Coordination Chemistry of [E(Idipp)]2+ Ligands (E = Ge, Sn): Metal

Apr 12, 2017 - The synthesis and full characterization of the NHC-stabilized tungstenochlorostannylene [Cp*(CO)3W–SnCl(Idipp)] (1Sn), the NHC-stabil...
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Coordination Chemistry of [E(Idipp)]2+ Ligands (E = Ge, Sn): Metal Germylidyne [Cp*(CO)2WGe(Idipp)]+ and Metallotetrylene [Cp*(CO)3W−E(Idipp)]+ Cations Yury N. Lebedev,*,§ Ujjal Das, Gregor Schnakenburg, and Alexander C. Filippou* Institut für Anorganische Chemie, Universität Bonn, Gerhard-Domagk-Str. 1, 53121 Bonn, Germany S Supporting Information *

ABSTRACT: The synthesis and full characterization of the NHCstabilized tungstenochlorostannylene [Cp*(CO) 3 W−SnCl(Idipp)] (1Sn), the NHC-stabilized chlorogermylidyne complex [Cp*(CO)2WGeCl(Idipp)] (2), the tungsten germylidyne complex salt [Cp*(CO)2WGe(Idipp)][B(C6H3-3,5-(CF3)2)4] (3), and the cationic metallostannylene [Cp*(CO)3W−Sn(Idipp)][Al(OC(CF3)3)4] (4Sn) are reported (Idipp = 2,3dihydro-1,3-bis(2,6-diisopropylphenyl)-1H-imidazol-2-ylidene, Cp* = η5-C5Me5). Metathetical exchange of SnCl2(Idipp) with Li[Cp*W(CO)3] afforded selectively 1Sn. Photolytic decarbonylation of the Ge analogue [Cp*(CO)3W−GeCl(Idipp)] (1Ge) afforded the NHC-stabilized chlorogermylidyne complex (2), featuring a trigonal-planar coordinated germanium center and a W−Ge double bond (W−Ge 2.3496(5) Å). Chloride abstraction from 2 with Na[B(C6H3-3,5-(CF3)2)4] yielded the germylidyne complex salt 3, which contains an almost linear W−Ge−C1 linkage (angle at Ge = 168.7(1)°) and a W−Ge triple bond (2.2813(4) Å). Chloride elimination from 1Ge afforded the tungstenogermylene salt [Cp*(CO)3W−Ge(Idipp)][B(C6H3-3,5-(CF3)2)4] (4Ge), which in contrast to 1Ge could not be decarbonylated to form 3 despite the less strongly bound carbonyl ligands. The tin compounds 1Sn and 4Sn did not afford products bearing multiple W−Sn bonds. Treatment of 4Ge with Me2NCCNMe2 yielded unexpectedly the neutral germyl complex 5 containing a pendant 1-germabicyclo-[3,2,0]-hepta-2,5-diene ligand instead of the anticipated [2 + 1]cycloaddition product at the Ge-center.

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INTRODUCTION In recent years, following the seminal discovery of [E(η5C5Me5)]+ (E = Si − Pb)1 by Jutzi et al., many research initiatives have been devoted to the development of Lewis basestabilized aryl-,2 alkyl-,3 halo-,4 and amino-5 tetryliumylidenes.6 This continuously growing interest arises mainly from the fact that tetryliumylidenes are highly reactive Lewis ambiphilic species containing four valence electrons. Isolation of these extraordinarily reactive classes of compounds, in particular, twocoordinate base-stabilized tetryliumylidenes (A, Chart 1a), relies on the successful implementation of monoanionic X-type and neutral L-type ligands,7 which provide steric and electronic stabilization of the highly reactive tetrel(II)-cations.3a,4e,5e In our recent studies on the NHC-stabilized phosphasilenylidene (Idipp)SiPMes* and a series of expository communications on the reactivities of Si2(Idipp)2, it was shown that [Si−Idipp]/ aryl-phosphinidenes ([P−Ar]) and imidazoliumyl-silyliumylidene ([Si−Idipp]2+)/aryl-silyliumylidene ([Si−Ar]+) are isolobal pairs.8 In a more general view, consideration of the molecular fragments EX+ and EL2+ as isolobal pairs lets one extend the isolobal concept to the series of compounds A−C as shown in Chart 1a, where [(η5-C5H5)M(CO)3]− is an 18valence-electron (VE) transition metal fragment. Following the continuous effort in advancing the chemistry of aryl-tetryliumylidenes ([E−Ar]+) as ligands for transition metals,9−11 we presumed that the isolobal series (Chart 1a) © 2017 American Chemical Society

could be extended to the transition metal compounds C, in which the imidazoliumyl-tetryliumylidene ligand [E−Idipp]2+ can be viewed as a 2e-acceptor ligand (Z-type ligand).7 In fact, the first example of a class C compound, the [Cp*(CO)3CrSi(SIdipp)]+ was synthesized recently by our group (Chart 1b).12,13 We have also succeeded in demonstrating that [Cp*(CO)3CrSi(SIdipp)]+ serves as a precursor for the synthesis of the first three-coordinate silanone derivative.12a The reactivity of the analogous germanium compound [Cp(CO)3WGe(NHC)]+ has been studied recently by Tobita and co-workers, and the potential of these compounds in bond activation and sterically controlled dimerization processes at the Ge-center affording dimetalla-digermenes was demonstrated.14 Compounds of class C are isolobal with the neutral metallotetrylenes of the general formula [LnM(E−Ar)], where [E−Ar]+ is a 2e-acceptor ligand and [LnM]− is a 18 VE fragment.15 To another novel class of tetrylium-ylidene complexes belongs the cationic silylidyne complex [Cp*Cr(CO)2Si(SIdipp)]+ (class D) in which the X group in a class A compound is formally replaced by the 15VE fragment [Cp*Cr(CO)2]. According to quantum chemical bonding analyses, the MSi bonding in D can be rationalized by the conventional Dewar−Chatt−Duncanson model and is reminisReceived: February 13, 2017 Published: April 12, 2017 1530

DOI: 10.1021/acs.organomet.7b00110 Organometallics 2017, 36, 1530−1540

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Organometallics

Chart 1. (a) Isolobal Analogy in Ylene Chemistry (X− = Monoanionic 2e-Donor Ligand, L = Neutral 2e-Donor Ligand); (b) Carbonylation of a Chromium Silylidyne Complex to a Cationic Chromiosilylenea

a

Formal charges are not shown.

cent of the Fischer carbyne complexes and other tetrylidyne complexes of general formula [LnME−Ar].9,12 These studies highlight the possibility of a dicationic [E−NHC]2+ ligand to alter its electronic properties (electrophilic in class D and ambiphilic in class C) as a function of the coordination number of the transition metal. Herein we report our further advances in the syntheses, complete characterization and reactivity studies of the germanium and tin homologues of [Cp*(CO)nWE(Idipp)]+ (n = 2, 3; E = Ge, Sn).16

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RESULTS AND DISCUSSION Entry to the chemistry presented below was provided by the NHC-stabilized metallochlorotetrylidenes 1Ge and 1Sn. Complex 1Ge was obtained from GeCl2(Idipp) and Li[Cp*W(CO)3] in n-hexane following a similar, recently reported protocol.14a The analogous tin compound [Cp*(CO)3W− SnCl(Idipp)] (1Sn) was prepared as 1Ge upon treatment of SnCl2(Idipp) with Li[Cp*W(CO)3] in n-hexane and isolated after workup and crystallization from a n-hexane/toluene mixture (3:1, v/v) at −60 °C as a yellow-orange powder in 71% yield. In comparison, the reactions of SiX2(NHC) (X = Br, I; NHC = Idipp, SIdipp) with Li[Cp*M(CO)3] (M = Cr−W) in toluene were previously shown to afford after CO-elimination the dicarbonyl complexes [Cp*(CO)2MSiX(NHC)] without any evidence for the intermediate formation of the Si analogues of 1Ge and 1Sn, [Cp*(CO)3M−SiX(NHC)].12a,13 Compound 1Sn is well soluble in benzene or toluene, partially soluble in nhexane, and decomposes upon melting at 139 °C. It was characterized by X-ray crystallography, IR, NMR spectroscopies, and elemental microanalysis. Suitable yellow-orange single crystals of 1Sn were obtained upon cooling a saturated nhexane/toluene (4:1, v/v) solution from ambient temperature to −30 °C. A DIAMOND plot of the molecular structure of 1Sn is depicted in Figure 1. The “four-legged-piano-stool” complex features a trigonal-pyramidal, stereogenic Sn center (sum of bond angles at Sn: 309.75°). The calculated degree of the tin center’s pyramidalization (DP)17 of 56% is considerably smaller than that of NHCstabilized chlorostannylenes (DP = 71% − 89%).18,19 The W− Sn bond length (2.9513(4) Å) is slightly longer than those of the two-coordinate tungstenostannylenes [Cp(CO)3WSn(ArMes)] (2.911(1) Å; ArMes = C6H3-2,6-(C6H2-2,4,6-Me3)) and [Cp(CO)3WSn(ArTrip)] (2.9030(8) Å, ArTrip = C6H3-2,6(C6H2-2,4,6-iPr3)) probably due to the higher coordination number.20 The Sn−C1 bond length (2.380(3) Å) is also slightly elongated in comparison to that of SnCl2(Idipp) (Sn− C1: 2.341(8) Å)18 and also longer than those of other NHCstabilized neutral chlorostannylenes reported in the literature.19

Figure 1. DIAMOND plot of the molecular structure of the complex 1Sn. Thermal ellipsoids are set at 50% probability level. Hydrogen atoms and the iPr-groups are omitted for clarity. The dotted line connects the W atom with the centroid Cg of the η5-bonded C5Me5 ring. Selected bond lengths [Å] and bond angles [°]:W−Sn2.9514(4), Sn−Cl 2.481(1), Sn−C1 2.380(3), W−Cg 2.025(1), W− C4 1.967(4), C4−O1 1.166(5), W−C5 1.952(4), C5−O2 1.163(4), W−C6 1.969(4), C6−O3 1.163(5), C1−N1 1.364(4), N1−C2 1.382(4), C2−C3 1.342(5); W−Sn−C1 111.37(8), W−Sn−Cl 101.36(3), C1−Sn−Cl 97.02(8), C4−W−C6 105.5(2), C5−W−Sn 134.8(1), N1−C1−N2 103.8(3), C1−N1−C2 111.4(3), N1−C2−C3 106.3(3), W−C4−O1 170.7(3), W−C5−O2 176.5(3), W−C6−O3 174.8(3); torsion angle [°]: C5−W−Sn−C1 6.2(2).

