Synthesis of the Bifunctional Phosphinidene Cluster, Fe₃(CO)₉(μ₃-PH)₂, and a Systematic Study of the Reactivity of the Cluster-Bound P−H Functional Group

Abstract

The synthesis and systematic study of the reaction chemistry of a bifunctional phosphinidene cluster, Fe3(CO)9(μ3-PH)2 (3) is reported. Reaction chemistry at one P−H functional site is effectively communicated through the Fe3(CO)9 core, and impacts on the reactivity of the second P−H site. Deprotonation of the acidic protons in 3 allows access to a lone electron pair on phosphorus. The first proton is readily removed with NEt3/[PPN]Cl ([PPN]+ = (Ph3P)2N+) to produce the [PPN]+ salt of [Fe3(CO)9(μ3-PH)(μ3-P)]- ([4]-). Removal of both phosphorus-bound hydrogen atoms in 3 requires the use of 2 equiv of n-BuLi, to produce Li2[Fe3(CO)9(μ3-P)2] (Li2[5]). Quenching of Li2[5] with MeOH-d 4 generates [Fe3(CO)9(μ3-PD)(μ3-P)]-. The lone electron pairs on the cluster-bound phosphorus atoms undergo analogous reaction chemistry to organophosphines. Alkylation at the phosphorus site is carried out by reaction of [Et3NH][4] with MeOSO2CF3 generating the monosubstituted cluster, Fe3(CO)9(μ3-PMe)(μ3-PH) (6) as the primary product. The cluster anions [4]- and [8]-, containing a phosphorus lone pair, are oxidized by elemental sulfur to produce the phosphine sulfide complexes, [Et3NH][Fe3(CO)9(μ3-PH)(μ3-PS)] ([Et3NH][10]) and [Et3NH][Fe3(CO)9 (μ3-PMe)(μ3-PS)] ([Et3NH][11]). Treatment of [10]- with an additional equivalent of NEt3 and S8 yields the dianionic cluster, [Et3NH]2[Fe3(CO)9(μ3-PS)2] ([Et3NH]2[12]). Without added base, reaction of the neutral clusters, 3 and 6, with S8 in THF solution yield the clusters Fe3(CO)9(μ3-PH)(μ3-PSCH2CH2CH2CH2OH) (13), Fe3(CO)9(μ3-PSCH2CH2CH2CH2OH)2 (14), and Fe3(CO)9(μ3-PMe)(μ3-PSCH2CH2CH2CH2OH) (15), with a ring-opened THF molecule appended to sulfur. Reaction of 3 with S8 in THF solution in the presence of ClAuPPh3 produces the gold derivative, Fe3(CO)9(μ3-PSAuPPh3)2 (17). Like PH groups in phosphines, the μ3-PH moieties in 3 react with activated alkenes to yield single- and double-insertion products, Fe3(CO)9(μ3-PH)(μ3-PCH2CH2R) (R = CN (18a), CO2Me (19a)) and Fe3(CO)9(μ3-PCH2CH2R)2 (R = CN (18b), CO2Me (19b)). The solid-state structures of 3, 17, and 18b were determined by single-crystal X-ray diffraction.

Metal-Assisted P−H Bond Formation: A Step towards the Hydrogenation of White Phosphorus

“…[33,34] Such compounds can be prepared by direct interaction of PH 3 with polymetallic clusters [34c] or by treating a preformed PH 3 metal complex with a carbonyl cluster. [35] The reactivity of 7, which is largely centered on the PϪH functionality, has been investigated thoroughly. A neat application of this preparative methodology has recently been reported by Schauer and co-workers, who synthesized the biphosphinidene cluster [Fe 3 (CO) 9 (µ 3 -PH) 2 ] (7) by controlled hydrolysis of PϪSi bonds.…”

[Cp2(OC)4Mo2(μ-PH2)(μ-H)] as a Useful Building Block toward Heterometallic Clusters Containing a Naked Phosphorus Atom

“…Recently, Johnson et al. have synthesized osmium complexes containing encapsulated phosphorus using the more easily handled reagent PH 4 I, which, on reaction with [Os 3 (CO) 10 (MeCN) 2 ], yields [Os 3 (CO) 10 (μ-PH 2 )(μ-H)], the H atoms of which may then be readily removed. − Encapsulation of phosphorus atoms may also be achieved by replacement of a P- SiMe 3 group by a transition metal fragment. − …”

New Main-Group-Element-Rich nido-Octahedral Cluster System: Synthesis and Characterization of [Et4N][Fe2(CO)6(μ3-As){μ3-EFe(CO)4}2]

“…The related M 3 E 2 nido- octahedral compounds have been known for some time, − and the compounds reported here may be viewed as an isolobal replacement of Fe­(CO) 3 – by P or As. [Et 4 N]­[ II ] and [Et 4 N]­[ III ] are electron precise, and the core electron count of each is consistent with that predicted by the Wade–Mingos rules for a nido- octahedron with seven skeletal electron pairs distributed across five vertices …”