Theoretical calculation of equilibrium
dissociation constants is a very computationally demanding and time-consuming
process since it requires an extremely accurate computation of the
solvation free energy changes for each of the species involved. By
correlating the minimum surface electrostatic potential (V
S,min) on the nitrogen atom of several aliphatic amino
groupscalculated at the density functional theory (DFT) ωB97X-D/cc-pVDZ
level of theorywe obtained regression models for each kind
of substitution pattern from which we interpolate their corresponding
pK
b values with remarkable accuracy: primary R
2 = 0.9519; secondary R
2 = 0.9112; and tertiary R
2 = 0.8172
(N = 20 for each family). These models were validated
with tests sets (N = 5) with mean absolute error
(MAE) values of 0.1213 (primary), 0.4407 (secondary), and 0.3057 (tertiary).
Combining this ansatz with another previously reported by our group
to estimate pK
a values [Caballero-García,
G.; et al. Molecules 2019, 24(1), 79] we are able
to reproduce the isoelectric points of 13 amino acids with no titrable
side chains with MAE = 0.4636 pI units.
A cyclic alkyl(amino)carbene-stabilized 1,4diborabenzene (DBB) ligand enables the isolation of 18electron two-legged parent piano-stool Fe 0 and Ru 0 complexes, [(η 6 -DBB)M(CO) 2 ], the ruthenium complex being the first of its kind to be structurally characterized.[(η 6 -DBB)Fe(CO) 2 ] reacts with E 4 (E = P, As) to yield mixed DBB-cyclo-E 4 sandwich complexes with planar E 4 2À ligands. Computational analyses confirm the strong electron-donating capacity of the DBB ligand and show that the E 4 ligand is bound by four equivalent FeÀ P σ bonds.
A (bisborane)triarylphosphine was developed to spontaneously generate H2 from water under ambient conditions, revealing an unprecedented multi-centered electron relay mechanism for a metal-free umpolung of proton to hydride.
The reaction of Power's digalladeltacyclane with Au(PPh 3 )Cl led to formation of a digallium gold complex (2) with both chloride and gold bridging between two gallium atoms. The bonding parameters from the solid-state structure of 2 suggested a 12e − Au center stabilized by weakly coordinated aryl groups. DFT calculations at the M05-2X/[LANL2TZ(f),6-311G(d)] level indicated a Ga−Au−Ga banana bond with no bonding interactions between gallium atoms. The gold carries an NBO charge of −0.0956 e − and is best viewed as an auride. The weak intramolecular interactions between Au p orbitals and σ C−C and σ C−H bonds of the adjacent aromatic rings amount to significant stabilization of the electron-deficient gold center. The digallium complex 2 represents the first structural example of a 12 e − organometallic auride complex, demonstrating its pseudohalide/hydride nature in bonding.
Synthetic strategies to access high‐valent iridium complexes usually require use of π donating ligands bearing electronegative atoms (e.g. amide or oxide) or σ donating electropositive atoms (e.g. boryl or hydride). Besides the η5‐(methyl)cyclopentadienyl derivatives, high‐valent η1 carbon‐ligated iridium complexes are challenging to synthesize. To meet this challenge, this work reports the oxidation behavior of an all‐carbon‐ligated anionic bis(CCC‐pincer) IrIII complex. Being both σ and π donating, the diaryl dipyrido‐annulated N‐heterocyclic carbene (dpa‐NHC) IrIII complex allowed a stepwise 4e– oxidation sequence. The first 2e– oxidation led to an oxidative coupling of two adjacent aryl groups, resulting in formation of a cationic chiral IrIII complex bearing a CCCC‐tetradentate ligand. A further 2e– oxidation allowed isolation of a high‐valent tricationic complex with a triplet ground state. These results close a synthetic gap for carbon‐ligated iridium complexes and demonstrate the electronic tuning potential of organic π ligands for unusual electronic properties.
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