Reactivity of the Anionic Diphosphorus Complex [Mo2Cp2(μ-PCy2)(CO)2(μ-κ2:κ2-P2)]− Toward ER3X Electrophiles (E = C to Pb): Insights into the Multisite Donor Ability and Dynamics of the P2 Ligand

Reactions of Heterometallic Phosphinidene-Bridged MoMn and MoRe Complexes with Sulfur and Selenium: From Chalcogenophosphinidene- to Trithiophosphonate-Bridged Derivatives

Reactions of [MoReCp(μ-PR*)(CO)₆] with S₈ were strongly dependent on experimental conditions (R* = 2,4,6-C₆H₂^tBu₃). When using 1 equiv of sulfur, complex [MoReCp(μ-η²:κ¹_S-SPR*)(CO)₆] was slowly formed at 313 K, with a thiophosphinidene ligand unexpectedly bridging the dimetal center in the novel μ-κ¹_S:η² coordination mode, as opposed to the μ-κ¹_P:η² mode usually found in related complexes. The latter underwent fast decarbonylation at 363 K to give [MoReCp(μ-η²:η²-SPR*)(CO)₅], with a six-electron donor thiophosphinidene ligand rearranged into the rare μ-η²:η² coordination mode. Depending on reaction conditions, reactions with excess sulfur involved the addition of two or three S atoms to the phosphinidene ligand to give new complexes identified as the dithiophosphinidene-bridged complex [MoReCp(μ-η²:κ²_S,S'-S₂PR*)(CO)₅], its dithiophosphonite-bridged isomer [MoReCp(μ-κ²_S,S':κ²_S,S'-S₂PR*)(CO)₅], or the trithiophosphonate-bridged derivative [MoReCp(μ-κ²_S,S':κ²_S,S'-S₃PR*)(CO)₅], all of them displaying novel coordination modes of their PRS₂ and PRS₃ ligands, as determined by X-ray diffraction studies. In contrast, the related MoMn complex yielded [MoMnCp(μ-η²:η²-SPR*)(CO)₅] under most conditions. A similar output was obtained in reactions with gray selenium for either MoRe or MoMn phosphinidene complexes, which under different conditions only gave the pentacarbonyl complexes [MoMCp(μ-η²:η²-SePR*)(CO)₅] (M = Re, Mn), these providing a new coordination mode for selenophosphinidene ligands.

Electronic Structure and Donor Ability of an Unsaturated Triphosphorus-Bridged Dimolybdenum Complex

The triphosphorus complex [Mo₂Cp₂(μ-η³:η³-P₃)(μ-P^tBu₂)] was prepared in 83% yield by reacting the methyl complex [Mo₂Cp₂(μ-κ¹:η²-CH₃)(μ-P^tBu₂)(μ-CO)] with P₄ at 333 K, a process also giving small amounts of the methyldiphosphenyl complex [Mo₂Cp₂(μ-η²:η²-P₂Me)(μ-P^tBu₂)(CO)₂]. The latter could be better prepared by first reacting the anionic complex Na[Mo₂Cp₂(μ-P^tBu₂)(μ-CO)₂] with P₄ to give the diphosphorus derivative Na[Mo₂Cp₂(μ-η²:η²-P₂)(μ-P^tBu₂)(CO)₂] and further reaction of the latter with MeI. Density functional theory calculations on the title complex revealed that its triphosphorus group can be viewed as an allylic-like P₃^- ligand acting as a six-electron donor via the external P atoms, while coordination of the internal P atom involves donation from the π orbital of the ligand and back-donation to its π* orbital, both interactions having a weakening effect on the Mo-Mo and P-P connections. The reactivity of the title compound is dominated by the electron-donor ability associated with the lone pairs located at the P atoms. Its reaction with CF₃SO₃Me gave [Mo₂Cp₂(μ-η³:η³-P₃Me)(μ-P^tBu₂)](CF₃SO₃) as a result of methylation at an external atom of the P₃ ligand, while its reaction with [Fe₂(CO)₉] enabled the addition of one, two, or three Fe(CO)₄ fragments at these P atoms, but only the diiron derivative [Mo₂Fe₂Cp₂(μ-η³:η³:κ¹:κ¹-P₃)(μ-P^tBu₂)(CO)₈] could be isolated. This complex bears a Fe(CO)₄ fragment at each of the external atoms of the P₃ ligand, and the central P atom of the latter displays the lowest ³¹P chemical shift reported to date (δ_P -721.8 ppm). The related complexes [Mo₂M₂Cp₂(μ-η³:η³:κ¹:κ¹-P₃)(μ-P^tBu₂)(CO)₁₀] (M = Mo, W) were prepared by reacting the title compound with the corresponding [M(CO)₅(THF)] complexes in toluene, while reaction with [Mo(CO)₄(THF)₂] also enabled the formation of the heptanuclear derivative [Mo₇Cp₄(μ-η³:η³:κ¹:κ¹-P₃)₂(μ-P^tBu₂)₂(CO)₁₄]. The interatomic distances in the above compounds indicate that the central Mo₂P₃ skeleton of these molecules is little modified by the attachment of 16-electron M(CO)_n fragments at the external atoms of the P₃ ligand.