Proton induced P–H and Mo–H bond activation at the phosphide bridged dimolybdenum complexes [Mo₂Cp₂(µ-H)(µ-PHR)(CO)₄] (R = Cy, 2,4,6-C₆H₂R′₃; R′ = H, Me,^tBu)

Abstract

The new hydride complexes [Mo2Cp2(mu-H)(mu-PHR)(CO)4] having bulky substituents (R = 2,4,6-C(6)H2tBu3= Mes*, R = 2,4,6-C6H2Me3= Mes) have been prepared in good yield by addition of Li[PHR] to the triply bonded [Mo2Cp2(CO)4] and further protonation of the resulting anionic phosphide complex [Mo2Cp2(mu-PHR)(CO)4]-. Protonation of the Mes* compound with either [H(OEt2)2][B{3,5-C6H3(CF3)2}4] or HBF4.OEt2 gives the cationic phosphinidene complex [Mo2Cp2(mu-H)(mu-PMes*)(CO)4]+ in high yield. In contrast, protonation of the analogous hydride compounds with Mes or Cy substituents on phosphorus give the corresponding unsaturated tetracarbonyls [Mo2Cp2(mu-PHR)(CO)4]+, which are unstable at room temperature and display a cis geometry. Decomposition of the latter give the electron-precise pentacarbonyls [Mo2Cp2(mu-PHR)(mu-CO)(CO)4]+, also displaying a cis arrangement of the metal fragments. In the presence of BF4- as external anion, fluoride abstraction competes with carbonylation to yield the neutral fluorophosphide hydrides [Mo2Cp2(mu-H)(mu-PFR)(CO)4]. Similar results were obtained in the protonation reactions of the hydride compounds having a Ph substituent on phosphorus. In that case, using HCl as protonation reagent gave the chloro-complex [Mo2ClCp2(mu-PHPh)(CO)4] in good yield. The structures and dynamic behaviour of the new compounds are analyzed on the basis of solution IR and 1H, 31P, 19F and 13C NMR data as well as the X-ray studies carried out on [Mo2Cp2(mu-H)(mu-PHMes)(CO)4](cis isomer), [Mo2Cp2(mu-H)(mu-PFMes)(CO)4](trans isomer), [Mo2Cp2(mu-PHCy)(mu-CO)(CO)4](BF4) and [Mo2ClCp2(mu-PHPh)(CO)4].

Dimolybdenum−Tin Derivatives of the Unsaturated Hydride [Mo2(η5-C5H5)2(μ-H)(μ-PCy2)(CO)2] and HSnR3 (R = Ph, Bu): Bridging versus Terminal Coordination of the Triorganostannyl Group

“…Alternatively, the intermediate trans - B might undergo an isomerization process to give cis - B , this having now the Cp ligands on the same side of the average Mo 2 PH plane. A related cis/trans equilibrium in solution has been recently reported by us for the structurally related tetracarbonyl species [Mo 2 Cp 2 (μ-H)(μ-PHMes)(CO) 4 ], and it has been also described for the thiolate-bridged complexes [Mo 2 Cp 2 (μ-H)(μ-SR)(CO) 4 ] . In our case, the isomerization proposed would involve the rearrangement of the less congested MoCp(CO)H moiety, and it would render a cis disposition of the terminal hydride with respect to the phosphide ligand, thus enabling the reductive elimination of the P−H bond to give the intermediate phosphine complex cis - 3 .…”

Phosphinidene-bridged binuclear complexes

“…The latter cation can be then easily deprotonated even by weak bases such as H 2 O to give the neutral complex. Similar reactions were carried out for other related phosphanyl complexes bearing smaller substituents at the P atom (Ph, Cy and Mes), but only phosphanyl-bridged cations were obtained, and no phosphinidene complexes were ever detected in these reactions [69].…”

Synthesis, characterization and structure of a low coordinate desoxomolybdenum cluster stabilized by a dithione ligand

“…Mo-Mo distances longer than 3 Å have been reported in binuclear complexes such as [Mo 2 Cp 2 (μ-H)(μ-PHR)(CO) 4 ] (R = Cy, 2,4,5-C 6 H 2 R′ 3 ; R′ = H, Me, t Bu) where the Mo–Mo distance is reported to be ~3.5=Å 36. In binuclear molybdenum complexes coordinated by bridging sulfur donors Mo–Mo distances ~2.6 Å, have also been reported.…”