Zwitterionic 2-Phosphaethene-thiolates [(LC)P=CS(LC/P)]+ as PCS Building Blocks (LC=NHC, LP=PR3)

The zwitterionic compounds [(LC)P=CS(LC/P)]+ (3+, LC=NHC, LP=PR3), featuring cationic substituents at the phosphorus and carbon atoms, are synthesized as their triflate salts at a multi-gram scale from the reaction of Lewis base adducts of CS2, namely LC/P-CS2 (4), with a combination of [(LCP)4][OTf]4 (1[OTf]4) and Ph3P. The feasibility of using 3+ as PCS building blocks is showcased in their reactions with representative electrophiles (MeOTf) and nucleophiles (MesMgBr, Ph3PCH2), leading to selective functionalization of the PCS core at the S- and P-terminus, respectively. Additionally, it is reported that 3+ can function as ambident nucleophiles with AgOTf (2 equivalents), affording unprecedented linear coordination polymer [Ag2(OTf)3-μ2:κP,κS-((LC)P=CS(PCy3))]+ (6 b), where the PCS moiety acts as a bridging ligand in transition metal complexes for the first time. Reduction of 3+ facilitates the cleavage of the P- and C-bound substituents leading to the formation of the [PCS]- anion. Moreover, cycloaddition reactions of 3+ with 1[OTf]4 are shown to selectively yield five- and eight-membered polyphosphorus heterocycles. Preliminary results suggest the possibility of activating the C-S bond in [(LC)P=CS(LC)]+, resulting in the formation of [(LC)P=C(LC)-P(LC)][OTf]2, 12[OTf]2, which may serve as a synthon for the PCP unit in future studies.

The Varied Frustrated Lewis Pair Reactivity of the Germylene Phosphaketene (CH{(CMe)(2,6-i Pr2 C6 H3 N)}2 )GePCO

The germylene species (CH{(CMe)(2,6-iPr2 C6 H3 N)}2 )GePCO 1 is shown to react with the Lewis acids (E(C6 F5 )3 E=B, Al). Nonetheless, 1 participates in FLP chemistry with electron deficient alkynes or olefins, acting as an intramolecular FLP. In contrast, in the presence of B(C6 F5 )3 and an electron rich alkyne, 1 behaves as Ge-based nucleophile to effect intermolecular FLP addition to the alkyne. This reactivity demonstrates that the reaction pathway is controlled by the nature of the electrophile and nucleophile generated in solution, as revealed by extensive DFT calculations.

Bis-Phosphaketenes LM(PCO)2 (M=Ga, In): A New Class of Reactive Group 13 Metal-Phosphorus Compounds

Phosphaketenes are versatile reagents in organophosphorus chemistry. We herein report on the synthesis of novel bis-phosphaketenes, LM(PCO)2 (M=Ga 2 a, In 2 b; L=HC[C(Me)N(Ar)]2 ; Ar=2,6-i-Pr2 C6 H3 ) by salt metathesis reactions and their reactions with LGa to metallaphosphenes LGa(OCP)PML (M=Ga 3 a, In 3 b). 3 b represents the first compound with significant In-P π-bonding contribution as was confirmed by DFT calculations. Compounds 3 a and 3 b selectively activate the N-H and O-H bonds of aniline and phenol at the Ga-P bond and both reactions proceed with a rearrangement of the phosphaethynolate group from Ga-OCP to M-PCO bonding. Compounds 2-5 are fully characterized by heteronuclear (1 H, 13 C{1 H}, 31 P{1 H}) NMR and IR spectroscopy, elemental analysis, and single crystal X-ray diffraction (sc-XRD).

Phosphorus-Atom Transfer from Phosphaethynolate to an Alkylidyne

A low-spin and mononuclear vanadium complex, (Me nacnac)V(CO)(η2 -P≡Ct Bu) (2) (Me nacnac- =[ArNC(CH3 )]2 CH, Ar=2,6-i Pr2 C6 H3 ), was prepared upon treatment of the vanadium neopentylidyne complex (Me nacnac)V≡Ct Bu(OTf) (1) with Na(OCP)(diox)2.5 (diox=1,4-dioxane), while the isoelectronic ate-complex [Na(15-crown-5)]{([ArNC(CH2 )]CH[C(CH3 )NAr])V(CO)(η2 -P≡Ct Bu)} (4), was obtained via the reaction of Na(OCP)(diox)2.5 and ([ArNC(CH2 )]CH[C(CH3 )NAr])V≡Ct Bu(OEt2 ) (3) in the presence of crown-ether. Computational studies suggest that the P-atom transfer proceeds by [2+2]-cycloaddition of the P≡C bond across the V≡Ct Bu moiety, followed by a reductive decarbonylation to form the V-C≡O linkage. The nature of the electronic ground state in diamagnetic complexes, 2 and 4, was further investigated both theoretically and experimentally, using a combination of density functional theory (DFT) calculations, UV/Vis and NMR spectroscopies, cyclic voltammetry, X-ray absorption spectroscopy (XAS) measurements, and comparison of salient bond metrics derived from X-ray single-crystal structural characterization. In combination, these data are consistent with a low-valent vanadium ion in complexes 2 and 4. This study represents the first example of a metathesis reaction between the P-atom of [PCO]- and an alkylidyne ligand.

