Rearrangement of a P4 Butterfly Complex-The Formation of a Homoleptic Phosphorus-Iron Sandwich Complex

Functionalization of Tetraphosphido Ligands by Heterocumulenes

Although numerous polyphosphido complexes have been accessed through the transition-metal-mediated activation and functionalization of white phosphorus (P4), the selective functionalization of the resulting polyphosphorus ligands in these compounds remains underdeveloped. In this study, we explore the reactions between cyclotetraphosphido cobalt complexes and heterocumulenes, leading to functionalized P4 ligands. Specifically, the reaction of carbon disulfide (CS2) with [K(18c-6)][(Ar*BIAN)Co(η4-P4)] ([K(18c-6)]1, 18c-6 = [18]crown-6) affords the adduct [K(18c-6)][(Ar*BIAN)Co(η3:η1-P4CS2)] ([K(18c-6)]3), in which CS2 is attached to a single phosphorus atom (Ar* = 2,6-dibenzhydryl-4-isopropylphenyl, BIAN = 1,2-bis(arylimino)acenaphthene diimine). In contrast, the insertion of bis(trimethylsilyl)sulfur diimide S(NSiMe3)2 into a P-P bond of [K(18c-6)]1 yields [K(18c-6)][(Ar*BIAN)Co(η3:η1-P4SN2(SiMe3)2)] (K(18c-6)]4). This salt further reacts with Me3SiCl to form [(Ar*BIAN)Co(η3:η1-P4SN2(SiMe3)3] (5), featuring a rare azatetraphosphole ligand. Moreover, treatment of the previously reported complex [(Ar*BIAN)Co(η3:η1-P4C(O)tBu)] (2) with isothiocyanates results in P-C bond insertion, yielding [(Ar*BIAN)Co(η3:η1-P4C(S)N(R)C(O)tBu)] (6a,b; R = Cy, Ph).

Inorganic Ferrocene Analogue [Fe(P4)2]2

Inorganic metallocene derivatives containing only cyclo-P_n ligands have been targeted for more than 20 years, but their syntheses have never been achieved by pursuing the conventional route of using P₄ phosphorus except for the generation of [Ti(η⁵-P₅)₂]^2-. Herein, we report a facile one-step method for the synthesis of the homoleptic iron complex [Fe(P₄)₂]^2- by the Zintl-phase-type precursor KP. ³¹P NMR analyses indicate that upon dissolving the KP phase in ethylenediamine P₄^2- was generated only in the presence of 2,2,2-crypt. The amounts of cation-sequestering agents, the type of iron precursor, and their consuming ratio have a decisive impact on the yield of [Fe(P₄)₂]^2-. Both the Fe^II and the Fe^III precursors can oxidize P₄^2- to give a concomitant product [(P₇)Fe(P₄)]^3-, which can be partially inhibited by the addition of potassium to produce relatively pure crystalline [K(2,2,2-crypt)]₂[Fe(P₄)₂].

Low-oxidation state cobalt-magnesium complexes: ion-pairing and reactivity

Magnesium cobaltates (Arnacnac)MgCo(COD)2 (1-3) were synthesised by reacting (Arnacnac)MgI(OEt2) with K[Co(η4-COD)2] (COD = 1,5-cyclooctadiene) [Arnacnac = CH(ArNCMe)2; Ar = 2,4,6-Me3-C6H2 (Mes), 2,6-Et2-C6H3 (Dep), 2,6-iPr2-C6H3Mes (Dipp)]. Compounds 1-3 form contact ion-pairs in toluene, while solvent separated ion-pairs are formed in THF. The effect of ion-pairing on the reactivity is illustrated by reaction of 2 with tert-butylphosphaalkyne, which affords distinct 1,3-diphosphacyclobutadiene complexes. The heteroleptic sandwich complex [(Depnacnac)MgCo(P2C2tBu2)]2 (4) is selectively formed in toluene, while the homoleptic bis(1,3-diphosphacyclobutadiene) complex [(Depnacnac)Mg(THF)3][Co(P2C2tBu2)2] (5) is obtained in THF. Complex 4 is a precursor to further unusual phosphaorganometallic compounds. Substitution of the labile COD ligand in 4 by white phosphorus (P4) enabled the synthesis of the phosphorus-rich sandwich compound [(Depnacnac)MgCoP4(P2C2tBu2)]2 (6). The heterobimetallic complex (Cp*NiP2C2tBu2)Co(COD) (7) was isolated after treatment of 4 with Cp*Ni(acac) (Cp* = C5Me5, acac = acetylacetonate).

