Photochemical Oxidative Addition of Germane and Diphenylgermane to Ruthenium Dihydride Complexes

Photochemical
reactions of germane and diphenylgermane with Ru­(PP)2H2 (PP = R2PCH2CH2PR2 or DuPhos, R = Ph dppe, R = Et depe, R = Me dmpe)
are reported. Reaction with GeH4 generates a mixture of cis and trans isomers of Ru­(PP)2(GeH3)H except for the DuPhos complex which yields the
product only in the cis form. In situ laser photolysis (355 nm) demonstrates that the initial product
is the cis isomer that undergoes thermal isomerization
to the trans isomer. The complex cis-[Ru­(dppe)2(GeH3)­H] crystallizes selectively,
allowing determination of its X-ray structure as a germyl hydride
with a long Ru–H···Ge separation of 2.64(3)
Å indicating that no residual interaction between the RuH and
Ge is present. DFT calculations are also consistent with full oxidative
addition. The structure of cis-[Ru­(DuPhos)2(GeH3)­H] reveals significant distortion from an octahedral
geometry. The major species in the crystal (95%) exhibits a structure
with a Ru–H···Ge distance of 2.42(5) Å
suggesting negligible interaction between these centers. DFT calculations
of the structure are consistent with the experimental determination.
The reactions of Ru­(PP)2H2 with diphenylgermane
yield cis-[Ru­(PP)2(GePh2H)­H]
exclusively for PP = dmpe and depe, while the cis isomer is dominant in the case of dppe. A photochemical competition
reaction between Ru­(dppe)2(H)2 and the two substrates
Ph2SiH2 and Ph2GeH2 results
in both Si–H and Ge–H oxidative addition activation
with a kinetic preference (0.18:1) for the germyl hydride product.
Thermal conversion of Ru­(dppe)2(SiPh2H)H to
Ru­(dppe)2(GePh2H)H is observed on heating.