Unsymmetrical Coordination of Bipyridine in Three-Coordinate Gold(I) Complexes

Abstract

The unsymmetrical coordination of gold(I) by 2,2′bipyridine (bipy) in some planar, three-coordinate cations has been examined by crystallographic and computational studies. The salts [(Ph 3 P)Au(bipy)]XF 6 (X = P, As, Sb) form an isomorphic series in which the differences in Au−N distances range from 0.241(2) to 0.146(2) Å. A second polymorph of [(Ph 3 P)Au(bipy)]AsF 6 has also been found. Both polymorphs exhibit similar structures. The salts [(Et 3 P)Au(bipy)]XF 6 (X = P, As, Sb) form a second isostructural series. In this series the unsymmetrical coordination of the bipy ligand is maintained, but the gold ions are disordered over two unequally populated positions that produce very similar overall structures for the cations. Although many planar, threecoordinate gold(I) complexes are strongly luminescent, the salts [(R 3 P)-Au(bipy)]XF 6 (R = Ph or Et; X = P, As, Sb) are not luminescent as solids or in solution. Computational studies revealed that a fully symmetrical structure for [(Et 3 P)Au(bipy)] + is 7 kJ/mol higher in energy than the observed unsymmetrical structure and is best described as a transition state between the two limiting unsymmetrical geometries. The Au−N bonding has been examined by natural resonance theory (NRT) calculations using the "12 electron rule". The dominant Lewis structure is one with five lone pairs on Au and one bond to the P atom, which results in a saturated (12 electron) gold center and thereby inhibits the formation of any classical, 2 e − bonds between the gold and either of the bipy nitrogen atoms. The nitrogen atoms may instead donate a lone pair into an empty Au−P antibonding orbital, resulting in a three-center, four-electron (3c/4e) P−Au−N bond. The binuclear complex, [μ 2bipy(AuPPh 3 ) 2 ](PF 6 ) 2 , has also been prepared and shown to have an aurophillic interaction between the two gold ions, which are separated by 3.0747(3) Å. Despite the aurophillic interaction, this binuclear complex is not luminescent.

Between T and Y: Asymmetry in the Interaction of LAu(I) with Bipy and β‐Diiminate‐like Ligands

“…Phosphines (PH 3 , PMe 3 ) are on the edge, with intermediate measures of asymmetry (entries 4–9, 15, 16, 22, 23). For these, the gold hopping barrier is extremely low (∼1 kcal/mol), in agreement with earlier computational work [4b,9b] . In view of the ease of deformation of these species, a detailed comparison of asymmetry values is probably not warranted.…”

“…Based on the computational results of Luong, [4b] the asymmetry of bonding corresponds to a very soft deformation mode, which might result in high sensitivity to the choice of functional. Before executing a systematic evaluation of geometries, we therefore assessed the performance of a few popular functionals (TPSSh, [18] BP86, [19] B3LYP, [20] PBE1PBE [21] and M06 [22] ) in reproducing the degree of asymmetry of Au−N bonding (see the SI ).…”

Perhalophenyl Three-Coordinate Gold(I) Complexes as TADF Emitters: A Photophysical Study from Experimental and Computational Viewpoints

“…Similar distorted structures have been reported for threecoordinated Au(I) complexes with rigid diphosphanes and halides, 23 carbenes, 24 monoarylphosphanes, 25 or a bipyridine and aryl/alkylphosphane. 26 The strong angle and bond length distortions observed for the complexes leading to deviations from the C 2 symmetry do not arise from crystal packing effects. Full optimization of a single molecule of complex 2 also gives rise to a symmetry-broken coordination of the P-donor ligands to Au(I) (see Supporting Information).…”

Synthetic Control of Mitochondrial Dynamics: Developing Three-Coordinate Au(I) Probes for Perturbation of Mitochondria Structure and Function

“… 26 − 28 Bourrisou and co-workers have demonstrated catalytic capability with tricoordinate complexes due to their distinct reactivity. 27 , 29 − 32 We sought to explore the effect of these geometrically unique gold complexes on mitochondria morphology and functional consequences in normal or cancerous epithelial cells.…”

“…The development of gold-based small-molecules for biological use received a major boost following the FDA approval of auranofin for the treatment of rheumatoid arthritis . Over the past decade, several gold compounds have been synthesized as potential therapeutic agents for a plethora of diseases. − Their unique properties have alluded to unique behavior both in vivo and in vitro in comparison to other transition metal-based alternatives. − Despite the breadth of gold complex libraries developed thus far, the unique geometry of tricoordinated Au­(I) complexes − are uncommon and their therapeutic potential left untapped. − Bourrisou and co-workers have demonstrated catalytic capability with tricoordinate complexes due to their distinct reactivity. ,− We sought to explore the effect of these geometrically unique gold complexes on mitochondria morphology and functional consequences in normal or cancerous epithelial cells.…”