Photochemical Synthesis of Transition Metal-Capped Uranium(VI) Nitride Complexes

State Key Laboratory of Coordination Chemistry, Jiangsu Key Laboratory of Advanced Organic Materials, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China LPCNO, CNRS & INSA, Université Paul Sabatier, 135 Avenue de Rangueil, 31077 Toulouse, France School of Medicine & Holistic Integrative Medicine, Nanjing University of Chinese Medicine, Nanjing 210023, China State Key Laboratory of Radiation Medicine and Protection, School for Radiological and interdisciplinary Sciences (RAD-X) and Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, Soochow University, Suzhou, China


Experimental Procedure
General Procedure: All manipulations were performed under an atmosphere of argon or nitrogen using standard Schlenk techniques or in a glovebox. Commercially available chemicals were used as received without further purification. The solvents were obtained by passing through a Solve Purer G5 (MIKROUNA) solvent purification system and further dried over 4 Å molecular sieves.
THF-d8 was dried over Na/K and stored under an Ar or N2 atmosphere prior to use. Nuclear magnetic resonance spectroscopy was performed using a Bruker AVIII-400 ( 1 H 400 MHz; 13 C{ 1 H} 101 MHz; 31 P{ 1 H} 162 MHz) spectrometer at room temperature (RT). The 1 H and 13 C{ 1 H} NMR chemical shifts (δ) are relative to tetramethylsilane, and 31 P{ 1 H} NMR chemical shifts are relative to 85% H3PO4. Absolute values of the coupling constants are provided in Hertz (Hz). Multiplicities are abbreviated as singlet (s), doublet (d), triplet (t), multiplet (m), and broad (br). Magnetic susceptibility measurements on crystalline samples were performed using a Quantum Design SQUID VSM magnetometer from 300 to 1.8 K under an external magnetic field of 1000 Oe. The sample was added to a pre-weighed SQUID capsule in a glovebox. The capsule was then sealed, weighed, and transferred to the SQUID cavity for the magnetic measurement. All magnetic data were corrected for the diamagnetic contributions of the sample holder and of the core diamagnetism of the samples using Pascal's constant. 1 Elemental analyses (C, H, N) were performed on a Vario EL III elemental analyzer at the Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences. Complex 1 was prepared according to previously reported procedure. 2
The solvents were removed under reduced pressure and the residues were extracted with toluene.
The mixture was filtered and the filtrate was concentrated to 0.5 mL and placed at RT for 48 h, brown crystals of 5a suitable for X-ray diffraction were obtained (21 mg, 65%). Brown crystals of 4b were obtained following the same procedure by exposing a THF solution of complex 5b (41 mg, 0.025 mmol, 1 equiv.) to UV light for 1 days (23 mg, 58%).

Method B:
A solution of complex 3a (59 mg, 0.05 mmol, 1 equiv.) in THF (5 mL) was transferred into a Schlenk tube under an atmosphere of nitrogen and then irradiated with a 40 W UV lamp for 4 days.
The mixture was filtered and the filtrate was concentrated to 0.5 mL and placed at RT for 48 h, brown crystals of 5a suitable for X-ray diffraction were obtained (24 mg, 38%). Brown crystals of 5b were obtained using the same procedure by exposing a THF solution of complex 3b (68 mg, 0.05 mmol, 1 equiv.) to UV light for 2 days (25 mg, 32%).