The Sn−Cl bond length (2.481(1) Å) is also longer than those of SnCl2(Idipp) (2.439(3) and 2.426(2) Å),18 but it compares well with that of the NHC-stabilized aminochlorostannylene [(dippNH)SnCl(Idipp)] (Sn−Cl: 2.4898(6) Å).19b The IR spectrum of 1Sn in n-hexane solution displays three ν(CO) bands at 1955, 1888, and 1835 cm−1, which appear at slightly lower wavenumbers than those of 1Ge (1958, 1890, and 1842 cm−1 in n-hexane). Because of the presence of the stereogenic tin center, the lateral CO ligands in 1Sn are diastereotopic giving rise to two different CO resonances in the 13C{1H} NMR spectrum. Remarkably, the 119Sn{1H} NMR signal of 1Sn (δ = 455.6 ppm, 1J(183W,Sn) = 80.6 Hz) is extremely downfield shifted compared to those of other neutral, threecoordinated NHC-stabilized chlorostannylenes (δ (ppm): (−61.5) − (−96.2) ppm).18,19 Irradiation of 1Ge in diethyl ether solution was accompanied by a fast color change from yellow-orange to yellow-brown and finally to brown-black (Scheme 1). Monitoring of the reaction by IR spectroscopy showed the selective transformation of 1Ge to the NHC-stabilized chlorogermylidyne complex 2 (Scheme 1531

DOI: 10.1021/acs.organomet.7b00110 Organometallics 2017, 36, 1530−1540

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Organometallics Scheme 1. Syntheses of the Ionic Tungsten Germylidyne Complex 3 and the Ionic Tungstenotetrylenes 4Ge and 4Sn

Figure 2. DIAMOND plot of the molecular structure of 2. Thermal ellipsoids are set at 50% probability level. Hydrogen atoms and the iPrgroups are omitted for clarity. The dotted line connects the W atom with the centroid Cg of the η5-bonded C5Me5 ring. Selected bond lengths [Å] and bond angles [°]: W−Ge 2.3496(5), Ge−Cl 2.247(1), Ge−C1 2.025(4), W−Cg 1.996(1), W−C4 1.945(6), C4−O1 1.177(6), W−C5 1.933(6), C5−O2 1.184(6), C1−N1 1.354(5), N1−C2 1.389(5), C2−C3 1.334(6); W−Ge−C1 139.9(1), W−Ge− Cl 125.34(4), C1−Ge−Cl 93.7(1), Ge−W−C4 97.2(1), Ge−W−C5 89.8(1), C4−W−C5 85.5(2), N1−C1−N2 106.1(4), C1−N1−C2 109.6(4), N1−C2−C3 107.4(4), W−C4−O1 173.3(4), W−C5−O2 175.4(4).

1). However, conversion of 1Ge to 2 was not complete even after prolonged irradiation presumably due to increasing absorption of the UV-light by the product. Compound 2 could be however separated from the starting material 1Ge by taking advantage of its lower solubility in aromatic solvents, and it was isolated in 56% yield as red brown, thermally robust crystals (mp 177 °C). Compound 2 is well soluble in benzene, toluene, THF, slightly soluble in diethyl ether and almost insoluble in n-hexane. Attempts to obtain an analogous tin compound under similar conditions failed, and only extensive decomposition of 1Sn was observed during photolysis. The solid-state structure of 2 was determined by single-crystal X-ray diffraction analysis. Suitable red-brown crystals of the diethyl ether solvate 2·0.25(Et2O) were obtained upon cooling a Et2O solution of 2 to −30 °C. A DIAMOND plot of the molecular structure of 2 with selected bond lengths and angles is presented in Figure 2 and in Table 1. The “three-legged pianostool” complex features a trigonal planar coordinated germanium center with the chlorine atom pointing toward the Cp* ligand. The W−Ge bond (2.3496(5) Å, Table 1) is even shorter than that found in [Cp(CO)2WGe(IMe4)C(SiMe3)3] (2.4004(5) Å)11 or [Cp*CO)2(H)WGe(H)C(SiMe3)3] (2.4289(8) Å),21 and is the shortest W−Ge double bond reported to date, revealing a particularly strong W → Ge π back-donation. Shortening of the Ge−Cl (2.247(1) Å) and Ge−C1 (2.025(4) Å) bonds in 2 compared to those in the starting material 1Ge (Ge−Cl 2.308(1) Å, Ge−C1 2.158(3) Å) can be rationalized with a rehybridization of the germanium valence orbitals (Table 1). The IR spectrum of 2 displays two ν(CO) absorption bands (1882 and 1802 cm−1 in toluene) of almost equal intensity corresponding to the A′ symmetric and the A″ antisymmetric stretching modes, respectively. These bands appear at a very close position to those of the analogous silicon compounds [Cp*(CO)2MSiX(NHC)] (1887, 1806 cm−1 (M = Cr, X = I, NHC = Idipp); 1890, 1808 cm−1 (M = Mo, X = I, NHC = Idipp); 1883, 1799 cm−1 (M = W, X = Br, NHC = SIdipp), all

values in toluene solution).13 The 1H NMR spectrum of 2 shows two doublets and one septet for the iPr groups of the Idipp ligand suggesting a free rotation of the NHC substituent about the Ge−C1 bond and an overall Cs symmetry of complex 2 in solution. In the 13C{1H} NMR spectrum, the carbene carbon signal (δ = 175.8 ppm) appears slightly upfield shifted relative to that in 1Ge (δ = 177.9 ppm) and GeCl2(Idipp) (δ = 179.9 ppm) (Table 1). It is noteworthy that the Ccarbene signal of 2 appears at significantly lower field than those of the silicon congeners [Cp*Cr(CO)2SiI(Idipp)] (δ = 157.1 ppm in benzene-d6)13 and [Cp*(CO)2MoSiI(Idipp)] (δ = 159.3 ppm in benzene-d6),13 which are closer to that of [IdippH]Br (δ = 140.3 ppm in dichloromethane-d2).22 The Ccarbonyl resonance appears as a singlet (δ = 232.7 ppm) at identical position to that of [Cp*(CO)2WSiBr(SIdipp)] (δ = 232.3 ppm in benzene-d6)13 but at lower field than that of the tungsten germylidyne complexes [Cp*(CO) 2 WGeC(SiMe3)3] (δ = 224.9 ppm in benzene-d6)21a and [Cp*(CO)2WGeArMes] (δ = 224.0 ppm in benzene-d6),16 confirming the stronger metal−carbonyl back-bonding in 2. Addition of Na[B(C6H3-3,5-(CF3)2)4] to a fluorobenzene solution of 2 was not accompanied by an obvious color change. However, monitoring of the reaction course by IR spectroscopy showed that the ν(CO) absorption bands of 2 were rapidly replaced by those of a new dicarbonyl complex (Scheme 1). The product was isolated after workup and crystallization from diethyl ether as a red-brown solid in 61% yield and was identified as the germylidyne complex salt 3. Compound 3 melts at 147 °C without decomposition and is also stable in fluorobenzene, chlorobenzene or diethyl ether solutions. It is, however, unstable in THF solution with the first signs of decomposition appearing after ca. 4 h according to 1H NMR spectroscopy. The solid-state structure of 3 was determined by single-crystal X-ray diffraction analysis. Suitable red-brown 1532

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Organometallics Table 1. Selected Spectroscopic and X-ray Crystallographic Data of 1−4 complex [Cp*(CO)3W−GeCl(Idipp)]a,g [Cp*(CO)3W−SnCl(Idipp)]b [Cp*(CO)2WGeCl(Idipp)]a [Cp*(CO)2W≡Ge(Idipp)]Ac [Cp*(CO)3W−Ge(Idipp)]Ad,g [Cp*(CO)3W−Sn(Idipp)]A′e

1Ge 1Sn 2 3 4Ge 4Sn

δ C2 [ppm]

δCO [ppm]

ν(CO) [cm−1]f

M−E/E−C [Å]

∠M−E−C [°]

177.9 178.7 175.8 176.8 186.0 193.1

218.3, 222.3, 228.3 217.7, 222.4, 226.3 232.7 218.5 215.8 214.3 (1J(W,C) = 155.8 Hz)

1951 (vs), 1878 (vs), 1838 (s) 1948 (vs), 1876 (vs), 1832 (s) 1878 (vs), 1800 (vs) 1963 (vs), 1902 (vs) 1998 (vs), 1929 (s), 1897 (vs) 1987 (vs), 1912 (vs), 1879 (s)

2.7927(4)/2.158(3) 2.9514(4)/2.380(3) 2.3496(5)/2.025(4) 2.2813(4)/1.952(4) 2.5850(7)/2.055(5) 2.8029(4)/2.287(4)

114.09(9) 111.37(8) 139.9(1) 168.7(1) 116.9(2) 110.7(1)

a NMR data in benzene-d6 at 298 K; bNMR data in toluene-d8 at 253 K; cA = [B(C6H3-3,5-(CF3)2)4], NMR data in chlorobenzene-d5 at 298 K; dA = [B(C6H3-3,5-(CF3)2)4], NMR data in THF-d8 at 298 K; eA′ = [Al(OC(CF3)3)4], NMR data in fluorobenzene-d5. fAll IR spectra were recorded in fluorobenzene solution; gThe structures of 1Ge and 4Ge have been deposited as private communication to the CCDC database under CCDC1538855 and CCDC-1538856.

