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Uranium diazomethanediide complexes can be prepared and their synthesis, structure and reactivity were explored. Reaction of the uranium imido compound [η5‐1,2,4‐(Me3Si)3C5H2]2U=N(p‐tolyl)(dmap) (1) or [η5‐1,3‐(Me3C)2C5H3]2U=N(p‐tolyl)(dmap) (4) with Me3SiCHN2 cleanly yields the first isocyanoimido metal complexes [η5‐1,2,4‐(Me3Si)3C5H2]2U(=NNC)(μ‐CNN=)U(dmap)[η5‐1,2,4‐(Me3Si)3C5H2]2 (2) and {[η5‐1,3‐(Me3C)2C5H3]2U[μ‐(=NNC)]}6 (5), respectively. Both compounds exhibit remarkable thermal stability and were fully characterized. According to density functional theory (DFT) studies the bonding between the Cp2U2+ and [NNC]2− moieties is strongly polarized with a significant 5 f orbital contribution, which is also reflected in the reactivity of these complexes. For example, complex 5 acts as a nucleophile toward alkylsilyl halides and engages in a [2+2] cycloaddition with CS2, but no reaction occurs in the presence of internal alkynes. [ABSTRACT FROM AUTHOR]

We report the preparation of enantiomerically pure constrained geometry complexes (cgc) of the rare‐earth metals bearing a pentadienyl moiety (pdl) derived from the natural product (1R)‐(−)‐myrtenal. The potassium salt 1, [Kpdl*], was treated with ClSiMe2NHtBu, and the resulting pentadiene 2 was deprotonated with the Schlosser‐type base KOtPen/nBuLi (tPen=CMe2(CH2Me)) to yield the dipotassium salt [K2(pdl*SiMe2NtBu)] (3). However, 3 rearranges in THF solution to its isomer 3' by a 1,3‐H shift, which elongates the bridge between the pdl and SiMe2NtBu moieties by one CH2 unit. This is crucial for the successful formation of various monomeric C1‐ or dimeric C2‐symmetric rare‐earth cgc complexes with additional halide, tetraborohydride, amido and alkyl functionalities. All compounds have been extensively characterised by solid‐state X‐ray diffraction analysis, solution NMR spectroscopy and elemental analyses. [ABSTRACT FROM AUTHOR]

The enantiomerically pure pentadienyl (Pdl*) ligand derived from the natural product (1R)-(−)-myrtenal forms with MCl3 (M = La, Ce, Pr, and Nd) the corresponding homoleptic [(η5-U-Pdl*)3M compounds (1-M). These complexes were fully characterised by 1H NMR spectroscopy, elemental analyses and X-ray diffraction. They exhibit in solution and solid state idealized C3 symmetry, and their molecular structures also reveal that the Pdl* ligand adopts a U-conformation and coordinates exclusively with its less sterically encumbered face to the rare-earth metal atom. For the paramagnetic representatives an assignment of the 1H NMR resonances based on a simple dipolar model gave satisfactory results. [ABSTRACT FROM AUTHOR]

The half-sandwich complex [Cp′Fe(μ-I)]2 (1; Cp′ = η5-1,2,4-(Me3C)3C5H2) is cleaved when heated in toluene to form a cation–anion pair [{Cp′Fe(η6-toluene)}+{Cp′FeI2}−] (2), in which the two Fe(ii) atoms adopt different spin states, i.e., a low-spin (S = 0) and a high-spin (S = 2) configuration. Upon oxidation of 1 with C2H4I2, the thermally stable 15VE species [Cp′FeI2] (3) can be isolated, in which the Fe(iii) atom adopts an intermediate spin (S = 3/2) configuration. Complex 3 is an excellent starting material for further functionalizations and it reacts with Mg(CH2SiMe3)2 to form the unprecedented Fe(iii) (S = 3/2) bis(alkyl) complex [Cp′Fe(CH2SiMe3)2] (4). The respective spin states of complexes 2–4 are confirmed by single-crystal X-ray crystallography, zero-field 57Fe Mössbauer spectroscopy, and solid-state magnetic susceptibility measurements. In contrast to the related 14VE high-spin (S = 2) Fe(ii) alkyl species [Cp′FeCH(SiMe3)2], which resists the reaction with H2 as a consequence of a spin-induced reaction barrier, complex 4 reacts cleanly with H2 (8 bar) in cyclohexane to yield iron hydrides [{Cp′Fe}2(μ-H)3] (5) and [Cp′Fe(μ-H)2]2 (6) in a 1 : 4 ratio. However, when the hydrogenation of 4 is carried out in benzene, a green 19VE [Cp′Fe(η6-C6H6)] (A) intermediate is formed, which dimerizes to the bis(cyclohexadienyl)-bridged product [(Cp′Fe)2(μ2–η5:η5-C12H12)] (7). Further evidence for the intermediacy of [Cp′Fe(η6-C6H6)] (A) was gathered by X-band EPR and UV/vis spectroscopy. Interestingly, attempts to oxidize 7 with AgSbF6 proceeded via C–C bond cleavage instead of metal oxidation to form [Cp′Fe(C6H6)][SbF6] (8). [ABSTRACT FROM AUTHOR]

