Influence of Ligand Modifications on Structural and Spectroscopic

Article pubs.acs.org/Organometallics

Influence of Ligand Modifications on Structural and Spectroscopic Properties in Terphenyl Based Heavier Group 14 Carbene Homologues Petra Wilfling,† Kathrin Schittelkopf,† Michaela Flock,† Rolfe H. Herber,*,‡ Philip P. Power,*,§ and Roland C. Fischer*,† †

Institute for Inorganic Chemistry, Graz University of Technology, Graz 8010, Austria Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel § Department of Chemistry, University of California, Davis, California 95616, United States ‡

S Supporting Information *

ABSTRACT: The synthesis and characterization of a series of heavier group 14 element (Ge, Sn, and Pb) carbene homologues based on the electronically modified, 2,6-dimesityl substituted terphenyl ligands Ar#-3,5-iPr2, Ar#-4-SiMe3, and Ar#-4-Cl (Ar#-3,5-iPr2 = C6H2-2,6-Mes2-3,5-iPr2; Ar#-4-Cl = C6H2-2,6-Mes2-4-Cl; Ar#-4-SiMe3 = C6H2-2,6-Mes2-4-SiMe3; Mes = C6H2-2,4,6-Me3) are presented. The consequences of introducing electron withdrawing and -releasing substituents on the solid state structures of the newly synthesized germylenes, stannylenes, and plumbylenes as well as their Mössbauer, NMR and UV−vis spectroscopic properties are presented and discussed in the context of a second order Jahn−Teller type mixing of frontier orbitals with appropriate symmetry. Experimental findings were supported by DFT calculations. More electron withdrawing ligands lead to a bonding situation with higher contribution of p-orbitals from the central heavier group 14 element in σ-bonding toward the ligands and thus increased s-electron character of the lone pair. Furthermore, this results in an increase in the energy separation between the frontier orbitals. Experimentally, these changes are manifested in narrower bending angles at the heavy tetrel atoms and hypsochromic in their UV−vis spectra. In contrast, derivatives of more electron rich m-terphenyl ligands are characterized by a smaller HOMO− LUMO gap and wider interligand angles.

■

INTRODUCTION The synthesis and characterization of low-valent group 14 element compounds stabilized by sterically encumbering ligands has been a central focus in main group chemistry research for 4 decades. Commencing with the pioneering reports by Lappert and co-workers on the dialkyl compounds {E[CH(SiMe3)2]2}2, E = Sn, Pb,1 and later the corresponding Ge species,2 the area has proven to be an extremely rich field and a highly diverse array of ligands have been employed in their stabilization.1−8 Among these, terphenyl ligands have played a significant role in the expansion of the number of known species either of this type or related multiple bonded group 14 derivatives.9−14 In 2010 we published studies on the variation of the substituents at the central aromatic ring of the terphenyl system and its consequences for bond lengths, bond angles, and UV−vis absorption maxima in the related group 14 alkyne analogues ArEEAr (Ar = terphenyl, E = Ge or Sn).15 These studies showed that small changes in the periphery of mterphenyl ligands can dramatically influence the EE multiple bonding. For example, the introduction of a trimethylsilyl group in the para-position of the central aromatic ring in Ar′, Ar′ = C6H3-2,6-Dipp2, Dipp = C6H3-2,6-iPr2, resulted in a © XXXX American Chemical Society

drastic change in the Sn−Sn bonding in the dimer 4-Me3Si− Ar′SnSnAr′-4-SiMe3. In the original compound Ar′SnSnAr′,13 the Sn−Sn distance was 2.6675(4) Å and the Sn−Sn−Cipso angle was 125.24(7)°, consistent with multiple Sn−Sn bonding. In striking contrast, the Sn−Sn distance in 4-Me3Si− Ar′SnSnAr′-4-SiMe3,12 was ∼0.4 Å longer at 3.066(10) Å, and the Sn−Sn−Cipso bending angle was 99.25(14) Å, which is about 26° narrower than that in the unsubstituted derivative. These changes indicated a transformation of the Sn−Sn multiple bond in Ar′SnSnAr′ to a single bond in 4-Me3Si− Ar′SnSnAr′-4-SiMe3. Another important structural difference was seen in the arrangement of the central aromatic ring of the terphenyl ligands with respect to the CipsoSnSnCipso core of the compound. In Ar′SnSnAr′, the central ring lies in the plane of the CipsoSnSnCipso unit, whereas in Me3Si−Ar′SnSnAr′-4-SiMe3 the planes of the central rings of the terphenyl ligands are perpendicular to the core, as in the singly bonded lead Special Issue: Mike Lappert Memorial Issue Received: September 15, 2014

A

dx.doi.org/10.1021/om500946e | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

Scheme 1. Synthesis of m-Terphenyl Ligands Modified in meta- and para-Positions of the Central Aromatic Ring

derivative Ar*PbPbAr*, Ar* = C6H3-2,6-Trip2, Trip = C6H22,4,6-iPr3.14 More subtle changes in the bonding of heavier group 14 alkyne analogues are observed with 4-Cl, 4-F, 4-MeO, or 4-tBu modified ligand derivatives of germanium and tin.15 The + I or − I effects of the substituents in the para-position of the central rings cause small but noticeable trends in the bonding of dimers that involve not only the bond distances and angles around the heavier tetrels but also their electronic and NMR spectra. Interestingly, both the 4-Me3Si and 4-Me3Ge substituted terphenyl ligands stabilize the single bonded isomer, whereas the similarly sized tBu-substituted ligand affords the multiple bonded isomers. Large changes in the bonding have been seen also with the use of the very bulky 3,5-di-iso-propyl substituted ligand 3,5-iPr2−Ar′ both in the group 14 alkyne analogue and in the neighboring group 13 metals. This ligand afforded access to a strictly monocoordinated Ga(I) compound16 in contrast to the Ar′GaGaAr′ dimeric structure that is observed when the less crowded Ar′ ligand is used.17 In addition, the 3,5-iPr2−Ar′ was shown to stabilize mononuclear Cr(I) species,18 whereas use of the Ar′ ligand led to the dimerized quintuple bonded Cr(I) species Ar′CrCrAr′.19 Large structural effects have been observed also in terphenylsubstituted low valent tin hydrides. These typically exist as hydrogen bridged dimers. However, in the case of the m-terphenyl ligand 3,5-iPr2−Ar′, an unsymmetrical mixed structure, i.e., 3,5-iPr2−Ar′Sn(H)2Sn-3,5-iPr2−Ar′, was observed in the solid state.20 Both isomers had been predicted to exist as isolable compounds by computational methods. The low valent tin hydrides were also shown to be accessible via H2 addition to stannylenes and distannynes.20−23 Herein, we report on the structural and electronic effects in a series of new, sterically less encumbered ligands in divalent heavier group 14 element derivatives. We describe the synthesis and characterization of the compounds E(Ar#-3,5-iPr2)2 (E = Ge (1), Sn (2), or Pb (3), (Ar#-3,5-iPr2 = C6H-2,6-Mes23,5-iPr2; Mes = C6H2-2,4,6-Me3), E(Ar#-4-Cl)2 (Ar#-4-Cl = C6H2-2,6-Mes2-4-Cl; M = Ge (4), Sn (5), and Pb(6)) and Ar#-4-SiMe3 = C6H2-2,6-Mes2-4-SiMe3 (M = Ge (7), Sn (8), or Pb (9)) as well as the synthesis of these ligands. The different ligands are illustrated in Figure 1. The new compounds 1−9

Lithiation of the modified ligands with nBuLi in hexanes provides the metalated transfer agents in nearly quantitative yields (see Scheme 2). Scheme 2. Generation of Lithiated m-Terphenyl Ligands from Iodides

