Chemistry of C-Trimethylsilyl-Substituted Heterocarboranes. 32. Synthetic and Structural Investigations on Half-Sandwich Lanthanacarboranes:  Important Synthons in Metallacarborane Chemistry

Abstract

The reactivities of the monosodium-complexed carborane precursors nido-1-Na(C4H8O)-2-(R)-3-(SiMe3)-2,3-C2B4H5 (R = SiMe3 (1) or Me (2)) with a number of lanthanide halides were investigated. The reaction of LnCl3 (or LnBr3) with 1 in a 1:2 molar ratio in dry THF at 60 °C produced the dimerized half-sandwich lanthanacarborane complexes [2,3-(SiMe3)2-1-X-1-(THF) m -1-Ln(η5-2,3-C2B4H4)]2·n(THF) (3, Ln = Y, X = Cl, m = 2, n = 1; 4, Ln = La, X = Br; m = 1, n = 0; 5, Ln = Ce, X = Br; m = 1, n = 0; 6, Ln = Pr, X = Br; m = 2, n = 1; 7, Ln = Nd; X = Cl, m = 2, n = 1; 8, Ln = Sm; X = Br, m = 2, n = 0; 9, Ln = Gd; X = Cl, m = 2, n = 1; 10, Ln = Tb, X = Cl, m = 2, n = 1; 11, Ln = Dy, X = Cl, m = 2, n = 1; 12, Ln = Ho, X = Cl, m = 2, n = 1; 13, Ln = Er, X = Cl, m = 2, n = 1; 14, Ln = Tm, X = Cl, m = 2, n = 1; 15, Ln = Yb, X = Cl, m = 2, n = 1; 16, Ln = Lu X = Cl, m = 2, n = 1) as crystalline solids in 70−92% isolated yields. In a similar manner, the reactions of 2 with LnCl3 at 65 °C gave the corresponding complexes [2-Me-3-(SiMe3)-1-Cl-1-(THF)2-1-Ln(η5-2,3-C2B4H4)]2 (17, Ln = Nd; 18, Ln = Dy; 19, Ln = Ho; 20, Ln = Er; 21, Ln = Yb) as crystalline solids in 72−80% yield. In both series of the reactions, 1 equiv of the particular neutral carborane was also produced. The substitution of the chloride ions in complexes 17 and 20 by 2 gave the half-sandwich lanthanacarborane clusters {2-Me-3-(SiMe3)-1-[4,5-(μ-H)-nido-2-Me-3-(SiMe3)-2,3-C2B4H5]-1-Ln(η5-2,3-C2B4H4)}2·n(THF) (22, Ln = Nd, n = 2; 24, Ln = Er, n = 1) as crystalline solids in 82−87% yield. The reaction of 19 and 2 produced the trimer {2-Me-3-(SiMe3)-1-[4,5-(μ-H)-nido-2-Me-3-(SiMe3)-2,3-C2B4H5]-1-Ho(η5-2,3-C2B4H4)}3·8(THF) (23) in 57% yield. Complexes 22, 23, and 24 could directly be obtained in good yield (56−67%) from the reaction of 2 with the corresponding LnCl3 at 65 °C in molar ratios of 3:1 in dry THF. Similarly, the mixed coordinated complex {2,3-(SiMe3)2-1-[4,5-(μ-H)-(nido-2-Me-3-(SiMe3)-2,3-C2B4H5)]-1-Gd(η5-2,3-C2B4H4)}2·3(THF) (25) was obtained by reacting compound 9 with 2. To investigate the importance of the halide in these reactions, (η5-Cp)LnCl2 (Ln = Tb, Dy, Er) with 1 in a 1:2 molar ratio produced lanthanacarborane complexes [1-(η5-C5H5)-2,3-(SiMe3)2-1-Ln(η5-2,3-C2B4H4)]2·n(THF) (26, Ln = Tb, n = 2; 27, Ln = Dy, n = 2; 28, Ln = Er, n = 3) as crystalline solids in 77−82% isolated yields. On the other hand, the reactions of (η5-Cp)2ErCl and (η8-C8H8)GdCl with 1 in 1:1 molar ratios did not produce the half-sandwich lanthanacarboranes, but rather gave the exo-polyhedral products {exo-(η5-C5H5)2Er[4,5-(μ-H)-2,3-(SiMe3)2-2,3-C2B4H4]}·(THF) (29) and {exo-(η8-C8H8)Gd[4,5-(μ-H)-2,3-(SiMe3)2-2,3-C2B4H4]·2(THF) (30) as crystalline solids in 76% and 73% isolated yield, respectively. All compounds were characterized by IR spectroscopy and elemental analysis, whereas compounds 3, 7−9, 10−16, 18−22, 29, and 30 were characterized by single-crystal X-ray diffraction studies. The diamagnetic compounds 3, 4, and 16 were additionally characterized by 1H, 13C, and 11B NMR s...

