Calcium, Strontium and Barium Homogeneous Catalysts for Fine Chemicals Synthesis

Influence of 18-Crown-6 Ether Coordination on the Catalytic Activity of Potassium and Calcium Diarylphosphinites in Hydrophosphorylation Reactions

The addition of 18-crown-6 ether (1,4,7,10,13,16-hexaoxacyclooctadecane) to tetranuclear [(thf)K(OPAryl₂)]₄ and [(thf)₄Ca(OPAryl₂)₂] yields the corresponding mononuclear complexes [(18C6)K(OPAryl₂)] [Aryl = Ph (1a), Mes (1b)] and [(18C6)Ca(OPAryl₂)₂] [Aryl = Ph (2a), Mes (2b)]. The metathesis reaction of [(thf)K(OPAryl₂)]₄ with CaI₂ yields the calciate [K₂Ca(thf)_x{OPMes₂}₄]. The addition of dimesitylphosphane oxide and crystallization from a hexane solution gives [K₂Ca{OPMes₂}₄{Mes₂P(O)H}] (3). The complexes [(thf)K(OPMes₂)]₄, [(thf)₄Ca(OPMes₂)₂], 1b, 2b, and the calciate 3 are tested as catalysts in the hydrophosphorylation of isopropylisocyanate with dimesitylphosphane oxide, quantitatively yielding N-isopropyl(dimesitylphosphoryl)formamide. The potassium complexes are more efficient catalysts than the calcium congeners, and coordination of 18-crown-6 decelerates the catalytic conversion.

Group 2 metal (Mg, Ca, Sr) silylamides supported by a cyclen-derived macrocyclic polyamine

Heteroleptic bis(silyl)amides of magnesium and calcium [(L)M{N(SiMe₃)₂}] [M = Mg, Ca; LH = 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane; (Me₃TACD)H] were previously synthesized from LH and [M{N(SiMe₃)₂}₂]. Strontium bis(silyl)amides [Sr{N(SiMe₃)₂}₂(thf)₂] and [Sr{N(SiHMe₂)₂}₂(thf)_2/3] reacted with LH to give different types of products, depending on the presence of the β-SiH function. While the former underwent protonolysis to give the amido-bridged dimer [(L)Sr{N(SiMe₃)₂}]₂ (1), the latter gave the adduct [(LH)Sr{N(SiHMe₂)₂}₂] (2) as a stable solid. 2 slowly underwent an intramolecular Si-H/H-N dehydrocoupling in solution to give [{(L)SiMe₂N(SiHMe₂)}Sr{N(SiHMe₂)₂}] (3) by liberating H₂. The results of transamination of 1 with HN(SiHMe₂)₂ depended on the relative stoichiometric ratio. A 1 : 1 mixture in n-pentane gave [{(L)SiMe₂N(SiHMe₂)}Sr{N(SiMe₃)₂}] (4) and H₂, while excess HN(SiHMe₂)₂ gave the adduct 2 under similar conditions. Compounds 2 and 3 exhibit Sr↼H-Si interactions according to X-ray crystallography, NMR, and IR spectroscopy. Lighter congeners of elusive [(L)Sr{N(SiHMe₂)₂}] were isolable for Mg (5) and Ca (6).

Insight into the local environment of magnesium and calcium in low-coordination-number organo-complexes using 25Mg and 43Ca solid-state NMR: a DFT study

With the increasing number of organocalcium and organomagnesium complexes under development, there is a real need to be able to characterize in detail their local environment in order to fully rationalize their reactivity. For crystalline structures, in cases when diffraction techniques are insufficient, additional local spectroscopies like ²⁵Mg and ⁴³Ca solid-state NMR may provide valuable information to help fully establish the local environment of the metal ions. In this current work, a prospective DFT investigation on crystalline magnesium and calcium complexes involving low-coordination numbers and N-bearing organic ligands was carried out, in which the ²⁵Mg and ⁴³Ca NMR parameters [isotropic chemical shift, chemical shift anisotropy (CSA) and quadrupolar parameters] were calculated for each structure. The analysis of the calculated parameters in relation to the local environment of the metal ions revealed that they are highly sensitive to very small changes in geometry/distances, and hence that they could be used to assist in the refinement of crystal structures. Moreover, such calculations provide a guideline as to how the NMR measurements will need to be performed, revealing that these will be very challenging.

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 complexes with imino-phosphinanilido chalcogenide ligands for heterofunctionalisation catalysis

Syntheses, characterisation and utilisation of the calcium complexes supported by imino-phosphinanilido chalcogenide ligands {Ph₂P(E)–N–C₆H₄–CHN(Dipp)} (E = S, Se) as molecular precatalysts for the heterofunctionalisation of styrene are reported.