The synthesis of C2 symmetric enantiomerically pure open Ca and Sr metallocenes, [(η5-pdl*)2Ca(thf)] (1) and [(η5-pdl*)2Sr(thf)2] (2) (pdl* = dimethylnopadienyl) is described and these complexes were fully characterized. The solid state structures confirm that the pdl* ligands coordinate exclusively with the less sterically demanding site to the Ca and Sr atoms. These complexes are active catalysts for the controlled ring opening polymerization (ROP) of rac-lactide to give heterotactically enriched polylactides (PL) with narrow polydispersities (PDI = 1.29–1.31) and without adding further activators. [ABSTRACT FROM AUTHOR]

The synthesis, structure, and reactivity of a thorium metallacyclopentadiene were comprehensively studied. The reduction of (η5-C5Me5)2ThCl2 (1) with potassium graphite (KC8) in the presence of diphenylacetylene (PhC≡CPh) yields the first thorium metallacyclopentadiene complex (η5-C5Me5)2Th(η2-C4Ph4) (2). Density functional theory (DFT) studies suggest that the 5f orbitals are involved in the bonding of the metallacyclopentadiene Th–(η2-C=C–C=C) moiety. Compared to the thorium metallacyclopropene, complex 2 shows a distinctively different reactivity towards diazoalkanes and organic azides such as Me3SiCHN2, 9-diazofluorene and p-tolylN3, leading to the formation of the six-membered hydrazido complexes (η5-C5Me5)2Th[N(N=CHSiMe3)(C4Ph4)] (3) and (η5-C5Me5)2Th[N(N=C(C12H8))(C4Ph4)] (4) and the seven-membered bis(triazenido) complex (η5-C5Me5)2Th[N(N=N(p-tolyl))(C4Ph4)N(N=N(p-tolyl))] (5), respectively. [ABSTRACT FROM AUTHOR]

A series of monomelic mono(cyclopentadienyl) iron amido, phenoxo, and alkyl complexes were synthesized, and their structure and reactivity are presented. The iron(II) centers in these 14VE one-legged piano stool complexes are high spin (S = 2) in solid state and solution independent of solvent The silylamide compound [Cp'FeN(SiMe3)2] (2a, Cp' = 1,2,4-(Me3C)3C5H2) is an excellent starting material for the reaction with more acidic substrates such as phenols. Sterically encumbered phenols 2,6-(Me3C)2(4-R)C6H2OH (R = H, Me, and tBu) were investigated. In all cases monomeric iron phenoxo half-sandwich complexes [Cp'FeOR'] (4-R) are initially formed. Rearrangement of 4-R to the diamagnetic oxocyclohexadienyl complex [Cp'Fe(η5 -O=C6H2R'2R")] (5-R) is observed for 2(6-(Me3C)2(4-R)C6H2OH (R = H and Me) and the Gibbs free enthalpy of activation (ΔG‡) was determined. In contrast this rearrangement is inhibited when the 4-position is blocked by a tBu group. Removing the steric bulk from the 2,6-positions leads to the formation of a μ-phenoxo dimer, [Cp'Fe(μ-OC6H3tBu2-3,5)]2 (5). Density functional theory (DFT) was used to further elucidate the structure--reactivity relationship in these molecules. The one-legged piano stool anilido complex [Cp'Fe(NHC6H2tBu3 2,4,6)] (7) is not accessible via acid--base reaction between 2a and H2NC6H2tBu3-2,4,6, but can be prepared by conventional salt metathesis reaction from [Cp'FeI]2 and [Li(NHC6H2tBu3-2,4,6)(OEt2)]2. In contrast, reaction of 2a with Ph2NH yields the bimetallic [Cp'Fe(N,C-k¹,η5-C6H5NPh)Fe(N-k¹-NPh2)Cp'] (8) which combines two iron centers in the same oxidation state (+2), but different spin-states (S = 0 and S = 2) which is reflected in very different Cp(cent)--Fe distances of 1.68 and 2.04 A, respectively. A monomeric iron alkyl half-sandwich complex [Cp'FeCH(SiMe3)2] (9) was prepared that exhibits no reactivity toward H, C2H4 or N2O. This behavior might be rationalized by a spin-state induced reaction barrier. However, 9 reacts in the presence of CO to the iron acyl-complex [Cp'Fe(CO)2(C(O)CH(SiMe3)2)] (10) and with a CO/H2 mixture [Cp'Fe(CO)2]2 (II) and CH2(SiMe3)2 are formed. [ABSTRACT FROM AUTHOR]

