Cationic aza-macrocyclic complexes of germanium(II) and silicon(IV)

Abstract

[GeCl₂(dioxane)] reacts with the neutral aza-macrocyclic ligands L, L = Me₃tacn (1,4,7-trimethyl-1,4,7-triazacyclononane), Me₄cyclen (1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane) or Me₄cyclam (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) and two mol. equiv. of Me₃SiO₃SCF₃ in thf solution to yield the unusual and hydrolytically very sensitive [Ge(L)][O₃SCF₃]₂ as white solids in moderate yield. Using shorter reaction times [Ge(Me₃tacn)]Cl₂ and [Ge(Me₃tacn)]Cl[O₃SCF₃] were also isolated; the preparation of [Ge(Me₄cyclen)][GeCl₃]₂ is also described. The structures of the Me₃tacn complexes show κ³-coordination of the macrocycle, with the anions interacting only weakly to produce very distorted five- or six-coordination at germanium. In contrast, the structure of [Ge(Me₄cyclen)][O₃SCF₃]₂ shows no anion interactions, and a distorted square planar geometry at germanium from coordination to the tetra-aza macrocycle. Crystal structures of the Si(IV) complexes, [SiCl₃(Me₃tacn)]Y (Y = O₃SCF₃, BAr^F; [B{3,5-(CF₃)₂C₆H₃}₄]) and [SiHCl₂(Me₃tacn)][BAr^F], obtained from reaction of SiCl₄ or SiHCl₃ with Me₃tacn, followed by addition of either Me₃SiO₃SCF₃ or Na[BAr^F], contain distorted octahedral cations, with facial κ³-coordinated Me₃tacn. The open-chain triamine, Me₂NCH₂CH₂N(Me)CH₂CH₂NMe₂ (pmdta), forms [SiCl₃(pmdta)][BAr^F] and [SiBr₃(pmdta)][BAr^F] under similar conditions, containing mer-octahedral cations.

---

Introduction

Elemental silicon and germanium and their compounds with oxygen and chalcogens are key technological materials, with applications in electronics, glasses, ceramics and optics.^1–3 We are currently developing routes to electrochemically deposit the elements and their binary and ternary alloys from both organic solvents and supercritical fluids.^4–6 In the search for silicon and germanium reagents with appropriate chemical stabilities and solubilities in these media for electrochemical studies, we have explored a variety of coordination complexes, to establish how the properties may be tuned by incorporating various ligands. Most coordination chemistry of germanium(II), germanium(IV) and silicon(IV) involves neutral adducts of the di- or tetra-halides,⁷ and cationic complexes are rather rare, while Si(II) halide complexes are limited to N-heterocyclic carbenes.⁸ Aza-macrocyclic complexes reported include [GeF₃(Me₃tacn)]₂[GeF₆] (Me₃tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane),⁹ [(GeF₄)₂(κ²κ′²-Me₄cyclam)] (Me₄cyclam = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane),⁹ [GeCl₃(Me₃tacn)]₂(H₃O)₂Cl₃,¹⁰ [SiF₃(Me₃tacn)][SiF₅],¹¹ [Ge(Me₃tacn)]Br[GeBr₃],¹² and [Ge(Me₄cyclam)][GeCl₃]₂.¹²

Here we report the synthesis of several new Ge(II) mono- and dications and Si(IV) monocations based upon neutral triaza- and tetra-aza macrocyclic ligands with a variety of anions. Single crystal X-ray structural studies on representative examples are described and compared.

Experimental

SiCl₄, SiHCl₃, Me₃SiO₃SCF₃, [GeCl₂(dioxane)] and the N-donor ligands were obtained from Sigma Aldrich, except for Me₃tacn which was prepared using the literature route.¹³ Na[BAr^F] ([BAr^F]⁻ = [B{3,5-(CF₃)₂C₆H₃}₄]⁻) was synthesised by a modification of Brookhart's procedure.¹⁴ Me₂NCH₂CH₂N(Me)CH₂CH₂NMe₂ (pmdta) was distilled from CaH₂. All experiments were performed under strictly anhydrous conditions using glove-boxes and Schlenk techniques. CH₂Cl₂ was dried by distillation from CaH₂, toluene was distilled from sodium, hexane was distilled from Na/K alloy and thf was distilled from Na/benzophenone ketyl. IR spectra were recorded as Nujol mulls between CsI plates using a Perkin Elmer Spectrum 100 spectrometer over the range 4000–200 cm⁻¹. ¹H and ¹⁹F NMR spectra were recorded using a Bruker DPX-400 spectrometer and referenced to the residual solvent resonance and external CFCl₃, respectively. Microanalytical measurements were performed by London Metropolitan University.

[Ge(Me₄cyclen)][O₃SCF₃]₂

[GeCl₂(dioxane)] (0.059 g, 0.26 mmol) was dissolved in thf (10 mL) and a solution of Me₃SiO₃SCF₃ (0.112 g, 0.50 mmol) in thf (5 mL) was added with stirring, giving a clear, colourless solution. After 10 min, a solution of Me₄cyclen (0.057 g, 0.25 mmol) in thf (5 mL) was added, causing the formation of a white precipitate. After stirring for a further 1 h, the product was collected by filtration and dried in vacuo. Yield: 0.120 g (80%). Anal. calc. for C₁₄H₂₈F₆GeN₄O₆S₂ (599.1): C, 28.08; H, 4.71; N, 9.35. Found: C, 28.19; H, 4.61; N, 9.26%. ¹H NMR (CD₃CN, 298 K): 2.78 (s, [12H], NCH₃), 3.20–3.40 (m, [16H], NCH₂). ¹⁹F{¹H} NMR (CD₃CN, 298 K): −79.4 (O₃SCF₃). IR (Nujol/cm⁻¹): 474w, 517m, 573m, 638s, 749m, 793w, 919w, 960w, 1030s, 1068w, 1155s, 1225s, 1260s.

