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Chelate Complexes of Functionalized Cycloheptatrienyl Ligands: 17‐ and 18‐Electron Molybdenum Complexes with Linked Cycloheptatrienyl−Phosphane Ligands and Their Use in Transition Metal Catalysis
Author(s) -
Tamm Matthias,
Baum Kim,
Lügger Thomas,
Fröhlich Roland,
Bergander Klaus
Publication year - 2002
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200203)2002:4<918::aid-ejic918>3.0.co;2-e
Subject(s) - chemistry , cycloheptatriene , ligand (biochemistry) , hydride , molybdenum , cationic polymerization , norbornene , transition metal , catalysis , metathesis , bimetallic strip , metal , medicinal chemistry , stereochemistry , inorganic chemistry , polymer chemistry , polymerization , organic chemistry , biochemistry , receptor , polymer
The synthesis of P ‐functionalized molybdenum chelate complexes incorporating the linked cycloheptatrienyl− phosphane ligand [2‐(diphenylphosphanyl)phenyl]cycloheptatrienyl, o ‐Ph 2 P−C 6 H 4 −C 7 H 6 , is described. The air‐stable ligand precursor [2‐(cyclohepta‐2,4,6‐trienyl)phenyl]diphenylphosphane ( 2 ) can be obtained in large quantities by addition of lithiated 2‐BrC 6 H 4 PPh 2 ( 1 ) to the tropylium cation C 7 H 7 + . Hydride abstraction employing the trityl cation, Ph 3 C + , results in the formation of the tricyclic phosphonium salt 3 . The P ‐functionalized cycloheptatriene 2 acts as an eight‐electron ligand on reaction with Mo(CO) 6 to afford the cycloheptatriene−phosphane complex [( o ‐Ph 2 PC 6 H 4 ‐η 6 ‐C 7 H 7 )Mo(CO) 2 ( P−Mo )] ( 4 ) as a single, chiral regioisomer, which undergoes clean hydride abstraction on treatment with (Ph 3 C)BF 4 . The resulting cationic cycloheptatrienyl−phosphane complex 5 reacts with sodium bromide to yield the uncharged “chiral‐at‐metal” complex [( o ‐Ph 2 PC 6 H 4 ‐η 7 ‐C 7 H 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 preparation of the 17‐electron mono‐ and dialkyl complexes [( o ‐Ph 2 PC 6 H 4 ‐η 7 ‐C 7 H 6 )Mo(CH 2 SiMe 3 )X( P−Mo )] (X = Br, 8 ; X = CH 2 SiMe 3 , 9 ). In combination with Me 3 SiCH 2 MgCl, complexes 7 and 9 prove to be active catalysts for the ring‐opening metathesis polymerization of norbornene. In addition, the X‐ray crystal structures of 2 , 4 , 5· CH 2 Cl 2 , 7· CHCl 3 , 8 , and 9· C 6 H 14 are reported.