Rhenium bonds

Dihalocarbene complexes are useful precursors to new carbenes by nucleophilic displacement of the chlorine substituents. This has been nicely illustrated for Fe(TPP)(=CCl2) by its reaction with two equivalents of Re(CO)5J to give the unusual /t-carbido complex Fe(TPP)=C=Re(CO)4Re(CO)5 which also contains a rhenium-rhenium bond. " The carbido carbon resonance was observed at 211.7 ppm in the C NMR spectrum. An X-ray crystal structure showed a very short Fe=C bond (1.605(13) A, shorter than comparable carbyne complexes) and a relatively long Re=C bond (1.957( 12) A) (Fig. 4, Table III). " ... 

In the imido series, however, the rhenium-nitrogen distances for rhenium(V) average 180.1pm, which is somewhat longer than the average of the values for several rhenium(VII) compounds, 174 pm. The one terminal thio-rhenium bond, 209.2 pm, is significantly shorter than any of the p-S bonds, which average 231pm. 

Me2Ph)(ri-C5Me5) -7-( r-H)-2,2,2-(CO)3-c/o.so-2,l-ReCBioHio] (127) which were characterized by X-ray diffraction (Chart 22). The nature of the isomerism derives from whether the B-H M bridge involves an a-BH (as in 126) or a p-BH (as in 127) in the rhenium-bonded CBBBti face, in combination with the relative disposition anti or syn) of the phosphine with respect to this hydride. A more detailed discussion of this system is presented elsewhere. ... 

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... 

For Mn2(CO)10, the ions corresponding to Mn2(CO)+ ( =8 or 9) were either not seen (247) or were of very low abundance (49,164), and Mn2(CO)7 was only apparent with less than the normal 70-V ionizing potential. All other Mn(CO)+ ( =0-5) and Mn2(CO)J (w=0-10) ions were observed, but no doubly charged ions were seen. The carbide ions MnC(CO)J (n=0-2) were observed in low abundance. Similar ions were found in the spectrum of Re2(CO)10, as also was the series Re2(CO) C+ ( = 0-5), and the doubly charged ions Re2(CO)2+ and Re2(CO) C2+ ( =0-6). Major differences in intensities in the two spectra can be attributed to the greater strength of the rhenium-rhenium bond. About 60% of the ions produced... 

R. I. Beattie, and P. J. Jones, Methyltrioxorhenium. An Air-Stable Compound Containing a Carbon-Rhenium Bond, Inorg. Chem. 18, 2318-2319 (1979). 

Dinuclear Complexes Containing a Rhenium-Rhenium Bond and Oxide and/or Halide Bridges 176... 

Studies by a group at the Shell Laboratories in Amsterdam (73) have been reported as evidence of interaction between platinum and rhenium in catalysts containing these two elements. These workers, on the basis of infrared spectroscopy studies of carbon monoxide chemisorbed on platinum-rhenium catalysts, and also of X-ray photoelectron spectroscopy measurements on the catalysts, concluded that platinum-rhenium bonds are present in the surface. 

Re(Tp)(CO)(L)(ri2-ethylene)] (L = BuNC, PMe3, py, Meim, NH3) (Fig. 2.50) have been prepared by the reaction of [Re(Tp)(CO)(L)(rj2-cyclohexene)] with ethylene. These complexes have been used to determine the rates of the propeller-like rotation of ethylene about the ethylene-rhenium bond using spin-saturation transfer experiments at low temperatures.223... 

An alternative procedure involves the photochemical cleavage of the rhenium-rhenium bond in dirhenium decacarbonyl in the presence of a chlorocarbon solvent.21,22 This method suffers from contamination by the tetracarbonylchloro-rhenium dimer, which forms in large quantities during photolysis.21,22 To prevent formation of dimer, the photolysis is performed under an atmosphere of carbon monoxide. The yield of ReCl(CO)5 is essentially quantitative using this procedure. 

The hydridic character of the rhenium-bonded hydrogen of 34a, b facilitated the hydride abstraction upon treatment with either Bronsted acids or Lewis acids [32]. Depending on the nature of the phosphine substituent, the 16e Re(—I) dinitrosyl cations [Re(NO)2(PR3)2][BAr 4] (35, R = iPr a, Cy b) could be accessed from the reaction of either 34a with [H(OEt2)2][BAr 4] or 34b with [PhaC] [BAi 4]. Further anion modification to access the corresponding [B(C6F5)4] salts [Re(NO)2(PR3)2l[B(C6F5)4] (36, R = Pr a, Cy b) showed enhanced solubilities in nonpolar solvents [105]. 

As already mentioned in the Introduction, Cotton [1,2] stated that the two Re atoms are bonded through a quadruple bond in Re2Clg . The short rhenium-rhenium bond between two ReCl4" moieties was described as one a, one degenerate n, and one 8 bond. This work inspired experimental research that brought about the discovery of homo- and hetero-dinuclear compounds with metal-metal quadruple bonds [16]. 

Another example Br4Re-ReBr4, structure III, has two unusual structural features. The bromines attached to the two different metal atoms are not staggered to minimize repulsive interactions, but are eclipsed. Moreover, the rhenium-rhenium bond is very short. These structural features and the magnetic properties have been interpreted as indicating that a quadruple bond links the metal atoms. The bonds include one o--bond, two r-bonds, and a S (delta)-bond. A S bond can be visualized by placing the bonded atoms on a z coordinate axis and having overlap between two orbitals (one from each metal atom), structure IV. 

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