A Monometallic Bis(cyaphido) Complex

The first example of a bis(cyaphido) complex, trans-[Ru(dppe)2(C≡P)2], is described, unequivocally demonstrating the synthetic accessibility and stability of complexes that feature more than one cyaphido ligand. Synthesis is achieved from the precedent cation [Ru(dppe)2(C≡P)]+ via sequential coordination and desilylation of the phosphaalkyne Me3SiC≡P. The heteroleptic analogue trans-[Ru(dppe)2(C≡N)(C≡P)] is also prepared from the same cation and NaCN; both cyaphido complexes are structurally characterized, enabling the first direct comparison of cyaphide with cyanide, its isoelectronic and isolobal counterpart. This demonstrates an enhanced π-acidity for -C≡P over -C≡N, while computational studies reveal also a higher π-donor character for the cyaphido ligand.

Recent advances in the chemistry of the phosphaethynolate and arsaethynolate anions

Over the past decade, the reactivity of 2-phosphaethynolate (OCP^-), a heavier analogue of the cyanate anion, has been the subject of momentous interest in the field of modern organometallic chemistry. It is used as a precursor to novel phosphorus-containing heterocycles and as a ligand in decarbonylative processes, serving as a synthetic equivalent of a phosphinidene derivative. This perspective aims to describe advances in the reactivities of phosphaethynolate and arsaethynolate anions (OCE^-; E = P, As) with main-group element, transition metal, and f-block metal scaffolds. Further, the unique structures and bonding properties are discussed based on spectroscopic and theoretical studies.

Photochemical C(sp)-C(sp2) Bond Activation in Phosphaalkynes: A New Route to Reactive Terminal Cyaphido Complexes LnM-C≡P

The photochemical activation of the C(sp)-C(sp²) bond in Pt(0)-η²-aryl-phosphaalkyne complexes leads selectively to coordination compounds of the type L_nPt(aryl)(C≡P). The oxidative addition reaction is a novel, clean, and atom-economic route for the synthesis of reactive terminal Pt(II)-cyaphido complexes, which can undergo [3 + 2] cycloaddition reactions with organic azides, yielding the corresponding Pt(II)-triazaphospholato complexes. The C-C bond cleavage reaction is thermodynamically uphill. Upon heating, the reverse and quantitative reductive elimination toward the Pt(0)-phosphaalkyne-π-complex is observed.

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.

Controlled Reactivity of Terminal Cyaphide Complexes: Isolation of the 5-Coordinate [Ru(dppe)2(C≡P)]. Inorg Chem 2019;58:14800-14807. [PMID: 31633922 DOI: 10.1021/acs.inorgchem.9b02471]

The novel cyaphide complex trans-[Ru(dppe)₂Me(C≡P)] is obtained in excellent yields and exhibits the first instance of controlled reactivity of any terminal cyaphide complex. Its treatment with ZnX₂/PPh₃ effects selective metathesis of the methyl moiety to afford the unprecedented halocyaphide complexes trans-[Ru(dppe)₂(X)(C≡P)] (X = Cl, Br, I), which are structurally characterized (X = Cl, Br). Exemplified with the trans-bromide, these compounds are susceptible to substitution of the halides by nucleophilic reagents-illustrated with Me₂Mg-and also readily undergo halide abstraction by TlOTf to afford the first hypocoordinate cyaphide complex, viz., [Ru(dppe)₂(C≡P)]·OTf, which is isolable in bulk and exhibits good stability. NMR spectroscopic and crystallographic data reveal the latter to adopt a square-pyramidal geometry with an accessible coordinate vacancy, which is susceptible to the addition of nucleophiles. This is illustrated analytically by reactions with Me₂Mg and LiC≡CPh and with its facile bulk carbonylation to afford trans-[Ru(dppe)₂(CO)(C≡P)]⁺.

Cyaphide–alkynyl complexes: metal–ligand conjugation and the influence of remote substituents

A series of cyaphide–alkynyl complexes exhibits significant cooperativity between the electron accepting “–CP” ligand and remote alkynyl substituents, indicative of long-range communication.

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.

Ligand- and Metal-Based Reactivity of a Neutral Ruthenium Diolefin Diazadiene Complex: The Innocent, the Guilty and the Suspicious

Coordination of the diazadiene diolefin ligand (trop2 dad) to ruthenium leads to various complexes of composition [Ru(trop2 dad)(L)]. DFT studies indicate that the closed-shell singlet (CSS), open-shell singlet (OSS), and triplet electronic structures of this species are close in energy, with the OSS spin configuration being the lowest in energy for all tested functionals. Singlet-state CASSCF calculations revealed a significant multireference character for these complexes. The closed-shell singlet wavefunction dominates, but these complexes have a significant (≈8-16 %) open-shell singlet [d7 -RuI (L)(trop2 dad.- )] contribution mixed into the ground state. In agreement with their ambivalent electronic structure, these complexes reveal both metal- and ligand-centered reactivity. Most notable are the reactions with AdN3 , diazomethane, and a phosphaalkyne leading to scission of the C-C bond of the diazadiene (dad) moiety of the trop2 dad ligand, resulting in net (formal) nitrene, carbene, or P≡C insertion in the dad C-C bond, respectively. Supporting DFT studies revealed that several of the ligand-based reactions proceed via low-barrier radical-type pathways, involving the dad.- ligand radical character of the OSS or triplet species.

Through-conjugation of two phosphaalkyne (‘CP’) moieties mediated by a bimetallic scaffold

The bis-cyaphide complex [{Ru(dppe)₂}₂{μ-(CC)₂C₆H₄-p}(CP)₂] is the first molecule to incorporate two phosphaalkyne ‘CP’ moieties within a through-conjugated scaffold, and demonstrates interesting redox behaviour.

Uranium and thorium complexes of the phosphaethynolate ion

New tris-amidinate actinide (Th, U) complexes containing a rare O-bound terminal phosphaethynolate (OCP ^- ) ligand were synthesized and fully characterized. The cyanate (OCN ^- ) and thiocyanate (SCN ^- ) analogs were prepared for comparison and feature a preferential N-coordination to the actinide metals. The Th(amid)₃(OCP) complex reacts with Ni(COD)₂ to yield the heterobimetallic adduct (amid) ₃ Th(μ-η ¹ (O):η ² (C,P)-OCP)Ni(COD) featuring an unprecedented reduced (OCP ^- ) bent fragment bridging the two metals.

Synthesis and electronic structure of the first cyaphide-alkynyl complexes

The novel complexes trans-[Ru(dppe)2(C≡CR)(C≡P)] (R = CO2Me, C6H4OMe), the first to incorporate cyaphide as part of a conjugated system, are obtained in facile manner. The electronic structure of these compounds is probed by X-ray, DFT and UV/Vis studies.