Article pubs.acs.org/Organometallics
Highly Fluorinated Tris(indazolyl)borate Hydrocarbyl Complexes of Calcium and Magnesium: Synthesis and Structural Studies Nuria Romero,†,‡,§ Quentin Dufrois,†,‡ Laure Vendier,†,‡ Chiara Dinoi,*,†,‡,∥ and Michel Etienne*,†,‡ †
CNRS, LCC (Laboratoire de Chimie de Coordination), 205 Route de Narbonne, 31077 Toulouse Cedex 4, France Université de Toulouse, UPS, INPT, LCC, 31077 Toulouse Cedex 4, France
‡
S Supporting Information *
ABSTRACT: Heteroleptic phenylacetylide complexes [{F12Tp4Bo,3Ph}Ae(CCPh)]x of calcium (Ae = Ca, x = 2; 2) and magnesium (Ae = Mg, x = 1; 4) containing the highly fluorinated 3-phenyl hydrotris(indazolyl)borate {F 12 Tp4Bo,3Ph}− ligand have been synthesized by acid−base reactions between the corresponding silylamido derivatives [{F12-Tp4Bo,3Ph}Ae{N(SiRMe2)2}] (R = Me, Ae = Ca (1); R = H, Ae = Mg (3)) and PhCCH. Compounds 2 and 4 have been characterized by NMR spectroscopy and X-ray diffraction analysis. 2 crystallizes as a dinuclear complex, showing two nonsymmetrical “side-on” (π-type) interactions between the acetylide units and the Ca centers, whereas 4 crystallizes as a mononuclear complex, displaying a four-coordinate magnesium. The molecular structure of the complex [{F12-Tp4Bo,3Ph}Mg{N(SiMe2H)2}] (3), obtained by the salt metathesis reaction between [Mg{N(SiMe2H)2}2] and [Tl{F12-Tp4Bo,3Ph}], is also reported. 3 is also four-coordinate and exhibits a Mg···β-Si−H agostic distortion. The synthesis and in situ characterization of the heteroleptic alkyl complex [{F12-Tp4Bo,3Ph}Ca{CH(SiMe3)2}(THF)] (5) is also reported, although attempts to isolate this compound failed due to its extreme sensitivity to temperature.
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INTRODUCTION The organometallic chemistry of calcium has attracted growing interest in recent years, leading to an improved understanding of the structural Ca chemistry and to the development of refined synthetic procedures.1−5 The main challenge hampering the development of calcium-based heteroleptic organometallics is their extremely high reactivity, often governed by Schlenklike redistribution processes in solution toward the formation of ill-defined oligomeric or polymeric species. Structurally characterized heteroleptic Ca organometallic compounds can be broadly divided into three categories depending on the hybridization of the carbon atom σ-bonded to calcium: (i) Ca− C(sp3), (ii) Ca−C(sp2), and (iii) Ca−C(sp) derivatives. Heteroleptic complexes displaying σ bonds between calcium and sp3-hybridized carbons are mainly represented by silylmethyl derivatives such as [{N∧N}Ca{CH(SiMe3)2}] and [{ToT}Ca{CH(SiMe3)2}],6,7 which contain the bulky iminoanilide {N∧N}− and tris(oxazolinyl)borate {ToT}− ligands, respectively. The [{(Me 3 Si) 2 CH-dipp-BIAN}Ca{CH(SiMe3)2}] species8,9 also belongs to this class of compounds. It is obtained through dearomatization of the 2,6-diisopropylphenyl-substituted bis(imino)acenaphthene ligand {dippBIAN} by migration of a {CH(SiMe3)2}− group from the homoleptic [Ca{CH(SiMe3)2}2(THF)2] precursor, highlighting the high reactivity of the Ca−C bond and the importance of a careful choice of the ligand. The negative hyperconjugation within the silylalkyl groups and the steric hindrance of the © 2017 American Chemical Society
monoanionic ligands confer to the complexes described above enough stability and reactivity to act as hydroelementation precatalysts. Heteroleptic aminobenzyl Ca derivatives containing differently substituted fluorenyl ligands may also be included in this category. Due to the additional N coordination of the benzyl moiety, they display increased stability, providing catalytically active species for alkene polymerization and hydrosilylation reactions.10−14 Remarkable examples of Ca− C(sp3) derivatives are finally represented by the simpler trimethylsilylmethyl complexes [(S)4CaI(CH2SiMe3)] (S = tetrahydrofuran (THF), tetrahydropyran (THP)), recently obtained by the direct synthesis of iodomethyltrimethylsilane with calcium.15 Heteroleptic compounds containing σ bonds between calcium and sp 2-hybridized carbon are exemplified by arylcalcium halides16,17 and 1-alkenylcalcium species,18 synthesized by a similar Grignard-type reaction. Heteroleptic complexes displaying a Ca−C(sp) σ bonding, finally, are chiefly represented by calcium acetylide derivatives such as [Cp′Ca(CCPh)(THF)]2 (Cp′ = (i-Pr)4C5H)19 and the βdiketiminate species [{BDI}Ca(CCR)]2 (BDI = {ArNC(Me)CHCN(Me)Ar}; Ar = 2,6-diisopropylphenyl; R = n-Bu, tBu, Ph, 4-MeC 6 H 4 , ferrocenyl, Si(i-Pr) 3 , CH 2 OPh, CH 2 NMe 2 ) 20−23 and [{BDI}Ca(THF)(μ-CCPh) 2 CaReceived: October 11, 2016 Published: February 1, 2017 564
DOI: 10.1021/acs.organomet.6b00783 Organometallics 2017, 36, 564−571
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1). Crystallization from a toluene/pentane mixture at −40 °C gave pure 2 as a white solid in 95% yield.
