Thermally Stable Diazoalkane Derivatives of the Unsaturated Ditungsten Hydride [W₂Cp₂(H)(μ-PCy₂)(CO)₂]

Abstract

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.

C–C and C–N Couplings in Reactions of the Benzylidyne-Bridged Complex [Mo2Cp2(μ-CPh)(μ-PCy2)(CO)2] with Small Unsaturated Organics

“…218.8 ppm for [Mo 2 Cp 2 (μ-H)(μ-PCy 2 )(CO) 4 ]). 18 This requires the retention of the 3-electron donor μ-κ 1 :η 2 coordination of the ketenyl ligand in solution, rather than adopting the more symmetrical μ-κ 1 :κ 1 mode found in complex 2, which is consistent with the large difference in the 13 C chemical shifts of the corresponding bridgehead carbon atoms of these two compounds (134.4 vs 15.8 ppm). Spectroscopic data for cisoid isomer cis-3 are similar to those of 3 as expected.…”

“…The structure of transoid isomer 3 was determined by an X-ray study during our preliminary analysis of the chemistry of 1 (Figure 1) 11 and will be only briefly discussed here. The terminal diazoalkane ligand displays an imido-like coordination 13 The superior donor ability of the diazoalkane ligand (compared to CO) is balanced by an alkenyl-like asymmetric coordination (μ-κ 1 :η 2 mode) of the three-electron donor ketenyl ligand, η 2 -bound to the carbonylbearing Mo atom, and by a stronger coordination of the PCy 2 ligand to that atom. Overall, the molecule formally is electronprecise, and this is in agreement with the relatively large intermetallic length of ca.…”

“…We note that no denitrogenation of the diazoalkane molecule is observed in the above reactions, a circumstance also observed in reactions of this reagent with triply bonded [Mo 2 Cp 2 (CO) 4 ] 12 and more recently in reactions with 30electron ditungsten hydride [W 2 Cp 2 H(μ-PCy 2 )(CO) 2 ]. 13 The formation of 3 gives experimental support to our previous hypothesis that carbonylation of 1 to yield ketenyl complex 2 would likely imply initial coordination of CO to the unsaturated dimetal center of 1 followed by reorganization, rather than direct attack of CO to the electron-rich carbyne ligand. 8 In line with this hypothesis, 31 P NMR monitoring of the carbonylation reaction of 4 revealed the transient formation of two new species A and B (identified by 31 P NMR resonances at 201.5 and 197.4 ppm) which were also detected as intermediate species in the reaction of 1 with N 2 CPh 2 .…”

Unlocking a Diazirine Long-Lived Nuclear Singlet State via Photochemistry: NMR Detection and Lifetime of an Unstabilized Diazo-Compound

“…This is not unexpected as diazo-compounds have been reported to act as good coordinating ligands. 53 However, the diazo-compound 4 cannot be hyperpolarized in the absence of pyridine. 15 We therefore propose a complex of the type [Ir(H) 2 (IMes)(py) 2 ( 4 )]Cl to be the SABRE active catalyst.…”

“…Hence, it can be concluded that diazo- 4 can also be polarized by SABRE through its reversible coordination to iridium in a way similar to that of 2 . This is not unexpected as diazo-compounds have been reported to act as good coordinating ligands . However, the diazo-compound 4 cannot be hyperpolarized in the absence of pyridine .…”