[η5-2,3-Bis(trimethylsilyl)-2,3-dicarba-nido-hexaborane(2−)]chlorido(N,N,N′,N′-tetramethylethylenediamine)dysprosium(III)

“…The average coordination bond distances (Å) are: Dy-Cl 2.5851 (9), Dy-N1 2.598 (3), Dy-N2 2.698 (3), Dy-B4,B5 2.728 (4), 2.692 (4), Dy-av(C1, C2, B3, B4, B5) 2.720 and the corresponding bond angles (°) are Cl-Dy-N1 95.98 (7), Cl-Dy-B5 143.74 (8), N(1)-Dy-N(2) 68.3 (1), B(5)-Dy-B(4) 35.7 (1). The Dy-av(C 2 B 3 ) distance of 2.712Å and the Dy-Cl distance of 2.5851 (9) Å in the structure are similar to the values of 2.717 Å and 2.5757 (14) Å, respectively, found in anther Dy compound (Wang et al 2006). This is one of the few instances where the substitution of THF by TMEDA molecules does not change either the cluster or intermolecular geometries.…”

“…The lanthanacarboranes (LnC 2 B 4 ) cage systems are of interest in that their structural chemistry depends on the number and nature of the metal ligands other than the particular carborane. For example, the reaction of the tetrahydrofuran (THF) solvated dilithium compounds of B 4 C 8 H 22 Si 2 2with LnCl 3 in 2:1 molar ratios produced exclusively a trinuclear clusters (Tomlinson et al 2005, Wang et al 2006, and literature cited therein). The methoxide and oxide ions were thought to be the result of a degradation of the THF molecules.…”

“…On the other hand, similar reactions with the TMEDA-solvated carborane dianions produced the corresponding closo-compound (Tomlinson et al 2005). The reaction of a nido-compound with a number of lanthanide halides in 2:1 carborane-to-lanthanide molar ratios produced only the corresponding dimers (Wang et al 2006). The presence of the reactive chlorides made these compounds potentially useful precursors in the syntheses of other lanthanacarboranes.…”

Synthesis and Characterization of Paramagnetic Lanthanide Benzyl Complexes

“…All the (NN fc )MBn(THF) and (NN fc )MI(THF) z complexes were characterized by X-ray crystallography. Structurally characterized organometallic complexes of holmium, − erbium, − and gadolinium ,− are rare. (NN fc )NdBn(THF) (Figure SX5), (NN fc )GdBn(THF) (Figure SX6), (NN fc )HoBn(THF) (Figure ), and (TBS)ErBn(THF) (Figure SX8) are isostructural with (NN fc )YBn(THF) .…”

Advances in the metallacarborane chemistry of f-block elements

“…A reasonable sequence of steps would involve the initial precipitation of two equivalents of NaCl by a 1 : 2 molar ratio reaction of LnCl 3 and nido-1-Na(THF)-2,3-(SiMe 3 ) 2 -2,3-C 2 B 4 H 5 , leading to the formation of an exo-commolanthanacarborane intermediate. 56 The intermediate could then undergo an intramolecular proton transfer, producing the halfsandwich halolanthanacarborane and the neutral nido-carborane product.…”