The lithium effect in ketenyl anion chemistry

Ketenyl lithium compounds of type [RC(Li)CO] (with R = Ph2P(E), E = O, S, Se) were found to exhibit lower thermal stabilities than their potassium analogues due to the stronger coordination of the oxygen of the ketene moiety to the harder metal cation, resulting in a more pronounced ynolate character. Using additional ligands allows manipulation of the O–Li interaction, thereby influencing the stability and reactivity of the ketenyl anions.


Chemical and Conditions
If not stated otherwise, all experiments were carried out using standard Schlenk techniques under an argon atmosphere, which was dry and free of oxygen.Argon (99.999%) was a product of Air Liquide and was used without any further drying.An MBraun SPS 800 was used to dry solvents before their usage (THF, toluene, DCM, ACN, n-pentane, n-hexane).All solvents were stored over molecular sieves under an argon atmosphere.Reagents were purchased from Sigma-Aldrich, ABCR, Acros Organics or TCI Chemicals and used without further purification if not stated otherwise.1a, 1b, 1c were synthesized following literature procedures. 1,2alytical methods NMR Spectroscopy. 1 H, 13 C{ 1 H}, 77 Se{ 1 H}, 31 P{ 1 H} NMR spectra were recorded on Avance-III-400 spectrometers at 22 °C if not stated otherwise.All values of the chemical shift are in ppm regarding the δ-scale.All spin-spin coupling constants (J) are printed in Hertz (Hz).To display multiplicities and signal forms correctly the following abbreviations were used: s = singlet, d = doublet, t = triplet m = multiplet, dd = doublet of doublet, br = broad signal.Signal assignment was supported by, HSQC ( 1 H / 13 C), HMBC ( 1 H / 13 C, 1 H / 31 P) correlation experiments.
IR spectra were recorded on a Shimadzu IRSpirit with QATR-S module in an argon filled glovebox and on a Thermo Nicolet iS5 FT-IR in transmission mode with a Specac "Omnicell" with KBr plates and a 0.1 mm spacer at 22 °C.Measurement and processing details for individual spectra can be extracted from the corresponding tables in the supporting information.
Melting points were measured with the SMP30 melting point apparatus from Stuart.
Elemental analyses were performed on an Elementar vario MICRO cube elemental analyzer.
For details about the single-crystal Xray diffraction analyses, see chapter 3.

Safety comments
Caution! Strong bases such as organolithium bases, especially as neat compounds, are severely air-/moisture-sensitive and pyrophoric organometallic compounds.These compounds need to be handled under an inert gas atmosphere to exclude reactions with oxygen and water.Guidelines for their handling can be found in literature: T. L. Rathman, J. A. Schwindeman, Org.Process Res.Dev.2014, 18, 1192.
Caution! Carbon monoxide (CO) is a highly toxic gas.Reactions should be performed in wellventilated fumehoods, ideally with a CO sensor. .

Synthesis of compounds 2a
20 mg (0.0406 mmol) of compound 1a and 4.93 mg (0.0447 mmol) LDA were dissolved in 1 mL THF-d8 and stirred for 10 min.After filtration, a yellow solution of 2a was obtained.The compound was not isolated but used as a solution for further reaction.The successful formation of 2a was confirmed by 1 P{ 1 H}-NMR spectroscopy.

Synthesis of compounds 2b
20 mg (0.0406 mmol) of compound 1b and 4.93 mg (0.0447 mmol) LDA were dissolved in 1 mL THF-d8 and stirred for 10 min.After filtration, a yellow solution of 2b was acquired.The compound was not isolated but used as a solution for further reaction.The successful formation of 2b was confirmed by 1 P{ 1 H}-NMR spectroscopy.In addition, few crystals suitable for X-ray diffraction (XRD) analysis could be grown by slow diffusion of hexane into toluene/THF solution.

Synthesis of compounds 2c
20 mg (0.0371 mmol) of compound 1c and 4.51 mg (0.0408 mmol) LDA were dissolved in 1 mL THF-d8 and stirred for 10 min.After filtration, a yellow solution of 2cwas acquired.The compound was not isolated but used as a solution for further reaction.The successful formation of 2a was confirmed by 1 P{ 1 H}-NMR spectroscopy.In addition, few crystals suitable for X-ray diffraction (XRD) analysis could be grown by slow diffusion of hexane into toluene/THF solution.

