Octacarbonyl Ion Complexes of Actinides [An(CO)8]+/− (An=Th,U) and the Role of f Orbitals in Metal–Ligand Bonding

The octacarbonyl cation and anion complexes of actinide metals [An(CO)₈]^+/− (An=Th, U) are prepared in the gas phase and are studied by mass-selected infrared photodissociation spectroscopy. Both the octacarbonyl cations and anions have been characterized to be saturated coordinated complexes. Quantum chemical calculations by using density functional theory show that the [Th(CO)₈]⁺ and [Th(CO)₈]⁻ complexes have a distorted octahedral (D_4h) equilibrium geometry and a doublet electronic ground state. Both the [U(CO)₈]⁺ cation and the [U(CO)₈]⁻ anion exhibit cubic structures (O_h) with a ⁶A_1g ground state for the cation and a ⁴A_1g ground state for the anion. The neutral species [Th(CO)₈] (O_h; ¹A_1g) and [U(CO)₈] (D_4h; ⁵B_1u) have also been calculated. Analysis of their electronic structures with the help on an energy decomposition method reveals that, along with the dominating 6d valence orbitals, there are significant 5f orbital participation in both the [An]←CO σ donation and [An]→CO π back donation interactions in the cations and anions, for which the electronic reference state of An has both occupied and vacant 5f AOs. The trend of the valence orbital contribution to the metal–CO bonds has the order of 6d≫5f>7s≈7p, with the 5f orbitals of uranium being more important than the 5f orbitals of thorium.     

The [B3(NN)3]+ and [B3(CO)3]+ Complexes Featuring the Smallest π‐Aromatic Species B3+

We report the spectroscopic identification of the [B₃(NN)₃]⁺ and [B₃(CO)₃]⁺ complexes, which feature the smallest π‐aromatic system B₃⁺. A quantum chemical bonding analysis shows that the adducts are mainly stabilized by L→[B₃L₂]⁺ σ‐donation.     

Boron as an Electron‐Pair Donor for B⋅⋅⋅Cl Halogen Bonds

MP2/aug′‐cc‐pVTZ calculations were performed to investigate boron as an electron‐pair donor in halogen‐bonded complexes (CO)₂(HB):ClX and (N₂)₂(HB):ClX, for X=F, Cl, OH, NC, CN, CCH, CH₃, and H. Equilibrium halogen‐bonded complexes with boron as the electron‐pair donor are found on all of the potential surfaces, except for (CO)₂(HB):ClCH₃ and (N₂)₂(HB):ClF. The majority of these complexes are stabilized by traditional halogen bonds, except for (CO)₂(HB):ClF, (CO)₂(HB):ClCl, (N₂)₂(HB):ClCl, and (N₂)₂(HB):ClOH, which are stabilized by chlorine‐shared halogen bonds. These complexes have increased binding energies and shorter B?Cl distances. Charge transfer stabilizes all complexes and occurs from the B lone pair to the σ* Cl?A orbital of ClX, in which A is the atom of X directly bonded to Cl. A second reduced charge‐transfer interaction occurs in (CO)₂(HB):ClX complexes from the Cl lone pair to the π* C≡O orbitals. Equation‐of‐motion coupled cluster singles and doubles (EOM‐CCSD) spin–spin coupling constants, ^1xJ(B‐Cl), across the halogen bonds are also indicative of the changing nature of this bond. ^1xJ(B‐Cl) values for both series of complexes are positive at long distances, increase as the distance decreases, and then decrease as the halogen bonds change from traditional to chlorine‐shared bonds, and begin to approach the values for the covalent bonds in the corresponding ions [(CO)₂(HB)?Cl]⁺ and [(N₂)₂(HB)?Cl]⁺. Changes in ¹¹B chemical shieldings upon complexation correlate with changes in the charges on B.     

