Pd(0) and Pt(0) Metallocryptands Encapsulating a Spinning Mercurous Dimer

The deep-red, air-stable complexes [Pt₂Hg₂(P₂phen)₃](PF₆)₂, 1, or [Pd₂Hg₂(P₂phen)₃](PF₆)₂, 2, (P₂phen is 2,9-bis(diphenylphosphino)-1,10-phenanthroline) are most conveniently prepared by the stoichiometric reaction of either Pt(dba)₂ or Pd₂(dba)₃·CHCl₃ (dba is dibenzylideneacetone) with P₂phen and a single drop of elemental mercury in refluxing dichloromethane under an atmosphere of nitrogen. The ³¹P{¹H} NMR spectrum (CD₃CN) of 1 shows a single sharp resonance at 43.1 ppm for the phosphorus atoms of the P₂phen ligand with both ¹⁹⁵Pt (¹J_P-Pt = 4350 Hz) and ¹⁹⁹Hg (²J_P-Hg = 620 Hz) satellites indicating the Hg₂²⁺ unit is dynamic. Compound 2 has a similar resonance at 44.9 ppm with ¹⁹⁹Hg satellites (²J_P-Hg = 638 Hz). The ¹⁹⁹Hg NMR (CD₂Cl₂, vs Hg(OAc)₂) spectrum of 2 shows a heptet pattern at 833 ppm while for 1 a heptet superimposed on a doublet of heptets is observed at 770.8 ppm. The ¹⁹⁵Pt NMR spectrum of 1 displays a quartet at −3071 ppm with ¹⁹⁹Hg satellites and a ¹J_Pt-Hg value of 1602 Hz. Characterization of 1 and of 2(BF₄)₂ by single-crystal X-ray diffraction studies confirms the metallocryptand structure consisting of three phosphine−imine ligands forming a D₃ symmetric cage with a Hg₂²⁺ ion in its center coordinated to two phenanthroline rings with the Hg−Hg bond (1, 2.7362(6); 2(BF₄)₂, 2.6881(4) Å) oriented perpendicular to the vector between the trigonally coordinated Pt(0) or Pd(0) atoms on each end. The Pt−Hg separations in 1 average 2.8143(6) Å while in 2(BF₄)₂ the average Pd−Hg separation is 2.7698(5) Å. Excitation into the low energy excitation bands of 1 (475 nm) and 2 (430 nm) produces weak emissions centered at 593 nm with shoulders at 530 and 654 nm in 1 and centered at 524 nm with a shoulder at 545 nm in 2.