Insertion of Phosphenium Ions into a Bicyclo[1.1.0]Tetraphosphabutane Iron Complex

By reacting [{Cp‴Fe(CO)₂}₂(µ,η^1:1-P₄)] (1) with in situ generated phosphenium ions [Ph₂P][A] ([A]^- = [OTf]^- = [O₃SCF₃]^-, [PF₆]^-), a mixture of two main products of the composition [{Cp‴Fe(CO)₂}₂(µ,η^1:1-P₅(C₆H₅)₂)][PF₆] (2a and 3a) could be identified by extensive ³¹P NMR spectroscopic studies at 193 K. Compound 3a was also characterized by X-ray diffraction analysis, showing the rarely observed bicyclo[2.1.0]pentaphosphapentane unit. At room temperature, the novel compound [{Cp‴Fe}(µ,η^4:1-P₅Ph₂){Cp‴(CO)₂Fe}][PF₆] (4) is formed by decarbonylation. Reacting 1 with in situ generated diphenyl arsenium ions gives short-lived intermediates at 193 K which disproportionate at room temperature into tetraphenyldiarsine and [{Cp‴Fe(CO)₂}₄(µ₄,η^1:1:1:1-P₈)][OTf]₂ (5) containing a tetracyclo[3.3.0.0^2,7.0^3,6]octaphosphaoctane ligand.

Reactivity of P4 butterfly complexes towards NHCs - generation of a metal-bridged P2 dumbbell complex

The reactivity of the P₄ butterfly complexes [{Cp'''Fe(CO)₂}₂(μ,η^1:1-P₄)] (A, Cp''' = C₅H₂^tBu₃) and [{Cp*Cr(CO)₃}₂(μ,η^1:1-P₄)] (B, Cp* = C₅(CH₃)₅) towards the N-heterocyclic carbene IMe (1,3,4,5-tetramethyl-imidazol-2-ylidene) is reported. The reaction of A affords [P(IMe)₂][Fe(CO)₂Cp'''] (1) or [P(IMe)₂][{Cp'''Fe}₂(μ,η^3:3-P₃)] (2), the latter possessing a P₃-allylic moiety. In contrast, the reaction of B yields [P(IMe)₂][Cr(CO)₃Cp*] (3) and [{Cp*Cr(CO)₂}(η²-P₂IMe₂)][Cr(CO)₃Cp*] (4), featuring a novel metal-bridged P₂ dumbbell.

Coordination Behavior of a P4 -Butterfly Complex towards Transition Metal Lewis Acids: Preservation versus Rearrangement

The reactivity of the P4 butterfly complex [{Cp'''Fe(CO)2 }2 (μ,η1:1 -P4 )] (1, Cp'''=η5 -C5 H2 tBu3 ) towards divalent Co, Ni and Zn salts is investigated. The reaction with the bromide salts leads to [{Cp'''Fe(CO)2 }2 (μ3 ,η2:1:1 -P4 ){MBr2 }] (M=Co (2Co), Ni (2Ni), Zn (2Zn)) in which the P4 butterfly scaffold is preserved. The use of the weakly ligated Co complex [Co(NCCH3 )6 ][SbF6 ]2 , results in the formation of [{(Cp'''Fe(CO)2 )2 (μ3 ,η4:1:1 -P4 )}2 Co][SbF6 ]3 (3), which represents the second example of a homoleptic-like octaphospha-metalla-sandwich complex. The formation of the threefold positively charged complex 3 occurs via redox processes, which among others also enables the formation of [{Cp'''Fe(CO)2 }4 (μ5 ,η4:1:1:1:1 -P8 ){Co(CO)2 }][SbF6 ] (4), bearing a rare octaphosphabicyclo[3.3.0]octane unit as a ligand. On the other hand, the reaction with [Zn(NCCH3 )4 ][PF6 ]2 yields the spiro complex [{(Cp'''Fe(CO)2 )2 (μ3 ,η2:1:1 -P4 )}2 Zn][PF6 ]2 (5) under preservation of the initial structural motif.

From a P4 butterfly scaffold to cyclo- and catena-P4 units

The reactivity of [{Cp'''Fe(CO)2}2(μ,η1 : 1-P4)] (1) towards half-sandwich complexes of Ru(ii), Rh(iii), and Ir(iii) is studied. The coordination of these Lewis acids leads to a rearrangement of the P4 butterfly unit to form complexes with either an aromatic cyclo-P4R2 unit (R = Cp'''Fe(CO)2) or a catena-tetraphosphaene entity.