(1.945(7) Å)21a bearing a single covalent Ge−C bond. The same trend was observed in related silylidyne complexes.12a The IR spectrum of 3 shows in solution and in the solid-state two ν(CO) absorption bands, which appear at much higher wavenumbers than those of 2 and reflect the decrease of the electron density at the metal center in 3 versus 2 (Table 1). A comparison of the ν(CO) absorption bands of 3 (1963 and 1902 cm−1 in fluorobenzene) with those of [Cp*(CO)2W GeC(SiMe3)3] (1911 and 1841 cm−1 in C6D6)11 and [Cp*(CO)2WGeArMes] (1918 and 1855 cm−1 in toluene)16 reveals a considerable shift to higher wavenumbers by ca. 50 cm−1, and it indicates that the [Ge(Idipp)]2+ ligand has a significantly lower σ-donor/π-acceptor ratio than the corresponding [Ge−R]+ ligands (R = m-terphenyl, C(SiMe3)3). Previously phosphoniocarbyne complexes, such as [Cl2(CO)2(PMePh2)WCPPh3],23 [CpCl2NbCPPh3],24 and [Tp′(CO)2WCPMe2Ph][PF6] (Tp′ = κ3-N,N′,N″hydridotris(3,5-dimethyl-1-pyrazolyl)borate),25 were isolated and structurally characterized. These compounds can be considered as carbon congeners of 3 bearing a phosphane instead of a NHC substituent. Notably, the same shift (ca. 50 cm−1) to higher values is observed for the ν(CO) absorption bands of [Tp′(CO)2WC(PMe2Ph)][PF6] (2022 and 1934 cm−1 in acetonitrile) versus those of [Tp′(CO)2WC(C6H44-Me)] (1974 and 1888 cm−1 in n-hexane)26 as that found for the Ge compounds described above. Chloride abstraction from 1Ge with Na[B(C6H3-3,5(CF3)2)4] afforded the metallogermylene salt 4Ge, which was isolated as a green, thermally robust solid in 79% yield. Similarly, treatment of 1Sn with Li[Al{OC(CF3)3}4] afforded the analogous green metallostannylene salt [Cp*(CO)3W− Sn(Idipp)][Al(OC(CF3)3)4] (4Sn) in 65% yield (Scheme 1). 4Ge is stable in diethyl ether, chloro-, and fluorobenzene for 2 days and also stable in THF for at least 10 h at ambient temperature, in sharp contrast to the tin analogue which decomposes in THF already at −20 °C. Attempts to obtain 3 by photochemical or thermal decarbonylation of 4Ge surprisingly failed despite the fact that, that the CO ligands in the cationic metallogermylene 4Ge are weaker bound than those in 1Ge according to IR spectroscopy (Scheme 1, Table 1). Similarly, thermolysis or photolysis of 4Sn did not provide any evidence for the formation of a tin analogue of 3Ge. The solid-state structure of 4Sn was determined by singlecrystal X-ray diffraction analysis. Suitable green crystals of the benzene hemisolvate 4Sn·0.5(C6H6) were obtained upon cooling a n-hexane/fluorobenzene/benzene solution (1:3:0.5, v/v/v) of 4Sn to −30 °C. The scXRD of 4Sn shows that the electrophilic metallostannylene cations are well separated from

crystals of the diethyl ether monosolvate 3·(Et2O) were obtained upon cooling a hexane/Et2O solution (1:3, v/v) of 3 to −30 °C. The scXRD of 3 shows that the counterions are well-separated. A DIAMOND plot of the molecular structure of the metal germylidyne complex cation is presented in Figure 3

Figure 3. DIAMOND plot of the molecular structure of the germylidyne complex cation in 3. Thermal ellipsoids are set at 50% probability level. Hydrogen atoms and the iPr-groups are omitted for clarity. The dotted line connects the W atom with the centroid (Cg) of the η5-bonded C5Me5 ligand. Selected bond lengths [Å] and bond angles [°]: W−Ge 2.2813(4), Ge−C1 1.952(4), W−Cg 1.987(1), W− C4 1.983(5), C4−O1 1.147(6), W−C5 1.953(5), C5−O2 1.163(6), C1−N1 1.343(5), N1−C2 1.369(5), C2−C3 1.355(5); W−Ge−C1 168.7(1), Ge−W−C4 91.9(1), Ge−W−C5 88.4(1), C4−W−C5 91.2(2), N1−C1−N2 106.3(3), N1−C2−C3 107.2(3), W−C4−O1 176.4(4), W−C5−O2 174.5(5).

and shows a typical “three-legged piano-stool” complex. The W−Ge bond length (2.2813(4) Å) is almost identical to those of [Cp(CO)2WGeC(SiMe3)3] (2.2842(6) Å),11 [Cp*(CO) 2 WGeC(SiMe 3 ) 3 ] (2.2830(6) Å) 21a and [Cp(CO)2WGeArMes] (2.277(1) Å).9g The presence of a W− Ge triple bond is additionally supported by the almost linear W−Ge−C1 atom sequence (168.7(1)°). The Ge−C1 bond is shorter (1.952(4) Å) than that of the starting material 2 (2.025(4) Å) due to rehybridization of the germanium center (Table 1). Interestingly, this distance compares well with that of the neutral germylidyne complexes [Cp(CO)2WGeC(SiMe3)3] (1.939(5) Å)11 and [Cp*(CO)2WGeC(SiMe3)3] 1533

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Organometallics

solution on the NMR time scale. Furthermore, the signal of the N-heterocyclic ring C4,5−H backbone protons is significantly downfield shifted (δ = 8.34 ppm (4Ge), 7.45 ppm (4Sn)) compared to that of the starting materials (δ = 6.58 ppm (1Ge), 6.55 ppm (1Sn), both values in benzene-d6). Notably, the 13C{1H} NMR spectra of 4Ge and 4Sn display only one sharp CO resonance signal (δ = 215.8 ppm (4Ge), 214.2 ppm (4Sn)), indicating that a fast position exchange of the lateral and diagonal CO ligands occurs in solution at 298 K on the NMR time scale. Remarkably, the 119Sn{1H} NMR spectrum of 4Sn displays a very broad singlet (ν1/2 = 180.4 Hz),27 which appears at even lower field (δ = 3318.1 ppm) than that of the metallostannylenes [Cp(CO)3W−SnR] (δ = 2367 ppm, (R = ArMes); δ = 2650 ppm (R = ArTrip)) and other two-coordinate Sn(II) compounds.20 To test the reactivity of the unsaturated 6VE germanium center in 4Ge, the complex was treated with the electron-rich alkyne bis(dimethylamino)acetylene (Me2NCCNMe2). The reaction takes place already at −30 °C in diethyl ether and is accompanied by an immediate color change of the solution from green to dark brown (Scheme 2). Remarkably, instead of

the borate anions. A DIAMOND plot of the molecular structure of the cation of 4Sn is presented in Figure 4. The

Figure 4. DIAMOND plot of the molecular structure of the complex cation in 4Sn. Thermal ellipsoids are set at 50% probability level. Hydrogen atoms and the iPr-groups are omitted for clarity. The dotted line connects the W atom with the centroid (Cg) of the η5-bonded C5Me5 ligand. Selected bond lengths [Å] and bond angles [°]: W−Sn 2.8029(4), Sn−C1 2.287(4), W−Cg 2.013(1), W−C4 1.977(5), C4− O1 1.161(6), W−C5 1.988(6), C5−O2 1.148(6), W−C6 1.984(5), C6−O3 1.148(6), C1−N1 1.348(5), N1−C2 1.388(6), C2−C3 1.351(7); W−Sn−C1 110.7(1), C4−W−C6 108.0(2), C5−W−Sn 132.2(2), N1−C1−N2 105.6(3), C1−N1−C2 110.6(4), N1−C2−C3 106.7(4), W−C4−O1 173.8(4), W−C5−O2 177.7(5), W−C6−O3 175.2(5); torsion angle [°]: C1−Sn−W−C5 55.5(2).

Scheme 2. Reaction of the Metallogemylene Salt 4Ge with Bis(dimethylamino)acetylene Leading to Cleavage of the Ge−CIdipp Bond

four-legged piano-stool complex cation adopts a C1 symmetric gauche conformation with one of the lateral CO ligands (C4− O1) lying in the coordination plane of the stannyliumylidene ligand (∠C1−Sn−W−C4 = 3.9°). The tin atom reveals a bent geometry with a bonding angle at Sn of 110.7(1)°, which compares favorably with that in the tungstenostannylene [Cp(CO)3W−SnArMes] (∠W−Sn−Caryl = 110.8(2)°)20 and suggests the presence of a nonbonding electron pair at tin. A comparison with the molecular structure of 1Sn reveals a considerable shortening of the W−Sn bond (W−Sn 2.8029(4) Å (4Sn), 2.9513(4) Å (1Sn)) upon chloride abstraction (Table 1). Notably, the W−Sn bond of 4Sn is also ca. 0.10 Å shorter than that of the tungstenostannylene [Cp(CO)3W−SnArMes] (2.911(1) Å).20 The IR spectra of 4Ge and 4Sn display in solution and in the solid-state three intense absorption bands, which are assigned to the A′ (all CO in phase), A′ (COlat in phase; COdiag out-ofphase) and A′′ (COlat out of phase) CO stretching modes of the local Cs symmetric W(CO)3 fragment (Table 1). The ν(CO) bands of 4Ge (1998, 1929, and 1897 cm−1 in fluorobenzene) appear at higher wavenumbers than those of 4Sn (1987, 1912, and 1879 cm−1 in fluorobenzene) suggesting that the Ge(Idipp)2+ ligand acts as a stronger σ-acceptor, Z-type ligand than Sn(Idipp)2+ due to the higher electronegativity of Ge versus Sn. In contrast to previous observations,14b compound 4Ge could be also fully characterized by 1H and 13 C NMR spectroscopy. The 1H NMR spectra of 4Ge (THFd8, 298 K) and of Sn (fluorobenzene-d5, 298 K) display two doublets and one septet for the iPr groups of the Idipp substituents indicating that both a rapid rotation of the [E(NHC)]2+ ligand about the W−E bond and of the NHC substituent about the E−CNHC bond (E = Ge, Sn) occurs in

the anticipated [2 + 1]-cycloaddition product, the neutral germyl complex 5 containing a pendant 1-germabicyclo-[3,2,0]hepta-2,5-diene ligand was formed in a complex cascade of C− C coupling reaction steps involving also a cleavage of the Ge− CNHC bond and deprotonation of one methyl group of the Cp* ligand. After workup and crystallization from diethyl ether complex 5 was isolated as red-brown, thermally robust crystals (mp: 132 °C) and fully characterized. The solid-state molecular structure of 5 was determined by a single crystal X-ray diffraction study (scXRD) (Figure 5). The W−Ge bond (2.6834(5) Å) is longer than that of the chlorogermyl complexes [Cp*(CO) (PMe3)2WGeCl3] (2.531(1) Å),28a trans-[Cp*(CO)2(PMe3)WGeCl3] (2.516(1) Å)28b [Cp*(CO)3WGeCl3] (2.563(2) Å),28c or [Cp*(CO)3WGeClMe2] (2.6272(4) Å)29 due to decreased hyperconjugation between the metal fragment and the germyl ligand in 5.28 The three Ge−C single bonds (Ge− C1 1.981(4) Å, Ge−C3 2.054(4) Å, Ge−C6 2.087(4) Å) are even slightly longer than the sum of single-bond covalent radii for this pair of elements (1.96 Å).30 The four-membered ring GeC3 displays a C1−C2 double bond (1.369(6) Å) and the five-membered GeC4 ring a C4−C5 double bond (1.365(6) Å). The IR spectrum of 5 in diethyl ether solution shows three ν(CO) absorption bands at 1979, 1909, and 1888 cm−1. These bands appear at considerably lower wavenumbers than those of the analogous trichlorogermyl complex [Cp*(CO)3WGeCl3] (2033, 1959, 1946 cm−1 in CH2Cl2) reflecting the decreased hyperconjugation between the metal fragment and the germyl ligand in 5.28 The 1H NMR spectrum of 5 (300.1 MHz, 1534

