catalysts Review Advances in Visible-Light-Mediated Carbonylative Reactions via Carbon Monoxide (CO) Incorporation Vinayak Botla 1, Aleksandr Voronov 1, Elena Motti 1, Carla Carfagna 2, Raffaella Mancuso 3 , Bartolo Gabriele 3 and Nicola Della Ca’ 1,* 1 Department of Chemistry, Life Sciences and Environmental Sustainability (SCVSA), University of Parma, Parco Area delle Scienze, 17/A, 43124 Parma, Italy; [email protected] (V.B.); [email protected] (A.V.); [email protected] (E.M.) 2 Department of Industrial Chemistry “T. Montanari”, University of Bologna, 40136 Bologna, Italy; [email protected] 3 Laboratory of Industrial and Synthetic Organic Chemistry (LISOC), Department of Chemistry and Chemical Technologies, University of Calabria, Via P. Bucci 12/C, 87036 Arcavacata di Rende Cosenza, Italy; [email protected] (R.M.); [email protected] (B.G.) * Correspondence: [email protected]; Tel.:+39-0521-905676 Abstract: The abundant and inexpensive carbon monoxide (CO) is widely exploited as a C1 source for the synthesis of both fine and bulk chemicals. In this context, photochemical carbonylation reactions have emerged as a powerful tool for the sustainable synthesis of carbonyl-containing compounds (esters, amides, ketones, etc.). This review aims at giving a general overview on visible light-promoted carbonylation reactions in the presence of metal (Palladium, Iridium, Cobalt, Ruthenium, Copper) and organocatalysts as well, highlighting the main features of the presented protocols and providing Citation: Botla, V.; Voronov, A.; useful insights on the reaction mechanisms. Motti, E.; Carfagna, C.; Mancuso, R.; Gabriele, B.; Della Ca’, N. Advances Keywords: carbon monoxide; carbonylation; photochemical reactions; visible light; carbonyl- in Visible-Light-Mediated containing compounds Carbonylative Reactions via Carbon Monoxide (CO) Incorporation. Catalysts 2021, 11, 918. https:// doi.org/10.3390/catal11080918 1. Introduction Carbon monoxide (CO) is largely used in the chemical industry for manufacturing Academic Editor: Ekaterina bulk chemicals (i.e., methanol, acetic acid) and fine chemicals (i.e., ibuprofen) and is fre- A. Kozlova quently employed as an inexpensive and readily available C1 source in a wide range of carbonylative transformations for the synthesis of high-value-added carbonyl-containing Received: 26 June 2021 compounds, such as acids, esters, amides and ketones [1–6]. The carbonyl unit is ubiqui- Accepted: 27 July 2021 Published: 29 July 2021 tous in a myriad of bioactive molecules, such as natural products, pharmaceuticals and agrochemicals, as well as materials. It can be also manipulated and transformed into a Publisher’s Note: MDPI stays neutral series of other functional groups, including amines, alcohols and olefins. In the era of with regard to jurisdictional claims in sustainability, the development of economically improved and environmentally friendly published maps and institutional affil- catalytic protocols is highly recommended. In recent years, visible-light photocatalysis has iations. received much attention from the synthetic chemists’ community since, unlike traditional thermal and catalytic reactions, it enables unprecedented reaction pathways, high selec- tivities and mild reaction conditions [7–10]. The combination of carbon monoxide-based carbonylation strategy with the advantages that come from the application of photocataly- sis can potentially lead to a highly sustainable process [11–15]. However, the first reports Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. displayed problems connected with a limited generality, poor selectivity and/or efficiency, This article is an open access article high pressure of carbon monoxide or high energy of light irradiation [16–23]. Over the distributed under the terms and last two decades, new and more performing catalytic systems allowed to solve in part conditions of the Creative Commons these issues. The present review will cover the major advances in the area of visible light- Attribution (CC BY) license (https:// mediated catalyzed carbonylations from 2000, with a focus on CO-based carbonylation creativecommons.org/licenses/by/ methodologies. Sometimes, for a better and more general overview, less recent reports 4.0/). will be mentioned. The review is organized into different sections; each one is related to a Catalysts 2021, 11, 918. https://doi.org/10.3390/catal11080918 https://www.mdpi.com/journal/catalysts Catalysts 2021, 11, x FOR PEER REVIEW 2 of 34 methodologies. Sometimes, for a better and more general overview, less recent reports will be mentioned. The review is organized into different sections; each one is related to a Catalysts 2021, 11, 918 2 of 35 different metal, and one section is dedicated