Crystals of [Ge(Me₄cyclen)][O₃SCF₃]₂·CH₃CN suitable for X-ray diffraction were obtained by layering an acetonitrile solution with diethyl ether.

[Ge(Me₄cyclam)][O₃SCF₃]₂

[GeCl₂(dioxane)] (0.058 g, 0.25 mmol) was dissolved in thf (10 mL), and a solution of Me₃SiO₃SCF₃ (0.115 g, 0.52 mmol) in thf (5 mL) was added with stirring, giving a colourless solution. After 10 min a solution of Me₄cyclam (0.065 g, 0.25 mmol) in thf (5 mL) was added, causing the formation of a white, microcrystalline precipitate. After 1 h, the product was collected by filtration, washed with diethyl ether and dried in vacuo. Yield: 0.092 g (59%). Anal. calc. for C₁₆H₃₂F₆GeN₄O₆S₂ (627.2): C, 30.65; H, 5.14; N, 8.93. Found: C, 30.81; H, 5.17; N, 8.86%. ¹H NMR (CD₃CN, 298 K): 1.96 (s, [4H], NCH₂CH₂), 2.56 (br s, [12H], NCH₃), 2.94–2.99 (v br, [16H], overlapping NCH₂CH₂CH₂ and NCH₂CH₂N). ¹⁹F{¹H} NMR (CD₃CN, 298 K): −79.4 (O₃SCF₃). ¹H NMR (DMF-d₇, 298 K): 2.09 (quintet, [4H], ³J_HH = 6.3 Hz, NCH₂CH₂), 2.68 (br s, [12H], NCH₃), 3.08 (v br, [8H], NCH₂CH₂CH₂) 3.21 (br s, [8H], NCH₂CH₂N). ¹⁹F{¹H} NMR (DMF-d₇, 298 K): −79.38 (O₃SCF₃). IR (Nujol/cm⁻¹): 517m, 574m, 592w, 639s, 743w, 757w, 802w, 1011m, 1034s, 1160s, 1226m, 1256s, 1278s, 1354m.

[Ge(Me₄cyclen)][GeCl₃]₂

[GeCl₂(dioxane)] (0.104 g, 0.45 mmol) was suspended in CH₂Cl₂ (20 mL) and a solution of Me₄cyclen (0.035 g, 0.15 mmol) in CH₂Cl₂ (10 mL) was added with stirring, giving a dense white suspension. After stirring at room temperature for 2 h, the product was collected by filtration, washed with Et₂O and dried in vacuo. Yield: 0.048 g (48%). Anal. calc. for: C₁₂H₂₈Cl₆Ge₃N₄ (658.9): C, 21.87; H, 4.28; N, 8.50. Found: C, 22.02; H, 4.19; N, 8.41%. ¹H NMR (CD₃CN, 298 K): 2.78 (s, [12H], NCH₃), 3.20–3.38 (m, [16H], NCH₂). IR (Nujol/cm⁻¹): 277s, vbr [GeCl₃]⁻, 317s, 413w, 472m, 547m, 737s, 747s, 791m, 917s, 945m, 958s, 1014s, 1024s, 1051s, 1064s, 1151m, 1262s, 1275s, 1298s.

[Ge(Me₃tacn)][O₃SCF₃]₂

[GeCl₂(dioxane)] (0.059 g, 0.26 mmol) was suspended in CH₂Cl₂ (10 mL) and a solution of Me₃SiO₃SCF₃ (0.112 g, 0.50 mmol) in CH₂Cl₂ (10 mL) was added with stirring, giving a colourless solution. After 10 min Me₃tacn (0.044 g, 0.26 mmol) was added, causing the formation of a white precipitate. After stirring for approximately 1 h, the product was collected by filtration and dried in vacuo. Yield: 0.085 g (62%). Anal. calc. for C₁₁H₂₁F₆GeN₃O₆S₂ (542.0): C, 24.38; H, 3.91; N, 7.75. Found: C, 24.51; H, 3.74; N, 7.84%. ¹H NMR (CD₃CN, 298 K): 3.02 (s, [9H], NCH₃), 3.34–3.54 (m, [12H], NCH₂). ¹⁹F{¹H} NMR (CD₃CN, 298 K): −79.4 (O₃SCF₃). IR (Nujol/cm⁻¹): 420m, 451w, 516m, 573m, 639s, 739m, 785m, 898m, 982w, 994m, 1030s, 1049m, 1138m, 1167s, 1226s, 1259s.

Crystals of [Ge(Me₃tacn)][O₃SCF₃]₂·CH₃CN suitable for X-ray diffraction were obtained by layering an acetonitrile solution with diethyl ether.

[Ge(Me₃tacn)]Cl[O₃SCF₃]

In a similar reaction using a 1 : 1 molar ratio of [GeCl₂(dioxane)] and Me₃tacn, conducted in MeCN solution, the mixture was stirred at room temperature for ca. 3 h following addition of Me₃SiO₃SCF₃, then concentrated in vacuo. This did not cause any precipitation, and the solution was layered with Et₂O and stored in the freezer. Small rod-shaped crystals formed, which were found to be [Ge(Me₃tacn)]Cl[O₃SCF₃] as identified by an X-ray crystal structure determination. Anal. calc. for C₁₀H₂₁ClF₃GeN₃O₃S (428.4): C, 28.04; H, 4.94; N, 9.81. Found: C, 28.76; H, 4.85; N, 9.77%. ¹H NMR (298 K, CD₂Cl₂): 2.94 (s, [9H], NCH₃), 3.21–3.47 (m, [12H], CH₂). (A second minor species is also evident in the NMR spectrum). ¹⁹F{¹H} NMR (298 K, CD₂Cl₂): −79.4 (O₃SCF₃).