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complexes with analogous silicon compounds reveals that the propensity to form multiple bonds to Group 6 metals via decarbonylation of M−E singly bonded precursors (M = transition metal; E = Si−Sn) reduces in the series Si > Ge > Sn.12,13 The metallotetrylenes [Cp*(CO)3W−E(NHC)]+ are expected to have small HOMO−LUMO and readily break strong chemical bonds.12a,14a Especially appealing is also the perspective to access heavier Group 14 elements analogous of the carbido complexes of the general formula [LnM = E:] (LnM = 16VE metal fragment; E = Si−Sn) via heterolytic cleavage of the E−CNHC bond of cationic metal ylidyne complexes such as [Cp*(CO)2WGe(NHC)]+. Recent theoretical calculations by Frenking et al. suggest at least the viability of [LnM = E:].31 Furthermore, the cationic nature in combination with the presence of a replaceable NHC substituent suggests a versatile, unusual chemistry of [Cp*(CO)3W−E(NHC)]+ and [Cp*(CO)2WGe(NHC)]+ with nucleophiles. The reaction of [Cp*(CO)3W−Ge(NHC)]+ (4Ge) with bis(dimethylamino)acetylene provides such an example of unusual reactivity involving a cleavage of the Ge−CNHC bond. In this context, the synthesis and full characterization of these complexes may become a valuable step in low-valent germanium and tin chemistry.

Figure 5. DIAMOND plot of the molecular structure of 5. Thermal ellipsoids are set at 50% probability level. Hydrogen atoms are omitted for clarity. The dotted line connects the W atom with the centroid (Cg) of the η5-bonded C5Me5 ligand. Selected bond lengths [Å] and bond angles [°]: W−Ge 2.6833(5), W−Cg 1.997(4), W−C7 1.995(5), C7−O1 1.124(6), W−C8 1.982(5), C8−O2 1.144(7), W−C9 1.980(4), C9−O3 1.149(6), Ge−C1 1.981(4), Ge−C3 2.054(4), Ge−C6 2.087(4), C1−C2 1.369(6), C2−C3 1.542(5), C3−C4 1.511(6), C4−C5 1.365(6), C5−C6 1.532(6), C6−C10 1.567(6), C1−N1 1.426(5), C2−N2 1.377(6), C3−N3 1.421(6), C4−N4 1.401(5), C6−N6 1.485(5); C1−Ge−C3 71.6(2), C3−Ge−C6 90.3(2), C1−Ge−C6 113.2(2), Ge−C1−C2 93.3(3), C1−C2−C3 108.8(4), Ge−C3−C2 85.3(3), Ge−C3−C4 104.4(3), C3−C4−C5 120.0(4), C4−C5−C6 121.2(4), C2−C3−C4 114.6(4); sum of angles [°] at N1 338.4, N2 357.3, N3 337.5, N4 359.2, N5 359.2, N6 341.5.

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EXPERIMENTAL SECTION

General Methods. All experiments were carried out under an atmosphere of argon using Schlenk or glovebox techniques. All glassware employed in the experiments was predried in an oven at 110 °C and baked in vacuo prior to use. The solvents were refluxed over an appropriate drying agent, purged several times during reflux with argon, distilled under argon and degassed by several freeze−pump− thaw cycles before storage in a glovebox. The following drying agents were used: CaH2 for petroleum ether (40−60 °C distillation fraction) and fluorobenzene; sodium/benzophenone ketyl/tetraglyme (0.5 vol %) for n-hexane; sodium followed by sodium/benzophenone ketyl for tetrahydrofuran (THF), 1,2-dimethoxyethane (DME) and diethyl ether (Et2O); sodium for toluene. The C, H, N analyses were carried out in triplicate for each sample using an Elementar Vario Micro elemental analyzer. The individual C, H, N values did not differ by more than ±0.3%. The mean C, H, N values are given below for each compound. The melting points were determined in triplicate for each sample using a Büchi melting point apparatus, which was linearly calibrated against vanillin (mp 83 °C), phenacetin (mp 136 °C) and caffeine (mp 237 °C). The samples were sealed in capillary tubes under vacuum and heated once with a gradient of approximately 6 K min−1 for a rough determination of the melting point or temperature of starting decomposition. Heating of the second and third sample was then repeated with a gradient of approximately 3 K min−1, starting 20 K below the temperature of melting or decomposition determined in the first experiment. The molten samples were cooled to room temperature and studied by IR spectroscopy to elucidate whether the samples had decomposed. The FT-IR spectra of solutions were recorded on a Nicolet 380 FT-IR spectrometer in the spectral range of 2100−1600 cm−1 using a cell of KBr windows, which were separated by a Teflon spacer with a thickness of 0.25 mm. The spectra were background corrected for the solvent absorptions. The IR spectra of solids were recorded in the spectral range of 3500−400 cm−1 on a Bruker Alpha FT-IR spectrometer inside the glovebox using the platinum single reflection diamond ATR module. The following abbreviations were used for the intensities and shape of the IR absorption bands: vs−very strong, s− strong, m−medium, w−weak, vw−very weak, sh−shoulder. The NMR spectra were recorded on a Bruker Avance DMX-300 NMR spectrometer in benzene-d6, toluene-d8, THF-d8, chlorobenzene-d5, fluorobenzene-d5 or acetonitrile-d3. The deuterated solvents were dried and deoxygenated upon trap-to-trap condensation from sodium

toluene-d8 298 K) displays six singlet signals for the dimethylamino groups indicating a rapid rotation of the NMe2 groups about the respective C-NMe2 bonds. Three of these singlets are however broadened indicating a beginning hindrance to rotation (see SI, Figure S42). In fact, variabletemperature NMR studies of 5 in toluene-d8 from 203 to 298 K (see SI, Figure S47) reveal that rotation of four of the six NMe2 groups is frozen out at low temperatures giving rise to ten NMe singlet signals in the 1H NMR spectrum of 5 at 203 K, two of which coincide at δ = 2.69 ppm (see SI, Figures S43 and S48) and 10 N-Me signals in the 13C{1H} NMR spectrum of 5 at 203 K (see SI, Figures S44−S46). Compound 5 contains a stereogenic Ge center, which renders the two lateral CO ligands chemically inequivalent. This is confirmed by the 13C{1H} NMR spectrum of 5 at 203 K, which displays three singlet signals for the CO ligands. Furthermore, the low-temperature 13C{1H} NMR spectrum displays six singlets for the ring carbon atoms of the [3,2,0]germabicycloheptadiene ring (GeC6), four of which appear at lower field (δ = 132.6, 138.5, 145.0, and 146.3 ppm) than the other two (δ = 91.2 and 117.2 ppm), which can be tentatively assigned to the two sp3-hybridized carbon atoms.

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CONCLUSIONS AND OUTLOOK In summary, the isolation of the cationic metallogermylenes and metallostannylenes [Cp*(CO)3W−E(NHC)]+ (E = Ge, Sn; NHC (N-heterocyclic carbene) = Idipp), the NHCstabilized chlorogermylidyne complex [Cp*(CO)2WGeCl(NHC)] and the cationic germylidyne complex [Cp*(CO)2WGe(NHC)]+ highlights the exceptional ability of N-heterocyclic carbenes to stabilize low-valent tetrel centers with unusual bonding modes. A comparison of the presented 1535

