Organoplatinum(IV) Complexes with Amide Groups: Supramolecular Structure as a Function of Ligand Flexibility

Supramolecular organometallic chemistry: the platinum(IV) paradigm

Supramolecular chemistry and the chemistry of alkyl derivatives of the transition metals are both topics of considerable current interest, but the combination of the two fields is still underdeveloped. The challenges are, in large part, experimental in nature. For example, the self-assembly of molecules in supramolecular chemistry often relies on intermolecular hydrogen bonding, but most alkyl-transition metal bonds are cleaved by the protic groups used in hydrogen bond formation. Alkyl-platinum(IV) bonds are inert to protonolysis or attack by other electrophiles under mild conditions, and this has allowed an extensive supramolecular chemistry of organoplatinum(IV) complexes to be developed, as outlined in this perspective review. Highlights include a zeolitic structure, a polyrotaxane, a double helix, a nanotube structure and an example of spontaneous resolution to form a chiral sheet structure.

Supramolecular Organoplatinum(IV) Chemistry: Dimers and Polymers Formed by Intermolecular Hydrogen Bonding

The reaction of [PtMe₂(6-dppd)], 1, where 6-dppd is a 1,4-bis(2-pyridyl)pyridazine derivative, with bromoalkanes BrCH₂R, having a hydrogen-bond donor group R, gave the corresponding chiral products of trans oxidative addition [PtBrMe₂(CH₂R)(6-dppd)], 2a, R = CO₂H; 3, R = 4-C₆H₄CO₂H; 4, R = 4-C₆H₄CH₂CO₂H; 7, R = 2-C₆H₄CH₂OH; 8, R = 4-C₆H₄B(OH)₂; 9, R = 3-C₆H₄B(OH)₂; and 10, R = 2-C₆H₄B(OH)₂. Complex 2a was formed in equilibrium with two isomers formed by cis oxidative addition, while the reaction of 1 with BrCH₂CH₂CO₂H gave mostly [PtBrMe(6-dppd)], 6. The supramolecular chemistry was studied by structure determination of six of the platinum(IV) complexes, with emphasis on the preference of the hydrogen bond acceptor (O, pyridyl N, or Br atom), formation of monomer, dimer, or polymer, and self-recognition or self-discrimination in self-assembly. Complex 7 formed a monomer with the OH···N hydrogen bond, and complexes 2a and 10 formed racemic dimers by complementary hydrogen bonding with self-discrimination between CO₂H or B(OH)₂ groups, respectively. Complexes 3, 4, and 9 formed polymers by intermolecular hydrogen bonding with self-recognition, with 4 containing OH···N and 3 and 9 containing OH···Br hydrogen bonds. It is concluded that there is no clear preference for the hydrogen bond acceptor group, and that the observed product depends also on the orientation of the hydrogen bond donor group.