{BDI}].24 As a consequence of the relatively low pKa of terminal alkynes, these acetylide complexes have been obtained by acid−base reactions between the appropriate heteroleptic calcium amido precursor and the relevant terminal acetylene. Some of them have found interesting catalytic applications in the head-to-head dimerization of alkynes into butatrienes or 1,3-enynes.22,23 These species generally adopt a dinuclear arrangement in the solid state, with the bridging acetylide ligands displaying a different extent of “side on” interaction between the CC units and the Ca centers. We recently reported the synthesis of a series of highly fluorinated tris(indazolyl)borate silylamido complexes of formula [{F12-Tp4Bo,3Ph}Ca(NR2)] (R = SiMe3, SiMe2H).25 These compounds displayed characteristic robustness in solution and remarkable inertness toward Schlenk equilibria. The hexamethyldisilazane derivative proved to be efficient for the catalytic cyclohydroamination of 1-amino-2,2-dimethyl-4pentene, representing one of the most active precatalysts reported to date for this reaction. This remarkable catalytic activity was attributed to the electron-withdrawing properties of the fluorinated {F12-Tp4Bo,3Ph}− ligand, which enhances the polarity and hence the reactivity of the Ca−N bond, yet avoiding Schlenk-type redistributions thanks to its bulky tripodal scaffold (Figure 1).25−28
Scheme 1. Synthesis of the Dinuclear Complex [{F12Tp4Bo,3Ph}Ca(CCPh)]2 (2)
The 19F NMR spectrum of 2 at room temperature showed four signals for the four equivalent benzo fluorine of the {F12Tp4Bo,3Ph}− ligand at δ −144.0, −151.4, −154.4 and −164.4. The 1H NMR showed three signals at δ 7.56, 6.96, and 6.81 for the ortho, meta, and para protons, respectively, of the Ph moiety of {F12-Tp4Bo,3Ph}− and three signals at δ 6.61, 6.53, and 6.23 for the para, meta, and ortho aromatic protons, respectively, of the (PhCC)− ligand. The two sets of resonances are in a 3:1 ratio according to the structure of 2. In the 13C{1H}{19F} spectrum, the signals corresponding to the (PhCC)− moiety were found at δ 130.1 (Cortho), 128.0 (Cpara), 127.1 (Cmeta), 124.0 (Cipso), and 119.3 (Cβ). Except for Cα of the (PhCC)− ligand, which was tentatively attributed to a large signal at δ 141.3, all of the other quaternary carbons of the {F12-Tp4Bo,3Ph}− ligand overlap each other and could not be confidently assigned. The downfield resonance of the Cβ signal, in particular, strongly suggests a dinuclear formulation for 2.21,23 Complex 2 is inert toward Schlenk equilibria but is very sensitive to temperature, decomposing in a few minutes at temperatures above −40 °C. Due to its high sensitivity to temperature, it proved a challenge to grow crystals of compound 2 suitable for X-ray diffraction analysis. After many repeated efforts, single crystals of 2 were obtained from a toluene/hexane mixture at −40 °C. Although the X-ray data were unsatisfactory (R = ca. 0.09) and preclude any detailed discussion of bond lengths and angles, the connectivity is unambiguous. Compound 2 crystallizes as a dinuclear species (Figure 2), exhibiting a four-membered Ca2C2 core with sp-hybridized carbons that bridge the calcium centers.
Figure 1. Highly fluorinated tris(indazolyl)borate silylamido calcium complexes.