Cover Feature: Rare Spin Avoided σ-σ Diradical Planar Tetracoordinate Boron Cluster: A Proto-Star for Planar Pentacoordination (ChemPhysChem 18/2023)

We report a global planar star-like cluster B₃Li₃ featuring three planar tetracoordinate boron centres with a rare spin avoided σ-σ diradical character. The cluster was found to be stable towards dissociation into different fragments. The spin density was found to be localized solely on the three boron atoms in the molecular plane. This spin avoided σ-σ diradical character leads to the extension of the coordination number to yield a neutral B₃Li₃H₃ and a cationic B₃Li₃H₃⁺ cluster with three planar pentacoordinate boron centres in their global minimum structures. The planar geometry of the aninonic B₃Li₃H₃⁻ cluster is slightly higher in energy. The planar global clusters were found to maintain planarity in their ligand protected benzene bound complexes, B₃Li₃(Bz)₃, B₃Li₃H₃(Bz)₃ and B₃Li₃H₃(Bz)₃⁺ with high ligand dissociation energies offering candidature for experimental detection.     

Ligand-Induced Tuning of the Electronic Structure of Rhombus Tetraboron Cluster

A neutral boron carbonyl complex B₄(CO)₃ is generated in the gas phase and is characterized by infrared plus vacuum ultraviolet (IR+VUV) two-color ionization spectroscopy and quantum chemical calculations. The complex is identified to have a planar C_2v structure with three CO ligands terminally coordinated to a rhombus B₄ core. It has a closed-shell singlet ground state that correlates to an excited state of B₄. Bonding analyses on B₄(CO)₃ as well as the previously reported B₄ and B₄(CO)₂ indicate that the electronic structure of rhombus tetraboron cluster changes from a close-shell singlet to an open-shell singlet in B₄(CO)₂ and to a close-shell singlet in B₄(CO)₃, demonstrating that the electronic structures of boron clusters can be effectively tuned via sequential CO ligand coordination.     

A density functional theory study of the Cu+·(CO)n (n = 1–3) complexes

Density functional theory calculations, with an effective core potential for the copper ion, and large polarized basis set functions have been used to construct the potential energy surface of the Cu⁺·(CO)_n (n = 1–3) complexes. A linear configuration is obtained for the global minimum of the Cu⁺·CO and Cu⁺·(CO)₂ complexes with a bond dissociation energy (BDE) of 35.9 and 40.0 kcal mol^-1, respectively. For the Cu⁺·(CO)₃ complex, a trigonal planar geometry is obtained for the global minimum with a BDE of 16.5 kcal mol^?1. C-coordinated copper ion complexes exhibit stronger binding energy than O-coordinated complexes as a result of C_lp → 4s σ-donation. The computed sequential BDEs of Cu⁺·(CO)_n (n = 1–4) complexes agree well with experimental findings, in which the electrostatic energy and σ-donation play an important role in the observed trend.     

Enantioselective Synthesis of Planar Chiral [Cr(η6-Arene)(CO)3] complexes via nucleophilic addition/hydride abstraction. Preliminary communication

Non-racemic, planar chiral 1, 2-disubstituted [Cr(η⁶-arene)(CO)₃] complexes were obtained via external chiral ligand-controlled nucleophilic addition of alkyl-, vinyl-, and aryllithium reagents to monosubstituted complexes followed by an endo-hydride abstraction with trityl cation. The reactions with [Cr(CO)₃(η⁶-phenyloxazoline)], [Cr(CO)₃(η⁶-phenylmethaneimine)], and [Cr(CO)₃ (η⁶-phenylmethanenydrazone)] took place with complete ortho-selectivity and a high degree of enantioselectivity (up to 98% ee).     

