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)3P (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,out-2·(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,out-2·(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.