Taking advantage of the stability of these highly fluorinated heteroleptic complexes, we decided to explore the organometallic chemistry of calcium based on the same ancillary {F12Tp4Bo,3Ph}− ligand. We first explored the formation of the Ca− acetylide bond, performing the synthesis of the dinuclear acetylide complex [{F12-Tp4Bo,3Ph}Ca(CCPh)]2 (2). In the solid state, 2 shows a highly distorted structure involving a nonsymmetrical Ca2C2 core with two different Ca···CCPh π interactions. For comparison purposes, we also synthesized the Mg analogue [{F12-Tp4Bo,3Ph}Mg(CCPh)] (4), which crystallizes as a mononuclear complex, displaying a fourcoordinate magnesium. In addition, we report on the synthesis and in situ characterization of the calcium bis(trimethylsilyl)methyl derivative [{F12-Tp4Bo,3Ph}Ca{CH(SiMe3)2}(THF)] (5). Attempts to isolate this compound failed due to its extreme temperature sensitivity.
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RESULTS AND DISCUSSION Synthesis of Heteroleptic Calcium and Magnesium Acetylides. The stoichiometric acid−base reaction between the heteroleptic amido complex [{F12 -Tp 4Bo,3Ph }Ca{N(SiMe3)2}] (1) and PhCCH proceeded rapidly at room temperature to yield the corresponding dinuclear heteroleptic calcium acetylide [{F12-Tp4Bo,3Ph}Ca(CCPh)]2 (2) (Scheme
Figure 2. ORTEP drawing of [{F12-Tp4Bo,3Ph}Ca(CCPh)]2 (2). 565
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fluorinated {F12-Tp4Bo,3Ph}− ligand. Finally, the Ca2C2 core is not planar but puckered with an angle of 150° between the C48Ca1C1 and the C1Ca2C48 planes (Figure 4a)). This distortion may be attributed to steric constraints imposed by the bulky {F12-Tp4Bo,3Ph}− ligand. In order to explore the coordination chemistry of the fluorinated {F12-Tp4Bo,3Ph}− ligand with the lighter alkalineearth metal Mg and to investigate the influence of the group 2 metal on the outcome of the reaction, we synthesized the analogous heteroleptic phenylacetylide Mg derivative. We first synthesized the heteroleptic amido complex [{F12-Tp4Bo,3Ph}Mg{N(SiHMe2)2}] (3). Treatment of [Tl{F12-Tp4Bo,3Ph}] with an excess of [Mg{N(SiMe2H)2}2]29 in toluene at 60 °C overnight provided 3 in 96% yield (Scheme 2).
Heteroleptic calcium acetylide complexes normally display dinuclear structures, with the exception of [{BDI}Ca(C CSi(iPr)3)(THF)2] which crystallizes in both mononuclear and dinuclear forms.21 In these compounds, the bridging acetylide moieties adopt either a symmetrical arrangement, with the acetylide ligand perpendicular to the Ca···Ca vector or a nonsymmetrical disposition with each CC unit approaching one of the two Ca centers. The nonsymmetry may be induced either by coordinated ether appendages in the acetylide moiety, as in [{BDI}Ca(μ-CCCH2OR)]2 (R = Me, Ph) complexes,22,23 or by π interaction between the CC moieties and the two Ca atoms. The strength of these interactions is quantified in terms of the M−Cα−Cβ (θ) and the M′−Cα−Cβ (ϕ) angles (Figure 3); for the fully symmetrical coordination θ
Scheme 2. Synthesis of the Mononuclear Complex [{F12Tp4Bo,3Ph}Mg{N(SiMe2H)2}] (3)
Figure 3. Dinuclear acetylide complexes: (a) symmetrical and (b) “side on” coordination of the bridging acetylide units.