The Ar#-3,5-iPr2 substituent was chosen to study the steric and electronic effect of bulky alkyl groups in the meta-positions of the products. Steric hindrance at the backbone pushes the flanking mesityl groups toward the core of the molecule and increases the steric demand around the divalent group 14 element atom. The Ar#-4-Cl group was employed to investigate the effect of using a more electronegative substituent (Cl) in para-position of the central ring. In Ar#-4-SiMe3, the electronreleasing Me3Si-group was chosen to probe the opposite effect. As reference structures, the tetrylenes based on the unaltered ligand Ar#, which carries hydrogen atoms in meta- and parapositions, were included in the comparative study. Salt metathesis reactions of the lithiated terphenyl ligands with 0.5 equiv of ECl2 (E = Ge, Sn, Pb) provides the respective tetrylenes in excellent yields as deeply colored, air and moisture sensitive compounds (see Scheme 3). Storage of diethyl ether solution of the terphenyl substituted tetrylenes at −30 °C yielded crystals of sufficient quality for X-ray diffraction studies and clean samples for analysis by multinuclear NMR and UV− vis spectroscopy. X-ray Crystal Structures. The solid state structures of compounds 1−9 were determined by single crystal X-ray diffraction. As representative examples, thermal ellipsoid plots of compounds 3, 5, and 7 are shown in Figures 2−4 (the thermal ellipsoid plots of compounds 1, 2, 4, 6, 8, and 9 are provided in the Supporting Information). Selected important structural data are given in Table 1. Table 2 features a listing of the bending angles as well as spectroscopic data for 1−9 and related diaryl-substituted species.25−46 Compounds 1−9 crystallize as discrete strictly two-coordinate, V-shaped monomers, and the structures of Ar#-4-SiMe3 derivatives 7−9 are characterized by the presence of a 2-fold rotation axis through the tetrel atom. Among the terphenyl compounds reported in this study, the widest interligand angles for the heavier group 14 tetrylenes are found in the E(Ar#-3,5-iPr2)2 compounds 1−3. The Ge

Figure 1. Modified, 2,6-dimesityl substituted m-terphenyl ligands.

were characterized by multinuclear (1H, 13C, 29Si, 119Sn, 207Pb) NMR methods, UV−vis absorption measurements, single crystal X-ray diffraction analysis and tin compounds 2, 5, and 9 by 119Sn Mössbauer (ME) spectroscopy.

■

RESULTS AND DISCUSSION Synthesis. The novel terphenyl ligands Ar#-4-Cl and Ar#-4SiMe3 were prepared by modification of literature procedures based on a protocol initially used by Du and Hart (see Scheme 1).24 Ar#-3,5-iPr2 was obtained by a previously reported procedure (see the Experimental Section). In their syntheses, instead of the 1,3-dichlorobenzene originally used, the modified phenyl chlorides 1,3,5-Cl3−C6H3, 5-Me3Si-1,3Cl2−C6H3, and 4,6-iPr2-1,3-Cl2−C6H2 were employed. B


Organometallics

Article

Scheme 3. Synthesis of m-Terphenyl Based Heavier Tetrylenes

Figure 2. Molecular structure of Pb(Ar#-3,5-iPr2)2, 3 (hydrogen atoms are not shown for clarity, ellipsoids drawn at 30% probability level, distances in Å, angles in deg). Structural parameters for the respective germanium and tin derivatives 1 and 2 are given in Table 1. Pb1−C1 2.353(3); Pb1−C31 2.357(1); C1−Pb1−C31 123.9(1).

Figure 4. Molecular structure of Ge(Ar#-4-SiMe3)2, 7 (hydrogen atoms are not shown for clarity, ellipsoids drawn at 30% probability level, distances in Å, angles in deg). Structural parameters for the respective tin and lead derivatives 8 and 9 are given in Table 1. Ge1− C1 2.023(4), C1−Ge1−C1A 116.3(2).

115.12(8) and 115.30(8)°, are very similar to the 114.7(2)° and 114.5(6)° in the respective EAr#2 species. The trimethylsilyl substituted compounds 7−9 display C−E−C angles that are slightly increased in comparison to values found in the unaltered compounds EAr#2. The germylene 7 features an angle of 116.3(2)° which compares to 114.4(1)° in GeAr#2. The respective angles for tin are 115.37(9)° in 8 and 114.7(2)° in SnAr#2 and for lead the angles are 114.92(8)° in 9 and 114.5(6)° in PbAr#2. It is noteworthy that the C−E−C angles in the three most crowded Ar#-3,5-iPr2 derivatives are all close to 124°. These angles are wider than the 112.7(2)° (Ge), 117.56(8)° (Sn), or 121.5(3)° (Pb) in the EAr2′ derivatives, which were the most crowded terphenyl group 14 species previously known.10 The C−E−C angle is of importance because, as was experimentally shown earlier, the bending angle can be correlated with chemical reactivity. For instance, the wide angle compounds EAr2′ (E = Ge, Sn) directly react with dihydrogen under formation of (Ar′SnH)2 despite the increased steric shielding of the tetrel atoms.22 The respective EAr#2 compounds, although less crowded around germanium and tin, have diminished reactivity and require higher temperatures and longer reaction times for complete conversion. The variation of the E−C distances with the substituent pattern is modest but is nevertheless in agreement with

Figure 3. Molecular structure of Sn(Ar#-4-Cl)2, 5 (hydrogen atoms are not shown for clarity, ellipsoids drawn at 30% probability level, distances in Å, angles in deg). Structural parameters for the respective germanium and lead derivatives 4 and 6 are given in Table 1. Sn1−C1 2.248(2); Sn1−C25 2.249(2); C1−Sn1−C25 115.12(8).

derivative in 1 features a C−Ge−C angle of 124.46(11)° that exceeds the widest angle in previously reported diorganogermylene species by over 10°.8,10,11 In contrast, in the chlorosubstituted compound 4 the C−Ge−C angle at the germanium atom is narrowed to 112.63(7)°, in comparison to 114.4(1)° in the GeAr#2. However, the C−Sn−C and C−Pb−C angles in the corresponding para-Cl substituted compounds 5 and 6, C


Organometallics

Article

Table 1. Structural Parameters for Compounds 1−9 #

i

Ge(Ar -3,5- Pr2)2, 1 Ge(Ar#-4-Cl)2, 4 Ge(Ar#-4-SiMe3)2, 7 Sn(Ar#-3,5-iPr2)2, 2 Sn(Ar#-4-Cl)2, 5 Sn(Ar#-4-SiMe3)2, 8 Pb(Ar#-3,5-iPr2)2, 3 Pb(Ar#-4-Cl)2, 6 Pb(Ar#-4-SiMe3)2, 9

E−Cipso [Å]

Cipso−E−C′ipso [deg]

Cpara′−Cipso−Cpara″ [deg]a

ArCent/Ar′Cent [deg]b

2.052(3)/2.053(3) 2.020(2)/2.028(2) 2.023(4) 2.250(4)/2.261(4) 2.248(2)/2.249(2) 2.243(2) 2.353(3)/2.357(3) 2.338(2)/2.347(2) 2.343(2)

124.46(11) 112.63(7) 116.3(2) 123.4(2) 115.12(8) 115.37(9) 123.9(1) 115.30(8) 14.92(8)

154.00/154.80 153.44/156.80 165.58 150.12/155.01 155.34/158.29 160.16 150.38/150.68 153.93/156.88 158.58

70.68 76.60 58.70 70.03 70.14 76.26 67.53 69.62 76.45

a

b

Twist angle between central rings (least-squares fit) of terphenyl ligands.

The transitions in the Dipp substituted compounds SnAr′2 and PbAr′2 are 600 and 586 nm (see Figure 5). In summary, the chromophores are shifted to the blue with increasing atomic number, consistent with the increasing stabilization of the nonbonded lone pair. Increasing electron withdrawing character of the ligand also causes a shift to the blue, so that the energy of the absorptions follow the sequence Ar#-4-Cl > Ar# ≈ Ar#-4-SiMe3 > Ar′ > Ar#-3,5-iPr2. Overall, the close correspondence between the UV−vis spectroscopic data for the Ar# and Ar#-4-SiMe3 (as well as the 119Sn and 207Pb chemical shift for the tin and lead derivatives, see below) point to the fact that the SiMe3 ring substituent does not exhibit a strong electronic effect on the spectra.47 Variation in ligands also result in considerable changes in NMR chemical shifts that are attributable to changes in the HOMO−LUMO gaps. Most significantly, the NMR resonances of the central, divalent group 14 metal are affected via the paramagnetic contributions to NMR chemical shifts. The most pronounced downfield shifts in 119Sn and 207Pb NMR spectra at +2081 and +9593 ppm, respectively, are observed for the Ar#-3,5-iPr2 compounds. The resonances of the 4-Clsubstituted derivatives, in contrast, are observed at +1891 (119Sn) and +8609 ppm (207Pb) and are slightly shifted to higher field with respect to the Ar#-4-SiMe3- and 4-H-carrying ligand (Ar#) derivatives which exhibit resonances at +1975 and +1971 in the 119Sn NMR spectrum and +8778 and +8844 ppm in the 207Pb NMR spectrum, respectively. Similarly, the 13C NMR shifts of the ipso carbon atoms of the terphenyl ligands show a strong direct correlation to the HOMO−LUMO gap. Again, the most pronounced downfield shifts are found in the E(Ar#-3,5-iPr2)2 compounds (+ 172 ppm E = Ge, +199 ppm E = Sn, + 328 ppm E = Pb). On the other hand, as expected, the 4−Cl-Ar# compounds have resonances at higher field with + 168 ppm E = Ge, + 189 ppm E = Sn, + 300 ppm E = Pb. The significant differences observed in NMR chemical shifts result from paramagnetic contributions, which increase with a decreasing HOMO−LUMO energy separation. Mössbauer Effect (ME) Studies. Spectra of 2, 5, and 8 consist of a main doublet resonance, accompanied by small additional absorbances due to an impurity not otherwise identified. A summary of the ME parameters of these tin species is presented in Table 3, and a representative spectrum of 2 is shown in Figure 6. In the subsequent discussion, only the principal Sn(II) resonance will be considered in detail.

