Stabilization and Reactivity of the Lewis Acidic Solvated Phenylcalcium Cation

Variable Ca-Caryl Hapticity and its Consequences in Arylcalcium Dimers

The dimeric β-diketiminato calcium hydride, [(Dipp BDI)CaH]2 (Dipp BDI = HC{(Me)CN-2,6-i-Pr2 C6 H3 }2 ), reacts with ortho-, meta- or para-tolyl mercuric compounds to afford hydridoarylcalcium compounds, [(Dipp BDI)2 Ca2 (μ-H)(μ-o-,m-,p-tolyl)], in which dimer propagation occurs either via μ2 -η1 -η1 or μ2 -η1 -η6 bridging between the calcium centers. In each case, the orientation and hapticity of the aryl units is dependent upon the position of the methyl substituent. While wholly organometallic meta- and para-tolyl dimers, [(Dipp BDI)Ca(m-tolyl)]2 and [(Dipp BDI)Ca(p-tolyl)]2 , can be prepared and are stable, the ortho-tolyl isomer is prone to isomerization to a calcium benzyl analog. Computational analysis of this latter process with density functional theory (DFT) highlights an unusual mechanism invoking the generation of an intermediate dicalcium species in which the group 2 centers are bridged by a toluene dianion formed by the formal attachment of the original hydride anion to the initially generated ortho-tolyl substituent. Use of a more sterically encumbered aryl substituent, {3,5-t-Bu2 C6 H3 }, facilitates the selective formation of [(Dipp BDI)Ca(μ-H)(μ-3,5-t-Bu2 C6 H3 )Ca(Dipp BDI)], which can be converted into the unsymmetrically-substituted σ-aryl calcium complexes, [(Dipp BDI)Ca(μ-Ph)(μ-3,5-t-Bu2 C6 H3 )Ca(Dipp BDI)] and [(Dipp BDI)Ca(μ-p-tolyl)(μ-3,5-t-Bu2 C6 H3 )Ca(Dipp BDI)] by reaction with the appropriate mercuric diaryl. Conversion of [(Dipp BDI)Ca(H)(Ph)Ca(Dipp BDI)] to afford [{{(Dipp BDI)Ca}2 (μ2 -Cl)}2 (C6 H5 -C6 H5 )], comprising a biphenyl dianion, is also reported. Although this latter transformation is serendipitous, AIM analysis highlights that, in a related manner to the ortho-tolyl to benzyl isomerization, the requisite C-C coupling may be facilitated in an "across dimer" fashion by the experimentally-observed polyhapto engagement of the aryl substituents with each calcium.

Synthesis of Molecular Phenylcalcium Derivatives: Application to the Formation of Biaryls

Hydrocarbon‐soluble β‐diketiminato phenylcalcium derivatives, which display various modes of Ca−μ₂‐Ph−Ca bridging, are accessible from reactions of Ph₂Hg and [(BDI)CaH]₂. Although the resultant compounds are inert toward the C−H bonds of benzene, they yield selective and uncatalyzed biaryl formation when reacted with readily available aryl bromides.

Hungry for charge – how a beryllium scorpionate complex “eats” a weakly coordinating anion

We present the reaction of a tris(pyrazolyl) beryllium scorpionate (TpBe) complex with a weakly coordinating anion (WCA), which yields the heteroleptic complex TpBeOC(CF3)3 1 (TpBeOR F). The product 1 has been characterized by multinuclear NMR spectroscopy (1H, 9Be, 13C) and single-crystal X-ray diffraction (scXRD). Quantum chemical calculations (DFT, NPA, LOL) were performed to study the bonding nature in 1.

Solvent-induced ion separation of a beryllium scorpionate complex

TpBeI undergoes a spontaneous ion separation upon treatment with THF, yielding [TpBe(thf)]I, which represents a rare example of a cationic beryllium complex.

Tethered cationic alkaline earth – olefin complexes

The utilisation of a specifically tailored aminofluoroalcohol possessing both a methoxy and an olefin dangling side arms enables the preparation of the first examples of discrete calcium- and strontium-olefin cationic complexes.

Calcium, Strontium and Barium Homogeneous Catalysts for Fine Chemicals Synthesis

The large alkaline earths (Ae), calcium, strontium and barium, have in the past 15 years yielded a brand new generation of heteroleptic molecular catalysts for the production of fine chemicals. However, the integrity of these complexes is often plagued by ligand redistribution equilibria in solution. This personal account retraces the paths followed in our research group towards the design of stable heteroleptic alkalino-earth complexes, including the use of intramolecular noncovalent Ae···H-Si and Ae···F-C interactions. Their implementation as homogenous precatalysts for reactions such as the intramolecular and intermolecular hydroamination and hydrophosphination of activated alkenes, the hydrophosphonylation of ketones, and the dehydrogenative coupling of amines and hydrosilanes that enable the efficient and controlled formations of CP, CN, or SiN σ-bonds, is presented in a synthetic perspective that highlights their overall outstanding catalytic performance.