Title: A hemilabile manganese( i )–phenol complex and its coordination induced O–H bond weakening
The known compound K[( PO ) 2 Mn(CO) 2 ] ( PO = 2-((diphenylphosphino)methyl)-4,6-dimethylphenolate) (K[ 1 ]) was protonated to form the new Mn( i ) complex ( HPO )( PO )Mn(CO) 2 ( H 1 ) and was determined to have a p K a approximately equal to tetramethylguanidine (TMG). The reduction potential of K[ 1 ] was determined to be −0.58 V vs. Fc/Fc + in MeCN and allowed for an estimation of an experimental O–H bond dissociation free energy (BDFE O–H ) of 73 kcal mol −1 according to the Bordwell equation. This value is in good agreement with a corrected DFT computed BDFE O–H of 68.0 kcal mol −1 (70.3 kcal mol −1 for intramolecular H-bonded isomer). The coordination of the protonated O-atom in the solid-state H 1 was confirmed using FTIR spectroscopy and X-ray crystallography. The phenol moiety is hemilabile as evident from computation and experimental results. For instance, dissociation of the protonated O-atom in H 1 is endergonic by only a few kcal mol −1 (DFT). Furthermore, [ 1 ] − and other Mn( i ) compounds coordinated to PO and/or HPO do not react with MeCN, but H 1 reacts with MeCN to form H 1 + MeCN . Experimental evidence for the solution-bound O-atoms of H 1 was obtained from 1 H NMR and UV-vis spectroscopy and by comparing the electronic spectra of bona fide 16-e − Mn( i ) complexes such as [{ PNP }Mn(CO) 2 ] ( PNP = − N{CH 2 CH 2 (P i Pr 2 )} 2 ) and [( Me3SiOP )( PO )Mn(CO) 2 ] ( Me3Si 1 ). Compound H 1 is only meta-stable ( t 1/2 0.5–1 day) and decomposes into products consistent with homolytic O–H bond cleavage. For instance, treatment of H 1 with TEMPO resulted in formation of TEMPOH, free ligand, and [Mn II {( PO ) 2 Mn(CO) 2 } 2 ]. Together with the experimental and calculated weakened BDFE O–H , these data provide strong evidence for the coordination and hemilability of the protonated O-atom in H 1 and represents the first example of the phenolic Mn( i )–O linkage and a rare example of a “soft-homolysis” intermediate in the bond-weakening catalysis paradigm. more »« less
Wong, Anthony; Chakraborty, Arunavo; Bawari, Deependra; Wu, Guang; Dobrovetsky, Roman; Ménard, Gabriel
(, Chemical Communications)
null
(Ed.)
We report the facile activation of aryl E–H (ArEH; E = N, O, S; Ar = Ph or C 6 F 5 ) or ammonia N–H bonds via coordination-induced bond weakening to a redox-active boron center in the complex, (1 − ). Substantial decreases in E–H bond dissociation free energies (BDFEs) are observed upon substrate coordination, enabling subsequent facile proton-coupled electron transfer (PCET). A drop of >50 kcal mol −1 in H 2 N–H BDFE upon coordination was experimentally determined.
Connor, Gannon P.; Delony, Daniel; Weber, Jeremy E.; Mercado, Brandon Q.; Curley, Julia B.; Schneider, Sven; Mayer, James M.; Holland, Patrick L.
(, Chemical Science)
Rhenium complexes with aliphatic PNP pincer ligands have been shown to be capable of reductive N 2 splitting to nitride complexes. However, the conversion of the resulting nitride to ammonia has not been observed. Here, the thermodynamics and mechanism of the hypothetical N–H bond forming steps are evaluated through the reverse reaction, conversion of ammonia to the nitride complex. Depending on the conditions, treatment of a rhenium( iii ) precursor with ammonia gives either a bis(amine) complex [(PNP)Re(NH 2 ) 2 Cl] + , or results in dehydrohalogenation to the rhenium( iii ) amido complex, (PNP)Re(NH 2 )Cl. The N–H hydrogen atoms in this amido complex can be abstracted by PCET reagents which implies that they are quite weak. Calorimetric measurements show that the average bond dissociation enthalpy of the two amido N–H bonds is 57 kcal mol −1 , while DFT computations indicate a substantially weaker N–H bond of the putative rhenium( iv )-imide intermediate (BDE = 38 kcal mol −1 ). Our analysis demonstrates that addition of the first H atom to the nitride complex is a thermochemical bottleneck for NH 3 generation.
