Supramolecular Organic and Organometallic Chemistry Centre

Abstract
The present proposal is focused on the organometallic chemistry of heavy pnicogens (Pn = Sb, Bi) of high interest for their valuable potential in catalysis. The compounds envisaged are neutral or cationic, well defined molecular and/or cluster species from the less explored class of alkoxides and completely unexplored classes of related oxo ligands - boryloxides, siloxides and germyloxides. Our research objectives are focused on (i) preparation of molecular organopnicogen(III) alkoxides, including chiral ones, enough stable to be investigated both in solution and in solid state; (ii) preparation of first boryloxide, siloxide and germyloxide analogues; (iii) evaluation of the tetrel nature on the reactivity of Pn–O bond in the Pn–O–Tet unit (Tet = C, Si, Ge); (iv) preparation of monoorganopnicogen(alkoxo) cations stabilized through intramolecular coordination; (v) studies regarding the potential of the new organopnicogen(III) species with oxo ligands in catalysis, including C–H activation, and exploration of their active role in reversible CO₂ fixation/activation.

Results

Stage 1 (January 2021 – December 2021) in the implementation of the project
During the first stage of the project the performed activities (management and scientific ones) were dedicated to the development of the objectives detailed in the research plan, part of the approved proposal (contract 224/2021):

• Several aromatic proligands with two pendant arms, 2,6-(R2NCH2)2C6H4, as well as triorganopnicogens(III), R₃Pn, organopnicogen(III) halides, R₂PnX and RPnX₂ (X = Cl, Br), oxides and sulfides, (RPnE)_n and (R₂Pn)₂E (E = O, S), oxy-chlorides, (RPnCl)₂O [Pn = Sb, Bi; R = 2-(Me₂NCH₂)C₆H₄, 2,6-(R₂NCH₂)₂C₆H₃] were prepared. All these compounds are non-commercial products and are raw materials necessary to carry out the proposed research within this project.
• The new compounds RBi(Cl)(S₂CNMe₂) and Bi(S₂CNMe₂)2 [R = 2-(Me₂NCH₂)C₆H₄] were prepared and characterized by IR, Raman, multinuclear NMR spectroscopies, mass spectrometry, thermogravimetric studies, single crystal X-ray diffraction, and computational methods. The results were published (DOI: 10.1016/j.molstruc.2021.131335).
• The new organopnicogen(III) amides, RPn[N(SiMe₃)₂]₂ and R₂Pn[N(SiMe₃)₂] [Pn = Sb, Bi; R = 2-(Me₂NCH₂)C₆H₄] were synthesized and characterized by multinuclear NMR spectroscopy. These compounds will be used in the next stages of the project as starting materials for the preparation of new organopnicogen(III) alkoxides.
• Several organopnicogen(III) alkoxides and aryloxides, RPn(OR′)₂ and R₂Pn(OR′) [Pn = Sb, Bi; R′= akyl, aryl], as well as related compounds were synthesized and characterized spectroscopically (multinuclear NMR – including variable temperature studies, MS). For some compounds the molecular structure was established by single crystal X-ray diffraction studies. Computational methods were performed on selected compounds to investigate the noncovalent interactions observed in the crystal.
• Related triorganopnicogen(V) aryloxides were also prepared and characterized spectroscopically (multinuclear NMR, MS).
• Several boronic and borinic acids, i.e. RB(OH)₂ and R₂B(OH), were prepared and used for the synthesis of organopnicogen(III) species containing [RB(OH)O]⁻ or [R₂BO]⁻ ligands.
• Preliminary studies have been performed on the synthesis of non-coordinating anions as [B(C₆F₅)₄]⁻ (or BArF⁻) and [Al{OC(CF₃)₃}]⁻. The compound [2-(Me₂NCH₂)C₆H₄Sb(O₃SCF₃)]₂O, containing a fluorinated anion with low coordinating properties, was prepared and investigated by multinuclear NMR spectroscopy and mass spectrometry.
• The reaction of RPnCl₂ with potassium aryloxides was investigated and studies on the reactivity of the isolated compounds were performed.

The obtained results were so far disseminated through one published article; two other manuscripts are in the final stages of writing and will be sent for publication at beginning of 2022. In addition, part of the results obtained within this first stage of the project were within two oral presentations at international conferences.

