Chelate Complexes of Functionalized Cycloheptatrienyl Ligands: Molybdenum Complexes with Linked Cycloheptatrienyl-Phosphane Ligands and Their Use in Catalytic Carbon-Carbon Bond Formation

摘要

The synthesis of P-functionalized molybdenum chelate complexes incorporating the linked cycloheptatrienyl-phosphane ligand [2-(diisopropylphosphanyl)phenyl]cycloheptatrienyl (o-iPr_2P-C_6G_4-C_7H_6) is described. From the ligand precursor [2-(cyclohepta-2,4,6-trienyl)phenyl]diisopropylphosphanyl (1) the paramagnetic 17-electron dibromide [(o-iPr_2PC_6G_4-eta~7-C_7H_6)MoBr_2(P-Mo)] (2) can readily be obtained. this is a versatile starting material for the preparation of cycloheptatrienyl molybdenum hydrides [(o-iPr_2PC_6G_4-eta~7-C_7H_6)Mo(eta~2-BH_4)(P-Mo)] (3) and [(o-iPr_2PC_6G_4-eta~7-C_7H_6)Mo(PPh_3)H(P-Mo)] (4). Treatment of 3 with dimethylanilinium tetraphenylborate ([PhNMe_2H][BPh_4]) allows the production of the cationic 14-electron complex fragment [(o-iPr_2PC_6G_4-eta~7-C_7H_6)Mo(P-Mo)]~+ (13), which can be stabilized in the presence of suitable ligands L. The complexes [(o-iPr_2PC_6G_4-eta~7-C_7H_6)MoL_2(P-Mo)]BPh_4 [L = dimethylphnyl isocyanide, (5)BPh_4; L_2 = eta~4-2,5-norbornadiene, (6)BPh_4; L_2 = eta~2-phenylacetylene, (7)BPh_4; L_2 = eta~2-tert-butylacetylene, (8)BPh_4] can thus be isolated in good yields. The alkyne complex (7)BPh_4 can be used as a single-source catalyst for the oligomerization of phenylacetylene, affording a mixture of triphenyl-benzenes and linear oligomers. Quantum chemical calculations reveal an intimate relationship between the catalytically active 14-electron complex fragment [(o-iPr_2PC_6G_4-eta~7-C_7H_6)Mo(P-Mo)]~+ (13) and hypothetical isoelectronic and isolobal complexes of the type [(o-iPr_2PC_6G_4-eta~5-C_5H_4)M(P-M)]~+ (M = Ru, 14; M = Os, 15), indicating that cycloheptatrienyl molybdenum systems might in general be a suitable replacement of cyclopentadienyl ruthenium and osmium catalysts.