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Migratory insertion of diphenyldiazomethane into both metal-carbon bonds of the bis(alkyl) and bis(aryl) complexes (C(5)Me(5))(2)AnR(2) yields the first f-element bis(hydrazonato) complexes (C(5)Me(5))(2)An[eta(2)-(N,N')-R-N-N=CPh(2)](2) [An = Th, R = CH(3) (18), PhCH(2) (15), Ph (16); An = U, R = CH(3) (17), PhCH(2) (14)], which have been characterized by a combination of spectroscopy, electrochemistry, and X-ray crystallography. The two hydrazonato ligands adopt an eta(2)-coordination mode leading to 20-electron (for Th) and 22-electron (for U) complexes that have no transition-metal analogues. In fact, reaction of (C(5)H(5))(2)Zr(CH(3))(2) or (C(5)Me(5))(2)Hf(CH(3))(2) with diphenyldiazomethane is limited to the formation of the corresponding mono(hydrazonato) complex (C(5)R(5))(2)M[eta(2)-(N,N')-CH(3)-N-N=CPh(2)](CH(3)) (M = Zr, R = H or M = Hf, R = CH(3)). The difference in the reactivities of the group 4 metal complexes and the actinides was used as a unique platform for investigating in depth the role of 5f orbitals on the reactivity and bonding in actinide organometallic complexes. The electronic structure of the (C(5)H(5))(2)M[eta(2)-(N,N')-CH(3)-N-N=CH(2)](2) (M = Zr, Th, U) model complexes was studied using density functional theory (DFT) calculations and compared to experimental structural, electrochemical, and spectroscopic results. Whereas transition-metal bis(cyclopentadienyl) complexes are known to stabilize three ligands in the metallocene girdle to form saturated (C(5)H(5))(2)ML(3) species, in a bis(hydrazonato) system, a fourth ligand is coordinated to the metal center to give (C(5)H(5))(2)ML(4). DFT calculations have shown that 5f orbitals in the actinide complexes play a crucial role in stabilizing this fourth ligand by stabilizing both the sigma and pi electrons of the two eta(2)-coordinated hydrazonato ligands. In contrast, the stabilization of the hydrazonato ligands was found to be significantly less effective for the putative bis(hydrazonato) zirconium(IV) complex, yielding a higher energy structure. However, the difference in the reactivities of the group 4 metal and actinide complexes does not arise on thermodynamic grounds but is primarily of kinetic origin. Unfavorable steric factors have been ruled out as the sole influence to explain these different behaviors, and electronic factors were shown to govern the reactivity. For the actinides, both the C(5)H(5) and more realistic C(5)Me(5) ligands have been taken into account in computing the energy surface. The reaction profile for the C(5)Me(5) system differs from that with the C(5)H(5) ligand by a uniform shift of approximately 5 kcal/mol in the relative energies of the transition state and products. The insertion of a second diazoalkane molecule into the sole metal-carbon bond in the mono(hydrazonato) complexes involves a high energy barrier (approximately 20 kcal/mol) for the zirconium(IV) system, whereas the actinides can facilitate the approach of the diazoalkane by coordination (formation of an adduct) and its insertion into the An-C bond with a very low barrier on the potential energy surface.

4,4′-Di-tert-butyl-2,2′-bipyridyl (tBu2bpy) stabilizes the thermally sensitive [Lu(CH2SiMe3)3] unit, giving the isolable lutetium(III) (trimethylsilyl)methyl complex (tBu2bpy)Lu(CH2SiMe3)3 (4). This tris(alkyl) complex does not undergo alkane elimination, and it readily reacts with Ph3COH, H2N-2,6-iPr2-C6H3, H2N-2,4,6-tBu3-C6H2, and N,N′-dicyclohexylcarbodiimide (DCHCDI) to afford a variety of Lu(III) tris(alkoxide), tris(amide), mono(amide) bis(alkyl), and amidinate bis(alkyl) compounds. Reaction of the amide bis(alkyl) complex (tBu2bpy)Lu(NH-2,4,6-tBu3-C6H2)(CH2SiMe3)2 (7) with triphenylphosphine oxide gives (Ph3P═O)2Lu(NH-2,4,6-tBu3-C6H2)(CH2SiMe3)2 (9), showing that the bidentate tBu2bpy ligand can be displaced.

