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Reaction of the open samarocene [(η5-pdl′)2Sm(thf)2] (1-Sm ; pdl′ = 2,4- t Bu2C5H5) towards IMes (= 1,3-dimesitylimidazolin-2-ylidene), I t Bu (= 1,3-di- tert -butylimidazolin-2-ylidene) and IiPr2Me2 (= 1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene) forms the corresponding NHC adducts, [(pdl′)2Sm(IMes)] (2-Sm), [(pdl′)2Sm(I t Bu)] (3-Sm) and [(pdl′)2Sm(IiPr2Me2)] (4-Sm), respectively in good to excellent yields. Diverging reactivity patterns emerge when we attempted to prepare the related adducts using the open ytterbocene [(pdl′)2Yb(thf)] (1-Yb). Attributed to the smaller ionic radius of YbII no adduct is observed for IMes. However, for the smaller I t Bu ligand iso-butene elimination occurs to yield the imidazole YbII adduct (3 ′ -Yb). For the slightly less sterically encumbered IiPr2Me2 two products were isolated, albeit in low yield: [(pdl′)2Yb(IiPr2Me2)] (4-Yb) and [{(pdl′)Yb(IiPr2Me2)(μ-S)}2] (5-Yb). The surprising formation of the μ-sulfido bridged species 5-Yb suggested that this product might result from trace impurities of imidazoline-2-thione originating from the synthesis of IiPr2Me2. To verify this hypothesis the first imidazoline-2-thione adducts in organolanthanide chemistry were prepared by the reaction of 1-Sm and 1-Yb towards S=IMe2Me2 and S=IiPr2Me2, respectively. All of these adducts were structurally authenticated. However, the imidazoline-2-thione adducts slowly degrade in solution with the Yb derivatives being less stable. Analyses of the organic degradation products suggest that reduction of imidazoline-2-thione to imidazoline-2-ylidene can indeed be accomplished by the lanthanide metal (providing one electron) as well as the (pdl′)− ligand (also delivering one electron). Reaction of the open samarocene [(η5-pdl′)2Sm(thf)2] (1-Sm) and open ytterbocene [(η5-pdl′)2Yb(thf)] (1-Yb) towards N -heterocyclic carbenes (NHC) and imidazoline-2-thione has been evaluated. While adduct formation occurs readily for 1-Sm , unexpected side reactions have been encountered for 1-Yb. [ABSTRACT FROM AUTHOR]

The uranium metallacyclocumulene, [η5-1,3-(Me3Si)2C5H3]2U(η4-C4Ph2) (3) was isolated from the reaction mixture containing [η5-1,3-(Me3Si)2C5H3]2UCl2 (1), potassium graphite (KC8) and 1,4-diphenylbutadiyne (PhC≡C–C≡CPh) in good yield. The reactivity of 3 towards various small organic molecules was evaluated. For example, while complex 3 shows no reactivity towards alkynes and 2,2′-bipyridine, it may deliver the [η5-1,3-(Me3Si)2C5H3]2U(II) fragment in the presence of Ph2E2 (E = S, Se) and Ph3CN3, or react as a nucleophile in the presence of carbodiimides, isothiocyanates, aldehydes, ketones, and pyridine derivatives, forming five-, seven- or nine-membered heterometallacycles. On the contrary, addition of Ph2CS to 3 induces C＝S bond cleavage yielding the dithiolate complex [η5-1,3-(Me3Si)2C5H3]2U[S2(C12H5Ph5)] (14). In contrast, the closely related, but sterically more encumbered uranium metallacyclocumulene [η5-1,2,4-(Me3Si)3C5H2]2U(η4-C4Ph2) (4) features a more limited reactivity which is restricted to mono- and double insertions with small unsaturated organic molecules such as isothiocyanates, ketones and nitriles. [ABSTRACT FROM AUTHOR]

Tetraisopropylcyclopentadienyl halides of the heavy alkaline earth metals are suitable starting compounds for nucleophilic substitution reactions. With a ring as large as the cyclooctatetraene dianion coming close to the dications of calcium, strontium or barium, steric bulk comparable to that of a tetraisopropylcyclopentadienyl ligand is achieved without bulky substituents, bending of Cp-M-COT angles are restricted to linear values and thermally stable structures are established.

This paper describes the synthesis and reactivity of [η5-1,3-(Me3Si)2C5H3]2U(＝P-2,4,6-iPr3C6H2)(OPMe3) (6) which is accessible from a ligand exchange reaction between [η5-1,3-(Me3Si)2C5H3]2U(＝P-2,4,6-iPr3C6H2)(OPPh3) (2) and Me3PO at ambient temperature. Phosphinidene 6 exhibits no reactivity towards internal alkynes, but readily reacts with various hetero-unsaturated molecules such as isothiocyanates, aldehydes, nitriles, isonitriles, and organic azides, forming uranium sulfido, oxido, imido, and uranaheterocyclic compounds. Nevertheless, with the bidentate ortho-dicyanobenzene o-C6H4(CN)2 the zwitterionic species [η5-1,3-(Me3Si)2C5H3]2U[NHC(N){C6H4CP(2,4,6-iPr3C6H2)CH2PMe2O}] (13) is isolated in good yield. Moreover, 6 converts with Ph2S2 to the uranium(III) phenylthiolate compound [η5-1,3-(Me3Si)2C5H3]2USPh(OPMe3) (7) in good isolated yield. Furthermore, the influence of the Lewis base on the reactivity of the uranium phosphinidene metallocenes has also been evaluated. [ABSTRACT FROM AUTHOR]