The synthesis of [(1,2,4-tBu3C5H2)FeI]2, [Cp′FeI]2(1), and its reaction chemistry are described. Complex 1shows remarkable stability toward ligand redistribution in solution and gas-phase due to kinetic stabilization with respect to formation. In coordinating solvents the dimer is homolytically cleaved to form paramagnetic mono-solvate 16 valence-electron (VE) adducts [Cp′FeI(L)]. These solvent adducts are labile, and 1is re-established on exposure to dynamic vacuum. Complex 1was demonstrated to be a suitable synthon for [Cp′Fe]+transfer to Ir pincer complexes and successful η6-coordination of this fragment to the arene ring of κ1-metallated POCOP–iridium pincer complexes [(Cp′Fe)(POCOP)Ir(H)(I)] ([5]+) and [(Cp′Fe)(POCOP)Ir(C2H4)] ([7]+) (POCOP = C6H3-2,6-(OPtBu2)2) was accomplished. In these heterometallic organometallic complexes, the π- and σ-electrons of the POCOP-pincer phenyl anion are involved in η6- and κ1-coordination to iron(ii) and iridium(iii) and iridium(i), respectively. [Cp′Fe]+coordination alters the charge distribution in the (POCOP)Ir complex by inducing significant charge transfer from the POCOP aryl π-system to the [Cp′Fe]+fragment, and therefore yielding an electron-poor and more electrophilic iridium center. Density functional theory (DFT) calculations provide a detailed understanding of this effect. Preliminary catalytic studies show that [7]+is an active catalyst in transfer dehydrogenation between cyclooctane (COA) and tert-butyl ethylene (TBE). [ABSTRACT FROM AUTHOR]

The first preparations of half-open and open manganocenes were accomplished. Treatment of KPdl' (Pdl' = 2,4-(Me3C)2C5H5)) with [{(η5-Cp")Mn(thf)(μ-I)}2] (Cp" = 1,2,4-(Me3C)3C5H2) and MnI2(thf)2 resulted in the formation of [(η5-Cp")Mn(Pdl')] (2) and [(Pdl')2Mn] (4), respectively. Both compounds adopt a high-spin (S = 5/2) ground state. Maximum spin states are rather unusual for pentadienyl complexes, since these ligands generally stabilize transition metal complexes in their low-spin state. In addition, the electronic structure of 2 was compared to its closed analogue [(η5-Cp")Mn(η5-Cp')] (Cp' = 1,3-(Me3C)2C5H3), which also adopts the high-spin configuration because of steric hindrance destabilizing the electronically more favorable low-spin state. Reaction of KPdl' with [(C5H5)2Mn] yields the trimetallic compound [{(η5-Pdl')Mn(η5-C5H5)]}2Mn] (5) concomitant with the formation of 2,4,7,9-tetra-tert-butyl-1,3,7,9-decatetraene (Pdl'2), indicating reduction of two Mn atoms. Solid-state magnetic susceptibility studies and density functional theory computations suggest that the electronic structure in 5 is best described as two diamagnetic (S = 0) [(η5-Pdl')Mn(η5-C5H5)]- Mn(I) anions, each being coordinated to a central Mn(II) cation with a high-spin (S = 5/2) configuration. [ABSTRACT FROM AUTHOR]

The formation of thorium metallacyclopentadiene and metallacyclopropene complexes is significantly influenced by the steric and electronic properties of the internal alkyne employed during their syntheses. The reduction of (η5-C5Me5)2ThCl2 (2) with potassium graphite (KC8) or lithium in the presence of internal phenyl(alkyl)acetylenes (PhC≡CR) selectively yields the corresponding Cs-symmetric thorium metallacyclopentadienes (η5-C5Me5)2Th[η²-C(Ph)=C(R)C(Ph)=C(R)] (R = Me (4), iPr (5), C6H11 (6)), while the phenyl(silyl)acetylene PhC≡CSiHMe2 gives the C2v-symmetric metallacyclopentadiene (η5-C5Me5)2Th[η²-C(SiHMe2)=C(Ph)C(Ph)=C(SiHMe2)] (7). However, the sterically more encumbered acetylene derivative PhC≡CSiMe3 affords the chloro metallacyclopropene complex [(η5-C5Me5)2Th(η²-C2Ph(SiMe3))(Cl)][Li(EDM)2] (8), whereas Me3SiC≡CSiMe3 forms the chloro alkenyl complex [(η5-C5Me5)2Th[C(SiMe3)=CHSiMe3](Cl) (9), in which the chloro metallacyclopropene intermolecularly activates a C-H bond of the solvent (C7H8). Density functional theory (DFT) studies complement the experimental findings and rationalize the selectivity observed in the C-C bond formation. [ABSTRACT FROM AUTHOR]