SiMe3). ESI-MS: m/z (%) 392.1 (100, [M + H]+). IR (KBr plate, cm−1): ν 3057, 2959, 2908, 1471, 1438, 1423, 1376, 1245, 1200, 1144, 1096, 919, 904, 887, 833, 748, 741, 706, 681, 580, 486, 463. Anal. Calcd for C24H30NPSi (Mr = 391.56): C, 73.62; H, 7.72; N, 3.58. Found: C, 73.62; H, 7.85; N, 3.79. Ph2PN(2,6-iPr2C6H3)SiMe3 (4b). The synthetic procedure of 4b with the same scale was similar to that of 2a, in which 2,6iPr2C6H3NH2 (1.13 mL, 6 mmol) and SiClMe3 (0.76 mL, 6 mmol) were used instead of the respective 2,4,6-Me3C6H2NH2 and SiCl3Me. Compound 4b was obtained as a light yellow oil, which was slowly solidified by keeping it at room temperature for 2 days. Yield: 2.3 g, 88%. Mp: 80 °C. 1H NMR (400 MHz, CDCl3, 298 K, ppm): δ 0.14 (s, 9 H, SiMe3), 0.52 (d, 3JHH = 6.7 Hz, 6 H, CHMe2), 1.09 (d, 3JHH = 6.8 Hz, 6 H, CHMe2), 3.27 (sept, 2 H, 3JHH = 6.8 Hz, CHMe2), 6.98−7.01 (m), 7.08−7.13 (m), 7.26−7.30 (m), 7.41−7.47 (m) (13 H, C6H3 and C6H5). 13C NMR (100 MHz, CDCl3, 298 K, ppm): δ 3.2 (d, JPC = 4.3 Hz, SiMe3), 24.3, 25.3, 28.5 (CHMe2), 124.3, 125.9, 128.1 (d, JPC= 7.4 Hz), 129.1, 134.7 (d, JPC = 24.2 Hz), 139.3 (d, JPC = 21.9 Hz), 143.2 (d, JPC = 3.1 Hz), 147.7 (d, JPC = 2.8 Hz) (C6H3 and C6H5). 31P{1H} NMR (162 MHz, CDCl3, 298 K, ppm): δ 53.2 (PPh2). 29Si NMR (79 MHz, CDCl3, 298 K, ppm): δ 8.4 (d, JPSi = 14.0 Hz, SiMe3). ESI-MS: m/z (%) 434.2 (75, [M + H]+). IR (KBr plate, cm−1): ν 3057, 2962, 2929, 2866, 1581, 1441, 1379, 1242, 1177, 1090, 1048, 1028, 928, 917, 909, 886, 835, 795, 739, 697, 599, 538, 512. Anal. Calcd for C27H36NPSi (Mr = 433.64): C,74.78; H, 8.37; N, 3.23. Found: C, 74.67; H, 8.47; N, 3.34. [Ph2PN(2,4,6-Me3C6H2)SiCl3](MeO2CCCCO2Me) (5a). At room temperature, a solution of MeO2CCCCO2Me (0.14 g, 1 mmol) in toluene (10 mL) was added dropwise to a solution of 1a (0.45 g, 1 mmol) in toluene (30 mL). After addition, the mixture was stirred for 12 h. The solvent was removed under reduced pressure, and the residue was washed with n-hexane to give an off-white solid of 5a. Yield: 0.49 g, 83%. Mp: 185 °C dec. 1H NMR (400 MHz, CDCl3, 298 K, ppm): δ 1.56 (s, 6 H, o-Me), 2.20 (s, 3 H, p-Me), 3.52 (s, 3 H, C(P)CO2Me), 3.97 (s, 3 H, C(Si)CO2Me), 6.61 (s, 2 H, C6H2), 7.47−7.60 (m), 7.68−7.73 (m) (10 H, C6H5). 13C NMR (100 MHz, CDCl3, 298 K, ppm): δ 19.5, 20.8 (o-Me and p-Me), 52.6 ( C(P)CO2Me), 52.9 (C(Si)CO2Me), 113.4 (d, JPC = 106.0 Hz, C(P)CO2Me), 119.3, 120.9, 129.0 (d, JPC = 13.2 Hz), 129.9, 132.7, 134.2 (d, JPC = 10.8 Hz), 134.5, 137.2, 139.3 (C6H2 and C6H5), 160.9 (d, JPC = 20.1 Hz, C(P)CO2Me), 168.6 (d, JPC = 24.0 Hz, C(Si) CO2Me), 189.5 (d, JPC = 17.4 Hz, C(Si)CO2Me). 31P{1H} NMR (162 MHz, CDCl3, 298 K, ppm): δ 27.2 (PPh2). 29Si NMR (79 MHz, CDCl3, 298 K, ppm): δ −105.6 (d, JPSi = 45.2 Hz, SiCl3). ESI-MS: m/z (%) 461.2 (79, [M − SiCl3]+). IR (KBr plate, cm−1): ν 2949, 2920,
