Highly Fluorinated Tris(indazolyl)borate Hydrocarbyl Complexes of Calcium and Magnesium: Synthesis and Structural Studies

Heteroleptic phenylacetylide complexes [{F12-Tp4Bo,3Ph}­Ae­(CCPh)]x of calcium (Ae = Ca, x = 2; 2) and magnesium (Ae = Mg, x = 1; 4) containing the highly fluorinated 3-phenyl hydrotris­(indazolyl)­borate {F12-Tp4Bo,3Ph}− ligand have been synthesized by acid–base reactions between the corresponding silylamido derivatives [{F12-Tp4Bo,3Ph}­Ae­{N­(SiRMe2)2}] (R = Me, Ae = Ca (1); R = H, Ae = Mg (3)) and PhCCH. Compounds 2 and 4 have been characterized by NMR spectroscopy and X-ray diffraction analysis. 2 crystallizes as a dinuclear complex, showing two nonsymmetrical “side-on” (π-type) interactions between the acetylide units and the Ca centers, whereas 4 crystallizes as a mononuclear complex, displaying a four-coordinate magnesium. The molecular structure of the complex [{F12-Tp4Bo,3Ph}­Mg­{N­(SiMe2H)2}] (3), obtained by the salt metathesis reaction between [Mg­{N­(SiMe2H)2}2] and [Tl­{F12-Tp4Bo,3Ph}], is also reported. 3 is also four-coordinate and exhibits a Mg···β-Si–H agostic distortion. The synthesis and in situ characterization of the heteroleptic alkyl complex [{F12-Tp4Bo,3Ph}­Ca­{CH­(SiMe3)2}­(THF)] (5) is also reported, although attempts to isolate this compound failed due to its extreme sensitivity to temperature.