Controlling Catenation in Germanium(I) Chemistry through Hemilability

Abstract We present a novel approach for constructing chains of Group 14 metal atoms linked by unsupported metal–metal bonds that exploits hemilabile ligands to generate unsaturated metal sites. The formation/nature of catenated species (oligo‐dimetallynes) can be controlled by the use of (acidic/basic) “protecting groups” and through variation of the ligand scaffold. Reduction of ArNiPr2GeCl (ArNiPr2=2,6‐(iPr2NCH2)2C6H3)—featuring hemilabile NiPr2 donors—yields (ArNiPr2Ge)4 (2), which contains a tetrameric Ge4 chain. 2 represents a novel type of a linear homo‐catenated GeI compound featuring unsupported E−E bonds. Trapping experiments reveal that a key structural component is the central two‐way Ge=Ge donor‐acceptor bond: reactions with IMe4 and W(CO)5(NMe3) give the base‐ or acid‐stabilized digermynes (ArNiPr2Ge(IMe4))2 (4) and (ArNiPr2Ge{W(CO)5})2 (5), respectively. The use of smaller N‐donors leads to stronger Ge‐N interactions and quenching of catenation behaviour: reduction of ArNEt2GeCl gives the digermyne (ArNEt2Ge)2, while the unsymmetrical system ArNEt2GeGeArNiPr2 dimerizes to give tetranuclear (ArNEt2GeGeArNiPr2)2 through aggregation at the NiPr2‐ligated GeI centres.

s2 (i) General considerations All manipulations were carried out using standard Schlenk line or dry-box techniques under an atmosphere of dry argon or dinitrogen. Solvents were degassed by sparging with argon and dried by passing through a column of the appropriate drying agent using a commercially available Braun SPS and stored over potassium. Diethyl ether and THF were dried over and distilled from sodium and benzophenone/potassium (respectively) and stored over a potassium mirror or sodium mirror, respectively. THF employed in the preparation of (Ar NEt2 Ge) 2 was dried over and distilled from potassium and degassed by three freeze-pump-thaw cycles; in this case the solvent was not stored over a sodium mirror. Hexamethyldisiloxane was dried over CaH 2 , distilled, degassed by three freezepump-thaw cycles and stored over activated 4 Å molecular sieves. NMR spectra were measured in benzene-d 6 which was dried over CaH 2 , with the solvent then being distilled under reduced pressure, degassed by three freeze-pump-thaw cycles and stored under argon in Teflon valve ampoules. NMR samples were prepared under argon in 5 mm Wilmad 507-PP tubes fitted with J. Young Teflon valves.
NMR spectra were measured on a Bruker Avance III HD Nanobay 400 MHz NMR spectrometer equipped with a 9.4 T magnet, Bruker Avance III 500 MHz NMR spectrometer equipped with a 11.75 T magnet or a Bruker Avance III NMR 500 MHz NMR spectrometer equipped with a 11.75 T magnet and a 13 C detect cryoprobe. 1 H and 13 C NMR spectra were referenced internally to residual protiosolvent ( 1 H) or solvent ( 13 C) resonances and are reported relative to tetramethylsilane (δ = 0 ppm).
Chemical shifts are quoted in δ (ppm) and coupling constants in Hz. Infra-red spectra were measured on a Nicolet 500 FT-IR spectrometer. Samples were measured as a Nujol mull and were prepared inside a glovebox before being sealed in an airtight cell. Elemental analyses were carried out at London Metropolitan University or by Elemental Microanalysis Ltd., Okehampton, Devon.

