Gold(I) Complexes

The complexes were synthesized by reaction of the respective phosphoryl anthracenes with [Me2SAuCl] in acetone. Displacement of the SMe2 donor afforded the gold(I) complexes [HAnPPh2(S)AuCl] (50), [HAnPⁱPr2(S)AuCl] (51), and [MeAnPPh2(S)AuCl] (52) (Scheme 3-30). All complexes were crystallized from acetone at –30°C. The obtained crystals were suitable for single crystal X-ray structure analysis.

Scheme 3-31: Synthesis of gold(I) complexes 50-52.

[HAnPPh2(S)AuCl] (50) crystallizes in the monoclinic space group P21/n. The typical linear S-Au-Cl fragment^[69] is not directed away from the anthracene moiety, but rather located behind it on the opposite side of the phenyl groups relative to the anthracene plane. This arrangement was also found in the complex [MeAnP(NEt2)2(S)AuCl] (24).

The S-Au-Cl fragment encloses an angle of 173.8°, which is nearly perfectly linear.

The S-Au bond distance measures 2.257 Å which is slightly shorter than corresponding S-Au bonds found in previous gold complexes of sulfur oxidized compounds. The tetrahedral geometry surrounding P1 is slightly distorted. The deformation of the anthracene moiety is moderately strong with folding and twist angles of 14.1° and 7.7°, respectively, which in fact indicates weaker deformation than observed for the mere ligand HAnPSPh2 (4).

Intermolecular interactions in the structure of 50 are limited to a single C-H^…π bond between a meta hydrogen atom of a phenyl substituent and a peripheral ring of the anthracene moiety which measures 2.818 Å at an angle of 53.8° to the ring plane (Figure 3-70, right).

The gold complex [HAnPⁱPr2(S)AuCl] (51) shows a different orientation of the S-Au-Cl fragment from the one observed in 50. While in 50, the torsion angle of the P=S bond to the anthracene plane measures 80°, it measures only 14.4° in the structure of 51.

Therewith it is nearly located in the anthracene plane, with both iso-propyl groups located on opposite side of the anthracene plane. This leads to an almost orthogonal orientation of the S-Au-Cl fragment to the anthracene plane.

Figure 3-70: left: crystal structure of [HAnPPh2(S)AuCl] (50), hydrogen atoms are omitted for clarity; right:

C-H^…π interaction in 50, one phenyl substituent and Au-Cl fragments are omitted for clarity.

Table 3-26: Selected bond lengths [Å] and angles [°] of [HAnPPh₂(S)AuCl] (50).

P1-S1 2.0217(9) S1-Au1-Cl1 173.77(3)

S1-Au1 2.2571(7) C9a-C9-P1-S1 80.00(2)

C9-P1-S1 116.18(9) Folding 14.1

P1-S1-Au1 105.99(3) Twist 7.7

Figure 3-71: Left: crystal structure of [HAnPⁱPr2(S)AuCl] (51), hydrogen atoms are omitted for clarity;

right: non-parallel π-π overlap of fluorophores in 51, side view (top) and top view (bottom).

Moreover, one would predict well distributed steric strain applied by phosphoryl substituent due to its nearly symmetrical alignment, which would result in a small expected deformation of the fluorophore. Though the actual deformation is moderate at folding and twist angles of 12.6° and 3.7°, it is stronger than expected. The observed distortion is induced by the Au-Cl fragment, as the anthracene moiety is folded in the opposite direction of it. The S-Au-Cl fragment is even closer to perfectly linear than in the structure of 50, enclosing an angle of 176.74°. The observed bond distances are within the expected range and differ only minimally, the tetrahedral geometry of the P-bound substituents is slightly distorted. While 50 crystallizes in a monoclinic space group, 51 crystallizes in the orthorhombic space group Fdd2. This leads to a distinctly different packing motif of the molecules. In the structure of [HAnPⁱPr2(S)AuCl] (51) the phosphanylanthracene molecules do not adapt the typical “head-to-tail” positioning with parallel orientation of the anthracene moieties. Although π-π overlap is found, the involved fluorophores are not parallel oriented, but exhibit an angle of ~35° to one another (Figure 3-71, right). In addition to the non-parallel π-π interactions, two sp³ type C-H^…π bonds are present in the structure of 51 between methyl hydrogen atoms and the π systems of both a central and a peripheral C6-perimeter. They measure 2.880 Å (45.9°) and 2.936 Å (44.0°), respectively (Figure 3-72). That makes them both fairly weak, taking into account the weak polarization of the sp³ C-H bonds.

Figure 3-72: C-H^…π interactions in 51. Au-Cl fragments are omitted for clarity.

Table 3-27: selected bond lengths [Å] and angles [°] of 51.

P1-S1 2.038(1)

S1-Au1 2.269 (1) C9-P1-S1 117.69(13) P1-S1-Au1 99.90(5) C9a-C9-P1-S1 14.4(4) Folding 12.6

Twist 3.7

The structure of [MeAnPPh2(S)AuCl] (52) is the first gold complex described so far which bears co-crystallized solvent molecules in its crystal structure. The asymmetric unit contains one molecule of 52 as well as one molecule of acetone. Aside from the lattice solvent, the local symmetry of the molecule is closely related to that of 50.

Table 3-28: Selected bond lengths [Å]

and angles [°] of 52.