[Ge(Me₃tacn)]Cl₂

In a further reaction conducted in MeCN solution, the mixture was stirred at room temperature for ca. 15 min following addition of Me₃SiO₃SCF₃, then concentrated in vacuo. This caused the rapid precipitation of a white solid, which redissolved on warming. Storage of this solution in the freezer furnished colourless rod-shaped crystals which were found by X-ray crystallographic analysis to be [Ge(Me₃tacn)]Cl₂·MeCN.

[SiCl₃(Me₃tacn)][O₃SCF₃]

SiCl₄ (0.170 g, 1.0 mmol) and Me₃SiO₃SCF₃ (0.222 g, 1.0 mmol) were dissolved in CH₂Cl₂ (10 mL) and stirred for 5 min. A solution of Me₃tacn (0.171 g, 1.0 mmol) in CH₂Cl₂ (5 mL) was added and the reaction was stirred for 16 h. After this time, a white solid had formed. This was collected by filtration and dried in vacuo. Yield: 0.204 g (45%). Anal. calc. for C₁₀H₂₁Cl₃F₃N₃O₃SSi (454.8): C, 26.40; H, 4.66; N, 9.24. Found: C, 26.61; H, 4.73; N, 9.25%. ¹H NMR (295 K, CD₃CN): 3.54–3.66 (m, [6H], NCH₂), 3.31–3.41 (m, [6H], NCH₂), 3.17 (s, [9H], NCH₃). ¹³C{¹H} NMR (295 K, CD₃CN): 122.20 (q, ¹J_C–F = 320 Hz, CF₃), 54.86 (CH₂), 53.49 (CH₃). ¹⁹F{¹H} NMR (295 K, CD₃CN): −78.7 (O₃SCF₃). IR (Nujol, cm⁻¹): 231s, 428s (SiCl), 460s (SiCl), 497m, 517m, 574m, 601m, 637s, 754m, 899m, 967m, 998m, 1029s, 1053m, 1155s, 1225m.

Crystals were obtained by layering a concentrated CH₂Cl₂ solution with hexane.

[SiHCl₂(Me₃tacn)][BAr^F]

SiHCl₃ (0.068 g, 0.50 mmol) and NaBAr^F (0.443 g, 0.50 mmol) were dissolved in toluene (10 mL) and stirred for 5 min. A solution of Me₃tacn (0.085 g, 0.50 mmol) in toluene (5 mL) was added then the reaction was stirred for 4 h. After this time, volatiles were removed in vacuo and the solid extracted into CH₂Cl₂ (5 mL), filtered and hexane (30 mL) added to precipitate a white solid. Yield: 0.421 g (74%). Anal. calc. for C₄₁H₃₄BCl₂F₂₄N₃Si (1134.12): C, 43.38; H, 3.02; N, 3.70. Found: C, 43.45; H, 3.11; N, 3.80%. ¹H NMR (295 K, CD₂Cl₂): 7.74 (s, [8H], BAr^F H2/6), 7.59 (s, [4H], BAr^F H4), 4.78 (s, [1H], Si–H), 3.54–3.70 (m, [4H], NCH₂), 3.26 (s, [3H], NCH₃), 3.21 (s, [4H], NCH₂), 3.12–3.17 (m, [4H], NCH₂), 2.99 (s, [6H], NCH₃). ¹³C{¹H} NMR (295 K, CD₂Cl₂): 162.33 (q, ¹J_C–B = 49.8 Hz, BAr^F C1), 135.42 (CH, BAr^F C2/6), 129.48 (C, q, ¹J_C–F = 3.3 Hz, BAr^F C3/5), 125.22 (C, q, ¹J_C–F = 272 Hz, CF₃), 118.11 (CH, BAr^F C4), 54.72, 53.77, 51.41, 50.45 (NCH₂ and NCH₃). IR (Nujol, cm⁻¹): 449 m (SiCl), 480 m (SiCl), 683s, 744m, 838m, 888m, 899m, 1005m, 1056m, 1086m, 1114s, 1163s, 1280s, 1289s, 1356s, 1612w, 2137w (SiH).

[SiCl₃(Me₃tacn)][BAr^F]

Made similarly using SiCl₄ (0.085 g, 0.50 mmol) in place of SiHCl₃. Yield: 0.466 g (82%). Anal. calc. for C₄₁H₃₃BCl₃F₂₄N₃Si (1168.9): C, 42.10; H, 2.85; N, 3.59. Found: C, 41.85; H, 3.08; N, 3.74%.

A concentrated CH₂Cl₂ solution of this complex layered with hexane deposited a few colourless crystals which were identified from an X-ray crystallographic study as [SiCl₃(Me₃tacn)]Cl. Attempts to prepare the latter directly from SiCl₄ and Me₃tacn in CH₂Cl₂ gave a pale yellow solid which was very poorly soluble in chlorocarbons and which was not analytically pure.

