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A general synthetic procedure to neutral homo- and heterobimetallic cage compounds exhibiting various structural motifs of the polypnictogen ligands starting from [Cp*Fe(η5-E5)] (E = P (1), As (2); Cp* = C5Me5) is reported. The impact of the implemented transition metal precursors {Cp′′′M} (M = Cr, Mn, Fe, Ni; Cp′′′ = 1,2,4-tBu3C5H2) emphasises the variability of the isolated complexes exhibiting a broad variety of structural motifs of the pnictogen ligands. Spectroscopic, crystallographic, and theoretical investigations provide insight into the structure of the partially unprecedented polypnictogen ligands. [ABSTRACT FROM AUTHOR]

Characterization of paramagnetic compounds, in particular regarding the detailed conformation and electronic structure, remains a challenge, and -- still today it often relies solely on the use of X-ray crystallography, thus limiting the access to electronic structure information. This is particularly true for lanthanide elements that are often associated with peculiar structural and electronic features in relation to their partially filled f-shell. Here, we develop a methodology based on the combined use of state-of-theart magnetic resonance spectroscopies (EPR and solid-state NMR) and computational approaches as well as magnetic susceptibility measurements to determine the electronic structure and geometry of a paramagnetic Yb(III) alkyl complex, Yb(III)[CH(SiMe3)2]3, a prototypical example, which contains notable structural features according to X-ray crystallography. Each of these techniques revealed specific information about the geometry and electronic structure of the complex. Taken together, both EPR and NMR, augmented by quantum chemical calculations, provide a detailed and complementary understanding of such paramagnetic compounds. In particular, the EPR and NMR signatures point to the presence of three-centre--two-electron Yb-γ-Me-β-Si secondary metal--ligand interactions in this otherwise tri-coordinate metal complex, similarly to its diamagnetic Lu analogues. The electronic structure of Yb(III) can be described as a single 4f13 configuration, while an unusually large crystal-field splitting results in a thermally isolated ground Kramers doublet. Furthermore, the computational data indicate that the Yb--carbon bond contains some p-character, reminiscent of the so-called a-H agostic interaction. [ABSTRACT FROM AUTHOR]

The Lewis base-supported uranium terminal imido metallocene [η5-1,2,4-(Me3Si)3C5H2]2UvN(p-tolyl) (dmap) (1) readily reacts with various small molecules such as internal alkynes, isothiocyanates, thioketones, amidates, organic nitriles and imines, chlorosilanes, copper iodide, diphenyl disulfide, organic azides and diazoalkane derivatives. For example, treatment of 1 with PhCuCCuCPh and PhNCS forms metallaheterocycles originating from a [2 + 2] cycloaddition to yield [η5-1-(p-tolyl)NC(Ph)vCHCvC(Ph) CH2Si(Me)2-2,4-(Me3Si)2C5H2][η5-1,2,4-(Me3Si)3C5H2]U (2) and [η5-1,2,4-(Me3Si)3C5H2]2U[N(p-tolyl)C (vNPh)S](dmap) (3), respectively. The reaction of 1 with the thioketone Ph2CS forms the known uranium sulfido complex [η5-1,2,4-(Me3Si)3C5H2]2US(dmap) (4), which reacts with a second molecule of Ph2CS to give the disulfido compound [η5-1,2,4-(Me3Si)3C5H2]2U(S2CPh2) (5). The imido moiety also promotes deprotonation reactions as illustrated in the reactions with the amide PhCONH(p-tolyl), the nitrile PhCH2CN and the imine (p-tolyl)2CvNH to form the bis-amidate [η5-1,2,4-(Me3Si)3C5H2]2U[OC(Ph)N(ptolyl)] 2 (7), and the iminato complexes [η5-1,2,4-(Me3Si)3C5H2]2U[N(p-tolyl)C(CH2Ph)vNH](NvCvCHPh) (8) and [η5-1,2,4-(Me3Si)3C5H2]2U[NH(p-tolyl)][NvC(p-tolyl)2] (9), respectively. Addition of PhSiH2Cl to 1 yields [η5-1,2,4-(Me3Si)3C5H2]2U(Cl)[N(p-tolyl)SiH2Ph] (10). In contrast, the uranium(V) imido complexes [η5-1,2,4-(Me3Si)3C5H2]2UvN(p-tolyl)(I) (11) and [η5-1,2,4-(Me3Si)3C5H2]2UvN(p-tolyl)(SPh) (12), may be isolated upon addition of CuI or Ph2S2 to 1, respectively. Uranium(VI) bis-imido metallocenes [η5-1,2,4-(Me3Si)3C5H2]2UvN(p-tolyl)(vNR) (R = p-tolyl (13), mesityl (14)) and [η5-1,2,4-(Me3Si)3C5H2]2UvN(ptolyl)[ vNNv(9-C13H8)] (15) are accessible from 1 on exposure to RN3 (R = p-tolyl, mesityl) and 9-diazofluorene, respectively. Complexes 2, 3, 5, and 7-15 were characterized by various spectroscopic techniques and, in addition, compounds 2, 3, 5, and 7-13 were structurally authenticated by single-crystal X-ray diffraction analyses. [ABSTRACT FROM AUTHOR]