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mL of n-hexane and stirred for 48 h at room temperature. The resulting red-yellow solution containing a gray-yellow solid was diluted with 15 mL of toluene and filtered. The filtrate was evaporated to dryness in vacuo. The resulting oily residue was dissolved in 5 mL of a n-hexane/toluene mixture (3:1, v/v), and the solution was stored at −60 °C for 24 h. The yellow-orange, flocculent precipitate of 1Ge was collected by filtration at −60 °C and dried in vacuo at ambient temperature for 3 h. Yield: 441 mg (0.49 mmol, 67%). mp = 148 °C. Elemental analysis calcd (%) for C40H51ClGeN2O3W (899.78): C, 53.39; H, 5.71; N, 3.11. Found: C, 53.99; H, 5.70; N, 3.11%. IR (nhexane, cm−1): ν̃ = 1958 (vs), 1890 (s), 1842 (s) [ν(CO)]. IR (toluene, cm−1): ν̃ = 1953 (vs), 1882 (vs), 1837 (s) [ν(CO)]. IR (fluorobenzene, cm−1): ν̃ = 1951 (vs), 1878 (s), 1838 (s) [ν(CO)]. IR (solid, cm−1): ν̃ = 3162 (m), 3135 (m), 2964 (s), 2926 (m), 2867 (m), 1948 (vs) [ν(CO)], 1876 (vs) [ν(CO)], 1816 (vs) [ν(CO)], 1590 (m), 1551 (m), 1442 (s), 1401 (m), 1383 (s), 1363 (m), 1327 (m), 1280 (m), 1206 (m), 1179 (m), 1121 (w), 1104 (m), 1061 (w), 1030 (m), 944 (m), 935 (m), 799 (vs), 750 (vs), 694 (m), 629 (m), 601 (m), 568 (vs), 503 (s), 492 (s), 481 (s), 454 (s), 417 (m), 386 (w). 1H NMR (300.1 MHz, benzene-d6, 298 K, ppm): δ = 0.99 (d, 3J(H,H) = 6.8 Hz, 6H, 2 × C2−CHMeAMeB, dipp), 1.00 (d, 3J(H,H) = 6.8 Hz, 6H, 2 × C6−CHMeAMeB, dipp), 1.55 (d, 3J(H,H) = 6.8 Hz, 6H, 2 × C6−CHMeAMeB, dipp), 1.67 (d, 3J(H,H) = 6.8 Hz, 6H, 2 × C2− CHMeAMeB, dipp), 1.68 (s, 15H, C5Me5), 3.08 (sept, 3J(H,H) = 6.8 Hz, 2H, 2 × C2−CHMeAMeB, dipp), 3.20 (sept, 3J(H,H) = 6.8 Hz, 2H, 2 × C6−CHMeAMeB, dipp), 6.58 (s, 2H, C4,5-H), 7.17−7.32 (three multiplets, 6H, 2 × C3-H + 2 × C4-H + 2 × C5-H, dipp).13C{1H} NMR (75.47 MHz, benzene-d6, 298 K, ppm): δ = 10.0 (s, 5C, C5Me5), 23.0 (s, 2C, 2 × C2−CHMeAMeB, dipp), 23.1 (s, 2C, 2 × C6−CHMeAMeB, dipp), 26.2 (s, 2C, 2 × C6−CHMeAMeB, dipp), 26.9 (s, 2C, 2 × C2−CHMeAMeB, dipp), 28.9 (s, 2C, 2 × C2CHMeAMeB, dipp), 29.1 (s, 2C, 2 × C6-CHMeAMeB, dipp), 101.8 (s, 1 183 J( W,13C) = 5.3 Hz, 5C, C5Me5), 124.2 (s, 2C, 2 × C3-H, dipp), 124.5 (s, 2C, 2 × C5-H, dipp), 125.2 (s, 2C, C4,5-H), 130.9 (s, 2C, 2 × C4-H, dipp), 134.8 (s, 2C, 2 × C1, dipp), 146.1 (s, 2C, 2 × C6CHMeAMeB, dipp), 146.2 (s, 2C, 2 × C2-CHMeAMeB, dipp), 177.9 (s, 1C, GeC2N2), 218.3 (s 1C, CO), 222.3 (s, 1C, CO), 228.3 (s 1C, CO). Synthesis of [Cp*(CO)3WSnCl(Idipp)] (1Sn). A Schlenk tube was charged with Li[Cp*W(CO)3] (300 mg, 0.73 mmol) and SnCl2(Idipp) (420 mg, 0.73 mmol), and the mixture was suspended in n-hexane (15 mL) and stirred for 48 h at ambient temperature. The resulting red-yellow suspension was diluted with toluene (15 mL), filtered, and the filtrate was evaporated to dryness in vacuo. The resulting oily residue was dissolved in 6 mL of a n-hexane/toluene mixture (3:1, v/v) and crystallized at −60 °C for 24 h. The yelloworange flocculent precipitate of 1Sn was collected by filtration at −60 °C and dried in vacuo at ambient temperature for 3 h. Yield: 490 mg (0.52 mmol, 71%). mp = 139 °C (decomposition). Elemental analysis calcd (%) for C40H51ClN2O3SnW (945.85): C, 50.79; H, 5.43; N, 2.96. Found: C, 50.98; H, 5.57; N, 2.91%. IR (n-hexane, cm−1): ν̃ = 1955 (vs), 1888 (vs), 1835 (s) [ν(CO)]. IR (toluene, cm−1): ν̃ = 1949 (vs), 1879 (vs), 1831 (s) [ν(CO)]. IR (fluorobenzene, cm−1): ν̃ = 1948 (vs), 1876 (vs), 1832 (s) [ν(CO)]. IR (THF, cm−1): ν̃ = 1949 (vs), 1879 (vs), 1834 (s) [ν(CO)]. IR (solid, cm−1): ν̃ = 3168 (w), 3133 (w), 3070 (w), 2961 (s), 2925 (s), 2868 (s), 2010 (w), 1945 (vs) [ν(CO)], 1876 (vs) [ν(CO)], 1831 (vs) [ν(CO)], 1766 (m), 1591 (w), 1562 (w), 1459 (s), 1442 (s), 1399 (m), 1381 (s), 1363 (m), 1328 (m), 1279 (w), 1205 (w), 1081 (w), 1118 (w), 1101 (m), 1061 (w), 1032 (m), 943 (w), 885 (vw), 800 (s), 754 (vs), 687 (w), 627 (w), 596 (m), 574 (vs), 501 (m), 479 (vs), 461 (s), 444 (s), 423 (s). 1 H NMR (300.1 MHz, benzene-d6, 298 K, ppm): δ = 0.99 (d, 3J(H,H) = 6.9 Hz, 6H, 2 × C2−CHMeAMeB, dipp), 1.00 (d, 3J(H,H) = 6.8 Hz, 6H, 2 × C6−CHMeAMeB, dipp), 1.58 (d, 3J(H,H) = 6.7 Hz, 6H, 2 × C6−CHMeAMeB, dipp), 1.67 (d, 3J(H,H) = 6.9 Hz, 6H, 2 × C2− CHMeAMeB, dipp), 1.69 (s, 15H, C5Me5), 3.03 (sept, 3J(H,H) = 6.8 Hz, 2H, 2 × C2−CHMeAMeB, dipp), 3.15 (sept, 3J(H,H) = 6.8 Hz, 2H, 2 × C6−CHMeAMeB, dipp), 6.55 (s, 2H, C4,5-H), 7.18−7.22 (m, 2H, 2 × C5-H, dipp), 7.23−7.27 (m, 2H, 2 × C3-H, dipp), 7.28−7.32 (m, 2H, 2 × C4-H, dipp). 13C{1H} NMR (75.47 MHz, benzene-d6, 298 K, ppm): δ = 10.2 (s, 5C, C5Me5), 23.1 (s, 2C, 2 × C6−

powder (benzene-d6, toluene-d8, and THF-d8) or CaH2 (chlorobenzene-d5, fluorobenzene-d5, and acetonitrile-d3). The 1H and 13C{1H} NMR spectra were calibrated against the residual proton and natural abundance 13C resonances of the deuterated solvent relative to tetramethylsilane (benzene-d6, δH 7.15 ppm and δC 128.0 ppm; toluene-d8, δH 2.09 ppm and δC 20.4 ppm; THF-d8, δH 1.73 ppm and δC 25.3 ppm; chlorobenzene-d5, δH 6.96 ppm and δC 125.96 ppm; acetonitrile-d3, δH 1.93 ppm and δC 1.30 ppm). The 1H and 13C{1H} NMR spectra of 4Sn in fluorobenzene-d5 were calibrated against the signals of residual Et2O present in 4Sn at δH = 1.10 ppm and δC = 15.35 ppm. The calibration was based in this case on the assumption that the signals of Et2O appear at the same position as in chlorobenzene-d5.32 The proton decoupled 19F, 119Sn, 11B, and27Al NMR spectra were calibrated at 298 K against external pure CFCl3, SnMe4, BF3·Et2O and a 1 M aqueous solution of Al(NO3)3, respectively. The external standard was filled in a capillary, which was sealed-off and introduced into a 5 mm NMR tube containing the corresponding deuterated solvent. The NMR tube was finally vacuumsealed and used for the calibration. The 19F NMR signal of fluorobenzene-d5 was observed under these conditions at δF − 114.4 ppm. The following abbreviations were used for the multiplicities and shape of the NMR signals: s−singlet, d−doublet, t−triplet, q−quartet, qq−quartet of quartets, sept−septet, m−multiplet, br−broad. The 1H and 13C NMR signals of all compounds except compound 5 were assigned by a combination of HMQC, HMBC, and DEPT experiments. This allowed an unequivocal assignment of all proton and carbon resonances including those of the diastereotopic methyl groups of the isopropyl substituents, which were labeled with the subscript letters A and B, respectively. The label A was used for the methyl group with the lower 1H chemical shift. In compounds 1Ge and 1Sn, the label A was used for the methyl group of the C2-bonded isopropyl substituent having the lower 1H chemical shift. The 13C NMR signals of 1Sn in toluene-d8 at 253 K were assigned by analogy to those obtained from the HMQC and HMBC experiments of 1Sn in benzene-d6. The acronym dipp was used for the 2,6-diisopropylphenyl substituents of Idipp. An HPK 125W high-pressure mercury vapor lamp was used for the photochemical experiments. The lamp provided maximum energy at 365 nm with substantial radiation also at 435, 404, 313, and 253 nm. The lamp was kept in a quartz vessel, which was cooled with running water during photolysis. The reaction flask was placed 3−5 cm near the light source. SnCl2 was purchased from Merck and stored in a Schlenk tube under argon. GeCl2(1,4-dioxane) was obtained upon reduction of GeCl4 with triethylsilane using the method of Kouvetakis et al.33 and shown by C, H, and Cl analyses to be pure. GeCl2(Idipp),18 SnCl2(Idipp),16,18 Li[Al{OC(CF3)3}4],34 2,3-dihydro-1,3-bis(2,6-diisopropylphenyl)-1H-imidazol-2-ylidene (Idipp)35 and Na[B{C6H3-3,5(CF3)2}4]36 were prepared following the published procedures. Bis(dimethylamino)acetylene was prepared as reported previously.31 Li[Cp*W(CO)3] was prepared as reported by Waltz and Hartwig37 upon deprotonation of [Cp*W(CO)3H] with one equiv of LinBu in nhexane, and isolated as a yellow solid in 95% yield. It was characterized by IR, 1H NMR, and 13C{1H} NMR spectroscopy. [Cp*W(CO)3H] was obtained from W(CO)6 in two steps. W(CO)6 was first heated with 1.05 equiv of LiCp* in refluxing DME for 25 h. Completion of the reaction was confirmed by IR spectroscopy, and the resulting solution of the metalate Li[Cp*W(CO)3] was then treated with 1.15 equiv of glacial acetic acid at −30 °C. After solvent evaporation, the product [Cp*W(CO)3H] was extracted with petroleum ether at +30 °C and isolated after concentration of the extract and crystallization at −60 °C as a yellow microcrystalline solid in 84% yield. [Cp*W(CO)3H] was characterized by IR, 1H NMR, and 13C{1H} NMR spectroscopy.38 During the preparation of this manuscript, the synthesis and analytical data of 1Ge were published by Tobita and co-workers.14b We provide here additional physical and analytical data along with a full assignment of the 13C NMR signals of 1Ge. Synthesis of [Cp*(CO)3WGeCl(Idipp)] (1Ge). A Schlenk tube was charged with Li[Cp*W(CO)3] (300 mg, 0.73 mmol) and GeCl2(Idipp) (388 mg, 0.73 mmol). The mixture was suspended in 15 1536

