The title anion can be conveniently prepared from the cationwhich is easily reduced with Na-amalgam. This anion reacts with different electrophiles both at the W and O sites to give unusual unsaturated molecules such as the hydrideand phosphinoxycarbyne [W 2 Cp 2 (μ-COP t Bu 2 )(μ-PCy 2 )(μ-CO)] derivatives, all of them exhibiting novel structural features or unparalleled compositions.

ARTICLEThis journal is © The Royal Society of Chemistry 2013 J. Name., 2013, 00, 1-3 | 1 12 in stark contrast with the exclusive bridging disposition found for its dimolybdenum analogue. 9 Then, it was of interest to further explore the potential of ditungsten anion 1 to build new unsaturated hydrides and related species, which is the main purpose of this work. In this paper we give full details of the protonation reactions of 1, which we have now extended to other Brönsted acids and also to H + -related electrophiles such as gold(I) complexes [AuCl(PR 3 )] and organometal chlorides ClEPh 3 (E = Sn, Pb). As it will be shown below, most of these reactions involve the addition of the corresponding electrophile at the dimetal site of the anion, to give new unsaturated compounds related to those obtained for the dimolybdenum analogue of 1. In contrast, only the ditungsten anion 1 is able to undergo double protonation to give stable dihydride derivatives, which are relatively stable towards dehydrogenation in the absence of coordinating anions. Scheme 1 Results and Discussion Protonation of compounds 1 and 2The sodium salt of anion 1 is easily protonated in tetrahydrofuran solution by weak acids such as [NH 4 and another one bearing only terminal hydrides [W 2 Cp 2 (H) 2 (-PCy 2 )(CO) 2 ]X (3T and 3T')] (Scheme 2). These isomers seem to be also in equilibrium in solution, and a ratio of ca. 6:5 was found in both cases. Unfortunately, these species could not be isolated as pure solids and decomposed progressively upon attempted purification, but their structures are well supported by spectroscopic data and DFT calculations (see below). In any case we note that the nature of the metal (W instead of Mo) is having a critical role in the stability of these products, because protonation of the Mo 2 analogue of 2 fails to yield any observable dihydrides and leads instead to complex mixtures of products that could not be isolated or characterized. Scheme 2To gain further insight into the role of the external anion in these reactions, we also examined reactions of 2 with some acids having coordinating anions. In particular, we have used three carboxylic acids of increasing acidity: acetic, benzoic and trifluoroacetic acid. No reaction was observed for the weaker acetic acid, but reaction of 2 with a slight excess of benzoic or trifluoroacetic acid gave the corresponding carboxylate-bridged complexes [W 2 Cp 2 (-PCy 2 )(-O:O´-O 2 CR)(CO) 2 ] [R = Ph(4a), CF 3 (4b)] (Chart 1), with the latter reaction taking place instantaneously at room temperature, while the former one requires thermal activation (completed within 30 min in refluxing toluene). There are two points of interest in these reactions: first, their rates correlate with the relative strength of these acids (CF 3 CO 2 H >> PhCO 2 H > CH 3 CO 2 H), which suggests that initial protonation to give cations analogous to 3 might be the first step of the process; secondly, the formation of the carboxylate complexes 4a,b requires release of hydrogen, likely occurring at...

Two molecules of C(2)(CO(2)Me)(2) or isocyanides could be added to the title hydride complex under mild conditions to give dienyl-[W(2)Cp(2){μ-η(1),κ:η(2)-C(CO(2)Me)=C(CO(2)Me)C(CO(2)Me)=CH(CO(2)Me)}(μ-PCy(2))(CO)(2)] (Cp = η(5)-C(5)H(5)), diazadienyl-[W(2)Cp(2){μ-κ,η:κ,η-C{CHN(4-MeO-C(6)H(4))}N(4-MeO-C(6)H(4))}(μ-PCy(2))(CO)(2)] or aminocarbyne-bridged derivatives [W(2)Cp(2){μ-CNH(2,6-Me(2)C(6)H(3))}(μ-PCy(2)){CN(2,6-Me(2)C(6)H(3))}(CO)]. In contrast, its reaction with excess (4-Me-C(6)H(4))C(O)H gave the C-O bond cleavage products [W(2)Cp(2){CH(2)(4-Me-C(6)H(4))}(O)(μ-PCy(2))(CO)(2)] and [W(2)Cp(2){μ-η:η,κ-C(O)CH(2)(4-Me-C(6)H(4))}(O)(μ-PCy(2))(CO)].