= ϕ, whereas for the completely “side on” coordination θ − ϕ = 90°. It has been proposed that large values of θ − ϕ enhance the dissipation of the negative charge of the acetylide over both alkynyl carbons.20 Complex 2 shows an unsymmetrical “side-on” coordination of the acetylide groups, each Ca−CC moiety interacting via π bonding with the second Ca center. Both Ca centers are pentacoordinated with a highly distorted environment (Figure 4a). As shown in Figure 4b, the θ angle for the acetylide based
Compound 3 was characterized by standard analytical/ spectroscopic techniques, and the solid state structure was analyzed by single-crystal X-ray diffraction. This complex proved to be stable in solution, providing no evidence for Schlenk-like redistribution. The 19F NMR spectrum in C6D6 shows four signals at δ −144.0, −152.4, −152.9, and −163.9 for the four benzo fluorine atoms of {F12-Tp4Bo,3Ph}−. In the 1H NMR spectrum at 298 K, the SiH resonance (δ 3.93) is shifted upfield with respect to the free amine (δ 4.71). In the 1H−29Si HMQC 2D NMR spectrum the SiH resonance is observed at δ −18.0 as a doublet with 1JSiH = 180 Hz. No change of the SiH signal was observed by variable-temperature 1H NMR from 298 to 173 K in toluene-d8. Compound 3 exhibits one main νSiH absorption at 2063 cm−1 along with a lower energy shoulder (ca. 2035 cm−1), likely reflecting the presence of a weak Mg··· H−Si agostic interaction. Although the X-ray data were recorded to 72% completeness only, the refined structure is of good quality and shows an unambiguous connectivity. The asymmetric unit of the crystal structure of 3 contains two independent molecules which exhibit a mononuclear structure with different arrangements around the metal center (Figure S6 in the Supporting Information). For the sake of clarity, only one of these two molecules is shown in Figure 5. In each molecule, the Mg is four-coordinate, with an additional Mg···βSi−H agostic distortion, as the two SiMe2H moieties are clearly nonequivalent. This is reflected by the difference between the obtuse Mg1−N7−Si2 and Mg2−N7B−Si4 angles (125.88(12) and 125.50(11)°, respectively) and much more acute Mg1− N7−Si1 and Mg2−N7B−Si3 angles (108.30(9) and 116.98(9)°, respectively), corresponding to much shorter Mg1···Si1 and Mg2···Si3 distances (2.9711(12) and 3.1347(11) Å) with respect to Mg1···Si2 and Mg2···Si4 (3.2637(10) and 3.2672(9) Å). In comparison to the Mg−N
Figure 4. Side view (a) and front view (b) of the Ca2C2 core of complex 2.
on C1 is wider than that based on C48, highlighting a strong π interaction between the C1C2 bond and Ca1 (θ − ϕ = 87.6°). This contrasts with the previously reported heteroleptic complexes, which always displayed two identical “side-on” coordination modes. Apart from the unique case of [{BDI}Ca(μ-CCCH2OR)]2, 2 displays the highest θ − ϕ value reported to date, overcoming that of the most asymmetric structure so far described in [{BDI}Ca{μ-CCCH2N(CH3)2}]2 (θ − φ = 83.4°). In comparison to the phenylacetylide analogue [{BDI}Ca(μ-CCPh)]2 (θ − ϕ = 76.2°), the stronger “side on” CC···Ca1 interaction in 2 likely reflects the higher electron-withdrawing power of the 566
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Tp4Bo,3Ph}MgCCPh] (4) in 80% yield. The complex is very stable in unsaturated hydrocarbons such as benzene and toluene even upon heating to 60 °C for several days. The 19F NMR spectrum of 4 at room temperature showed three overlapping signals assigned to the four benzo fluorines of the {F12-Tp4Bo,3Ph}− ligand at δ −143.2, −152.8, and −163.8. The 13 C NMR spectrum of 4 in benzene-d6 displays the Mg−CCβ resonance at δ 110.6, and we tentatively assign the Mg−CαC resonance to a broad (5 Hz) signal at δ 117. An X-ray diffraction crystal structure has been obtained for 4. The asymmetric unit contains three independent molecules with very similar arrangements around the metal center (Figure S8 in the Supporting Information). One of them is shown in Figure 6 together with relevant bond distances and angles. In
Figure 5. ORTEP drawing of one of the two [{F12-Tp4Bo,3Ph}Mg{N(SiMe2H)2}] (3) molecules of the asymmetric unit. Selected bond lengths (Å) and bond angles (deg): Mg1−N7 1.963(2), Mg1−N2 2.1402(18), Mg1−N4 2.129(2), Mg1−N6 2.167(2), Mg1−Si1 2.9711(12), Mg1−Si2 3.2637(10); Mg1−N7−Si1 108.30(9), Mg1− N7−Si2 125.88(12), Si1−N7−Si2 125.79(13).
