COMPARISON OF ORTHO-ALKYL AND ORTHO-PERFLUOROALKYL GROUPS AS LIGANDS .1. CRYSTAL AND MOLECULAR-STRUCTURES OF THE METHYLPLATINUM(II), (TRIFLUOROMETHYL)PLATINUM(II), AND (PENTAFLUOROETHYL)PLATINUM(II) COMPLEXES TRANS-PTCIR(PMEPH2)2 (R = CH3, CF3, C2F5)

The crystal and molecular structures of the platinum(II) complexes trans-PtClR(PMePh2)2 (R = CH3, 1; R = CF3, 2; R = C2F5, 3) have been determined by three-dimensional X-ray structural analysis using data collected by counter methods. The methyl complex 1 crystallizes in the space group P21/c with a = 11.5476 (4) Å,b= 11.3826 (4) Å, c = 21.2390 (5) Å, β = 113.40 (1)Δ, and Z = 4; the trifluoromethyl complex 2 crystallizes in the same space group with a = 9.3544 (8) Å,β= 15.7237 (14) Å, c = 10.6846 (11) Å,β = 121.62 (2)Δ, and Z = 2; the pentafluoroethyl complex 3 crystallizes in the space group Pna21 with a = 15.4957 (4) Å, b = 9.9831 (3) Å, c = 38.7764 (11) Å, and Z = 8 (two formula units per equipoint). The structures were solved by conventional heavy-atom techniques and were refined by block-diagonal least-squares methods to final weighted and unweighted R factors of 0.033 and 0.044 (1), 0.045 and 0.098 (2), and 0.035 and 0.050 (3). 1 and 3 show small but significant distortions from planarity toward tetrahedral geometry, probably owing to steric crowding in the coordination sphere. Important bond lengths in 1 are Pt-C = 2.081 (6) Å, Pt-Cl = 2.412 (2) Å, and Pt-P = 2.292 (2) and 2.291 (2) Å and important bond lengths in 3 (averaged over two independent molecules) are Pt-C = 2.002 (9) Å, Pt-Cl = 2.363 (2) Å, Pt-P = 2.328 (2) and 2.341 (2) Å, C(α)-F(av) = 1.39 (2) Å, C(β)-F(av) = 1.33 (2) Å, and C(α)-C(β) = 1.546 (14) Å. Inversion disorder of the Cl and CF3 groups about the platinum atom of 2 precludes accurate determination of the Pt-Cl, Pt-C, or C-F bond lengths, but IR v(Pt-Cl) data indicate that CF3 and C2F5 have similar structural trans influences. The Pt-P bond lengths of 2 [2.320 (2) Å, crystallographically equivalent] are intermediate between those of 1 and 3. The Pt-P distances in 3 are not equivalent (Δ/σ ≈ 4), the longer bond of the pair in each molecule being adjacent to the CF3 substituent of the pentafluoroethyl group. The contraction of the Pt-C and Pt-Cl distances in 3 relative to 1 is attributed to the electrostatic effect of a positive charge induced on the ligating carbon atom by the electronegative fluorine atoms. C2F5 resembles CO in being higher in the trans-influence series based on NMR than in that based on Pt-Cl bond lengths or related parameters and also in tending to lengthen cis Pt-P bonds. Possible reasons for these similarities are discussed in the light of current views of transition-metal-fluoroalkyl bonding. © 1979, American Chemical Society. All rights reserved.