Synthesis of platinum complexes of 2-methyl-2,4,6-tris(trifluoromethyl)pyran. X-Ray crystal structure of (cyclo-octa-1,5-diene)[2-methyl-2,4,6-tris(trifluoromethyl)pyran]platinum

Abstract

Bis(cyclo-octa-1,5-diene)platinum reacts with 2-methyl-2,4,6-tris(trifluoromethyl)pyran to afford the complex [Pt{η²-[graphic omitted](CF₃)Me}(cod)]. Fluorine-19, ¹H, and ¹³C n.m.r. spectroscopy showed that the pyran ligand was η²-co-ordinated to platinum. In order to define the structure rigorously an X-ray diffraction study was carried out at 218 K. Crystals are triclinic, space group P, Z= 2, in a unit cell with lattice parameters a= 10.136(12), b= 9.062(11), c= 11.455(9)Å, α= 93.22(8), β= 106.23(8), and γ= 109.32(9)°. The structure was refined to R 0.056 (R′ 0.057) for 4 832 independent reflections with 2.9 ⩽ 2θ⩽ 50°(Mo-K_αX-radiation). The X-ray structure determination confirmed that the pyran ligand is η²-co-ordinated to the platinum atom. Moreover, the linkage is such that the platinum atom is attached to the CC double bond having the C(Me)(CF₃) substituent. The pyran ring is essentially planar with the three CF₃ substituents bent away from this plane to the far side from the platinum, while the Me substituent projects from the plane on the near side to the metal atom. Reaction of [Pt{[graphic omitted](CF₃)Me}(cod)] with PPh₃ affords [Pt{[graphic omitted](CF₃)Me}(PPh₃)₂]. Related complexes [Pt{[graphic omitted](CF₃)Me}L₂](L = CNBu^t or CNC₆H₃Me₂-2,6) are obtained by reacting 2-methyl-2,4,6-tris(trifluoromethyl)pyran with the triplatinum compounds [Pt₃(CNR)₆]. Reaction between the pyran and [Pt(C₂H₄)₂(PPh₃)] yields [Pt{[graphic omitted](CF₃)Me}(C₂H₄)(PPh₃)]. Fluorine-19 and ¹³C n.m.r. studies reveal that the η² mode of attachment of the pyran to the platinum is similar to that established for the cyclo-octa-1,5-diene analogue. In contrast, 2-methyl-2,4,6-tris(trifluoromethyl) pyran reacts with [Rh(acac)(C₂H₄)₂](acac = acetylacetonate, pentane-2,4-dionate) to give [Rh(acac){η⁴-[graphic omitted](CF₃)Me}].