DOI: 10.1021/acs.organomet.7b00110 Organometallics 2017, 36, 1530−1540

Article

Organometallics CHMeAMeB, dipp), 23.2 (s, 2C, 2 × C2−CHMeAMeB, dipp), 26.2 (s, 2C, 2 × C6−CHMeAMeB, dipp), 26.8 (s, 2C, 2 × C2−CHMeAMeB, dipp), 28.9 (s, 2C, 2 × C2-CHMeAMeB, dipp), 29.1 (s, 2C, 2 × C6CHMeAMeB, dipp), 100.9 (s, 1J(183W,13C) = 5.6 Hz, 5C, C5Me5), 124.3 (s, 2C, 2 × C3-H, dipp), 124.6 (s, 2C, 2 × C5-H, dipp), 125.2 (s, 2C, C4,5-H), 130.9 (s, 2C, 2 × C4-H, dipp), 135.2 (s, 2C, 2 × C1, dipp), 146.08 (s, 2C, 2 × C6-CHMeAMeB, dipp), 146.11 (s, 2C, 2 × C2CHMeAMeB, dipp), 179.4 (s, 1C, SnC2N2); the CO signals were not observed. 13C{1H} NMR (75.47 MHz, toluene-d8, 253 K, ppm): δ = 10.0 (s, 5C, C5Me5), 22.9 (s, 2C, 2 × C2−CHMeAMeB, dipp), 23.0 (s, 2C, 2 × C6−CHMeAMeB, dipp), 26.2 (s, 2C, 2 × C6−CHMeAMeB, dipp), 26.8 (s, 2C, 2 × C2−CHMeAMeB, dipp), 28.8 (s, 2C, 2 × C2CHMeAMeB, dipp), 29.0 (s, 2C, 2 × C6-CHMeAMeB, dipp), 100.5 (s, 1 183 J( W,13C) = 5.2 Hz, 5C, C5Me5), 124.1 (s, 2C, 2 × C3-H, dipp), 124.5 (s, 2C, 2 × C5-H, dipp), 130.8 (s, 2C, 2 × C4-H, dipp), 134.9 (s, 2C, 2 × C1, dipp), 145.74 (s, 2C, 2 × C6-CHMeAMeB, dipp), 145.76 (s, 2C, 2 × C2-CHMeAMeB, dipp), 178.7 (s, 1C, SnC2N2), 217.7 (1C, CO), 222.4 (1C, CO), 226.3 (1C, CO); the C4,5-H signal is obscured by the triplet signal of the deuterated solvent at δ = 125.0 ppm. 119 Sn{1H} NMR (111.9 MHz, benzene-d6, 298 K, ppm): δ = 455.5 (s, 1 183 J( W,119Sn) = 80.6 Hz). Synthesis of [Cp*(CO)2WGeCl(Idipp)] (2). A quartz Schlenk tube was charged with 1Ge (500 mg, 0.56 mmol). The complex was dissolved in 30 mL of diethyl ether, and the solution was irradiated with UV-light of a HPK125W high pressure mercury vapor lamp for 5 h at ambient temperature under vigorous stirring. During this time, the color of the solution turned from yellow-brown to brown-black. Completion of the reaction was verified by IR spectroscopy and the solution was evaporated to dryness in vacuo. The residue was extracted with toluene (3 × 10 mL), and the brown-black extract was filtered. The filtrate was concentrated in vacuo to approximately 7 mL and stored at −30 °C for 48 h to afford red-brown crystals of 2. Yield: 270 mg (0.31 mmol, 56%). mp = 177 °C. Elemental analysis calcd (%) for C39H51ClGeN2O2W (871.77): C, 53.73; H, 5.90; N, 3.21. Found: C, 54.01; H, 6.03; N, 2.94%. IR (diethyl ether, cm−1): ν̃ = 1886 (vs), 1808 (vs) [ν(CO)]. IR (toluene, cm−1): ν̃ = 1882 (vs), 1802 (vs) [ν(CO)]. IR (fluorobenzene, cm−1): ν̃ = 1878 (vs), 1800 (vs) [ν(CO)]. IR (solid, cm−1): ν̃ = 3149 (m), 3120 (w), 3077 (w), 2961 (vs), 2926 (s), 2868 (s), 2280 (w), 1856 (vs) [ν(CO)], 1772 (vs) [ν(CO)], 1592 (w), 1551 (m), 1459 (s), 1416 (m), 1383 (s), 1364 (m), 1349 (w), 1327 (m), 1305 (w), 1272 (vw), 1255 (vw), 1211 (w), 1182 (vw), 1150 (vw), 1121 (m), 1060 (w), 1033 (m), 975 (vw), 947 (w), 936 (w), 911 (vw), 800 (s), 780 (m), 753 (s), 732 (vw), 703 (vw), 636 (vw), 605 (w), 561 (m), 524 (vw), 499 (m), 489 (m), 424 (vw), 384 (vw). 1H NMR (300.1 MHz, benzene-d6, 298 K, ppm): δ = 1.00 (d, 3J(H,H) = 6.8 Hz, 12H, 2 × C2,6-CHMeAMeB, dipp), 1.62 (d, 3 J(H,H) = 6.9 Hz, 12H, 2 × C2,6-CHMeAMeB, dipp), 2.11 (s, 15H, C5Me5), 3.03 (sept, 4H, 2 × C2,6−CHMeAMeB, dipp), 6.30 (s, 2H, C4,5-H), 7.16−7.19 (m, 4H, 2 × C3,5-H, dipp), 7.23−7.26 (m, 2H, 2 × C4-H, dipp). 13C{1H} NMR (75.47 MHz, benzene-d6, 298 K, ppm): δ = 12.1 (s, 5C, C5Me5), 23.0 (s, 4C, 2 × C2,6-CHMeAMeB, dipp), 26.1 (s, 4C, 2 × C2,6-CHMeAMeB, dipp), 29.3 (s, 4C, 2 × C2,6-CHMeAMeB, dipp), 100.8 (s, 1J(183W,13C) = 5.5 Hz, 5C, C5Me5), 123.8 (s, 2C, C4,5H), 125.0 (s, 4C, 2 × C3,5-H, dipp), 131.4 (s, 2C, 2 × C4-H, dipp), 133.0 (s, 2C, 2 × C1, dipp), 145.5 (s, 4C, 2 × C2,6-CHMeAMeB, dipp), 175.8 (s, 1C, GeC2N2), 232.7 (s, 2C, 2 × CO). Synthesis of [Cp*(CO)2WGe(Idipp)][B{C6H3-3,5-(CF3)2}4] (3). A solution of Na[B{C6H3-3,5-(CF3)2}4] (290 mg, 0.33 mmol) in 15 mL of fluorobenzene was added dropwise to a solution of 2 (300 mg, 0.34 mmol) in 10 mL of fluorobenzene at ambient temperature. The solution turned turbid, but no obvious color change was observed. After stirring for 30 min, an IR spectrum of the reaction mixture was recorded, which revealed the complete conversion of complex 2 to the product 3. The brown cloudy solution was filtered, and the filtrate was evaporated to dryness in vacuo. The resulting oily residue was dissolved in 5 mL of diethyl ether, and the brown ethereal solution was stored at −60 °C for 24 h. Red-brown crystals of 3 were grown, which were collected by filtration at −60 °C and dried in vacuo at ambient temperature for 3 h. Yield: 358 mg (0.21 mmol, 61% from 2). mp = 147 °C. Elemental analysis calcd (%) for C71H63BF24GeN2O2W

