Reactivity of a triamidoamine terminal uranium(vi)-nitride with 3d-transition metal metallocenes

Reactions between [(TrenTIPS)UVI 
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Created by potrace 1.16, written by Peter Selinger 2001-2019
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 N] (1, TrenTIPS = {N(CH2CH2NSiPri3)3}3−) and [MII(η5-C5R5)2] (M/R = Cr/H, Mn/H, Fe/H, Ni/H) were intractable, but M/R = Co/H or Co/Me afforded [(TrenTIPS)UV 
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Created by potrace 1.16, written by Peter Selinger 2001-2019
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 N-(η1:η4-C5H5)CoI(η5-C5H5)] (2) and [(TrenTIPS)UIV–NH2] (3), respectively. For M/R = V/H [(TrenTIPS)UIV–NVIV(η5-C5H5)2] (4), was isolated. Complexes 2–4 evidence one-/two-electron uranium reductions, nucleophilic nitrides, and partial N-atom transfer.

area detectors using Cu Kα radiation (λ = 1.54184Å).Intensities were integrated from data recorded on narrow (1.0 °) frames by ω rotation.Cell parameters were refined from the observed positions of all strong reflections in each data set.Gaussian grid face-indexed absorption corrections with a beam profile correction were applied.The structures were solved by direct methods and all non-hydrogen atoms were refined by full-matrix least-squares on all unique F 2 values with anisotropic displacement parameters with exceptions noted in the respective cif files.Except where noted, Hydrogen atoms were refined with constrained geometries and riding thermal parameters.CrysAlisPro 2 was used for control and integration, SHELXS 3,4 was used for structure solution, and SHELXL 5 and Olex2 6 were employed for structure refinement.ORTEP-3 7 and POV-Ray 8 were employed for molecular graphics. 1H, 13 C{ 1 H}, and 29 Si{ 1 H} spectra were recorded on a Bruker 400 spectrometer operating at 400.1, 125.8, and 79.5 MHz, respectively; chemical shifts are quoted in ppm and are relative to tetramethylsilane ( 1 H, 13 C, 29 Si).FTIR spectra were recorded on a Bruker Alpha spectrometer with a Platinum-ATR module in the glovebox.UV/Vis/NIR spectra were recorded on a Perkin Elmer Lambda 750 spectrometer where data were collected in 1mm path length cuvettes and were run versus the appropriate reference solvent.Variable-temperature magnetic moment data were recorded in an applied direct current (DC) field of 0.1 or 0.5 Tesla on a Quantum Design MPMS3 superconducting quantum interference device magnetometer using recrystallised powdered samples.Samples were carefully checked for purity and data reproducibility between independently prepared batches.
Samples were crushed with a mortar and pestle under an argon atmosphere and immobilised in an eicosane matrix within a borosilicate glass NMR tube to prevent sample reorientation during measurements.The tube was flame-sealed under dynamic vacuum (1x10 -3 mbar) to a length of approximately 3 cm and mounted in the centre of a drinking straw, with the straw fixed to the end of an MPMS 3 sample rod.Care was taken to ensure complete thermalisation of the sample before each data point was measured by employing delays at each temperature point and the sample was held at 1.8 K for 60 minutes before isothermal magnetisation measurements to account for slow thermal equilibration of the sample.Diamagnetic corrections were applied using tabulated Pascal constants and measurements were corrected for the effect of the blank sample holders (flame sealed Wilmad NMR tube and straw) and eicosane matrix.Elemental microanalyses were carried out by Mr Martin Jennings at the Micro Analytical Laboratory, Department of Chemistry, University of Manchester.