bond distances reported for tris(pyrazolyl)methanide30 and BDI-substituted31 hexamethyldisylamido heteroleptic Mg compounds (1.987(2) and 2.0213(9) Å, respectively), the Mg1−N7 bond (1.963(2) Å) is shorter, likely reflecting the electronwithdrawing properties of the {F12-Tp4Bo,3Ph}− ligand. Only two heteroleptic bis(dimethylsilyl)amido Mg complexes have been previously described: the amides [{C(Me2pz)3}Mg{N(SiHMe2)2] and [{L1}MgN(SiHMe2)2] (L1 = −OAr1N(Me)(CH2)2N(Me)Ar2O−), containing the tris(pyrazolyl)methanide and the salan-like tetradentate aminophenolate ligand, respectively.30,32 Only the latter has been characterized by X-ray diffraction: in contrast with compound 3, it contains a five-coordinate Mg center, displaying as a consequence a less distorted structure with Mg−N−Si angles of 114.34(11) and 119.32(11)°. Complex 3 is therefore the first (dimethylsilyl)amido heteroleptic four-coordinate Mg complex structurally characterized. Compound 3 has been used as a precursor for the synthesis of the heteroleptic Mg phenylacetylide species [{F12-Tp4Bo,3Ph}Mg(CCPh)] (4) (Scheme 3). Treatment of 3 with an excess of phenylacetylene in toluene over a period of 5 days at 50 °C, followed by pentane addition and filtration, provided [{F12-
Figure 6. ORTEP drawing (a) and space-filling model (b) (aromatic ring of the acetylide omitted for clarity) of one of the three [{F12Tp4Bo,3Ph}Mg(CCPh)] (4) molecules of the asymmetric unit. Selected bond lengths (Å) and bond angles (deg): Mg1−C1 2.045(3), Mg1−N2 2.139(2), Mg1−N4 2.142(2), Mg1−N6 2.121(2), C1−C2 1.216(4), C2−C3 1.440(4); Mg1−C1−C2 175.8(2), C1−C2−C3 177.5(3).
contrast to other heteroleptic phenylacetylide Mg and Ca compounds,23,33−35 4 crystallizes as a mononuclear species where the Mg atom is four-coordinate in a distorted tetrahedral geometry. The only previous examples of mononuclear phenylacetylide Mg species concern [{dpp-BIAN(H)}Mg(CCPh)(THF)2], obtained by oxidative addition of phenylacetylene through CH bond cleavage.36 In the series of mononuclear heteroleptic Mg acetylide compounds we finally mention a three-coordinate Mg 1-hexynyl species containing the bulky 2,6-bis(diphenylmethyl)-p-tolyl-substituted β-diketiminate ligand ArL−, [{ArL}Mg(CCnBu)].37 Likely due to the electron-withdrawing properties of the fluorinated ligand, the Mg−CC bond lengths in 4, Mg1−C1 = 2.045(3) Å, Mg1A−C1A = 2.037(4) Å, and Mg1B−C1B = 2.053(3) Å, are among the shortest Mg−C bonds and compare well with that reported for the three-coordinate β-diketiminate Mg 1-hexynyl compound (Mg−C = 2.049(3) Å).37 They are significantly shorter than the Mg−Cα bond length reported for the dinuclear phenylacetylide β-diketiminate Mg complex [{BDI}Mg(C CPh)]2 (Mg−Cα = 2.3485(15) and 2.1740(16) Å).23 The Mg− CC moiety is almost linear, the Mg1−C1−C2, Mg1A− C1A−C2A, and Mg1B−C1B−C2B angles measuring 175.8(2), 173.6(3), and 175.7(2)°, respectively. The Cα−Cβ bond length
Scheme 3. Synthesis of the Mononuclear Complex [{F12Tp4Bo,3Ph}Mg(CCPh)] (4)
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Tp4Bo,3Ph}− ligand. Resonances at δ 0.29 and −2.32 are assigned to the SiMe3 and CHSiMe3 groups, respectively. Two pairs of THF signals are observed by 1H NMR at low temperature. They coalesce at room temperature. This exchange process, confirmed by a ROESY experiment (Figure S10 in the Supporting Information), is also responsible for the dynamic behavior of the fluorine signals. In the 19F NMR spectrum of 5 at 223 K, each fluorine signal displays three resonances which coalesce to a single resonance at room temperature (Figure S11 in the Supporting Information). The lability of coordinated THF molecules is common for alkaline-earth complexes;38 this dynamic behavior may often prevent the crystallization of the species. Remarkably, there is no evidence for a Schlenk equilibrium for 5, as this would generate the known homoleptic complex [{F12-Tp4Bo,3Ph*}2Ca] containing rearranged indazolyl groups with a unique NMR signature.27 13 C NMR signals were assigned by 2D HMQC and HMBC NMR experiments. Two signals corresponding to the {CH(SiMe3)2}− moiety at δ 17.1 (d, 1JCH = 89 Hz, Ca−CH) and δ 5.7 (q, 1JCH = 116 Hz, SiMe3) were observed. The 1JCαH coupling constant for 5 has a very low value (1JCH = 89 Hz), similar to that for [Ca{CH(SiMe3)2}2(THF)2] (1JCH = 96 Hz).39 These low values are more likely due to a large p orbital contribution in the CH bond than to the presence of an agostic C−H interaction. The X-ray structure of [Ca{CH(SiMe3)2}2(THF)2],39 indeed, does not show any agostic Ca···C−H distortion. In order to probe the formation and reactivity of the Ca−C bond in 5, 2 bar of 13CO2 was added to a toluene-d8 solution of complex 5 in a NMR tube at −80 °C. The reaction mixture immediately changed from red to orange and finally to pale yellow. The 19F, 1H, and 13C NMR spectra indicate the formation of [{F12-Tp4Bo,3Ph}Ca{O213CCH(SiMe3)2}(THF)x] (6) as the major product (Scheme 5). Again, no Schlenk equilibrium was detected.
