CATALYTIC THERMAL C-H ACTIVATION WITH MANGANESE COMPLEXES - EVIDENCE FOR ETA-2-H2 COORDINATION IN A NEUTRAL MANGANESE COMPLEX AND ITS ROLE IN C-H ACTIVATION

The reactivity of MnH3(dmpe)2 has been examined for its ability to activate C-H bonds. The complex loses H-2 readily and is characterized as having an eta2-H-2 ligand on the basis of NMR spectroscopic and electrochemical studies. Reaction of MnH3(dmpe)2 with added ligands gives MnH(L)(dmpe)2 (L = CO, N2, C2H4, CNR; R = t-Bu, CH2CMe3, 2,6-xylyl). The complex activates aromatic and benzylic C-H bonds under both thermal and photochemical conditions as determined by catalytic H/D exchange with C6D6 or D2. Selectivity studies were also carried out by employing catalytic H/D exchange. A mechanism is proposed, and the neighboring group participation effect is discussed for explaining C-H activation selectivity The complex MnH(CN-2,6-XYIYI)(dmpe)2 Crystallizes in orthorhombic space group Cmcm, with a = 12.129 (5) angstrom, b = 13.136 (3) angstrom, c = 16.80 (3) A, and Z = 4, and was found to have a trans geometry. The complex MnH(N2)(dmpe)2 crystallizes in orthorhombic space group Pna2(1), with a = 17.648 (4) angstrom, b = 9.191 (3) angstrom, c = 12.303 (2) angstrom, and Z = 4. The analogous hydride MnH3(depe)2 shows two distinct types of hydrogen ligands at low temperature, the larger of which has an extremely short T1.