Figure 5. Normalized UV−vis spectra for compounds 1−9, showing that the shift in the n → p chromophore with tetrel atomic weight and ligand type. The solid lines represent Ge-compounds, dashed lines Sn-, and dotted lines Pb -compounds. Ar#-3,5-iPr2 derivatives are in red, Ar#-4-SiMe3 in green, and Ar#-4-Cl species in blue.

expectations. Thus, the longest E−C distances are observed in the (Ar#-3,5-iPr2) derivatives, with the most pronounced increase in bond distance for the germanium compound, where the average E−C distance exceeds those in the respective chloro- and trimethylsilyl compounds by an average of 0.03 Å. Spectroscopic Studies. The electronic transitions in the visible range, to which the heavier terphenyl-based tetrylenes owe their intense purple to dark blue colors, arise from n−p transitions which are directly correlated to the HOMO− LUMO energy gap, and are therefore an indirect measure for the degree of orbital mixing. For the germanium compounds 1, 4, and 7, the transitions in the visible range vary between 622 nm for the Ar#-3,5-iPr2 (1), 583 nm for the Ar#-4-SiMe3 (7), and 566 nm for the Ar#-4-Cl (4) derivatives. For comparison, GeAr#2 features a transition at 578 nm (very close to that of 7), whereas the n−p excitation in the bulkier GeAr′2 is observed at 608 nm, which is closest to that of 1. Upon descending group 14, the trends in batho- and hypsochromic shifts with respect to the substituent pattern persist but become somewhat less pronounced for the tin and lead species. In the tin derivatives, the UV maxima are observed 591 nm (Ar#-3,5-iPr2), 555 nm (Ar#-4-SiMe3), and 544 nm (Ar#-4-Cl) (cf. 553 nm (Ar#)), in the case of lead, these range from 566 nm (Ar#-3,5-iPr2), 528 (Ar#-4-SiMe3), 526 nm (Ar#) to 513 nm (Ar#-4-Cl). D


Organometallics

Article

Table 2. Structural Parameters and Spectroscopic Data for Aryl-Substituted Heavier Tetrylenesa C−E−C [deg]

λ max [nm]

∂ NMR 13Cipso [ppm]

∂ NMR,

119

Sn,

207

Pb [ppm]

ref

Germanium Ge(Ar#-3,5-iPr2)2, 1 Ge(Ar#-4-Cl)2, 4 Ge(Ar#-4-SiMe3)2, 7 Ge(C6H-2-tBu-4,5,6-Me3)2 Ge(C6H2-2,4,6-tBu3)2 Ge{C6H2-2,4,6-(CF3)3}2 Ge(C6H2-2,4,6-Ph3)2 GeAr#2 Ge{C6H3-2,6-(NMe2)2}2 Ge{C6H3-2,6-(1-naphthyl)2}2 GeAr′2 Ge(Eind)2 Ge(Bbt)Trip

124.46(11) 112.63(7) 116.3(2) n/a 108.0(2) 99.5(10) n/a 114.4(2) 105.1(3) 102.72(9) 112.7(2) 111.98(5) n/a

Sn(Ar#-3,5-iPr2)2, 2 Sn(Ar#-4-Cl)2, 5 Sn(Ar#-4-SiMe3)2, 8 Sn(C6H-2-tBu-4,5,6-Me3)2 Sn(C6H2-2,4,6-tBu3)2 Sn{C6H2-2,4,6-(CF3)3}2 Sn(Bbt)Trip SnAr#2 Sn{C6H3-2,6-(NMe2)2}2 SnAr′2 Sn(Ph)Ar′ Sn(Tbt){C6H3-2,6(C6H3-2,4-iPr2)2}

123.4(2) 115.12(8) 115.37(2) n/a 103.6(1) 98.2(2) n/a 114.7(2) 105.6(2) 117.56(8) 96.87(10) 106.4(2)

Pb(Ar#-3,5-iPr2)2, 3 Pb(Ar#-4-Cl), 6 Pb(Ar#-4-SiMe3)2, 9 Pb(C6H-2-tBu-4,5,6-Me3)2 Pb{C6H2-2,4,6-(CF3)3}2 Pb(C6H2-2,4,6-Ph3)2 PbBbt2 Pb(Bbt)Trip PbTbt2 PbAr#2 Pb{C6H3-2,6-(NMe2)2}2 Pb{C6H3-2,6-(1-naphthyl)2}2 PbAr′2 Pb(Ph)Ar* Pb(C6H4-4-tBu)Ar′ Pb{C6H4-2,6-(OiPr)2}2

123.9(1) 115.30(8) 114.92(8) 103.04(13) 95.1(1) 92.7(5)/ 95.8(2) n/a n/a 116.3(7) 114.5(6) 102.2(1) 100.4(1) 121.5(3) 95.64(11) 94.53(19) 93.0(2)

622 565 583 440 430 374 orange-red 578 yellow red 608 578 580 Tin 591 544 555 479 476 345 561 553 yellow 600 462 547 Lead 566 513 528 490 yellow red-purple 610 550 560 526 yellow orange 586 460 462 orange/red

172.0 167.5 170.3 150.8 162.1 165.3 162.7 169.6 n/a 168.6 175.0 172.5 n/a

this work this work this work 25 26 27 28 11 29, 30 28 10 31 32

198.7 188.8 192.0 154.6 156.7 179.7 n/a n/a n/a 199.2 n/a 190.1

2081 1891 1975 1331 980 723 2208 1971 442 2235 2870 1657

this work this work this work 33 34 35 36 11 29 11 37 38

328.2 300.6 306.0 275.6 258.5 n/a 152.9 n/a n/a n/a n/a n/a 147.1 n/a 260.3/276.2 221.1

9593 8609 8778 6927 4878 n/a 9751/8971 8888 8873 8844 3919 n/a 9430 7987 7275 5859

this work this work this work 39 40 41 42 43 43 11 29, 30 41 11 44 45 46

a

Bbt = [C6H2-2,6-{CH(SiMe3)2}2-4-C(SiMe3)3], Tbt= [C6H2-2,4,6-{CH(SiMe3)2}3]. Ar′ = C6H3-2,6-(C6H3-2,6-iPr2)2. Ar* = C6H3-2,6-(C6H22,4,6-iPr3)2, Trip = C6H2-2,4,6-iPr3. Eind = 1,1,3,3,5,5,7,7-octaethyl-3,3,5,5-s-hydrindacene.

Table 3. Summary of ME Parameters and Derived Values for 2, 5, and 8a

a

compound

2

5

8

IS(90) QS(90) − d IS/dT −d ln A/dT k2⟨Xave2⟩M,100 k2⟨Xave2⟩X,100

C60H74Sn 2.194(3) 4.412(3) 3.23(23) 22.14(6) 2.20(4) 2.57(2)

C48H48Cl2Sn 2.892(4) 4.487(4) 2.18(17) 17.45(8) 1.76(4) 1.93(2)

C54H66Si2Sn2 2.864(6) 4.459(6) T independent 20.90(2) 2.094 2.73(2)

units mm s−1 mm s−1 mm s−1 K−1 × 10−4 K−1 × 10−3

The parenthetical number indicated the error in the last digit(s). E


Organometallics

Article

123.4(5)° at 100 K, and this configuration is reflected in the dynamical data of the Sn atom. The intensity ratio R = [A(+)/ A(−)] of the two components of the (major) ME resonance is slightly temperature-dependent, suggesting that the vibrational motion of the Sn atom is not strictly isotropic (see Figure 8).

Figure 6. Mössbauer spectrum of 2 at 93.7 K.

Because of the relatively high ME gamma ray energy and the relatively low lattice temperature of these compounds, the useful temperature range over which ME data could be acquired was limited to ∼90−250 K. Compound 2. The principal resonance is clearly due to Sn(II). Of the two minor resonances, one is due to Sn(IV), while the smallest is due to an Sn(II) impurity. The isomer shift (IS) is reasonably well fitted by a linear regression with a correlation coefficient of 0.982 for 13 data points. The quadrupolar splitting (QS) parameter, which as usual shows a negative temperature dependence,48 is not well fitted by such a linear regression and reflects the influence of low-lying librational and/or rotational modes (vide inf ra) and is summarized graphically in Figure 7.