1732, 1709, 1584, 1435, 1414, 1262, 1197, 1149, 1108, 1019, 972, 954, 915, 890, 853, 782, 743, 668, 620, 584, 529, 505. Anal. Calcd for C27H27Cl3NO4P (Mr = 566.84): C, 57.21; H, 4.80; N, 2.47. Found: C, 57.17; H, 5.01; N, 2.88. Colorless crystals of 5a were obtained by recrystalliztion in n-hexane/toluene (1/1) at −20 °C within 72 h. [Ph2PN(2,6-iPr2C6H3)SiCl3](MeO2CCCCO2Me) (5b). At room temperature, a solution of MeO2CCCCO2Me (0.14 g, 1 mmol) in toluene (10 mL) was added dropwise to a solution of 1b (0.49 g, 1 mmol) in toluene (30 mL). After addition, the mixture was stirred for 12 h, during which an off-white solid of 5b was precipitated. To obtain 5b in a great degree, the suspension was concentrated to ca. 2 mL. Finally, 5b was collected by filtration and washed with n-hexane (2 mL). Yield: 0.57 g, 89%. Mp: 180 °C dec. 1H NMR (400 MHz, CDCl3, 298 K, ppm): δ −0.04 (d, 6 H, 3JHH = 6.8 Hz, CHMe2), 1.14 (d, 6 H, 3JHH = 6.8 Hz, CHMe2), 2.88 (sept, 2 H, 3JHH = 6.8 Hz, CHMe2), 3.45 (s, 3 H, C(P)CO2Me), 3.95 (s, 3 H, C(Si)CO2Me), 6.94 (s), 6.96 (s), 7.15−7.25 (m), 7.47 (br), 7.61− 7.66 (m) (13 H, C6H3 and C6H5). 13C NMR (100 MHz, CDCl3, 298 K, ppm): δ 22.3, 26.6, 29.4 (CHMe2), 52.8 (C(P)CO2Me + C(Si)CO2Me), 114.3 (d, JPC = 106.3 Hz, C(P)CO2Me), 120.5, 121.1, 125.2 (d, JPC = 1.2 Hz), 128.5, 129.3 (d, JPC = 10.6 Hz), 133.2, 134.5 (d, JPC = 2.9 Hz), 134.8 (d, JPC = 9.6 Hz), 149.1 (C6H3 and C6H5), 161.2 (d, JPC = 21.0 Hz, C(P)CO2Me), 168.8 (d, JPC = 24.1 Hz, C(Si)CO2Me), 188.5 (d, JPC = 17.0 Hz, C(Si)CO2Me). 31 1 P{ H} NMR (162 MHz, CDCl3, 298 K, ppm): δ 28.6 (PPh2). 29Si NMR (79 MHz, CDCl3, 298 K, ppm): δ −104.7 (d, JPSi = 43.8 Hz, SiCl3). ESI-MS: m/z (%) 503.3 (55, [M − SiCl3]+). IR (KBr plate, cm−1): ν 2958, 2917, 2860, 1735, 1712, 1646, 1533, 1453, 1435, 1384, 1253, 1182, 1108, 1044, 932, 793, 748, 694, 528. Anal. Calcd for C30H33Cl3NO4PSi (Mr = 637.01): C, 56.56; H, 5.22; N, 2.20. Found: C, 56.60; H, 5.51; N, 1.92. Colorless crystals of 5b·1.5CHCl3 were obtained by recrystalliztion in n-hexane/CHCl3 (3/1) at room temperature for 24 h. [Ph2PN(2,4,6-Me3C6H2)SiCl3](HCCCO2Me) (5c). A mixture of HCCCO2Me (0.084 g, 1 mmol) and 1a (0.45 g, 1 mmol) in toluene (40 mL) was stirred at room temperature for 12 h. After reaction, the solvent was removed under reduced pressure and the residue was washed with n-hexane to give a light-brown solid of 5c. Yield: 0.46 g, 84%. Mp: 98 °C dec. 1H NMR (400 MHz, C6D6, 298 K, ppm): δ 1.84 (s, 6 H, o-Me), 2.04 (s, 3 H, p-Me), 3.70 (s, 3 H, C(Si)CO2Me), 6.53 (s, 2 H, C6H2), 6.60 (d, JPH = 35.5 Hz, 1 H, C(P)H), 6.74− 6.80 (m), 6.92−7.03 (m), 7.23−7.29 (m) (10 H, C6H5). 