(Arylimido)niobium(V)–Alkylidenes as the Catalysts for Ring-Opening Metathesis Polymerization (ROMP) of Cyclic Olefins: Z-Specific ROMP of Cyclooctene by Nb(CHSiMe₃)(NC₆H₅)[OC(CF₃)₃](PMe₃)₂

Abstract

(Arylimido)niobium(V)–alkylidene complexes, Nb(CHSiMe3)(NAr)[OC(CF3)3](PMe3)2 (Ar = C6H5 (4), 2,6-F2C6H3, C6F5 (6)), Nb(CHSiMe3)(N-2,6-Cl2C6H3)(OC6F5)(PMe3)2 (7), and Nb(CHSiMe3)(N-2,6-F2C6H3)(OC6Cl5)(PMe3)2, have been prepared and identified. The pentafluorophenylimido analogue 6 and 7 showed superior catalytic activities for the ring-opening metathesis polymerization (ROMP) of norbornene (TOF = 56.1, 53.7 s–1, respectively, at 25 °C) and the activities increased at 50 °C (TOF ≥ 352 s–1). The prepared alkylidenes catalyzed the ROMP of cis-cyclooctene (COE), and the activity increased at high temperature (up to 80 °C). The Z-specific ROMP of COE has been demonstrated especially by the phenylimido analogue 4 at 80 °C, affording polymers possessing olefinic double bonds with exclusive cis selectivity (99%).

Synthesis of (Arylimido)niobium(V) Bis(diethylamide) Complexes Containing Phenoxide Ligands

“…The present method enabled synthesis of various four coordinate (arylimido)niobium(V)-phenoxide complexes from the starting tris(diethylamide) complexes, Nb(NAr)(NEt 2 ) 3 , which could be readily obtained from Nb(NAr)Cl 3 (dme) by treatment with LiNEt 2 . [28,32] Since unique reactivities in the phenoxide modified niobium(V)-alkylidene catalysts for ring-opening metathesis polymerization of cyclic olefins were demonstrated, [19] we hope that these catalysts also exhibit unique characteristics in olefin coordination polymerization.…”

“…Introduction of the steric bulk in the imido ligand also play a role to avoid the formation of dimeric bridged imido species, as exemplified in certain vanadium(V) complexes. [4,6,7,[9][10][11][12][13] However, synthesis of the low coordinative (four coordinate) unsaturated niobium(V) complexes containing a monodentate anionic donor ligands still have been limited, [14][15][16][17][18][19] although the (arylimido)vanadium(V) complexes containing the phenoxide-, [12,20,21] imidazolin-2-iminato-, [22] imidazolidin-2-iminato [22] and the others [23,24] exhibit high catalytic activities for ethylene (co)polymerization. This is because, as described previously, [15,16] reactions of Nb(NAr)Cl 3 (dme) (dme = 1,2-dimethoxyethane), widely available precursors from NbCl 5 , [25,26] with 1.0 equiv.…”

Olefin Metathesis and Stereoselective Ring-Opening Metathesis Polymerization with Neutral and Cationic Molybdenum(VI) Imido and Tungsten(VI) Oxo Alkylidene Complexes Containing N-Chelating N-Heterocyclic Carbenes

“…The area of stereoselective ring-opening metathesis polymerization − (ROMP) by well-defined group 5, 6 and group 8 metal alkylidenes has blossomed into a mature field over the last two decades, given the large number of publications and that all possible stereoregular structures can now be accessed, though with different ease and generality. In this regard, neutral and cationic molybdenum imido, tungsten imido, and tungsten oxo alkylidene N-heterocyclic carbene (NHC) complexes have evolved as highly active and stereoselective catalysts. ,,,− Recently, we reported on molybdenum imido alkylidene complexes containing N-, O-, and C-chelating NHCs. , In view of their unique reactivity but also stability, we extended our research to cationic molybdenum and tungsten­(VI) imido and oxo alkylidene complexes containing N-chelating NHCs.…”