Synthesis, structure, and reactivity of [(dfepe)Pt(mu-H)](2). An unusual example of conformational polymorphism

Treatment of the methyl complex (dfepe)Pt(Me)(O2CCF3) (dfepe = (C2F5)(2)PCH2CH2P(C2F5)(2)) With 1 atm of H-2 in acetone at 20 degrees C cleanly affords the hydride-bridged dimer [(dfepe)Pt(mu-H)](2) (1), which crystallizes in both green (1a, monoclinic) and purple (1b, orthorhombic) forms. Diffraction data indicate that 1a and 1b are conformational polymorphs which primarily differ in the degree of rotation about the Pt-Pt bond (interchelate angle = 7 degrees (1a), 49 degrees (1b)) and intermolecular crystal packing. DSC experiments reveal a mildly exothermic (0.51 kT mol(-1)) irreversible phase transition from 1a to 1b at 91 degrees C (mp of 1b = 112 degrees C). In CH2Cl2, 1 exhibits a distinctive d pi --> d sigma* transition at 428 nm (epsilon similar to 4000 mol(-1) cm(-1)) and a reversible redox couple at +0.63 V (CH2Cl2, vs SCE). [(dfepe)Pt(mu-H)](2) serves as a versatile precursor to (dfepe)Pt-0 compounds: exposure of acetone solutions of 1 to 1 atm of C2H4, C2F4, or CO results in clean conversions to (dfepe)Pt(eta(2)-C2H4) (2), (dfepe)Pt-(eta(2)-C2F4) (3), and (dfepe)Pt(CO) (4) (v(CO) = 2044 cm(-1)), respectively. With the exception of 3, these Pt(O) derivatives readily revert to the hydride dimer under 1 atm of H-2 at ambient temperature. Under 2 atm of CO, the reversible formation of (dfepe)Pt(CO)(2) (5) from 4 is observed. X-ray data for 1a: a = 23.527(5) Angstrom, b = 10.451(2) Angstrom, c = 16.623(3) Angstrom, beta = 110.20(3)degrees, monoclinic, C2/c, Z = 4, R = 0.0670. Data for 1b: a = 13.354(3) Angstrom, b = 16.232(3) Angstrom, c = 18.525(4) Angstrom, orthorhombic, Peen, Z = 4, R = 0.0423.