Figure 8. Temperature dependence of the logarithm of the recoil-free fraction f for compound 2.

Compound 5. The data in Table 3 indicate that the major ME resonance is due to Sn(II). While the QS at 90 K is almost the same as for 2, the IS is significantly larger, reflecting a somewhat greater electron density at the metal site. Again, the temperature-dependence of ln f is well fitted by a linear regression with a correlation coefficient of 0.98 for 11 data points. As previously noted, this leads to FM,100 = 1.76(4) and FX,100 = 1.93(2) and, as before, with FX,100 slightly larger than FM,100. The local configuration at the Sn atom is similar to that observed in 2 but both the temperature dependence of the QS and the area ratio parameter follow a linear regression, suggesting that in this compound, the low-lying vibrational/ librational modes play a much smaller part in the dynamics of the Sn atom in the temperature range 93 < T < 256 K. The two Cl atoms are remote from tin and thus are not expected to influence the dynamical properties of the central metal atom. Compound 8. As above, the major ME resonance confirms the formal oxidation state of the metal atom as Sn(II). For this compound, the IS is essentially temperature independent [2.86(2) mm s−1] over the temperature range 92 < T < 217 K. The QS parameter shows a negative T dependence as expected. The temperature-dependence of ln f is again well fitted by a linear regression, with a correlation coefficient of 0.998 for 7 data points. For this compound, FM,100 = 2.09(3) and FX,100 = 2.73(2). Here, again, the Sn atom is ligated to the two neighboring C atoms by bonds of 2.241 and 2.342 Å with a bond angle of 115.68°. The area ratio, R, is essentially T independent, and the F value difference between the ME and X-ray data is presumed to arise from low-lying optical modes, as in the case of 2. The ME spectra for 2, 5, and 8 represent rare examples of such data for divalent two-coordinate, organotin(II) compounds. The earliest data were reported for Sn{CH(SiMe3)2}2 and its transition metal compounds by Lappert, Donaldson, and co-workers in 1976. IS and QS values in the ranges 2.13− 2.21 mm s−1 and 2.31−4.57 mm s−1, respectively,51 confirmed their low valency, but all the compounds featured 3-coordinate tin(II) owing to Sn−Sn bonding or Sn−transition metal complexation. Zuckerman and co-workers reported IS and QS

Figure 7. Quadrupole splitting for 2.

The logarithm of the recoil-free fraction, f, which scales with the area under the resonance curve for an optically thin absorber, is well fitted by a linear regression, with a correlation coefficient of 0.98 for 16 data points. As pointed out previously,49 this dependence permits the evaluation of the F parameter (= k2⟨xave2⟩) and comparison of the ME derived value (FM,T) and the X-ray-diffraction value (FX,T) elucidated from the Ui,j parameters. For 2, the two values are FM,100 = 2.20(4) and FX,100 = 2.57(2). The larger vibrational amplitude extracted from the X-ray data compared to the ME data has been observed earlier50 and can be ascribed to low lying optical modes involving the central Sn atom. Inspection of the structure of 2 shows that the Sn atom is ligated by two single bonds (2.250(4) and 2.261(4) Å) with a bond angle of F


Organometallics

Article

values of 3.28 and 1.90 mm−1 for Sn(C6H2-2,4,6-tBu3)2 and values of 3.37 and 1.93 mm−1 for Sn{C6H2-2,4,6-(CF3)3}2 in 1981.52 These compounds involve formally two-coordinate, divalent Sn(II), but their structures feature close approaches from substituent atoms on the ligands.34,35 Nonetheless, the IS values in all these compounds are consistent with a divalent Sn(II) formulation. Other ME studies of two-coordinate tin bound to organic groups include the mixed valent (Sn(I)/Sn(III)) tin−tin bonded Ar*SnSnMe2Ar* (Ar* = C6H3-2,6(C6H2-2,4,6-iPr3)2) and Ar*SnSnPh2Ar*, which have identical IS and QS values of 2.70 mm s−1 and 4.50 mm s−1. The distannynes of the type ArSnSnAr (Ar = terphenyl group)15,53 have IS values in the range 2.60−2.908 mm s −1 and QS values between ∼3.0 and 4.7 mm s−1, the latter depending on the multiple character of the Sn−Sn bond. The IS values for 5 and 8 in Table 3 are close to those observed earlier for the two-coordinate tins in all these terphenyl derivatives, regardless of any multiple bonded character they contain. The IS shift of 2 is significantly lower than those of either 5 or 8, suggesting that the electron density from the lone pair is also lower, possibly as a result of a very wide C−Sn−C angle. The QS values of 2, 5, and 8 are close to each other and those in Ar*SnSnMe2Ar*, Ar*SnSnPh2Ar*, and in the single Sn−Sn bonded ArSnSnAr derivatives. Thus, they tentatively establish a pattern of values for two-coordinate, divalent diaryl tin(II) species which can be expected to exhibit IS values in the range 2.6−2.9 mm s−1 and QS values near 4.7 mm s−1. Computational Studies. The bent structure of closed shell 6-electron tetrylenes ER2 can be viewed as the consequence of second order Jahn−Teller type orbital mixing based on a hypothetical, linear ER2 molecule with D∞h-symmetry.54 Overall, the mixing of p- and s- orbitals located at the central atom E with the symmetric σg+ combination of ligand orbitals leads to bending of the ER2 molecule and will be stronger with increasing electronegativity of the ligands R. Consequently, the contribution of an initially nonbonding in-plane p-orbital at the central atom E to ER2 bonding is greater with increasing ligand electronegativity and will thus lead to greater energy separation of the frontier orbitals. The HOMO, which essentially respresents the lone pair at E thus adopts an increasing degree of s-electron character. In the context of ligands used in this study, the strongest bending should be encountered in the 4-Cl-Ar# compounds 4−6. As a higher degree of bending is associated with a larger gap between the frontier orbitals, the 4−Cl-Ar#-supported tetrylenes are expected to show the largest hypsochromic UV− vis shifts and less pronounced paramagnetic contributions to NMR shift values. In order to assess the influence of the ligand modifications, compounds 1−9 were investigated by DFT methods. As exploratory calculations have shown, the energy hypersurface of the substituted m-terphenyl based compounds is very shallow and calculations were based on the experimental geometries available from the single crystal X-ray diffraction analyses. For all substances studied, the HOMOs of the heavier group 14 carbene analogues are essentially nonbonding and centered at the heavy tetrel atom. They represent a lone pair of electrons at the heavy atom with a small contribution from the π-system of the central aromatic ring of the ligands. The LUMO is best described as a p-orbital in essentially orthogonal orientation with respect to the coordination plane of the tetrel atom. The HOMO and LUMO of 4 are shown in Figure 9; the respective orbitals for 1, 7, and GeAr#2 are given in the Supporting

Figure 9. HOMO (−5.279 eV, left) and LUMO (−2.340 eV, right) of Ge(Ar#-4-Cl)2, 4.

Information. Inspection of the frontier orbitals in 4 reveals a small yet significant contribution of chloro substituents. The orbital contribution of the central aryl rings is significantly lower in the other compounds, which is in agreement with diminished redistribution of electron density toward the ligands (i.e., reduced electronegativity) but higher spin density around the heavier tetrel. Time dependent DFT calculations on the germanium and tin compounds 1, 2, 4, 5, 7, and 8 show that the energetically lowest lying transition is dominated by the n−p transition. Hence, as expected, the energy separation between the HOMO and LUMO orbitals correlates directly with the lowest energy transitions in the UV−vis spectra. It is also this transition from which the deep blue to purple colors of the compounds originate. Inspection of the calculated orbital energies shows that substitution at the ligand backbone with the electronegative chlorine atom in the para-position lowers both HOMO and LUMO in energy but has greater impact on the highest molecular orbital and therefore in total leads to an increased energy gap between the frontier orbitals. The effect is most pronounced in the germanium compound 4 and less apparent in the tin and lead derivatives. The electron-rich iso-propyl substituted compounds 1−3, on the other hand, show weaker orbital mixing. Therefore, their HOMOs and LUMOs, are both higher in energy but also separated by a smaller energy difference of 2.775 eV (Ge) to 3.266 eV (Pb). Again, the trend is most apparent in the germanium compound 1, which shows the smallest energy gap and strongest bathochromic shift. Table 4 contains a summary of the calculated orbital energies Tables 3. For a summary of the calculated UV−vis absorption bands in 1, 2, 4, 5, 7, and 8, see Table S1 of the Supporting Information.