The Lewis base supported terminal uranium phosphinidene metallocene [η5-1,3-(Me3C)2C5H3]2U(＝P-2,4,6-iPr3C6H2)(OPMe3) (2) could be isolated from a salt metathesis reaction in toluene at ambient temperature between [η5-1,3-(Me3C)2C5H3]2U(Cl)Me (1) and 2,4,6-iPr3C6H2PHK in the presence of Me3PO, and its structure and reactivity were probed in detail. No reaction of 2 with internal alkynes was observed, but it reacts in the presence of various heterounsaturated molecules such as CS2, isothiocyanates, aldehydes, imines, diazenes, carbodiimides, nitriles, isonitriles, diazoalkane, and organic azides, forming carbodithioates, sulfidos, oxidos, metallaheterocycles, and imido complexes, in good yields. Moreover, on reaction with the diazoalkane derivative Me3SiCHN2 the pseudophosphinimido uranium(III) complex [η5-1,3-(Me3C)2C5H3]2U(N＝P-2,4,6-iPr3C6H2)(OPMe3) (20) can be isolated in good yield. [ABSTRACT FROM AUTHOR]

In the title compound, formally K+ C6H16B-, the contact sphere of potassium consists of eleven hydrogen atoms from three different anions, assuming an arbitrary cut-off of 3 Å . The shortest interaction, 2.53 (2) Å, involves the hydridic hydrogen H01, which fulfils a bridging function in the formation of chains of KHBEt3 units parallel to the a axis [K1—H01i 2.71 (2) Å, K1—H01— K1ii 126.7 (9)°, operators x∓1/2, y + 3 /2, z + 1]. [ABSTRACT FROM AUTHOR]

The synthesis, electronic structure, and reactivity of a uranium metallacyclopropene were comprehensively studied. Addition of diphenylacetylene (PhC≡CPh) to the uranium phosphinidene metallocene [η5‐1,2,4‐(Me3C)3C5H2]2U=P‐2,4,6‐tBu3C6H2 (1) yields the stable uranium metallacyclopropene, [η5‐1,2,4‐(Me3C)3C5H2]2U[η2‐C2Ph2] (2). Based on density functional theory (DFT) results the 5f orbital contributions to the bonding within the metallacyclopropene U‐(η2‐C=C) moiety increases significantly compared to the related ThIV compound [η5‐1,2,4‐(Me3C)3C5H2]2Th[η2‐C2Ph2], which also results in more covalent bonds between the [η5‐1,2,4‐(Me3C)3C5H2]2U2+ and [η2‐C2Ph2]2− fragments. Although the thorium and uranium complexes are structurally closely related, different reaction patterns are therefore observed. For example, 2 reacts as a masked synthon for the low‐valent uranium(II) metallocene [η5‐1,2,4‐(Me3C)3C5H2]2UII when reacted with Ph2E2 (E=S, Se), alkynes and a variety of hetero‐unsaturated molecules such as imines, ketazine, bipy, nitriles, organic azides, and azo derivatives. In contrast, five‐membered metallaheterocycles are accessible when 2 is treated with isothiocyanate, aldehydes, and ketones. [ABSTRACT FROM AUTHOR]

Significant orbital mixing is rare in lanthanide complexes because of the limited radial extent of the 4f orbitals, which results in a generally small stabilization due to 4f orbital interactions. Nevertheless, even a small amount of additional stabilization could enhance lanthanide separations. One lanthanide complex in which orbital mixing has been extensively studied both experimentally and computationally is cerocene, COT2Ce, where COT is cyclooctatetraene. This compound has a singlet ground state with a low-lying, triplet excited state. Previous fluorescence studies on trimethylsilyl-substituted cerocenes indicate the triplet state is 0.4 eV higher in energy than the singlet state. In addition, computational studies predict that the triplet is 0.3 to 1 eV higher in energy than the singlet. The synthesis of highly pure COT2Ce by Walter and Andersen allowed its physical properties to be accurately measured. Using these measurements, we evaluate the stabilization of the 4f orbitals using two, independent approaches. A Hubbard model is used to evaluate the stabilization of the ground state due to orbital mixing. This stabilization, which is also the singlet–triplet gap, is −0.29 eV using this model. This gap was also from the temperature independent paramagnetism of COT2Ce, which yielded a value of −0.32 eV. [ABSTRACT FROM AUTHOR]

A study was conducted to establish multiconfigurational, intermediate valent ground states in several methyl-substituted bipyridine complexes of bis(pentamethylcyclopentadienyl)ytterbium, [Cp.sub.2]*Yb ([Me.sub.x]-bipy). In contrast to [Cp.sub.2]*Yb(bipy) and other substituted-bipy complexes, the nature of both the ground state and the first excited state could be altered by changing the position of the methyl or dimethyl substitutions on the bipyridine rings.

Mesitylene is displaced by norbornene (NB) to form an agostic intermediate in which NB has acted as a bidentate ligand and is bound to the cationic Pd center via the [pi]-system and a [gamma]-agostic interaction with the syn hydrogen at C7. The NMR studies have shown that the insertion of NB in the agostic intermediate is the slow initiation step and the subsequent insertions are extremely fast and hence the slow chelate opening is the main limitation preventing a living polymerization.

The data obtained for ytterbium valence measurements were used to establish the partial ytterbium f-orbital occupancy and open-shell singlet formation of a variety of bipyridine and diazabutadiene adducts with decamethylytterbocene, [([C.sub.5][Me.sub.5]).sub.2]Yb, abbreviated as [Cp*.sub.2]Yb. The results obtained have significant implication to understand the chemical bonds in organolanthanide complexes and f-element chemistry as well as magnetic interactions in nanoparticles and devices.