Mechanochemical Formation, Solution Rearrangements, and Catalytic Behavior of a Polymorphic Ca/K Allyl Complex.

Without solvents present, the often far-from-equilibrium environment in a mechanochemically driven synthesis can generate high-energy, non-stoichiometric products not observed from the same ratio of reagents used in solution. Ball milling 2 equiv. K[A'] (A'=[1,3-(SiMe ) C H ] ) with CaI yields a non-stoichiometric calciate, K[CaA' ], which initially forms a structure (1) likely containing a mixture of pi- and sigma-bound allyl ligands.

An η -Bound Allyl Ligand on Magnesium in a Mechanochemically Generated Mg/K Allyl Complex.

Milling two equivalents of K[1,3-(SiMe ) C H ] (=K[A']) with MgX (X=Cl, Br) produces the allyl complex [K MgA' ] (1). Crystals grown from toluene are of the solvated species [((η -tol)K) MgA' ] ([1⋅2(tol)]), a trimetallic monomer with both bridging and terminal (η ) allyl ligands. When recrystallized from hexanes, the unsolvated 1 forms a 2D coordination polymer, in which the Mg is surrounded by three allyl ligands.

Halide metathesis in overdrive: mechanochemical synthesis of a heterometallic group 1 allyl complex.

As a synthesis technique, halide metathesis ( RM + M'X → R M' + MX) normally relies for its effectiveness on the favorable formation of a metal halide byproduct (MX), often aided by solubility equilibria in solution. Owing to the lack of significant thermodynamic driving forces, intra-alkali metal exchange is one of the most challenging metathetical exchanges to attempt, especially when conducted without solvent. Nevertheless, grinding together the bulky potassium allyl [KA'] (A' = [1,3-(SiMe)CH]) and CsI produces the heterometallic complex [CsKA'] in low yield, which was crystallographically characterized as a coordination polymer that displays site disorder of the K and Cs ions.

Reaction environment and ligand lability in group 4 CpMXY (X, Y = Cl, OtBu) complexes.

Despite their usefulness in catalytic and materials chemistry, the mixed cyclopentadienyl/alkoxide complexes of Ti, Zr, and Hf (CpM(OR)) have few reliable synthetic routes available to them. We describe the use of mechanical ball milling to promote halide metathesis from CpMCl, and compare these results to those obtained in hexanes and THF. Even without solvent, ring lability is extensive with titanium complexes, and alkoxide compounds with 0-3 Cp rings are isolated.

Advances in organometallic synthesis with mechanochemical methods.

Solvent-based syntheses have long been normative in all areas of chemistry, although mechanochemical methods (specifically grinding and milling) have been used to good effect for decades in organic, and to a lesser but growing extent, inorganic coordination chemistry. Organometallic synthesis, in contrast, represents a relatively underdeveloped area for mechanochemical research, and the potential benefits are considerable. From access to new classes of unsolvated complexes, to control over stoichiometries that have not been observed in solution routes, mechanochemical (or 'M-chem') approaches have much to offer the synthetic chemist.