(1699.52): C, 50.18; H, 3.74; N, 1.65. Found: C, 50.40; H, 3.89; N, 1.65%. IR (diethyl ether, cm−1): ν̃ = 1966 (vs), 1907 (vs) [ν(CO)]. IR (fluorobenzene, cm−1): ν̃ = 1963 (vs), 1902 (vs) [ν(CO)]. IR (solid, cm−1): ν̃ = 3165 (w), 3137 (vw), 2971 (m), 2931 (m), 2876 (m), 1967 (vs) [ν(CO)], 1899 (vs) [ν(CO)], 1610 (m), 1537 (m), 1457 (m, sh), 1389 (m), 1352 (vs), 1274 (vs), 1213 (w), 1162 (s), 1120 (vs), 1061 (s), 1032 (s), 978 (w), 950 (w), 927 (w), 897 (m, sh), 886 (vs), 839 (s), 804 (s), 761 (m, sh), 753 (m), 745 (m, sh), 714 (vs), 701 (w, sh), 681 (vs), 668 (vs), 637 (w), 574 (m), 514 (s), 495 (w), 465 (s), 448 (m), 427 (w). 1H NMR (300.1 MHz, chlorobenzene-d5, 298 K, ppm): δ = 1.05 (d, 3J(H,H) = 6.8 Hz, 12H, 2 × C2,6CHMeAMeB, dipp), 1.24 (d, 3J(H,H) = 6.8 Hz, 12H, 2 × C2,6CHMeAMeB, dipp), 1.79 (s, 15H, C5Me5), 2.27 (sept, 4H, 2 × C2,6− CHMeAMeB, dipp), 7.04 (s, 2H, C4,5-H), 7.14 (d, 3J(H,H) = 7.8 Hz, 4H, 2 × C3,5-H, dipp), 7.35 (t, 3J(H,H) = 7.8 Hz, 2H, 2 × C4-H, dipp), 7.60 (br s, 4H, 4 × C4-H, B{C6H3-3,5-(CF3)2}4), 8.23 (m, 8H, 4 × C2,6-H, B{C6H3-3,5-(CF3)2}4). 13C{1H} NMR (75.47 MHz, chlorobenzene-d5, 298 K, ppm): δ = 11.7 (s, 5C, C5Me5), 23.5 (s, 4C, 2 × C2,6-CHMeAMeB, dipp), 24.1 (s, 4C, 2 × C2,6-CHMeAMeB, dipp), 29.5 (s, 4C, 2 × C2,6-CHMeAMeB, dipp), 104.3 (s, 5C, C5Me5), 117.8 (sept, 3 13 J( C, 19F) = 3.6 Hz, 4C, 4 × C4-H, B{C6H3-3,5-(CF3)2}4), 125.0 (q, 1 13 19 J( C, F) = 272 Hz, 8C, 8 × CF3, B{C6H3-3,5-(CF3)2}4), 125.4 (s, 4C, 2 × C3,5-H, dipp), 125.5 (s, 2C, 2 × C4,5-H), 129.1 (s, 2C, 2 × C1, dipp), 129.6 (qq, 2J(13C,19F) = 32 Hz, 3J(13C,11B) = 3.0 Hz, 8C, 4 × C3,5-CF3, B{C6H3-3,5-(CF3)2)}4; the signal overlaps partially with the triplet signal of chlorobenzene-d5 at δ = 129.2 ppm),133.1 (s, 2C, 2 × C4-H, dipp), 135.2 (br s, 8C, 4 × C2,6-H, B{C6H3-3,5-(CF3)2}4), 145.4 (s, 4C, 2 × C2,6-CHMeAMeB, dipp), 162.4 (q, 1J(13C,11B) = 49.8 Hz, 4C, 4 × C1, B{C6H3-3,5-(CF3)2}4), 176.8 (s, 1C, GeC2N2), 218.5 (s, 2C, 2 × CO).19F{1H} NMR (282.4 MHz, chlorobenzene-d5, 298 K, ppm): δ = −62.1 (s, 24F, 4 × C3,5-CF3, B{C6H3-3,5-(CF3)2}4). 11 1 B{ H} NMR (96.3 MHz, chlorobenzene-d5, 298 K, ppm): δ = −6.7 (s, 1B, B{C6H3-3,5-(CF3)2}4). Synthesis of [Cp*(CO) 3WGe(Idipp)][B{C6 H 3 -3,5-(CF 3) 2} 4] (4Ge). A solution of Na[B{C6H3-3,5-(CF3)2}4] (194 mg, 0.22 mmol) in 15 mL of fluorobenzene was added dropwise to a yellow solution of 1Ge (200 mg, 0.22 mmol) in 5 mL of fluorobenzene at ambient temperature. The solution became cloudy, and its color changed from yellow to green. The reaction mixture was stirred for 2 h at ambient temperature and filtered. The filtrate was evaporated to dryness in vacuo, and the obtained green oil was dissolved in ca. 3 mL of diethyl ether. The ethereal solution was treated with 1 mL of nhexane and stored at −60 °C for 48 h to afford green crystals of 4Ge, which were collected by filtration at −60 °C and dried in vacuo for 3 h. Yield: 303 mg (0.18 mmol, 79% from 1Ge). mp = 148 °C (decomposition). Elemental analysis calcd (%) for C72H63BF24GeN2O3W (1727.53): C, 50.06; H, 3.68; N, 1.62. Found: C, 50.19; H, 3.74; N, 1.57%. IR (diethyl ether, cm−1): ν̃ = 1998 (vs), 1930 (s), 1900 (vs) [ν(CO)]. IR (fluorobenzene, cm−1): ν̃ = 1998 (vs), 1929 (s), 1897 (vs) [ν(CO)]. IR (THF, cm−1): ν̃ = 1994 (vs), 1926 (s), 1896 (vs) [ν(CO)]. IR (solid, cm−1): ν̃ = 2972 (m), 2934 (w), 2874 (w), 1994 (s) [ν(CO)], 1931 (vs) [ν(CO)], 1899 (vs) [ν(CO)], 1609 (w), 1589 (vw), 1546 (vw), 1459 (m), 1413 (w), 1389 (m), 1352 (vs), 1274 (vs), 1209 (w), 1160 (vs), 1119 (vs), 1062 (s, sh), 1032 (m, sh), 948 (w), 929 (m), 898 (m, sh), 887 (s), 838 (s), 802 (m), 754 (m), 744 (s), 714 (s), 701 (w, sh), 682 (s), 668 (vs), 632 (vw), 570 (m), 548 (m), 488 (m), 449 (s), 425 (m), 393 (w). 1H NMR (300.1 MHz, THF-d8, 298 K, ppm): δ = 1.24 (d, 3J(H,H) = 6.8 Hz, 12H, 4 × C2,6-CHMeAMeB, dipp), 1.26 (d, 3J(H,H) = 6.8 Hz, 12H, 4 × C2,6-CHMeAMeB, dipp), 2.00 (s, 15H, C5Me5), 2.92 (sept, 4H, 2 × C2,6−CHMe2, dipp), 7.37 (d, 4H, 3J(H,H) = 7.7 Hz, 2 × C3,5-H, dipp), 7.52 (t 3J(H,H) = 7.7 Hz, 2H, 2 × C4-H, dipp; the triplet signal belongs to an AB2 spin system and shows a small second-order splitting), 7.58 (br s, 4H, 4 × C4-H, B{C6H3-3,5-(CF3)2}4), 7.80 (m, 8H, 4 × C2,6-H, B{C6H3-3,5-(CF3)2}4), 8.43 (s, 2H, C4,5-H). 13C{1H} NMR (75.47 MHz, THF-d8, 298 K, ppm): δ = 10.2 (s, 5C, C5Me5), 23.1 (s, 4C, 2 × C2,6-CHMeAMeB, dipp), 26.4 (s, 4C, 2 × C2,6CHMeAMeB, dipp), 30.1 (s, 4C, 2 × C2,6-CHMeAMeB, dipp), 108.2 (s, 5C, C5Me5), 118.2 (sept, 3J(13C,19F) = 3.6 Hz, 4C, 4 × C4-H, B{C6H33,5-(CF3)2}4), 125.5 (q, 1J(13C,19F) = 272 Hz, 8C, 8 × CF3, B{C6H31537

DOI: 10.1021/acs.organomet.7b00110 Organometallics 2017, 36, 1530−1540

Article

Organometallics Table 2. Crystallographic Data and Structure Refinement of 1, 2·0.25(Et2O), 3·(Et2O), 4Sn·0.5(C6H6), and 5·(Et2O) 1Sn formula

C40H51ClN2O3SnW

Mw T [K] crystal system space group a [Å] b [Å] c [Å] α [Å] β [Å] γ [Å] V [Å3] Z ρcalc. [g·cm−3] μ [mm−1] 2θ [°] reflns collected/unique

945.82 123(2) monoclinic P21/n 10.589(2) 18.986(3) 19.570(3) 90 93.433(3) 90 3927.4(9) 4 1.600 3.668 4.77−55.99 27861/9424 [R(int) = 0.0253] 0.0309/0.0578 0.0394/0.0601 1.93/−2.03

final R1/wR2 indices [I > 2σ(I)] R1/wR2 indices (all data) largest diff. peak/hole [e·Å−3]

2·0.25(Et2O)

3·(Et2O)

C40H53.5ClGe N2O2.25W 890.23 123(2) monoclinic P 21/c 10.8687(2) 25.9736(5) 16.0387(2) 90 118.827(1) 90 3966.6(1) 4 1.491 3.758 5.30−56.00 41735/9485 [R(int) = 0.0727] 0.0404/0.0808 0.0842/0.0911 1.74/−1.46

C75H73BF24Ge N2O3W

C59H54AlF36N2O7SnW

C35H60Ge N6O4W

1773.60 123(2) monoclinic P21/c 20.8610(3) 18.8392(3) 21.7896(3) 90 111.7740(9) 90 7952.4(2) 4 1.481 1.925 4.62−56.00 102498/18966 [R(int) = 0.0781] 0.0450/0.1290 0.0675/0.1411 1.82/−1.40

1916.56 123(2) monoclinic P21/n 18.6260(4) 21.2391(6) 18.8550(3) 90 104.024(1) 90 7236.7(3) 4 1.759 2.088 5.52−54.00 55484/15727 [R(int) = 0.0552] 0.0422/0.1060 0.0682/0.1157 2.08/−1.48

885.33 123(2) triclinic P−1 9.7329(4) 11.4817(4) 17.9096(7) 74.516(3) 87.849(3) 83.575(3) 1916.6(1) 2 1.534 3.826 5.90−56.00 25594/9236 [R(int) = 0.1084] 0.0445/0.1105 0.0498/0.1124 2.73/−3.36

3,5-(CF3)2}4), 126.2 (s, 4C, 2 × C3,5-H, dipp), 130.0 (qq, 2J(13C,19F) = 32 Hz, 3J(13C,11B) = 2.9 Hz, 8C, 4 × C3,5-CF3, B{C6H3-3,5-(CF3)2}4), 130.5 (s, 2C, C4,5-H), 131.7 (s, 2C, 2 × C1, dipp), 132.9 (s, 2C, 2 × C4H, dipp), 135.6 (br s, 8C, 4 × C2,6-H, B{C6H3-3,5-(CF3)2}4), 146.5 (s, 4C, 2 × C2,6-CHMeAMeB, dipp), 162.8 (q, 1J(13C,11B) = 49.8 Hz, 4C, 4 × C1, B{C6H3-3,5-(CF3)2}4), 186.0 (s, 1C, GeC2N2), 215.8 (s, 3C, 3 × CO). 19F{1H} NMR (282.4 MHz, THF-d8, 298 K, ppm): δ = −63.3 (s, 24F, 4 × C3,5-CF3, B{C6H3-3,5-(CF3)2}4). 11B{1H} NMR (96.3 MHz, THF-d8, 298 K, ppm): δ = −6.5 (s, 1B, B{C6H3-3,5-(CF3)2}4). Synthesis of [Cp*(CO)3WSn(Idipp)][Al{OC(CF3)3}4] (4Sn). A solution of Li[Al{OC(CF3)3}4] (206 mg, 0.21 mmol) in 15 mL of fluorobenzene was added dropwise to a solution of 1Sn (200 mg, 0.21 mmol) in 5 mL of fluorobenzene. The color changed from yellow to green during the addition. The reaction mixture was stirred for 1 h at ambient temperature, filtered, and the filtrate was evaporated to dryness in vacuo. The resulting green oily residue was dissolved in ca. 3 mL of fluorobenzene and approximately 1 mL of n-hexane was added. The green solution was stored at −30 °C for 48 h to afford green crystals of 4Sn. The crystals were collected by filtration at −30 °C and dried at ambient temperature in vacuo for 3 h. Yield: 259 mg (0.14 mmol, 65% from 1Sn). mp = 200 °C (decomposition). Elemental analysis calcd (%) for C56H51AlF36N2O7SnW (1877.49): C, 35.82; H, 2.74; N, 1.49. Found: C, 36.65; H, 2.91; N, 1.46%. IR (fluorobenzene, cm−1): ν̃ = 1987 (vs), 1912 (s), 1879 (vs) [ν(CO)]. IR (solid, cm−1): ν̃ = 2972 (m), 2934 (w), 2875 (w), 1990 (vs) [ν(CO)], 1912 (s) [ν(CO)], 1877 (vs) [ν̃(CO)], 1595 (w), 1548 (vw), 1496 (vw), 1460 (m), 1444 (m), 1412 (w), 1389 (m), 1352 (s), 1297 (s), 1274 (vs), 1238 (vs), 1213 (vs), 1165 (vs), 1120 (w), 1106 (w), 1060 (w), 1033 (w), 970 (vs), 896 (vw), 832 (m), 802 (m), 754 (s), 726 (vs), 695 (w), 686 (w), 633 (vw), 559 (s), 537 (s), 492 (m), 479 (w), 441 (vs). 1H NMR (300.1 MHz, fluorobenzene-d5, 298 K, ppm): δ = 1.04 (d, 3J(H,H) = 6.8 Hz, 12H, 2 × C2,6-CHMeAMeB, dipp), 1.20 (d, 3J(H,H) = 6.8 Hz, 12H, 2 × C2,6-CHMeAMeB, dipp), 1.67 (s, 15H, C5Me5), 2.80 (sept, 4H, 2 × C2,6−CHMeAMeB, dipp), 7.13 (d, 3J(H,H) = 7.8 Hz, 4H, 2 × C3,5-H, dipp), 7.34 (t, 3J(H,H) = 7.8 Hz, 2H, 2 × C4-H, dipp), 7.45 (s, 2H, C4,5-H). 13C{1H} NMR (75.47 MHz, fluorobenzene-d5, 298 K, ppm): δ = 9.6 (s, 5C, C5Me5), 22.8 (s, 4C, 2 × C2,6-CHMeAMeB, dipp), 26.1 (s, 4C, 2 × C2,6CHMeAMeB, dipp), 29.5 (s, 4C, 2 × C2,6-CHMeAMeB), 105.4 (s, 5C, C5Me5), 122.3 (q, 1J(C,F) = 292 Hz, 12C, 4 × OC(CF3)3), 125.6 (s, 4C, 2 × C3,5-H, dipp), 128.1 (s, 2C, C4,5-H), 131.3 (s, 2C, 2 × C1, dipp), 132.4 (s, 2C, 2 × C4-H, dipp), 145.8 (s, 4C, 2 × C2,6-

