SOLUTION AND SOLID-STATE CONFORMATIONAL ISOMERS OF THE MOLECULAR DIHYDROGEN COMPLEX RECL(H2)(PMEPH2)4 - DOES IT CONTAIN AN ASYMMETRIC MOLECULAR DIHYDROGEN LIGAND

The complex ReCl(H2)(PMePh2)4 with four PMePh2 ligands in the equatorial plane and the Cl- ligand trans to an eta-2-H2 ligand has been investigated by means of variable-temperature H-1 and P-31(H-1) NMR spectroscopies in different solvents, namely, CD2Cl2, acetone-d6, and toluene-d8. In this crowded molecule metastable conformational isomers based on rotational orientations about the Rc-P bonds can arise. The data obtained indicate that different percentages of conformational isomers are formed in the different solvents. The T(1)(min) time of 92 ms at 400 MHz in CD2Cl2 is obtained for the metal-bonded H atoms in ReCl-(H2) (PMePh2)4. Structural data are reported for ReCl(H2)(PMePh2)4.2C4H8O (1a) at 292 and 193 K, ReCl(H2)(PMePh2)4.0.5(CH3)2CO (1b), and ReCl(H2)(PMePh2)4.0.5(CH3)2CO (1c). These different crystalline forms were obtained under different crystallization conditions. Crystal data: compound 1a, triclinic, space group P1BAR, a = 12.287 (3) angstrom, b = 19.318 (8) angstrom, c = 12.275 (3) angstrom, alpha = 101.06 (3)-degrees, beta = 104.42 (2)-degrees, gamma = 103.83 (3)-degrees, V = 2640 (4) angstrom-3, Z = 2, T = 292 K, R = 0.055 (R(w) = 0.073) for 446 parameters and 5091 unique data having F(o) > 3-sigma(F(o)2; compound 1a, triclinic, space group P1BAR, a = 12.287 (3) angstrom, b = 19.269 (9)-angstrom, c = 12.138 (4) angstrom, alpha = 101.10 (3)-degrees, beta = 103.92 (2)-degrees, gamma = 104.13 (3)-degrees, V = 2590 (4) angstrom-3, Z = 2, T = 193 K, R = 0.041 (R(w) = 0.058) for 449 parameters and 7334 unique data having F(o) > 3-sigma-(F(o)2; compound 1b, triclinic, space group P1BAR, a = 13.044 (3) angstrom, b = 18.434 (5) angstrom, c = 11.701 (4) angstrom, alpha = 94.12 (3)-degrees, beta = 113.44 (2)-degrees, gamma = 80.58 (2)-degrees, V = 2547 (2) angstrom 3, Z = 2, T = 292 K, R = 0.046 (R(w) = 0.063) for 467 parameters and 6089 unique data having F(o) > 3-sigma-(F(o))2; compound 1c, triclinic, space group P1BAR, a = 14.186 (4) angstrom, b = 17.317 (4) angstrom, c = 11.675 (3) angstrom, alpha = 108.57 (2)-degrees, beta = 96.32 (2)-degrees, gamma = 76.39 (2)-degrees, V = 2640 (2) angstrom 3, Z = 2, T = 292 K, R = 0.036 (R(w) = 0.067) for 487 parameters and 8763 unique data having F(o) > 3-sigma-(F(o))2. In forms 1a and 1b the main molecule was ordered and the final difference maps revealed two electron density maxima near the Re atom and trans to the Cl- ligand that could be representative of two H atoms bonded to the Re atom in an eta-1-H2 mode. For both data sets with form 1a these H atoms failed to refine freely to reasonable parameters. However, the positions of these atoms fron the difference maps are reported. In form 1b the two H atoms were refined freely, which resulted in the following parameters: Re-H(1) = 1.49 (9) angstrom, Re-H(2) = 1.98 (9) angstrom, H(1)-H(2) = 1.17 (13) angstrom, Re-H(1)-H(2) = 95 (8)-degrees, and Re-H(2)-H(1) = 48 (6)-degrees. Form 1c contains disorder between the trans Cl- and eta-H2 ligands.