Synthesis of (Imido)niobium(V)–Alkylidene Complexes That Exhibit High Catalytic Activities for Metathesis Polymerization of Cyclic Olefins and Internal Alkynes

Abstract

The (imido)­niobium­(V)–alkylidene complexes Nb­(CHSiMe3)­(NR)­[OC­(CF3)3]­(PMe3)2 (R = 2,6-Me2C6H3, 2,6- i Pr2C6H3, 1-adamantyl), which could be isolated from the dialkyl analogues by α-hydrogen elimination in the presence of PMe3, exhibited remarkable catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene, and the polymerizations proceeded in a living manner. Metathesis polymerizations of (unstrained) disubstituted acetylenes also took place, affording polymers with uniform (narrow) molecular weight distributions.

Synthesis of (Arylmido)niobium(V) Complexes Containing Ketimide, Phenoxide Ligands, and Some Reactions with Phenols and Alcohols

“…Nb( N -2,6-Me 2 C 6 H 3 )Cl 3 (dme), 40 Nb( N -2,6- i Pr 2 C 6 H 3 )Cl 3 (dme), 33 and Nb(NAd)Cl 3 (dme) 33 (Ad = 1-adamantyl) were prepared according to a published procedure. 33,40 Ethylene for polymerization was of polymerization grade (purity >99.9%, Sumitomo Seika Co., Ltd.) and was used as received. Elemental analyses were performed using EAI CE-440 CHN/O/S Elemental Analyzer (Exeter Analytical, Inc.).…”

Unexpected Selective Methyl Group Abstractions from SiMe3 Moieties of CH2SiMe3 Ligands To Give New Cationic Titanium Complexes

“…As mentioned in the introduction, it is known for alkyl‐substituted complexes to undergo α‐H abstractions to give alkylidene complexes, which are often thermally induced processes, if a suitable leaving group or an acceptor functionality for protons is present in these systems; such an example was recently presented by Nomura and co‐worker for the niobium imido complex Nb(NR)(CH 2 SiMe 3 ) 2 (OC(CF 3 ) 3 ) . Consequently, complex 2 was heated at temperatures that corresponded to the boiling points of n ‐hexane or toluene for seven days to induce α‐H abstraction followed by formal migration of the resulting H + to the C q, exo atom (Scheme ).…”

“…if as uitable leaving group or an acceptor functionality for protons is presenti nt hese systems;s uch an example was recently presented by Nomura and co-worker for the niobium imido complex Nb(NR)(CH 2 SiMe 3 ) 2 (OC(CF 3 ) 3 ). [20] Consequently,c omplex 2 was heated at temperatures that corresponded to the boiling points of n-hexaneo rt oluene for seven days to induce a-H abstractionf ollowedb yf ormal migration of the resulting H + to the C q,exo atom (Scheme 2). After removal of allv olatiles, complex 2 was reisolated and spectroscopic analysis revealed no indicationsf or the formation of the corresponding alkylidene complex I,w hich is further supported by the relatively high thermals tabilityo fc omplex 2 with ad ecompositiont em-peratureof132 8C.…”

Three Fluorinated Trityl Alcohols and their Lithium Salts – Synthesis, Molecular Structures, and Acidity

“…Interactions between organically bound fluorine atoms and metal ions across the periodic table have been the subject of intensive scientific interest, which was highlighted in two review articles by Plenio . For instance, metal salts with lithium, sodium, potassium, alkaline earth metals,[4b], vanadium, niobium, molybdenum, tungsten, iron, cobalt, copper, silver,[3a], zinc, tin, thallium,[11b] uranium or europium revealing various metal fluorine contacts are described for complexes derived from (CF 3 ) 3 COH. Furthermore, the combination of sterically demanding fluorinated alcohols with group 13 metals is a recurrent strategy for the design of extraordinarily strong Lewis acids as documented by Krossing's PhF · Al(OC(CF 3 ) 3 ) 3 and Al(O(C 6 F 10 (C 6 F 5 ))) 3 .…”