Chiral Ag(i) and Pt(ii) complexes of ditopic NHC ligands: synthesis, structural and spectroscopic properties

Abstract

The butyl and isopropyl derivatives (4I, 5Br) of chiral pool derived bis-imidazolium dehydrohexitol salts have been prepared. The ditopic N-heterocyclic carbenes 4 and 5 form dinuclear Ag(I) and Pt(II) complexes. All compounds were fully characterised by multinuclear NMR spectroscopy. The bis-imidazolium salt 4I and platinum complexes cis-[Pt(2)(μ-2)(dmso)(2)Cl(4)] and cis-[Pt(2)(μ-4)(dmso)(2)Cl(4)] were characterised by X-ray crystallography. In the case of the Pt(II) complexes, the carbene ring is positioned in a sterically preferred orientation, approximately perpendicular to the platinum coordination plane. The (1)H, (13)C, (15)N and (195)Pt NMR spectra of the platinum complexes show the presence of rotamers due to hindered rotation about the carbene-metal bond.

Sulfonated Water-Soluble N-Heterocyclic Carbene Silver(I) Complexes: Behavior in Aqueous Medium and as NHC-Transfer Agents to Platinum(II)

“…The Pt−C(1) distance of 1.97(2) Å is in the range of those reported for neutral cis-[PtCl 2 (dmso)(NHC)] complexes (1.88−1.99 Å). 21,22,49 The chlorine atoms are mutually arranged in a cis position, with the Pt−Cl distance of the chloride trans to the NHC ligand being significantly larger (2.359(5) versus 2.309(5) Å), as expected in light of the high sensitivity of Pt−Cl distances to the different influences of their trans ligands. 50 Hydration of Terminal Alkynes in Water.…”

“…The above 13 C and 195 Pt chemical shifts are in agreement with those previously reported for cis-[PtCl 2 (dmso)(NHC)] complexes. 21,22,49 The 1 H and 13 C{ 1 H} NMR spectra recorded in dimethyl sulfoxide revealed the existence of some asymmetry in mono(carbenes) 4a−d, as seen by the lack of equivalence between (a) the two methylene protons α to the imidazole nitrogen in the sulfonatepropyl chains of 4a−d; (b) the proton and carbon-13 nuclei in the ortho and meta positions of the mesityl or 2,6-bis(isopropyl)phenyl groups in 4c−e; and (c) the two methyl groups of the dmso molecule coordinated to Pt in the case of complexes with asymmetrically substituted NHCs. These observations can only be explained by assuming a cis stereochemistry of the square-planar metal environment, with a chloride trans to the carbene ligand and with the NHC ring arranged perpendicularly to the coordination plane rotating slowly around the Pt−NHC bond on the NMR time scale.…”

Synthesis of 2‐Ethyl‐19‐nor Analogs of 1α,25‐Dihydroxyvitamin D3

“…The C NHC ‐Pt bond distances measuring 2.019(8) and 2.029(9) Å (for C(1)‐Pt(1) and C(4)‐Pt(1)) are slightly longer than in few selected Pt‐NHC complexes 11a. 29 The Pt‐Cl(1) and Pt‐C(7) bond distances are 2.385(2) and 1.936(9) Å, respectively. Both of the NHC fragments and the central phenylene bridge of the tridentate ligand are in a coplanar configuration.…”

Enantiopure cycloplatinated pentahelicenic N-heterocyclic carbenic complexes that display long-lived circularly polarized phosphorescence

“…9 Although many types of chiral NHC-complexes with diverse stereogenic elements have been developed to date, especially for enantioselective catalysis, there are very few examples of enantiopure chiroptical materials based on NHC-Pt complexes, and they are mainly limited to those bearing monodentate NHCs. 10…”