[SiCl₃(pmdta)][BAr^F]

SiCl₄ (0.085 g, 0.50 mmol) and Na[BAr^F] (0.443 g, 0.50 mmol) were dissolved in toluene (10 mL) and stirred for 5 min. A solution of pmdta (0.087 g, 0.50 mmol) in toluene (5 mL) was added, then the reaction was stirred for 4 h. After this time, volatiles were removed in vacuo and the solid extracted into CH₂Cl₂ (5 mL), filtered and hexane (30 mL) added to precipitate a white solid. Yield: 0.447 g (76%). Anal. calc. for C₄₁H₃₅BCl₃F₂₄N₃Si (1170.58): C, 42.03; H, 3.01; N, 3.59. Found: C, 41.88; H, 3.12; N, 3.71%. ¹H NMR (295 K, CD₂Cl₂): 7.72 (s, [8H], BAr^F H2/6), 7.57 (s, [4H], BAr^F H4), 2.76–2.98 (br s, [4H], NCH₂), 2.65 (v br s, [16H], N(CH₃)₂ and NCH₂), 2.35 (s, [3H], NCH₃) ppm. ¹³C{¹H} NMR (295 K, CD₂Cl₂): 162.37 (q, ¹J_C–B = 49.7 Hz, BAr^F C1), 135.41 (CH, BAr^F C2/6), 129.45 (C, q, ¹J_C–F = 3.3 Hz, BAr^F C3/5), 125.22 (C, q, ¹J_C–F = 272 Hz, CF₃), 118.10 (CH, BAr^F C4), 57.91, 57.16 (CH₂), 45.08 (N(CH₃)₂), 44.51 (NCH₃). IR (Nujol cm⁻¹): 448w, 506w (SiCl), 522w (SiCl), 682m, 713m, 889w, 1112s, 1143s, 1358s, 1367s.

Crystals were obtained by layering a concentrated CH₂Cl₂ solution with hexane.

[SiBr₃(pmdta)][BAr^F]

SiBr₄ (0.174 g, 0.50 mmol) and Na[BAr^F] (0.443 g, 0.50 mmol) were dissolved in toluene (10 mL) and stirred for 5 min. A solution of pmdta (0.087 g, 0.50 mmol) in toluene (5 mL) was added then the reaction was stirred for 4 h. After this time, volatiles were removed in vacuo and the solid extracted into CH₂Cl₂ (5 mL), filtered and hexane (30 mL) added to precipitate a white solid. Yield: 0.291 g (45%). Anal. calc. for C₄₁H₃₅BBr₃F₂₄N₃Si (1303.93): C, 37.73; H, 2.71; N, 3.22. Found: C, 37.57; H, 2.80; N, 3.26%. ¹H NMR (CD₂Cl₂): 7.72 (s, [8H], BAr^F H2/6), 7.57 (s, [4H], BAr^F H4), 2.76–2.98 (br s, [4H], NCH₂), 2.65 (br s, [16H], N(CH₃)₂ and NCH₂), 2.35 (s, [3H], NCH₃). IR (Nujol, cm⁻¹): 363 m (SiBr), 471w, 521w, 584w, 682s, 712s, 838m, 887m, 898m, 925w, 955w, 1112s, 1144s, 1279s, 1358s.

X-ray crystallography

Crystals were obtained as described above. Details of the crystallographic data collection and refinement are in Table 1. Diffractometer: Rigaku AFC12 goniometer equipped with an enhanced sensitivity (HG) Saturn724+ detector mounted at the window of an FR-E+ SuperBright molybdenum rotating anode generator (λ₁ = 0.71073 Å) with VHF Varimax optics (70 or 100 μm focus). Cell determination, data collection, data reduction, cell refinement and absorption correction: CrystalClear-SM Expert 2.0 r7.4.^15a Structure solution and refinement were carried out using WinGX or Olex2 and software packages within.^15b–d No positional disorder was observed in complexes of [BAr^F]⁻, despite this being a common issue with weakly-coordinating anions containing CF₃ groups, especially [BAr^F]⁻.¹⁶ [Ge(Me₃tacn)]Cl₂·MeCN crystallised as an inversion twin with a BASF of 0.21. Unusually large Z values were observed for [Ge(Me₄cyclen)][O₃SCF₃]₂·0.8MeCN and [SiCl₃(Me₃tacn)]Cl (10 and 24, respectively) which is explained by the presence of multiple cation units with very similar, but not identical, metrical parameters in the asymmetric unit. H atoms attached to C atoms were placed in geometrically assigned positions, with C–H distances of 0.95 Å (CH), 0.98 Å (CH₃) or 0.99 Å (CH₂) and refined using a riding model, with U_iso(H) = 1.2U_eq(C) (CH, CH₂) or 1.5U_eq(C) (CH₃). Si–H and N–H protons were located in the Fourier difference map and allowed to refine freely. enCIFer was used to prepare CIFs for publication.^15e

Table 1 Selected X-ray crystallographic data^a

Compound	[Ge(Me3tacn)]-[O3SCF3]2·MeCN	[Ge(Me4cyclen)]-[O3SCF3]2·0.8MeCN	[Ge(Me3tacn)]-Cl[O3SCF3]	[Ge(Me3tacn)]-Cl2·MeCN
Formula	C13H24F6GeN4O6S2	C15.6H30.4F6GeN4.8O6S2	C10H21ClF3GeN3O3S	C11H24Cl2GeN4
M/g mol^–1	583.07	631.96	438.40	355.83
Crystal system	Monoclinic	Tetragonal	Monoclinic	Orthorhombic
Space group (No.)	P21/n (14)	P4cc (103)	P21/c (14)	Pna21 (33)
a/Å	13.541(5)	17.1253(3)	8.1521(9)	14.399(5)
b/Å	8.543(5)	17.1253(3)	13.9764(15)	10.139(5)
c/Å	19.620(5)	22.1160(10)	14.2804(16)	21.491(5)
α/°	90	90	90	90
β/°	97.495(5)	90	101.705(7)	90
γ/°	90	90	90	90
U/Å^3	2250.3(17)	6486.1(4)	1593.2(3)	3138(2)
Z	4	10 (Z′ = 1.25)	3	8
μ(Mo-Kα)/mm^–1	1.634	1.425	2.267	2.284
F(000)	1184	3236	872	1472
Total reflections	10 515	34 358	8862	11 548
Unique reflections	5123	7099	3647	5491
R int	0.041	0.042	0.074	0.0823
Goodness-of-fit on F^2	1.036	1.030	0.987	1.025
R 1 ^b [Io > 2σ(Io)]	0.037	0.054	0.047	0.061
R 1 (all data)	0.050	0.071	0.060	0.108
wR2 ^b [Io> 2σ(Io)]	0.082	0.131	0.108	0.103
wR2 (all data)	0.088	0.142	0.116	0.119

