Cristian G. Hrib

Preparation of cyclophanes by room-temperature ring-closing alkyne metathesis with imidazolin-2-iminato tungsten alkylidyne complexes.

Room-temperature ring-closing alkyne metathesis of 1,2-, 1,3-, and 1,4-bis(3-pentynyloxymethyl)benzenes has been investigated in the presence of catalytic amounts of an imidazolin-2-iminato tungsten alkylidyne complex. The m- and p-diynes selectively form the respective [10]metacyclophane or [10.10]paracyclophane, respectively, whereas a mixture of monomeric and dimeric cycloalkynes is obtained in the case of the o-diyne. DFT calculations reveal that the different selectivities can be attributed to the relative thermodynamic stability of the emerging cyclophanes.

Facile Access to Tetravalent Cerium Compounds: One-Electron Oxidation Using Iodine(III) Reagents

Readily accessible and easy-to-use phenyliodine(III) dichloride, PhICl(2), has been established as an innovative and superior reagent for the one-electron oxidation of cerium(III) complexes, comprising amide, amidinate, and cyclopentadienyl derivatives. Its use allowed the successful synthesis and structural characterization of the first members of three new classes of chloro-functionalized (organo)cerium(IV) compounds, including the long sought-after Cp(3)CeCl.

Secondary Interactions in Phosphane-Functionalized Group 4 Cycloheptatrienyl–Cyclopentadienyl Sandwich Complexes

Twice as reactive: The coordination chemistry of phosphane-functionalized Zr and Hf cycloheptatrienyl-cyclopentadienyl complexes gives rise to unusual secondary interactions associated with the presence of Lewis acidic 16-electron sandwich moieties. These structures can develop weak dative bonds as exemplified by the noncovalent Pd-->Zr interaction in the heterobimetallic {Zr(2)Pd} complex (see picture). Phosphane-functionalized cycloheptatrienyl-cyclopentadienyl Group 4 metal complexes of the type [(eta(7)-C(7)H(7))M(eta(5)-C(5)H(4)PR(2))] (M=Ti (9); M=Zr (10); M=Hf (11); R=Ph (a); R=iPr (b)) have been prepared by the reduction of [(eta(5)-C(5)H(4)PR(2))TiCl(3)] or [(eta(5)-C(5)H(4)PR(2))(2)MCl(2)] (M=Zr, Hf) with magnesium in the presence of cycloheptatriene (C(7)H(8)). In the solid state, the Ti complex 9 a and the complex 11 b are monomeric, whereas 10 a, 10 b, and 11 a form dimers, in which the sandwich units are linked by long Zr-P or Hf-P bonds. Density-functional theory (DFT) calculations indicate that the metal-phosphane interaction is weak, and accordingly, both the Ti complex 9 b and the Zr complex 10 b act as monodentate phosphane ligands upon reaction with [{(cod)RhCl}(2)] (cod=eta(4)-1,5-cyclooctadiene). The X-ray crystal structures of [(cod)Rh(9 b)Cl] (12) and [(cod)Rh(10 b)Cl] (13) reveal that only the latter exhibits a secondary intramolecular Cl-metal interaction. The complex [(10 b)(2)Pd] (14) was obtained by reaction of [(eta(5)-C(5)H(5))Pd(eta(3)-C(3)H(5))] with two equivalents of 10 b. The solid-state structure of 14 reveals a T-shaped Pd(0) center with a long Pd-Zr bond of 2.9709(3) A, which can be interpreted as a weak noncovalent Pd(0)-->Zr(+IV) bond, as indicated by the calculated relaxed force constant of 5.68 N m(-1).

Unprecedented Bending and Rearrangement of f-Element Sandwich Complexes Induced by Superbulky Cyclooctatetraenide Ligands

The use of the superbulky cyclooctatetraenide dianion ligand [C(8)H(6)(SiPh(3))(2)](2-) (= COT(BIG)) in organo-f-element chemistry leads to unprecedented effects such as the formation of a significantly bent anionic Ce(III) sandwich complex, a novel cerocene formed by sterically induced SiPh(3) group migration, as well as the first example of a bent uranocene.

Homoleptic gadolinium amidinates as precursors for MOCVD of oriented gadolinium nitride (GdN) thin films.

