Isomerization, Ring Expansion, and Ring Contraction of 1,3-Diphosphete Complexes

Synthesis and Reactivity of Hetero-Pnictogen Diazonium Analogs Stabilized by Transition Metal Units

The reactivity of the mixed dipnictogen complexes [{CpMo(CO)2 }2 (μ,η2 : 2 -PE)] (E=P, As, Sb) towards different group 14 electrophiles is reported. The resulting library of cationic compounds [{CpMo(CO)2 }2 (μ,η2 : 2 -EPR)]+ (R=Mes (2,4,6-C6 H2 Me3 ), CH3 , CPh3 , SnMe3 ) represents formally inorganic diazonium homologs which are stabilized by transition metal units. Modifying the steric and electronic properties of the electrophile drastically impacts the respective P-R bond lengths and is accompanied by increasing (SnMe3 >CPh3 >CH3 ) dynamic behavior in solution. In contrast to the well-studied organic analogs, the prepared compounds are stable at room temperature. The subsequent reaction of the model substrate [{CpMo(CO)2 }2 (μ,η2 : 2 -P2 Me)][OTf] ([OTf]- =[CF3 SO3 ]- ) with different N-heterocyclic carbenes (NHCs) leads to an addition at the unsubstituted P atom which is also predicted by computational methods. NMR spectroscopy confirms the formation of two isomers sync/gauche-[{CpMo(CO)2 }(μ,η2 : 1 -P(NHC)PMe){CpMo(CO)2 }][OTf]. X-ray crystallographic characterization and additional DFT calculations shed light on the spatial arrangement as well as on the possible formation pathways of the isomers.

Diverse Reactions of o-Carborane-Fused Silylenes with C≡E (E = C, P) Triple Bonds

The reactivities of o-carborane-fused silylenes toward molecules with C≡E (E = C, P) bonds are reported. The reactions of bis(silylene) [(LSi:)C]₂B₁₀H₁₀ (1a, L = PhC(NtBu)₂) with arylalkynes afforded bis(silylium) carborane adducts 2 and 3, showing a Si(μ-C₂)Si structure with an open-cage nido-carborane backbone. In contrast, the reaction of 1a with a phosphaalkyne AdC≡P (Ad = 1-adamantyl) smoothly furnished compound 4, comprising fused CPSi rings with a C=Si double bond and Si-Si single bond, and the related formation mechanism was investigated by DFT calculations. Furthermore, when monosilylene [(LSi:)C]CHB₁₀H₁₀ (1b) was employed to react with AdC≡P, compound 5 was isolated. The structure of 5 features a 1,2,3-triphosphetene core. All products were characterized by NMR spectroscopy and/or X-ray crystallography.

Di-tert-butyldiphosphatetrahedrane as a Source of 1,2-Diphosphacyclobutadiene Ligands

Reactions of di‐tert‐butyldiphosphatetrahedrane (1) with cycloocta‐1,5‐diene‐ or anthracene‐stabilised metalate anions of iron and cobalt consistently afford complexes of the rarely encountered 1,2‐diphosphacyclobutadiene ligand, which have previously been very challenging synthetic targets. The subsequent reactivity of 1,2‐diphosphacyclobutadiene cobaltates toward various electrophiles has also been investigated and is compared to reactions of related 1,3‐diphosphacyclobutadiene complexes. The results highlight the distinct reactivity of such isomeric species, showing that the 1,2‐isomers can act as precursors for previously unknown triphospholium ligands. The electronic structures of the new complexes were investigated by several methods, including NMR, EPR and Mößbauer spectroscopies as well as quantum chemical calculations.

Activation of Di-tert-butyldiphosphatetrahedrane: Access to (tBuCP)n (n=2, 4) Ligand Frameworks by P-C Bond Cleavage

The first mixed phosphatetrahedranes were reported only recently and their reactivity is virtually unexplored. Herein, we present a reactivity study on di‐tert‐butyldiphosphatetrahedrane (1), which is the dimer of tert‐butylphosphaalkyne. The (tBuCP)₂ tetrahedron is activated selectively by N‐heterocyclic carbene (NHC) nickel(I) and nickel(0) complexes, resulting in novel complexes featuring diverse (tBuCP)_n‐frameworks (n=2, 4). Release of the (tBuCP)₄ framework from one of the complexes was achieved by addition of CO gas. Furthermore, 1 can be used as a source for P₂ units by elimination of di‐tert‐butylacetylene in the coordination sphere of nickel.

