Parallel vs. perpendicular alkyne coordination in binuclear complexes. The first examples of reactivity differences in isomers differing in their alkyne coordination modes

George, Darren S. A.; McDonald, Robert; Cowie, Martin

doi:10.1139/v96-257

Cited by 10 publications

(6 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These assignments have been confirmed by 13 C− 1 H NMR correlation experiments. The observed pattern suggests that the bonding of the allyl ligand approaches the σ, π-coordination mode, as is found for [RhM(η 3 -C 3 H 5 )(CO) 3 (dppm) 2 ] (M = Os, Ru). 6b,43b Although the chemical shifts are also consistent with an η 1 -allyl group, which normally gives rise to signals at δ 2.0−3.5 for the methylene protons and δ 3.5−5.5 for the olefinic hydrogens, coupling observed between the iridium-bound phosphines and all five hydrogens on the allyl ligand is consistent with η 3 -coordination. In addition, the high-field protons (H a H b ) would be expected to be equivalent in an η 1 -allyl.…”

Section: Results and Compound Characterizationsupporting

confidence: 53%

“…Alkynyl groups have also been implicated as intermediates in the transformation of 1-alkynes to vinylidenes . Certainly, in binuclear late-metal complexes we have shown that this transformation is extremely facile and have proposed that it is facilitated by the μ-η 1 :η 2 -alkynyl binding mode, in which migration of the hydride ligand from an intermediate such as C to the alkynyl β-carbon occurs readily, as diagrammed in eq 1. 6h, Intermediate C can be considered as containing a metal-substituted alkyne moiety (RC⋮CM), which is π-bound to the second metal, with the process shown in eq 1 being analogous to migratory insertion involving mutually cis hydride and alkyne ligands. We sought to extend this analogy to carbanionic ligands in efforts to induce migration of an alkyl or related group from one metal to the adjacent β-carbon of an μ-η 1 :η 2 -alkynyl group.…”

Section: Introductionmentioning

confidence: 91%

“…Certainly the analogous migrations of alkyls to coordinated alkynes are well-known. 14d, Although most previous examples of C−C bond formation involving alkynyl groups occur at the alkynyl α-carbon, 1f,o,q,4a,b,8b,3l we are aware of two examples of apparent migration to the β-carbon of a bridging alkynyl group to generate vinylidene-bridged complexes. In the first case, migration of an aryl group in a Ti/Cu complex occurs, whereas in the second, migration of a methyl ligand in a diiridium complex was observed 6h. In this report we describe our studies aimed at probing this uncommon mode of carbon−carbon bond formation.…”

Section: Introductionmentioning

confidence: 95%

“…Not only does it serve as a common precursor to vinylidenes, themselves versatile ligands in carbon−carbon bond formation, but alkynyl complexes have also been implicated in a number of carbon−carbon bond-forming processes such as alkyne oligomerization and polymerization and cycloaddition reactions . As part of an ongoing effort to determine how adjacent metals can influence the reactivity of hydrocarbyl ligands, we have undertaken a study of bridging alkynyl groups in binuclear complexes …”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

An Unusual Example of Allyl-to-Alkynyl Migration in a Phenylacetylide-Bridged Heterobinuclear Complex of Rhodium and Iridium

et al. 1999

Self Cite

View full text Add to dashboard Cite

The reactivity of the alkynyl-bridged complex [RhIr(CO) 2 (µ 2 -η 1 :η 2 -C 2 Ph)(dppm) 2 ][X] (X ) BF 4 (1a), SO 3 CF 3 (1b); dppm ) Ph 2 PCH 2 PPh 2 ) with electrophiles has been demonstrated. Protic acids HX (X ) BF 4 , SO 3 CF 3 ) first yield the oxidative-addition products [RhIr(X)(CO) 2 -(µ-H)(µ-C 2 Ph)(dppm) 2 ][X], which under carbon monoxide result in displacement of the weakly coordinating BF 4or SO 3 CF 3anions and subsequent conversion to the vinylidene-bridged 5), Cl ( 6)), by coupling of the alkynyl and allyl groups at the β-position of the alkynyl moiety. NMR studies at low temperatures show coordination of allyl halide at Ir at -80 °C, followed by allyl halide loss and subsequent oxidative addition at -50 °C. The oxidative-addition intermediates, [RhIr( 9), Cl ( 10)), rearrange to the allylvinylidene products (5 and 6) at ambient temperature. Although halide removal from compounds 5 and 6, using AgBF 4 , does not result in destabilization of the allylvinylidene fragment, resulting instead in replacement of halide by fluoborate ion, the reaction of 1 with allyl halide in the presence of a silver salt does not lead to coupling of the allyl and alkynyl moieties, but gives [RhIr(ηAddition of halide ion to this η 3 -allyl complex at ambient temperature again leads to formation of 5 or 6. On the basis of these results a mechanism is proposed for the allyl/alkynyl coupling reaction.

