Aqueous Reduction of [Cp*₂W₂O₅]: Characterization of the Triangular Clusters [Cp*₃W₃O₄(OH)₂]²⁺ and [Cp*₃W₃O₆]⁺ – Comparison with Molybdenum

Abstract

Zinc reduction of Cp*2W2O5 in an acidified water–methanol medium affords the green 3‐electron trinuclear cluster [Cp*3W3O4(OH)2]2+, isolated and crystallographically characterized as the triflate salt, 1. Upon exposure to air, this complex is oxidized to a related 2‐electron cluster, [Cp*3W3O6]+, which was crystallized and characterized in three different salts, 2–4. The 3‐electron cluster exhibits a near‐tetragonal frozen‐glass EPR spectrum, and it shows evidence of coupling of the unpaired electron to only one of the three W atoms. The two‐electron cluster is diamagnetic. An electrospray ionization MSn study revealed a stepwise expulsion of neutral [Cp*WO2] units as the main fragmentation process. DFT calculations unveiled the intimate details of the electronic structures of these complexes and fully rationalized the structural and spectroscopic properties.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

High oxidation state organomolybdenum and organotungsten chemistry in protic environments

“…In fact, even the Cp * Mo VI system where the metal is in the highest oxidation state generates an open coordination site at low pH (rapid equilibrium between [Cp * MoO 2 (H 2 O)] + and [Cp * MoO 2 ] + in water) [123]. Upon [141,143]. The reduced metal centres in these clusters assemble in a triangular fashion in order to share electrons and bridging ligands, thereby saturating their coordination sphere, but the M(-OH)M bridge opening process (perhaps after an additional protonation) appears feasible by a number of substrates.…”

“…the same protocol used previously for the Mo system [143]. The reduction leads to a green product, [(Cp * W) 3 O 4 (OH) 2 ] 2+ (a W 3 15+ , 3-electron cluster), which is air sensitive and is oxidized in air to orange [(Cp * W) 3 O 6 ] + (a W 3 16+ , 2-electron cluster).…”

“…The rationalization of this result was possible, as for the related Mo cluster (vide supra), by the DFT calculations. In fact, the symmetry lowering allows mixing between the a(z 2 ) and e 1 (xy) orbitals (both becoming a in C 2 symmetry), with the result that the latter, where the unpaired electron resides, has a major component from only one W atom (spin density = 0.911) and minor from the other two (spin density = 0.028 and 0.036) [143].…”

Reaction of [Cp∗2W2O5] with mercaptocarboxylic acids: Addition rather than reduction. Isolation and characterization of Cp∗WO2(SCH2CH2COOH)

“…The SCH 2 protons are downfield shifted upon coordination by almost 1 ppm relative to the free substrate, whereas the CH 2 COO protons are nearly unaffected, in agreement with the proposed coordination of only one of the two functions. The two corresponding 13 C NMR resonances are observed at d 34.9 and 31.9. The substrate binding via the S function, rather than via the COO function, is suggested by the loss, upon coordination, of the SH resonance.…”