Low-Coordinate Iron(II) Amido Half-Sandwich Complexes with Large Internal Magnetic Hyperfine Fields.

The half-sandwich complex [Cp'Fe{N(dipp)(SiMe3)}] (Fe-dipp; Cp' = 1,2,4-tri-tert-butylcyclopentadienyl and dipp = 2,6-diisopropylphenyl) and the mixed metallocene [Cp'Fe{(η5-C6H3iPr2)═N(SiMe3)}] (Fe-chd) formed in the reaction between [{Cp'Fe(µ-I)}2] and [Li{N(dipp)(SiMe3)}]2 were characterized by NMR spectroscopy and X-ray diffraction analysis. Fe-dipp complements the series of low-coordinate, quasi-linear iron amido half-sandwich complexes [Cp'Fe{N(tBu)(SiMe3)}] (Fe-tBu) and [Cp'Fe{N(SiMe3)2}] (Fe-tms) reported earlier, and all three compounds were characterized in the solid state by zero-field 57Fe Mössbauer spectroscopy and magnetic susceptibility measurements, confirming their S = 2 electronic ground state. Moreover, the Mössbauer absorption spectra reveal slow paramagnetic relaxation at low temperatures with large internal magnetic hyperfine fields of Bhf = 96.4 T (Fe-dipp, 20 K), Bhf = 101.3 T (Fe-tBu, 15 K), and Bhf = 96.9 T (Fe-tms, 20 K). The magnetic measurements further confirm that the presence of significant axial zero-field splitting and slow relaxation of magnetization is detected, which is revealed even in the absence of a static magnetic field in the case of Fe-tBu. Supplementary ab initio and density functional theory calculations were performed and support the experimental data.

Intrinsic reactivity of [η5-1,3-(Me3Si)2C5H3]2U(η4-C4Ph2) in small molecule activation.

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.

Small-Molecule Activation Mediated by [η5-1,3-(Me3Si)2C5H3]2U(bipy).

The uranium bipyridyl metallocene, [η5-1,3-(Me3Si)2C5H3]2U(bipy) (2), is readily accessible in good yield by adding potassium graphite (KC8) to a mixture of [η5-1,3-(Me3Si)2C5H3]2UCl2 (1) and 2,2'-bipyridine. Compound 2 was fully characterized and employed for small-molecule activation. It has been demonstrated that 2 may serve as a synthon for [η5-1,3-(Me3Si)2C5H3]2U(II) fragment in the presence of Ph2E2 (E = S, Se), alkynes, and a variety of hetero-unsaturated molecules such as diazabutadienes, azine (Ph2C═N)2, o-benzoquinone, pyridine N-oxide, CS2, isothiocyanates, and organic azides. However, upon exposure of 2 to thio-ketone Ph2CS, aldehyde p-MePhCHO, ketone Ph2CO, imine PhCH═NPh, azine (PhCH═N)2, and nitrile PhCN, it may also promote C-C coupling reactions forming [η5-1,3-(Me3Si)2C5H3]2U[(bipy)(Ph2CS)] (16), [η5-1,3-(Me3Si)2C5H3]2U[(bipy)(p-MePhCHO)] (17), [η5-1,3-(Me3Si)2C5H3]2U[(bipy)(Ph2CO)] (18), [η5-1,3-(Me3Si)2C5H3]2U[(bipy)(PhCHNPh)] (19), [η5-1,3-(Me3Si)2C5H3]2U[(bipy)(PhCHNN═CHPh)] (20), and [η5-1,3-(Me3Si)2C5H3]2U[(N2C10H7C(Ph)NH)] (22), respectively, in quantitative conversion. Furthermore, in the presence of CuI, a single-electron transfer (SET) process is observed to yield the uranium(III) iodide complex [η5-1,3-(Me3Si)2C5H3]2U(I)(bipy) (15).

Synthesis and characterisation of an enantiomerically pure scandium pentadienyl complex and its application in the polymerisation of rac-lactide.

The alkyl-functionalised scandium complex [(pdl*SiMe2NtBu)Sc(thf)(CH2SiMe3)] (2) was synthesised in enantiomerically pure form and characterised by NMR spectroscopy and X-ray diffraction analysis. Complex 2 features a chiral constrained geometry ligand derived from the natural compound (1R)-(-)-myrtenal, in which the pentadienyl (pdl*) fragment coordinates in η3:η2-allyl-en fashion to the scandium atom. Compound 2 catalyses the polymerisation of rac-lactide at 30 °C and 50 °C yielding amorphous poly(lactide) with slightly heterotactic enchainment (Pm = 0.36 and 0.37). In agreement with the data obtained from GPC and DSC measurements, a chain-end control mechanism is proposed with fast chain propagation relative to the initiation, which leads to broad molecular weight distributions (D ≈ 1.80) and higher than expected molecular weights. Furthermore, chain transfer processes are observed, but only small amounts of transesterification and racemisation occur. Kinetic studies reveal a second-order dependence in rac-lactide (monomer) concentration and a first-order dependence in the concentration of catalyst 2.

