Comment

Research in the field of asymmetric hydrogenation catalysis has developed significantly in recent years. De Rege et al. (2000) have shown that it is possible to immobilize chiral molecules in mesoporous silica via non-covalent interactions. Consequently, we are interested in the synthesis and direct application of chiral catalysts for asymmetric hydrogenation catalysis, which takes place within mesoporous materials (Raynor et al., 2000). In particular, we are investigating the use of chiral amines to induce chirality in the final product. For this purpose, we have synthesized the title compound in an analogous fashion to a previous literature precedent (Pertici et al., 1996).

The reaction between [RhCl(1,5-cyclo-octadiene)]₂ and AgCF₃SO₃ in tetrahydrofuran (THF) leads to the formation of the [Rh(THF)₂(1,5-cyclo-octadiene)]⁺ cationic species. The addition of (R)-(+)-1,1-binaphthyl-2,2'-diamine displaces the THF ligands, affording the title compound (I) in near quantitative yield. The structure contains the complex cation {Rh[(R)-(+)-1,1-binaphthyl-2,2'-diamine] (1,5-cyclo-octadiene)}⁺ (Fig. 1), with the Rh⁺ metal centre in a pseudo-square-planar geometry. The Rh-N and Rh- bond distances (Table 1) are comparable to those found in similar complexes (Beller et al., 1998).

Figure 1 A view of the complex cation, showing the labelling scheme for non-H atoms. Ellipsoids are drawn at the 30% probability level.

Experimental

All chemicals were purchased from Aldrich and used without further purification. Solvents were dried and degassed using appropriate methods. Standard Schlenk line techniques were employed. [RhCl(1,5-cyclo-octadiene)]₂ (50 mg) was dissolved in tetrahydrofuran (THF), followed by the addition of AgCF₃SO₃ (55 mg). The resulting solution was stirred at ambient temperature for one hour, after which it was filtered in order to remove AgCl. The filtrate was added to a solution of (R)-(+)-1,1-binaphthyl-2,2'-diamine (60 mg) in THF and stirred for another hour. Yellow crystals of the title compound were precipitated by the addition of hexane (ca. 30 ml). The mixture was then filtered, the yellow powder was washed with hexane (3 x ca. 20ml) and diethylether (3 x ca. 20 ml), and then dried in vacuo. Crystals suitable for X-ray diffraction analysis were obtained by recrystallization from a CH₂Cl₂/Et₂O solution. Elemental composition, calculated: C 54.04%, H 4.34%, N 4.34%. Found: C 54.22%, H 4.39%, N 4.20%. M⁺ = 495 g mol^-1. ¹H NMR (CD₃OD): 1.90 (br, m, 4H, CH₂ cod); 2.40 (br, m, 4H, CH₂ cod); 4.04 (br, m, 2H, CH); 4.42 (br, m, 2H, CH); 6.95-8.10 (10H, naph). ¹³C NMR: 30.99; 32.08 (CH₂); 81.16 (d, J_C-Rh = 12.8 Hz); 82.30 (d, J_C-Rh = 12.5 Hz); 121.23, 126.02, 128.17, 129.61, 131.71, 134.77, 139.98 (Ph).