Stage 2 (January 2022 – December 2022) in the implementation of the project

The main results obtained during stage 2 of the project are summarized bellow:

• Starting from the oxide [2-(Me₂NCH₂)C₆H₄SbO]₃ a series of mononuclear organoantimony(III) aryloxides were obtained: [2-(Me₂NCH₂)C₆H₄]Sb(OAr)₂ [Ar = C₆H₃-2-^tBu-6-Me (68), C₆H₃Cl₃-2,4,6 (69)] together with a dinuclear derivative [{2-(Me₂NCH₂)C₆H₄}Sb(OC₆H₂Cl₃-2,4,6)]₂O (70). The studies were completed with the synthesis of mononuclear chiral compounds [2-(Me₂NCH₂)C₆H₄]Sb(Cl)[(E=PPh₂)₂N] [E = S (74), Se (75)], with a dynamic behaviour evidenced by a vt ³¹P NMR investigation. These compounds will be used as starting materials to obtain ionic species with weak or non-coordinating anions;
  
• Studies regarding organoantimony(V) derivatives which were obtained in the first stage of the project by oxidation of the organoantimony(III) species with o-chloranil were extended to other compounds, i.e. [2-(Me₂NCH₂)C₆H₄]Sb(pinF)(o-C₆Cl₄O₂) (76) [pinF = OC(CF₃)₂(CF₃)₂O]^2-];
• Investigation of the monoorganopnicogen(III) bis(aryloxides), RSb(OC₆H₃ⁱPr-2,6)₂ (50), RSb[OC₆H₃(OMe)₂-2,6]₂ (51) and RBi[OC₆H₃(OMe)₂-2,6]₂ (53), [R = 2,6-(Me₂NCH₂)C₆H₃], was finished with a manuscript which is in the final stage before submission.
• The structural and spectroscopic characterization of organopnictogen(III) bis(arylthiolates), [2,6-(Me₂NCH₂)₂C₆H₃]Pn(SC₆H₃Me₂-2,6)₂ [Pn = Sb, Bi], [2,6-{MeN(CH₂CH₂)₂NCH₂}C₆H₃]Pn(SC₆H₃Me₂-2,6)₂ [Pn = Sb, Bi] and [2,6-{O(CH₂CH₂)₂NCH₂}C₆H₃]Pn(SC₆H₃Me₂-2,6)₂ [Pn = Sb, Bi] was now accomplished as the synthesis of these compounds was reported in a previous project (PN-III-P4-ID-PCE-2016-0857). Reactivity studies over chalcogens were performed for these derivatives giving ciclo-[{2,6-(Me₂NCH₂)₂C₆H₃}Pn(μ-O)]₂ [Pn = Sb (77), Bi (78)] or ciclo-[{2,6-(Me₂NCH₂)₂C₆H₃}Pn(μ-E)]₂ [E = S (79), Se (80)] and the disulfide ArS–SAr (Ar = C₆H₃Me₂-2,6) and over elemental iodine with the isolation of the diiodide [2,6-{O(CH₂CH₂)₂NCH₂}C₆H₃]BiI₂ (81) and an adduct 81∙0.5I₂ formed via halogen bonds. The results were included in the paper Dalton Trans., 2022, 51, 10406-10419 (DOI: 10.1039/d2dt01436j)
• The siloxide [2-(Me₂NCH₂)C₆H₄]₂Bi(OSiPh₃) was successfully prepared as only the second member of the organopnicogen(III) siloxides family. The compound was characterized by multinuclear NMR and its molecular structure was established by single-crystal X-ray diffraction.
• The following types of ionic chiral species were also synthesized and characterized: [{2,6-(Me₂NCH₂)₂C₆H₃}Pn(Cl)]⁺[X]^-, [{2-(Me₂NCH₂)C₆H₄}Pn]⁺[X]^- [{2-{2',6'-(ⁱPr₂C₆H₃)N=CH}C₆H₄}₂Pn]⁺[X]^-. Some of these compound were also investigated for their Mannich catalytic activity.
• Studies on the C-H activation in reactions of organopnicogen(III) dihalides with KOC₆H₃^tBu₂-2,6 were also continued, as well as, the reactivity of the [2,6-(Me₂NCH₂)₂C₆H₃]Sb(C₆H₃^tBu₂-3,5-O-4) towards CE₂ (E = O, S).
• The catalytic activity of some organoantimony(III) compounds was investigated on Mannich reaction of the benzaldehyde, aniline and cyclohexanone in different organic solvents.
• Most of the new compounds were characterized by multinuclear NMR spectroscopy, MS spectrometry and single-crystal X-ray diffraction.