Synthesis and reactivity of the uranium phosphinidene metallocene [η5-1,3-(Me3Si)2C5H3]2U(P-2,4,6-iPr3C6H2)(OPMe3): influence of the coordinated Lewis base.

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.

Crystal structure of potassium tri-ethyl-hydridoborate ('superhydride').

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 inter-action, 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 + , -z + 1].

Reactivity studies involving a Lewis base supported terminal uranium phosphinidene metallocene [η5-1,3-(Me3C)2C5H3]2U([double bond, length as m-dash]P-2,4,6-iPr3C6H2)(OPMe3).

The Lewis base supported terminal uranium phosphinidene metallocene [η5-1,3-(Me3C)2C5H3]2U([double bond, length as m-dash]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[double bond, length as m-dash]P-2,4,6-iPr3C6H2)(OPMe3) (20) can be isolated in good yield.

Experimental evaluation of the stabilization of the COT orbitals by 4f orbitals in COT2Ce using a Hubbard model.

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.

Uranium versus Thorium: Synthesis and Reactivity of [η5 -1,2,4-(Me3 C)3 C5 H2 ]2 U[η2 -C2 Ph2 ].

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-(Me3 C)3 C5 H2 ]2 U=P-2,4,6-tBu3 C6 H2 (1) yields the stable uranium metallacyclopropene, [η5 -1,2,4-(Me3 C)3 C5 H2 ]2 U[η2 -C2 Ph2 ] (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-(Me3 C)3 C5 H2 ]2 Th[η2 -C2 Ph2 ], which also results in more covalent bonds between the [η5 -1,2,4-(Me3 C)3 C5 H2 ]2 U2+ and [η2 -C2 Ph2 ]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-(Me3 C)3 C5 H2 ]2 UII when reacted with Ph2 E2 (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.

A Lewis Base Supported Terminal Uranium Phosphinidene Metallocene.

A Lewis base supported terminal uranium phosphinidene, [η5-1,3-(Me3C)2C5H3]2U(═P-2,4,6-tBu3C6H2)(OPMe3) (5), is isolated from the reaction of the uranium methyl chloride [η5-1,3-(Me3C)2C5H3]2U(Cl)Me (4) with 2,4,6-(Me3C)3C6H2PHK in toluene in the presence of Me3PO. Moreover, the reactivity of uranium phospinidene 5 toward a series of small molecules was comprehensively explored. While no reactivity of 5 with internal alkynes is observed attributed to steric hindrance, it readily reacts in good yields with various small molecules including isothiocyanates, aldehydes, imines, diazenes, carbodiimides, nitriles, isonitriles, and organic azides, yielding uranium sulfidos, oxidos, metallaheterocycles, and imido complexes.

Enantiomerically Pure Constrained Geometry Complexes of the Rare-Earth Metals Featuring a Dianionic N-Donor Functionalised Pentadienyl Ligand: Synthesis and Characterisation.

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 ClSiMe2 NHtBu, and the resulting pentadiene 2 was deprotonated with the Schlosser-type base KOtPen/nBuLi (tPen=CMe2 (CH2 Me)) to yield the dipotassium salt [K2 (pdl*SiMe2 NtBu)] (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 SiMe2 NtBu 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.

Experimental and Computational Studies on a Base-Free Terminal Uranium Phosphinidene Metallocene.

The first stable base-free terminal uranium phosphinidene metallocene is presented; and its structure and reactivity have been studied in detail and compared to that of the corresponding thorium derivative. Salt metathesis reaction of the methyl iodide uranium metallocene Cp'''2 U(I)Me (2, Cp'''=η5 -1,2,4-(Me3 C)3 C5 H2 ) with Mes*PHK (Mes*=2,4,6-(Me3 C)3 C6 H2 ) in THF yields the base-free terminal uranium phosphinidene metallocene, Cp'''2 U=PMes* (3). In addition, density functional theory (DFT) studies suggest substantial 5f orbital contributions to the bonding within the uranium phosphinidene [U]=PAr moiety, which results in a more covalent bonding between the [Cp'''2 U]2+ and [Mes*P]2- fragments than that for the related thorium derivative. This difference in bonding besides steric reasons causes different reactivity patterns for both molecules. Therefore, the uranium derivative 3 may act as a Cp'''2 U(II) synthon releasing the phosphinidene moiety (Mes*P:) when treated with alkynes or a variety of hetero-unsaturated molecules such as imines, thiazoles, ketazines, bipy, organic azides, diazene derivatives, ketones, and carbodiimides.

