& Organocatalysis Hydrogen Sulfide Induced Carbon Dioxide Activation by Metal- Free Dual Catalysis Manoj Kumar and Joseph S. Francisco* [a] Abstract: The role of metal free dual catalysis in the hy- drogen sulfide (H 2 S)-induced activation of carbon dioxide (CO 2 ) and subsequent decomposition of resulting mono- thiolcarbonic acid in the gas phase has been explored. The results suggest that substituted amines and monocar- boxylic type organic or inorganic acids via dual activation mechanisms promote both activation and decomposition reactions, implying that the judicious selection of a dual catalyst is crucial to the efficient C ÀS bond formation via CO 2 activation. Considering that our results also suggest a new mechanism for the formation of carbonyl sulfide from CO 2 and H 2 S, these new insights may help in better understanding the coupling between the carbon and sulfur cycles in the atmospheres of Earth and Venus. Carbon dioxide (CO 2 ) emissions into the atmosphere are in- creasing at an alarming rate with every passing year. [1] Accord- ing to a recent report, [2] CO 2 levels in the atmosphere have al- ready crossed the 400 ppm mark, and continue to rise relent- lessly. Because of its involvement in global warming, there is an immediate need to better understand the chemistry of CO 2 and identify sequestration or other processes for its removal. Utilizing CO 2 as a renewable source of carbon is an attractive strategy for a sustainable, low-carbon society. This has led to significant interest in developing CO 2 as a C 1 feedstock for carbon–carbon bond formation and carbon–heteroatom func- tionalization reactions in chemical synthesis. [3] However, the considerable thermodynamic stability of CO 2 renders it relative- ly inert as a chemical reactant. [4] Therefore, low-energy catalytic activation of CO 2 is highly desirable. Several transition-metal catalysts have been employed to transform CO 2 into valuable commodity chemicals. [5] Metal-free catalysis presents an alternative approach for CO 2 capture under ambient reaction conditions. [6] The potential of N-heter- ocyclic carbenes, [7, 8] frustrated Lewis pairs (FLPs), [9–13] and vari- ous other main-group catalysts [14] for CO 2 activation has been recently established. FLPs contain sterically hindered Lewis acid and Lewis base that makes them catalytically interest- ing. [15] For example, Grimme, Stephan, and Erker et al. have re- ported the usefulness of phosphine–borane FLPs in CO 2 activa- tion. [9a] Piers and co-workers have used B(C 6 H 5 ) 3 and amines to convert CO 2 into methane with silanes. [10] Fontaine and co-workers have established the catalytic effect of R 2 PC 6 H 4 B(O 2 C 6 H 4 ) in the hydroboration of CO 2 en route to methanol formation. [11] Zhu and An have recently examined the CO 2 sequestration with a series of amidophosphoranes at the DFT level and suggested the role of the interplay of the ring strain and the trans influence in determining the reactivity, which provides a new platform for the design of FLPs for the CO 2 capture. [12] In a subsequent study, An and Zhu performed a comparative analysis of the sequestration of CO 2 and CS 2 using the P/N-based FLPs and provided useful mechanistic in- sights into the factors controlling the sequestration. [13] Herein we report the role of metal-free dual organocatalysis in the CO 2 insertion into the S ÀH bond of hydrogen sulfide (H 2 S) in the gas phase that leads to the unprecedented C ÀS bond formation. The mechanistic beauty of dual organocataly- sis lies in the fact that the coexistence of acidic and basic sites in a catalyst (an organic or inorganic acid) causes the concert- ed activation of the electrophile CO 2 and nucleophile H 2 S, and results in the low-energy reaction (Scheme 1). To the best of our knowledge, C ÀS bond formation in the presence of a metal-free dual catalyst has yet to be achieved. Scheme 1. Proposed mechanism for the gas-phase formation of carbonyl sulfide by carbon dioxide insertion into the HÀS bond of hydrogen sulfide under metal-free dual organocatalysis. [a] Dr. M. Kumar, Prof. J. S. Francisco Department of Chemistry University of Nebraska-Lincoln, Lincoln, NE 68588 (USA) E-mail : jfrancisco3@unl.edu Supporting information for this article is available on the WWW under http ://dx.doi.org/10.1002/chem.201504953. Chem. Eur. J. 2016, 22, 4359 – 4363 # 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 4359 Communication DOI: 10.1002/chem.201504953