13C NMR (100 MHz, C6D6, 298 K, ppm): δ 20.0, 20.9 (o-Me and p-Me), 52.4 (C(Si)CO2Me), 113.0 (d, JPC = 100.0 Hz, C(P)H), 121.8, 122.9, 129.0 (d, JPC = 12.7 Hz), 130.3, 134.0, 134.1, 136.9 (d, JPC = 2.11 Hz), 140.0 (d, JPC = 2.9 Hz) (C6H2 and C6H5), 168.3 (d, JPC = 27.8 Hz, C(Si)CO2Me), 179.2 (d, JPC = 14.3 Hz, C(Si)CO2Me). 31P{1H} NMR (162 MHz, C6D6, 298 K, ppm): δ 23.6 (PPh2). 29Si NMR (79 MHz, C6D6, 298 K, ppm): δ −102.9 (d, JPSi = 50.0 Hz, SiCl3). ESI-MS: m/z (%) 501.3 (100, [M − Cl]+). IR (KBr plate, cm−1): ν 3009, 2946, 2917, 1726, 1587, 1453, 1384, 1256, 1197, 1152, 1117, 1102, 1036, 968, 949, 873, 748, 699, 599, 567, 517, 481. Anal. Calcd for C25H25NO2PsiCl3 (Mr = 536.89): C, 55.93; H, 4.69; N, 2.61. Found: C, 55.66; H, 4.49; N, 2.39. [Ph2PN(2,4,6-Me3C6H2)SiCl2Me](MeO2CCCCO2Me) (6a). At room temperature, a solution of MeO2CCCCO2Me (0.14 g, 1 mmol) in toluene (10 mL) was added dropwise to a solution of 2a (0.43 g, 1 mmol) in toluene (30 mL). After addition, the mixture was stirred for 12 h. The solution was concentrated to ca. 10 mL, and to it n-hexane was added until all the solids of 6a were precipitated. The solids were collected and washed with n-hexane (2 mL). Yield: 0.48 g, 84%. Mp: 169 °C dec. 1H NMR (400 MHz, CDCl3, 298 K, ppm): δ 0.79 (s, 3 H, SiCl2Me), 1.26 (s, 6 H, o-Me), 1.92 (s, 3 H, p-Me), 3.38 (s, 3 H, C(P)CO2Me), 3.75 (s, 3 H, C(Si)CO2Me), 6.45 (s, 2 H, C6H2), 7.30−7.46 (m), 7.61−7.66 (m) (10 H, C6H5). 13C NMR (100 MHz, CDCl3, 298 K, ppm): δ 4.8 (SiCl2Me), 18.9, 20.2 (o-Me and pMe), 53.2 (C(P)CO2Me), 53.6 (C(Si)CO2Me), 128.0 (d, JPC = 80.6 Hz, C(P)CO2Me), 116.5, 117.6, 126.6, 129.6 (d, JPC = 13.5 Hz), 130.3, 133.4 (d, JPC = 11.3 Hz), 135.8 (d, JPC = 2.5 Hz), 137.3 (d, JPC = 2.9 Hz), 138.4 (C6H2 and C6H5), 159.4 (d, JPC = 19.4 Hz, F
DOI: 10.1021/om501288t Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics C(P)CO2Me), 164.5 (d, JPC = 22.9 Hz, C(Si)CO2Me), 170.1 (br, C(Si)CO2Me). 31P{1H} NMR (162 MHz, CDCl3, 298 K, ppm): δ 39.9 (PPh2). 29Si NMR (79 MHz, CDCl3, 298 K, ppm): δ −12.4 (br, SiCl2Me). ESI-MS: m/z (%) 574.4 (25, [M + H]+). IR (KBr plate, cm−1): ν 2997, 2949, 2920, 1729, 1709, 1578, 1468, 1435, 1283, 1224, 1194, 1143, 1105, 1018, 997, 963, 881, 845, 771, 747, 704, 689, 645, 593, 562, 517, 495. Anal. Calcd for C28H30Cl2NO4PSi (Mr = 574.51): C, 58.54; H, 5.26; N, 2.44. Found: C, 58.15; H, 5.52; N, 2.29. Colorless crystals of 6a were obtained by recrystallization in