Hydride, gold(i) and related derivatives of the unsaturated ditungsten anion [W₂Cp₂(μ-PCy₂)(μ-CO)₂]⁻

Abstract

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...

Structural and Chemical Effects of the PtBu2Bridge at Unsaturated Dimolybdenum Complexes Having Hydride and Hydrocarbyl Ligands

“…In addition, the spectra of both salts display additional weak high- Finally, we must note that the presence of all these associative phenomena denoted by the IR data is not reflected in the NMR spectra of 2, which otherwise display averaged 31 ] exists in solution as an equilibrium mixture of isomers with either a terminal or a bridging hydride, although the latter isomer is dominant at all temperatures, so that the structural information about the terminal isomer is yet quite limited. 9 Finally, we must note that the hydride 3 can be converted selectively back into the corresponding anion by reaction with different reducing agents (i.e. Na(Hg), Li[BHEt 3 ], etc.…”

Trapping of an Heterometallic Unsaturated Hydride: Structure and Properties of the Ammonia Complex [MoMnCp(μ-H)(μ-PPh2)(CO)5(NH3)]

“…Analysis of the electron density at the intermetallic region, under the Atoms in Molecules (AIM) framework [31], also supports the presence of substantial multiplicity in the intermetallic bond of hydride H. Thus, although a bond critical point was not strictly located, the minimum electron density at the intermetallic axis was found to be 0.284 eÅ −3 , a figure substantially higher than the corresponding value computed by us at the same level for the electron-precise anion [MoMnCp(μ-PPh2)(CO)6] − (0.204 eÅ −3 ) and only a bit below the value of 0.319 eÅ −3 computed at the intermetallic bond critical point in the unsaturated anion 1 [13]. In [28][29][30]. Analysis of the electron density at the intermetallic region, under the Atoms in Molecules (AIM) framework [31], also supports the presence of substantial multiplicity in the intermetallic bond of hydride H. Thus, although a bond critical point was not strictly located, the minimum electron density at the intermetallic axis was found to be 0.284 eÅ −3 , a figure substantially higher than the corresponding value computed by us at the same level for the electron-precise anion [MoMnCp(µ-PPh 2 )(CO) 6 ] − (0.204 eÅ −3 ) and only a bit below the value of 0.319 eÅ −3 computed at the intermetallic bond critical point in the unsaturated anion 1 [13].…”

“…0.05 Å ) when compared to distances measured by X-ray diffraction [25,26]. [28][29][30]. Analysis of the electron density at the intermetallic region, under the Atoms in Molecules (AIM) framework [31], also supports the presence of substantial multiplicity in the intermetallic bond of hydride H. Thus, although a bond critical point was not strictly located, the minimum electron density at the intermetallic axis was found to be 0.284 eÅ −3 , a figure substantially higher than the corresponding value computed by us at the same level for the electron-precise anion [MoMnCp(μ-PPh2)(CO)6] − (0.204 eÅ −3 ) and only a bit below the value of 0.319 eÅ −3 computed at the intermetallic bond critical point in the unsaturated anion 1 [13].…”

“…Calcd. for C30 H 23 MnMoNO 6 P: C, 53.35; H, 3.43; N, 2.07. Found: C, 52.97; H, 3.20; N, 2.35. ν(CO)(CH 2 Cl 2 ): 2147 (w, C-N), 2010(s), 1949 (vs), 1933 (s, sh), 1870 (m).…”

Reply to the ‘Comment on “Hydride, gold(i) and related derivatives of the unsaturated ditungsten anion [W2Cp2(μ-PCy2)(μ-CO)2]−”’ by M. Green, Dalton Transactions, 2018, 47, DOI: 10.1039/C8DT00044A

“…Without entering into a lengthy discussion on the matter, we would like to note that the unsaturated compounds 1 can display, depending on M and R, a second isomer (1T) having a terminal hydride and a linear semibridging carbonyl (Figure 2). Isomer 1T coexists in solution with the hydride-bridged isomer when M = W and R = Cy, 3,4 while it is fully dominant when M = Mo and R = t Bu. 5 The representation of the intermetallic interaction for this second isomer is a triple bond under all schemes, including the CBC method.…”