(ii) Starting materials
The syntheses of 2,6-(BrCH 2 ) 2 C 6 H 3 Br, [S1] [2,6-(R 2 NCH 2 ) 2 C 6 H 3 ]GeCl (R = Et, i Pr), [S2]  Synthesis of (Ar NEt2 Ge) 2 (1): A rapidly stirred mixture of Ar NEt2 GeI (500 mg, 1.12 mmol) and KC 8 (174 mg, 1.29 mmol) was cooled to -78 °C and to it was added tetrahydrofuran (3.5 mL). The resulting slurry was stirred for 5 min at -78 °C before being allowed to warm to room temperature and stirred for a further 20 min. Following this, volatiles were removed in vacuo and the resulting residue was treated with hexamethyldisiloxane (HMDSO) (10 mL). The resulting orange solution was filtered and concentrated until orange oil was deposited onto the walls of the Schlenk tube (to ca. 5 mL). The oil was redissolved and the solution stored at -30 °C overnight. After allowing the solution to warm again to room temperature, small orange crystals of (Ar NEt2 Ge) 2 began to grow from the solution. After storage of the solution overnight at room temperature, the crystals were isolated and dried in vacuo.
Further concentration of the supernatant solution, followed by storage at -30 °C overnight and then at room temperature for a further 24 h yielded a second crop of crystals. Combined yield: 263 mg (73%).
Single crystals of X which were suitable for X-ray crystallography were obtained from the storage of a s7 precipitation of a colourless powder. Storage of the reaction mixture at room temperature for 48 h led to the formation of a small number of single, dark red crystals which were suitable for X-ray crystallography.
Reaction of (Ar NiPr2 Ge{IMe 4 }) 2 (4) and BPh 3 : To a solution of (Ar NiPr2 Ge(IMe 4 )) 2 (0.02 g, 0.020 mmol) in benzene-d 6 (0.5 mL) in an NMR tube fitted with a J. Young's valve was added BPh 3 (0.01 g, 0.041 mmol). Upon addition of the Lewis acid, the orange-red solution immediately changed colour to deep red. The resulting solution was analysed by 1 H and 11 B NMR spectroscopy which showed that complete consumption of (Ar NiPr2 Ge(IMe 4 )) 2 occurs, accompanied by formation of IMe 4 ·BPh 3 ; 1 H and 11 B NMR data are consistent with that reported by Inoue et al. [S8] Over the course of 12 h, dark red powder precipitated from the benzene solution. Dark red crystals of (Ar NiPr2 Ge) 4 could be grown from the solution by redissolving this powder at 60 °C and allowing the solution to cool slowly to room temperature; the identity of the crystals was confirmed by analysis by X-ray crystallography.
(iv) 1 H and 13 C NMR spectra of novel compounds Figure S1. 1 H NMR spectrum of Ar NiPr2 GeI measured in benzene-d 6 at 298 K. Toluene impurity has been labelled.

Figure S2.
13 C NMR spectrum of Ar NiPr2 GeI measured in benzene-d 6 at 298 K.
s9 Figure S3. 1 H NMR spectrum of Ar NEt2 GeI measured in benzene-d 6 at 298 K. Figure S4. 13 C NMR spectrum of Ar NEt2 GeI measured in benzene-d 6 at 298 K.

s15 (v) X-ray crystallographic studies
Single-crystal X-ray diffraction data for all compounds were collected at 150 K on an Oxford Diffraction/Agilent SuperNova diffractometer using Cu-K α radiation (λ = 1.54184 Å) or Mo-K α (λ = 0.71073 Å), and equipped with a nitrogen gas Oxford Cryosystems cooling unit. [S9] Raw frame data were reduced using CrysAlisPro. [S10] The structures were solved using SHELXT [S11] and refined to convergence on F 2 by full-matrix least-squares using SHELXL [S12] in combination with OLEX2. [S13] Distances and angles were calculated using the full covariance matrix. Restraints were used to maintain sensible geometries for the disordered groups and approximate the displacement parameters to typical values. Selected crystallographic data are summarized in Table S2 and full details are given in the supplementary deposited CIF files (CCDC 2075218-2075226). These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Figure S14. The molecular structures of Ar NiPr2 GeCl (left), Ar NiPr2 GeI (middle) and Ar NEt2 GeI (right).
Thermal ellipsoids set at the 40% probability level. Hydrogen atoms omitted and i Pr/Et substituents shown in wireframe format for clarity. Table S1. Selected bond lengths and angles for Ar NiPr2 GeCl, Ar NiPr2 GeI and Ar NEt2 GeI.