Abstract
The reaction of PtBr2 with NaOAc and 1,3-diisopropylbenzimidazolium bromide (A) in DMSO afforded the mixed monocarbene−DMSO complex cis-[PtBr2(DMSO)(iPr2-bimy)] (cis-1) and the bis(carbene) complex trans-[PtBr2(iPr2-bimy)2] (trans-2). The DMSO ligand in cis-1 can be easily replaced by stronger donors such as triphenylphosphine and pyridine to give novel benzannulated monocarbene complexes trans-[PtBr2(iPr2-bimy)(PPh3)] (trans-3), cis-[PtBr2(iPr2-bimy)(PPh3)] (cis-3), and trans-[PtBr2(iPr2-bimy)(Pyridine)] (trans-4), respectively. All compounds have been fully characterized by multinuclei NMR spectroscopies and mass spectrometry (ESI, FAB). X-ray diffraction studies on single crystals of cis-1, trans-2, cis-3, and trans-4 revealed a square-planar geometry and a fixed orientation of the N-isopropyl substituents with the C−H protons pointing to the metal center to maximize interesting and rare C−H···Pt preagostic interactions. These interactions are also retained in solution, as indicated by the large downfield shift of the isopropyl C−H protons in the 1H NMR spectrum compared to that in the precursor salt A.
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