Transient species, organometallic

Detection of Transient Organometallic Species by Fast Time-Resolved IR Spectroscopy... 

Already a considerable number of transient organometallic species have been characterized by IR kinetic spectroscopy (see Table I). Like most other sporting techniques for structure determination, IR kinetic spectroscopy will not always provide a complete solution to every problem. What it can do is to provide more structural information, about metal carbonyl species at least, than conventional uv-visible flash photolysis. This structural information is obtained without loss of kinetic data, which can even be more precise than data from the corresponding uv-visible... 

Poliakoff, M. Weitz, E. Detection of Transient Organometallic Species by Fast Time-Resolved IR Spectroscopy, in Stone, F.G.A. R. West, Eds Advances in Organometallic Chemistry, 1986, 25, 277. 

Halogen on both trivalent and pentavalent phosphorus is susceptible to such displacement. Control of the reaction to provide synthetic utility will be noted. Both isolable organometallics and transient species generated and used in situ will be surveyed. 

An important development for detection of transient organometallic species is fast time-resolved infrared. The transient is generated rapidly by uv-visible flash photolysis and monitored by ir with ps resolution. Spectra are obtained from a series of kinetic traces recorded at about 4 cm interval. 

Transient absorption measurements have recently been recorded from the organometallic species chromium hexacarbonyl in ethanol solution [94], Absorption of a 65-fs, 310-nm excitation pulse was followed by measurement of excited-state absorption of a 65-fs, 480-nm probe pulse. The data shown in Figure 14 indicate a rapid nonexponential decay at short times followed by a gradual exponential rise. The slower feature was observed previously [95] and is known to correspond to the solvent complexation of Cr(CO)5 to yield Cr(CO)j(MeOH). The initial feature, which is observed at other probe wavelengths as well, is believed to correspond to the initial ligand loss reaction. Note that this case is different from ICN in that the initially excited wavepacket is not on the side of the Sj potential but rather (as is clear from the molecular symmetry) on a local potential maximum. The wavepacket must then spread that is, dissociation along either direction is equally likely. The rapid nonexponential decay was analyzed in terms of classical kinematics along a dissociative potential. 

It has been well established that the monoanionic teidentate 2,6-bis[(di-methylamino)methyl]phenyl ligand stabilizes otherwise unstable or transient organometallic species to such an extent that they become isolable (85). Especially in late transition metal chemistry, the three hard donor atoms of this ligand have been shown to enhance the nucleophilic character of Ni(II) and Pt(II) centers and, moreover, stabilize oi nometallic species in which the metal has an unusual oxidation number, e.g., Fe(IlI), ( (II), and Ni(III) (67-69) for an organometallic compound. Previously it was thought that this ligand enforces a coordination geometry to the... 

One unique aspect of anionic polymerization is that the reactive propagating species are not transient intermediates. Carbanions and organometallic species can be prepared and investigated independently of the polymerization process. These species can also be characterized and monitored during the polymerization. 

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