n-hexane/ toluene (1/1) at −20 °C within 24 h. [Ph2PN(2,6-iPr2C6H3)SiCl2Me](MeO2CCCCO2Me) (6b). At room temperature, a solution of MeO2CCCCO2Me (0.14 g, 1 mmol) in toluene (10 mL) was added dropwise to a solution of 2b (0.47 g, 1 mmol) in toluene (30 mL). After addition, the mixture was stirred for 12 h. The solvent was removed under reduced pressure, and the residue was washed with n-hexane to give an off-white solid of 6b. Yield: 0.55 g, 89%. Mp: 175 °C dec. 1H NMR (400 MHz, CDCl3, 298 K, ppm): δ −0.13 (d, 3JHH = 6.8 Hz, 6 H, CHMe2), 0.99 (d, 3JHH = 6.8 Hz, 6 H, CHMe2), 1.14 (s, 3 H, SiCl2Me), 2.64 (sept, 2 H, 3JHH = 6.8 Hz, CHMe2), 3.40 (s, 3 H, C(P)CO2Me), 3.87 (s, 3 H, C(Si)CO2Me), 6.89 (s), 7.13−7.17 (m), 7.28−7.34 (m), 7.44−7.50 (m), 7.62−7.67 (m) (13 H, C6H3 and C6H5). 13C NMR (100 MHz, CDCl3, 298 K, ppm): δ 10.4 (SiCl2Me), 22.3, 26.4, 29.0 (CHMe2), 53.2 (C(P)CO2Me), 53.3 (C(Si)CO2Me), 124.3 (d, JPC = 105.2 Hz, C(P)CO2Me), 118.6, 119.6, 125.2, 128.6, 129.5 (d, JPC = 13.4 Hz), 129.8, 133.9 (d, JPC = 10.8 Hz), 135.0, 148.3 (d, JPC = 2.9 Hz) (C6H3 and C6H5), 159.9 (d, JPC = 20.9 Hz, C(P)CO2Me), 167.2 (d, JPC = 24.5 Hz, C(Si)CO2Me), 180.3 (br, C(Si)CO2Me). 31P{1H} NMR (162 MHz, CDCl3, 298 K, ppm): δ 36.6 (PPh2). 29Si NMR (79 MHz, CDCl3, 298 K, ppm): δ −43.5 (br, SiCl2Me). ESI-MS: m/z (%) 616.4 (21, [M + H]+). IR (KBr plate, cm−1): ν 2952, 2928, 2863, 1744, 1712, 1584, 1465, 1375, 1432, 1375, 1280, 1230, 1161, 1114, 1102, 1051, 1018, 996, 889, 836, 800, 784, 748, 702, 655, 609, 549, 459. Anal. Calcd for C31H36Cl2NO4PSi (Mr = 616.59): C, 60.39; H, 5.88; N, 2.27. Found: C, 60.25; H, 6.07; N, 2.07. Colorless crystals of 6b·(toluene) were obtained by recrystallization in n-hexane/toluene (1/1) at −20 °C within 30 h. [Ph2PN(2,4,6-Me3C6H2)SiClMe2](MeO2CCCCO2Me) (7a). At room temperature, a solution of MeO2CCCCO2Me (0.14 g, 1 mmol) in toluene (10 mL) was added dropwise to a solution of 3a (0.41 g, 1 mmol) in toluene (30 mL). After addition, the mixture was stirred for 12 h. The solvent was removed under reduced pressure, and the residue was washed with n-hexane to give an off-white solid of 7a. Yield: 0.51 g, 92%. Mp: 138 °C dec. 1H NMR (400 MHz, CDCl3, 298 K, ppm): δ 0.55 (s, 6 H, SiClMe2), 1.27 (s, 6 H, o-Me), 2.02 (s, 3 H, pMe), 3.48 (s, 3 H, C(P)CO2Me), 3.87 (s, 3 H, C(Si)CO2Me), 6.57 (s, 2 H, C6H2), 7.34−7.40 (m), 7.53−7.59 (m), 7.20−7.77 (m) (10 H, C6H5). 13C NMR (100 MHz, CDCl3, 298 K, ppm): δ −0.3 (SiClMe2), 18.9, 20.4 (o-Me and p-Me), 53.7 (C(P)CO2Me), 54.0 (C(Si)CO2Me), 128.3 (d, JPC = 81.3 Hz, C(P)CO2Me), 117.5, 118.5, 124.9, 125.3, 130.2 (d, JPC = 13.4 Hz), 130.9, 133.1 (d, JPC = 11.0 Hz), 136.1, 137.1 (d, JPC = 3.2 Hz), 138.9 (C6H2 and C6H5), 159.2 (d, JPC = 3.2 Hz, C(P)CO2Me), 164.6 (d, JPC = 22.4 Hz, C(Si)CO2Me), 169.3 (d, JPC = 15.7 Hz, C(Si)CO2Me). 