Five new homoleptic gadolinium tris-amidinate complexes are reported, which were synthesized via the salt-elimination reaction of GdCl(3) with 3 equiv of lithiated symmetric and asymmetric amidinates at ambient temperature. The Gd-tris-amidinates [Gd{(N(i)Pr)(2)CR}(3)] [R = Me (1), Et (2), (t)Bu (3), (n)Bu (4)] and [Gd{(NEt)(N(t)Bu)CMe}(3)] (5) are solids at room temperature and sublime at temperatures of about 125 °C (6 × 10(-2) mbar) with the exception of compound 4, which is a viscous liquid at room temperature. According to X-ray diffraction analysis of 3 and 5 as representative examples of the series, the complexes adopt a distorted octahedral structure in the solid state. Mass spectrometric (MS) data confirmed the monomeric structure in the gas phase, and high-resolution MS allowed the identification of characteristic fragments, such as [{(N(i)Pr)(2)CR}GdCH(3)](+) and [{(N(i)Pr)(2)CR}GdNH](+). The alkyl substitution patterns of the amidinate ligands clearly show an influence on the thermal properties, and specifically, the introduction of the asymmetric carbodiimide leads to a lowering of the onset of volatilization and decomposition. Compound 5, which is the first Gd complex with an asymmetric amidinate ligand system to be reported, was, therefore, tested for the MOCVD of GdN thin films. The as-deposited GdN films were capped with Cu in a subsequent MOCVD process to prevent postdeposition oxidation of the films. Cubic GdN on Si(100) substrates with a preferred orientation in the (200) direction were grown at 750 °C under an ammonia atmosphere and exhibited a columnar morphology and low levels of C or O impurities according to scanning electron microscopy, Rutherford backscattering, and nuclear reaction analysis.

One ligand fits all: lanthanide and actinide sandwich complexes comprising the 1,4-bis(trimethylsilyl)cyclooctatetraenyl (=COT′′) ligand

The series of anionic lanthanide(III) sandwich complexes of the type [Ln(COT′′)2]− (COT′′ = 1,4-bis(trimethylsilyl)cyclooctatetraenyl dianion) has been largely extended by the synthesis of eight new derivatives ranging from lanthanum to lutetium. The new compounds [Li(DME)3][Ln(COT′′)2] (Ln = Y (1), La (2), Pr (3), Gd (4), Tm (6), Lu (8)) and [Li(THF)4][Ln(COT′′)2] (Ln = Ho (5), Tm (7)) were prepared in good yields following a straightforward synthetic protocol which involves the treatment of LnCl3 with 2 equiv. of in situ-prepared Li2COT′′ in either DME (=1,2-dimethoxyethane) or THF. The neutral actinide sandwich complexes An(COT′′)2 (An = Th (9), U (10)) and An(COT′′′)2 (COT′′′ = 1,3,6-tris(trimethylsilyl)cyclooctatetraenyl dianion; An = Th (11), U (12)) were synthesized in a similar manner, starting from ThCl4 or UCl4, respectively. The COT′′ ligand imparts excellent solubility even in low-polar solvents as well as excellent crystallinity to all new compounds studied. All twelve new f-element sandwich complexes have been structurally authenticated by single-crystal X-ray diffraction. All are nearly perfect sandwich complexes with little deviation from the coplanar arrangement of the substituted COT′′ rings. Surprisingly, all six [Li(DME)3][Ln(COT′′)2] complexes covering the entire range of Ln3+ ionic radii from La3+ to Lu3+ are isostructural (space group P). Compound 10 is the first uranocene derivative for which 13C NMR data are reported.

Investigation of the “bent sandwich-like” divalent lanthanide hydro-tris(pyrazolyl)borates Ln(TpiPr2)2 (Ln = Sm, Eu, Tm, Yb)

The series of homoleptic lanthanide(II) “bent sandwich-like” hydro-tris(pyrazolyl)borate complexes Ln(TpiPr2)2 (Ln = Sm (1), Eu (2), Tm (3), Yb (4); TpiPr2 = hydro-tris(3,5-diisopropylpyrazolyl)borate) has been completed by the synthesis of the hitherto unknown europium and ytterbium derivatives 2 and 4. Both compounds were prepared in high yields by treatment of LnI2(THF)2 (Ln = Eu, Yb) with 2 equiv. of KTpiPr2 in a THF solution. Although the molecules are sterically highly congested, an X-ray diffraction study of bright red 4 revealed a similar bent B–Yb–B arrangement (151.1° and 153.9°, two independent molecules) as in the previously investigated Sm(II) and Tm(II) complexes 1 and 3. An initial reactivity study showed a very different behavior with acetonitrile. While 2 and 4 proved to be unreactive toward acetonitrile, the more strongly reducing Sm(II) complex 1 yielded two new products. The major product was the dark green-black acetonitrile solvate SmII(TpiPr2)2·CH3CN (5), while the second product, the colorless (TpiPr2)SmIII(3,5-iPr2pz)2(NCCH3) (6) with two 3,5-diisopropyl-pyrazolate ligands, resulted from oxidation of samarium to the trivalent state and degradation of a TpiPr2 ligand. Disappointingly, from the most reducing Tm(II) complex 3 only the ligand fragmentation product pyrazabole, [HB(3,5-iPr2pz)2]2 (7), could be isolated and the fate of the Tm containing by-product(s) remains unknown. The new compounds 4–6 were structurally authenticated through single-crystal X-ray diffraction. The europium compound 2 shows an extremely bright yellow emission in solution, which can be observed also at daylight excitation, as well as in the solid state. The high intensity is even remarkable when compared to other Eu(II) containing materials. The photoluminescence was investigated with the conclusion that the rigidity of this complex is responsible for these outstanding luminescence properties.