(1.216(4) Å) is fully similar to that observed in the dinuclear βdiketiminate Mg analogue [{BDI}Mg(CCPh)]2 (1.222(2) Å). As shown in the space-filling model in Figure 6b, the monomeric nature of 4 is likely due to both the small size of the Mg2+ center and the large steric hindrance of the fluorinated tris(indazolyl)borate ligand, which encapsulates the metal in a pocket-like structure. The different structures obtained for the Ca and Mg phenylacetylide compounds, therefore, highlight how the alkaline-earth chemistry depends on the fine tuning of three important parameters: the hardness of the metal, the steric hindrance and the Lewis basicity of the ligand. We next investigated the influence of the alkyl group on the nature and properties of the corresponding heteroleptic alkyl calcium complexes, performing the synthesis of heteroleptic {F12-Tp4Bo,3Ph}Ca species containing the {CH(SiMe3)2}− functionality. Treatment of [{F12-Tp4Bo,3Ph}Tl] with an excess of [Ca{CH(SiMe3) 2}2(THF)2] in toluene afforded the heteroleptic complex [{F12-Tp4Bo,3Ph}Ca{CH(SiMe3)2}(THF)] (5) within 5 min (Scheme 4). The formation of a black Scheme 4. Synthesis of the Mononuclear Complex [{F12Tp4Bo,3Ph}Ca{CH(SiMe3)2}(THF)] (5)
precipitate was observed during the course of the reaction. This precipitate is most probably metallic Tl originating from the decomposition of [Tl{CH(SiMe3)2}]. Compound 5 is extremely sensitive to the temperature, decomposing readily at room temperature; it has to be stored at −40 °C. All attempts to isolate 5 were unsuccessful. Furthermore, due to its high solubility, addition of pentane to a concentrated solution of the crude reaction mixture at −40 °C failed to precipitate 5, precluding any attempt at purification. Complex 5 is bright red in solution, and the disappearance of the color was always associated with its decomposition. Characterization of complex 5 includes 1H, 19F, and 13C 1D and 2D NMR spectra in toluene-d8. Experiments were usually performed at 223 K to avoid decomposition, although fast 1H or 19F NMR experiments could be also carried out at room temperature. The 19F and 1H NMR spectra of 5 at room temperature show only one set of signals for each type of fluorine and protons of the {F12-Tp4Bo,3Ph}− ligand, indicating a symmetrical disposition of the three indazolyl moieties in solution. The 1H NMR spectrum of the crude reaction mixture reveals the formation of 5 as the major product. Among the byproducts, the [Ca{CH(SiMe3)2}2(THF)2] precursor (usually added in slight excess in order to fully complete the reaction) and CH2(SiMe3)2 (originating from the decomposition of [Tl{CH(SiMe3)2}]) can be identified (Figure S9 in the Supporting Information). Complex 5 displays the characteristic 1 H NMR resonances of the phenyl groups in the {F12-
Scheme 5. Synthesis of the Mononuclear Complex [{F12Tp4Bo,3Ph}Ca{O213CCH(SiMe3)2}(THF)x] (6)
Complex 6 decomposes rapidly at room temperature in solution to give several products and a yellowish solid. Due to the extreme sensitivity of 6 to temperature, no isolation was attempted. Among the byproducts, CH2(SiMe3)2, derived from the synthesis of 5, and traces of [Ca{O 2 1 3 CCH(SiMe3)2}2(THF)2], resulting from the insertion of 13CO2 into the Ca−C bond of the [Ca{CH(SiMe3)2}2(THF)2] precursor, could be identified in the 1H NMR spectra of the crude reaction mixture (Figures S13 and S14 in the Supporting Information). Salient features of the 1H NMR of 6 include one doublet (δ 1.12, 2J13CH = 8 Hz) for the CH proton of 13CO2− CH(SiMe3)2 and one singlet (δ 0.06) for the SiMe3 groups. In the 13C NMR spectrum, the carboxylate resonance Ca−O213C 568
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Article
Organometallics of 6 is observed at δ 188.3 as a doublet (2JCH = 8 Hz). We assign the signal at δ 4.62 (d, 1JCC = 99 Hz) to the methine carbon of CH(SiMe3)2 and the signal at δ 1.33 (d, 3JCC = 17 Hz) to the SiMe3 carbons. The absence of the Schlenk equilibrium for both complexes 5 and 6 is a rare and remarkable feature for organocalcium compounds, which can be ascribed to the use of the original highly fluorinated tris(indazolyl) ligand.
