Unlocking Structural Diversity in Gold(III) Hydrides: Unexpected Interplay of cis/trans-Influence on Stability, Insertion Chemistry, and NMR Chemical Shifts

Abstract

The synthesis of new families of stable or at least spectroscopically observable gold(III) hydride complexes is reported, including anionic cis-hydrido chloride, hydrido aryl, and cis-dihydride complexes. Reactions between (C^C)AuCl(PR3) and LiHBEt3 afford the first examples of gold(III) phosphino hydrides (C^C)AuH(PR3) (R = Me, Ph, p-tolyl; C^C = 4,4′-di-tert-butylbiphenyl-2,2′-diyl). The X-ray structure of (C^C)AuH(PMe3) was determined. LiHBEt3 reacts with (C^C)AuCl(py) to give [(C^C)Au(H)Cl]−, whereas (C^C)AuH(PR3) undergoes phosphine displacement, generating the dihydride [(C^C)AuH2]−. Monohydrido complexes hydroaurate dimethylacetylene dicarboxylate to give Z-vinyls. (C^N^C)Au pincer complexes give the first examples of gold(III) bridging hydrides. Stability, reactivity and bonding characteristics of Au(III)–H complexes crucially depend on the interplay between cis and trans-influence. Remarkably, these new gold(III) hydrides extend the range of observed NMR hydride shifts from δ −8.5 to +7 ppm. Relativistic DFT calculations show that the origin of this wide chemical shift variability as a function of the ligands depends on the different ordering and energy gap between “shielding” Au(dπ)-based orbitals and “deshielding” σ(Au–H)-type MOs, which are mixed to some extent upon inclusion of spin–orbit (SO) coupling. The resulting 1H hydride shifts correlate linearly with the DFT optimized Au–H distances and Au–H bond covalency. The effect of cis ligands follows a nearly inverse ordering to that of trans ligands. This study appears to be the first systematic delineation of cis ligand influence on M–H NMR shifts and provides the experimental evidence for the dramatic change of the 1H hydride shifts, including the sign change, upon mutual cis and trans ligand alternation.

Trans‐philicity (trans‐influence/trans‐effect) ladders for square planar platinum(II) complexes constructed by 35Cl NMR probe

“…Accurate linear correlations between σ SO ( 15 N) and the Au−N distances in a series of Au(I) complexes were also reported . Very recently, Rocchigiani et al employing detailed quantum‐chemical calculations and analysis including relativistic spin−orbit coupling effects established an excellent linear relationship between the computed Au−H bond distances and the hydride NMR chemical shifts for a series of Au(III) complexes.…”

“…Magnetic shielding tensors have been computed with the gauge‐including atomic orbitals DFT method, as implemented in the Gaussian09 series of programs. It is well established that relativistic and spin orbit effects besides influencing the NMR signal of the heavy atom (HA) itself (HAHA effect), the NMR chemical shifts of the light atoms (LA) bound to the HA center are affected as well (HALA effect) and therefore strongly contribute to computed isotropic magnetic shielding constants in Pt(II) coordination compounds . In this context, 35 Cl shielding constants were calculated by inclusion of scalar relativistic effects and switching on the DKH approximation as implemented in the Gaussian 09 program suite.…”

“…A chemical link between the structural altered paramagnetic contributions to the light atom NMR shielding constants and the energy and composition characteristics of M − L bonding was provided. More recently, Rocchigiani et al . performing relativistic DFT calculations at the 2c‐ZORA(SO)/PBE0‐XC/TZ2P level of theory on a series of trans ‐[HAu III (C 6 H 5 ) 2 L] q , cis ‐[HAu III (bph)L] q and cis ‐[HAu III (ppy)L] q (L = H 2 O, NO 3 − , F − , NCS − , py, NH 3 , Cl − , H 2 S, I − , SCN − , CN − , CO, C 6 F 5 − , PH 3 , Ph − , Me − , H − , and SiH 3 − ) complexes showed that the origin of the wide chemical shift variability of the ligands depends on the different ordering and energy gap between “shielding” Au(d π )‐based orbitals and “deshielding” σ (Au−H)‐type MOs.…”

“…and the catalytic activity of Pd(II)-and Pt(II)based catalysts. [5] Although there has been much experimental [1][2][3][4]6] and theoretical [7][8][9][10][11][12][13][14] work done on the overall trans-effect and the trans-influence, it has often proved difficult to produce a systematic set of data; hence, the proliferation of different series concerning the magnitude of the effect for various trans-ligands. The transeffect of a ligand in square planar d 8 complexes is evident in its overall effect on the rate of ligand substitutions, while the transinfluence is generally evident in changes in the metal-ligand bond length, IR frequencies, and NMR chemical shifts.…”

Stability andtransInfluence in Fluorinated Gold(I) Coordination Compounds

“…[13][14][15][16][17] If the atom of the ligand interacting directly with the metal center is an NMR active species, this technique becomes a powerful tool to get insights into this phenomenon. [18][19][20] Because gold(I) coordination compounds commonly exhibit linear geometries, they are ideal systems to study the trans influences among different ligands. [20,21] Given this background, we investigated the trans influence that anionic ligands exert over phosphorus atoms in gold phos-…”