The Butterfly Complex [{Cp*Cr(CO)3 }2 (μ,η1:1 -P4 )] as a Versatile Ligand and Its Unexpected P1 /P3 Fragmentation

The versatile coordination behavior of the P4 butterfly complex [{Cp*Cr(CO)3 }2 (μ,η1:1 -P4 )] (1) towards Lewis acidic pentacarbonyl compounds of Cr, Mo and W is reported. The reaction of 1 with [W(CO)4 (nbd)] (nbd=norbornadiene) yields the complex [{Cp*Cr(CO)3 }2 (μ3 ,η1:1:1:1 -P4 ){W(CO)4 }] (2) in which 1 serves as a chelating P4 butterfly ligand. In contrast, reactions of 1 with [M(CO)4 (nbd)] (M=Cr (a), Mo (b)) result in the step-wise formation of [{Cp*Cr(CO)2 }2 (μ3 ,η3:1:1 -P4 ){M(CO)5 }] (3 a,b) and [{Cp*Cr(CO)2 }2 -(μ4 ,η3:1:1:1 -P4 ){M(CO)5 }2 ] (4 a,b) which contain a folded cyclo-P4 unit. Complex 4 a undergoes an unprecedented P1 /P3 -fragmentation yielding the cyclo-P3 complex [Cp*Cr(CO)2 (η3 -P3 )] (5) and the as yet unknown phosphinidene complex [Cp*Cr(CO)2 {Cr(CO)5 }2 (μ3 -P)] (6). The identity of 6 is confirmed by spectroscopic methods and by the in situ formation of [{Cp*Cr(CO)2 (tBuNC)}P{Cr(CO)5 }2 (tBuNC)] (7). DFT calculations throw light on the bonding situation of the reported products.

Nucleophilic Activation of Red Phosphorus for Controlled Synthesis of Polyphosphides

Reactions between red phosphorus (P_red) and potassium ethoxide in various organic solvents under reflux convert this rather inert form of the element to soluble polyphosphides. The activation is hypothesized to proceed via a nucleophilic attack by ethoxide on the polymeric structure of P_red, leading to disproportionation of the latter, as judged from observation of P(OEt)₃ in the reaction products. A range of solvents has been probed, revealing that different polyphosphide anions (P₇^3-, P₁₆^2-, P₂₁^3-, and P₅^-) can be stabilized depending on the combination of the boiling point and dielectric constant (polarity) of the solvent. The effectiveness of activation also depends on the nature of nucleophile, with the rate of reaction between P_red and KOR increasing in the order t-Bu < n-Hex < Et < Me, which is in agreement with the increasing order of nucleophilic strength. Thiolates and amides were also examined as potential activators, but the reaction with these nucleophiles were substantially slower; nonetheless, all reactions between P_red and NaSR yielded exclusively P₁₆^2- as a soluble polyphosphide product.

The Chatt reaction: conventional routes to homoleptic arenemetalates of d-block elements

Joseph Chatt was the first to discover in the early 1960s that previously unknown transition metal compounds were accessible and isolable via the reactions of alkali metal arene radical anions with transition metal precursors containing good leaving groups, such as weakly basic neutral or anionic ligands, especially halides. Later Peter Timms confirmed the importance of these early studies with the synthesis of several new bis(arene)metal(0) sandwich compounds by a variant of Chatt's route. Following a brief historical survey of alkali metal arene compounds, first examined in some detail by Wilhelm Schlenk, use of these reagents in the conventional syntheses of anionic homoleptic arene metal complexes of the d-block elements will be described. In several cases these species are quite useful because they function as storable "naked" atomic metal anion reagents, especially in their reactions with carbon monoxide and isocyanides. In view of Chatt's seminal contributions to an often unique route to organometallic and inorganic compounds, it is proposed that this valuable synthetic method be named the "Chatt reaction" in honor of a giant of chemistry.

Mono- and dinuclear tetraphosphabutadiene ferrate anions

Reduction of [Cp^ArFe(μ-Br)]₂ (1, Cp^Ar = C₅(C₆H₄-4-Et)₅) by potassium napthalenide, followed by the addition of white phosphorus, affords [K(18-c-6){Cp^ArFe(η⁴-P₄)}] (2, 18-c-6 = [18]crown-6), which features a planar cyclo-P₄^2- ligand. The related diiron complex [Na₂(THF)₅(Cp^ArFe)₂(μ,η^4:4-P₄)] (3) was obtained by reducing 1 with sodium amalgam in the presence of P₄. Protonation of 3 affords [Na(THF)₃][(Cp^ArFe)₂(μ,η^4:4-P₄)(H)] (4), while the reaction of 3 with trimethylchlorosilane gives the nortricyclane compound P₇(SiMe₃)₃ as the main product.