Moore, Shawn M.; Sun, Chen; Steele, Jennifer L.; Laaker, Ellen M.; Rheingold, Arnold L.; Doerrer, Linda H.
(, Chemical Science)
There is considerable interest in MnOH x moieties, particularly in the stepwise changes in those O–H bonds in tandem with Mn oxidation state changes. The reactivity of aquo-derived ligands, {MOH x }, is also heavily influenced by the electronic character of the other ligands. Despite the prevalence of oxygen coordination in biological systems, preparation of mononuclear Mn complexes of this type with all O-donors is rare. Herein, we report several Mn complexes with perfluoropinacolate (pin F ) 2− including the first example of a crystallographically characterized mononuclear {Mn( iii )OH} with all O-donors, K 2 [Mn(OH)(pin F ) 2 ], 3. Complex 3 is prepared via deprotonation of K[Mn(OH 2 )(pin F ) 2 ], 1, the p K a of which is estimated to be 18.3 ± 0.3. Cyclic voltammetry reveals quasi-reversible redox behavior for both 1 and 3 with an unusually large Δ E p , assigned to the Mn( iii / ii ) couple. Using the Bordwell method, the bond dissociation free energy (BDFE) of the O–H bond in {Mn( ii )–OH 2 } is estimated to be 67–70 kcal mol −1 . Complex 3 abstracts H-atoms from 1,2-diphenylhydrazine, 2,4,6-TTBP, and TEMPOH, the latter of which supports a PCET mechanism. Under basic conditions in air, the synthesis of 1 results in K 2 [Mn(OAc)(pin F ) 2 ], 2, proposed to result from the oxidation of Et 2 O to EtOAc by a reactive Mn species, followed by ester hydrolysis. Complex 3 alone does not react with Et 2 O, but addition of O 2 at low temperature effects the formation of a new chromophore proposed to be a Mn( iv ) species. The related complexes K(18C6)[Mn( iii )(pin F ) 2 ], 4, and (Me 4 N) 2 [Mn( ii )(pin F ) 2 ], 5, have also been prepared and their properties discussed in relation to complexes 1–3.
Abdullayev, Yusif; Abbasov, Vagif; Nasirov, Fuzuli; Rzayeva, Nigar; Nasibova, Leyla; Autschbach, Jochen
(, International Journal of Quantum Chemistry)
Abstract The industrial importance of the CC double bond difunctionalization in vegetable oils/fatty acid chains motivates computational studies aimed at helping to improve experimental protocols. The CC double bond epoxidation is studied with hydrogen peroxide, peracetic acid (CH3CO3H), and performic acid (HCO3H) oxidizing agents. The epoxide ring‐opening mechanism is calculated in the presence of ZnCl2, NiCl2, and FeCl2Lewis acidic catalysts. Computations show that H2O2(∆G‡= 39 kcal/mol,TS1HP) is not an effective oxidizing agent compared to CH3CO3H (∆G‡= 29.8 kcal/mol,TS1PA) and HCO3H (∆G‡= 26.7 kcal/mol,TS1PF). The FeCl2(∆G‡= 14.7 kcal/mol,TS1FC) coordination to the epoxide oxygen facilitates the ring‐opening via lower energy barriers compared to the ZnCl2(∆G‡= 19.5 kcal/mol,TS1ZC) and NiCl2(∆G‡= 29.4 kcal/mol,TS1NC) coordination. ZnCl2was frequently utilized as a catalyst in laboratory‐scale procedures. The energetic span model identifies the FeCl2(FC) catalytic cycle as the best option for the epoxide ring‐opening.
Niu, Zhihao; Wu, Qiaozhuo; Li, Qingzhong; Scheiner, Steve
(, International Journal of Molecular Sciences)
The tetrel bond (TB) between 1,2-benzisothiazol-3-one-2-TF3-1,1-dioxide (T = C, Si) and the O atom of pyridine-1-oxide (PO) and its derivatives (PO-X, X = H, NO2, CN, F, CH3, OH, OCH3, NH2, and Li) is examined by quantum chemical means. The Si∙∙∙O TB is quite strong, with interaction energies approaching a maximum of nearly 70 kcal/mol, while the C∙∙∙O TB is an order of magnitude weaker, with interaction energies between 2.0 and 2.6 kcal/mol. An electron-withdrawing substituent on the Lewis base weakens this TB, while an electron-donating group has the opposite effect. The SiF3 group transfers roughly halfway between the N of the acid and the O of the base without the aid of cooperative effects from a third entity.
