Chlorido{N-[2-(diphenylphosphanyl)benzyl]-1-(pyridin-2-yl)methanamine-κP}gold(I)

In the title compound, [AuCl(C25H23N2P)], the AuI atom is in a typical almost linear coordination environment defined by phosphane P and Cl atoms [bond angle = 175.48 (4)°]. Helical supramolecular chains along the b axis and mediated by N—H⋯Cl hydrogen bonds feature in the crystal packing.

In the title compound, [AuCl(C 25 H 23 N 2 P)], the Au I atom is in a typical almost linear coordination environment defined by phosphane P and Cl atoms [bond angle = 175.48 (4) ]. Helical supramolecular chains along the b axis and mediated by N-HÁ Á ÁCl hydrogen bonds feature in the crystal packing.

Related literature
For previously published crystal structures of related P,N-type Au(I) complexes, see: Williams et al. (2007). For catalytic reactions of these types of complexes, see: Williams & Pretorius (2008). For related structures, see: Baenziger et al. (1976); Bellon et al. (1969). For the synthesis of the ligand, see: Shirakawa et al. (1997).

Comment
We have previously published crystal structure data regarding three related P,N type Au(I) complexes, two of which exhibited inter-and intra-molecular gold-gold interactions, as well as displaying differential gold binding affinity for the phosphorus and nitrogen atoms, respectively (Williams et al., 2007). These complexes were obtained as a part of our continued interest in the versatility and transition metal complexation of heteroditopic, multifunctional P,N-based ligands. We are especially interested in this class of compounds for their proven efficiency as catalysts in certain chemical reactions (Williams et al., 2008), as well as for their potential in medicinal applications, an aspect which has not received much attention in literature..
As a part of this on-going study, we have prepared an amino-phosphine ligand (II) from 2-(diphenylphosphanyl)benzaldehyde as starting material (I), proceeding via the Schiff base which is reduced to amine (II).
This P,N product formed the crystalline title Au(I) complex (III) from a saturated chloroform solution. This complex is of particular interest as the two N atoms should in theory have different gold binding affinities due to the difference in the state of their hybridization (sp 2 vs sp 3 ), in keeping with previously published results (Williams, et al., 2007).
The title compound (III), Fig. 1, crystallizes in the monoclinic space group P2 1 /c. The crystal packing is stabilized by weak intra-molecular N-H···Cl interactions (Fig. 2). The coordination at the gold metal centre showed a virtually linear P-Au-Cl system (bond angle of 175.48 (4)°) as is common for two-coordinate Au(I) compounds. The Au-P distance of 2.241 (1) Å compares favourably to the Au-P distance in the similar (triphenylphosphine)gold(I) chloride structure of 2.235 (3) Å (Baenziger et al., 1976), but is shorter than the corresponding bond distance in the related (triphenylphosphine)gold(I) cyanide of 2.27 (1) Å (Bellon et al., 1969). As expected, the Au-Cl distance of 2.292 (1) Å compares well with that observed for (triphenylphosphine)gold(I) chloride at 2.279 (3) Å.

Experimental
The ligand (II) was synthesized in a similar manner to a literature procedure (Shirakawa et al., 1997) and the title compound was prepared as per previously described methods (Williams et al., 2007).
The amino-phosphine ligand (II) employed in this study was prepared from the 2-(diphenylphosphanyl)benzaldehyde starting material (I). The synthesis involved reacting (I) (300 mg, 0.689 mmol) with 1.5 equivalents of 2-(aminomethyl)pyridine (0.106 ml, 1.033 mmol) in toluene (15 ml) as solvent. The reaction mixture was stirred under reflux (oil bath temperature 140-150 °C) for 5 h, after which the solvent was removed in vacuo. The intermediate imino-phosphine product was dissolved in dried MeOH (10 ml). NaBH 4 (3 equivalents) was added and the reaction mixture stirred at room temperature for 15 h. The reduction reaction was quenched by the addition of deionized H 2 O, and the mixture was extracted with H 2 O and DCM and the resultant organic phase dried over Na 2 SO 4 . Solids were removed via filtration and the solvent supplementary materials sup-2 removed in vacuo. The pure amino-phosphine ligand (II) was recovered in high yield (85%) after bulb-to-bulb vacuum distillation.
Amino-phosphine ligand (II) (120 mg, 0.314 mmol) was dissolved in 20 mL of diethyl ether. To this solution were added 0.95 equivalents of (THT)AuCl (96 mg, 0.298 mmol) dissolved in 2 mL of chloroform. The (THT)AuCl solution was slowly added to the ligand solution and the mixture stirred at room temperature for 5 minutes. The solvent was evaporated in vacuo to ca 5 ml and the white, powdered product (III) was precipitated from the solution by the addition of 10 ml cold hexane (x3). Colourless monoclinic crystals were grown from a chloroform solution of the product. Yield 108 mg, 56%.

Refinement
The H atoms were positioned geometrically and allowed to ride on their respective parent atoms, with C-H = 0.93 (Ar-H) or 0.97 (CH 2 ) Å, and with U eq = 1.2U eq (C). The amine-H atom was refined. The maximum and minimum residual electron density peaks of 1.96 and 1.30 eÅ -3 , respectively, were located 0.88 Å and 0.76 Å from the Au1 atom. Fig. 1. Molecular structure of the title compound drawn with dispacement ellipsoids at the 50% probability level. Hydrogen atoms have been omitted for clarity.