¹H bridging and terminal hydride T₁ values. Comments on classical vs non‐classical hydride identification using T₁ criteria

Abstract

Hydride 'H T, values are reported for a selected series of ruthenium, iridium and platinum complexes. These T, values range from 6.9 to 0.05 s with the shortest value, 0.05 s, assigned to a complex containing both hydride and coordinated molecular hydrogen, i.e. 'M(H2)'. There are nuclear Overhauser enhancements arising both from protons on coordinated ligands and other hydride ligands. It is suggested that the molecular weight of the complex and the measurement conditions can be important factors for T,.

Synthesis and Application of Pyrrole-Based PNP–Ir Complexes to Catalytic Transfer Dehydrogenation of Cyclooctane

“…The 1 H NMR spectrum of the crude product in C 6 D 6 exhibited a characteristic hydride signal at δ H −22.62 ppm and C 2 v symmetrical pattern of the remaining signals. The long T 1 (3.95 s) also supported the conclusion that two hydrogen atoms existed as hydride ligand . Thus, we tentatively assigned this species as mononuclear dihydride complex 5a-Ir .…”

“…The X-ray crystallographic analysis confirmed the C 2 v symmetrical structure of 5b-Ir with two hydride ligands which could be located on the differential Fourier map (Figure ). The T 1 measurement (398 ms) also supported the hydridic feature of two hydrogen atoms . Two strong Ir–H vibrations at 2147 and 2170 cm –1 , which were assigned by DFT calculations, also supported the existence of two hydride ligands.…”

“…Two peaks in the differential Fourier map were assigned as dihydrogen ligand [H44–H45 0.97(5) Å] in 5b-Rh . Existence of two hydrogen atoms as dihydrogen ligand was confirmed with its short T 1 (66 ms). , …”

Binuclear rhodium hydride complexes: synthesis, structure, and reactivity

“…method at various temperatures, values of 7) were determined which gave a 7) minimum value of 560 and 651 ms for terminal and bridging hydrides, respectively, at 243 K (400 MHz). [36][37][38][39][40][41][42][43][44][45] Both values are well outside of the range expected for a molecular hydrogen complex and are consistent with a classical tetrahydride formulation. Further support for this conclusion comes from the absence of any HD coupling when complex 3 is dissolved in CeD6 and placed under 1 atm of HD.…”

Synthesis and Reactivity of the Labile Dihydrogen Complex [{MeC(CH2PPh2)3}Ir(H2)(H)2]BPh4

“…In the meanwhile, the T 1 of the other resonance decreases significantly without showing a minimum value even at the lowest temperature investigated (−110 °C) (trace B). Despite the possibility that the T 1 criterion to assess the nature of polyhydride complexes may lead to erroneous conclusions, 16a-c,21,22 one can safely conclude that the very short T 1 value at −110 °C (13 ms) points to the presence of an intact H 2 ligand in which an efficient dipole−dipole relaxation mechanism is at work. , …”