■

CONCLUSION Modifications of the central aryl rings of terphenyl substituents at the meta and para positions result in significant changes to the solid state structures of their divalent low valent group 14 compounds and also to their NMR, Mössbauer, and UV−vis spectra. Compounds 1−3, which are based on the ligand Ar#3,5-iPr2, are characterized by unusually wide angles at the tetrel atom and display bathochromically shifted UV−vis absorption bands and a downfield shift in their NMR spectra. Compounds 4−6, which are derivatives of the electron withdrawing Ar#-4-Cl ligand, show the opposite trend. Compounds of the SiMe3 derivatized ligand, Ar#-4-SiMe3, 7−9 display similar structural and spectroscopic characteristics to those of the “parent” Ar# ligand derivatives. Overall, an excellent correlation between structural and spectroscopic data is observed. Notably, the bending angle of the C−Sn−C moiety in compounds 2, 5, and G


Organometallics

Article

Table 4. Calculated Energies (eV) of HOMOs und LUMOs for compounds 1−9 Ge # i

Ar - Pr2 Ar#-Cl Ar#-SiMe3

Sn

LUMO

gap [eV]

HOMO

LUMO

gap [eV]

HOMO

LUMO

gap [eV]

−4.680 −5.279 −5.089

−1.905 −2.340 −2.177

2.775 2.939 2.912

−4.844 −5.333 −5.061

−2.014 −2.367 −2.122

2.830 2.966 2.939

−4.708 −5.252 −4.952

−1.442 −1.769 −1.496

3.266 3.483 3.456

off, and the solid residue was washed with methanol, iso-propanol, and Et2O (at −30 °C). The crystalline, colorless product was filtered off and dried in vacuo. Yield: 64%. Mp: 184−186 °C. 1H NMR (300.23 MHz, CDCl3): δ 2.00 (s, 12H, o-CH3), 2.35 (s, 6H, p-CH3), 6.96 (s, 4H, m-Mes), 7.11 (s, 2H, m-C6H2) ppm. 13C {1H} NMR (75.50 MHz, CDCl3): δ 20.43, 21.45, 105.67, 127.93, 128.43, 135.07, 135.39, 137.86, 141.08, 149.04 ppm. Elemental analysis (%) calcd for C24H24ClI (474.80): C, 60.71; H, 5.09. Found: C, 60.43; H, 5.12. Li−Ar#-4-Cl. With rapid stirring, I−Ar#-4-Cl (10 g, 22 mmol) was dissolved in 100 ml hexane and nBuLi (10 mL, 25 mmol) was added slowly via syringe (at 0 °C). The solution became cloudy upon stirring for 1 h and was allowed to come to room temperature. After stirring overnight, the supernatant liquid was removed via canula and the colorless product was dried in vacuo. Yield: 93%. Mp: 132−134 °C (decomposition). 1H NMR (300.23 MHz, C6D6): δ 2.59 (s, 12H, o-CH3), 2.76 (s, 6H, p-CH3), 7.17 (s, 2H, m-C6H2), 7.33 (s, 4H, m-Mes) ppm. 13C {1H} NMR (75.50 MHz, C6D6): δ 20.64, 21.17, 122.02, 127.82, 128.38, 129.30, 133.78, 135.64, 148.19, 154.27 ppm. Elemental analysis (%) calcd for C24H24ClLi (354.84): C, 81.24; H, 6.82. Found: C, 80.96; H, 6.94. C6H3-1,3-Cl2-5-SiMe3. To a solution of the Grignard reagent C6H3-1,3-Cl2-5-MgBr (111 mmol) in 400 ml THF, Me3SiCl (14 mL, 111 mmol) was added dropwise at 0 °C. Cu(I)CN (∼30 mg) was added and the reaction mixture was stirred for 3 days at room temperature. Afterward, the reaction solution was heated to the reflux temperature for 1 h and hydrolyzed. The phases were separated, and the organic phase was dried over anhydrous Na2SO4. The solvent was removed and the residue was fractionally distilled (36−38 °C, 1 mbar). Yield: 58%. 1H NMR (300.23 MHz, CDCl3): δ 0.35 (s, 9H, Si(CH3)3, 7.36 (t, 1H, aromat.), 7.42 (d, 2H, aromat.) ppm. 13C {1H} NMR (75.50 MHz, CDCl3): δ −1.12, 129.05, 131.48, 135.11, 145.17 ppm. 29 Si {1H} NMR (59.64 MHz, CDCl3): δ −2.51 ppm. Elemental analysis (%) calcd for C9H12Cl2Si (219.18): C, 49.32; H, 5.52. Found: C, 49.45; H, 5.63. I−Ar#-4-SiMe3. C6H3-1,3-Cl2-5-SiMe3 (24 g, 111 mmol) was dissolved in THF, cooled to −78 °C (MeOH/N2,liq) and slowly treated with a solution of nBuLi (49 mL, 122 mmol). The reaction solution was stirred at −78 °C for 1 h and yielded a colorless, crystalline precipitate. A freshly prepared solution of Grignard reagent (232 mmol) was added dropwise, via canula, at −78 °C. After the addition was complete, the reaction mixture was maintained at −78 °C for another 2 h and then allowed to reach room temperature overnight. The next day, the solution was refluxed for 2 h. I2 (42 g, 166 mmol) was added (at 0 °C), and the solution was allowed to reach room temperature and stirred for 4 h. Then, water was added and the excess I2 was quenched with Na2S2O3. The organic layer was separated, dried over anhydrous Na2SO4, the solvent was pumped off, and the solid residue was washed with methanol and iso-propanol. The crystalline, colorless product was filtered off and dried in vacuo. Yield: 54%. Mp: 109−110 °C. 1H NMR (300.23 MHz, CDCl3): δ 0.29 (s, 9H, SiMe3), 2.03 (s, 12H, o-CH3), 2.40 (s, 6H, p-CH3), 7.02 (s, 4H, m-Mes), 7.23 (s, 2H, m-C6H2) ppm. 13C {1H } NMR (75.50 MHz, CDCl3): δ −0.83, 20.60, 21.52, 108.71, 128.34, 132.67, 135.78, 137.42, 141.65, 142.54, 146.45 ppm. 29Si {1H } NMR (59.64 MHz, CDCl3): δ −3.12 ppm. Elemental analysis (%) calcd for C27H33ISi (512.54): C, 63.27; H, 6.49. Found: C, 63.12; H, 6.41. Li−Ar#-4-SiMe3. With rapid stirring, I−Ar#-4-SiMe3 (441 mg, 0.86 mmol) was dissolved in 10 ml Et2O and tBuLi (1 mL, 1.72 mmol) was added slowly via syringe. The solution became cloudy upon stirring for 1 h and was allowed to come to room temperature. After stirring overnight, the supernatant liquid was removed via canula and

8 and IS values, which are both obtained from solid state samples, show a strictly linear relation (see the Supporting Information, Figure S29). Similarly, the solution based data on UV−vis absorption maxima, 13C, 119Sn, and 207Pb NMR chemical shift of compounds 2, 3, 5, 6, 8, and 9 are strictly linearly correlated with R2 values above 0.9 (see the Supporting Information, Figures S30 and S31). Somewhat larger deviations, however, are observed between solid state properties like X-ray based bending angles C−E−C and UV−vis maxima or NMR shifts, which is likely a consequence of structural changes upon dissolution as suggested by the computationally observed shallow potential hypersurface. The structural and spectroscopic changes are in full agreement with bonding models based on second order Jahn−Teller orbital interactions.54 These predict increased bending and associated with larger energy separation between the frontier orbitals, supported by more electron withdrawing ligands and vice versa in the case of more electron releasing ligands. DFT calculations on the target compounds support this model. Since the reactivity of heavier group 14 carbene analogues is generally inversely proportional to the HOMO− LUMO energy separation, compounds 1−3 are thus expected to show increased reactivity toward substrate molecules such as H2, NH3, etc. Investigations of the reactivity of compounds 1−9 are in hand.