A Primary Acyl Phosphine Stabilized by a Phosphonium Ylide

Primary acyl-phosphines are scarce in the literature. Here we show that the reaction of Ph₃ GePCO with the ylide Ph₃ PCH₂ proceeds to give the species Ph₃ PCHC(O)PH(GePh₃ ) 1. Deprotonation of 1 with Na[N(SiMe₃ )₂ ] generates the salt [Na(THF)₂ ][Ph₃ PCHC(O)P(GePh₃ )] 2 which provides subsequent access to the bis-germanylated acylphosphine, Ph₃ PCHC(O)P(GePh₃ )₂ 3. Alternatively, treatment of 1 with HCl in dioxane affords the primary acylphosphine Ph₃ PCHC(O)PH₂ 4. Compound 4 is a rare example of an air stable primary acyl-phosphines and the first devoid of a stabilizing heteroatom adjacent to the carbonyl fragment.

η3 -Coordination and Functionalization of the 2-Phosphaethynthiolate Anion at Lanthanum(III)*

We present the η3 -coordination of the 2-phosphaethynthiolate anion in the complex (PN)2 La(SCP) (2) [PN=N-(2-(diisopropylphosphanyl)-4-methylphenyl)-2,4,6-trimethylanilide)]. Structural comparison with dinuclear thiocyanate-bridged (PN)2 La(μ-1,3-SCN)2 La(PN)2 (3) and azide-bridged (PN)2 La(μ-1,3-N3 )2 La(PN)2 (4) complexes indicates that the [SCP]- coordination mode is mainly governed by electronic, rather than steric factors. Quantum mechanical investigations reveal large contributions of the antibonding π*-orbital of the [SCP]- ligand to the LUMO of complex 2, rendering it the ideal precursor for the first functionalization of the [SCP]- anion. Complex 2 was therefore reacted with CAACs which induced a selective rearrangement of the [SCP]- ligand to form the first CAAC stabilized group 15-group 16 fulminate-type complexes (PN)2 La{SPC(R CAAC)} (5 a,b, R=Ad, Me). A detailed reaction mechanism for the SCP-to-SPC isomerization is proposed based on DFT calculations.

Multi-Talented Gallaphosphene for Ga-P-Ga Heteroallyl Cation Generation, CO2 Storage, and C(sp3 )-H Bond Activation

Gallaphosphene L(Cl)GaPGaL (2; L=HC[C(Me)N(2,6-i-Pr2 C6 H3 )]2 ), which is synthesized by reaction of LGa(Cl)PCO (1) with LGa, reacts with [Na(OCP)(dioxane)2.5 ] to LGa(OCP)PGaL (3), whereas chloride abstraction with LiBArF 4 yields [LGaPGaL][BArF 4 ] (4; BArF 4 =B(C6 F5 )4 ). 4 represents a heteronuclear analog of the allyl cation according to quantum chemical calculations. Remarkably, 2 reversibly reacts with CO2 to yield L(Cl)Ga-P[μ-C(O)O]2 GaL (5), while reactions with acetophenone and acetone selectively give compounds 6 and 7 by C(sp3 )-H bond activation.

Phosphanyl Cyanophosphide Salts: Versatile PCN Building Blocks

The facile preparation of alkali salts of phosphanyl cyanophosphides [NHP-PCN]^- (NHP=N-heterocyclic phosphenium) is reported. Their formation is achieved by isoelectronic replacement of O for [N]^- in the phosphaketenes NHP-PCO using alkaline hexamethyldisilazide M[N(SiMe₃ )₂ ] (M=Na, K) as reagent. The new anionic entities are versatile PCN building blocks which allow the formation of a diversity of new cyanophosphine derivates including the first example of a PCNB hetero-cumulene and a PCN-ligated transition metal complex.

Bent Phosphaallenes With "Hidden" Lone Pairs as Ligands

Phosphaheteroallenes R-P=C=L, with L = N-heterocyclic carbenes (NHCs), can be viewed to a certain extent as phosphaisonitriles stabilized with NHCs, R-P=C:←L. The suitability of these molecules as ligands for coinage-metal ions was investigated and coordination through the central carbon center was observed in most cases. A combination of experiments, spectroscopic methods, and DFT calculations indicates the presence of a hidden electron pair at the carbon center of R-P=C:←L. Remarkably, this lone pair also inserts intramolecularly in C-H bonds showing the carbene-type reactivity which is expected for phosphaisonitriles.