---

Compound	[SiCl3(Me3tacn)][O3SCF3]	[SiCl3(Me3tacn)]Cl	[SiCl3(pmdta)][BAr^F]
a Common items: T = 100 K; wavelength (Mo-Kα) = 0.71073 Å; θ(max) = 27.5°. b R 1 = ∑||Fσ| − |Fc||/∑|Fo|; wR2 = [∑w(Fo^2 − Fc^2)^2/∑wFo^2]^1/2.
Formula	C10H21Cl3F3N3O3SSi	C9H21Cl4N3Si·^2/3(CH2Cl2)	C41H35BCl3F24N3Si
M/g mol^–1	454.80	397.80	1170.97
Crystal system	Triclinic	Monoclinic	Orthorhombic
Space group (no.)	P1̄ (2)	C2/c (15)	Pbca (61)
a/Å	6.997(2)	34.475(8)	17.728(5)
b/Å	10.820(4)	26.707(6)	19.613(6)
c/Å	11.974(4)	11.820(3)	26.662(8)
α/°	99.110(7)	90	90
β/°	93.245(5)	106.684(5)	90
γ/°	92.108(8)	90	90
U/Å^3	892.7(5)	10 425(4)	9270(5)
Z	2	24 (Z′ = 3)	8
μ(Mo-Kα)/mm^–1	0.743	0.946	0.357
F(000)	468	4944	4704
Total reflections	7788	46 773	17 463
Unique reflections	4019	10 659	8124
R int	0.019	0.114	0.070
Goodness-of-fit on F^2	1.042	1.107	1.176
R 1 ^b [Io > 2σ(Io)]	0.032	0.094	0.097
R 1 (all data)	0.039	0.121	0.147
wR2 ^b [Io> 2σ(Io)]	0.069	0.227	0.137
wR2 (all data)	0.072	0.247	0.155

---

Results and discussion

Germanium(II) complexes

We have previously reported¹² that reaction of GeBr₂ with Me₃tacn in anhydrous MeCN solution gives colourless [Ge(Me₃tacn)]Br[GeBr₃], containing unusual discrete three-coordinate [Ge(Me₃tacn)]²⁺ dications (Ge–N = 2.124(3)–2.156(3) Å), with Br⁻ and [GeBr₃]⁻ anions providing charge balance. We find that reaction of [GeCl₂(dioxane)] with Me₃tacn in anhydrous CH₂Cl₂ followed by addition of Me₃SiO₃SCF₃ gave a colourless powder, [Ge(Me₃tacn)][O₃SCF₃]₂, subsequently obtained as colourless crystals of [Ge(Me₃tacn)][O₃SCF₃]₂·MeCN by recrystallisation from MeCN/Et₂O. The structure (Fig. 1) also reveals a pyramidal GeN₃ unit, however, in this species there are also weak directional Ge⋯O interactions from one oxygen in each triflate anion at 2.850(2) and 3.179(2) Å, well within the sum of vdW radii for O and Ge (3.79 Å).¹⁷

Fig. 1 The X-ray structure of [Ge(Me₃tacn)][O₃SCF₃]₂·MeCN. Thermal ellipsoids are drawn at 50% probability, and hydrogen atoms omitted for clarity. Selected bond lengths (Å) and angles (°): N1–Ge1 = 2.084(2), N2–Ge1 = 2.106(2), N3–Ge1 = 2.089(2), O5⋯Ge1 = 2.850(2), O3⋯Ge1 = 3.179(2), N1–Ge1–N3 = 82.73(8), N1–Ge1–N2 = 82.84(8), N3–Ge1–N2 = 83.23(9).

While there is no evidence for 2 : 1 Me₃tacn : Ge species (presumably due to steric clashing of the Me groups on the relatively small Ge(II) centre), the anions present in the products proved to be very sensitive to the reaction conditions; if the reaction of [GeCl₂(dioxane)], Me₃tacn and Me₃SiO₃SCF₃ was conducted in MeCN solution as described in the Experimental section, concentrated in vacuo, and the solution layered with Et₂O, the product was isolated as rod-like crystals of [Ge(Me₃tacn)]Cl[O₃SCF₃]. The X-ray structure of this species (Fig. 2) shows the complex forms a weakly associated dimer in the solid state via the chloride bridges (Ge⋯Cl = 3.0254(9), 3.214(1) Å) and with a similar pyramidal ‘Ge^II(Me₃tacn)’ core. These Ge⋯Cl interactions are substantially within the sum of vdW radii for Ge and Cl (4.11 Å). One κ¹-coordinated triflate completes a distorted six-coordinate environment at each germanium centre.

Fig. 2 The X-ray structure of [Ge(Me₃tacn)]Cl[O₃SCF₃] showing the dimeric unit. Thermal ellipsoids are drawn at 50% probability, and hydrogen atoms omitted for clarity. Selected bond lengths (Å) and angles (°): N1–Ge1 = 2.119(3), N2–Ge1 = 2.139(3), N3–Ge1 = 2.130(2), Cl1⋯Ge1 = 3.0254(9), O1⋯Ge1 = 3.381(2), Cl1ⁱ⋯Ge1 3.214(1), N1–Ge1–N3 = 82.48(10), N1–Ge1–N2 = 81.63(10), N3–Ge1–N2 = 80.98(10).