■

Pb

HOMO

EXPERIMENTAL SECTION

General Procedures. All manipulations were carried out using modified Schlenk techniques under an atmosphere of N2 or in a MBRAUN UNIlab drybox. Solvents were dried using an Innovative Technologies column solvent purification system. Chemicals were used as received. 1H, 13C, 29Si, and 119Sn NMR spectroscopic data were recorded on a Varian Mercury 300 MHz spectrometer (operating at 300.23 MHz for 1H, 75.50 MHz for 13C, 59.64 MHz for 29Si, and 112.17 MHz for 119Sn). Data were recorded on a Varian Inova 300 MHz spectrometer (operating at 63.25 MHz). NMR spectra were referenced to solvent residual signals of CDCl3 and C6D6 and recorded at 25 °C. UV−vis data were recorded on a PerkinElmer (Lambda 35) spectrometer. Decomposition regions were determined using a Büchi 535 instrument. Elemental analyses of the ligands, the ligand precursors, and of compounds 1, 2, 4, 5, 7, and 8 were performed on a Elementar Vario EL III instrument. No satisfactory data was obtained for the lead derivatives 3, 6, and 9. 1-I-Ar#-3,5-iPr2 and 1-Li-Ar#-3,5-iPr2 were obtained as described in an earlier publication.55 Preparation of the other ligands and Li derivatives is based on this route. I−Ar#-4-Cl. C6H3-1,3,5-Cl3 (40 g, 220 mmol) was dissolved in THF, cooled to ∼−78 °C and slowly treated with a solution of nBuLi (97 mL, 242 mmol). The reaction solution was stirred at ∼−78 °C for 1 h and yielded a colorless, crystalline precipitate. A freshly prepared THF soluton of Grignard reagent MesMgBr (463 mmol) was added dropwise, via canula, at −78 °C. After the addition was complete, the reaction mixture was maintained at ∼−78 °C for 2 h and then allowed to reach room temperature overnight. The solution was then refluxed for 2 h. I2 (84 g, 331 mmol) was added (at ∼0 °C) and the solution was stirred for 2 h at reflux temperature. Then, water was added and the excess I2 was quenched with Na2S2O3. The organic layer was separated and dried over anhydrous Na2SO4, the solvent was pumped H


Organometallics

Article

the colorless product was dried in vacuo. Yield: 87%. Mp: 103−106 °C (decomposition). 1H NMR (300.23 MHz, C6D6): δ 0.66 (s, 9H, SiMe3), 2.56 (s, 12H, o-CH3), 2.73 (s, 6H, p-CH3), 7.29 (2s, 4H+2H, m-Mes + m-C6H2) ppm. 13C {1H} NMR (75.50 MHz, C6D6): δ −0.86, 20.68, 21.32, 126.69, 127.67, 128.21, 130.98, 133.02, 135.81, 149.83, 152.23 ppm. 29Si {1H }NMR (59.64 MHz, C6D6): δ −6.24 ppm. Elemental analysis (%) calcd for C27H33LiSi (392.58): C, 82.61; H, 8.47. Found: C, 82.39; H, 8.53. Ge(Ar#-3,5-iPr2)2 (1). To a solution of Li−Ar#-3,5-iPr2 (400 mg, 0.99 mmol) in Et2O (20 mL), GeCl2·dioxane (113 mg, 0.49 mmol) was added at ambient temperature. The resultant solution changed from yellow to teal and was stirred for 12 h. Salts were removed by centrifugation. Storage of the solution at −30 °C yielded teal, air, and moisture sensitive crystals of 1. Yield: 89%. Mp: 164−170 °C (decomposition). 1H NMR (300.23 MHz, C6D6): δ 1.02 (d, 24H, CH(CH3)2), 1.65 (s, 24H, o-CH3), 2.10 (sept, 4H, CH(CH3)2), 2.30 (s, 12H, p-CH3), 6.79 (s, 8H, m-Mes), 7.28 (s, 2H, p-C6H1) ppm. 13 C {1H} NMR (75.50 MHz, C6D6): δ 21.16, 22.10, 24.67, 29.52, 124.08, 129.08, 136.70, 137.76, 137.83, 140.54, 145.80, 173.03 ppm. UV−vis: λ max (Et2O)/nm 622 (ε/dm3 mol−1 cm−1 853). Elemental analysis (%) calcd for C60H74Ge (867.87): C, 83.04; H, 8.59. Found: C, 82.86; H, 8.38. Sn(Ar#-3,5-iPr2)2 (2). In the same manner Li−Ar#-3,5-iPr2 (400 mg, 0.99 mmol) was reacted with SnCl2 (93 mg, 0.49 mmol) to yield blue crystals of 2. Yield: 82%. Mp: 143−149 °C (decomposition). 1H NMR (300.23 MHz, C6D6): δ 1.02 (d, 24H, CH(CH3)2), 1.70 (s, 24H, o-CH2), 2.33 (s, 12H, p-CH2), 2.67 (sept, 4H, CH(CH2)2), 6.82 (s, 8H, m-Mes), 7.24 (s, 2H, p-C6H1) ppm. 13C {1H } NMR (75.50 MHz, C6D6): δ 21.22, 21.81, 24.67, 29.68, 122.97, 129.27, 136.73, 137.70, 138.17, 142.17, 146.66, 198.65 ppm. 119Sn {1H } NMR (112.17 MHz, C6D6): δ 2080.89 ppm. UV−vis: λ max (Et2O)/nm 591 (ε/dm3 mol−1 cm−1 756). Elemental analysis (%) calcd for C60H74Sn (913.94): C, 78.85; H, 8.16. Found: C, 78.41; H, 8.23. Pb(Ar#-3,5-iPr2)2 (3). In the same manner Li−Ar#-3,5-iPr2 (400 mg, 0.99 mmol) was reacted with PbCl2 (136 mg, 0.49 mmol) to yield deep violet crystals of 3. Yield: 91%. Mp: 100−109 °C (decomposition). 1 H NMR (300.23 MHz, C6D6): δ 1.03 (d, 24H, CH(CH3) 2), 1.75 (s, 24H, o-CH3), 2.33 (s, 12H, p-CH3), 2.85 (sept, 4H, CH(CH3)2), 6.85 (s, 8H, m-Mes), 7.29 (s, 2H, p-C6H1) ppm. 13C {1H } NMR (75.50 MHz, C6D6): δ 21.20, 21.48, 24.80, 30.62, 120.86, 129.21, 136.31, 137.10, 139.13, 144.26, 154.12, 328.18 ppm. 207Pb {1H } NMR (63.25 MHz, C6D6): δ 9593.41 ppm. UV−vis: λ max (Et2O)/nm 566 (ε/dm3 mol−1 cm−1 655). Ge(Ar#-4-Cl)2 (4). In the same manner, Li−Ar#-4-Cl (400 mg, 1.13 mmol) was reacted with GeCl2 (130 mg, 0.56 mmol) to yield violet crystals of 4. Yield: 59%. Mp: 1H NMR (300.23 MHz, C6D6): δ 1.81 (s, 24H, o-CH3), 2.44 (s, 12H, p-CH3), 6.86 (s, 4H, m-C6H2), 6.92 (s, 8H, m-Mes) ppm. 13C {1H } NMR (75.50 MHz, C6D6): δ 20.63, 21.34, 128.98, 129.35, 135.10, 136.27, 137.44, 137.71, 147.12, 167.50 ppm. UV−vis: λ max (Et2O)/nm 565 (ε/dm3 mol−1 cm−1 740). Elemental analysis (%) calcd for C48H48GeCl2 (768.44): C, 75.02; H, 6.30. Found: C, 74.77; H, 6.24. Sn(Ar#-4-Cl)2 (5). In the same manner Li−Ar#-4-Cl (400 mg, 1.13 mmol) was reacted with SnCl2 (106 mg, 0.56 mmol) to yield red-violet crystals of 5. Yield: 78%. Mp: 183−189 °C (decomposition). 1 H NMR (300.23 MHz, C6D6): δ 1.81 (s, 24H, o-CH3), 2.43 (s, 12H, p-CH3), 6.87 (s, 8H, m-Mes), 6.92 (s, 4H, m-C6H2) ppm. 13C {1H } NMR (75.50 MHz, C6D6): δ 20.69, 20.97, 129.03, 129.93, 134.22, 136.42, 137.49, 137.85, 149.21, 188.84 ppm. 119Sn {1H } NMR (112.17 MHz, C6D6): δ 1890.76 ppm. UV−vis: λ max (Et2O)/nm 544 (ε/dm3 mol−1 cm−1 1391). Elemental analysis (%) calcd for C48H48SnCl2 (814.51): C, 70.78; H, 5.94. Found: C, 70.43; H, 6.03. Pb(Ar#-4-Cl)2 (6). In the same manner Li−Ar#-4-Cl (400 mg, 1.13 mmol) was reacted with PbCl2 (156 mg, 0.56 mmol) to yield brown-violet crystals of 6. Yield: 63%. Mp: 121−125 °C.1H NMR (300.23 MHz, C6D6): δ 1.74 (s, 24H, o-CH3), 2.48 (s, 12H, p-CH3), 7.00 (s, 8H, m-Mes), 7.41 (s, 4H, m-C6H2) ppm. 13C {1H } NMR (75.50 MHz, C6D6): δ 20.64 (2 peaks), 128.96, 131.86, 136.05, 137.11, 137.21, 138.26, 151.46, 300.61 ppm. 207Pb {1H } NMR

