Chelate Compexes of Functionalized Cycloheptatrienyl Ligands: 17-and 18-Electron Molybdenum Complexes with Linked Cycloheptatrienyl-Phosphane Ligands and Their Use in Transition Metal Catalysis

摘要

The synthesis of P-functionalized molybdenum chelate complexes incorporating the linked cycloheptatrienylphosphane ligand [2-(diphenylphosphanyl)phenyl]cycloheptetrienyl, o-Ph_2-P-C_6-H_4-C_7H_6, is described. The air-stable ligand precursor [2-(cyclohepta-2,4,6-trienyl)phenyl]diphenylphosphane (2) canb e obtaiend in large quantities by addition of lithiated 2-BrC_6H_4PPh_2 (1) to the tropylium cation C_7H_7~+, Hydride abstractin employing th trityl cation, Ph_3C~+, results in the formation empolying the trityl cation, Ph_3C~+, results in the foramtion of the tricyclicy phosphonium salt 3. The P-functionalized cycloheptatriene 2 acts as an eight-electron ligand on reaction with Mo(CO)_6 to afford the cycloheptatriene-phohsane complex [(o-Ph_2PC_6H_4-#eta#~6-C_7H_7)Mo(CO)_2(P-MO)] (4) as a single, chiral regiosiomer, which undergoes chean hydride abstractin on treatment with (Ph_3C)BF_4. The resutling cationic cycloheptatrienyl-phosphane complex 5 reacts with sodium bromide to yield the uncharged "chiral-at-metal" complex [(o-Ph_2PC_6H_4-#eta#~7-C_7H_6)Mo(CO)Br(P-Mo)] (6). This 18-electron complex can be oxidized with 0.5 equiv. of Br)__2 to give the paramagnetic dibromo complex 7, which is a versatile starting material for the prepaatin of the 17-electron mono-and dialkyl complexes [(o-Ph_2PC_6H_4-#eta#~7-C_4H_6)Mo(CH_2SiMe_3)X(P-Mo)] (X=Br, 8; X=CH_2SiMe_3, 9). In combination with me_3SiCh_2MgCl, compelxes 7 and 9 prove to be active catalysts for the ring-opening metalhesis polymerization of norbornene. In addition, the X-ray crystla structures of 2,4, 5centre dotCH_2Cl, 7-centre dotCHCl_3, 8, and 9centre dotC_6H_(14) are reported.