Multiple Isomerism (cis/trans; syn/anti) in [(dmso)₂Pt(aryl)₂] Complexes:  A Combined Structural, Spectroscopic, and Theoretical Investigation

Abstract

The occurrence of cis or trans configurations in square planar diarylbis(dimethyl sulfoxide)platinum(II) complexes with S-bonded dmso ligands and aryl = 2,3,4,5,6-pentamethylphenyl, 2,4,6-trimethylphenyl, 2,6-dimethylphenyl, 2-, 3-, and 4-methylphenyl, and phenyl has been investigated by multinuclear (1H, 13C, and 195Pt) NMR spectroscopy and crystal structure analysis. Both methods confirm the cis configuration for complexes with the smaller phenyl and methylphenyl (tolyl) ligands and the trans configuration for the compounds with the bulkier ligands, starting from 2,6-dimethylphenyl. Spectroscopic criteria could thus be established to identify configurational isomers. For the 2-tolyl complex an additional kind of isomerism arises from the relative orientation of the two methyl substituents on the same side (syn) or on different sides of the coordination plane (anti). 2D-NMR spectroscopy allowed us to identify the conformers and to study isomerization mechanisms. DFT calculation results agree well with the experimental structures and with the spectroscopic data.

Oxido Pincer Ligands – Exploring the Coordination Chemistry of Bis(hydroxymethyl)pyridine Ligands for the Late Transition Metals

“…There are medium‐strong hydrogen‐bonding interactions between the OH group and the co‐crystallised water molecules, with an O ··· H distance of 2.225(5) Å [O ··· O 2.780(4) Å] and an O–H ··· O angle of 161.1(6)°. Due to the steric demand of the pydimH 2 ligands the complexes are trans ‐configured, although the cis configuration would be preferred on electronic grounds 30. This finding strongly supports the proposal that the failure to form complexes with the bulky ligands pydipH 2 and pydotH 2 is due to repulsion of the ancillary R′ groups of the bulkier RR′pydimH 2 ligands.…”

“…From the series of ligand strengths, we assume that the cis isomer of[(pydimH 2 )(dmso)PtCl 2 ] is thermodynamically favoured, and the trans isomer is presumably the kinetic product. The latter finding leads to the assumption of an associative ligand‐exchange reaction through a five‐coordinate transition state (or intermediate) 30,32. This, and its superior solubility, enabled us to isolate it.…”

Mechanistic elucidation of linker and ancillary ligand substitution reactions in Pt(ii) dinuclear complexes

“…S1, † ESI), which stabilizes the five-coordinate trigonal bipyramidal transition state. Such a phenomenon was reported by Klein and coworkers 54 while investigating intramolecular C-H bond activation by the Pt(II) centre and its ability to form hydrogen bonding amongst the dimethylpyrazine ligands. 55 Similarly, unconventional hydrogen bonding has also been reported by Munro et al in a crystallographic study.…”

195Pt NMR—theory and application

“…The effect of solvent coordination and ligand changes on the chemical shift 128 of the cis-and trans-configuration in square planar [Pt(DMSO) 2 (Ar) 2 ], where Ar = Ph, Tol, Mes, Xyl, Me 2 Ph, have been studied. 129 d 195 Pt and coupling constants (see Table 8) allowed the identification of these configurational isomers and their isomerisation mechanisms.…”