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

When isomers of the dibridgehead diphosphine P((CH 2 ) 14 ) 3 P ( 2 ) are treated with Me 2 SAuCl, 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 PCH 2 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 CH 3 Li, out, out - 2 ·(AuCH 3 ) 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.