Lutetium alkyl complexes supported by a monoanionic, tridentate ligand system formed by the dearomatization and functionalization of a 2,2′:6′,2′′-terpyridine have been reacted with 2,4,6-triphenylaniline or the fluorinated anilines 4-F-C6H4NH2 and C6F5NH2 to give both terminal mono(amide) and bis(amide) lutetium(III) complexes, which have been fully characterized. Both [tBu3(2′-Me3SiCH2)tpy]Lu[NH(2,4,6-Ph3-C6H2)]2 (3) and [tBu3(2′-Me3SiCH2)tpy](C5Me5)Lu(NHC6F5) (7) have been structurally characterized. The fluorinated anilide complexes [tBu3(2′-Me3SiCH2)tpy](C5Me5)Lu(NHArF) (ArF = 4-F-C6H4 (6), C6F5 (7)) provide rare examples of lutetium organofluorine complexes, with 7 featuring an intramolecular F···H−C interaction that is present in both solid state and solution.

Thorium(IV) is often considered to show similar chemistry to Group IV transition metals. However, studies in our laboratory have shown that this generalization is incorrect. This report presents direct comparisons where the Th(IV) metallocene complexes (C5Me5)2ThR2 (R = CH3, Ph, CH2Ph) undergo unique chemical reactivity with pyridine, 2-picoline, pyridine N-oxide, 2-picoline N-oxide, and benzonitrile, while the Group IV metal analogues (C5R5)2M(CH3)2 (R = H, CH3; M = Zr, Hf) do not. We also report revised high-yield syntheses for the zirconium and hafnium starting materials, (C5H5)2MR2 (M = Zr, Hf; R = CH3, Ph, CH2Ph), using Grignard reagents for alkylation in addition to the X-ray crystal structures of (C5H5)2Hf(Ph)2 and (C5H5)2Hf(CH2Ph)2.

Reaction of (C5Me5)Lu(CH2SiMe3)2(THF) with pyridine results in the activation of an ortho C−H bond to form the corresponding η2-(N,C)-pyridyl complex with elimination of SiMe4. This is a rare example of pyridine metalation at a lanthanide metal center in the absence of a bent metallocene framework. The η2-(N,C)-pyridyl coordination mode was confirmed by X-ray crystallographic analysis. The pyridyl complex adopts a distorted square-pyramid geometry with the C5Me5 unit residing in the apical position and the pyridyl ligand and remaining ligands residing in the basal plane. Isotopic labeling studies suggest that C−H bond activation is consistent with a σ-bond metathesis mechanism.

