N-heterocyclic complexes

General methods for the preparation of N-heterocyclic complexes have been well summarized previously (2). One of the new synthetic procedures involves the use of triflato complexes, e.g., cis-... 

The properties of the N-heterocyclic complexes of silver(II) have recently been reviewed and it was found that in most complexes square planar coordination occurs about the central ion although higher coordination numbers are known.496... 

Table 64 Spin Hamiltonian Parameters Obtained from ESR Studies of N-heterocyclic Complexes of Ag 1... 

The magnetic moments for solid silver(II) N-heterocyclic complexes are generally close to 1.8 BM suggesting quenched orbital angular momentum and spin-only paramagnetism (Table... 

Table 22 Structures Six-membered N-Heterocyclic Complexes (Pyridine, Pyrazine, Bipyridyl, Phenanthroline...

Table 25 Structures Five-membered N-Heterocyclic Complexes of Cobalt (II, III)...

The bidentate diborane 126 selectively complexes fluoride anion (see Scheme 13) with an association constant >5x 10 M in THE, and can serve as a colorimetric anion sensor <2004CC1284>. Four-coordinate boron N-heterocycle complexes (L-N,N )BPh2 exhibit luminescence and electroluminescence in a broad range of visible wavelengths depending on the substituents on the chelate heterocycle <2005MI143>. 

The neutral radical 11.12 is an interesting heterocyclic analogue of 2,2 -bipyridyl. This paramagnetic (spin-bearing) ligand forms an N, -chelated complex with bis(hexafluoroacetylacetonato)cobalt(ir). ... 

Versatile supramolecular helicatedmetal complexes with N-heterocyclic ligands 97CRV2005. 

Isolation and characterization of stereoisomers in di- and trinuclear complexes with N-heterocyclic ligands 98CSR185. 

Complexes of N-heterocycles with boron compounds 99JOM(581)129. 

Rhenium(VI) complexes, 4,194 alkoxides, 4,196 amides, 4,194 amines, 4,199 carboxylates, 4,199 dimethylformamide, 4,199 dioxane, 4,198 halides, 4,195,199 2-hydroxypyridine, 4,199 imides, 4,194 magnetic behavior, 1,271 mixed sulfur-nitrogen compounds, 4,196 N heterocycles, 4,199 nitrides, 4,194 oxide halides, 4, 195 oxoanions,4,196 pyridine, 4,199 sulfates, 4,198 sulfur compounds, 4,196 tellurates, 4,198... 

The surprising stability of N-heterocyclic carbenes was of interest to organometallic chemists who started to explore the metal complexes of these new ligands. The first examples of this class had been synthesized as early as 1968 by Wanzlick [9] and Ofele [10], only 4 years after the first Fischer-type carbene complex was synthesized [2,3] and 6 years before the first report of a Schrock-type carbene complex [11]. Once the N-heterocyclic ligands are attached to a metal they show a completely different reaction pattern compared to the electrophilic Fischer- and nucleophilic Schrock-type carbene complexes. 

During the last decade N-heterocyclic carbene complexes of transition metals have been developed for catalytic applications for many different or-... 

The search for even more active and recyclable ruthenium-based metathesis catalysts has recently led to the development of phosphine-free complexes by combining the concept of ligation with N-heterocyclic carbenes and benzyli-denes bearing a coordinating isopropoxy ligand. The latter was exemplified for Hoveyda s monophosphine complex 13 in Scheme 5 [12]. Pioneering studies in this field have been conducted by the groups of Hoveyda [49a] and Blechert [49b], who described the phosphine-free precatalyst 71a. Compound 71a is prepared either from 56d [49a] or from 13 [49b], as illustrated in Scheme 16. 

Independently, Caddick et al. reported microwave-assisted amination of aryl chlorides using a palladium-N-heterocyclic carbene complex as the catalyst (Scheme 99) [lOlj. Initial experiments in a domestic microwave oven (reflux conditions) revealed that the solvent is crucial for the reaction. The Pd source also proved very important, since Pd(OAc)2 at high power in DMF gave extensive catalyst decomposition and using it at medium and low power gave no reaction at all. Pd(dba)2/imidazohum salt (1 mol% catalyst loading) in DME with the addition of some DMF was found to be suitable. Oil bath experiments indicated that only thermal effects are governing the amination reactions. 

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