P1-S1 2.0287(15)

S1-Au1 2.2722(12) C9-P1-S1 115.16(15) P1-S1-Au1 95.93(6) C9a-C9-P1-S1 79.6(3)

Folding 10.6

Twist 4.8

Figure 3-73: Crystal structure of [MeAnPPh₂(S)AuCl] (52), lattice solvent and hydrogen atoms are omitted for clarity.

This is especially reflected by the similar torsion angles of the P=S bonds to the anthracene plane which deviate by only 0.4°. The resultant orientation of the S-Au-Cl fragment is accordingly also nearly identical, as well as the steric strain applied to the anthracene moiety. The induced deformation of the fluorophore shows only minor deviations from that found in the structure of 50, which is underlined by the superposition of both compounds depicted in Figure 3-74. The predominant difference in structure between the two complexes is the remarkably small P-S-Au angle of only 95.9° in 52, which leads to the deviation in the orientations of both S-Au-Cl fragments.

The S-Au-Cl angle of 52 measures 178.5°, which is the closest to ideal linear geometry encountered so far.

Figure 3-74: Superposition of [HAnPPh₂(S)AuCl] (50) (regular spheres, solid bonds) and [MeAnPPh₂(S)AuCl] (52) (small spheres, dashed bonds). Hydrogen atoms are omitted for clarity.

The distorted tetrahedral geometry surrounding the phosphorus atom is nearly identical to the corresponding geometry in 50. In spite of the strong similarities in the local structures of 50 and 52, the methyl group in 10-position of 52 leads to a completely different packing motif than observed for 50. It not only crystallizes in the orthorhombic space group Pbca, also the intermolecular interactions differ significantly. While 50 showed virtually no π-π overlap, [MeAnPPh2(S)AuCl] (52) exhibits an overlap of ~40% at a distance of 3.61 Å (Figure 3-75).

Figure 3-75: π-π overlap in the structure of 52, side view (left) and top view (right), hydrogen atoms and Au-Cl fragments are omitted for clarity.

Reactions of symmetric phosphanylanthracenes with gold(I) and silver(I) salts have repeatedly produced cyclic complexes in the past.[65, 71, 84]

Therefore the feasibility of producing cyclic complexes from oxidized symmetric phosphorylanthracenes was sighted. Hence, the symmetric phosphorylanthracene (Et2N)2SePAnPSe(NEt2)2 (38) was reacted with [Me2SAuCl].

Scheme 3-32: Synthesis of gold (I) complex 53.

Although the molecule bears two selenium donor atoms, only one equivalent of [Me2SAuCl] was added to promote the formation of a cyclic complex which also exhibits a ligand/metal ion ratio of 1:1. Crystallization from acetone at –30°C surprisingly afforded the symmetric gold complex

[ClAu(Se)(Et2N)2PAnP(Et2N)2(Se)AuCl] (53), which has a 1:2 ligand/metal ion ratio (Scheme 3-31). Despite the ratio of the utilized substances, the formation of the

symmetric complex appears to be favored over the formation of a cyclic arrangement.

53 crystallizes in the monoclinic space group P21/c and the asymmetric unit contains one molecule. The linear Se-Au-Cl fragments are directed in opposite directions away from the anthracene moiety on the identical side of the anthracene plane in a cisoid conformation. Both show nearly perfectly linear geometry, with Se-Au-Cl angles of 174.8° and 173.2°, respectively (Table 3-29).

Figure 3-76: Crystal structure of 53, hydrogen atoms are omitted for clarity.

Table 3-29: Selected bond lengths [Å] and angles [°] of 53.

Se1–Au1 2.3798(7) C9–P1–N1 113.2 (3) Se2–Au2 2.346(2) C9a–C9–P1–Se1 –131.5(5) P1–Se1–Au1 98.81(5) C4a–C10–P2–Se2 136.3(5)

P2–Se2–Au2 104.70(8) Folding 19.0

C9–P1–Se1 104.4(2) Twist 1.6

The bonding partners of the phosphorus atoms form distorted tetrahedra, the deviations from the ideal tetrahedral angle are moderate. The Se-Au distances are not identical, but differ by only 0.034 Å and are both in the range of the Se-Au distances observed in 26 and 28 (see 3.3). In contrast, P-Se-Au angles are similar but differ by over 5° which is the strongest deviation found between the two coordination sites of the complex. The presence of two bulky bis(diethylamino)selenophosphoryl substituents in the structure combined with two large coordinated gold ions leads to a strong steric strain on the fluorophore affording a folding angle of 19.0° and a twist deformation of 1.6°. This is a major difference to the uncoordinated

(Et2N)2SePAnPSe(NEt2)2 (38) which exhibits an extreme twist deformation of 24.4°.

Generally the strong folding and weak twist deformation is in accordance with the deformations observed for other symmetric phosphoryl anthracenes in a cisoid conformation (see 3.2). Due to the strong steric demand of the substituents which prevent the anthracene moieties from close contact, there are no noteworthy intermolecular interactions in terms of π interactions present in the structure of 53.

Although the primary goal of synthesizing a cyclic complex was not attained, a different interesting feature of 53 was discovered. 53 is the first gold complex of a phosphoryl anthracene to exhibit a gold-gold contact in its solid state structure.

Figure 3-77: Gold-gold contact in the structure of 53. Ethyl groups, hydrogen atoms and terminal Au-Cl fragments are omitted for clarity.

shorter than the Se-Au bond of the fragment participating in Au-Au bonding. This also applies to the Au-Cl bonds.