31P{1H} NMR (162 MHz, CDCl3, 298 K, ppm): δ 44.0 (PPh2). 29Si NMR (79 MHz, CDCl3, 298 K, ppm): δ 27.0 (d, JPSi = 21.3 Hz, SiClMe2). ESIMS: m/z (%) 555.3 (72, [M + H]+). IR (KBr plate, cm−1): ν 2952, 2920, 1726, 1706, 1607, 1581, 1477, 1432, 1381, 1280, 1253, 1227, 1200, 1143, 1102, 969, 881, 851, 802, 783, 742, 692, 516. Anal. Calcd for C29H33ClNO4PSi (Mr = 554.09): C, 62.86; H, 6.00; N, 2.53. Found: C, 62.96; H, 6.19; N, 2.33. [Ph2PN(2,6-iPr2C6H3)SiClMe2](MeO2CCCCO2Me) (7b). At room temperature, a solution of MeO2CCCCO2Me (0.14 g, 1 mmol) in toluene (10 mL) was added dropwise to a solution of 3b (0.45 g, 1 mmol) in toluene (30 mL). After addition, the mixture was stirred for 12 h. The solvent was removed under reduced pressure, and the residue was washed with n-hexane to give a white solid of 7b. Yield: 0.50 g, 83%. Mp: 140 °C dec. 1H NMR (400 MHz, CDCl3, 298 K, ppm): δ 0.01 (d, 3JHH = 6.8 Hz, 6 H, CHMe2), 0.87 (s, 6 H, SiClMe2), 1.03 (d, 3JHH = 6.8 Hz, 6 H, CHMe2), 2.61 (sept, 2 H, 3JHH
= 6.8 Hz, CHMe2), 3.62 (s, 3 H, C(P)CO2Me), 4.07 (s, 3 H, C(Si)CO2Me), 7.07 (s), 7.09 (s), 7.31−7.47 (m), 7.71−7.77 (m), 7.86−7.91 (m) (13 H, C6H3 and C6H5). 13C NMR (100 MHz, CDCl3, 298 K, ppm): δ 0.3 (SiClMe2), 22.1, 26.2, 28.3 (CHMe2), 53.6 ( C(P)CO2Me), 53.7 (C(Si)CO2Me), 133.0 (d, JPC= 102.2 Hz, C(P)CO2Me), 116.8, 117.8, 124.7 (d, JPC = 2.9 Hz), 125.8 (d, JPC = 1.7 Hz), 129.5 (d, JPC = 2.0 Hz), 130.1 (d, JPC = 13.4 Hz), 133.1 (d, JPC = 10.7 Hz), 135.8 (d, JPC = 2.8 Hz), 147.7 (d, JPC = 3.2 Hz) (C6H3 and C6H5), 158.9 (d, JPC = 20.4 Hz, C(P)CO2Me), 164.3 (d, JPC = 22.7 Hz, C(Si)CO2Me), 167.3 (d, JPC = 15.7 Hz, C(Si)CO2Me). 31 1 P{ H} NMR (162 MHz, CDCl3, 298 K, ppm): δ 45.9 (PPh2). 29Si NMR (79 MHz, CDCl3, 298 K, ppm): δ 24.8 (d, JPSi = 20.5 Hz, SiClMe2). ESI-MS: m/z (%) 597.5 (15, [M + H]+). IR (KBr plate, cm−1): ν 2949, 2860, 1729, 1712, 1584, 1429, 1381, 1283, 1227, 1161, 1117, 1003, 962, 884, 801, 753, 725, 685, 645, 594, 548, 502. Anal. Calcd for C32H39ClNO4PSi (Mr = 596.17): C, 64.47; H, 6.59; N, 2.35. Found: C, 64.57; H, 6.70; N, 2.19. Colorless crystals of 7b were obtained by recrystallization in n-hexane/toluene (1/1) at −20 °C within 48 h. 2,4,6-Me3C6H2NP(Ph2)C(CO2Me)C(CO2Me)SiMe3 (8a). At room temperature, a solution of MeO2CCCCO2Me (0.14 g, 1 mmol) in toluene (10 mL) was added dropwise to a solution of 4a (0.39 g, 1 mmol) in toluene (15 mL). After addition, the mixture was stirred for 12 h. The solvent was removed under reduced pressure, and the residue was washed with n-hexane to give a light yellow solid of 8a. Yield: 0.45 g, 85%. Mp: 127 °C dec. 1H NMR (400 MHz, CDCl3, 298 K, ppm): δ −0.03 (s, 9 H, SiMe3), 2.24 (s, 3 H, p-Me), 2.27 (s, 6 H, oMe), 3.18 (s, 3 H, C(P)CO2Me), 3.74 (s, 3 H, C(Si)CO2Me), 6.82 (s, 2 H,C6H2), 7.35−7.50 (m), 7.71−7.78 (m) (10 H, C6H5). 