Articles

1. Synthesis, physicochemical properties, crystal molecular structure and DFT investigation of an organobismuth(III) bis(dimethyldithiocarbamate),
   A. Anton, A. Soran, C. Silvestru, J. Mol. Struct., 2021, 1247, 131335.
   DOI: 10.1016/j.molstruc.2021.131335
   
   
2. Organopnictogen(III) bis(arylthiolates) containing NCN-aryl pincer ligands: from synthesis and characterization to reactivity,
   G. Duneş, A. Soran, C. Silvestru, Dalton Trans., 2022, 51, 10406-10419.
   DOI: 10.1039/d2dt01436j
   
   
3. [2,6-{O(CH₂CH₂)2NCH₂}₂C₆H₃]SbCl₂ – a new pincer ligand-containing organoantimony(III) compound. Molecular structure and supramolecular aspects,
   G. Duneş, A. Soran, C. Silvestru, Rev. Roum. Chim., 2022, 67, 385-392.
   DOI: 10.33224/rrch.2022.67.6-7.05
   
   
4. NCN-pincer organopnictogen(III) bis(aryloxides),
   G. Duneş, C. Silvestru, 2022, to be submitted.
   
   

Conferences

1. Aerobic decomposition of new NCN-type pincer organopnictogen(III) bis(arylthiolates),
   G. Duneș, C. Silvestru
   at The 24th Conference on Organometallic Chemistry (EuCOMC XXIV) (on-line), Alcala de Henares, Madrid, Spain, September 1^st-3^rd, 2021 (oral presentation).
   
   
2. Hypercoordinated organopnicogen(III) (Sb, Bi) compounds - C-H bond activation and reactivity,
   A. Sava, G. Duneș, A. Pöllnitz, C. Silvestru
   at New trends and strategies in the chemistry of advanced materials, (on-line), Timișoara, Romania, October 7^th-8^th, 2021 (invited plenary lecture).
   
   
3. Synthesis, physicochemical properties, crystal molecular structure and DFT investigation of an organobismuth(III) bis(dimethyldithiocarbamate),
   A. Anton, A. Soran, C. Silvestru
   at 13th International Conference Processes in Isotopes and Molecules (hybrid event), INCDTIM, Cluj-Napoca, September 22^th-24^th, 2021 (poster presentation).
   
   
4. Organometallic chemistry of heavy pnicogens (Sb, Bi) at CCSOOM – FCIC (1993 – present) – from unusual structures to potential uses,
   C. Silvestru,
   at The 18^th International Conference Students for Students, Cluj-Napoca, April, 6^th-10^th, 2022 (invited plenary lecture).
   
   
5. Chimia organometalică a pnictogenilor grei (Sb, Bi) – de la structuri neobișnuite la utilizări potențiale,
   C. Silvestru,
   at Simpozionul „120 de ani de la nașterea Academicianului Costin D. Nenițescu”, Academia Română, București, September, 22^th-23^th, 2022 (invited plenary lecture).
   
   
6. Novel organoantimony(III) aryloxides. Synthesis and reactivity,
   M.-C. Afloarei, M. Mehring, C. Silvestru,
   at A XXXVI-a Conferință Națională de Chimie, Călimănești-Căciulata, October, 4^th-7^th, 2022 (oral presentation).
   
   
7. Arylantimony(III) nicotinates and isonicotinates. Synthesis and structural characterization,
   A. Tomuță, C. Silvestru, C. I. Raț
   at A XXXVI-a Conferință Națională de Chimie, Călimănești-Căciulata, October, 4^th-7^th, 2022 (poster presentation).
   
   
8. Lewis acidic organoantimony(V) compounds with pendant arms,
   R. G. Dornea, C. I. Raț
   at A XXXVI-a Conferință Națională de Chimie, Călimănești-Căciulata, October, 4^th-7^th, 2022 (poster presentation).
   
   
9. Organopnicogen(III) compounds containing Pn−chalcogen (Pn = Sb, Bi) - structure and reactivity,
   C. Silvestru,
   at The 14^th Symposium “New Trends and Strategies in the Chemistry of Advanced Materials with Relevance in Biological systems, techniques and Environmental Protection”, Timișoara, October, 21^st-22^nd, 2022 (invited plenary lecture).
   
   
10. Hypercoordinated organopnicogen(III) compounds containing Pn−E (Pn = Sb, Bi; E = O, S, Se) – structure and reactivity,
    C. Silvestru,
    at The 10^th Workshop of the Selenium and Sulfur Redox and Catalysis Network (WSeS-10), Niteroi, Brazil, November, 25^th-26^th, 2022 (invited lecture).
    
    
11. Hypercoordinate organoantimony(III) compounds with antimony-chalcogen bonds
    A. L. Corjuc, A. Farris, E. Kapronczai, V. Lippolis, C. Silvestru,
    at The 15^th International Conference on the Chemistry of Selenium and Tellurium (ICCST-15), Florianopolis, Brazil, November, 28^th- December, 2^nd, 2022 (poster).
    
    

PhD Thesis

1. Hypercoordinated organopnictogen(III) (Sb, Bi) compounds − structure and reactivity −,
   Gabriel-Iulian Duneş
   Scientific advisor: Acad. Prof. Dr. Cristian Silvestru
   Defended on: September, 30^th, 2022.
   
   

Reports

For information about unpublished results contact Prof. Dr. Cristian Silvestru at cristian.silvestru (at) ubbcluj.ro.