New Triosmium Complexes Containing a Partially Hydrogenated Bis(ferrocenyl)butadiyne Ligand. Their Structures and Electrochemical Responses

The reaction of Os3(CO)10(μ3-FcC4Fc) (3) (Fc = C5H5FeC5H4) with water in thf solvent at
reflux yielded three new cluster complexes:  Os3(CO)9(μ3-η3-E-FcC3CHFc)(μ-H) (4) (54%), Os3(CO)9(μ3-η3-Z-FcC3CHFc)(μ-OH) (5) (11%), and Os3(CO)9(μ3-η3-E-FcC3CHFc)(μ-OH) (6) (16%
yield) in 40 h. The same products were obtained from the reaction of 3 with Me3NO·2H2O
in 35 min at 25 °C, but the yield of 4 was lower (13%), the yield of 5 was higher (34%), and
the yield of 6 was about the same (12%). Compounds 4−6 were characterized by single-crystal X-ray diffraction analyses. All three compounds contain a triply bridging η3-bis(ferrocenyl)ynenyl, FcCCCC(H)Fc, ligand formed by the addition of one hydrogen atom to
the FcC4Fc ligand in 3. Compound 4 contains a closed triangular triosmium cluster with
one bridging hydride ligand. Compounds 5 and 6 are isomers. Both contain an open triosmium
cluster with a bridging hydroxo ligand. The isomers differ by E- and Z-configurations of the
enyl group of the FcCCCC(H)Fc ligand. All three compounds show two resolved one-electron
oxidations for the ferrocenyl groups:  for 4 at E° = +0.43 and +0.56 V vs Ag/AgCl, ΔE° =
0.13 V; for 5 at E° = +0.38 and +0.46 V, ΔE° = 0.08 V; for 6 at E° = +0.39 and +0.49 V,
ΔE° = 0.10 V. The potential differences ΔE are all larger than that in 3. This may be due
in part to increased bonding between the carbon atoms in the C−C triple bond and C−C
double bond in the bis(ferrocenyl)ynenyl ligand caused by the coordination to the metal atoms.