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]

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]

A general synthetic procedure to neutral homo- and heterobimetallic cage compounds exhibiting various structural motifs of the polypnictogen ligands starting from [Cp*Fe(η 5 -E 5 )] (E = P (1), As (2); Cp* = C 5 Me 5 ) is reported. The impact of the implemented transition metal precursors {Cp'''M} (M = Cr, Mn, Fe, Ni; Cp''' = 1,2,4- t Bu 3 C 5 H 2 ) emphasises the variability of the isolated complexes exhibiting a broad variety of structural motifs of the pnictogen ligands. Spectroscopic, crystallographic, and theoretical investigations provide insight into the structure of the partially unprecedented polypnictogen ligands.

Halide exchange of (Cp 3tms ) 2 ThCl 2 ( 1 ; Cp 3tms = η 5 -1,2,4-(Me 3 Si) 3 C 5 H 2 ) with Me 3 SiI furnishes (Cp 3tms ) 2 ThI 2 ( 2 ), which is then reduced with potassium graphite (KC 8 ) in the presence of 2,2'-bipyridine to give the thorium bipyridyl metallocene (Cp 3tms ) 2 Th(bipy) ( 3 ) in good yield. Complex 3 was fully characterized and readily reacted with various small molecules. For example, 3 may serve as a synthetic equivalent for the (Cp 3tms ) 2 Th(II) fragment when exposed to CuI, Ph 2 S 2 , organic azides, and CS 2 . Moreover, upon the addition of thiobenzophenone Ph 2 CS, p -methylbenzaldehyde ( p -MeC 6 H 4 )CHO, benzophenone Ph 2 CO, amidate PhCONH( p -tolyl), seleno-ketone ( p , p '-dimethoxy), selenobenzophenone ( p -MeOPh) 2 CSe, di( p -tolyl)methanimine ( p -tolyl) 2 C═NH, 1,2-di(benzylidene)hydrazine (PhCH═N) 2 , and nitriles PhCN, PhCH 2 CN, and Ph 2 CHCN C-C coupling results to give (Cp 3tms ) 2 Th[(bipy)(Ph 2 CS)] ( 8 ), (Cp 3tms ) 2 Th[(bipy)( p -MePhCHO)] ( 9 ), (Cp 3tms ) 2 Th[(bipy)(Ph 2 CO)] ( 10 ), (Cp 3tms ) 2 Th[(bipy){( p -tolylNH)(Ph)CO}] ( 11 ), (Cp 3tms ) 2 Th[(bipy){( p -MeOPh) 2 CSe}] ( 12 ), (Cp 3tms ) 2 Th[(bipy){( p -tolyl) 2 CNH}] ( 13 ), (Cp 3tms ) 2 Th[(bipy)(PhCHNN═CHPh)] ( 14 ), (Cp 3tms ) 2 Th[(bipy)(PhCN)] ( 16 ), (Cp 3tms ) 2 Th[(bipy)(PhCH 2 CN)] ( 17 ), and (Cp 3tms ) 2 Th[(bipy)(Ph 2 CHCN)] ( 18 ), respectively. However, when thiazole is added to 3 , the dimeric sulfido complex [(Cp 3tms ) 2 Th] 2 [μ-(bipy)CH 2 NCHCHS] 2 ( 15 ) can be isolated. Moreover, the addition of isonitriles such as Me 3 CNC and PhCH 2 NC to 3 results in C-N bond cleavage and C-C coupling processes to form the thorium isocyanido amido complexes (Cp 3tms ) 2 Th[4-(Me 3 C)bipy](NC) ( 19 ) and (Cp 3tms ) 2 Th[4-(PhCH 2 )bipy](NC) ( 20 ), respectively. Nevertheless, upon exposure of 3 to (trimethylsilyl)diazomethane Me 3 SiCHN 2 , the bis-amido complex (Cp 3tms ) 2 Th[5,6-(Me 3 SiCH)bipy] ( 21 ), concomitant with N 2 release, is isolated.