complex 2 (95% yield). Complex 2 is temperature sensitive. Crystals suitable for X-ray diffraction analysis were obtained from a saturated toluene/hexane solution of 2 at −40 °C. 1H NMR (400 MHz, toluened8, 298 K): δ 7.56 (d, 12H, 3JHH = 7.3 Hz, TpF, o-C6H5), 6.96 (t, 12H, 3 JHH = 7.7 Hz, TpF, m-C6H5), 6.81 (t, 6H, 3JHH = 7.5 Hz, TpF, pC6H5), 6.61 (t, 2H, 3JHH = 7.5 Hz, PhCC−, p-C6H5), 6.53 (t, 4H, 3JHH = 7.5 Hz, PhCC−, m-C6H5), 6.23 (d, 4H, 3JHH = 7.1 Hz, PhCC−, oC6H5). 19F NMR (376 MHz, toluene-d8, 298 K): δ −143.97 (t, 6F, JFF = 16.8 Hz, F-4), −151.42 (br, 6F, F-6), −154.37 (t, 6F, JFF = 17.3 Hz, F-7), −164.44 (t, 6F, JFF = 20.1 Hz, F-5). 1H NMR (400 MHz, toluene-d8, 233 K): δ 7.56 (d, 12H, 3JHH = 6.6 Hz, TpF, o-C6H5), 6.96 (t, 12H, 3JHH = 7.5 Hz, TpF, m-C6H5), 6.76 (t, 6H, 3JHH = 7.4 Hz, TpF, p-C6H5), 6.62 (br, 2H, PhCC−, p-C6H5), 6.49 (br, 4H, PhCC−, mC6H5), 6.25 (br, 4H, PhCC−, o-C6H5). 19F NMR (376.44 MHz, toluene-d8, 233 K): δ −143.64 (br, 6F, F-4), −151.15 (br, 6F, F-6), 154.11 (br, 6F, F-7), −164.10 (t, 6F, JFF = 20.5 Hz, F-5). 13C{1H19F} NMR (100.62 MHz, toluene-d8, 233 K): δ 148.57 (IndH, C-3), 131.19 (IndH, ipso-C6H5, C-10), 130.07 (PhCC−, o-C6H5), 130.01 (IndH, pC6H5, C-13), 129.77 (IndH, o-C6H5, C-11), 129.17 (IndH, m-C6H5, C12), 128.01 (PhCC−, p-C6H5), 127.15 (PhCC−, m-C6H5), 124.00 (PhCC−, ipso-C6H5), 119.30 (PhCC, Cβ). Elemental analysis failed due to the extreme sensitivity of the complex. Synthesis of [{F12-Tp4Bo,3Ph}Mg{N(SiHMe2)2}] (3). [Mg{N(SiMe2H)2}2] (740 mg, 2.56 mmol, 3.5 equiv) and [Tl{F12-Tp4Bo,3Ph}] (724 mg, 0.716 mmol, 1 equiv) were combined in a Schlenk flask with 20 mL of toluene. The mixture was stirred at 60 °C overnight and darkened as Tl(0) started to precipitate. Filtering, drying under vacuum, and washing with 3 × 3 mL of pentane afforded an analytically pure white powder of [{F12-Tp4Bo,3Ph}Mg{N(SiHMe2)2}] (3; 664 mg, 0.689 mmol, 96% yield). 1H NMR (400 MHz, C6D6, 298 K): δ 7.55 (d, 6H, 3JHH = 7.0 Hz, o-C6H5), 7.35 (t, 6H, 3JHH = 7.7 Hz, m-C6H5), 7.25 (t, 3H, 3JHH = 7.2 Hz, p-C6H5), 6.50 (bs, 1H, BH), 3.93 (sept., 2H, 3JHH = 2.9 Hz, SiMe2H), −0.30 (d, 12 H, 3JHH = 2.9 Hz, SiMe2H). 19F NMR (377 MHz, C6D6, 298 K) δ −144.02 (t, 3F, JFF = 19.1 Hz, F), −152.39 (q, 3F, JFF = 8.4 Hz, F), −152.88 (t, 3F, JFF = 18.7 Hz, F), −163.91 (t, 3F, JFF = 20.0 Hz, F). 13C{1H} NMR (100.6 MHz, C6D6, 298 K) δ 130.74 (p-C6H5), 130.29 (o-C6H5), 129.52 (mC6H5), 4.02 (SiMe2H). 29Si NMR (79.49 MHz, C6D6, 298 K) δ −18.0 (d sext., 1JSiH = 180 Hz, 2JSiH = 6.7 Hz, SiH). Anal. Calcd for C43H30BF12MgN7Si2: C, 53.57; H, 3.14; N, 10.17. Found: C, 53.69; H, 3.26; N, 10.0. Crystals suitable for XRD analysis were obtained by slow diffusion of pentane in a concentrated solution of 3 in toluene at room temperature. Synthesis of [{F12-Tp4Bo,3Ph}Mg(CCPh)] (4). [{F12-Tp4Bo,3Ph}Mg{N(SiHMe2)2}] (3; 130 mg, 0.135 mmol, 1 equiv) was dissolved in a mixture of toluene (3 mL) and phenylacetylene (88 mg, 0.86 mmol, 6.4 equiv). The medium was heated at 50 °C for 5 days. The solution was concentrated under vacuum, pentane (10 mL) was slowly added, and the resulting solution was stored at −40 °C. After 3 days, a white crystalline powder had precipitated. It was filtered, washed with 3 × 1 mL of pentane, and gently dried under vacuum to give pure 4 (102 mg, 0.107 mmol, 80% yield). 