Kadassery, Karthika J., Crawley, Matthew R., MacMillan, Samantha N., and Lacy, David C. A hemilabile manganese( i )–phenol complex and its coordination induced O–H bond weakening. Retrieved from https://par.nsf.gov/biblio/10147649. Dalton Transactions . Web. doi:10.1039/d0dt00973c.
Kadassery, Karthika J., Crawley, Matthew R., MacMillan, Samantha N., & Lacy, David C. A hemilabile manganese( i )–phenol complex and its coordination induced O–H bond weakening. Dalton Transactions, (). Retrieved from https://par.nsf.gov/biblio/10147649. https://doi.org/10.1039/d0dt00973c
Kadassery, Karthika J., Crawley, Matthew R., MacMillan, Samantha N., and Lacy, David C.
"A hemilabile manganese( i )–phenol complex and its coordination induced O–H bond weakening". Dalton Transactions (). Country unknown/Code not available. https://doi.org/10.1039/d0dt00973c.https://par.nsf.gov/biblio/10147649.
@article{osti_10147649,
place = {Country unknown/Code not available},
title = {A hemilabile manganese( i )–phenol complex and its coordination induced O–H bond weakening},
url = {https://par.nsf.gov/biblio/10147649},
DOI = {10.1039/d0dt00973c},
abstractNote = {The known compound K[( PO ) 2 Mn(CO) 2 ] ( PO = 2-((diphenylphosphino)methyl)-4,6-dimethylphenolate) (K[ 1 ]) was protonated to form the new Mn( i ) complex ( HPO )( PO )Mn(CO) 2 ( H 1 ) and was determined to have a p K a approximately equal to tetramethylguanidine (TMG). The reduction potential of K[ 1 ] was determined to be −0.58 V vs. Fc/Fc + in MeCN and allowed for an estimation of an experimental O–H bond dissociation free energy (BDFE O–H ) of 73 kcal mol −1 according to the Bordwell equation. This value is in good agreement with a corrected DFT computed BDFE O–H of 68.0 kcal mol −1 (70.3 kcal mol −1 for intramolecular H-bonded isomer). The coordination of the protonated O-atom in the solid-state H 1 was confirmed using FTIR spectroscopy and X-ray crystallography. The phenol moiety is hemilabile as evident from computation and experimental results. For instance, dissociation of the protonated O-atom in H 1 is endergonic by only a few kcal mol −1 (DFT). Furthermore, [ 1 ] − and other Mn( i ) compounds coordinated to PO and/or HPO do not react with MeCN, but H 1 reacts with MeCN to form H 1 + MeCN . Experimental evidence for the solution-bound O-atoms of H 1 was obtained from 1 H NMR and UV-vis spectroscopy and by comparing the electronic spectra of bona fide 16-e − Mn( i ) complexes such as [{ PNP }Mn(CO) 2 ] ( PNP = − N{CH 2 CH 2 (P i Pr 2 )} 2 ) and [( Me3SiOP )( PO )Mn(CO) 2 ] ( Me3Si 1 ). Compound H 1 is only meta-stable ( t 1/2 0.5–1 day) and decomposes into products consistent with homolytic O–H bond cleavage. For instance, treatment of H 1 with TEMPO resulted in formation of TEMPOH, free ligand, and [Mn II {( PO ) 2 Mn(CO) 2 } 2 ]. Together with the experimental and calculated weakened BDFE O–H , these data provide strong evidence for the coordination and hemilability of the protonated O-atom in H 1 and represents the first example of the phenolic Mn( i )–O linkage and a rare example of a “soft-homolysis” intermediate in the bond-weakening catalysis paradigm.},
journal = {Dalton Transactions},
author = {Kadassery, Karthika J. and Crawley, Matthew R. and MacMillan, Samantha N. and Lacy, David C.},
}
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