Abstract

AbstractThe synthesis of P‐functionalized molybdenum chelate complexes incorporating the linked cycloheptatrienyl‐phosphane ligand [2‐(diisopropylphosphanyl)phenyl]cycloheptatrienyl (o‐iPr2P−C6H4−C7H6) is described. From the ligand precursor [2‐(cyclohepta‐2,4,6‐trienyl)phenyl]diisopropylphosphane (1) the paramagnetic 17‐electron dibromide [(o‐iPr2PC6H4‐η7‐C7H6)MoBr2(P−Mo)] (2) can readily be obtained. This is a versatile starting material for the preparation of cycloheptatrienyl molybdenum hydrides [(o‐iPr2PC6H4‐η7‐C7H6)Mo(η2‐BH4)(P−Mo)] (3) and [(o‐iPr2PC6H4‐η7‐C7H6)Mo(PPh3)H(P−Mo)] (4). Treatment of 3 with dimethylanilinium tetraphenylborate ([PhNMe2H][BPh4]) allows the production of the cationic 14‐electron complex fragment [(o‐iPr2PC6H4‐η7‐C7H6)Mo(P−Mo)]+ (13), which can be stabilized in the presence of suitable ligands L. The complexes [(o‐iPr2PC6H4‐η7‐C7H6)MoL2(P−Mo)]BPh4 [L = dimethylphenyl isocyanide, (5)BPh4; L2 = η4‐2,5‐norbornadiene, (6)BPh4; L2 = η2‐phenylacetylene, (7)BPh4; L2 = η2‐tert‐butylacetylene, (8)BPh4] can thus be isolated in good yields. The alkyne complex (7)BPh4 can be used as a single‐source catalyst for the oligomerization of phenylacetylene, affording a mixture of triphenylbenzenes and linear oligomers. Quantum chemical calculations reveal an intimate relationship between the catalytically active 14‐electron complex fragment [(o‐iPr2PC6H4‐η7‐C7H6)Mo(P−Mo)]+ (13) and hypothetical isoelectronic and isolobal complexes of the type [(o‐iPr2PC6H4‐η5‐C5H4)M(P−M)]+ (M = Ru, 14; M = Os, 15), indicating that cycloheptatrienyl molybdenum systems might in general be a suitable replacement for cyclopentadienyl ruthenium and osmium catalysts. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

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