Rare‐Earth Metal Allyl and Hydrido Complexes Supported by an (NNNN)‐Type Macrocyclic Ligand: Synthesis, Structure, and Reactivity toward Biomass‐Derived Furanics

Abstract

The preparation and characterization of a series of neutral rare-earth metal complexes [Ln(Me(3)TACD)(η(3)-C(3)H(5))(2)] (Ln=Y, La, Ce, Pr, Nd, Sm) supported by the 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane anion (Me(3)TACD(-)) are reported. Upon treatment of the neutral allyl complexes [Ln(Me(3)TACD)(η(3)-C(3)H(5))(2)] with Brønsted acids, monocationic allyl complexes [Ln(Me(3)TACD)(η(3)-C(3)H(5))(thf)(2)][B(C(6)X(5))(4)] (Ln=La, Ce, Nd, X=H, F) were isolated and characterized. Hydrogenolysis gave the hydride complexes [Ln(Me(3)TACD)H(2)](n) (Ln=Y, n=3; La, n=4; Sm). X-ray crystallography showed the lanthanum hydride to be tetranuclear. Reactivity studies of [Ln(Me(3)TACD)R(2)](n) (R=η(3)-C(3)H(5), n=0; R=H, n=3,4) towards furan derivatives includes hydrosilylation and deoxygenation under ring-opening conditions.

Methylaluminum‐Supported Rare‐Earth‐Metal Dihydrides

“…The disorder in one tert-butyl group, toluene solvent, and hydrogen atoms except for BÀH and bridging hydrido ligands are omitted for clarity. Selected bond lengths [] and angles [8] for 4: Y-N1 2.428(2), Y-N3 2.433(2), Y-N5 2.430(2), Y-N7 2.133(2), Y-H2 2.18(5), Al-H2 1.61(4), Al-N7 1.891(2), Y···Al 3.0534 (7); N1-Y-H2 173(2), N5-Y-N7 132.56 (7), N1-Y-N7 115.79 (7), N7-Y-H2 68(2), N7-Al-H2 87(2), Y-N7-C28 145.1(2), Y-H2-Al 107(2).…”

“…While mono hydride complexes can exist as monomers, e.g., [(C 5 H 2 tBu 3 ) 2 CeH], [4] dihydrido species "LLnH 2 ", carrying only one ancillary ligand per lanthanide center, tend to form polynuclear complexes (see Supporting Information) containing as few as two [5] and up to six lanthanide metal centers. [6] Several types of ancillary ligands have been employed in an effort to stabilize complexes of low nuclearity, including sterically demanding cyclopentadienyl derivatives such as C 5 Me 4 SiMe 3[6] tris(pyrazolyl)borato scorpionates, [7] tetraazacycloamido, [8] bis(phosphinophenyl)amido pincer, [5] and pyridylamido [9] ligands as well as chelating diamido ligands (see Supporting Information). [10] However, the synthesis of a monomeric rare-earth-metal dihydride was not successful to date.The group of Takats used the sterically demanding hydrotris(3-tert-butyl-5-methylpyrazolyl)borato ligand (Tp tBu,Me ) to stabilize Ln 2+ centers in species such as alkyls, [11] carbenes, [12] amides, [11b] halides, [11,13] or hydrides [14] and was also able to obtain lanthanide dihydride complexes using the less-bulky dimethyl, diisopropyl, or unsubstituted derivative of the Tp ligand, but reported the formation of a mixture of products for the more bulky Tp tBu,Me ligand because of possible side reactions involving the ligand tertbutyl group.…”

“…[6] tris(pyrazolyl)borato scorpionates, [7] tetraazacycloamido, [8] bis(phosphinophenyl)amido pincer, [5] and pyridylamido [9] ligands as well as chelating diamido ligands (see Supporting Information). [10] However, the synthesis of a monomeric rare-earth-metal dihydride was not successful to date.…”

“…While mono hydride complexes can exist as monomers, e.g., [(C 5 H 2 tBu 3 ) 2 CeH], [4] dihydrido species "LLnH 2 ", carrying only one ancillary ligand per lanthanide center, tend to form polynuclear complexes (see Supporting Information) containing as few as two [5] and up to six lanthanide metal centers. [6] Several types of ancillary ligands have been employed in an effort to stabilize complexes of low nuclearity, including sterically demanding cyclopentadienyl derivatives such as C 5 Me 4 SiMe 3 [6] tris(pyrazolyl)borato scorpionates, [7] tetraazacycloamido, [8] bis(phosphinophenyl)amido pincer, [5] and pyridylamido [9] ligands as well as chelating diamido ligands (see Supporting Information). [10] However, the synthesis of a monomeric rare-earth-metal dihydride was not successful to date.…”

“…Hydrogen atoms except for BÀH and bridging hydrido ligands are omitted for clarity. Selected bond lengths [] and angles[8] for 2: Y-N1 2.389(2), Y-N3 2.314(2), Y-N5 2.312(2), Y-H1 2.05(2), Y-H2 2.11(2), Al-H1 1.72(2), Al-H2 1.70(2), Y···Al1 3.7471(7), Y···Al2 3.712(2); H1-Y-H2 92.7(7), Y-H1-Al1 165(2), Y-H2-Al2 153(2), N1-Y-H2 154.2(5), N5-Y-H1 134.1(5), N3-Y-H1 131.0(5); and 1: Lu-N1 2.351(2), Lu-N3 2.264(2), Lu-N5 2.261(2), Lu-H1 2.04(3), Lu-H2 2.09(2), Al-H1 1.71(3), Al-H2 1.68(2), Lu···Al1 3.7090(8), Lu···Al2 3.6667(9); H1-Lu-H2 94.6(10), Lu-H1-Al1 162(2), Lu-H2-Al2 153(2), N1-Lu-H2 156.1(7), N5-Lu-H1 134.6(8), N3-Lu-H1 128.8(8).…”