1H NMR (400 MHz, C6D6, 298 K): δ 7.63 (d, 6H, 3JHH = 7.5 Hz, TpF, o-C6H5) 7.39 (d, 2H, 3JHH = 8.2 Hz, o-C6H5-CC), 7.25 (m, 8H, TpF, m-C6H5 and m-C6H5-CC), 7.13 (m, 4H, TpF, p-C6H5 and p-C6H5-CC), 6.54 (bs, 1H, BH). 19F NMR (377 MHz, C6D6, 298 K) δ −143.16 (t, 3F, JFF = 18.7 Hz, F), −152.85 (m, 6F, F and F) −163.82 (t, 3F, JFF = 19.0 Hz, F). 13C{1H} NMR (100.6 MHz, C6D6, 298 K): δ 131.99 (o-C6H5-CC), 130.71 (p-C6H5), 130.36 (o-C6H5), 129.28 (m-C6H5), 128.17 (m-C6H5-CC), 126.33 (p-C6H5CC), 110.64 (C6H5-CβC). Anal Calcd for C47H21BF12MgN6: C, 60.52; H, 2.27; N, 9.01. Found: C, 60.30; H, 2.19; N, 8.87. Crystals suitable for XRD analysis were obtained by slow diffusion of pentane in a concentrated solution of 4 in toluene at −40 °C. Synthesis of [{F12-Tp4Bo,3Ph}Ca{CH(SiMe3)2}(THF)] (5). [{F12Tp4Bo,3Ph}Tl] (0.094 g, 0.093 mmol) and [Ca{CH(SiMe3)2}2(THF)2] (0.06 g, 0.139 mmol) were combined in a flask into the glovebox, and deuterated toluene (1.5 mL) was added with stirring at room temperature. The mixture became instantaneously a red solution, changing after 5 min of stirring to a black slurry (precipitation of metallic Tl). The solution was filtered, placed in a Young NMR tube,
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CONCLUSION Highly fluorinated 3-phenyl hydrotris(indazolyl)borate-supported calcium and magnesium phenylacetylide complexes have been reported and structurally characterized. In the case of calcium, a dinuclear complex displaying an extremely distorted structure is formed. The complex contains a nonsymmetrical Ca2C2 core with two different Ca···CC π interactions. This highly distorted structure is due to the electropositive character of the Ca atoms, probably enhanced by the highly electron withdrawing and steric properties of the fluorinated ligand. When the smaller magnesium center is involved, a mononuclear phenylacetylide complex is formed. The synthesis and characterization of [{F12-Tp4Bo,3Ph}Ca{CH(SiMe3)2}(THF)], a rare heteroleptic alkyl calcium complex, has been also performed. Although its isolation was not possible owing to stability issues, its reactivity toward 13CO2 in an NMR-scale reaction yielded the carboxylate complex [{F12-Tp4Bo,3Ph}Ca{O213CCH(SiMe3)2}(THF)x], resulting from the insertion of CO2 into the Ca−C bond.
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EXPERIMENTAL SECTION
All operations were performed with rigorous exclusion of air and moisture, using standard Schlenk, high-vacuum, and glovebox (Jacomex GP Concept) techniques under Ar (O2