Optimized structures of Cr2(CO)6+ with three different symmetries by density functional calculation

Density functional calculations have been made on a binuclear metal carbonyl ion Cr₂(CO)₆⁺ found in our laser ablation–molecular beam (LAMB) experiment. Optimized structures are calculated for three different conformations: T33 of D_3d symmetry with three terminal carbonyl groups on each chromium atom, B2T22 of D_2h symmetry with two bridging carbonyl groups and two terminal carbonyl groups on each chromium atom, and B4T11 of D_4h symmetry with four bridging carbonyl groups and one terminal carbonyl group on each chromium atom. The most stable conformation is T33 which is 36.76 and 286.44 kJ mol⁻¹ lower in energy than B2T22 and B4T11, respectively. The difference of conformation exerts a significant influence on the internuclear distance between chromium and the carbon of terminal CO, but hardly on the Cr–Cr bond length. For B2T22 and B4T11, longer C–O distances for bridging carbonyls compared with those for terminal ones indicate effective π*-back donation from the chromium atom to the bridging carbonyl groups. Furthermore, the relative abundance of Cr₂(CO)_n⁺ (n = 0–6) observed in our previous experimental study can be explained qualitatively by comparison of the excess energy produced in the formation of a Cr⁺–Cr bond with the CO dissociation energy of Cr₂(CO)₆⁺. © 1998 John Wiley & Sons, Ltd.     

Perfect Core-Shell Octahedral B@B38+, Be@B38, and Zn@B38 with an Octa-Coordinate Center as Superatoms Following the Octet Rule

Planar, tubular, cage-like, and bilayer boron clusters B_n^+/0/− (n=3∼48) have been observed in joint experimental and theoretical investigations in the past two decades. Based on extensive global searches augmented with first-principles theory calculations, we predict herein the smallest perfect core-shell octahedral borospherene O_h B@B₃₈⁺ ( 1 ) and its endohedral metallo-borospherene analogs O_h Be@B₃₈ ( 2 ), and O_h Zn@B₃₈ ( 3 ) which, with an octa-coordinate B, Be or Zn atom located exactly at the center, turn out to be the well-defined global minima of the systems highly stable both thermodynamically and dynamically. B@B₃₈⁺ ( 1 ) represents the first boron-containing molecule reported to date which contains an octa-coordinate B center covalently coordinated by eight face-capping boron atoms at the corners of a perfect cube in the first coordination sphere. Detailed natural bonding orbital (NBO) and adaptive natural density partitioning (AdNDP) bonding analyses indicate that these high-symmetry core-shell complexes X@B₃₈^+/0/− (X=B, Be, Zn) as super-noble gas atoms follow the octet rule in coordination bonding patterns (1S²1P⁶), with one delocalized 9c-2e S-type coordination bond and three delocalized 39c-2e P-type coordination bonds formed between the octa-coordinate X center and its octahedral O_h B₃₈ ligand to effectively stabilize the systems. Their IR, Raman, and UV-Vis spectra are computationally simulated to facilitate their spectroscopic characterizations.     

Stibinidene and Bismuthinidene as Two‐Electron Donors for Transition Metals (Co and Mn)

The reaction of stibinidene and bismuthinidene ArM [where Ar=C₆H₃‐2,6‐(CH=NtBu)₂; M=Sb ( 1 ), Bi ( 2 )] with transition metal (TM) carbonyls Co₂(CO)₈ and Mn₂(CO)₁₀ produced unprecedented ionic complexes [(ArM)₂Co(CO)₃]⁺[Co(CO)₄]^? and [(ArM)₂Mn(CO)₄]⁺[Mn(CO)₅]^? [where M=Sb ( 3 , 5 ), Bi ( 4 , 6 )]. The pnictinidenes 1 and 2 behaved as two‐electron donors in this set of compounds. Besides the M→TM bonds, the topological analysis also revealed a number of secondary interactions contributing to the stabilization of cationic parts of titled complexes.     