Explosive Werner-type cobalt(III) complexes

A series of potentially explosive Werner-type cobalt(III) complexes comprising the anions azotetrazolate, nitrotetrazolate, picrate and dipicrylamide were prepared via simple metathetical routes. Treatment of [Co(NH3)5NO2]Cl2, trans-[Co(NH3)4(py)NO2]Cl2 (py = pyridine), trans-[Co(NH3)4(NO2)2]Cl, and [Co(NH3)5N3]Cl2 with equimolar amounts of disodium azotetrazolate, (Na2C2N10·5H2O, 1), in aqueous solutions afforded new cobalt(III) azotetrazolate salts [Co(NH3)5NO2](C2N10)·2H2O (2), trans-[Co(NH3)4(py)NO2](C2N10)·2H2O (3), trans-[Co(NH3)4(NO2)2]2(C2N10) (4), and [Co(NH3)5N3](C2N10)·H2O (5) in moderate to excellent yields (46–88%). Similar treatment of trans-[Co(NH3)4(NO2)2]Cl with 1 equiv. of sodium 5-nitrotetrazolate dihydrate (= NaNT, 6) afforded the novel cobalt(III) 5-nitrotetrazolate derivative trans-[Co(NH3)4(NO2)2](NT)·H2O (7) as orange, rectangular prismatic crystals in 64% yield. Two complex cobalt(III) picrates, trans-[Co(NH3)4(NO2)2](picrate)·H2O (9) and [Co(NH3)5N3](picrate)2 (10), were prepared in a similar manner from the corresponding chloride precursors and equimolar amounts of sodium picrate. The reaction of trans-[Co(NH3)4(NO2)2]Cl with sodium dipicrylamide (= NaDPA) in a 1 : 1 molar ratio gave the first cobalt(III) dipicrylamide, trans-[Co(NH3)4(NO2)2](DPA)·H2O (12). Finally, the highly explosive, dark blue-green dichroitic non-electrolyte complex mer-[Co(en)(py)(N3)3] (13) was formed upon treatment of [Co(en)(py)2(NH3)Cl]Cl2·H2O with excess NaN3 in hot water (93% yield). The molecular and crystal structures of 2, 3, 4, 5, 7, 9, 10, 12, and 13 were determined by single-crystal X-ray diffraction. In the solid state, all compounds comprised extensive hydrogen-bonded supramolecular networks. Representative studies of the energetic properties (impact and friction sensitivity, combustion) revealed that some of the new compounds can be classified as primary explosives.

A stable chiral diaminocyclopropenylidene

The chiral carbene bis[bis(R-1-phenylethyl)amino]cyclopropenylidene 2 and its dicarbene-silver complex [Ag(2)2]BF4 (3) have been isolated in good yields from the reactions of bis[bis(R-1-phenylethyl)amino]cyclopropenylium tetrafluoroborate (1)BF4 with potassium bis(trimethylsilyl)amide or with Ag2O, respectively; the molecular structures of (1)ClO4, 2 and 3 have been determined by X-ray diffraction analyses.

Synthesis and catalytic activity of homoleptic lanthanide-tris(cyclopropylethinyl)amidinates

Reactions of anhydrous lanthanide trichlorides, LnCl3 (Ln = Nd, Sm, Ho), with 3 equiv. of lithium-cyclopropylethinylamidinates, Li[c-C3H5–CC–C(NR)2] (1a: R = cyclohexyl (Cy), 1b: R = iPr), afforded the new homoleptic lanthanide(III) tris(cyclopropylethinylamidinate) complexes [c-C3H5–CC–C(NCy)2]3Sm (2a) and [c-C3H5–CC–C(NiPr)2]3Ln (Ln = Nd (2b), Sm (2c), Ho (2d)) as air- and moisture-sensitive crystalline solids in moderate to good isolated yields (45–79%). The formation of unsolvated, homoleptic Ln(III) tris(cyclopropylethinylamidinate) was confirmed by an X-ray diffraction study of the holmium derivative [c-C3H5–CC–C(NiPr)2]3Ho (2d). EI mass spectra of the new rare-earth metal amidinates indicated a significant volatility. An initial catalysis study revealed that these complexes catalyze the addition of terminal alkynes to carbodiimides to give propiolamidines of the type R–CC–C(NR′)(NHR′). The molecular structure of N,N′-dicyclohexyl-phenylpropiolamidine, Ph–CC–C(NCy)(NHCy) (4), was also determined by X-ray diffraction.