Fluxional complex

Protonation of IrH5(Pcy3)2 affords a fluxional complex thought to be IrH6(Pcy3)2 with two (7y2-H2) ligands and two classical hydrides (Figure 2.99) from the H NMR (6 = -8.3 ppm at room temperature ... 

Cyclopentadienylcobalt(l) complexes react with 1,2,3-selenadiazoles 16 annulated with unsaturated cyclooctane rings to afford fluxional complexes 23 <1987JOMC39, 19890M800>, as illustrated in Equation (3). Reaction of these... 

These fluxional complexes have been fully characterized in solution by multinuclear NMR techniques. The data are consistent with a c -arrangement of the hydride and the silyl ligand. In the H NMR spectrum of 2a (in CDCI3 at 243 K) the hydride resonance is found at 6 = -2.66 ppm and consists of a doublet of doublets (Vp-h = 19.6, 152.7 Hz), which is flanked by platinum satellites ( pt-H = 972.3 Hz). A single crystal X-ray determination performed on 2a revealed that intramolecular short contacts between a thioether group and the platinum center are absent in the solid state. 

The fluxional complex [ZrCl2(Tp )(LL)] (LL = 4,6-dimethyl-2-thiolatepyrimidine) has been prepared by the reaction of [ZrCl3(Tp )] with the lithium salt or the protic form of the thiolato pyrimidine.11... 

This has a low energy barrier ( 25 kJ mol-1) and occurs rapidly ( 2 x 1010 s-1). However, for pyramidal PR3 compounds, the activation barrier has climbed to over 100 kJ mol-1, so inversion is very slow, sufficiently so to even allow enantiomer separation in the case of chiral phosphines. Coordination of the lone pair freezes the configuration. Examples of fluxional complexes tend to be found mostly, but not exclusively, amidst organometallic compounds. Spectroscopic methods, particularly NMR spectroscopy, assist in defining the fluxional behaviour. 

Although all of the compounds studied form columnar phases, differences between them become apparent according to the metal involved in the complex. Thus, the fluxional complexes (Fe(III)-(6.36) and Mn(III)-(6.36)) exhibit a hexagonal columnar phase (Colli) at low temperatures, whereas the nonfluxional complexes show a rectangular columnar phase (Coif). In the case of the Colh phase, microdomains composed of (A) or (A) configuration are present. This arises due to the possible... 

More recently Marx et al. [97] addressed the problem of the proton mobility in water through ab initio path integral simulations. They concluded that both H5O2 and H9O4 are only important as limiting structures and that numerous unclassifiable situations exist in between. Hence, they suggested that the solvated proton should be best visualized as a fluxional complex. 

The activation of Si-H bonds by adjacent transition metals, or main group elements " is important for the transformation of silanes. In many cases, the Si nuclear shielding is markedly reduced (extremely so in the fluxional complex 32, Scheme 9), accompanied by smaller values of coupling constants 7( Si, H) (see also the silylene complex 14 ). However, the 8 Si values are not really a criterion for M-H-Si bridging, as can be seen from the data for 35 and 36 (Scheme 9). 

We have also reacted activated catalyst "[Ph3P]2RuCO" with dimethyldivinylsilane and obtained a 1 1 complex which demonstrates dynamic NMR spectra depending on temperature. This fluxional complex is also capable of catalyzing the copolymerization of acetophenone and 1,3-divinyltetramethyldisiloxane [17]. 

VT-multinuclear NMR studies have allowed one to establish unequivocally whether the M-coordinated-C02 framework is a rigid structure or not To this end, it is necessary that other nuclei (such as the P-donor atoms of phosphanes) are bonded to the metal centre so that, when the metal favours the coupling, it is possible to observe whether the solid state stmcture is maintained in solution or the framework exhibits some fluxionality. Complex 1 has been extensively investigated and the fluxional behaviour has been well explained by coupling IR and NMR studies [6, 40],... 

H4Ru4(CO)i2 yields (136) and (137) as two previously uncharacterized organo-metallic products, and both may also be prepared by reaction of Ru3(CO)ia with cot (137) is fluxional, and may be carbonylated to yield an Ru2(CO) -(C sHie) derivative. Reaction of (cot)Fe(CO)3 with cot yields (138). H4RU4-(CO)x2 or Ru3(CO)i2 reacts with a cot-cyclopentadiene mixture to yield the fluxional complex (139), and structurally related derivatives may be obtained using chpt-cyclopentadiene and cot-chpt mixtures. Oxidation of (cot)Fe(CX))8-L [L=CO, PPhg, P(OPh)3] with AgPF yields the dimeric cation (140), characterized crystallographically, where L=P(OPh)3. ... 

The synthesis of a trinuclear cyclopentadienyl trihydrido complex having carbonyl ligands had been reported prior to the synthesis of 6 and 7. Treatment of (CpRu)2(CO)2( -CO)( -CHR) 17 with H2 (1 atm) under UV irradiation provides fluxional complex 18. The fluxionality involves the passage of tj-CsHs and CO ligands from one side of the Ru3 plane to the other. Protonation of 18 yields a non-fluxional cation 19 in which all three cyclopentadienyl ligands are on the same side of the RU3 plane (Equation (3)). Compound 18 has been shown to react readily with a wide... 

With many metal complexes, for a given coordination number, the energy difference between the two possible geometries in solution is low. Consequently, in solution the two structures may coexist in equilibrium. Such complexes are often referred to as fluxional complexes. Fluxionality with five coordinated complexes is particularly common. Note that in 2.3-2.S, all Ls need not be identical, in which case the symmetry properties of the metal complex would he affected. 

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