show abstract

Section: Results and Compound Characterizationsupporting

confidence: 53%

Section: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

An Unusual Example of Allyl-to-Alkynyl Migration in a Phenylacetylide-Bridged Heterobinuclear Complex of Rhodium and Iridium

et al. 1999

Self Cite

View full text Add to dashboard Cite

show abstract

“…These spectroscopic data do not distinguish between a bridging phenylacetylene ( C ) or a phenylvinylidene ligand ( D ), and location of the phenylacetylene-derived carbons in the 13 C{ 1 H} NMR spectrum in order to differentiate between the two bonding modes was unsuccessful. Coordination of terminal alkynes in a bridging mode or in a rearranged vinylidene mode is common in binuclear complexes. 6b,,, In both structures C and D , the phenyl group derived from phenylacetylene is shown to be directed away from the molybdenum center in order to minimize steric interactions with the molybdenum-bound ligands. The possibility of having the alkyne η 2 -bound to molybdenum is ruled out, based on the already crowded environment at this metal.…”

Section: Results and Compound Characterizationmentioning

confidence: 99%

Mixed-Metal Hydrocarbyl Complexes Involving the Rh/Mo and Rh/W Metal Combinations

et al. 1999

Self Cite

View full text Add to dashboard Cite

Reaction of [RhMo(H)(CO) 4 (dppm) 2 ] (dppm ) Ph 2 PCH 2 PPh 2 ) with a number of alkynes, RCtCR′ (R ) R′ ) C(O)OCH 3 , CF 3 ; R ) H, R′ ) C(O)CH 3 , C(O)OCH 3 ) yields the alkenyl complexes [RhMo(C(R′)dC(H)R)(CO) 4 (dppm) 2 ], which in all cases have an electron-withdrawing substituent on the R-carbon. A series of analogous complexes [RhMo(R)(CO) 4 (dppm) 2 ] (R ) CHCH 2 , CH 3 , CH 2 CHCH 2 , CH 2 C 6 H 5 , C 6 H 5 ) are prepared by the reaction of [RhMoCl-(CO) 4 (dppm) 2 ] and the appropriate Grignard reagent. The analogous Rh/W complex (R ) CHCH 2 ) was prepared from [RhWCl(CO) 4 (dppm) 2 ] and vinylmagnesium chloride. In all cases the hydrocarbyl fragment is η 1 -bound to Rh, with the four carbonyl ligands primarily bound to the group 6 metal; two carbonyls assume a semibridging arrangement. The reaction of both vinyl complexes (Rh/Mo and Rh/W) with HBF 4 at -80 °C yields the respective ethylidene products [RhM(dC(H)CH 3 )(CO) 4 (dppm) 2 ][BF 4 ] by protonation at the β-carbon of the vinyl group. Upon warming, these carbenes transform to the ethylene adducts [RhM(C 2 H 4 )(CO) 4 -(dppm) 2 ][BF 4 ]. Owing to uncertainties concerning the structure of the halide precursor [RhMoCl(CO) 4 (dppm) 2 ], its structure was determined by X-ray techniques and the chloro ligand was found to bridge the metals giving a square planar coordination at Rh and an octahedral coordination at Mo. One carbonyl on Mo assumes a weak semibridging interaction with Rh.

show abstract

Phase stabilization in cinnarizine complexes using X-ray profile analysis

et al. 2001

View full text Add to dashboard Cite

Characterization of cobalt(II), cadmium(II), copper(II) and tin(II) cinnarizine complexes have been carried out using conductivity, electronic spectra, infrared, nmr, thermogravimetric and Xray analyses to establish the nature of phase stabilization in these materials. Also, the intrinsic strain components present in these materials during the formation have been computed using wide-angle X-ray scattering analysis. The variation of the crystallite shape ellipsoid in these materials has been discussed on the basis of Hosemann's paracrystalline model.

show abstract

Parallel vs. perpendicular alkyne coordination in binuclear complexes. The first examples of reactivity differences in isomers differing in their alkyne coordination modes

Cited by 10 publications

References 40 publications

An Unusual Example of Allyl-to-Alkynyl Migration in a Phenylacetylide-Bridged Heterobinuclear Complex of Rhodium and Iridium

An Unusual Example of Allyl-to-Alkynyl Migration in a Phenylacetylide-Bridged Heterobinuclear Complex of Rhodium and Iridium

Mixed-Metal Hydrocarbyl Complexes Involving the Rh/Mo and Rh/W Metal Combinations

Phase stabilization in cinnarizine complexes using X-ray profile analysis

Contact Info

Product

Resources

About