The same reaction conducted in MeCN solution, but worked up after 15 min and placed in a freezer, deposited a few rod-like crystals that were identified as [Ge(Me₃tacn)]Cl₂·MeCN by X-ray crystallography (Fig. 3). In this case the ‘Ge^II(Me₃tacn)’ core has two long contacts to the chlorides at 3.028(4) and 3.028(3) Å. The closest intermolecular contact is to a chloride of an adjacent molecule, but the Ge⋯Cl distance is the same as the sum of vdW radii for Ge and Cl (within experimental error), most likely a consequence of crystal packing.

Fig. 3 The X-ray structure of [Ge(Me₃tacn)]Cl₂·MeCN showing the Ge1-centred molecule. The crystallographically independent Ge2-centred molecule is very similar. Thermal ellipsoids are drawn at 50% probability, and hydrogen atoms omitted for clarity Selected bond lengths (Å) and angles (°): N1–Ge1 = 2.124(10), N2–Ge1 = 2.147(10), N3–Ge1 = 2.154(9), Cl1⋯Ge1 = 3.028(4), Cl2⋯Ge1 = 3.028(3), N1–Ge1–N3 = 80.9(3), N1–Ge1–N2 = 81.2(4), N3–Ge1–N2 = 80.8(4).

Comparison of the Ge–N distances in this series of complexes shows only small differences as a function of the anion(s) present, suggesting that the structures are dominated by the ‘Ge^II(Me₃tacn)’ core. All of the Ge–N distances are considerably longer than the sum of the covalent radii (1.85 Å),¹⁸ but well within the sum of the van der Waals radii (3.66 Å).¹⁷

The spectroscopic data provide very limited information; the IR spectra show the Me₃tacn and the [O₃SCF₃]⁻ (when present), whilst the ¹H NMR spectra show small high frequency shifts corresponding to coordinated Me₃tacn. The complexes are extremely sensitive to hydrolysis by trace water, readily forming protonated Me₃tacn.

The reaction of [GeCl₂(dioxane)] and Me₃SiO₃SCF₃ in thf followed by addition of Me₄cyclam gave [Ge(Me₄cyclam)][O₃SCF₃]₂. Attempts to obtain crystals of this complex were unsuccessful with recrystallisation from MeCN/Et₂O or CH₂Cl₂/Et₂O giving [Me₄cyclamH₂][O₃SCF₃]₂ (identified crystallographically). We reported the structure of [Ge(Me₄cyclam)][GeCl₃]₂ in our preliminary communication,¹² which revealed an essentially coplanar N₄ with the Ge out of the plane by 0.83 Å, and with no significant interaction with the anions. The data also revealed a spread of Ge–N distances (2.151(2)–2.349(2) Å), suggesting germanium(II) is not a good fit to the relatively large 14-membered macrocycle cavity; this may correlate with the very ready hydrolysis in solution.

Replacing the 14-membered Me₄cyclam ring by the 12-membered Me₄cyclen (1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclotetradecane) gave colourless [Ge(Me₄cyclen)][O₃SCF₃]_2. Crystals of [Ge(Me₄cyclen)][O₃SCF₃]₂·0.8CH₃CN suitable for X-ray diffraction were obtained by layering an acetonitrile solution of the complex with diethyl ether. The structure (Fig. 4) also shows the Ge(II) centre coordinated to a tetradentate Me₄cyclen macrocycle with the Ge–N bonds alternating short-long-short-long around the ring, Ge–N = 2.165(6)–2.244(5) Å, with the Ge lying 1.009(3) Å above the mean N₄ plane. In both complexes the methyl substituents on nitrogen are directed to the same side of the plane as the germanium centre. There are no significant interactions to the triflate anions, therefore, the germanium is in a highly distorted square planar, or tetragonal pyramidal, environment.

Fig. 4 The X-ray structure of the dication present in [Ge(Me₄cyclen)][O₃SCF₃]₂·0.8CH₃CN showing the Ge1-containing molecule. Thermal ellipsoids are drawn at 50% probability, and hydrogen atoms omitted for clarity. Selected bond lengths (Å) and angles (°): Ge1–N1 = 2.244(5), Ge1–N2 = 2.168(9), Ge1–N3 = 2.206(6), Ge1–N4 = 2.165(6), N1–Ge1–N3 = 131.8(2), N2–Ge1–N4 = 118.5(3), N2–Ge1–N1 = 78.2(2), N2–Ge1–N3 = 77.6(3), N4–Ge1–N1 = 77.8(2), N4–Ge1–N3 = 78.2(2). Symmetry codes: (i) x, y, 0.5 + z; (ii) −x, 1 − y, 0.5 + z.

The reaction of [GeCl₂(dioxane)] in CH₂Cl₂ with Me₄cyclen in a 3 : 1 molar ratio gave the corresponding [Ge(Me₄cyclen)][GeCl₃]₂ which was less stable in solution.

Silicon(IV) complexes

The reaction of SiCl₄, Me₃tacn and Me₃SiO₃SCF₃ in anhydrous CH₂Cl₂ solution produced [SiCl₃(Me₃tacn)][O₃SCF₃], which is much more hydrolytically sensitive than the [SiF₃(Me₃tacn)][SiF₅] salt.¹¹ Crystals of this chloro-complex were obtained by layering a concentrated CH₂Cl₂ solution with hexane. The structure of the cation shows the expected fac-octahedral coordination (Fig. 5). Comparison with the [SiF₃(Me₃tacn)]⁺ cation shows negligible differences between the Si–N distances.

Fig. 5 View of the cation present in [SiCl₃(Me₃tacn)][O₃SCF₃]. Thermal ellipsoids are drawn at 50% probability, hydrogen atoms omitted for clarity. Selected bond lengths (Å) and angles (°): Si1–Cl1 = 2.1867(9), Si1–Cl2 = 2.1688(8), Si1–Cl3 = 2.1416(9), Si1–N1 = 2.010(2), Si1–N2 = 2.013(2), Si1–N3 = 2.026(2); N1–Si1–N2 = 85.61(7), N2–Si1–N3 = 84.70(6), N1–Si1–N3 = 85.37(6), Cl1–Si1–Cl2 = 91.79(4), Cl1–Si1–Cl3 = 92.18(3), Cl2–Si1–Cl3 = 92.76(3).