Reaction of (C5Me5)2Th(CH3)2 with 2 equiv of NC-ArF gives the corresponding fluorinated thorium(IV) bis(ketimide) complexes (C5Me5)2Th[-N=C(CH3)(ArF)]2 (where ArF = 3-F-C6H4 (4), 4-F-C6H4 (5), 2-F-C6H4 (6), 3,5-F2-C6H3 (7), 3,4,5-F3-C6H2 (8), 2,6-F2-C6H3 (9), 2,4,6-F3-C6H2 (10), and C6F5 (11)). The complexes have been characterized by a combination of single-crystal X-ray diffraction, cyclic voltammetry and NMR, and UV-visible absorption and low-temperature luminescence spectroscopies. Density functional theory (DFT) and time-dependent DFT (TD-DFT) results are reported for complexes 5, 11, and (C5Me5)2Th[-N=C(Ph)2]2 (1) for comparison with experimental data and to guide in the interpretation of the spectroscopic results. The most significant structural perturbation imparted by the fluorine substitution in these complexes is a rotation of the fluorophenyl group (ArF) out of the plane defined by the N=C(CMe)(Cipso) fragment in complexes 9-11 when the ArF group possesses two ortho fluorine atoms. Excellent agreement is obtained between the optimized ground state DFT calculated structures and crystal structures for 11, which displays the distortion, as well as 5, which does not. In complexes 9-11, the out-of-plane rotation results in large interplanar angles (phi) between the planes formed by ketimide atoms N=C(CMe)(Cipso) and the ketimide aryl groups in the range phi = 49.1-88.8 degrees , while in complexes 5, 7, and 8, phi = 5.7-34.9 degrees . The large distortions in 9-11 are a consequence of an unfavorable steric interaction between one of the two ortho fluorine atoms and the methyl group [-N=C(CH3)] on the ketimide ligand. Excellent agreement is also observed between the experimental electronic spectroscopic data and the TD-DFT predictions that the two lowest lying singlet states are principally of nonbonding nitrogen p orbital to antibonding C=N pi* orbital (pN--pi*C=N or npi*) character, giving rise to moderately intense transitions in the mid-visible spectral region that are separated in energy by less than 0.1 eV. Low-temperature (77 K) luminescence from both singlet and triplet excited states are also observed for these complexes. Emission lifetime data at 77 K for the triplet states are in the range 50-400 mus. These emission spectral data also exhibit vibronic structure indicative of a small Franck-Condon distortion in the ketimide M-N=C(R1)(R2) linkage. Consistent with this vibronic structure, resonance enhanced Raman vibrational scattering is also observed for (C5Me5)2Th[-N=C(Ph)(CH2Ph)]2 (2) when exciting into the visible excited states. These systems represent rare examples of Th(IV) complexes that engender luminescence and resonance Raman spectral signatures.

Detailed cyclic voltammetric and UV−visible−near-infrared electronic absorption spectral data have been obtained for a series of pentamethylcyclopentadienyl complexes of uranium(IV) and thorium(IV) of the general formula (C5Me5)2An(L1)(L2), where L1, L2 = Cl, SO3CF3, CH3, CH2Ph, imido (N-2,4,6-tBu3C6H2), hydrazonato (η2(N,N‘)-RNNCPh2; R = CH3, CH2Ph, Ph), ketimido (−NC(Ph)(R); R = CH3, CH2Ph, Ph) ligands, and for the hexavalent uranium bis(imido) complex (C5Me5)2U(NPh)2. The electrochemical and spectroscopic behavior of the tetravalent uranium complexes falls cleanly into distinct categories based on the nature of L1 and L2. If both ligands are simple σ-donors (Cl, SO3CF3, CH3, CH2Ph), a reversible U(IV)/U(III) voltammetric wave is the only metal-based process observed, and it occurs between ∼−1.8 and −2.6 V vs [(C5H5)2Fe]+/0. If either L1 or L2 is a nitrogen-donor ligand (imido, hydrazonato, ketimido), then both a U(IV)/U(III) reduction wave and a U(V)/U(IV) oxidation wave are observed. The reduction ste...

Migratory insertion of benzonitrile into both An-C bonds of the bis(alkyl) and bis(aryl) complexes (C 5 Me 5 ) 2 AnR 2 yields the actinide ketimido complexes (C 5 Me 5 ) 2 An[-N=C(Ph)(R)] 2 (where An = Th, R = Ph, CH 2 Ph, CH 3 ;An = U, R = CH 2 Ph, CH 3 ) and provides a versatile method for the construction of electronically and sterically diverse ketimide ligands. The Th(IV) compounds represent the first examples of thorium ketimide complexes. The uranium complexes are surprisingly unreactive, and both the uranium and thorium bis(ketimido) complexes display unusual electronic structure properties. The combined chemical and physical properties of these complexes suggest a higher An-N bond order due to significant ligand-to-metal π-bonding in the actinide ketimido interactions and indicate that the f-electrons in mid-valent organouranium complexes might be far more involved in chemical bonding and reactivity than previously thought. We also report herein the structures of the known thorium and uranium complexes (C 5 Me 5 ) 2 Th(CH 2 Ph) 2 , (C 5 Me 5 ) 2 ThMe 2 , (C 5 Me 5 ) 2 U-(CH 2 Ph) 2 , and (C 5 Me 5 ) 2 UMe 2 .