Attempted Reactions of 1 with [M II (h 5 -C5H5)2] (M = Cr, Mn, Fe, and Ni)
Cr: To a Schlenk flask was added a solid mixture of 1 (0.35 g, 0.40 mmol) and freshly sublimed [Cr II (h 5 -C5H5)2] (0.073 g, 0.40 mmol).At -78 °C, toluene (20 mL) was added, and the solution was allowed to warm to room temperature before being stirred for 16 hours.Volatiles were removed in vacuo to afford a yellow-brown solid.Despite exhaustive attempts, an isolable product could not be obtained. 1H NMR spectroscopic analysis of the solid (C6D6, 298 K) exhibited multiple resonances across the range δ +32 to -14 ppm.
Mn: To a Schlenk flask was added a solid mixture of 1 (0.35 g, 0.40 mmol) and freshly sublimed [Mn II (h 5 -C5H5)2] (0.074 g, 0.40 mmol).At -78 °C, toluene (20 mL) was added, and the solution was allowed to warm to room temperature before being stirred for 16 hours.Volatiles were removed in vacuo to afford a brown solid.Despite exhaustive attempts, an isolable product could not be obtained. 1H NMR spectroscopic analysis of the solid (C6D6, 298 K) exhibited multiple resonances across the range δ +28 to -6 ppm.
Fe: To a Schlenk flask was added a solid mixture of 1 (0.35 g, 0.40 mmol) and freshly sublimed [Fe II (h 5 -C5H5)2] (0.074 g, 0.40 mmol).At -78 °C, toluene (20 mL) was added, and the solution was allowed to warm to room temperature before being stirred for 16 hours.Volatiles were removed in vacuo to afford a brown solid.Despite exhaustive attempts, an isolable product could not be obtained.Ni: To a Schlenk flask was added a solid mixture of 1 (0.35 g, 0.40 mmol) and freshly sublimed [Ni II (h 5 -C5H5)2] (0.076 g, 0.40 mmol).At -78 °C, toluene (20 mL) was added, and the solution was allowed to warm to room temperature before being stirred for 16 hours.Volatiles were removed in vacuo to afford a brown solid.Despite exhaustive attempts, an isolable product could not be obtained. 1H NMR spectroscopic analysis of the solid (C6D6, 298 K) exhibited multiple resonances across the range δ +28 to -38 ppm.

Preparation of [(Tren TIPS )U V =N-(h 1 :h 4 -C5H5)Co I (h 5 -C5H5)] (2)
To a Schlenk flask was added a solid mixture of 1 (0.35 g, 0.40 mmol) and freshly sublimed [Co II (h 5 -C5H5)2] (0.151 g, 0.80 mmol).At -78 °C, toluene (20 mL) was added, and the solution was allowed to warm to room temperature before being stirred for 16 hours.Volatiles were removed in vacuo to afford a dark red solid.Soluble residues were then extracted into hexanes (2 ´ 10 mL), and the resultant dark red solution was concentrated to approximately 5 mL and stored at 5 °C for 24 hours to afford 2 as red crystals, along with both crystalline 1 and [Co II (h 5 -C5H5)2].Despite exhaustive efforts, it was not possible to isolate 2 cleanly, with 1 H NMR spectroscopic analysis of the solid mixture revealing the three complexes present -1, 2, and [Co II (h 5 -C5H5)2] in varying ratios.Further analysis was conducted on this mixed component solid. 1

Reaction of 1 with [Co II (h 5 -C5Me5)2] and Isolation of [(Tren TIPS )U IV -NH2] (3)
To a Schlenk flask was added a solid mixture of 1 (0.35 g, 0.40 mmol) and freshly sublimed [Co II (h 5 -C5Me5)2] (0.132 g, 0.40 mmol).At -78 °C, toluene (20 mL) was added, and the solution was allowed to warm to room temperature before being stirred for 16 hours.Volatiles were removed in vacuo to afford a turquoise-blue solid.Soluble residues were then extracted into hexanes (2 ´ 10 mL), and the resultant solution was concentrated to approximately 5 mL and stored at 5 °C for 24 hours to afford 3 as emerald-green crystals.Characterisation data matched that previously reported. 9

Density Functional Theory Calculations
Complex 2 was geometry optimised without constraints and then a single point energy calculation was conducted on the optimised coordinates.Attempts to geometry optimise 4 resulted in the central N-atom of the U-N-V unit moving such that the U-N and V-N distances were both ~1.95 Å.Given the poor agreement of geometry optimised 4 to the experimentally observed crystal structure metrics, we used the crystal structure coordinates, froze the heavy atom positions, and geometry optimised the H-atom positions.Single point energy calculations were then performed on the resulting coordinates.
Complex 2 was computed with a doublet (1 unpaired electron) formulation, and given the results of the state-averaged complete active space self-consistent field (SA-CASSCF) calculations below we computed 4 with doublet (1 unpaired electron, 4') and quartet (3 unpaired electrons, 4'') spin-states to probe any possible U-V antiferromagnetic coupling.The calculations were performed using the Amsterdam Density Functional (ADF) suite version 2017 with standard convergence criteria. 10,11The DFT calculations employed Slater type orbital (STO) triple-ζ-plus polarisation all-electron basis sets (from the Dirac and ZORA/TZP database of the ADF suite).Scalar relativistic approaches (spin-orbit neglected) were used within the ZORA Hamiltonian [12][13][14] for the inclusion of relativistic effects and the local density approximation (LDA) with the correlation potential due to Vosko et al was used in all of the calculations. 15Generalised gradient approximation (GGA) corrections were performed using the functionals of Becke and Perdew. 16,17Natural Bond Order (NBO) and Natural Localised Molecular Orbital (NLMO) analyses were carried out with NBO 6.0.19. 18The Quantum Theory of Atoms in Molecules analysis 19,20 was carried out within the ADF program.We quote Nalewajski-Mrozek bond orders since they reproduce expected bond multiplicities reliably in polar heavy atom structures whereas Mayer bond orders for polar bonds often do not conform with chemical intuition. 21e ADF-GUI (ADFview) was used to prepare the three-dimensional plots of the electron density.