(63.25 MHz, C6D6): δ 8609.09 ppm. UV−vis: λ max (Et2O)/nm 513 (ε/dm3 mol−1 cm−1 627). Ge(Ar#-4-SiMe3)2 (7). In the same manner 1-Li−Ar#-4-SiMe3 (400 mg, 1.02 mmol) was reacted with GeCl2 (118 mg, 0.51 mmol) to yield blue crystals of 7. Yield: 69%. Mp: 58−60 °C. 1H NMR (300.23 MHz, C6D6): δ 0.23 (s, 9H, Si(CH3)3), 1.73 (s, 24H, o-CH3), 2.38 (s, 12H, p-CH3), 6.85 (s, 8H, m-Mes), 6.93 (s, 4H, m-C6H2) ppm. 13C NMR (75.50 MHz, C6D6): δ −1.72, 20.66, 21.46, 128.77, 134.30, 136.49, 136.55, 139.56, 141.16, 143.97, 170.33 ppm. 29Si {1H } NMR (59.64 MHz, C6D6): δ −4.52 ppm. UV−vis: λ max (Et2O)/nm 583 (ε/dm3 mol−1 cm−1 780). Elemental analysis (%) calcd for C54H66GeSi2 (843.91): C, 76.85; H, 7.88. Found: C, 76.38; H, 7.64. Sn(Ar#-4-SiMe3)2 (8). In the same manner Li−Ar#-4-SiMe3 (400 mg, 1.02 mmol) was reacted with SnCl2 (97 mg, 0.51 mmol) to yield violet crystals of 8. Yield: 74%. Mp: 60−65 °C (decomposition). 1H NMR (300.23 MHz, C6D6): δ 0.17 (s, 9H, Si(CH3)3), 1.72 (s, 24H, o-CH3), 2.34 (s, 12H, p-CH3), 6.79 (s, 8H, m-Mes), 6.92 (s, 4H, m-C6H2) ppm. 13C {1H } NMR (75.50 MHz, C6D6): δ −1.83, 20.54, 20.86, 128.57, 134.52, 136.21, 136.45, 139.39, 139.44, 146.13, 192.02 ppm. 29Si {1H } NMR (59.64 MHz, C6D6): δ −4.23 ppm. 119Sn {1H} NMR (112.17 MHz, C6D6): δ 1974.85 ppm. UV−vis: λ max (Et2O)/ nm 555 (ε/dm3 mol−1 cm−1 603). Elemental analysis (%) calcd for C54H66SnSi2 (889.98): C, 72.88; H, 7.47. Found: C, 72.51; H, 7.59. Pb(Ar#-4-SiMe3)2 (9). In the same manner 1-Li−Ar#-4-SiMe3 (400 mg, 1.02 mmol) was reacted with PbCl2 (142 mg, 0.51 mmol) to yield red-violet crystals of 9. Yield: 61%. Mp: 73−76 °C. 1H NMR (300.23 MHz, C6D6): δ 0.17 (s, 9H, Si(CH3)3), 1.78 (s, 24H, o-CH3), 2.34 (s, 12H, p-CH3), 6.84 (s, 8H, m-Mes), 6.91 (s, 4H, m-C6H2) ppm. 13C {1H } NMR (75.50 MHz, C6D6): δ −1.83, 20.53, 20.57, 128.44, 135.86, 136.06, 137.33, 139.69, 141.21, 148.00, 305.98 ppm. 29 Si {1H } NMR (59.64 MHz, C6D6): δ −3.98 ppm. 207Pb {1H } NMR (63.25 MHz, C6D6): δ 8778.34 ppm. UV−vis: λ max (Et2O)/nm 528 (ε/dm3 mol−1 cm−1 643). X-ray Crystallography. X-ray diffraction data collections were performed on a Bruker Apex II diffractometer with use of Mo Kα radiation (λ = 0.710 73 Å) and a CDD area detector. Suitable crystals for X-ray structural analyses were selected and mounted on the tip of a glass fiber. Diffraction data were collected unless otherwise stated at 100 K on a Bruker D8 Kappa diffractometer equipped with a Smart Apex II CCD detector with Mo Kα (λ = 0.710 73 Å) radiation. Data were integrated with SAINT,56 and empirical methods as implemented in SADABS57 were used to correct for absorption effects. Structures were solved with direct or Patterson methods using SHELXS-97. SHELXL-97 was used for refinement against all data by full-matrix least-squares methods on F2.58 The space group assignments and structural solutions were evaluated using PLATON.59 Non-hydrogen atoms were refined anisotropically. Hydrogen atoms were located in calculated positions corresponding to standard bond lengths and angles. The crystal structures were visualized, and the packing diagrams were generated using Mercury 3.0 visualization program.60 Mö ssbauer Spectroscopy (ME). Samples of 2, 5, and 8 were received in sealed ampules and transferred to perspex sample holders in an inert atmosphere glovebox and immediately cooled to liquid nitrogen temperature prior to mounting in the ME spectrometer. These samples were examined in transmission geometry using a 10mCi 119mSn CaSnO3 source as described previously.61 All isomer shifts (IS) are reported with respect to the centroid of a BaSnO3 absorber spectrum at room temperature. Spectrometer calibration was effected using a standard α-Fe absorber at room temperature. Temperature monitoring was effected using the Daswin software of Glaberson.62 Computational Details. All calculations were performed with the Gaussian 09 program package.63 Time dependent DFT methods at the B3LYP level of theory using 6-31+G* basis sets for all elements except for tin and lead were used. For tin64 and lead, ADZP65 basis sets, which do not include a correction of dispersion effects, were employed. Calculations were based on experimental geometries of the tetrylenes as derived from solid state X-ray diffraction crystal structures. I


Organometallics

Article

Temperature-Dependent ME Studies. As noted above, the ME studies were carried out as described in detail earlier.20,49 The experimental temperatures extant over the extended data acquisition times required for each point (up to 36 h at the higher temperatures) were monitored using the megadaq program of Glaberson.62 The transmission rate was monitored before and after each data point acquisition. The line widths (fwhm) in the 119Sn spectra were on the order of 0.76 mm s−1 and in good agreement with expected single line values.

