Hydrosilylation of Aldehydes by a Manganese
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inorganics Article ArticleHydrosilylation of Aldehydes by a Manganese α- HydrosilylationDiimine Complex of Aldehydes by a Manganese α-Diimine Complex Veeranna Yempally 1, Azal Shahbaz 1, Wai Yip Fan 2, Sherzod T. Madrahimov 1,* and Ashfaq A. VeerannaBengali 1,* Yempally 1, Azal Shahbaz 1, Wai Yip Fan 2, Sherzod T. Madrahimov 1,* and Ashfaq A. Bengali 1,* 1 Science Department, Texas A&M University at Qatar, PO Box 23874 Doha, Qatar; [email protected] 1 (V.Y.);Science [email protected] Department, Texas A&M (A.S.) University at Qatar, PO Box 23874 Doha, Qatar; 2 [email protected] of Chemistry, (V.Y.); 3 Science [email protected] Drive, National University (A.S.) of Singapore, Singapore 117543, Singapore; 2 [email protected] of Chemistry, 3 Science Drive, National University of Singapore, Singapore 117543, Singapore; * Correspondence:[email protected] sherzod.madrahimov.qatar.tamu.edu (S.T.M.); [email protected] (A.A.B.) * Correspondence: [email protected] (S.T.M.); [email protected] (A.A.B.) Received: 21 October 2020; Accepted: 06 November 2020; Published: 10 November 2020 Received: 21 October 2020; Accepted: 6 November 2020; Published: 10 November 2020 Abstract: This paper describes the catalytic activity of air stable and easy to handle manganese Abstract:complexesThis towards paper describes the hydrosilylation the catalytic activity of aldehydes of air stable. andThese easy catalysts to handle incorporate manganese complexesa bulky towardsdiazabutadiene the hydrosilylation ligand and ofexhibit aldehydes. good Thesefunctional catalysts group incorporate tolerance a and bulky chemoselectivity diazabutadiene ligandin the andhydrosilylation exhibit good of functional aldehydes group, utilizing tolerance primary and silanes chemoselectivity as the reducing in the agent. hydrosilylation The reactions of aldehydes, proceed utilizingwith turnover primary frequenci silaneses asapproaching the reducing 150 agent. h−1 in some The reactions instances, proceed similar withto those turnover observed frequencies for other 1 approachingmanganese-based 150 h −catalysts.in some instances,The conversion similar of to aromatic those observed aldehydes for other to the manganese-based corresponding catalysts.alcohols Thewas conversionfound to be of more aromatic efficient aldehydes than that to for the the corresponding analogous aliphatic alcohols systems. was found to be more efficient than that for the analogous aliphatic systems. Keywords: catalysis; manganese; hydrosilylation Keywords: catalysis; manganese; hydrosilylation 1. Introduction 1. Introduction Hydrosilylation, the largest volume industrial reaction using homogenous catalysts, is an importantHydrosilylation, step in the the generation largest volume of valuable industrial building reaction blocks using for homogenous the synthesis catalysts, of organic is an importantchemicals stepand functional in the generation materials of valuable(Scheme building1) [1,2,3,4] blocks. The formation for the synthesis of silyl of ether organic protected chemicals alcohols and functionalin a single materialsstep with (Schemea high atom1)[ 1economy–4]. The using formation easy ofto silylhandle ether liquid protected hydrosilanes, alcohols makes in a singlethis reaction step with an aattractive high atom alternative economy to using hydrogenation easy to handle [5,6,7] liquid. The past hydrosilanes, decade has makes seen a this drama reactiontic rise an in attractive the base alternativemetal-catalyzed to hydrogenation hydrosilylation [5–7 ].of Thealkenes past and decade carbonyl has seen compounds a dramatic, with rise in efficiencies the base metal-catalyzed rivaling those hydrosilylationobserved for precious of alkenes metal and catalysts carbonyl [8,9,10,11,12] compounds,. Recently, with e ffimanganeseciencies rivaling-based catalysts those observed have been for preciousemployed metal in the catalysts hydrosilylation [8–12]. of Recently, carbonyl manganese-basedcompounds [13,14,15] catalysts. Manganese, have been the fourth employed most in earth the hydrosilylationabundant element of carbonyl by mass, compounds is inexpensive [13–15]. Manganese,and bio-compatible, the fourth mostthus earthmaking abundant the resulting element byorganometallic mass, is inexpensive complexes and attractive bio-compatible, catalysts for thus organic making transformations the resulting, organometallic including hydrosilylation complexes attractivereactions. catalysts for organic transformations, including hydrosilylation reactions. Scheme 1. Metal catalyzed hydrosilylation of organic carbonyls.carbonyls. Several manganese complexes incorporating nitrogen nitrogen-based-based chelating and other ligands have been