The corresponding [SiCl₃(Me₃tacn)][BAr^F] was obtained by reacting SiCl₄ and Na[BAr^F] in toluene, followed by addition of a solution of Me₃tacn. As we have described elsewhere,¹⁹ if the reagents are added simultaneously, the product is the sodium complex of the ligand, rather than the silicon cation. Crystals of [SiCl₃(Me₃tacn)][BAr^F] were not obtained, however, a concentrated CH₂Cl₂ solution of the [BAr^F]⁻ salt, layered with hexane, produced a few colourless crystals identified by an X-ray structure determination as [SiCl₃(Me₃tacn)]Cl (see Fig. S1 in ESI†) which separate adventitiously due to the lower solubility of this salt. Direct reaction of SiCl₄ and Me₃tacn in CH₂Cl₂ resulted in precipitation of a pale yellow solid containing the same [SiCl₃(Me₃tacn)]Cl, however we have been unable to obtain it in analytically pure form by this route.

The ¹H NMR spectrum of [SiCl₃(Me₃tacn)]⁺ in CD₃CN at 298 K shows sharp second order multiplets characteristic of symmetrical fac-coordinated Me₃tacn in solution.²⁰

Similar reaction of SiHCl₃ with Na[BAr^F] in toluene, followed by addition of Me₃tacn, produced the corresponding dichlorosilane complex, [SiHCl₂(Me₃tacn)][BAr^F]. The presence of the Si–H group is shown by a singlet in the ¹H NMR spectrum at δ = 4.78 and by ν(SiH) in the IR spectrum at 2137 cm⁻¹. The presence of the fac-SiHCl₂ removes the three-fold symmetry of the Me₃tacn found in [SiCl₃(Me₃tacn)]⁺, and this is reflected in both the ¹H and ¹³C{¹H} NMR spectra, which show two δ(Me) resonances and corresponding splitting of the NCH₂ resonances. Attempts to determine the structure of this complex have been unsuccessful. Poor quality crystals were obtained, but structure solution showed disordered [SiCl₃(Me₃tacn)]⁺ and [SiHCl₂(Me₃tacn)]⁺ were both present (note that [SiCl₃(Me₃tacn)]⁺ is not present in the NMR spectra of the bulk product). Disproportionation of silane complexes of amine ligands has been noted in other systems, and presumably occurs here slowly over the time taken to grow crystals from the [SiHCl₂(Me₃tacn)]⁺ solution.²¹

Finally, two complexes of the linear triamine, Me₂NCH₂CH₂N(Me)CH₂CH₂NMe₂ (pmdta), [SiX₃(pmdta)][BAr^F] (X = Cl or Br) were isolated by reacting the appropriate SiX₄ with Na[BAr^F] in toluene, followed by addition of pmdta. The X-ray crystal structure of the chloride reveals a mer-geometry (Fig. 6) which contrasts with the fac arrangement found in the Me₃tacn complexes. The geometry of the [SiCl₃(pmdta)]⁺ cation is close to octahedral, and the Si–N and Si–Cl distances are little different from those found in [SiCl₃(Me₃tacn)]⁺ despite the different donor arrangements. The geometry is also similar to that found in mer-[SiHCl₂(pmdta)]⁺ (which has H trans to Cl).²²

Fig. 6 View of the cation in [SiCl₃(pmdta)][BAr^F]. Thermal ellipsoids are drawn at 50% probability and hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): Si1–Cl1 = 2.147(2), Si1–Cl2 = 2.124(2), Si1–Cl3 = 2.184(2), Si1–N1 = 2.059(5), Si1–N2 = 2.028(5), Si1–N3 = 2.075(5); N1–Si1–N2 = 85.6(2), N2–Si1–N3 = 85.0(2) Cl1–Si1–Cl2 = 91.12(9), Cl2–Si1–Cl3 = 89.82(9).

The spectroscopic data are unexceptional, but consistent with the mer geometries, although it is notable that the terminal –NMe₂ groups appear as a broad singlet rather than the two resonances expected due to the inequivalence produced by the central –NMe group lying out of the N₃Cl plane. The ease of formation of the [SiX₃(pmdta)]⁺ cations (X₃ = Cl₃, Br₃, HCl₂) is in contrast with the κ²-coordinated pmdta adduct formed with SiF₄, reflecting the much higher Si–F bond strength.¹¹

Conclusions

Two series of complexes with neutral aza-macrocyclic coordination to Ge(II) and Si(IV) are reported and structurally characterised. The hydrolytically sensitive Ge(II) triaza macrocyclic complexes show pyramidal GeN₃ coordination with very weak, but variable, interactions from the chloride and triflate anions. This contrasts with the ‘naked’ dication identified in the previously reported [Ge(Me₃tacn)]Br[GeBr₃].¹² The tetra-aza macrocyclic complexes of Ge(II) give GeN₄ dications in highly distorted square planar geometries, with no significant anion interactions towards Ge(II).

The triaza ligand complexes of Si(IV), formed by halide abstraction using either Me₃SiO₃SCF₃ or Na[BAr^F], adopt distorted octahedral coordination geometries, and the trichloro-, tribromo- and hydridodichloro-species reported here are significantly more readily hydrolysed than [SiF₃(Me₃tacn)]⁺.¹¹

Acknowledgements

We thank EPSRC for support (EP/I010890/1 and EP/I033394/1). The SCFED Project (http://www.scfed.net) is a multidisciplinary collaboration of British universities investigating the fundamental and applied aspects of supercritical fluids.

