RESUMEN
Compounds [M2Cp2(µ-PPh2)(CO)3(NO)] (M = Mo, W) were prepared by reacting the corresponding radicals [M2Cp2(µ-PPh2)(CO)4] with NO, and displayed a terminal, linear NO ligand arranged cis to the P-donor ligand (Mo-Mo = 3.1400(7) Å). The related PCy2-bridged complex [W2Cp2(µ-PCy2)(CO)3(NO)] was prepared in a one-pot, three step procedure first involving deprotonation of the hydride complex [W2Cp2(µ-H)(µ-PCy2)(CO)4] with K[BH(sec-Bu)3], then oxidation of the resulting salt K[W2Cp2(µ-PCy2)(CO)4] with [FeCp2]BF4 at 243 K, and eventually by reacting the so-formed radical [W2Cp2(µ-PCy2)(CO)4] with NO. Photochemical decarbonylation of the Mo2 complex gave intractable mixtures of products. In contrast, photolysis of the ditungsten complexes yielded the corresponding dicarbonyls [W2Cp2(µ-PR2)(µ-κ1:η2-CO)(CO)(NO)] (R = Ph, Cy) as major products, which were characterized spectroscopically. The latter reacted readily with P(OMe)3 to give the corresponding derivatives [W2Cp2(µ-PR2)(CO)2(NO){P(OMe)3}], displaying a cisoid conformation of the P-donor ligands (P-W-P = 83.7(1)° when R = Cy). Density functional theory calculations on [W2Cp2(µ-PCy2)(µ-κ1:η2-CO)(CO)(NO)] and several potential isomers revealed that this electron-precise molecule (W-W = 3.121 Å) is almost isoenergetic with an unsaturated isomer having a µ-κ1:κ1-NO ligand (W-W = 2.677 Å) but their interconversion has a large kinetic barrier. It was concluded that formation of the κ1:η2-CO-bridged isomers in the photolytic experiment is favoured by the cisoid disposition of NO and PR2 ligands at the parent tricarbonyls, which precludes the NO ligand from easily rearranging into a bridging position after decarbonylation. The above calculations also revealed that the CO ligand is much better suited than NO for the µ-κ1:η2 coordination mode, since it can establish stronger end-on and side-on interactions with the dimetal centre.
RESUMEN
The phosphide-bridged dimolybdenum complexes (H-DBU)[Mo2Cp2(mu-PR2)(CO)4] (R= Cy, Ph; DBU = 1,8-diazabicyclo[5.4.0.]undec-7-ene) react with p-benzoquinone to give the hemiquinone complexes [Mo(2)Cp2(OC6H4OH)(mu-PR2)(CO)4]. The latter experience facile homolytic cleavage of the corresponding Mo-O bonds and react readily at room temperature with HSPh or S2Ph2 to give the thiolate complexes [Mo2Cp2(mu-PCy2)(mu-SPh)(CO)4] or [Mo2Cp2(mu-PR2)(mu-SPh)(CO)2]. In contrast, PRH-bridged substrates experience overall insertion of quinone into the P-H bond to give the anionic compounds (H-DBU)[Mo(2)Cp2{mu-PR(OC6H4OH)}(CO)4], which upon acidification yield the corresponding neutral hydrides. The cyclohexyl anion experiences rapid nucleophilic displacement of the hemiquinone group by different anions ER- (ER = OH, OMe, OC4H5, OPh, SPh) to give novel anionic compounds (H-DBU)[Mo2Cp2{mu-PCy(ER)}(CO)4], which upon acidification yield the corresponding neutral hydrides. The structure of four of these hydride complexes [PPh(OC6H4OH), PCy(OH), PCy(OMe), and PCy(OPh) bridges] was determined by X-ray diffraction methods and confirmed the presence of cis and trans isomers in several of these complexes. In addition, it was found that the hydroxyphosphide anion [Mo2Cp2{mu-PCy(OH)}(CO)4]- displays in solution an unprecedented tautomeric equilibrium with its hydride-oxophosphinidene isomer [Mo2Cp2(mu-H){mu-PCy(O)}(CO)4]-.