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1. 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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2. 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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3. An aryl diimine cobalt( i ) catalyst for carbonyl hydrosilylation

   https://doi.org/10.1039/d2cc04089a  

   Sharma, Anuja; So, Sangho; Kim, Jun-Hyeong; MacMillan, Samantha N.; Baik, Mu-Hyun; Trovitch, Ryan J. (September 2022, Chemical Communications)

   Through the application of a redox-innocent aryl diimine chelate, the discovery and utilization of a cobalt catalyst, ( Ph 2 PPr ADI)Co, that exhibits carbonyl hydrosilylation turnover frequencies of up to 330 s −1 is described. This activity is believed to be the highest ever reported for metal-catalyzed carbonyl hydrosilylation. 

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4. 14-Electron Rh and Ir silylphosphine complexes and their catalytic activity in alkene functionalization with hydrosilanes

   https://doi.org/10.1039/D1DT00677K  

   Abeynayake, Niroshani S.; Zamora-Moreno, Julio; Gorla, Saidulu; Donnadieu, Bruno; Muñoz-Hernández, Miguel A.; Montiel-Palma, Virginia (August 2021, Dalton Transactions)

   Herein we report an experimental and computational study of a family of four coordinated 14-electron complexes of Rh( iii ) devoid of agostic interactions. The complexes [X–Rh(κ 3 ( P,Si,Si )PhP( o -C 6 H 4 CH 2 Si i Pr 2 ) 2 ], where X = Cl (Rh-1), Br (Rh-2), I (Rh-3), OTf (Rh-4), Cl·GaCl 3 (Rh-5); derive from a bis(silyl)- o -tolylphosphine with isopropyl substituents on the Si atoms. All five complexes display a sawhorse geometry around Rh and exhibit similar spectroscopic and structural properties. The catalytic activity of these complexes and [Cl–Ir(κ 3 ( P,Si,Si )PhP( o -C 6 H 4 CH 2 Si i Pr 2 ) 2 ], Ir-1, in styrene and aliphatic alkene functionalizations with hydrosilanes is disclosed. We show that Rh-1 catalyzes effectively the dehydrogenative silylation of styrene with Et 3 SiH in toluene while it leads to hydrosilylation products in acetonitrile. Rh-1 is an excellent catalyst in the sequential isomerization/hydrosilylation of terminal and remote aliphatic alkenes with Et 3 SiH including hexene isomers, leading efficiently and selectively to the terminal anti-Markonikov hydrosilylation product in all cases. With aliphatic alkenes, no hydrogenation products are observed. Conversely, catalysis of the same hexene isomers by Ir-1 renders allyl silanes, the tandem isomerization/dehydrogenative silylation products. A mechanistic proposal is made to explain the catalysis with these M( iii ) complexes. 

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5. 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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