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1. Tetragonal phosphorus( v ) cations as tunable and robust catalytic Lewis acids

   https://doi.org/10.1039/C9SC02463H  

   Gilhula, James C. ; Radosevich, Alexander T. ( July 2019 , Chemical Science)

   The synthesis and catalytic reactivity of a class of water-tolerant cationic phosphorus-based Lewis acids is reported. Corrole-based phosphorus( v ) cations of the type [ArP(cor)][B(C 6 F 5 ) 4 ] (Ar = C 6 H 5 , 3,5-(CF 3 ) 2 C 6 H 3 ; cor = 5,10,15-(C 6 H 5 ) 3 corrolato 3− , 5,10,15-(C 6 F 5 ) 3 corrolato 3− ) were synthesized and characterized by NMR and X-ray diffraction. The visible electronic absorption spectra of these cationic phosphacorroles depend strongly on the coordination environment at phosphorus, and their Lewis acidities are quantified by spectrophotometric titrations. DFT analyses establish that the character of the P-acceptor orbital comprises P–N antibonding interactions in the basal plane of the phosphacorrole. Consequently, the cationic phosphacorroles display unprecedented stability to water and alcohols while remaining highly active and robust Lewis acid catalysts for carbonyl hydrosilylation, C sp3 –H bond functionalization, and carbohydrate deoxygenation reactions. 

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2. Re–Silane complexes as frustrated lewis pairs for catalytic hydrosilylation

   https://doi.org/10.1039/d0dt02084b  

   Brown, Caleb A. ; Abrahamse, Michael ; Ison, Elon A. ( August 2020 , Dalton Transactions)

   null (Ed.)

   A pathway for the catalytic hydrosilylation of carbonyl substrates with M(C 6 F 5 ) 3 (M = B, Al and Ga) was calculated by DFT (B3PW91-D3) and it was shown that in the case of the Al reagent, the carbonyl substrate binds irreversibly and inhibits catalysis by generating a stable carbonyl adduct. In contrast, the reduced electrophilicity of B(C 6 F 5 ) 3 disfavors the binding of the carbonyl substrate and increases the concentration of an activated silane adduct which is the species responsible for catalytic turnover. A similar mechanism was found for both cationic and neutral Re( iii ) species. Further, it was shown by tuning the electrophilicity of the rhenium catalysts, conditions can be found that would enable the catalytic hydrosilylation of ketone and nitrile substrates that were unreactive in previously reported systems. Thus the mechanisms proposed in this work, lay the foundation for the design of new catalytic systems. 

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3. Manganese Salan Complexes as Catalysts for Hydrosilylation of Aldehydes and Ketones

   https://doi.org/10.3390/catal13040665  

   Almutairi, Nora ; Vijjamarri, Srikanth ; Du, Guodong ( April 2023 , Catalysts)

   Manganese has attracted significant recent attention due to its abundance, low toxicity, and versatility in catalysis. In the present study, a series of manganese (III) complexes supported by salan ligands have been synthesized and characterized, and their activity as catalysts in the hydrosilylation of carbonyl compounds was examined. While manganese (III) chloride complexes exhibited minimal catalytic efficacy without activation of silver perchlorate, manganese (III) azide complexes showed good activity in the hydrosilylation of carbonyl compounds. Under optimized reaction conditions, several types of aldehydes and ketones could be reduced with good yields and tolerance to a variety of functional groups. The possible mechanisms of silane activation and hydrosilylation were discussed in light of relevant experimental observations. 

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4. Carbonyl and ester C–O bond hydrosilylation using κ 4 -diimine nickel catalysts

   https://doi.org/10.1039/C8DT01857J  

   Rock, Christopher L. ; Groy, Thomas L. ; Trovitch, Ryan J. ( January 2018 , Dalton Transactions)

   The synthesis of alkylphosphine-substituted α-diimine (DI) ligands and their subsequent addition to Ni(COD) 2 allowed for the preparation of ( iPr2PPr DI)Ni and ( tBu2PPr DI)Ni . The solid state structures of both compounds were found to feature a distorted tetrahedral geometry that is largely consistent with the reported structure of the diphenylphosphine-substituted variant, ( Ph2PPr DI)Ni . To explore and optimize the synthetic utility of this catalyst class, all three compounds were screened for benzaldehyde hydrosilylation activity at 1.0 mol% loading over 3 h at 25 °C. Notably, ( Ph2PPr DI)Ni was found to be the most efficient catalyst while phenyl silane was the most effective reductant. A broad scope of aldehydes and ketones were then hydrosilylated, and the silyl ether products were hydrolyzed to afford alcohols in good yield. When attempts were made to explore ester reduction, inefficient dihydrosilylation was noted for ethyl acetate and no reaction was observed for several additional substrates. However, when an equimolar solution of allyl acetate and phenyl silane was added to 1.0 mol% ( Ph2PPr DI)Ni , complete ester C–O bond hydrosilylation was observed within 30 min at 25 °C to generate propylene and PhSi(OAc) 3 . The scope of this reaction was expanded to include six additional allyl esters, and under neat conditions, turnover frequencies of up to 990 h −1 were achieved. This activity is believed to be the highest reported for transition metal-catalyzed ester C–O bond hydrosilylation. Proposed mechanisms for ( Ph2PPr DI)Ni -mediated carbonyl and allyl ester C–O bond hydrosilylation are also discussed. 

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5. Phosphorous-substituted redox-active ligands in base metal hydrosilylation catalysis

   https://doi.org/10.1039/D1DT02879K  

   Sharma, Anuja ; Trovitch, Ryan J. ( November 2021 , Dalton Transactions)

   This article highlights the utilization of phosphine-containing redox-active ligands for efficient hydrosilylation catalysis. Manganese, iron, cobalt, and nickel precatalysts featuring these chelates have been described and leading activities for carbonyl, carboxylate, and ester C–O bond hydrosilylation have been achieved. Mechanistic studies have provided insight into the importance of phosphine hemilability. 

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