Characterization of paramagnetic compounds, in particular regarding the detailed conformation and electronic structure, remains a challenge, and - still today it often relies solely on the use of X-ray crystallography, thus limiting the access to electronic structure information. This is particularly true for lanthanide elements that are often associated with peculiar structural and electronic features in relation to their partially filled f-shell. Here, we develop a methodology based on the combined use of state-of-the-art magnetic resonance spectroscopies (EPR and solid-state NMR) and computational approaches as well as magnetic susceptibility measurements to determine the electronic structure and geometry of a paramagnetic Yb(III) alkyl complex, Yb(III)[CH(SiMe 3 ) 2 ] 3 , a prototypical example, which contains notable structural features according to X-ray crystallography. Each of these techniques revealed specific information about the geometry and electronic structure of the complex. Taken together, both EPR and NMR, augmented by quantum chemical calculations, provide a detailed and complementary understanding of such paramagnetic compounds. In particular, the EPR and NMR signatures point to the presence of three-centre-two-electron Yb-γ-Me-β-Si secondary metal-ligand interactions in this otherwise tri-coordinate metal complex, similarly to its diamagnetic Lu analogues. The electronic structure of Yb(III) can be described as a single 4f 13 configuration, while an unusually large crystal-field splitting results in a thermally isolated ground Kramers doublet. Furthermore, the computational data indicate that the Yb-carbon bond contains some π-character, reminiscent of the so-called α-H agostic interaction.

The uranium metallacyclocumulene, [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 U(η 4 -C 4 Ph 2 ) (3) was isolated from the reaction mixture containing [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 UCl 2 (1), potassium graphite (KC 8 ) 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 [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 U(II) fragment in the presence of Ph 2 E 2 (E = S, Se) and Ph 3 CN 3 , 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 Ph 2 CS to 3 induces CS bond cleavage yielding the dithiolate complex [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 U[S 2 (C 12 H 5 Ph 5 )] (14). In contrast, the closely related, but sterically more encumbered uranium metallacyclocumulene [η 5 -1,2,4-(Me 3 Si) 3 C 5 H 2 ] 2 U(η 4 -C 4 Ph 2 ) (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.

The uranium bipyridyl metallocene, [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 U(bipy) ( 2 ), is readily accessible in good yield by adding potassium graphite (KC 8 ) to a mixture of [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 UCl 2 ( 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 [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 U(II) fragment in the presence of Ph 2 E 2 (E = S, Se), alkynes, and a variety of hetero-unsaturated molecules such as diazabutadienes, azine (Ph 2 C═N) 2 , o -benzoquinone, pyridine N -oxide, CS 2 , isothiocyanates, and organic azides. However, upon exposure of 2 to thio-ketone Ph 2 CS, aldehyde p -MePhCHO, ketone Ph 2 CO, imine PhCH═NPh, azine (PhCH═N) 2 , and nitrile PhCN, it may also promote C-C coupling reactions forming [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 U[(bipy)(Ph 2 CS)] ( 16 ), [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 U[(bipy)( p -MePhCHO)] ( 17 ), [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 U[(bipy)(Ph 2 CO)] ( 18 ), [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 U[(bipy)(PhCHNPh)] ( 19 ), [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 U[(bipy)(PhCHNN═CHPh)] ( 20 ), and [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 U[(N 2 C 10 H 7 C(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 [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 U(I)(bipy) ( 15 ).