Oleg. V. Ozerov

Boryl/bis­(phosphine) complexes of (POBOP)Ru were assembled by first preparing intermediates containing two bidentate phosphino/phenoxide ligands coordinated to Ru, followed by their reactions with BH₃·SMe₂.

A new triarylmethyl cation (*Tr⁺), designed to closely mimic Ph₃C⁺ in reactivity, has been prepared as a [HCB₁₁Cl₁₁]⁻ salt. *Tr⁺ very slightly exceeds the Lewis acidity of Ph₃C⁺ in chloride and hydride transfer reactions, but possesses two orders of magnitude higher solubility in organic solvents of low polarity.

Preparation of a triflimide-bridged bis-silylium monocation [(Me₃Si)₂NTf₂]⁺ has been accomplished as a [HCB₁₁Cl₁₁]⁻ salt.

New procedures for the conversion of [HCB₁₁H₁₁]⁻ into [HCB₁₁Cl₁₁]⁻ using SbCl₃/SbCl₅ mixture at reflux or TCCA in a solid-solid reaction, as well as syntheses of [XCB₁₁Cl₁₁]⁻ salts (X = Cl, Br, I, NH₂) are reported.

Lewis acids play a central role in a large variety of chemical transformations. The reactivity of the strongest Lewis acids is typically studied in the context of affinity towards hard bases, such as fluoride or oxygenous species. Carbocations can be viewed as soft Lewis acids, possessing significant affinity for softer bases, such as hydride. This work presents the ambient‐temperature isolation of salts of the perfluorotrityl cation ((C₆F₅)₃C⁺ or F₁₅Tr⁺) in combination with halogenated carborane anions. The F₁₅Tr⁺ cation exhibits remarkable hydride affinity, illustrated by the observation of hydride abstraction from dihydrogen, and of the rapid abstraction of hydride from −CH₂−groups in alkanes. Theoretical studies support the favorability of hydride abstraction from dihydrogen, and indicate that the hydride abstraction from alkanes proceeds via a concerted hydride transfer process that is sensitive to steric effects.

Lewis acids play a central role in a large variety of chemical transformations. The reactivity of the strongest Lewis acids is typically studied in the context of affinity towards hard bases, such as fluoride or oxygenous species. Carbocations can be viewed as soft Lewis acids, possessing significant affinity for softer bases, such as hydride. This work presents the ambient‐temperature isolation of salts of the perfluorotrityl cation ((C₆F₅)₃C⁺ or F₁₅Tr⁺) in combination with halogenated carborane anions. The F₁₅Tr⁺ cation exhibits remarkable hydride affinity, illustrated by the observation of hydride abstraction from dihydrogen, and of the rapid abstraction of hydride from −CH₂−groups in alkanes. Theoretical studies support the favorability of hydride abstraction from dihydrogen, and indicate that the hydride abstraction from alkanes proceeds via a concerted hydride transfer process that is sensitive to steric effects.

Protolysis of AlMe₃ or AlEt₃ with 2-diisopropylphosphinopyrrole (1) resulted in alane/bis(phosphine) pincer ligands containing two flanking phosphines and a central Al-Me (2-Me), Al-Et (2-Et) unit. Reactions of 2-Me with [(COD)MI]₂ (COD = 1,5-cyclooctadiene; M = Rh or Ir) in the presence of pyridine produced pincer complexes (3-Rh-I and 3-Ir-I) with M supported by the PAlP tridentate ligand, and pyridine, methyl, and iodide as monodentate ligands for Al or M. The analogous reaction of 2-Et with [(COD)MI]₂ and pyridine resulted in the formation of the analogous compounds 4-Rh-I and 4-Ir-I with hydride in place of methyl. DFT calculations were used to analyze the thermodynamic preferences for the positioning of pyridine, methyl or hydride, and the halide (chloride or iodide) on M vs Al. Cobalt was included with Rh and Ir among M for the purposes of DFT calculations. Theoretical studies suggested that different isomers are preferred for the iodide complexes (M-I and Al-Py) than for the chloride ones (M-py and Al-Cl, previously reported for Rh and Ir). X-ray structural study of 3-Rh-I and analysis of the ¹H NMR data of the Rh and Ir compounds in benzene corroborated these predictions.

The conventional synthetic approach to transition metal pincer complexes calls for the preparation of the tridentate pincer (pro)ligand first, with subsequent introduction of the transition metal center as the last step. This work demonstrates that the alternative synthetic logic, where the central main group element is introduced last, can be applicable to a number of PEP pincer complexes (E=B, Al, Si, P) derived from phosphinophenols and phosphinopyrroles. This approach obviates the need to isolate well‐behaved propincer precursors, and instead relies on the formation of phosphine‐metal adducts first, whose nature determines the stoichiometry of the needed main group reagent to complete the synthesis.

The conventional synthetic approach to transition metal pincer complexes calls for the preparation of the tridentate pincer (pro)ligand first, with subsequent introduction of the transition metal center as the last step. This work demonstrates that the alternative synthetic logic, where the central main group element is introduced last, can be applicable to a number of PEP pincer complexes (E=B, Al, Si, P) derived from phosphinophenols and phosphinopyrroles. This approach obviates the need to isolate well‐behaved propincer precursors, and instead relies on the formation of phosphine‐metal adducts first, whose nature determines the stoichiometry of the needed main group reagent to complete the synthesis.