■

(15) Peng, Y.; Fischer, R. C.; Merrill, W. A.; Fischer, J.; Pu, L.; Ellis, B. D.; Fettinger, J. C.; Herber, R. H.; Power, P. P. Chem. Sci. 2010, 1, 461. (16) Zhu, Z.; Fischer, R. C.; Ellis, B. D.; Rivard, E.; Merrill, W. A.; Olmstead, M. M.; Power, P. P.; Guo, J. D.; Nagase, S.; Pu, L. Chem. Eur. J. 2009, 15, 5263. (17) Hardman, N. J.; Wright, R. J.; Phillips, A. D.; Power, P. P. J. Am. Chem. Soc. 2003, 125, 2667. (18) Wolf, R.; Brynda, M.; Ni, C.; Long, G. J.; Power, P. P. J. Am. Chem. Soc. 2007, 129, 2971. (19) Nguyen, T.; Sutton, A. D.; Brynda, M.; Fettinger, J. C.; Long, G. J.; Power, P. P. Science 2005, 310, 844. (20) Rivard, E.; Fischer, R. C.; Wolf, R.; Peng, Y.; Merrill, W. A.; Schley, N. D.; Zhu, Z.; Pu, L.; Fettinger, J. C.; Teat, S. J.; Nowik, I.; Herber, R. H.; Takagi, N.; Nagase, S.; Power, P. P. J. Am. Chem. Soc. 2007, 129, 16197. (21) Peng, Y.; Ellis, B. D.; Wang, X.; Power, P. P. J. Am. Chem. Soc. 2008, 130, 12268. (22) Peng, Y.; Guo, J. D.; Ellis, B. D.; Zhu, Z. L.; Fettinger, J. C.; Nagase, S.; Power, P. P. J. Am. Chem. Soc. 2009, 131, 16272. (23) Peng, Y.; Brynda, M.; Ellis, B. D.; Fettinger, J. C.; Rivard, E.; Power, P. P. Chem. Commun. 2008, 6042. (24) Du, C. J. F.; Hart, H.; Ng, K. K. D. J. Org. Chem. 1986, 51, 3162. (25) Weidenbruch, M.; Stürmann, M.; Kilian, H.; Pohl, S.; Saak, W. Chem. Ber. 1997, 130, 735. (26) Jutzi, P.; Schmidt, H.; Neumann, B.; Stammler, H.-G. Organometallics 1996, 15, 741. (27) Bender, J. E.; Banaszak Holl, M. M.; Kampf, J. W. Organometallics 1997, 16, 2743. (28) Wegner, G. L.; Berger, R. J. F.; Schier, A.; Schmidbaur, H. Organometallics 2001, 20, 418. (29) Drost, C.; Hitchcock, P. B.; Lappert, M. F.; Pierssens, L. J.-M. Chem. Commun. 1997, 1141. (30) Drost, C.; Hitchcock, P. B.; Lappert, M. F. Organometallics 1998, 17, 3838. (31) Li, L.; Fukawa, T.; Matsuo, T.; Hashizume, D.; Fueno, H.; Tanaka, K.; Tamao, K. Nat. Chem. 2012, 4, 361. (32) Tokitoh, N.; Manmaru, K.; Okazaki, R. Organometallics 1994, 13, 167. (33) Weidenbruch, M.; Kilian, H.; Peters, K.; von Schnering, H. G.; Marsmann, H. Chem. Ber. 1995, 128, 983. (34) Weidenbruch, M.; Schlaefke, J.; Schaefer, A.; Peters, K.; von Schnering, H. G.; Marsmann, H. Angew. Chem., Int. Ed. Engl. 1994, 33, 1846. (35) Grützmacher, H.; Pritzkow, H.; Edelmann, F. T. Organometallics 1991, 10, 23. (36) Tokitoh, N.; Saito, M.; Okazaki, R. J. Am. Chem. Soc. 1993, 115, 2065. (37) Phillips, A. D.; Hino, S.; Power, P. P. J. Am. Chem. Soc. 2003, 125, 7520. (38) Tajima, T.; Takeda, N.; Sasamori, T.; Tokitoh, N. Organometallics 2006, 25, 3552. (39) Stürmann, M.; Weidenbruch, M.; Klinkhammer, K. W.; Lissner, F.; Marsmann, H. Organometallics 1998, 17, 4425. (40) Brooker, S.; Buijink, J. K.; Edelmann, F. T. Organometallics 1991, 10, 25. (41) Yang, X.-J.; Wang, Y.; Wei, P.; Quillian, B.; Robinson, G. H. Chem. Commun. 2006, 403. (42) Tokitoh, N.; Kano, N.; Shibata, K.; Okazaki, R. Organometallics 1995, 14, 3121. (43) Kano, N.; Shibata, K.; Tokitoh, N.; Okazaki, R. Organometallics 1999, 18, 2999. (44) Pu, L.; Twamley, B.; Power, P. P. Organometallics 2000, 19, 2874. (45) Hino, S.; Olmstead, M.; Phillips, A. D.; Wright, R. J.; Power, P. P. Inorg. Chem. 2004, 43, 7346. (46) Drost, C.; Lönnecke, P.; Sieler, J. Chem. Commun. 2012, 3778. (47) Montilla, F.; Galindo, A.; Rosa, V.; Avilés, T. Dalton Trans. 2004, 2588.

ASSOCIATED CONTENT

* Supporting Information S

CIFs; a text .xyz file of the Cartesian coordinates of all computed molecules and tables containing crystallographic data for 1−9; ellipsoid drawings of the molecular structures of compounds 1,2,4,6,8, and 9; comparison of normalized UV−vis spectra of 1, 4, and 7 and 2, 5, and 8 and 3, 6, and 9; HOMOs and LUMOs of compounds 1 and 7; 1H NMR spectra for compounds 1−9; 119Sn NMR spectra for 2, 5, and 8 and 207Pb NMR spectra for 3, 6, 9; and ME spectra for 5 and 8. This material is available free of charge via the Internet at http:// pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. *E-mail: roland.fi[email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We thank the U.S. Department of Energy (Grant DE-FG0207ER46475) Office of Basic Energy Sciences for financial support. P.W. gratefully acknowledges the Marshall Plan Foundation for a Marshall Plan Scholarship.

■

REFERENCES

(1) Davidson, P. J.; Lappert, M. F. J. Chem. Soc., Chem. Commun. 1973, 317. (2) Davidson, P. J.; Harris, D. H.; Lappert, M. F. J. Chem. Soc., Dalton Trans. 1976, 2268−2274. (3) Hitchcock, P. B.; Lappert, M. F.; Miles, S. J.; Thorne, A. J. Chem. Commun. 1984, 480. (4) Lee, V. Y.; Sekiguchi, A. Organometallic Compounds of LowCoordinated Si, Ge, Sn, and Pb; Wiley: Chichester, U.K., 2010. (5) Fjeldberg, T.; Haaland, A.; Schilling, B. E. R.; Lappert, M. F.; Thorne, A. J. J. Chem. Soc., Dalton Trans. 1986, 1551. (6) Stürmann, M.; Weidenbruch, M.; Klinkhammer, K. W.; Lissner, F.; Marsmann, H. Organometallics 1998, 17, 4425. (7) Tokitoh, N.; Okazaki, R. Coord. Chem. Rev. 2000, 210, 251. (8) Mizuhata, Y.; Sasamori, T.; Tokitoh, N. Chem. Rev. 2009, 109, 3479. (9) Rivard, E.; Power, P. P. Inorg. Chem. 2007, 46, 10047−1106. (10) Spikes, G. H.; Peng, Y.; Fettinger, J. C.; Power, P. P. Z. Anorg. Allg. Chem. 2006, 632, 1005. (11) Simons, R. S.; Pu, L.; Olmstead, M. M.; Power, P. P. Organometallics 1997, 16, 1920. (12) Fischer, R. C.; Pu, L.; Fettinger, J. C.; Brynda, M. A.; Power, P. P. J. Am. Chem. Soc. 2006, 128, 11366. (13) Phillips, A. D.; Wright, R. J.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 2002, 124, 5930. (14) Pu, Li.; Twamley, B.; Power, P. P. J. Am. Chem. Soc. 2000, 122, 3524. J


Organometallics

Article

(48) Herber, R. H. Inorg. Chim. Acta 1999, 291, 74. (49) Herber, R. H.; Nowik, I. J. Nucl. Radiochem. Sci. 2008, 9, 33. Herber, R. H.; Nowik, I.; Mochida, T. J. Organomet. Chem. 2011, 696, 1698 and references therein.. (50) Herber, R. H.; Nowik, I. Phosphorus, Sulfur, Silicon 2011, 186, 1336 and references therein. (51) Cotton, J. D.; Davidson, P. J.; Lappert, M. F.; Donaldson, J. D.; Silver, J. Dalton Trans. 1976, 2286. (52) Bigwood, M. P.; Corvan, P. J.; Zuckerman, J. J. J. Am. Chem. Soc. 1981, 103, 7643. (53) Spikes, G. H.; Giuliani, J.; Augustine, M. P.; Nowik, I.; Herber, R. H.; Power, P. P. Inorg. Chem. 2006, 45, 9132. (54) Burdett, J. K. Molecular Shapes; Wiley: Chichester, U.K., 1980; p 52. (55) Stanciu, C.; Richards, A. F.; Fettinger, J. C.; Brynda, M.; Power, P. P. J. Organomet. Chem. 2006, 691, 2540. (56) SAINT, Bruker AXS Inc.: Madison, WI, 2000. (57) Sheldrick, G. M. SADABS: Program for Performing Absorption Corrections to Single-Crystal X-ray Diffraction Patterns; University of Göttingen: Göttingen, Germany, 2002. (58) Sheldrick, G. M. SHELXTL: Suite of Programs for Crystal Structure Analysis, Incorporating Structure Solution (XS), Least- Squares Refinement (XL), and Graphics (XP); University of Gö ttingen, Göttingen, Germany, 2001. (59) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7. (60) Macrae, C. F.; Bruno, I. J.; Chisholm, J. A.; Edgington, P. R.; McCabe, P.; Pidcock, E.; Rodriguez-Monge, L.; Taylor, R.; van de Streek, J.; Wood, P. A. J. Appl. Crystallogr. 2008, 41, 466. (61) Macdonald, C. L. B.; Bandyopadhyay, R.; Cooper, B. F. T.; Friedl, W. W.; Rossini, A.; Schurko, R. W.; Eichhorn, S. H.; Herber, R. H. J. Am. Chem. Soc. 2012, 134, 4332−4345. (62) Glaberson, W. personal communication. Also http://www. megadaq.com. (63) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A.; , Jr., Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Keith, T.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Revision C.01; Gaussian, Inc.: Wallingford, CT, 2010. (64) de Oliveira, P. J. P.; Barros, C. L.; Jorge, F. E.; Canal Neto, A.; Campos, M. J. Mol. Struct. Theochem. 2010, 948, 43. (65) Canal Neto, A.; Jorge, F. E. Chem. Phys. Lett. 2013, 582, 158.

K


Influence of Ligand Modifications on Structural and Spectroscopic

Recommend Documents