Wavelegth-, Medium-, and Temperature-Dependent Competition between Photosubstitution and Photofragmentation in Ru3(CO)12 and Fe3(CO)12: Detection and Characterization of Coordinatively Unsaturated M3(CO)11 Complexes

Article abstract of DOI:10.1021/ja00249a016

Irradiation of 0.1 mM Ru3(CO)12 (λ = 313 nm) or 0.02 mM Fe3(CO)12 (λ = 366 nm) in a methylcyclohexane or 2-methyltetrahydrofuran (2-MeTHF) glass at 90 K yields loss of one CO as the only IR detectable photoreaction to yield products formulated as M3(CO)11 or M3(CO)11(2-MeTHF), respectively.An initially observed axially vacant form of Ru3(CO)11 (II) having no bridging CO's rearranges at 90 K to an axially vacant form (III), having at least one bridging CO, also adopted by Fe3(CO)11 in an alkane glass.An initially observrd, equatorially substituted form of Ru3(CO)11(2-MeTHF) (I') rearranges at 90 K to III or a 2-MeTHF adduct of III.I' is extremely photosensitive with respect to further substitution by 2-MeTHF for up to three CO ligands.Ru3(CO)11 (III) reacts with N2 or 13CO to yield Ru3(CO)11(N2) or axial-13CO-Ru3(CO)11(13CO) complexes, respectively.Ru3(CO)11 and Fe3(CO)11 react with C2H4 to yield M3(CO)11(C2H4) complexes.M3(CO)11 (III) reacts with PPh3 to yield Ru3(CO)11(Ph3) at 298 K and Fe3(CO)11(PPh3) at 195 K.Long wavelegth excitation of Ru3(CO)12 (λ = 366 nm) or Fe3(CO)12 (λ = 436 nm) yields negligible photochemistry in alkane or 2-MeTHF glasses but yields associative photosubstitution of C2H4, C5H10, and 13CO but not N2 or 2-MeTHF for CO at 90 K.Long wavelegth (λ > 540 nm) excitation of Fe3(CO)12 yields no photochemistry at 90 K but gives assymetric fragmentation in C2H4-containing alkane solutions at 298 K to yield 1 equiv each of Fe(CO)5, Fe(CO)4(C2H4), and Fe(CO)3(C2H4)2; competitive photosubstitution occurs in the presence of PPh3 to yield Fe3(CO)11(PPh3).At 195 K, the Fe3(CO)11L/Fe(CO)5-n(L)n (L = C2H4, PPh3; n = 0-2) product ratios increase with decreasing irradiation wavelegth.Long wavelegth (λ > 420 nm) irradiation of o.2 mM Ru3(CO)12 in 195 K alkane solutions containing excess L = CO or C2H4 initially yields 1 equiv each of Ru(CO)4L and Ru2(CO)8L; Ru2(CO)8(C2H4) fragments at 195 K to yield 2 more equiv of Ru(CO)4(C2H4).Long wavelength irradiation of Ru3(CO)12 in PPh3-containing solutions at 195 K yields conversion to a CO-bridged product which reacts thermally at 195 K to form Ru(CO)11(PPh3), in competition with Ru3(CO)12 regeneration; Ru(CO)4(PPh3) and Ru(CO)3(PPh3)2 are only observed as secondary photoproducts at 195 K.The low temperature photochemistry of Ru3(CO)12 is discussed in terms of a wavelength-dependent competition between dissociative loss of equatorial CO from higher energy excitation and generation of a nonradical, reactive isomer of Ru(CO)12 from long wavelength excitation.Implications of the new results for the photocatalyzed isomerization of 1-pentene to cis- and trans-2-pentene by M3(CO)12 (M = Ru, Fe) precursors are discussed.