References

1. D. Vaughn II and R. E. Schaak, Chem. Soc. Rev., 2013, 42, 2861.
2. S. Raoux, W. Welnic and D. Ielmini, Chem. Rev., 2010, 110, 240.
3. D. V. Talapin, J. S. Lee, M. V. Kovalenko and E. V. Shevchenko, Chem. Rev., 2010, 110, 389.
4. (a) J. Ke, W. Su, S. M. Howdle, M. George, D. Cook, M. Perdjon-Abel, P. N. Bartlett, W. Zhang, F. Cheng, W. Levason, G. Reid, J. Hyde, J. Wilson, D. C. Smith, K. Mallik and P. Sazio, Proc. Natl. Acad. Sci. U. S. A., 2009, 106, 14768; (b) J. Ke, P. N. Bartlett, D. Cook, T. L. Easun, M. George, W. Levason, G. Reid, D. C. Smith, W. Su and W. Zhang, Phys. Chem. Chem. Phys., 2014, 16, 9202.
5. P. N. Bartlett, S. L. Benjamin, C. H. de Groot, A. L. Hector, A. Jolleys, R. Huang, G. P. Kissling, W. Levason, S. J. Pearce, G. Reid and Y. Wang, Mater. Horizons, 2015, 2, 420.
6. (a) P. N. Bartlett, C. Y. Cummings, W. Levason, D. Pugh and G. Reid, Chem. – Eur. J., 2014, 20, 5019; (b) J. Ke, P. N. Bartlett, D. Cook, T. L. Easun, M. W. George, W. Levason, G. Reid, D. Smith, W. Su and W. Zhang, Phys. Chem. Chem. Phys., 2012, 14, 1517.
7. W. Levason, G. Reid and W. Zhang, Coord. Chem. Rev., 2011, 255, 1319.
8. (a) R. S. Ghadwal, H. W. Roesky, S. Merkel, J. Henn and D. Stalke, Angew. Chem., Int. Ed., 2009, 48, 5683; (b) A. C. Filippou, O. Chernov and G. Schnakenburg, Angew. Chem., Int. Ed., 2009, 48, 5687.
9. F. Cheng, M. F. Davis, A. L. Hector, W. Levason, G. Reid, M. Webster and W. Zhang, Eur. J. Inorg. Chem., 2007, 4897.
10. G. Willey, T. J. Woodman, U. Somasundaram, D. R. Aris and W. Errington, J. Chem. Soc., Dalton Trans., 1998, 2573.
11. F. Cheng, A. L. Hector, W. Levason, G. Reid, M. Webster and W. Zhang, Chem. Commun., 2009, 1334.
12. F. Cheng, A. L. Hector, W. Levason, G. Reid, M. Webster and W. Zhang, Angew. Chem., Int Ed., 2009, 48, 5152.
13. K. Wieghardt, P. Chaudhuri, B. Nuber and J. Weiss, Inorg. Chem., 1982, 21, 3086.
14. M. Brookhart, B. Grant and A. F. Volpe Jr., Organometallics, 1992, 11, 3920.
15. (a) CrystalClear-SM Expert 2.0 r7.4, Rigaku Corporation, Tokyo, Japan, 2011; (b) L. J. Farrugia, J. Appl. Crystallogr., 2012, 45, 849; (c) O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard and H. Puschmann, J. Appl. Crystallogr., 2009, 42, 339; (d) G. M. Sheldrick, Acta Crystallogr., Sect. C: Cryst. Struct. Commun., 2015, 71, 3; (e) F. H. Allen, O. Johnson, G. P. Shields, B. R. Smith and M. Towler, J. Appl. Crystallogr., 2004, 37, 335.
16. See for example: J. Dyke, W. Levason, M. E. Light, D. Pugh, G. Reid, H. Bhakhoa, P. Ramasami and L. Rhyman, Dalton Trans., 2015, 44, 13853.
17. M. Mantina, A. C. Chamberlin, R. Valero, C. J. Cramer and D. G. Truhlar, J. Phys. Chem. A, 2009, 113, 5806.
18. B. Cordero, V. Gomez, A. E. Platero-Prats, M. Reves, J. Echeverrıa, E. Cremades, F. Barragan and S. Alvarez, Dalton Trans., 2008, 2832.
19. M. Everett, A. Jolleys, W. Levason, D. Pugh and G. Reid, Chem. Commun., 2014, 50, 5843.
20. R. Bhalla, C. Darby, W. Levason, S. K. Luthra, G. McRobbie, G. Reid, G. W. Sanderson and W. Zhang, Chem. Sci., 2014, 5, 381.
21. (a) P. Boudjouk, S. D. Kloos, B.-K. Kim, M. Page and D. Thweatt, J. Chem. Soc., Dalton Trans., 1998, 877; (b) H. J. Campbell-Ferguson and E. A. V. Ebsworth, J. Chem. Soc. A, 1966, 1508.
22. B.-K. Kim, S.-B. Choi, S. D. Kloos and P. Boudjouk, Inorg. Chem., 2000, 39, 728.

---

Footnote

† Electronic supplementary information (ESI) available: CCDC 1430051 ([Ge(Me₃tacn)][O₃SCF₃]₂·MeCN), 1430052 ([Ge(Me₄cyclen)][O₃SCF₃]₂·0.8MeCN), 1430053 ([Ge(Me₃tacn)]Cl[O₃SCF₃]₂), 1430054 ([Ge(Me₃tacn)]Cl₂·MeCN), 1430055 ([SiCl₃(Me₃tacn)][O₃SCF₃]), 1430056 ([SiCl₃(Me₃tacn)]Cl) and 1430057 ([SiCl₃(pmdta)][BAr^F]). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5dt03941j

---