Synthesis and crystal structure of [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene](isocyanato-κN)gold(I)

The title complex was synthesized by ligand metathesis from [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene]gold(I) chloride and sodium cyanate in anhydrous tetrahydrofuran and crystallized from toluene at 233 K as a neutral complex with the central Au atom di-coordinated by an N-heterocyclic carbene and an isocyanate, with a linear CAuNCO moiety.


Chemical context
Transition-metal complexes with N-heterocyclic carbene (NHC) ligands have been frequently used as ligands in inorganic and organometallic synthesis, chemical catalysis, and medicinal chemistry (Hopkinson et al. 2014;Collado et al., 2021).NHC complexes of gold are typically linear dicoordinate Au I complexes, however, square-planar Au III complexes are also known (Baron et al., 2017).The former, where the dicoordinate state of Au I is sterically and electronically stabilized by NHC ligands, have interesting bonding properties (Pyykko ¨, 2004) and are prospective as catalysts (Collado et al., 2021) and medicines (Dada et al., 2017).An important class of Au I compounds are those with pseudohalide anions, such as CN À , SCN À , N 3 À or NCO À .In the present work, we attempted to synthesize an Au I -cyanato complex, (IPr)AuOCN, where IPr = 1,3-bis(2,6-di-iso-propylphenyl)imidazol-2-ylidene, as no Au I -cyanato complex had been isolated and structurally characterized previously, while those of Cu and Ag are very rare (see Section 4).In the attempt, we reacted (IPr)AuCl with sodium cyanate in anhydrous THF, which yielded the title isocyanato complex (IPr)Au-N C O (1), as proven by X-ray crystallography.
The IR spectrum of 1 (ATR, Thermo Scientific Nicolet iS10 spectrometer) shows the asymmetric stretching frequency � NCO of 2234 cm À 1 , in good agreement with other isocyanate Au I complexes (see Section 4).

Supramolecular features
In the crystal, discrete molecules of 1 are oriented with their CAuNCO 'rods' roughly parallel to the crystallographic b axis, with no indication of �-� stacking.While di-coordinate Au I atoms (d 10 centers) often form attractive aurophilic Au� � �Au interactions, which play an important role in determining the solid-state structures of Au I complexes (Pyykko ¨, 1997), in the structure of 1 no such interactions occur, the closest Au� � �Au distance being 7.738 A ˚.This is probably due to effective shielding of the Au center by 2,6-di-iso-propylphenyl groups.The intermolecular hydrogen bond C2-H2� � �O1(x, y + 1, z) is relatively strong, with the distances C� � �O 3.127 (3), C-H 0.94 (3), H� � �O 2.25 (3) A ˚and C-H� � �O angle of 155 (2) � (Fig. 2).The asymmetric unit of 1 contains only one molecule.

Database survey
Structurally characterized cyanate complexes of Group 11 metals with M-O-C N core (M = Cu, Ag, Au) are very rare.In the literature, there are only six examples of copper cyanato complexes and only one example of a silver cyanato complex is known so far (CSD version 5.43, last update November 2023; Groom et al., 2016).Thus far, there is no example of an isolated and structurally characterized Au Icyanato complex in the literature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1.Atoms H2 and H3 were refined in an isotropic approximation.Other H atoms were treated as riding in idealized positions (for methyl groups, optimized by rotation about R-CH 3 bonds) with U iso (H) = 1.5U eq for methyl H atoms, or 1.2U eq (C) for the rest.

Special details
Experimental.One distinct cell was identified using APEX3 (Bruker, 2016).Six frame series were integrated and filtered for statistical outliers using SAINT (Bruker, 2016) then corrected for absorption by integration using SAINT/SADABS v2014/2 (Bruker, 2016) to sort, merge, and scale the combined data.No decay correction was applied.Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.Refinement.Structure was phased by intrinsic methods (Sheldrick, 2015a).Systematic conditions suggested the ambiguous space group.The space group choice was confirmed by successful convergence of the full-matrix leastsquares refinement on F 2 .The final map had no significant features.A final analysis of variance between observed and calculated structure factors showed little dependence on amplitude and resolution.

Figure 2
Figure 2 Crystal packing of 1 with hydrogen bonds shown as red dotted lines.Au atoms are shown in yellow, N in blue and O in red.H atoms except H2 and H3 are omitted for clarity.

Table 1
Experimental details.