13C NMR (100 MHz, CDCl3, 298 K, ppm): δ 0.1 (SiMe3), 20.6, 21.9 (oMe and p-Me), 52.0 (C(P)CO2Me), 52.2 (C(Si)CO2Me), 127.5 (d, JPC = 2.3 Hz), 128.2 (d, JPC = 12.8 Hz), 128.8, 131.5 (d, JPC = 2.7 Hz), 132.3 (d, JPC = 10.1 Hz), 133.3, 134.4, 143.2 (C6H2 and C6H5), 150.0 (d, JPC = 76.4 Hz, C(P)CO2Me), 155.9 (d, JPC = 11.3 Hz, C(Si)CO2Me), 168.3 (d, JPC = 17.1 Hz, C(P)CO2Me), 171.2 (d, JPC = 23.6 Hz, C(Si)CO2Me). 31P{1H} NMR (162 MHz, CDCl3, 298 K, ppm): δ −22.0 (PPh2). 29Si NMR (79 MHz, CDCl3, 298 K, ppm): δ −2.1 (d, JPSi = 5.8 Hz, SiMe3). ESI-MS: m/z (%) 534.4 (100, [M + H]+). IR (KBr plate, cm−1): ν 2955, 2902, 1723, 1709, 1575, 1554, 1474, 1432, 1420, 1343, 1289, 1230, 1108, 1054, 998, 874, 847, 757, 735, 693, 537, 504. Anal. Calcd for C30H36NO4PSi (Mr = 533.67): C, 67.52; H, 6.80; N, 2.62. Found: C, 67.36; H,7.02; N, 2.64. 2,6-iPr2C6H3NP(Ph2)C(CO2Me)C(CO2Me)SiMe3 (8b). At room temperature, a solution of MeO2CCCCO2Me (0.28 g, 2 mmol) in toluene (10 mL) was added dropwise to a solution of 4b (0.87 g, 2 mmol) in toluene (20 mL). After addition, the mixture was stirred for 12 h. The solvent was removed under reduced pressure, and the residue was washed with n-hexane to give a light yellow solid of 8b. Yield: 0.98 g, 85%. Mp: 162 °C dec. 1H NMR (400 MHz, CDCl3, 298 K, ppm): δ 0.00 (s, 9 H, SiMe3), 1.09 (d, 3JHH = 6.8 Hz, 6 H, CHMe2), 3.13 (s, 3 H, C(P)CO2Me), 3.49 (sept, 2 H, 3JHH = 6.8 Hz, CHMe2), 3.73 (s, 3 H, C(Si)CO2Me), 6.86−6.91 (m), 7.05−7.08 (m), 7.37−7.49 (m), 7.68−7.74 (m) (13 H, C6H3 and C6H5). 13C NMR (100 MHz, CDCl3, 298 K, ppm): δ 0.3 (s, SiMe3), 24.1, 28.7 (CHMe2), 51.9 (C(P)CO2Me), 52.3 (C(Si)CO2Me), 119.4 (d, JPC = 2.2 Hz), 123.1, 128.3 (d, JPC = 12.7 Hz), 131.7 (d, JPC = 2.9 Hz), 132.3, 132.4 (d, JPC = 9.7 Hz), 142.5 (d, JPC = 7.3 Hz), 142.8 (d, JPC = 1.4 Hz) (C6H3 and C6H5), 149.4 (d, JPC = 76.5 Hz, C(P)CO2Me), 155.9 (d, JPC = 11.6 Hz, C(Si)CO2Me), 168.4 (d, JPC = 17.4 Hz, C(P)CO2Me), 171.5 (d, JPC = 23.8 Hz, C(Si)CO2Me). 31P{1H} NMR (162 MHz, CDCl3, 298 K, ppm): δ −22.5 (PPh2). 29Si NMR (79 MHz, CDCl3, 298 K, ppm): δ −1.9 (d, JPSi = 5.9 Hz, SiMe3). ESIMS: m/z (%) 576.3 (42, [M + H]+). IR (KBr plate, cm−1): ν 2961, 2863, 1723, 1703, 1581, 1462, 1435, 1358, 1298, 1230, 1105, 1062, 1025, 1005, 879, 843, 797, 754, 736, 712, 698, 540, 526. Anal. Calcd for C33H42NO4PSi (Mr = 575.75): C, 68.84; H, 7.35; N, 2.43. Found: C, 68.65; H, 7.61; N,2.39. Light yellow crystals of 8b were obtained by recrystallization in n-hexane/toluene (1/1) solution at −20 °C within 24 h. G