Transformations of the cyclo-P4 ligand in [Cp'''Co(η4-P4)]

The reactivity of the cyclo-P₄ ligand complex [Cp′′′Co(η⁴-P₄)] (1) (Cp′′′ = 1,2,4-tri-tert-butyl-cyclopentadienyl) towards reduction and main group nucleophiles was investigated. By using K[CpFe(CO)₂], a selective reduction to the dianionic complex [(Cp′′′Co)₂(μ,η³:η³-P₈)]²⁻ (2) was achieved. The reaction of 1 with ^tBuLi and LiCH₂SiMe₃ as carbon-based nucleophiles yielded [Cp′′′Co(η³-P₄R)]⁻ (R = ^tBu (4), CH₂SiMe₃ (7)), which, depending on the reaction conditions, undergo subsequent reactions with another equivalent of 1 to form [(Cp′′′Co)₂(μ,η³:η³-P₈R)]⁻ (R = ^tBu (5), CH₂SiMe₃ (8)). In the case of 4, a different pathway was observed, namely a dimerisation followed by a fragmentation into [Cp′′′Co(η³-P₅^tBu₂)]⁻ (6) and [Cp′′′Co(η³-P₃)]⁻ (3). With OH⁻ as an oxygen-based nucleophile, the synthesis of [Cp′′′Co(η³-P₄(O)H)]⁻ (9) was achieved. All compounds were characterized by X-ray crystal structure analysis, NMR spectroscopy and mass spectrometry. Their electronic structures and reaction behavior were elucidated by DFT calculations.

The reactivity of the cyclo-P₄ ligand complex [Cp′′′Co(η⁴-P₄)] (1) (Cp′′′ = 1,2,4-tri-tert-butyl-cyclopentadienyl) towards reduction and main group nucleophiles was investigated.

1,3-Diphosphacyclobutene Cobalt Complexes

The synthesis and characterization of rare 1,3-diphosphacyclobutene transition-metal complexes is described. Reactions of the cobalt-hydride complex [Co(P₂ C₂ tBu₂ )₂ H] (G) with nBuLi, tBuLi, or PhLi afforded [Li(solv)_x {Co(η³ -P₂ C₂ tBu₂ HR)(η⁴ -P₂ C₂ tBu₂ )}] (1: R=nBu, (solv)_x =(Et₂ O)₂ ; 2: R=tBu, (solv)_x =(thf)₂ ; 3: R=Ph, (solv)_x =(Et₂ O)(thf)₂ ), with an η³ -coordinated 1,3-diphosphacyclobutene ligand as a result of organyl-anion attack at one of the phosphorus atoms of the bis(1,3-diphosphacyclobutadiene) backbone. In contrast to the reactions with PhLi, the aryl-magnesium compounds p-tolyl magnesium chloride and p-fluorophenyl magnesium bromide deprotonate [Co(P₂ C₂ tBu₂ )₂ H] to give the magnesium salt [Mg(MeCN)₆ ][Co(η⁴ -P₂ C₂ tBu₂ )₂ ]₂ (4), which contains a bis(1,3-diphosphacyclobutadiene)-cobaltate anion. The [Co(η⁴ -P₂ C₂ tBu₂ )₂ ]^- anions are well separated from the octahedral [Mg(MeCN)₆ ]²⁺ cation in the molecular structure of 4. Compound 1 reacts with Me₃ SiCl to give neutral [Co(η³ -P₂ C₂ tBu₂ HnBu)(η⁴ -P₂ C₂ tBu₂ SiMe₃ )] (5, 52 % yield) with an SiMe₃ group attached to one of the P atoms of the previously unfunctionalized backbone.