Protonation of complexes 4 and 5 with acid
An excess of pyridine hydrochloride (10.7 mg, 0.093 mmol, 25 equiv.) was added to a brown solution of 4a (5.0 mg, 0.0037 mmol, 1 equiv.) in THF (1 ml). The mixture was stirred at RT overnight, affording a pale-yellow solution and a white precipitate. The supernatant was removed and the solid was washed three times with 1.0 mL of THF. The solid was dried under vacuum. The amount of ammonia was evaluated by quantitative 1 H NMR with dibromomethane as an internal standard. The NH4Cl was formed in 73% yield (Fig. S9).
An excess of pyridine hydrochloride (9.0 mg, 0.078 mmol, 25 equiv.) was added to a brown solution of 4b (5.0 mg, 0.0031 mmol, 1 equiv.) in THF (1 ml). The mixture was stirred at RT overnight, affording a pale-yellow solution with a white precipitate. The supernatant was removed and the solid was washed three times with 1.0 mL of THF. The solid was dried under vacuum. The amount of ammonia was evaluated by quantitative 1 H NMR with dibromomethane as an internal standard. The NH4Cl was formed in 82% yield (Fig. S10).
An excess of pyridine hydrochloride (22.5 mg, 0.13 mmol, 50 equiv.) was added to a brown solution of 5a (5.0 mg, 0.0039 mmol, 1 equiv.) in THF (1 ml). The mixture was stirred at RT overnight, affording a pale-yellow solution with a white precipitate. The supernatant was removed and the solid was washed three times with 1.0 mL of THF. The solid was dried under vacuum. The amount of ammonia was measured by quantitative 1 H NMR with dibromomethane as an internal standard. The NH4Cl was formed in 75% yield (Fig. S11).
An excess of pyridine hydrochloride (18.6 mg, 0.13 mmol, 50 equiv.) was added to a brown solution of 5b (5.0 mg, 0.0032 mmol, 1 equiv.) in THF (1 ml). The mixture was stirred at RT overnight, affording a pale-yellow solution with a white precipitate. The supernatant was removed and the solid was washed three times with 1.0 mL of THF. The solid was dried under vacuum. The amount of ammonia was measured by quantitative 1 H NMR with dibromomethane as an internal standard. The NH4Cl was formed in 68% yield (Fig. S12).

Reaction of complexes 4 and 5 with H2 and PyHCl
In an NMR tube, a brown solution of 4a (5.0 mg, 0.0037 mmol, 1 equiv.) in 0.5 ml of THF-d8 was frozen and degassed three times then exposed to 1 atm of H2 at RT.  S13).
In an NMR tube, a brown solution of 4b (5.0 mg, 0.0031 mmol, 1 equiv.) in 0.5 ml of THF-d8 was frozen and degassed three times and exposed to 1 atm of H2 at RT. The NMR tube was closed and In an NMR tube, a brown solution of 5a (5.0 mg, 0.0039 mmol, 1 equiv.) in 0.5 ml of THF-d8 was frozen and degassed three times and exposed to 1 atm of H2 at RT. The NMR tube was closed and In an NMR tube, a brown solution of 5b (5.0 mg, 0.0032 mmol, 1 equiv.) in 0.5 ml of THF-d8 was frozen and degassed three times and exposed to 1 atm of H2 at RT. The NMR tube was closed and  Fig. S1. The 1 H NMR (THF-d8, 400 MHz) spectrum of complex 2a.

X-ray crystallographic analysis
The crystallographic data were collected using a Bruker APEX-II CCD area detector with a radiation source of Ga(K) (1.34139 Å) or Mo(K) (0.71073 Å). Multi-scan or empirical absorption corrections (SADABS) were applied. The structures were solved using Patterson methods, expanded using difference Fourier syntheses, and refined using full-matrix least squares fitting on F 2 using the Bruker SHELXTL-2014 program package. 3,4 All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were introduced at their geometric positions and refined as riding atoms. In complexes 3a and 3b, the restraint (SIMU) was employed to refine the disordered N atoms.

Theoretical Calculations
All calculations were performed using Gaussian09 suite of programs 5 using the Becke's 3-parameter hybrid functional 6 combined with the non-local correlation functional provided by Perdew/Wang. 7 The U, Ir, Rh, Cl and P atoms were represented with a small-core Stuttgart-Dresden relativistic effective core potential associated with their adapted basis set. [8][9][10] Additionally, the P and Cl basis set were augmented by a d-polarization function (P= 0.340 and C = 0.632) 11 to represent the valence orbitals. All the other atoms C, N and H were described with a 6-31G (d,p), double -ζ quality basis set. 12,13 The enthalpy energy was computed at T = 298 K in the gas phase.