Syntheses and Structures of Digold Complexes of Macrobicyclic Dibridgehead Diphosphines That Can Turn Themselves Inside Out

When isomers of the dibridgehead diphosphine P((CH2)(14))(3)P (2) are treated with Me2SAuCl, 2.(AuCl)(2) is obtained in high yields. With in,in-/out,out-2 (97:3 equilibrium mixture), only a single isomer can be detected by low-temperature NMR, which is assigned as out,out-2.(AuCl)2 on the basis of the crystal structure. With in,out-2, in,out2-(AuCl)(2) is obtained, as confirmed by a crystal structure. Both lattices show hydrogen bonding between the AuCl moieties of one molecule and the PCH2 hydrogen atoms of a neighboring molecule. This requires access to the backside of the P-Au-Cl linkages, distorting the diphosphine cages. When out,out-2.(AuCl)(2) is treated with CH3Li, out,out2.(AuCH3)(2) can be isolated (91%). Analogous hydrogen bonding is impossible, and this molecule crystallizes with a much more symmetrical cage, the center of which is occupied by a methylcyclopentane solvate.