PHOTOCHEMICAL ISOMERIZATION OF METAL ETHENE TO METAL VINYL HYDRIDE COMPLEXES - A MATRIX-ISOLATION AND SOLUTION NMR-STUDY

CpRh(PMe3)(C2H4) (1), CpIr(PMe3)(C2H4) (6), and CpIr(C2H4)2 (8) (Cp = η5-C5H5) are isomerized on photolysis in argon matrices at 12-20 K to metal vinyl hydride complexes CpM(L)(C2H3)H (L = PMe3, C2H4). The products are identified by their characteristic metal hydride and vinyl group vibrations in the IR spectra and by the effect of 2H-labeling experiments. The same products may be generated by photolysis of a frozen toluene solution at 77 K (1 and 8) or a cold toluene solution (6) and characterized by 1H, 13C, and 31P NMR. The vinyl hydride complexes exhibit a wide range of thermal stabilities isomerizing to their precursors at the following temperatures: CpRh(PMe3)(C2H3)H at ˜253 K, CpIr(PMe3)(C2H3)H at ˜393 K, CpIr(C2H4)(C2H3)H at ˜273 K. Photolysis of 1 in toluene solution at 188 K generates a mixture of CpRh-(PMe3)(C2H3)H and isomers of CpRh(PMe3)(tolyl)H; at higher temperatures only insertion into toluene C-H bonds is observed. These and other studies lead to the proposal of an intermediate cage complex, [CpM(L)···C2H4], in the isomerization pathway. The reaction mechanism tends toward the intramolecular limit in the order 1 < 8 < 6. Secondary photolysis of CpIr(C2H4)(C2H3)H in Ar matrices causes ethene loss and formation of a product identified as the vinylidene complex CpIr(C̳CH2)H2. Photolysis of 8 in CO and N2 matrices leads to substitution products CpIr(C2H4)L (L = CO, N2), CpIr(CO)(C2H3)H, and CpIr-(C2H4)(C2H3)H. Photolysis of 1 in CO matrices generates CpRh(PMe3)CO only; use of N2 matrices results in formation of CpRh(PMe3)N2 and CpRh(PMe3)(C2H3)H. The photoproducts of 6 in CO matrices include CpIr(PMe3)(C2H3)H and CpIr(PMe3)CO. © 1990, American Chemical Society. All rights reserved.