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)

The new hydride complexes [Mo2Cp2(mu-H) (mu-PHR) (CO)(4)] having bulky substituents (R = 2,4,6-C6H2t Bu-3 = 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 H-1, P-31, F-19 and C-13 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)].