Vanadium

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

“…1 H NMR (C 6 D 6 ): δ 7.33 (d, 2H, J = 7.80 Hz, Ar-H), 6.92 (t, 1H, J = 7.81 Hz, Ar-H), 6.89 (d, 2H, J = 7.48 Hz, Ar-H), 6.72 (t, 1H, J = 7.47 Hz, Ar-H), 3.67 (m, 8H, J = 6.43 Hz, -CH 2 -CH 3 ), 2.36 (s, 6H, À CH 3 ), 1.54 (s, 18H, À (CH 3 ) 3 ), 1.05 (t, 12H, J = 6.97 Hz, À CH 2 -CH 3 ). 13 6.89 (t, 1H, J = 7.75 Hz, Ar-H), 3.85 (m, 2H, J = 6.83 Hz, À CH-(CH 3 ) 2 ), 3.73 (m, 8H, J = 4.78 Hz, À CH 2 -CH 3 ), 1.54 (s, 18H, À (CH 3 ) 3 ), 1.14 (d, 12H, J = 6.81 Hz, À CH-(CH 3 ) 2 ), 1.06 (t, 12H, J = 6.96 Hz, À 2 -CH 3 ). 13 (3 a).…”

“…Certain high oxidation state group 5 and 6 transition metal complexes containing arylimido ligands are known to be efficient catalysts or catalyst precursors for olefin metathesis as well as olefin polymerization/oligomerization. [1][2][3][4][5][6][7][8] The arylimido ligand modification plays a role not only to stabilize the oxidation state, but also to tune their electronic and steric natures of the complexes through the metal-nitrogen double bond. 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.…”

“…The arylimido ligand modification plays a role not only to stabilize the oxidation state, but also to tune their electronic and steric natures of the complexes through the metal‐nitrogen double bond. 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 [4,6,7,9–13] . However, synthesis of the low coordinative (four coordinate) unsaturated niobium(V) complexes containing a monodentate anionic donor ligands still have been limited, [14–19] 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.…”

“…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.…”

(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

“…Certain high-oxidation-state metal–alkylidene complexes with early transition metals − have been known to play essential roles as catalysts in olefin metathesis reactions, − ,− which have been recognized as useful methods for the synthesis of functional polymers − as well as fine chemicals. − In particular, ring-opening metathesis polymerization (ROMP) of cyclic olefins is widely employed for the synthesis of advanced polymers. − ,, In contrast to successful examples of ROMP demonstrated by molybdenum­(VI)– and tungsten­(VI)–alkylidene catalysts, − , and later by vanadium­(V)–alkylidene catalysts, − reports of organo-niobium complex catalysts still have been limited until recently (Chart ). − After the first report by Mashima et al in 1997 (catalyst A ), there were two reports for the ROMP of norbornene (NBE) in 2016 (catalysts B and C ). , In particular, (imido)­niobium–alkylidenes, Nb­(CHSiMe 3 )­(NR)­[OC­(CF 3 ) 3 ]­(PMe 3 ) 2 ( C ), not only exhibited much higher catalytic activ...…”