Oxidative Additions of Coordinated Ligands at Unsaturated Molybdenum and Tungsten Diphosphine-Bridged Carbonyl Dimers. 1. Decarbonylation Reactions of [W₂(η⁵-C₅H₅)₂(CO)₄(μ-R₂PCH₂PR₂)] (R = Ph, Me)

Abstract

The new complexes [W2Cp2(CO)4(μ-L2)] (Cp = η5-C5H5; L2 = Ph2PCH2PPh2 (dppm), Me2PCH2PMe2 (dmpm)) have been prepared from [W2Cp2(CO)4] and the corresponding diphosphine at room temperature. Decarbonylation of the dppm complex in refluxing n-octane gives the triply bonded compound [W2Cp2(CO)2(μ-dppm)] as the major product, along with a small amount of the oxo complex [W2Cp2(μ-CH2PPh2)(O)(μ-PPh2)(CO)], which results from a P−C(sp3) cleavage in the dppm ligand. Both compounds (as their dibenzene and toluene solvates, respectively) have been characterized through single-crystal X-ray studies. The analysis of the dicarbonyl complex, carried out at 200 K, reveals the presence of linear semibridging carbonyls experiencing an incipient dynamic disorder that at higher temperatures might be observed as a fully developed disorder of each carbonyl between its two asymmetric dispositions. The latter is consistent with a structure determination carried out previously on the same compound at 291 K and with its dynamic behavior in solution. This air-sensitive complex adds oxygen readily to give the W(I)−W(V) oxo derivative [W2Cp2(O)2(CO)2(η1-dppm)]. Photochemical decarbonylation of [W2Cp2(CO)4(μ-L2)] proceeds via the hydrido cyclopentadienylidene complexes [W2(μ-η1:η5-C5H4)Cp(μ-H)(CO)3(μ-L2)] to finally give the corresponding dicarbonyls [W2Cp2(CO)2(μ-L2)]. The latter react readily with tBuNC at room temperature or below to give [W2Cp2(μ-η1:η2-CNtBu)(CO)2(μ-L2)], which, when L2 = dppm, isomerizes at room temperature to give [W2(μ-η1:η5-C5H4)Cp(μ-H)(CNtBu)(CO)2(μ-dppm)].

Oxidative Additions of Coordinated Ligands at Unsaturated Molybdenum and Tungsten Diphosphine-Bridged Carbonyl Dimers. 3. Decarbonylation Reactions of [MoW(η5-C5H5)2(CO)4(μ-Ph2PCH2PPh2)]

“…Spectroscopic data for 1 (Table and Experimental Section) are strongly related to those of the homonuclear dimers, thus indicating a close structural relationship. As expected, , two isomers are observed in solution, their ratio ( ca. 1:1 in Me 2 CO- d 6 at 248 K) being midway between those observed for the dimolybdenum and ditungsten complexes.…”

“…Complex 7 can be taken as a model for the tricarbonylic intermediate presumably formed after ejection of the first CO molecule in compound 1 (see later). , Thus, the anomalous presence of the cyclopentadienylidene ligand specifically σ-bonded to molybdenum in complex 5 would be the result of the specific coordination (σ to tungsten and π to molybdenum) of a bridging carbonyl ligand in the tricarbonylic precursor of 5 .…”

“…For compounds 2 and 3 , the disposition of the phosphinomethyl ligand P-bonded to molybdenum is denoted by the similarity of their 31 P chemical shifts (Table ) to those of the dimolybdenum analogues 2,6 and the reduced value of the corresponding P−W couplings (30−60 Hz), almost an order of magnitude lower than one-bond couplings measured in related ditungsten complexes . The oxo ligand in 3 can be safely placed on tungsten by exclusion, because the single carbonyl of the molecule exhibits chemical shifts and P−C couplings (to both phosphorus atoms) almost identical with those of the dimolybdenum analogue …”

“…In the previous parts of this series , we have shown that the unsaturated species generated through ejection of carbon monoxide from the single-metal−metal-bonded dimers [M 2 Cp 2 (CO) 4 (μ-dppm)] (Cp = η 5 -C 5 H 5 ; dppm = Ph 2 PCH 2 PPh 2 ; M = W, Mo 2 ) are able to activate C−H or P−C (sp 3 ) bonds in the coordinated cyclopentadienyl or diphosphine ligands, respectively. The results are strongly dependent on the metal.…”

Terminal vs. bridging coordination of CO and NO ligands after decarbonylation of [W2Cp2(μ-PR2)(CO)3(NO)] complexes (R = Ph, Cy). An experimental and computational study

“…Typical rearrangements include changes in the coordination of terminal carbonyls to bridging (- 1 : 1 ) or semibridging modes, which do not modify the formal intermetallic bond order, as illustrated for the Mo 2 and W 2 complexes shown in Scheme 1. 6,7 Another possibility is that a remaining terminal carbonyl rearranges into the 4-electron donor, - 1 : 2 coordination mode, as found first for the dimanganese complex [Mn 2 (- 1 : 2 -CO)(CO) 4 (-Ph 2 PCH 2 PPh 2 ) 2 ], 8 in which case the intermetallic bond order is not increased by the carbonyl loss (Scheme 1). Even in the latter event, however, the decarbonylated product remains highly reactive, since the bridging - 1 : 2 -CO ligand readily reverts to the terminal mode upon addition of different reagents, as previously shown for the above Mn 2 complex, 9 and also for related Recently we became interested in the study of nitrosyl ligands at unsaturated dimetal centres based on the general idea that the inherent reactivity of these centres might facilitate transformations in the robust NO molecule that could be of interest in the context of the metal-catalyzed abatement of nitrogen oxides.…”