DOI: 10.1021/om501288t Organometallics XXXX, XXX, XXX−XXX
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Organometallics Me3SiNP(Ph2)C(CO2Me)C(CO2Me)SiMe3 (9). At room temperature, a precooled (−20 °C) solution of MeO2CC CCO2Me (0.35 g, 2.45 mmol) in toluene (10 mL) was added dropwise to a solution of Ph2PN(SiMe3)2(0.85 g, 2.45 mmol) in toluene (15 mL). After addition, the mixture was stirred for 12 h. The solvent was removed under reduced pressure, and the residue was extracted with n-hexane (5 mL). The extract was kept at room temperature for 12 h, affording colorless crystals of 9. Yield: 0.93 g, 78%. Mp: 94 °C. 1H NMR (400 MHz, CDCl3, 298 K, ppm): δ −0.07 (s, 9 H, SiMe3), 0.19 (s, 9 H, SiMe3), 3.18 (s, 3 H, C(P)CO2Me), 3.73 (s, 3 H, C(Si)CO2Me), 7.39−7.50 (m), 7.65−7.72 (m) (10 H, C6H5). 13C NMR (100 MHz, CDCl3, 298 K, ppm): δ 0.8 (SiMe3), 3.8 (d, JPC = 3.5 Hz, SiMe3), 52.0 (C(P)CO2Me), 52.1 (C(Si)CO2Me), 128.2 (d, JPC = 12.5 Hz), 131.3 (d, JPC = 2.9 Hz), 132.1 (d, JPC = 10.9 Hz), 134.9 (d, JPC = 97.7 Hz) (C6H5), 145.8 (d, JPC = 105.7 Hz, C(P)CO2Me), 159.3 (d, JPC = 10.5 Hz, C(Si)CO2Me), 167.9 (d, JPC = 19.7 Hz, C(P)CO2Me), 171.9 (d, JPC = 24.1 Hz, C(Si) CO2Me). 31P{1H} NMR (162 MHz, CDCl3, 298 K, ppm): δ −0.6 (PPh2). 29Si NMR (79 MHz, CDCl3, 298 K, ppm): δ −1.9 (d, JPSi = 18.0 Hz, SiMe3), −2.5 (d, JPSi = 6.3 Hz, SiMe3). ESI-MS: m/z (%) 488.3 (89, [M + H]+). IR (KBr plate, cm−1): ν 2952, 2899, 1729, 1715, 1435, 1384, 1286, 1224, 1108, 1063, 1026, 999, 896, 851, 827, 762, 720, 700, 674, 626, 603, 539, 511. Anal. Calcd for C24H34NO4PSi2 (Mr = 487.68): C, 59.11; H, 7.03; N, 2.87. Found: C, 59.48;H, 7.04; N, 2.91. X-ray Crystallographic Analysis. Crystallographic data for compounds 5a, 5b·1.5CHCl3, 6a, 6b·(toluene), 7b·1.5(toluene), 8b, and 9 were collected on an Oxford Gemini S Ultra system. During measurements graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) was used. Absorption corrections were applied using the spherical harmonics program (multiscan type). All structures were solved by direct methods (SHELXS-96)32 and refined against F2 using SHELXL-97.33 In general, the non-hydrogen atoms were located by difference Fourier synthesis and refined anisotropically, and hydrogen atoms were included using a riding model with Uiso tied to the Uiso of the parent atoms unless otherwise specified. In 5b·1.5CHCl3, two CHCl3 molecules were disclosed with