The synthesis of alkaline earth (Ae) metal complexes and their use in catalysis, especially in ROP and hydroelementation processes, is only now starting to emerge. The main challenge of this chemistry is to control the Schlenk equilibrium that scrambles the ligands in heteroleptic complexes (2 AeXX’ = AeX2 + AeX’2). Highly fluorinated indazoles and hydrotris(indazolyl)borate proligands TpF with tunable electronic and steric properties have been developed in our group. We describe herein our initial attempts at unraveling the chemistry of TpFAe complexes. The very electron poor ligand F21-Tp4Bo,CF3 failed to coordinate to Ca2+, whereas adding two equiv. of Tl(F12-Tp4Bo,Ph) to CaI2 gave the homoleptic [(F12-Tp4Bo,Ph*)2Ca] with a sterically induced 1,2-borotropic shift in the ligand. The heteroleptic amido complexes [(F12-Tp4Bo,Ph)AeNR2] (Ae = Ca, Sr; R = SiMe3, SiMe2H) have been synthesized. Agostic distortions, especially strong for Sr, stabilize the structures (Figure). The [(F12-Tp4Bo,Ph)Ca{N(SiMe3)2}] complex is a very active catalyst for the cyclohydroamination reaction. Heteroleptic phenylacetylide complexes [{F12-Tp4Bo,3Ph}Ae(C≡CPh)]x of calcium (Ae = Ca, x = 2) and magnesium (Ae = Mg, x= 1) have also been synthesized. The Ca compound crystallizes as a dinuclear complex, showing two non-symmetrical “side-on” (π-type) interactions between the acetylide units and the Ca centers, whereas the Mg analogue crystallizes as a mononuclear complex, displaying a four-coordinate magnesium. The synthesis and in situ characterization of the rare heteroleptic alkyl complex [{F12-Tp4Bo,3Ph}Ca{CH(SiMe3)2}(THF)], finally, will be also reported.

Amido and alkyl complexes of magnesium, calcium and strontium containing highly fluorinated Tp’ ligands

253rd National Meeting (2017)

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