State-Averaged Complete Active Space Self-Consistent Field Calculations
SA-CASSCF calculations were performed with OpenMolcas v21.06. 22Basis sets were exclusively of the ANO-RCC type, with VTZP quality for U, V and the bridging N atoms, VDZ quality for all other non-H atoms, and MB quality for all H atoms. [23][24][25] The DKH-2 relativistic Hamiltonian 26 and Cholesky decomposition of the two-electron integrals at a threshold of 10 -8 were employed.The starting materials contain U VI (5f 0 ) and V II (3d 3 ), but the distribution of oxidation states in 4 is unknown a priori.Preliminary state-averaged complete active space self-consistent field (SA-CASSCF) calculations with and active space of 3 electrons in 12 orbitals (3d and 5f) examining high spin (Stot = 3/2) and low spin (Stot = 1/2) multiplicities suggest that the ground state is dominated by U IV (5f 2 ) and V IV (3d 1 ) configurations.Hence, it appears that [V(Cp)2] has doubly-reduced [U(N)(Tren TIPS )] in this case.The 3d 1 configuration for V IV defines five SV = 1/2 roots in the basis of configuration state functions (CSFs) while the 5f 2 configuration for U IV defines 21 SU = 1 and 28 SU = 0 roots; this would lead to 105 Stot = 3/2 and 245 Stot = 1/2 roots excluding charge transfer (CT) excitations.However, it is likely that this excitation space will be polluted with ligand to metal CT, metal to ligand CT or intervalence CT states.Hence, we performed SA-CASSCF calculation restricted to the subspace defined by product of the 2 D term of V IV and the lowest-lying 3 H term of U IV , comprising 55 Stot = 3/2 and 55 Stot = 1/2 roots, and then mix the resulting states with spin-orbit (SO) coupling.We note, however, that due to covalency and crystal field splitting that the assignment of these roots to the 2 D⊗ 3 H space is only approximate.Indeed, the resulting states should include m K, m I, m H, m G and m F terms (where m = 4 for Stot = 3/2 and m = 2 for Stot = 1/2); however, upon projection of the wavefunction onto an angular momentum basis using irreducible spherical tensor methods, 27 only the m H, m G and m F terms were found.Hence, we then performed a CAS configuration interaction (CI) calculation for 105 Stot = 3/2 and 175 Stot = 1/2 roots (followed by SO coupling) using the optimised orbitals to attempt to capture the 3 H, 3 F, 3 P, 1 G and 1 D terms of U IV .Projection of the resulting wavefunctions yielded more components of the desired spectrum (Table S4), however even still the maximal angular momentum of the m K terms (Ltot = LV + LU = 2 + 5 = 7) is not realised.This indicates that the significant covalency and crystal field splitting of the 3d and 5f orbitals quenches the total orbital angular momentum of the complex.None-the-less, we can project the SO states onto an angular momentum basis to inspect the low-lying spectrum of 4 (Table S4).The ground Kramers doublet is dominated by Stot = 1/2 states, suggesting that the interaction between the V IV and U IV is antiferromagnetic.Clearly though, the states are very mixed in terms of angular momentum projections, which arises from non-trivial interplay between exchange coupling, crystal field splitting (covalency) and SO coupling effects.The ground Kramers doublet has easy axis anisotropy parallel to the U-V vector (Figure S33), and while some other doublets share this axis as one of their principal g-vectors, many do not and many show significant rhombicity.Hence, we have also reported the effective g-value along the U-V vector (gzz in Table S5).

1 H
NMR spectroscopic analysis of the solid (C6D6, 298 K) exhibited multiple resonances across the range δ +28 to -38 ppm.

Figure S16 .
Figure S16.UV/Vis/NIR spectrum of 4 (black line), and 2 obtained by a subtraction method (red

Figure S17 .
Figure S17.UV/Vis/NIR spectrum of 4 (black line), and 2 obtained by a subtraction method (red

Figure S22 .
Figure S22.X-band (9.38 GHz) EPR spectrum of a powdered sample of 4 at 15 K (black) and its

Figure S24 .
Figure S24.X-band (9.38 GHz) EPR spectrum of a powdered sample of 4 at 7 K (black line) and a

Figure S25 .
Figure S25.X-band (9.38 GHz) EPR spectrum of a powdered sample of 4 at 7 K (black line) and a

Figure S32 .
Figure S32.Illustration of the easy axis anisotropy of the Kramers doublet of 4.