respective occupations of 1.0 and 0.5, the former of which was disordered and treated in a splitting mode by the PART method, and the latter was seriously disordered and was not allowed to complete by the hydrogen addition. The carbon and chlorine atoms in these two molecules were isotropically refined. In 7b·1.5(toluene), two toluene molecules were disclosed with the respective occupations of 1.0 and 0.5, the former of which was disordered and treated in a splitting mode by the PART method. The latter molecule was in a higher symmetry and only 3.5 hydrogen atoms were added in the geometry after a symmetric operation. A summary of cell parameters, data collection, and structure solution and refinements is given in Tables 1s and 2s in the Supporting Information. Computational Methodology. All of the geometries were optimized at the gradient-corrected BP8624 density functional with the basis set def2-SVP.25 The calculations were performed using the Gaussian 09 package.26 The meta-GGA exchange correlation functional M0627 with def2-TZVPP25 basis set was used for single-point calculations on geometries optimized at the BP86/def2-SVP level of theory. The energies at the M06/def2-TZVPP level were corrected by adding the zero-point energies from the BP86/def2-SVP level of theory. Natural bond orders (NBOs)28 of the molecules were computed at the same level of theory.
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1020510 for the respective compounds 5a,b, 6a,b, 7b, 8b, and 9.
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AUTHOR INFORMATION
Corresponding Authors
*E-mail for H.Z.:
[email protected]. *E-mail for P.P.:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the 973 Program (2012CB821704), the National Nature Science Foundation of China (91027014, 21473142, and 2013B019), and the Department of Science and Technology of India.
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REFERENCES
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ASSOCIATED CONTENT
S Supporting Information *
Tables, figures, and xyz and CIF files giving X-ray crystallographic data and crystal structures for 5a,b, 6a,b, 7b, 8b, and 9, computational details, and all computed molecule Cartesian coordinates in a format for convenient visualization. This material is available free of charge via the Internet at http:// pubs.acs.org. In addition, crystallographic data have been deposited at the CCDC with the file numbers 1020503− H
DOI: 10.1021/om501288t Organometallics XXXX, XXX, XXX−XXX
Article
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DOI: 10.1021/om501288t Organometallics XXXX, XXX, XXX−XXX