The title complex reacted with stoichiometric amounts of CNR rapidly at room temperature or below to give two types of formimidoyl derivatives: the symmetrically bridged complexes [W 2 Cp 2 (μ-C,N:C,N-HCNR)(μ-PCy 2 )(CO) 2 ] (R = t Bu (W−W = 2.8645(5) Å), 4-C 6 H 4 OMe), and the asymmetrically bridged [W 2 Cp 2 {μ-C:N-HCN(Xyl)}(μ-PCy 2 )(CO) 2 ] (Cp = η 5 -C 5 H 5 ; Xyl = 2,6-C 6 H 3 Me 2 ). The latter complex underwent slow isomerization at room temperature to give the corresponding aminocarbyne derivative [W 2 Cp 2 {μ-CNH(Xyl)}(μ-PCy 2 )(CO) 2 ], which in turn could be decarbonylated through irradiation with UV−vis light to yield the 30-electron aminocarbyne complex [W 2 Cp 2 {μ-CNH(Xyl)}(μ-PCy 2 )(μ-CO)] (W−W = 2.4928(4) Å). Density functional theory calculations revealed that the aminocarbyne complex was the most stable isomer for the three isocyanides under study, while subtle steric effects marked the relative stability of the formimidoyl isomers, which therefore are the kinetic products of these reactions. The reaction of the title complex with excess CN(4-C 6 H 4 OMe) at room temperature gave in good yield the complex [W 2 Cp 2 (μ-C,N:C,C′-HCN(4-C 6 H 4 OMe)C{N(4-C 6 H 4 OMe)})(μ-PCy 2 )(CO) 2 ] (W−W = 2.9370(2) Å), having a 5-electron donor aminocarbene-iminoacyl ligand derived from the N−C coupling of formimidoyl and isocyanide ligands, whereas the analogous reaction with CNXyl gave the aminocarbyne complex [W 2 Cp 2 {μ-CNH(Xyl)}(μ-PCy 2 ){CN(Xyl)}(CO)] (W−W = 2.677(2) Å) having a terminal bent isocyanide ligand.

The title compound reacted rapidly with N 2 CH(SiMe 3 ) at room temperature to give the electron-precise hydride [W 2 Cp 2 (H)(μ-PCy 2 )(CO) 2 {N-N 2 CH(SiMe 3 )}] (W−W = 2.9907(5) Å), in which the diazoalkane molecule is N-bound strongly to one of the metal centers, formally acting as an imido-like four-electron donor. 2 ], the latter having no metal−metal bond and bearing two inequivalent diazoalkane ligands bound to the same metal center (W−N = 1.78(1), 1.82(1) Å), whereas its dicarbonyl metal fragment displays a transoid geometry in the crystal, but a cisoid one in solution. These two compounds follow from competitive reaction pathways, since independent experiments revealed that the above mono(diazoalkane) complexes did not add a second diazoalkane molecule even under thermal activation. In contrast, the title compound reacted with excess N 2 CH 2 to yield two new methyl derivatives requiring the participation of two molecules of reagent, the diazomethane complex [W 2 Cp 2 (CH 3 )(μ-PCy 2 )(CO) 2 (N-N 2 CH 2 )] and the 30-electron phosphinomethyl-bridged complex [W 2 Cp 2 (CH 3 )(μ-C:P-CH 2 PCy 2 )(μ-CO)(CO)], along with small amounts of the known methyl-bridged complex [W 2 Cp 2 (μ-CH 3 )(μ-PCy 2 )(CO) 2 ]. The two new complexes follow from denitrogenation of one diazomethane molecule followed by insertion of methylene into the W−H bond to yield a methyl ligand, while the second diazomethane molecule either remains bound through its nitrogen atom or undergoes denitrogenation followed by insertion of methylene into a W−P bond, to yield a phosphinomethyl ligand. Once more, no denitrogenation of the coordinated diazomethane ligand in the first complex was observed even under thermal or photochemical activation.