Rhenium complexes protonation

With rhenium there are several possible or probable H2 complexes as well as some cases that are very equivocal. It is believed that the [Re(PR3)2H8]+ ion, obtained by protonation of ReH7(PR3)2 must contain at least one H2 ligand, since a classical structure containing eight H ligands exceeds the possible valence of rhenium. Other protonated species, e.g., [Re(PR3)3H<]+, may well be classical polyhydrides. It is to be noted that protonation occurs only at low temperature otherwise there is a reaction such as the following in which H2 is evolved ... 

These -propargyl rhenium complexes undergo kinetic addition of nucleophiles at the central C atom to produce rhenacyclobutenes. The nucleophiles range from PR3 to malonate, acetylides, pyridines, and water. The derivatives of the addition of pyridines, however, are unstable and undergo further rearrangements to allene or acetylene complexes. Protonation of the metaUacyclobutenes produces u -allyl complexes. 

Disappointingly, the rhenium complex also was not capable of producing ammonia. Most generally, protonation of dinitrogen complexes led to evolution of the dinitrogen as the gas, often with the production of metal hydrides, a not unexpected result in view of the electron-richness of the metal sites to which dinitrogen was bound. That we were eventually successful was due to a combination of factors, all important in research, as seasoned practitioners will know. These were persistence, preparedness and serendipity. 

Acids, acyl, and aroyl halides all react with [ReCl(N2)(PMe2Ph)4]. However, protonation occurs at the metal to give the hydride [ReClH(N2)-(PMe2Ph)4], whereas slow acylation and aroylation occur at the end nitrogen atom. Interestingly, this latter reaction is the reverse of the preparation of the rhenium dinitrogen complexes. Alkyl halides do not react with rhenium complexes of dinitrogen. 

The introduction of a tetrazolate ligand on rhenium complexes allows for a tunability of the photophysical properties of these species. The use of a simple protonation-deprotonation protocol enables to reversibly change, light-emission output and performance of a series of Re(i)-aryl tetrazolate-based phosphors. ... 

Hieber and coworkers first prepared the pentacarbonyl hydride complex of rhenium by protonation of tte corresponding pentacarbonyl anion, [Re(CO)5]. Modified versions of the original syntheses have been reported, but these procedures still require extensive vacuum-line manipulations. Furthermore, the yield of ReH(CO)5 is only < 30% based on pure Na[Re(CO)5], which means that the overall yield from Re2(CO)io is much lower. 

Anion dissociation during the second reduction step create the vacant site. The key step is the formation of a metallocarboxylic complex, formed by nucleophilic attack of the formal Re(-I) center on the electrophilic carbon of the CO2 substrate. Decomposition of this intermediate by protonation leads to the formation of carbon monoxide, water and the starting rhenium complex. 

Reaction of 3 with Ph3C+PF6" resulted in the formation of methylidene complex [(n-C5H5)Re(N0)(PPh3)(CH2)]+ PF6 (8) in 88-100% spectroscopic yields, as shown in Figure 11. Although 8 decomposes in solution slowly at -10 °C and rapidly at 25 °C (She decomposition is second order in 8), it can be isolated as an off-white powder (pure by H NMR) when the reaction is worked up at -23 °C. The methylidene H and 13C NMR chemical shifts are similar to those observed previously for carbene complexes [28]. However, the multiplicity of the H NMR spectrum indicates the two methylidene protons to be non-equivalent (Figure 11). Since no coalescence is.observed below the decomposition point of 8, a lower limit of AG >15 kcal/mol can be set for the rotational barrier about the rhenium-methylidene bond. 

The infrared, NMR, and electronic absorption spectra of the two complexes H2FeRu2Os(CO)i3 and H2FeRuOs2(CO)13 have been taken to indicate a structure for these compounds similar to H2FeRu3(CO)13. However, the infrared and low-temperature proton NMR spectra of both compounds indicate that they exist as a mixture of isomers the two projected isomers for H2FeRu2Os(CO)13 are shown in Fig. 58 (247). The mixed manganese and rhenium-osmium complexes, H3MOs3(CO)13, have been prepared by acidification of the reaction mix-... 

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