An Ab initio Computational study of Monodentate Palladium ligand Complexes with Möbius-Aromatic Chiral Character

Christian J. Kastrup, Steven V. Oldfield and Henry S. Rzepa*


Department of Chemistry, Imperial College of Science Technology and Medicine, London, SW7 2AY.
The 8 p homologues 3 of the planar aromatic carbene and silylene ligands 1 are predicted on the basis of ab initio calculations to adopt twisted C2 geometries resulting from a novel attenuation of ring anti-aromaticity induced by Möbius-type aromaticity, and for which we suggest that appropriately sterically substituted forms might act as chiral mondentate metal ligands in coordination to metals such as palladium.
Scheme

Supplemental Information

Coordinates are provided in the form of MDL Molfiles. These can be viewed using appropriate Browser plugins such as Chime. Please note that due to a bug in the Chime plugin (at release 2.6, SP2) distances measured are not correct, and such measurements should be made in other programs that can load Molfiles.
Table 1. Computed B3LYP/DZVP Energies, Geometries and NICS values for 1-4.§
Structure; Substituents Energy, Hartree (B3LYP/dzvp) NICS, ppm Geometrya Point Group Symmetry (Ring) DE Coordination (Kcal/mol)b
2; R=CH3, L=P(Me)3 -5705.7038 -10.8 2.13,1.37,1.39,1.36; 0.0 C2v -9.4
1; R=CH3 -304.8242 -11.8 1.37,1.39,1.36; 0.0 C2v -
4; Z=C, R,R',R"=H, L=P(Me)3 -5704.4513 14.7 2.10,1.37,1.43,1.34,1.47; 22.43 C2 -8.4
4; Z=C, R,R',R"=H, L=PH3 -5586.4758 15.0 2.12,1.36,1.43,1.34,1.47; 22.69 C2 -12.5
4; Z=C, R,R',R"=H, L=PH3 0.5c 22.7 2.12,1.36,1.43,1.34,1.47; 0.0 C2v -
3; Z=C,R,R',R"=H -303.5733 19.2 1.36,1.43,1.34,1.47; 18.45 C2 -
4; Z=C, R=H,R',R"=F, L=PH3 -5983.4949 -1.4 2.08,1.37,1.41,1.34,1.45; 34.06 C2 -10.8
4; Z=C, R=H, R',R"=F, L=PH3 7.1c 12.2 2.10,1.36,1.42,1.34,1.47; 0.0 C2v -
3; Z=C, R=H, R',R"=F -700.5951 0.3 1.37,1.41,1.34,1.45; 34.68 C2 -
4; Z=C, R,R',R"=CH3, L=PH3 -5822.3607d 3.9 2.15,1.37,1.45,1.35,1.48; 46.16 C2 -12.3
3; Z=C, R,R',R"=CH3 -539.4585 5.6 1.37,1.45,1.35,1.48; 47.59 C2 -
4; R=CH3,R'+R"=benzo, L=PH3 -5972.4158 5.3 2.14,1.37,1.44,1.41,1.48; 43.31 C2 -10.7
4; R=CH3,R'+R"=benzo, L=PH3 21.7c running 2.28,1.36,1.45,1.43,1.51; 0.0 C2v -
3; R=CH3,R'+R"=benzo -689.5161 6.9 1.37,1.44,1.41,1.48; 45.36 C2 -
4; Z=Si, R,R',R"=H, L=PH3 -5837.9274 9.9 2.30,1.74,1.42,1.35,1.47; 25.70 C2 -12.0
4; Z=Si,R,R',R"=H, L=PH3 0.5c 14.8 2.30,1.73,1.42,1.35,1.47; 0.0 C2v -
3; Z=Si,R,R',R"=H -555.0256 12.5 1.75,1.42,1.35,1.47; 25.15 C2 -
4; Z=Si, R=H, R',R"=F, L=PH3 -6234.9566 -2.2 2.27,1.75,1.39,1.34,1.45; 40.79 C2 -11.7
4; Z=Si, R=H,R',R"=F, L=PH3 7.9c 8.1 2.27,1.74,1.40,1.34,1.40; 0.0 C2v -
4; Z=Si, R=H,R',R"=F -952.0553 -0.8 1.77,1.39,1.34,1.45; 41.40 C2 -
a bond length, Å (Pd-C2, C2-N3, N3-C4, C4-C5, C5-C6); dihedral angle (C4-C5-C6-C7). bFor the equilibrium 1/3 + PdL2 = 2/4 + L c Energy of planar form relative to C2 geometry. d Because of the geared methyl interactions, a formal transition state for inversion of chirality proved difficult to locate. We estimate the barrier to be > 30.5 kcal/mol.