3H-Phosphaallenes Revisited: Facile Synthesis by Hydroalumination of Alkynylphosphines and β-Elimination, Stability and Trapping of Transient Species by Coordination to Transition Metal Atoms

A facile method for the efficient synthesis of 3H-phosphaallenes, R-P=C=C(H)-R', is presented, which comprises treatment of dialkynylphosphines with dialkylaluminium hydrides (hydroalumination) and elimination of aluminium alkynides from intermediate alkenyl-alkynylphosphines. The stability of the phosphaallenes depends on steric shielding by the substituents at phosphorus (aryl or CH(SiMe₃ )₂ groups). Only supermesityl compounds are persistent at room temperature in solution. This simple method starting with easily accessible dialkynylphosphines and commercially available aluminium hydrides (HAlEt₂ , HAliBu₂ ) allows the generation of transient species, which were trapped by coordination to transition metals. The η¹ -coordination via a P-W bond was observed for tungsten, while the side-on coordination via the P=C bond resulted with platinum. Decomposition of the mesityl derivative yielded an unprecedented product, which may be formed by 1,3-H shift to the P atom, hydrophosphination of the P=C bond of a second phosphaallene and formation of a P-P bond.

The Chemistry of the 2-Phosphaethynolate Anion

In all likelihood the first synthesis of the phosphaethynolate anion, PCO^- , was performed in 1894 when NaPH₂ was reacted with CO in an attempt to make Na(CP) accompanied by elimination of water. This reaction was repeated 117 years later when it was discovered that Na(OCP) and H₂ are the products of this remarkable transformation. Li(OCP) was synthesized and fully characterized in 1992 but this salt proved to be too unstable to allow for a detailed investigation of its chemistry. It was not until the heavier analogues of this lithium salt were isolated, Na(OCP) and K(OCP) (both of which are remarkably stable and can be even dissolved in water), that the chemistry of this new functional group could be explored. Here we review the chemistry of the 2-phosphaethynolate anion, a heavier phosphorus-containing analogue of the cyanate anion, and describe the wide breadth of chemical transformations for which it has been thus far employed. Its use as a ligand, in decarbonylative and deoxygenative processes, and as a building block for novel heterocycles is described. In the mere twenty-six years since Becker first reported the isolation of this remarkable anion, it has become a fascinating reagent for the synthesis of a vast library of, often unprecedented, molecules and compounds.

Synthesis and Reactivity of the Phosphorus Analogues of Cyclopentadienone, Tricyclopentanone, and Housene

The phosphorus analogues of cyclopentadienone, tricyclopentanone, and housene were accessed from bis(cyclopropenyl)diphosphetanedione 3, which was prepared by mixing 1,2,3-tris-tert-butylcyclopropenium tetrafluoroborate (1) and sodium phosphaethynolate [Na(OCP)(dioxane)_n ]. While photolysis of 3 results in decarbonylation, yielding bis(cyclopropenyl)diphosphene 4 and after rearrangement diphosphahousene 5, thermolysis of 3 leads to phosphatricyclo[2.1.0.0]pentanone 7. Metal-mediated valence isomerization of 7 and subsequent demetalation provides access to phosphacyclopentadienone 12.

Unexpected Photodegradation of a Phosphaketenyl-Substituted Germyliumylidene Borate Complex

The first zwitterionic borata-bis(NHC)-stabilized phosphaketenyl germyliumylidene [(L₂ (O=C=P)Ge:] 2 (L₂ =(p-tolyl)₂ B[1-(1-adamantyl)-3-yl-2-ylidene]₂ ) has been synthesized by salt-metathesis reaction of [L₂ (Cl)Ge:] 1 with sodium phosphaethynolate [(dioxane)_n NaOCP]. Unexpectedly, its exposure to UV light affords, after reductive elimination of the entire PCO group, the unprecedented [L₂ Ge-GeL₂ ] complex 3 in 54 % yields bearing the Ge₂²⁺ ion with Ge in the oxidation state +1. In addition, the 1,3-digermylium-2,4-diphosphacyclobutadiene [L₂ Ge(μ-P)₂ GeL₂ ] 4 and bis(germyliumylidenyl)-substituted diphosphene [(L₂ Ge-P=P-GeL₂ )] 5 could also be obtained in moderate yields. The formation of 3-5 and their electronic structures have been elucidated with DFT calculations.

A Monoanionic Arsenide Source: Decarbonylation of the 2-Arsaethynolate Anion upon Reaction with Bulky Stannylenes

We report fundamental studies on the reactivity of the 2-arsaethynolate anion (AsCO- ), a species that has only recently become synthetically accessible. The reaction of AsCO- with the bulky stannylene Ter2 Sn (Ter=2,6-bis[2,4,6-trimethylphenyl]phenyl) is described, which leads to the unexpected formation of a [Ter3 Sn2 As2 ]- cluster compound. On the reaction pathway to this cluster, several intermediates were identified and characterized. After the initial association of AsCO- to Ter2 Sn, decarbonylation occurs to give an anion featuring monocoordinate arsenic, [Ter2 SnAs]- . Both species are not stable under ambient conditions, and [Ter2 SnAs]- rearranges to form [TerSnAsTer]- , an unprecedented anionic mixed Group 14/15 alkene analogue.