developeddeveloped as as catalysts catalysts for for the the conversion conversion of aldehydes of aldehydes and ketones and ketones into alcohols into alcohols [14]. For [14] example,. For Luganexample, et al.Lugan demonstrated et al. demonstrated that manganese that complexesmanganese bearing complexes NHC bearing ligands NHC are effi ligandscient photocatalysts are efficient forphotocatalysts the reduction for of the ketones reduction with diphenylsilanesof ketones with under diphenylsilanes UV irradiation under at room UV irradiation temperature at [ 16room,17]. Similarly, Cutler and coworkers utilized manganese carbonyl complexes containing acyl ligands for Inorganics 2020, 8, x; doi: www.mdpi.com/journal/inorganics Inorganics 2020, 8, 61; doi:10.3390/inorganics8110061 www.mdpi.com/journal/inorganics Inorganics 2020, 8, x 2 of 11 Inorganics 2020, 8, x 2 of 11 photocatalysts for the reduction of ketones with diphenylsilanes under UV irradiation at room photocatalysts for the reduction of ketones with diphenylsilanes under UV irradiation at room Inorganicstemperature2020, 8,[16,17]. 61 Similarly, Cutler and coworkers utilized manganese carbonyl complexes2 of 11 temperature [16,17]. Similarly, Cutler and coworkers utilized manganese carbonyl complexes containing acyl ligands for the efficient reduction of carbonyl compounds [18], while Chung et al. containing acyl ligands for the efficient reduction of carbonyl compounds [18], while Chung et al. reported the generation of a pre-catalyst from a manganese tricarbonyl complex with an indenyl thereported efficient the reduction generation of of carbonyl a pre-catalyst compounds from [18a manganese], while Chung tricarbonyl et al. reported complex the with generation an indenyl of a ligand for the hydrosilylation of ketones [19,20]. Currently, the highest reported turnover number (up pre-catalyst from a manganese tricarbonyl complex with an indenyl ligand for the hydrosilylation ligand for the−1 hydrosilylation of ketones [19,20].Currently, the highest reported turnover number (up to 76,800 h ) for a first-row metal-based hydrosilylation catalyst is for a bis(imino)pyridine1 ligated ofto 76,800 ketones h−1 [)19 for,20 a]. first-row Currently, metal-based the highest hydrosilylation reported turnover catalyst numberis for a bis(imino)pyridine (up to 76,800 h− )ligated for a manganese carbonyl complex [21]. first-rowmanganese metal-based carbonyl complex hydrosilylation [21]. catalyst is for a bis(imino)pyridine ligated manganese carbonyl Manganese-based carbonyl complexes with diazabutadiene (DAB) ligands are effective catalysts complexManganese-based [21]. carbonyl complexes with diazabutadiene (DAB) ligands are effective catalysts for the electrochemical reduction of CO2, and have been extensively studied for their promise as for theManganese-based electrochemical carbonyl reduction complexes of CO2, and with have diazabutadiene been extensively (DAB) studied ligands arefor etheirffective promise catalysts as visible light-assisted CO release agents (photo-CORM) [22–26]. However, these complexes have not forvisible the electrochemicallight-assisted CO reduction release ofagents CO2 ,(photo-COR and have beenM) extensively[22–26]. However, studied forthese their complexes promise ashave visible not yet been investigated as hydrosilylation catalysts for the reduction of aldehydes and ketones. Our light-assistedyet been investigated CO release as agentshydrosilylation (photo-CORM) catalyst [22s –for26 ].the However, reduction these of aldehydes complexes and have ketones. not yet beenOur interest in the application of these complexes towards the hydrosilylation of carbonyl compounds investigatedinterest in the as application hydrosilylation of these catalysts complexes for the reductiontowards the of aldehydes hydrosilylation and ketones. of carbonyl Our interest compounds in the stemmed from a recent report by Royo et al. that highlighted the use of the cationic [Mn(CO)3(bis- application of these complexes towards the hydrosilylation of carbonyl compounds stemmed from3 a stemmedMe from a recent report by Royo et al. that highlighted the use of the cationic [Mn(CO) (bis- NHC )(NCMe)]BF4 complex for this reaction [27]. The authors demonstrated that theMe NHC ligand recentNHCMe report)(NCMe)]BF by Royo4 complex et al. that for highlighted this reaction the use[27]. of The the authors cationic demonstrated [Mn(CO)3(bis-NHC that the )(NCMe)]BFNHC ligand4 enhanced catalytic performance, for the reduction of ketones and aldehydes by phenylsilane. An complexenhanced for catalytic this reaction performance, [27]. The for authors the reduction demonstrated of ketones that and the NHCaldehydes ligand by enhanced phenylsilane. catalytic An important role for the acetonitrile ligand was also proposed,