to metal-free protocols, which include the use of organic photocatalysts. different1.1. Visible-Light-Promoted metal, and one section Palladium-Catalyzed is dedicated to metal-free Carbonylations protocols, which include the use of organic photocatalysts. The major achievements in the area of visible-light-driven photocatalysis have been 1.1.reached Visible-Light-Promoted with palladium, Palladium-Catalyzed thanks to its superior Carbonylations versatility. One of the first reports was relatedThe to major the achievementssynthesis of unsymmetrical in the area of visible-light-driven ketones, which photocatalysiswere readily accessed have been by means reachedof a palladium-catalyzed with palladium, thanks cross-coupling to its superior reaction versatility. of Oneiodoalkanes of the first and reports 9-alkyl-9-borabicy- was re- latedclo[3.3.l]nonane to the synthesis derivatives of unsymmetrical (9-alkyl-9-BBN) ketones, which under were atmospheric readily accessed pressure by means of CO of a (Scheme palladium-catalyzed1) [24]. The presence cross-coupling of K3PO4 was reaction essential, of iodoalkanes while the and reaction 9-alkyl-9-borabicyclo[3.3.l] was significantly acceler- nonaneated by derivatives the irradiation (9-alkyl-9-BBN) of light. underAlkyl atmospherichalides bearing pressure β hydrogens of CO (Scheme often1)[ lead24]. The to competi- presence of K PO was essential, while the reaction was significantly accelerated by the tive pathways3 in4 traditional cross-coupling reactions, such as the formation of alkenes by irradiation of light. Alkyl halides bearing β hydrogens often lead to competitive pathways inβ–hydride traditional elimination. cross-coupling In this reactions, case, various such as theprimary, formation secondary of alkenes and by tertiaryβ–hydride alkyl iodides elimination.afforded unsymmetrical In this case, various ketones primary, in moderate secondary to andgood tertiary yields. alkyl Different iodides functional afforded groups unsymmetrical(i.e., acetal, nitrile, ketones carbomethoxy in moderate to groups) good yields. were Different well tolerated functional on groups both iodoalkanes (i.e., acetal, and 9- nitrile,alkyl-9-BBN carbomethoxy under groups)the optimized were well reaction tolerated co onnditions. both iodoalkanes Selected and examples 9-alkyl-9-BBN are shown in underScheme the 1. optimized reaction conditions. Selected examples are shown in Scheme1. R2 B O hv, 3% Pd(PPh3)4 1 R -I CO R1 R2 (1atm) K3PO4,C6H6 r.t., 24h 50–76% 9 examples R1 = primary, secondary and tertiary alkyl groups Features: 1991 Suzuki R2 = primary alkyl groups -hv: 100 W tungsten light - Alkyl iodides with hydrogens Selected examples: -1atmofCO O O O CO2Me H CO2Me 5 7 10 H 67% 76% O 65% O OMe O O O 73% AcO 50% OMe Proposed mechanism: CO hv Pd(PPh3)4 Pd(CO)(PPh3)3 Pd(CO)(PPh3) - PPh 3 I - 2PPh3 II CO L SET 9-R2-9-BBN R1 I +RII 1PdX R1COPdX base L III L IV L R1COPdR2 R1COR2 + Pd(0)L 2 L = CO, PPh3 L V SchemeScheme 1. 1.The The synthesis synthesis of of ketones ketones from from iodoalkanes, iodoalkanes, 9-alkyl-9-BBN 9-alkyl-9-BBN derivatives derivatives and and CO viaCO avia a light- light-acceleratedaccelerated Pd-catalyzed Pd-catalyzed reaction. reaction. The reaction is supposed to proceed through a free radical mechanism at the oxidative The reaction is supposed to proceed through a free radical mechanism at the oxida- addition step [25]. Firstly, Pd(PPh3)4 likely converts to the low reactive Pd(CO)(PPh3)3 complextive additionI under step CO [25]. atmosphere. Firstly, InPd(PPh the presence3)4 likely of lightconverts irradiation, to the complexlow reactiveI undergoes Pd(CO)(PPh3)3 Catalysts 2021, 11, x FOR PEER REVIEW 3 of 34 Catalysts 2021, 11, 918 3 of 35 complex I under CO atmosphere. In the presence of light irradiation, complex I undergoes dissociation of ligands to give the unsaturated palladium species II. The latter enables an electron transfer to the alkyl iodide with the formation of a radical pair (Pd(I)X + R˙) that dissociation of ligands to give the unsaturated palladium species II. The latter enables could provide the oxidative intermediate RPdX (III). The migration of the alkyl group to an electron transfer to the alkyl iodide with the formation of a radical pair (Pd(I)X + R˙) thata coordinated could provide CO the molecule oxidative intermediateaffords complex RPdX (RCOPdXIII). The migration IV. Then, of thethe alkyl base group facilitates the totransfer a coordinated of the R CO2 group molecule from affords 9-R2-9-BBN complex to RCOPdXpalladiumIV .providing Then, the V base, which facilitates yields the ke- thetone transfer and a of palladium(0) the R2 group species from 9-R through2-9-BBN a toreductive palladium elimination providing Vstep, which