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1. Diruthenium aryl compounds – tuning of electrochemical responses and solubility

   https://doi.org/10.1039/D1DT03957A  

   Miller-Clark, Lyndsy A. ; Christ, Peter E. ; Ren, Tong ( January 2022 , Dalton Transactions)

   Reported herein are the two new series of diruthenium aryl compounds: Ru 2 (DiMeOap) 4 (Ar) (1a–6a) (DiMeOap = 2-(3,5-dimethoxyanilino)pyridinate) and Ru 2 ( m - i PrOap) 4 (Ar) (1b–5b) ( m - i PrOap = 2-(3-iso-propoxyanilino)pyridinate), prepared through the lithium-halogen exchange reaction with a variety of aryl halides (Ar = C 6 H 4 -4-NMe 2 (1), C 6 H 4 -4- t Bu (2), C 6 H 4 -4-OMe (3), C 6 H 3 -3,5-(OMe) 2 (4), C 6 H 4 -4-CF 3 (5), C 6 H 5 (6)). The molecular structures of these compounds were established with X-ray diffraction studies. Additionally, these compounds were characterized using electronic absorption and voltammetric techniques. Compounds 1a–6a and 1b–5b are all in the Ru 2 5+ oxidation state, with a ground state configuration of σ 2 π 4 δ 2 (π*δ*) 3 ( S = 3/2). Use of the modified ap ligands (ap′) resulted in moderate increases of product yield when compared to the unsubstituted Ru 2 (ap) 4 (Ar) (ap = 2-anilinopyridinate) series. Comparisons of the electrochemical properties of 1a–6a and 1b–5b against the Ru 2 (ap′)Cl starting material reveals the addition of the aryl ligand cathodically shifted themore »Ru 2 6+/5+ oxidation and Ru 2 5+/4+ reduction potentials. These oxidation and reductions potentials are also strongly dependent on the p -substituent of the axial aryl ligands.« less
2. Steric and electronic control of an ultrafast isomerization

   https://doi.org/10.1039/c9sc02359c  

   Porter, Tyler M. ; Ostericher, Andrew L. ; Kubiak, Clifford P. ( August 2019 , Chemical Science)

   Synthetic control of the influence of steric and electronic factors on the ultrafast (picosecond) isomerization of penta-coordinate ruthenium dithietene complexes (Ru((CF 3 ) 2 C 2 S 2 )(CO)(L) 2 , where L = a monodentate phosphine ligand) is reported. Seven new ruthenium dithietene complexes were prepared and characterized by single crystal X-ray diffraction. The complexes are all square pyramidal and differ only in the axial vs. equatorial coordination of the carbonyl ligand. Fourier Transform Infrared (FTIR) spectroscopy was used to study the ν (CO) bandshapes of the complexes in solution, and these reveal rapid exchange between two or three isomers of each complex. Isomerization is proposed to follow a Berry psuedorotation-like mechanism where a metastable, trigonal bipyramidal (TBP) intermediate is observed spectroscopically. Electronic tuning of the phosphine ligands L = PPh 3 , P(( p -Me)Ph) 3 , (( p -Cl)Ph) 3 , at constant cone angle is found to have little effect on the kinetics or thermodynamic stabilities of the axial, equatorial and TBP isomers of the differently substituted complexes. Steric tuning of the phosphine ligands over a range of phosphine cone angles (135 < θ < 165°) has a profound impact on the isomerization process, and inmore »the limit of greatest steric bulk, the axial isomer is not observable. Temperature dependence of the FTIR spectra was used to obtain the relative thermodynamic stabilities of the different isomers of each of the seven ruthenium dithietene complexes. This study details how ligand steric effects can be used to direct the solution state dynamics on the picosecond time scale of discrete isomers energetically separated by <2.2 kcal mol −1 . This work provides the most detailed description to date of ultrafast isomerization in the ground states of transition metal complexes.« less
3. Synthesis, Structure, and Bonding of d ³ Molybdenum–Oxo Complexes

   https://doi.org/10.1002/ange.202001379  

   Vibbert, Hunter B. ; Filatov, Alexander S. ; Hopkins, Michael D. ( April 2020 , Angewandte Chemie)