The high-yield synthesis and spectroscopic and structural characterization of two new dimeric uranium(IV) and thorium(IV) halide complexes {[tBuNON]AnCl2}2 (An = U (1), Th (2)) supported by the dou...

A series of new diamidoether ligands of the form {[RN(SiMe2)]2O}2- (R = 2,4,6-Me3Ph, 2,6-iPr2Ph, 3,5-(CF3)2Ph), termed [RNON]2-, were prepared via dilithiation of the precursors H2[RNON], which were synthesized from the reaction of O(SiMe2Cl)2 with the appropriate lithium amide. Reaction of the previously reported Li2[tBuNON] with FeX3 (X=C1, Br) yields dinuclear halide-bridged iron(III) complexes that show an unusual quantum spin-admixed magnetic state. Complexes of iron(III) with the aryl-NON ligands, however, form rare lithium “ate” structures. {[RNON]Co}2 complexes (R=tBu, 2,4,6-Me3Ph) are dinuclear with amido bridges and Co-Co bonds. Each Co(II) centre is roughly trigonal monopyramidal. The analogous reactions with UO2C12(THF)3 give dark red powders. For R=tBu, {UO2[tBuNON]}2 complexes are formed that may have structures similar to {[RNON]Co}2.

The first lanthanide complex featuring a phosphinidene functional group has been prepared and isolated. Preliminary reactivity studies demonstrate that the lutetium(III) phosphinidene complex, [{2-(iPr2P)-4-Me-C6H3}2NLu]2(μ-PMes)2, behaves as a phospha-Wittig reagent with aldehydes and ketones to give the corresponding phosphaalkenes. Attempts to use the bulky phosphine H2P-2,4,6-tBu3-C6H2 to kinetically stabilize a terminal phosphinidene resulted in C−H activation of an ortho-tBu group and formation of a phosphaindole.

Lutetium(III)-bis(alkyl) and -tris(alkyl) fragments supported by either 2,2‘:6‘,2‘ ‘-terpyridine or 4,4‘,4‘ ‘-tri-tert-butyl-2,2‘:6‘,2‘ ‘-terpyridine are not stable and undergo facile 1,3-alkyl migration under ambient conditions resulting in dearomatization and ortho (2‘ or 6‘) functionalization of the terpyridyl ligand, clearly demonstrating that the terpyridyl ligand framework is not as innocent as previously thought.

Organometallic actinide bis(ketimide) complexes (C5Me5)2An[-N=C(Ph)(R)]2 (where R = Ph, Me, and CH2Ph) of thorium(IV) and uranium(IV) have recently been synthesized that exhibit chemical, structural, and spectroscopic (UV-Visible, resonance-enhanced Raman) evidence for unusual actinide-ligand bonding. [Da Re et al., J. Am. Chem. Soc., 2005, 127, 682; Jantunen et al., Organometallics, 2004, 23, 4682; Morris et al., Organometallics, 2004, 23, 5142.] Similar evidence has been observed for the group 4 analogue (C5H5)2Zr[-N=CPh2]2. [Da Re et al., J. Am. Chem. Soc., 2005, 127, 682.] These compounds have important implications for the development of new heavy-element systems that possess novel electronic and magnetic properties. Here, we have investigated M-ketimido bonding (M = Th, U, Zr), as well as the spectroscopic properties of the highly colored bis-ketimido complexes, using density functional theory (DFT). Photoelectron spectroscopy (PES) has been used to experimentally elucidate the ground-state electronic structure of the thorium and uranium systems. Careful examination of the ground-state electronic structure, as well as a detailed modeling of the photoelectron spectra, reveals similar bonding interactions between the thorium and uranium compounds. Using time-dependent DFT (TDDFT), we have assigned the bands in the previously reported UV-Visible spectra for (C5Me5)2Th[-N=CPh2]2, (C5Me5)2U[-N=CPh2]2, and (C5H5)2Zr[-N=CPh2]2. The low-energy transitions are attributed to ligand-localized N p --> C=N pi excitations. These excited states may be either localized on a single ketimido unit or may be of the ligand-ligand charge-transfer type. Higher-energy transitions are cyclopentadienyl pi --> CN pi or cyclopentadienyl pi --> phenyl pi in character. The lowest-energy excitation in the (C5Me5)2U[-N=Ph2]2 compound is attributed to f-f and metal-ligand charge-transfer transitions that are not available in the thorium and zirconium analogues. Geometry optimization and vibrational analysis of the lowest-energy triplet state of the zirconium and thorium compounds also aids in the assignment and understanding of the resonance-enhanced Raman data that has recently been reported. [Da Re et al., J. Am. Chem. Soc., 2005, 127, 682.].