4Sn·0.5(C6H6)

5·(Et2O)

CHMeAMeB, dipp), 193.1 (s, 1C, SnC2N2), 214.3 (s, 1J(183W,13C) = 155 Hz, 3C, 3 × CO); the C(CF3)3 signal of the counteranion [Al(OC(CF3)3)4]− was not detected in the 13C{1H} spectrum. 19F NMR (282.4 MHz, fluorobenzene-d5, 298 K, ppm): δ = −75.5 (s, 36F, 12 × CF3, Al(OC(CF3)3)4). 27Al NMR (78.2 MHz, fluorobenzene-d5, 298 K, ppm): δ = +34.1 (s, Al(OC(CF3)3)4). 119Sn{1H} NMR (111.9 MHz, fluorobenzene-d5, 298 K, ppm): δ = +3318 (s br, ν1/2 = 180 Hz). Synthesis of [W(CO) 3{(η 5 ,η 1 -C 5Me 4 CH 2 -1-Germabicyclo[3,2,0]-hexa(dimethylamino)hepta-2,5-diene}] (5). Bis(dimethylamino)acetylene (0.15 mL, 0.79 g/mL, 1.06 mmol) was added in a single portion at −30 °C into a solution of 4Ge (300 mg, 0.17 mmol) in 10 mL of diethyl ether. The color of the reaction mixture immediately turned from green to dark brown. The dark brown reaction mixture was stirred for 5 min at ambient temperature, and the resulting solution was evaporated to dryness in vacuo. The dark brown residue was extracted with 10 mL of diethyl ether, and the extract was filtered. The filtrate was concentrated in vacuo to approximately 7 mL and stored at −60 °C for 48 h to afford redbrown crystals of 5. Yield: 71 mg (0.088 mmol, 51%). mp = 132 °C. Elemental analysis calcd (%) for C31H50GeN6O3W (811.25): C, 45.90; H, 6.21; N, 10.36. Found: C, 45.78; H, 6.08; N, 9.91%. IR (n-hexane, cm−1): ν̃ = 1982 (vs), 1913 (s), 1892 (vs) [ν(CO)]. IR (diethyl ether, cm−1): ν̃ = 1979 (vs), 1909 (s), 1888 (vs) [ν(CO)]. IR (solid, cm−1): ν̃ = 2961 (m), 2929 (m), 2867 (m), 2832 (m), 2794 (m), 1988 (vs) [ν(CO)], 1898 (vs) [ν(CO)], 1649 (w), 1610 (w), 1574 (m), 1455 (m), 1352 (m), 1337 (s), 1318 (m, sh), 1273 (m), 1256 (m), 1140 (s, sh), 1120 (vs), 1057 (s), 1016 (m), 986 (m), 970 (m), 951 (m), 915 (m), 877 (w), 850 (w), 825 (w), 809 (w), 767 (w), 720 (vw), 683 (vw), 670 (vw), 649 (vs), 621 (m), 581 (m), 564 (s), 493 (s), 463 (s), 418 (s). 1H NMR (300.1 MHz, toluene-d8, 298 K, ppm): δ = 1.74, 1.841, 1.845, 1.91 (s each, 3H each, C-Me, C5Me4CH2−), 2.09 (d, 1H, 2 J(H,H) = 15 Hz, C5Me4CHACHB), 2.75 (d, 1H, 2J(H,H) = 15 Hz, C5Me4CHACHB), 2.55, 2.68, 2.71, 2.87, 2.91, 2.99 (s each, 6H each, CNMe2). 1H NMR (300.1 MHz, toluene-d8, 203 K, ppm): δ = 1.62, 1.67, 1.72, 1.82 (s each, 3H each, C-Me, C5Me4CH2−), 1.97 (d, 1H, 2 J(H,H) = 15 Hz, C5Me4CHACHB; the other methylene proton doublet is obscured by the NMe2 singlet signals appearing between δ = 2.60 and 2.79 ppm), 2.55 (3H), 2.60 (3H), 2.69 (6H), 2.73 (6H), 2.79 (3H), 2.94 (3H), 3.05 (6H), 3.10 (3H), 3.16 (3H) (s each, NMe2). 13 C{1H} NMR (75.47 MHz, toluene-d8, 203 K, ppm): δ = 10.5, 10.6, 10.8, 14.0 (s each, 1C each, C-Me, C5Me4CH2−), 30.6 (s, 1C, CH2, 1538

DOI: 10.1021/acs.organomet.7b00110 Organometallics 2017, 36, 1530−1540

Article

Organometallics C5Me4CH2−), 36.3 (1C), 38.8 (2C), 40.0 (1C), 41.3 (1C), 42.8 (1C), 44.5 (1C), 44.9 (2C), 46.2 (1C), 46.3 (1C), 47.3 (1C) (s each, NMe2), 98.7, 99.3, 103.3, 104.9, 123.3 (s each, 1C each, C-Me, C5Me4CH2−), 91.2, 117.2, 132.6, 138.5, 145.0, 146.3 (s each, 1C each, CNMe2), 220.3 (s, 1C, CO), 222.4 (s, 1C, CO), 226.8 (s, 1C, CO). The 1H and 13C NMR signals of 5 in toluene-d8 at 203 K were assigned by 1H,13C HMQC and HMBC experiments. In addition, variable-temperature 1H NMR spectroscopy of 5 in toluene-d8 from 203 to 298 K revealed that rotation of four of the six NMe2 groups is frozen out at low temperatures (see SI, Figure S47), giving rise to 10 N-Me signals in the 13C{1H} NMR spectrum of 5 at 203 K (see SI, Figures S44−S46) and 10 N-Me singlet signals in 1H NMR spectrum of 5 at 203 K, two of which coincide at δ = 2.69 ppm (see SI, Figures S43 and S48). Crystal Structure Determination of 1Sn 2·0.25(Et2O), 3· (Et2O), 4Sn·0.5(C6H6), and 5·(Et2O). Suitable single crystals for the scXRD studies were grown as follows: yellow-orange crystals of 1Sn upon cooling a n-hexane/toluene (4:1, v/v) solution from ambient temperature to −30 °C; red-brown crystals of 2·0.25(Et2O) upon cooling of a Et2O solution of 2 from ambient temperature to −30 °C; red-brown crystals of 3·(Et2O) upon cooling an n-hexane/Et2O (1:3, v/v) solution of 3 from ambient temperature to −30 °C; green crystals of 4Sn·0.5(C6H6) upon cooling of an n-hexane/fluorobenzene/ benzene (1:3:0.5, v/v/v) solution of 4Sn from ambient temperature to −30 °C; red-brown crystals of 5·(Et2O) upon cooling an Et2O solution of 5 from room temperature to −30 °C. The data collection of 1Sn, 2·0.25(Et2O), 3·(Et2O), and 4Sn·0.5(C6H6) was performed on a Nonius Kappa CCD diffractometer (area detector) and the data collection of 5·(Et2O) on a STOE IPDS 2T diffractometer (area detector). The diffractometers used graphite monochromated Mo Kα radiation (λ = 0.71073 Å) and were equipped with low-temperature devices (Nonius KappaCCD diffractometer: Cryostream 600er series, Oxford Cryosystems, 123 K; STOE IPDS-2T diffractometer: Cryostream 700er series, Oxford Cryosystems). Intensities were measured by fine-slicing ω and φ-scans and corrected for background, polarization, and Lorentz effects. An empirical absorption correction was applied for all data sets. The structures were solved by direct methods and refined anisotropically by the least-squares procedure implemented in the SHELX program system. Hydrogen atoms were included isotropically using the riding model on the bound carbon atoms. 1Sn contains a small disorder, where the Sn−Cl moiety is partially mirrored at a virtual mirror plane close by the Sn atom, which contains the W and C1 atom. The occupancy sum of this side is 5.4(1)%. See Table 2 for crystallographic data and structure refinement.

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Notes

The authors declare no competing financial interest. CCDC-1524135 (1Sn), CCDC-1524136 (2·0.25(Et2O)), CCDC-1524137 (3·(Et 2 O)), CCDC-1524138 (4Sn·0.5(C 6 H6 )), and CCDC-1524139 (5·(Et2 O)) contain the supplementary crystallographic data for this paper, which can be obtained free of charge from The Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/data_request/cif

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ACKNOWLEDGMENTS We thank the Deutsche Forschungsgemeinschaft (SFB813, “Chemistry at Spin Centers”) and University of Bonn for the financial support of this work. We appreciate the assistance of C. Schmidt, K. Prochnicki, and H. Spitz for recording the solution NMR spectra and A. Martens for the elemental microanalyses.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00110. 1 H, 13C{1H}, 19F{1H}, 11B{1H}, 119Sn{1H} NMR and IR spectra of complexes 1 − 5, and selected spectroscopic data of silicon analogues of 2, 3 and 4Sn prepared in our laboratory (PDF) X-ray data (CIF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*E-mail for Y.N.L.: [email protected]. *E-mail for A.C.F.: fi[email protected]. ORCID

Yury N. Lebedev: 0000-0003-2985-6876 Present Address §

(Y.N.L.) King Abdullah University of Science and Technology, KAUST Catalysis Center, Thuwal 23955, Saudi Arabia). 1539

DOI: 10.1021/acs.organomet.7b00110 Organometallics 2017, 36, 1530−1540

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NOTE ADDED AFTER ASAP PUBLICATION In the version of this paper published on April 12, 2017, an incorrect chemical name and abbreviation was given in the second paragraph of the Introduction. The version that appears as of April 24, 2017, has the correct name and abbreviation.

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DOI: 10.1021/acs.organomet.7b00110 Organometallics 2017, 36, 1530−1540