   Reduction of d²metal–oxo ions of the form [MO(PP)₂Cl]⁺(M=Mo, W; PP=chelating diphosphine) produces d³MO(PP)₂Cl complexes, which include the first isolated examples in group 6. The stability and reactivity of the MO(PP)₂Cl compounds are found to depend upon the steric bulk of the phosphine ligands: derivatives with bulky phosphines that shield the oxo ligand are stable enough to be isolated, whereas those with phosphines that leave the oxo ligand exposed are more reactive and observed transiently. Magnetic measurements and DFT calculations on MoO(dppe)₂Cl indicate the d³compounds are low spin with a²[(d_xy)²(π*(MoO))¹] configuration. X‐ray crystallographic and vibrational‐spectroscopic studies on d²and d³[MoO(dppe)₂Cl]^0/+establish that the d³compound possesses a reduced M−O bond order and significantly longer Mo−O bond, accounting for its greater reactivity. These results indicate that the oxo‐centered reactivity of d³complexes may be controlled through ligand variation.
4. Synthesis, Structure, and Bonding of d ³ Molybdenum–Oxo Complexes

   https://doi.org/10.1002/anie.202001379  

   Vibbert, Hunter B. ; Filatov, Alexander S. ; Hopkins, Michael D. ( April 2020 , Angewandte Chemie International Edition)

   Reduction of d²metal–oxo ions of the form [MO(PP)₂Cl]⁺(M=Mo, W; PP=chelating diphosphine) produces d³MO(PP)₂Cl complexes, which include the first isolated examples in group 6. The stability and reactivity of the MO(PP)₂Cl compounds are found to depend upon the steric bulk of the phosphine ligands: derivatives with bulky phosphines that shield the oxo ligand are stable enough to be isolated, whereas those with phosphines that leave the oxo ligand exposed are more reactive and observed transiently. Magnetic measurements and DFT calculations on MoO(dppe)₂Cl indicate the d³compounds are low spin with a²[(d_xy)²(π*(MoO))¹] configuration. X‐ray crystallographic and vibrational‐spectroscopic studies on d²and d³[MoO(dppe)₂Cl]^0/+establish that the d³compound possesses a reduced M−O bond order and significantly longer Mo−O bond, accounting for its greater reactivity. These results indicate that the oxo‐centered reactivity of d³complexes may be controlled through ligand variation.
5. Highly covalent metal–ligand π bonding in chelated bis- and tris(iminoxolene) complexes of osmium and ruthenium

   https://doi.org/10.1039/d0dt01287d  

   Gianino, Jacqueline ; Brown, Seth N. ( June 2020 , Dalton Transactions)

   The bis(aminophenol) 2,2′-biphenylbis(3,5-di- tert -butyl-2-hydroxyphenylamine) (ClipH 4 ) forms trans -(Clip)Os(py) 2 upon aerobic reaction of the ligand with {( p -cymene)OsCl 2 } 2 in the presence of pyridine and triethylamine. A more oxidized species, cis -β-(Clip)Os(OCH 2 CH 2 O), is formed from reaction of the ligand with the osmium( vi ) complex OsO(OCH 2 CH 2 O) 2 , and reacts with Me 3 SiCl to give the chloro complex cis -β-(Clip)OsCl 2 . Octahedral osmium and ruthenium tris-iminoxolene complexes are formed from the chelating ligand tris(2-(3′,5′-di- tert -butyl-2′-hydroxyphenyl)amino-4-methylphenyl)amine (MeClampH 6 ) on aerobic reaction with divalent metal precursors. The complexes’ structural and electronic features are well described using a simple bonding model that emphasizes the covalency of the π bonding between the metal and iminoxolene ligands rather than attempting to dissect the parts into discrete oxidation states. Emphasizing the continuity of bonding between disparate complexes, the structural data from a variety of Os and Ru complexes show good correlations to π bond order, and the response of the intraligand bond distances to the bond order can be analyzed to illuminate the polarity of the bonding between metal and the redox-active orbital on the iminoxolenes. The osmiummore »compounds’ π bonding orbitals are about 40% metal-centered and 60% ligand-centered, with the ruthenium compounds’ orbitals about 65% metal-centered and 35% ligand-centered.« less