Oligomerization of phosphaalkynes mediated by bulky N-heterocyclic carbenes: avenues to novel phosphorus frameworks

Reactions of RCP (R = tBu or Ad (admantyl)) with NHCs (SIMes, 1a; IMes, 1b and IDipp, 1d), leading to 1,2,3-triphosphetenes 2 and 3, a triphosphole 4, and a di-1,2-dihydro-1,2-diphosphete-substituted diphosphene 5, are reported.

Functionalization of 1,3-diphosphacyclobutadiene cobalt complexes via Si–P bond insertion

We report the synthesis of functionalized 1,3-bis(diphosphacyclobutadiene) complexes via the insertion of carbon-oxygen bonds of ethers, esters, aldehydes and amides into the P–Si bond of silylated complexes. Reactions of [K(tol)2][Co(η 4-P2C2R2)2] [[K(tol)2][1a]: R=tBu, [K(tol)2][1b]: R=tPent (=tert-pentyl)] with Me3SiCl afford the trimethylsilyl-substituted derivatives [Co(η 4-P2C2R2SiMe3)(η 4-P2C2R2)] (2a, b, R=tBu, tPent). The Me3Si group is connected to a phosphorus atom of one of the 1,3-diphosphacyclobutadiene ligands. 2a, b readily react with organic substrates containing C–O single and C=O double bonds at ambient temperature. [Co(η 4-P2C2R2(CH2)4OSiMe3)(η 4-P2C2R2)] (3a, b) are formed by reaction of 2a, b with traces of THF. They can also be isolated by reacting the THF solvates [K(thf)2{Co(P2C2 tBu2)2}] ([K(thf)2][1a]) and [K(thf)3{Co(P2C2 tPent2)2}] ([K(thf)3][1b]) with Me3SiCl in toluene or THF. The adamantyl-substituted complex [Co(η 4-P2C2Ad2(CH2)4OSiMe3)(η 4-P2C2Ad2)] (3c) was prepared analogously from [K(thf)4{Co(P2C2Ad2)2}] and Me3SiCl. [K(thf)2][1a] reacts cleanly with Ph3SnCl affording [Co(η 4-P2C2 tBu2SnPh3)(η 4-P2C2 tBu2)] (4) in high yield. Reaction of 2a with styrene oxide affords [Co(η 4-P2C2 tBu2PhC2H3OSiMe3)(η 4-P2C2 tBu2)] (5) as a single regioisomer. By contrast, multinuclear NMR spectroscopic studies indicate mixtures of two isomeric insertion products 6/6′ and 7/7′, respectively, which result from the insertion of 1,2-epoxy-2-methylpropane and 1,2-epoxyoctane. Moreover, these monitoring studies show that reactions of 2a with acyclic ethers afford alkyl substituted complexes such as [Co(η 4-P2C2 tBu2Et)(η 4-P2C2 tBu2)] (8) and alkylsilyl ethers. Reaction of 2a with γ-butyrolactone gives [Co(η 4-P2C2 tBu2(CH2)3C(O)OSiMe3)(η 4-P2C2 tBu2)] (9) via cleavage of the endocyclic C–O single bond of the lactone. Benzaldehyde and acetone cleanly react with 2a to [Co(η 4-P2C2 tBu2CH(Ph)OSiMe3)(η 4-P2C2 tBu2)] (10) and [Co(η 4-P2C2 tBu2CMe2OSiMe3)(η 4-P2C2 tBu2)] (11), while the sterically more demanding ketones 3-pentanone and acetophenone selectively yield the known hydride complex [Co(η 4-P2C2 tBu2)2H] (A). Phenyl isocyanate reacts with 2a at elevated temperature to form [Co(η 3-P2C2 tBu2CON(Ph)SiMe3)(η 4-P2C2 tBu2)] (12) with a functionalized η 3-coordinated ligand. [K(tol)2][1a], [K(tol)2][1b], 2a, 2b, 3a–c, 4, 5, and 9–12 were isolated and characterized by multinuclear NMR spectroscopy, UV/Vis spectroscopy and elemental analysis. [K(tol)2][1b], 2a, 2b, 3c, 4, 5, and 9–12 were additionally characterized by X-ray crystallography.