Cyclometallated Platinum(II) Complexes with a Phenylpropene‐Derived π/σ‐Chelator and N‐Heterocyclic Carbenes

Abstract

A series of heteroleptic platinum(II) complexes of the general formula [PtX( i PrEug)(NHC)] (2-7) bearing the organometallic π/σ-chelator i PrEug (isopropyl eugenoxyacetate), with varying X (halido) and NHC (N-heterocyclic carbene) ligands derived from imidazole, benzimidazole, and triazole, were prepared and fully characterized by elemental analyses, ESI mass spectrometry, and IR and NMR spectroscopy. Complexes 3 and 5-7 were also characterized by single-crystal X-ray diffraction. These air-stable complexes are rare examples of platinum(II)

Study on the interaction between [Pt(μ‐Cl)(isopropyl eugenoxyacetate‐1H)]2 and 1,3‐diisopropylbenzimidazolium bromide

“…For instance, the four methyl groups of i Pr2-bimy give rise to one signal in the spectrum of i Pr2-bimy·HBr but give four separated signals in the spectrum of 2. Similar to the case of its analogues [PtX( i PrEug)(NHC)] [12] , 13 CNHC resonance in 2 is notably more downfield in comparison to other mono-and bis(NHC) platinum(II) complexes. [4,17] This indicates that 2 is a significantly electron-rich complex, which is promising applications in catalysis.…”

“…The formation of the analogous pseudomolecular ion, [Pt( i PrEug)(NHC)] + , was also observed in the positive mode ESI MS of a series of complexes with type of [PtX( i PrEug)(NHC)]. [12] The strong absorption band at 1749 cm -1 in the IR spectrum of 2 indicates the presence of i PrEug in the coordination entity. Furthermore, frequency of characteristic band for the νC=Callyl in i PrEug decreases from 1640 cm -1 in non-coordinated i PrEugH to 1593 ÷ 1482 cm -1 in 2 showing that i PrEug has coordinated with Pt(II) via the C=Callyl.…”

“…The 1 H and 13 C signals are assigned basing on their chemical shift (δ), intensity, shape, spin-spin splitting pattern and references. [10,12] The HSQC spectrum was also used for assignment the ambiguous 13 C signals. For example, the C9 resonance signal at 110.6 ppm is clearly distinguished from the signal of C3 at 111.6 ppm by their cross peaks with the multiple signal of H9 at 5.84 ppm in the HSQC spectrum.…”

“…These values are comparable in magnitude to 2 JPtH and 3 JPtH in analogous Pt(II) complexes. [12] The absence of the NCHN proton of the i Pr2-bimy·HBr at 11.37 ppm [13] in the 1 H NMR spectrum of 2 suggests the formation of the metal-NHC bond. Besides, the coordination of i Pr2-bimy with Pt(II) makes proton and carbon groups which are equivalent in free i Pr2-bimy become inequivalent in 2.…”

“…[5][6][7][8] Many mono and dinuclear complexes of platinum(II) with ditopic / chelators derived from natural sources such as eugenol, methyl eugenol and methyl/ethyl/isopropyl eugenoxyacetate have been synthesized and studied their properties. [9][10][11] In our recent work, [12] NHC was introduced into the platinum(II) coordination sphere for the first time by the interaction between dinuclear platinacyclic complex bearing isopropyl eugenoxyacetate ( i PrEugH), [Pt(μ-Cl)( i PrEug)]2, and azolium chloride salt. The obtained complexes with type of [PtCl( i PrEug)(NHC)] are scarce examples of platinum(II) compounds bearing three different types of carbon donors, i.e.…”