Influence of Aryl Substituents on the Alignment of Ligands in the Dirhodium Tetrakis(1,2,2‐Triarylcyclopropane‐ carboxylate) Catalysts

Abstract

Computational studies revealed that dirhodium tetrakis(1,2,2‐triarylcyclopropanecarboxylate) (Rh2(TPCP)4) catalysts adopt distinctive high symmetry orientations, which are dependent on the nature of the aryl substitution pattern. The parent catalyst, Rh2(TPCP)4, and those with a p‐substituent at the C1 aryl, such as Rh2(p‐BrTPCP)4 and Rh2(p‐PhTPCP)4, adopt a C2‐symmetric structure. Rh2(3,5‐di(p‐tBuC6H4)TPCP)4, 3,5‐disubstituted at the C1 aryl, adopts a D2‐symmetric structure, whereas catalysts with an o‐substituent at the C1 aryl, such as Rh2(o‐Cl‐5‐BrTPCP)4, adopt a C4‐symmetric structure.

Comparison of 1,2-Diarylcyclopropanecarboxylates with 1,2,2-Triarylcyclopropanecarboxylates as Chiral Ligands for Dirhodium-Catalyzed Cyclopropanation and C–H Functionalization

“…Previous extensive studies on the Rh 2 (TPCP) 4 catalysts have established that their preferred orientation is strongly dependent on the functionality of the C1 aryl group . When the C1 aryl group is unsubstituted or para -substituted, the most stable orientations are C 2 symmetric structures, as shown in Figure for Rh 2 ( S -TPCP) 4 ( 2a ) . This structure is typically 3–6 kcal mol –1 more stable than any other structural arrangement.…”

“…13 When the C1 aryl group is unsubstituted or para-substituted, the most stable orientations are C 2 symmetric structures, as shown in Figure 1 for Rh 2 (S-TPCP) 4 (2a). 34 This structure is typically 3−6 kcal mol −1 more stable than any other structural arrangement. The substitution pattern at the C1 aryl group can have a dramatic effect on the orientation of the ligands in the catalysts.…”

“…Previously, our study on a Rh-TPCP series of catalysts has shown that the X-ray structures are not always the lowest energy conformation of the catalyst. 34 For example, for catalyst Rh 2 (S-p-BrTPCP) 4 (2b), the crystal structure was reported to be D 2 symmetric, 15 while conformational analysis revealed that its C 2 -symmetric structure is strongly preferred. 34 The X-ray structures of 3a and 3d suggested that the catalysts may be too open to have a strongly favored specific orientation.…”

“…34 For example, for catalyst Rh 2 (S-p-BrTPCP) 4 (2b), the crystal structure was reported to be D 2 symmetric, 15 while conformational analysis revealed that its C 2 -symmetric structure is strongly preferred. 34 The X-ray structures of 3a and 3d suggested that the catalysts may be too open to have a strongly favored specific orientation. To evaluate this hypothesis, here, a computational study, at the B3LYP-D3BJ/[Lanl2dz(for Rh)+ [6-31(d,p)](for other atoms) level of theory (see below for more details), was conducted on the parent (E)-Rh 2 (DPCP) 4 catalyst 3a.…”

Recent advances in transition-metal-catalyzed carbene insertion to C–H bonds

“…The effect of the substituents on the aryl moieties was obvious on the aligment of ligand in the dirhodium tetrakis(1,2,2-triarylcyclopro-panecarboxylate) catalysts of type Rh 2 (TPCP) 4 and their catalytic activity for C–H functionalization by carbene insertion. 478 Because of the sterically limited active site constructed by the four bulky aryl rings in the catalyst, carbene insertion to the C(2)–H bonds with the less steric bulkiness is preferred. Thus, a 82% yield was obtained with 96 : 4 rr (C2 : benzylic), 95 : 5 dr (C2), and 93% ee by means of complex Rh 2 ( S -2-Cl-5-CF 3 TPCP) 4 which was shown the highest asymmetric induction (Table 23).…”