Heterometallic Derivatives of the Unsaturated Methyl-Bridged Complex [Mo₂(η⁵-C₅H₅)₂(μ-CH₃)(μ-PCy₂)(CO)₂]. Photochemical Generation of Methylidyne-Bridged Clusters

Abstract

The photochemical reactions of the methyl-bridged complex [Mo 2 Cp 2 (μ-CH 3 )(μ-PCy 2 )(CO) 2 ] ( 1) (Cp = η 5 -C 5 H 5 ) with the carbonyl complexes [M(CO) 6 ] (M = Cr, Mo, W) and [MnCp 0 (CO) 3 ] (Cp 0 = η 5 -C 5 H 4 CH 3 ) give the corresponding electron-precise methylidyne-bridged derivatives [MMo 2 Cp 2 (μ 3 -CH)(μ-PCy 2 )(CO) 7 ] (Mo-Mo = 2.9340(13) A ˚for M = W) and [MnMo 2 Cp 2 Cp 0 (μ 3 -CH)(μ-PCy 2 )(CO) 4 ] (Mo-Mo = 2.9678(6) A ˚) in good yields. Under similar conditions, the reaction of 1 with [Ru 3 (CO) 12 ] gives the 46-electron methylidyne-bridged cluster [Mo 2 RuCp 2 (μ 3 -CH)(μ-PCy 2 )(CO) 5 ] (Mo-Mo = 2.6824(7) A ˚), along with a small amount of the methoxy-bridged analogue [Mo 2 RuCp 2 (μ 3 -OCH 3 )(μ-PCy 2 )(CO) 5 ]. A related iron species [FeMo 2 Cp 2 (μ 3 -OCH 3 )(μ-PCy 2 )(CO) 5 ] (Mo-Mo = 2.667(1) A ˚) can be prepared in moderate yield from the reaction of the 30-electron methyl complex [Mo 2 Cp 2 (μ-κ 1 :η 2 -CH 3 )(μ-PCy 2 )(μ-CO)] and [Fe 2 (CO) 9 ]. Compound 1 reacts with [Fe 2 (CO) 9 ] at room temperature to give the acetyl-bridged cluster [FeMo 2 Cp 2 {μ 3 -κ 1 :η 2 :κ 1 -C(O)CH 3 }(μ-PCy 2 )(CO) 5 ] (Mo-Mo = 2.8474(5) A ˚) in high yield, which undergoes full cleavage of the acetyl C-O bond under thermal or photolytic activation to give the oxoethylidyne derivative [FeMo 2 Cp 2 (μ 3 -CCH 3 )(μ-PCy 2 )(O)(CO) 4 ] (Mo-Mo = 2.8469(4) A ˚). Under photochemical conditions, however, compound 1 reacts with [Fe 2 (CO) 9 ] to give the methylidyne-bridged compound [Fe 2 Mo 2 Cp 2 (μ 4 -CH)(μ-PCy 2 )(CO) 8 ] (Mo-Mo = 2.8351(7) A ˚) as major species. This 60-electron cluster displays a butterfly Mo 2 Fe 2 core with no agostic interactions of the methylidyne ligand.Article

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

“…These products follow from fast decarbonylation of the dimetallic unit and full dehydrogenation of the benzyl ligand through a multistep process for which no intermediates were detected. , Interestingly the irradiation of [Mo 2 Cp 2 (μ–κ 1 :η 2 -CH 3 )­(μ-PCy 2 )­(CO) 2 ] in the presence of transition metal complexes (i.e., [M­(CO) 6 ], [Fe 2 (CO) 9 ], etc.) yielded tri- or tetranuclear clusters bearing bridging methylidyne (μ-CH) ligands, this proving that under photochemical conditions fast dehydrogenation of the CH 3 group might also be achieved, yet at that time we could not find any connection between the agostic monocarbonyl complex and the dehydrogenation products. , Taking into account these precedents, we resorted to study the photochemical behavior of the P t Bu 2 -bridged alkyl complexes 4a,b to evaluate if the presence of a bulkier phosphanyl could exert any influence on the stability or evolution of these highly unsaturated species.…”

“…The resulting solutions can be transferred to Schlenk tubes or J. Young-valved NMR tubes without apparent decomposition, so allowing for further studies on the reactivity of 7 , even if this compound could not be further purified due to its progressive decomposition. We were particularly interested in the dehydrogenation of this complex as a possible route to the corresponding methylidyne derivative, a reaction we could not test at the time for the corresponding PCy 2 -bridged complex, even if the corresponding product [Mo 2 Cp 2 (μ-CH)­(μ-PCy 2 )­(μ-CO)] could be prepared through alternative (but more difficult) routes . We have now found that moderate heating (353 K) of freshly prepared toluene solutions of 7 in a sealed NMR tube for 3 h yielded selectively the corresponding unsaturated methylidyne complex [Mo 2 Cp 2 (μ-CH)­(μ-P t Bu 2 )­(μ-CO)] ( 8 ) (Chart ).…”

“…yielded tri-or tetranuclear clusters bearing bridging methylidyne (μ-CH) ligands, this proving that under photochemical conditions fast dehydrogenation of the CH 3 group might also be achieved, yet at that time we could not find any connection between the agostic monocarbonyl complex and the dehydrogenation products. 35,37 Taking into account these precedents, we resorted to study the photochemical behavior of the P t Bu 2bridged alkyl complexes 4a,b to evaluate if the presence of a bulkier phosphanyl could exert any influence on the stability or evolution of these highly unsaturated species.…”

Methyl Complexes of the Transition Metals

“…Ruiz and co‐workers have reported on the migratory insertion of carbon monoxide and other unsaturated species over a μ‐CH 3 ligand that bridges two molybdenum centers, including the unprecedented insertion of a cyclopentadienyl ligand (Scheme c, left) . Remarkably, photolysis of solutions of binuclear Mo/Mo complexes in the presence of [M(CO) 6 ] (M=Mo, W) result in the formation of trinuclear methylydine clusters after acceptorless dehydrogenation of the bridging μ‐CH 3 ligand (Scheme c, right), an unknown transformation in monometallic systems ,…”

Dehydrogenation, Methyl Elimination and Insertion Reactions of the Agostic Methyl‐Bridged Complex [Mo2Cp2(μ‐κ1:η2‐CH3)(μ‐PtBu2)(μ‐CO)]

“…Indeed we found that the targeted methyl complex [Mo 2 Cp 2 (μ‐κ 1 :η 2 ‐CH 3 )(μ‐P t Bu 2 )(μ‐CO)] ( 1 ) could be conveniently prepared in situ upon photolysis of the corresponding dicarbonyl precursor [Mo 2 Cp 2 (μ‐κ 1 :η 2 ‐CH 3 )(μ‐P t Bu 2 )(CO) 2 ] (Scheme ), and this gave us the opportunity to explore in detail its chemical behaviour. At the time, it was clear that compound 1 was significantly activated with respect to C−H bond cleavage, since it undergoes clean intramolecular dehydrogenation upon gentle heating at 353 K to yield the corresponding methylidyne derivative, in contrast to the behaviour of dicarbonyl complex [Mo 2 Cp 2 (μ‐κ 1 :η 2 ‐CH 3 )(μ‐PCy 2 )(CO) 2 ], which only yielded methylidyne derivatives under photochemical activation . In this paper we report our preliminary results on the general reactivity of 1 which involves, among other processes, several unusual or unprecedented transformations of the methyl ligand, such as room temperature dehydrogenation, reductive elimination with phosphorus, and migratory insertion of borane.…”