LOW-TEMPERATURE NEUTRON-DIFFRACTION STUDY OF HMN2RE(CO)14 AND STUDIES OF A METAL METAL EXCHANGE EQUILIBRIUM THAT CONVERTS HMN2RE(CO)14 INTO HMNRE2(CO)14

The crystal and molecular structure of (CO)5Re(mu-H)Mn(CO)5, prepared from reaction of Mn2(CO)9(eta-1-tolualdehyde) with HRe(CO)5, has been determined from neutron diffraction measurements at 15 K; unit-cell constants, a = 9.145 (1) angstrom, b = 15.557 (3) angstrom, c = 14.040 (3) angstrom, beta = 106.60 (2)-degrees, monoclinic, space group P2(1)/n, Z = 4, V = 1914.2 (6) angstrom3. R(F2) = 0.110 for 4859 reflections with F-0(2) greater-than-or-equal-to 3-sigma(F02) and (sin-theta/lambda)max = 1.054 angstrom-1. The Re-H distance (1.827 (4) angstrom) is longer than the Mn-H distance (1.719 (5) angstrom). Spectroscopic and crystallographic data indicate that a small amount (approximately 9%) of (CO)5Re(mu-H)Mn(CO)4Re(CO)5 has cocrystallized with the major component. Further evidence for the identity of (CO)5Re(mu-H)Mn(CO)4Re(CO)5 comes from an independent synthesis by a known route. A mechanism is proposed that accounts for the formation of (CO)5Re(mu-H)Mn(CO)4Re(CO)5 from the reaction of (CO)5Re(A-H)Mn(CO)4Mn(CO)5 with HRe(CO)5. The equilibrium constant for the metal-metal exchange equilibrium, (CO)5Re(mu-H)Mn(CO)4Mn(CO)5 + HRe(CO)5 half arrow right over half arrow left (CO)5Re(mu-H)Mn(CO)4Re(CO)5 + HMn(CO)5, has been determined; K(eq) = 1.00 +/- 0.05 at 22-degrees-C in C6D6.