Comparative photochemistry of ring-substituted half-sandwich tetracarbonylvanadium complexes in low-temperature matrices at ca. 12 K

An investigation into the photochemical reactions of M(η5-C5H5)(CO)4 and M(η5-C9H7)(CO)4 (M = Nb or Ta) with H2 and N2 in polyethylene matrices and liquid xenon at low temperature

“…Further photolysis of 2 and 4 produced no evidence for formation of double-CO loss products. Previous studies in frozen Nujol 26 and frozen gas matrices 24, 25 have observed photoproducts which have been assigned to ring-slip species. However, in all of the experiments performed in this investigation no evidence for photoproducts with IR bands previously 24-26 assigned to ring-slip species were observed.…”

“…[21][22][23] There have been relatively few investigations concerning the photochemistry of the Group 5 carbonyl compounds. V(η 5 25 following irradiation of the parent tetracarbonyl complexes in frozen nitrogen matrices at 12 K. The unsaturated complexes V(η 5 -C 5 R 5 )(CO) x (R = H, Me, or Cl; x = 2 or 3), V(η 5 -C 5 H 4 Me)(CO) x (x = 2 or 3) and V(η 5 -C 9 H 7 )(CO) 3 were observed following irradiation in frozen inert matrices. Photolysis of MCpЈ(CO) 4 (M = Nb or Ta; CpЈ = Cp or indenyl) in frozen Nujol 26 yielded the unsaturated CO-loss products MCpЈ(CO) 3 and MCpЈ(CO) 2 .…”

Ultrafast Infrared Studies of the Reaction Mechanism of Silicon−Hydrogen Bond Activation by η5-CpV(CO)4

“…George et al have shown that the photolysis of η 5 -CpV(CO) 4 in the presence of Et 3 SiH results in the arrested oxidative addition product η 5 -CpV(CO) 3 (η 2 -HSiEt 3 ) . Thus, the coordinated triethylsilane molecule acts as a σ-donor ligand and some residual Si−H interaction remains in the final product. , Rest and Hitam have proposed that a coordinatively unsaturated, 16-e - η 5 -CpV(CO) 3 photoproduct is formed upon UV irradiation of η 5 -CpV(CO) 4 in low-temperature matrices (Scheme ). , Substitution studies of η 5 -CpV(CO) 4 under ambient conditions suggest that the tricarbonyl species coordinates to the solvent to form η 5 -CpV(CO) 3 (solvent), which then reacts with an entering ligand. − There have been no studies, however, of the early time dynamics of the reaction mechanism due to the extremely fast reaction rates.

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Photochemistry of CpMn(CO)3 and Related Derivatives: Spectroscopic Observation of Singlet and Triplet CpMn(CO)2

“…Logical candidates for the second dicarbonyl isomer that we observed in our experiments (Scheme ) include a ring-slipped species, (η 3 -L)­Mn­(CO) 2 , or the triplet state, 3 (η 5 -L)­Mn­(CO) 2 . Ring-slipped intermediates are commonly invoked in mechanistic organometallic chemistry. − Dechelation processes, of which η 5 -Cp → η 3 -Cp ring slippage is a specific example, occur under both thermal − and photochemical − conditions. In certain cases, the elusive, coordinatively unsaturated species that are formed by dechelation (ring slippage) can be trapped by nucleophilic addition. − , Only in rare cases, however, have coordinatively unsaturated ring-slipped intermediates been characterized spectroscopically. − ,,, In considering the alternate structural assignment as a triplet species, the literature provides considerably less precedent.…”