Pressure-Enhanced C-H Bond Activation in Chloromethane Platinum(II) Complexes

The nature of the interaction between chloromethanes CH4-nCln and Pt(II) complexes has been studied by high-pressure X-ray diffraction and infrared spectroscopy in combination with DFT calculations. In case of electron rich complexes such as d(8)-Pt(btz-N,N ')(phenyl)L with L = phenyl, Cl, Br and btz = 2,2 '-Bi-5,6-dihydro-4H-1,3-thiazine stable chloroform adducts with bridging hydrogen atoms in the eta(1)(C-H)Pt moieties were isolated which display highly activated C-H bonds. This activation is a consequence of a pronounced Pt(d(z2))->sigma*(C-H) back donation and is signaled by large red-shifts of the isolated nu(is)(C-H) stretching modes. The extent of the C-H bond activation and covalent Pt-H bond formation in the eta(1)(C-H)Pt moieties is thereby controlled by (i) the sigma/pi donor capabilities of the ligands L, (ii) the orientation of the coordinating C-H bond with regard to the Pt(d(z2)) orbital and (iii) the applied pressure.