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 clea nly affords the hydride-bridged dimer [(dfepe)Pt(mu-H)](2) (1), which crystallizes in both green (1a, monoclinic) and purple (1b, orthorhomb ic) 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 exoth ermic (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 dist inctive d pi --> d sigma transition at 428 nm (epsilon similar to 400 0 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, C 2F4, 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 re adily revert to the hydride dimer under 1 atm of H-2 at ambient temper ature. 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) Angst rom, b = 16.232(3) Angstrom, c = 18.525(4) Angstrom, orthorhombic, Pee n, Z = 4, R = 0.0423.