Methyl formate, rhenium complex

Alkyl ligands are strong a -donors, and coordination of such ligands to metal centers such as rhenium(I) and ruthenimn(II) would perturb the electronic structures of the metal centers and give complexes with remarkable photochemical properties. Irradiation of the complexes [Re(CO)3(R)(4,4 -Me2-bpy)j (R = Ft, Tr, Bz) into their visible MLCT absorption bands (ca. 400-500 nm) resulted in extremely efficient homolytic cleavage of the Re-R bonds with the formation of the radicals [Re(CO)3(4,4 -Me2-bpy)]- and R-.i Tiss -pjjg methyl analogue underwent a similar photochemical reaction, but with a quantum yield of only 0.4. It was proposed that... 

Re(CO)3(/t-OCH3)3Re(CO)3] (64) whereas decreasing pressure favoured production of rhenium clusters of higher nuclearity with mixed (/t-oxo)- and (/r-methanolato) bridges. The presence of 1.33 equivalent of base per metal atom in the clusters 44 and 44b facilitates subsequent reactions, that demand base. The reaction of 44 with (HCsMes), for example, resulted in the quantitative formation of 45 [79], In the case of the trinuclear rhenium cluster 44b, reaction with the caibene precursor 1,1 -methylene-bis(3-methyl-1 //-imidazolium)-diiodide yielded the corresponding mononuclear Re(I) complex (65) with the bidentate caibene ligand (see Scheme 14) [80]. 

Perhaps the strongest evidence for the formation of an alkane complex comes from the low temperature NMR experiments with CpRe(CO)3. Irradiation at —80°C in cyclopentane results in the formation of CpRe(CO)2(c-pentane), for which a resonance for theCH2 bound to the metal is observed in the NMR spectrum at 5 —2.32, consistent with either a symmetrical binding of both hydrogens ( 7 -H,H) or a rapid interchange between two cr-C-H ( -C,H) complexes. Irradiation in pentane solvent leads to the formation of three distinct species, assigned as coordination of rhenium to the methyl, Q-methylene, and central methylene of pentane (Equation (7)). ... 

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