Rhenium carbonyl compounds

Various rhenium carbonyl compounds can be prepared on the surface of Si02 or MgO (Scheme 16.1), as described below. 

Re(CO)3(MeCN)3]PF6 has been prepared and this compound appears to be a useful precursor for the preparation of cationic rhenium carbonyl compounds.625 Carbonylation of tertiary phosphino-complexes under reducing conditions provides a convenient synthetic route to rhenium mono- and poly-carbonyl complexes.626... 

Unlike most metal complexes containing the fa c-(diim i n c) Re1 (CO). unit, which are typically highly luminescent in solution, trinuclear rhenium carbonyl compounds 7 and 8 (see Fig. 11a) show only weak luminescence ( em = 0.0015) in CH3CN at room temperature [36], The quenching appears to occur via intramolecular... 

The pentacarbonylrhenium halides, first prepared by Hieber,12 are starting materials for the syntheses of many novel rhenium carbonyl compounds.3"7 Pho-... 

The pentacarbonylrhenium halides, first prepared by Hieber, are starting materials for the syntheses of many novel rhenium carbonyl compounds. Photochemical, vibrational, and kinetic " properties of these molecules have been studied. A rhenium carbonyl halide-alkyl aluminum halide system polymerizes acetylene and is a useful olefin-metathesis catalyst. " ... 

Rhenium carbides can be afforded by pyrolysis of simple rhenium carbonyl compounds. 

Manganese and rhenium carbonyl compounds, such as 8, react with AgAsFe in liquid SO2 to give the carbonyl complexes 9 incorporating the sulfur dioxide. ... 

Only scare data is available in the literature on the application of rhenium containing mono- or bimetallic catalysts in the hydrogenolysis of esters to alcohols. Decades ago Broadbent and co-workers studied the hydrogenation of organic carbonyl compounds (aldehydes, ketones, esters, anhydrides, acids,... 

Reaction of the manganese and rhenium carbonyls, M2(CO)10, with Ru3(CO)12 or Os3(CO)12 in a 3 1 ratio yields the products [M(CO)5]2M (CO)4, with M = Re or Mn, M = Ru or Os. These are considered to be linear trinuclear metal systems. The only other trinuclear carbonyl derivative isolated is OsCo2(CO)n, obtained as one of a number of compounds from the reaction of Co2(CO)8 with H2Os(CO)4. No structural data are available for this compound (241). 

The existence of the neutral rhenium carbonyl [Re(C0)4] was first claimed in 1965 206 but, although it is easily sublimed, it has not yet been characterized by mass spectrometry and the value of n is still not known. This colourless substance [v (CO) 2055 and 1995 cm-1 in CHC13] has been obtained as a by-product in the synthesis of Re2(CO)i0 starting from Re2S7, copper powder, and carbon monoxide at 85 atm, 200 °C206>. There has also been a report of the compound Re4(CO)10(PPh2Me)6, which can be considered to be a substitution product of the hypothetical species, Re4(CO)i6 it has been obtained by a photochemical reaction between Re2(CO)j0 and PPh2Me194. In both cases, and particularly in the phosphine derivative, a tetrahedral structure seems improbable because of steric constraints. 

Silicon and germanium hydrides react with cobalt, manganese and rhenium carbonyls affording complexes having a silicon (or germanium)-metal bond. These reactions, described previously for inactive compounds have been used in the synthesis of optically active silyl and germyl-transition metals ... 

Rhenium(0) compounds are rare and frequently lie in the realm of the organometallic chemistry. A simple example is decacarbonyldirhenium(0) in which two staggered, square-pyramidal Re(CO)5 fragments are held together by a single rhenium-rhenium bond. Substitution of carbonyl ligands is possible by tertiary phosphines and arsines, silanes and isocyanides, and binuclear Re-Re, Mn-Re, and Co-Re complexes have been studied. " Successive replacement of CO ligands can readily be observed by vibrational spectroscopy. This has been demonstrated... 

Metal complexes of pyrrole have also been investigated as substrates for lithiation reactions, with both iron and rhenium Tj -pyrrole derivatives having been found to undergo a-lithiation [90H(31 )383]. Azaferrocene was the first derivative of this type to be studied [83JOM(25l)C41], but it was found that lithiation was not selective and occurred equally in both rings. However, notwithstanding this, it has recently been reported that isomer-ically clean products can be obtained in certain circumstances from reaction with certain carbonyl compounds (Scheme 12) (89MI2). 

These expressions have been applied to the series isocyanide and carbonyl complexes of rhenium(I) tr ns-[ReL2(dppe)2]" (L = CNR, CO) [19, 20] and of nitrile and carbonyl compounds of iron(II) tmns-[FeL2(depe)2]2+ (L = NCR, CO) [35], and the Es and /J values of the corresponding trons- ReL(dppe)2 " and trans- FeL(depe)2 " " centers, which are given in Table 9, have been discussed earlier. 

Unlike manganese, rhenium is reported to form an alkyl compound, dimethyl rhenium. Re(CH )3. Like manganese, it forms a dirhenium compound with carbon monoxide, (CO)5ReRe(CO)5, as well as hydrogen-halogen and alkyl-carbonyl compounds. It also forms a dicyclopentadienyl compound, (CsHjJReH. 

High-valent rhenium dioxo complexes, ReC>2l(PR3)2, catalyse the hydrosilylation of carbonyl compounds.264 DFT calculations suggest rate-determining dissociative addition of the Si-H bond (of H-Si-alkyl3) across the Re=0 bond, with subsequent carbonyl coordination and reduction. 

In contrast to the chalcogen-bridged complexes, no similar oxygen-bridged compounds of iron, cobalt, or nickel exist. However, we obtained such oxo or i-ol-carbonyl complexes of chromium and its homologs, as well as of rhenium. The compounds are the products of the reactions of the respective metal carbonyls with bases (VII). 

Fig. 11 (a) Trinuclear rhenium carbonyl complexes 7 and 8 and (b) UV-Vis difference spectra (Aabs = At - At = 0) of compound 7 in CH3CN at 293 K after irradiation at 366 nm for 0, 1,2, 3, 4, 6 h, and inset shows the emission spectral changes before and after photolysis (reproduced with permission from [39])... 

No carbonyl compounds of manganese are known but there are however compounds of rhenium, namely Re2(CO)10 the existence of which can be understood in the same way on comparison with Os(CO)5 which has a radon configuration. 

---