Synthesis of compounds 3-Li
Synthesis of compounds 3a-Li 1.5 g (3.15 mmol) of 1a and 382.0 mg (03.46 mmol) of LDA were dissolved in 30 mL tol/thf (9:1) mixture.The solution was stirred for 20 min.After filtration the atmosphere in the flask was changed from argon to CO and the reaction was stirred for 24 hours.After concentrating the solution to 5ml, 30 mL pentane was added resulting in the precipitation of a solid.The solid was filtered and washed with toluene (3 times) and pentane (3 times).After drying in vacuo, lithium ketenyl 3a-Li was obtained as off-white solid.(702 mg, 3.15 mmol, 70 %).PMDETA complex of 3a-Li 1.5 g (3.15 mmol) of 1a and 382.0 mg (03.46 mmol) of LDA were dissolved in 30 mL tol/thf (9:1) mixture.The solution was stirred for 20 min.1.1 eq. of N,N,N',N"N"-pentamethyldiethylenetriamine (PMDETA) (606 mg, 3.46 mmol) was added to the reaction mixture.After filtration the atmosphere in the flask was changed from argon to CO and the reaction was stirred for 24 hours.After concentrating the solution to 5ml, 30 mL pentane was added resulting in the precipitation of a solid.The solid was filtered and washed with toluene (3 times) and pentane (3 times).After drying in vacuo, 3a-Li(PMDETA) was obtained as off-white solid (938 mg, 2.23 mmol, 70.7 %).

Synthesis of compounds 3c-Li
200 mg (0.37 mmol) of 1c and 45.1 mg (0.41 mmol) of LDA were dissolved in 10 mL tol/thf(9:1) mixture.The solution was stirred for 20 min.After filtration the atmosphere in the flask was changed from argon to CO and the reaction was stirred for 24 hours.The solution was concentrated to 5 mL.Subsequently, 5 mL pentane were added resulting in the precipitation of a solid.The solid was filtered and washed with toluene (3 times) and hexane (3 times).After drying in vacuo, lithium ketenyl 3c-Li was obtained as off-white solid (82 mg, 0.37 mmol, 58 %).3c-Li is not stable for longer time in THF solution, but slowly converts to benzene derivative 4. PMDETA complex of 3c-Li 200 mg (0.37 mmol) of 1c and 45.1 mg (0.41 mmol) of LDA were dissolved in 10 mL tol/thf(9:1) mixture.The solution was stirred for 20 min.1.1 eq. of N,N,N',N"N"-pentamethyldiethylenetriamine (PMDETA) (71.5 mg, 0.41 mmol) was added.After filtration the atmosphere in the flask was changed from argon to CO and the reaction was stirred for 24 hours.The solution was concentrated to 5 mL.Subsequently, 5 mL pentane were added resulting in the precipitation of a solid.The solid was filtered and washed with toluene (3 times) and hexane (3 times).After drying in vacuo, lithium ketenyl 3c-Li(PMDETA) was obtained as off-white solids off-white solid (129 mg, 0.27 mmol, 72 %).Single crystal of 3c-Li(PMDETA) were grown by slow diffusion of hexane into a toluene/THF solution of the compound at −30  C.

General information
Good quality single crystals were hand-picked under polarized optical microscopy and then mounted on the diffractometer.The data collection was done at 100 K. X-ray intensity data measurements of all compounds were carried out on an Oxford SuperNova diffractometer with graphite-monochromatized (CuK= 1.54184 Å) radiation.The X-ray generator was operated at 50 kV and 30 mA.All the structures were solved using direct methods, refined with the Shelx software package [3][4][5][6]

Figure S45 .Figure S46 .
Figure S45.Molecular structure of compound 4c.Thermal ellipsoids at 50% probability level.H atoms and THF molecules are omitted for clarity.The bond lengths and bond angles are not discussed due to the low quality of the crystal.

Table S1 .
and expanded using Fourier techniques.The crystals of all compounds were mounted in an inert oil such as perfluoropolyalkylether. Crystallographic data including structure factors have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no.CCDC-236206 to CCDC-236209 Copies of the data can be gained free of charge on application to Cambridge Crystallographic Data Centre, 12 Data collection and structure refinement details for compounds 2b and 2c.