NH3 formation from N2 and H2 mediated by molecular tri-iron complexes.

Living systems carry out the reduction of N2 to ammonia (NH3) through a series of protonation and electron transfer steps under ambient conditions using the enzyme nitrogenase. In the chemical industry, the Haber-Bosch process hydrogenates N2 but requires high temperatures and pressures. Both processes rely on iron-based catalysts, but molecular iron complexes that promote the formation of NH3 on addition of H2 to N2 have remained difficult to devise. Here, we isolate the tri(iron)bis(nitrido) complex [(Cp'Fe)3(µ3-N)2] (in which Cp' = η5-1,2,4-(Me3C)3C5H2), which is prepared by reduction of [Cp'Fe(µ-I)]2 under an N2 atmosphere and comprises three iron centres bridged by two µ3-nitrido ligands. In solution, this complex reacts with H2 at ambient temperature (22 °C) and low pressure (1 or 4 bar) to form NH3. In the solid state, it is converted into the tri(iron)bis(imido) species, [(Cp'Fe)3(µ3-NH)2], by addition of H2 (10 bar) through an unusual solid-gas, single-crystal-to-single-crystal transformation. In solution, [(Cp'Fe)3(µ3-NH)2] further reacts with H2 or H+ to form NH3.

Non-oxidative Methane Coupling over Silica versus Silica-Supported Iron(II) Single Sites.

Non-oxidative CH4 coupling is promoted by silica with incorporated iron sites, but the role of these sites and their speciation under reaction conditions are poorly understood. Here, silica-supported iron(II) single sites, prepared via surface organometallic chemistry and stable at 1020 °C in vacuum, are shown to rapidly initiate CH4 coupling at 1000 °C, leading to 15-22 % hydrocarbons selectivity at 3-4 % conversion. During this process, iron reduces and forms carburized iron(0) nanoparticles. This reactivity contrasts with what is observed for (iron-free) partially dehydroxylated silica, that readily converts methane, albeit with low hydrocarbon selectivity and after an induction period. This study supports that iron sites facilitate faster initiation of radical reactions and tame the surface reactivity.

Pogo-Stick Iron and Cobalt Complexes: Synthesis, Structures, and Magnetic Properties.

The synthesis, structures, and magnetic properties of monomeric half-sandwich iron and cobalt imidazolin-2-iminato complexes have been comprehensively investigated. Salt metathesis reactions of [Cp'M(µ-I)]2 (1-M, M = Fe, Co; Cp' = η5-1,2,4-tri-tert-butylcyclopentadienyl) with [ImDippNLi]2 (ImDippN = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-iminato) furnishes the terminal half-sandwich compounds [Cp'M(NImDipp)] (2-M, M = Fe, Co), which can be regarded as models for elusive half-sandwich iron and cobalt imido complexes. X-ray diffraction analysis confirmed the structure motif of a one-legged piano stool. Complex 2-Co can also be prepared by an acid-base reaction between [Cp'Co{N(SiMe3)2}] (3-Co) and ImDippNH. The electronic and magnetic properties of 2-M and 3-Co were probed by 57Fe Mössbauer spectroscopy (M = Fe), X-band EPR spectroscopy (M = Co), and solid-state magnetic susceptibility measurements. In particular, the central metal atom adopts a high-spin (S = 2) state in 2-Fe, while the cobalt complex 2-Co represents a rare example of a Co(II) species with a coordination number different from six displaying a low-spin to high-spin spin-crossover (SCO) behavior. The experimental observations are complemented by DFT calculations.

Synthesis and molecular structure of enantiomerically pure pentadienyl complexes of the rare-earth metals.

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.

Experimental and computational studies on a three-membered diphosphido thorium metallaheterocycle [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2].

A three-membered thorium metallaheterocycle [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2] (4) is readily prepared besides H2 from [η5-1,3-(Me3C)2C5H3]2Th(PH-2,4,6-iPr3C6H2)2 (3) upon heating in toluene solution. Density functional theory (DFT) studies were performed to elucidate the 5f orbital contribution to the bonding within Th-(η2-P-P) revealing more covalent bonds between the [η5-1,3-(Me3C)2C5H3]2Th2+ and [η2-P2(2,4,6-iPr3C6H2)2]2- fragments than those in the related thorium metallacyclopropene. Consequently, distinctively different reactivity patterns emerge, e.g., while 4 reacts with pyridine derivatives such as 4-dimethyaminopyridnie (DMAP) and forms the DMAP adduct [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2](DMAP) (5), it may also act as a [η5-1,3-(Me3C)2C5H3]2Th(ii) synthon when reacted with bipy, Ph2S2 or Ph2Se2. Nevertheless, no reaction of complex 4 with alkynes is observed, but it reacts as a nucleophile towards nitriles and aldehydes resulting in five- or seven-membered metallaheterocycles, respectively. DFT computations provide some additional insights into the experimental observations.

