Heterofunctionalization catalysis with organometallic complexes of calcium, strontium and barium

Abstract

Despite the routine employment of Grignard reagents and Hauser bases as stoichiometric carbanion reagents in organic and inorganic synthesis, a defined reaction chemistry encompassing the heavier elements of Group II (M = Ca, Sr and Ba) has, until recently, remained unreported. This article provides details of the recent progress in heavier Group II catalysed small molecule transformations mediated by well-defined heteroleptic and homoleptic complexes of the form LMX or MX 2 ; where L is a mono-anionic ligand and X is a reactive s-bonded substituent. The intra-and intermolecular heterofunctionalization (hydroamination, hydrophosphination, hydrosilylation and hydrogenation) of alkenes, alkynes, dienes, carbodiimides, isocyanates and ketones is discussed.

Highly Fluorinated Tris(indazolyl)borate Silylamido Complexes of the Heavier Alkaline Earth Metals: Synthesis, Characterization, and Efficient Catalytic Intramolecular Hydroamination

“…[38] The strontium analogue of 1 has also been similarly synthesized. [ 8 ]toluene. An X-ray crystal structure has been obtained for 3 for which an ORTEP drawing is given in Figure 4 along with selected bond lengths and angles.…”

“…[1] Whereas the catalytic activity of transition metal and rare earth complexes for the addition of a NÀH bond across CÀC multiple bonds has been largely described in the literature, [2][3][4][5][6] the use of alkaline earth (Ae) metal complexes as hydroamination catalysts is only now starting to emerge. [7,8] Ae metals are abundant, oxophilic, and redox-inactive in their cationic form. They are characterized by a wide range of ionic radii and cation charge densities (Mg 2 + = 0.72 ; Ca 2 + = 1.00 ; Sr 2 + = 1.18 , Ba 2 + = 1.35 for six-coordinate ions).…”

Cationic organoaluminum compounds as intramolecular hydroamination catalysts

“…Base-catalyzed systems have been known for a long time [4], but the application of metal-based catalysts began with Marks' report on lanthanide compounds [5]. Since then, numerous metals have been investigated including lanthanides [6e8], early [9e11] and late transition metals [12e14] and more recently alkaline earth metals [15]. Neutral complexes of the latter metals are isoelectronic with cationic group 13 species.…”

Insertion of Pyridine into the Calcium Allyl Bond: Regioselective 1,4‐Dihydropyridine Formation and CH Bond Activation

“…The presence of methyl groups on the pyridine ring resulted in 1,4-addition under kinetic control, followed by CÀH bond activation of the methyl group. Organocalcium reagents [16] evidently display an unprecedented reactivity pattern with respect to the balance between nucleophilicity and basicity.…”