Electronic absorption and resonance-enhanced Raman spectra for ketimido (azavinylidene) complexes of tetravalent uranium, (C(5)Me(5))(2)U[-N=C(Ph)(R)](2) (R = Ph, Me, and CH(2)Ph), have been recorded. The absorption spectra exhibit four broad bands between 13 000 and 24 000 cm(-1). The highest-energy band is assigned to the ketimido-localized p( perpendicular)(N)--pi(N=C) transition based on comparison to the spectra of (C(5)H(5))(2)Zr[-N=CPh(2)](2) and (C(5)Me(5))(2)Th[-N=CPh(2)](2). Upon excitation into any of these four absorption bands, the (C(5)Me(5))(2)U[-N=C(Ph)(R)](2) complexes exhibit resonance enhancement for several Raman bands attributable to vibrations of the ketimido ligands. Raman bands for both the symmetric and nominally asymmetric N=C stretching bands are resonantly enhanced upon excitation into the p( perpendicular)(N)--pi(N=C) absorption bands, indicating that the excited state is localized on a single ketimido ligand. Raman excitation profiles for (C(5)Me(5))(2)U[-N=CPh(2)](2) confirm that at least one of the lower-energy electronic absorption bands (E(max) approximately 16300 cm(-1)) is a charge-transfer transition between the U(IV) center and the ketimido ligand(s). The observations of both charge-transfer transitions and resonance enhancement of Raman vibrational bands are exceedingly rare for tetravalent actinide complexes and reflect the strong bonding interactions between the uranium 5f/6d orbitals and those on the ketimido ligands.

The high-yield synthesis, spectroscopic and structural determination of three new uranium(IV) and thorium(IV) “ate” complexes supported by three different diamido ether ligands are reported. The reaction of Li2[2,6-iPr2PhN(CH2CH2)]2O (Li2[DIPPNCOCN]) with 1 equiv. of UCl4 in THF generates [DIPPNCOCN]UCl3Li(THF)2 (1), while reaction in toluene/ether gives salt-free [DIPPNCOCN]UCl2·½C7H8 (2), which was identified by paramagnetically shifted 1H NMR. Reaction of 0.5 equiv. of {[tBuNON]UCl2}2 ([tBuNON] = [(CH3)3CN(Si(CH3)2)]2O2−) with 3.5 equiv. LiI in toluene and a minimal amount of THF results in [tBuNON]UI3Li(THF)2 (3) and is very similar in structure to 1. {[MesNON]ThCl3Li(THF)}2 (4), a dimeric complex with a Th2Li2Cl6 core, is prepared by reaction of Li2[2,4,6-Me3PhN(Si(CH3)2)]2O (Li2[MesNON]) with ThCl4 in THF. The analogous reaction in toluene did not yield the salt-free complex but rather a sterically crowded diligated compound, [MesNON]2Th (5), which was also structurally characterized. Complex 5 was prepared rationally by reacting 2 equiv. Li2[MesNON] with ThCl4 in toluene. The reaction of 1 and 3 with 2 equiv. of LiCH2Si(CH3)3 generates the stable, salt-free organoactinides [DIPPNCOCN]U(CH2Si(CH3)3)2 (6) and [tBuNON]U(CH2Si(CH3)3)2 (7). Complex 6 was structurally characterized. These reactions illustrate the viability of “ate” complexes as useful synthetic precursors.