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Carbene complexes bridging

One-electron oxidation of the vinylidene complex transforms it from an Fe=C axially symmetric Fe(ll) carbene to an Fe(lll) complex where the vinylidene carbon bridges between iron and a pyrrole nitrogen. Cobalt and nickel porphyrin carbene complexes adopt this latter structure, with the carbene fragment formally inserted into the metal-nitrogen bond. The difference between the two types of metalloporphyrin carbene, and the conversion of one type to the other by oxidation in the case of iron, has been considered in a theoretical study. The comparison is especially interesting for the iron(ll) and cobalt(lll) carbene complexes Fe(Por)CR2 and Co(Por)(CR2) which both contain metal centers yet adopt... [Pg.245]

A dinuclear silver(i) carbene complex, 22, was also isolated using a pyridyl-bridged biscarbene ligand (Scheme 7).65a,65b Complex 22 possessed a double helical structure with Ag-C bond distances of 2.080(4) and 2.087(4) A and a C-Ag-C angle of 165.5(2)°.65a Weak Ag-Ag interaction could also be observed with an Ag-Ag distance of 3.158 A.65a... [Pg.206]

With the long alkyl chain substitutions on the A-heterocyclic carbenes, lamella-structured silver(i) carbene complexes 27a and 27b (Figure 14) were isolated.74 It is interesting to note that the synthetic procedures for the two complexes are the same except for the use of different solvents of crystallization. The dinuclear 27a was obtained from recrystallization in dichloromethane- -hexane while the tetranuclear 27b was obtained from acetone. The structure of 27a could be interpreted as the dimeric form of [Ag(carbene)Br] bridged by intermolecular Ag-Br interactions. The Ag-G bond has a distance of 2.094(5) A. The tetranuclear 27b, on the other hand, could be regarded as two monocationic bis(carbene)silver(i) bridged by an [Ag2Br4]2 anion, with the presence of short Ag(cationic)-Ag(anionic) contact (3.0038(18) A) and comparable Ag-G bond distances (2.0945(5), 2.138(13) A). A related... [Pg.208]

A homoleptic methylene-bridged bis(carbene) dinuclear silver(i) complex, 55, was isolated in 81% yield from a two-step reaction, as shown in Scheme 13.100 The structure of 55 reveals a boat conformation with the two methylene groups protruding away from the Ag2 core in one direction. The Ag-C distances of 2.081(2)-2.095(2) A were in the normal range for silver(i) TV-heterocyclic carbene complexes, while an uncommonly short intramolecular Ag-Ag contact of 3.2039(3) A was observed in the homoleptic silver(i) carbene complexes. [Pg.215]

An impressive series of carbene- and carbyne-bridged complexes of platinum have been formed by reaction of metal carbene complexes with a platinum complex (equation 141). These complexes have been verified by X-ray crystallography, and the synthetic method appears to be one of some generality. Among the complexes of this type formed from carbenes are ones having metal frameworks with Pt—W,409-413 Pt—Mn414-418 and Pt—Cr413,417 bonds. [Pg.385]

Another broad class of compounds are the bridged carbene complexes. These compounds contain two identical or two different metal centers with the carbene centers bonded to both of the metal atoms in a bridging relationship. However, these binuclear complexes generally do not show classical carbene reactivity and will therefore not be discussed further, except to mention briefly the special case of the titanium-aluminum complex (3) developed by Tebbe and Grubbs and their coworkers.101 This, and related complexes, has proven to be particularly useful in organic synthesis, although its principal importance is in reactions other than cyclopropanations. [Pg.979]

One other carbene complex, a p2-vinylidene, has been prepared, from the xenophilic metal-metal bonded [Tp C2 4BrNi—RuCp(CO)2] (62) upon its reaction with PhC=CH. This affords 63, which is bridged by both i2-C=C(H)Ph and i2-CO ligands (Scheme 5).17... [Pg.119]

Ruthenium vinylidene and carbene complexes containing cyclopenta-dienyl ligands such as [(i75-C5H5)(PPh3)2Ru=C=CH2]+ are known and an excellent review describing the structures and reactivities of these classes of complexes is available (103). Treatment of the -vinyl-bridged porphyrin with Ru3(CO)12 yielded (TPP)Ru C=C(p-Cl-C6H4)2, ... [Pg.253]

The binaphthohydroquinone skeleton is accessible by a double benzannulation of a bi-phenylbis(carbene) complex using two equivalents of alkyne. Application of one alkyne equivalent affords the mono-benzannulated product the second benzannulation step proceeds with distinctly lower yield [68a]. A complementary approach to biaryls is based on 1,3-dialkynes (for example, 64) which undergo a stepwise benzannulation sequence (for example, yielding 65 and 66) (Scheme 26) [68c]. A one-step protocol starting from the ethylene-bridged bis-carbene complex 67 affords the conformationally less flexible biaryl 68, albeit in only moderate yield. [Pg.273]

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See also in sourсe #XX -- [ Pg.288 , Pg.289 ]

See also in sourсe #XX -- [ Pg.327 , Pg.328 , Pg.329 ]

See also in sourсe #XX -- [ Pg.305 ]



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Bridging carbenes

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