A base-free terminal thorium phosphinidene metallocene and its reactivity toward selected organic molecules.

The stable base-free terminal phosphinidene thorium metallocene, [η5-1,2,4-(Me3C)3C5H2]2Th[double bond, length as m-dash]P-2,4,6-tBu3C6H2 (2), can be isolated from the reaction of the thorium dichloride complex [η5-1,2,4-(Me3C)3C5H2]2ThCl2 (1) with 2 equiv. of 2,4,6-(Me3C)3C6H2PHK in THF. The reactivity of 2 in the activation of various small organic molecules such as diselenides, phosphines, imines, ketones, phosphine oxides, thiazole, imidazole derivatives and amines was explored. For example, when complex 2 is treated with Ph2Se2, the phosphinidene is replaced, yielding diselenido compound [η5-1,2,4-(Me3C)3C5H2]2Th(SePh)2 (3). Moreover, E-H (E = P, N, C) bond activation occurs on exposure of 2 to 2,4,6-iPr3C6H2PH2, PhPH2, (p-tolyl)2C[double bond, length as m-dash]NH, 1-indanone, cyclohexanone, Me3PO, thiazole, 1-methylimidazole and p-toluidine, resulting in the phosphido complex [η5-1,2,4-(Me3C)3C5H2][η5,κ-C-1,2-(Me3C)2-4-(CH2CMe2)C5H2]Th(PH-2,4,6-iPr3C6H2) (4), the metallaheterocycle [η5-1,2,4-(Me3C)3C5H2]2Th(η2-P2Ph2) (5), the iminato phosphido complex [η5-1,2,4-(Me3C)3C5H2]2Th(PH-2,4,6-tBu3C6H2)[N[double bond, length as m-dash]C(p-tolyl)2] (6), the phosphido enolyl compound [η5-1,2,4-(Me3C)3C5H2]2Th(PH-2,4,6-tBu3C6H2)(κ-O-1-OC9H7) (7), the enolyl complex [η5-1,2,4-(Me3C)3C5H2][η5,κ-C-1,2-(Me3C)2-4-(CH2CMe2)C5H2]Th(κ-O-1-OC6H9) (8), the alkyl complex [η5-1,2,4-(Me3C)3C5H2][η5,κ-C-1,2-(Me3C)2-4-(CH2CMe2)C5H2]Th(κ-O,C-OPMe2CH2) (9), the phosphido thiazolyl complex [η5-1,2,4-(Me3C)3C5H2]2Th(PH-2,4,6-tBu3C6H2)(C3H2NS) (10), the bis-imidazolyl complex [η5-1,2,4-(Me3C)3C5H2]2Th[2-(1-MeC3H2N2)]2 (11), and the imido complex [η5-1,2,4-(Me3C)3C5H2]2Th[double bond, length as m-dash]N(p-tolyl) (12), respectively. Several spectroscopic techniques were employed for the characterisation of the new complexes 3-11, and in addition the solid-state molecular structures of compounds 3-6, 8-9 and 11 were further confirmed by X-ray diffraction analyses.

An Alkali-Metal Halide-Bridged Actinide Phosphinidiide Complex.

The salt metathesis reaction of the thorium methyl chloride complex [η5-1,3-(Me3C)2C5H3]2Th(Cl)Me (3) with 2,4,6-(Me3C)3C6H2PHK in benzene furnishes an alkali-metal halide-bridged phosphinidiide actinide metallocene, {[η5-1,3-(Me3C)2C5H3]2Th(═P-2,4,6- tBu3C6H2)(ClK)}2 (4), whose structure and reactivity was investigated in detail. On the basis of density functional theory (DFT) studies, the 5f orbitals in the model complex [η5-1,3-(Me3C)2C5H3]2Th(═P-2,4,6- tBu3C6H2) (4') contribute significantly to the bonding of the phosphinidene Th═P(2,4,6- tBu3C6H2) moiety. Furthermore, compared to the related thorium imido complex, the bonds between the [η5-1,3-(Me3C)3C5H2]2Th2+ and [P-2,4,6- tBu3C6H2]2- fragments are more covalent. The reactivity of compound 4 toward alkynes and a variety of heterounsaturated molecules such as nitriles, isonitriles, carbodiimides, imines, isothiocyanates, aldehydes, ketones, thiazoles, quinolines, organic azides, pyridines, and imidazoles, forming metallacycles, phospholes, imidos, metallaheterocycles, sulfidos, oxidos, pinacolates, pseudophosphinimidos, and phosphidos, was comprehensively studied. Moreover, complex 4 reacts with elemental selenium and PhSSPh, yielding selenido and sulfido compounds, respectively. DFT computations were performed to complement these experimental investigations and to provide further insights.