Observation of Main‐Group Tricarbonyls [B(CO)3] and [C(CO)3]+ Featuring a Tilted One‐Electron Donor Carbonyl Ligand

A combined experimental and theoretical study on the main‐group tricarbonyls [B(CO)₃] in solid noble‐gas matrices and [C(CO)₃]⁺ in the gas phase is presented. The molecules are identified by comparing the experimental and theoretical IR spectra and the vibrational shifts of nuclear isotopes. Quantum chemical ab initio studies suggest that the two isoelectronic species possess a tilted η¹(μ₁‐CO)‐bonded carbonyl ligand, which serves as an unprecedented one‐electron donor ligand. Thus, the central atoms in both complexes still retain an 8‐electron configuration. A thorough analysis of the bonding situation gives quantitative information about the donor and acceptor properties of the different carbonyl ligands. The linearly bonded CO ligands are classical two‐electron donors that display classical σ‐donation and π‐back‐donation following the Dewar–Chatt–Duncanson model. The tilted CO ligand is a formal one‐electron donor that is bonded by σ‐donation and π‐back‐donation that involves the singly occupied orbital of the radical fragments [B(CO)₂] and [C(CO)₂]⁺.     

Benzocyclobutenylidene-h5-cyclopentadienyldicarbonyl-iron(II). A hydride abstractor more specific than the triphenylcarbenium ion

Benzocyclobutenylidene-h⁵-cyclopentadienyldicarbonyliron(II) hexafluorophosphate converts h⁵-CpFe(CO)₂R (R = cyclo-C₃H₅, CH₂-cyclo-C₃H₅) to the respective allene and butadiene complexes whereas Ph₃C⁺ primarily yields addition products; both carbenium ions add to h¹- allyl- and substituted h¹ -allyl-iron complexes with the exception of the 3,3-dimethylpropenyl complex which is converted in both cases to h⁵-CpFe(CO)₂(CH₂CHCMeCH₂)⁺.     

The Triboracyclopropenyl Dianion: The Lightest Possible Main‐Group‐Element Hückel π Aromatic

Hückel π aromaticity is typically a domain of carbon‐rich compounds. Only very few analogues with non‐carbon frameworks are currently known, all involving the heavier elements. The isolation of the triboracyclopropenyl dianion is presented, a boron‐based analogue of the cyclopropenyl cation, which belongs to the prototypical class of Hückel π aromatics. Reduction of Cl₂BNCy₂ by sodium metal produced [B₃(NCy₂)₃]^2?, which was isolated as its dimeric Na⁺ salt (Na₄[B₃(NCy₂)₃]₂?2 DME; 1 ) in 45 % yield and characterized by single‐crystal X‐ray diffraction. Cyclic voltammetry measurements established an extremely high oxidation potential for 1 (E_pc=?2.42 V), which was further confirmed by reactivity studies. The Hückel‐type π aromatic character of the [B₃(NCy₂)₃]^2? dianion was verified by various theoretical methods, which clearly indicated π aromaticity for the B₃ core of a similar magnitude to that in [C₃H₃]⁺ and benzene.     

Using Ylide Functionalization to Stabilize Boron Cations

The metalated ylide YNa [Y=(Ph₃PCSO₂Tol)⁻] was employed as X,L‐donor ligand for the preparation of a series of boron cations. Treatment of the bis‐ylide functionalized borane Y₂BH with different trityl salts or B(C₆F₅)₃ for hydride abstraction readily results in the formation of the bis‐ylide functionalized boron cation [Y−B−Y]⁺ ( 2 ). The high donor capacity of the ylide ligands allowed the isolation of the cationic species and its characterization in solution as well as in solid state. DFT calculations demonstrate that the cation is efficiently stabilized through electrostatic effects as well as π‐donation from the ylide ligands, which results in its high stability. Despite the high stability of 2 [Y−B−Y]⁺ serves as viable source for the preparation of further borenium cations of type Y₂B⁺←LB by addition of Lewis bases such as amines and amides. Primary and secondary amines react to tris(amino)boranes via N−H activation across the B−C bond.     

A Zwitterionic Phosphonio‐1, 2, 4‐Diazaphospholide and Neutral 1, 2, 4‐Diazaphosphole — A Comparative Study of Molecular Structures and Co‐ordination Properties

The bis‐phosphonio‐1, 2, 4‐diazaphospholide salt ( 1 [Cl]) reacts with complex boron hydrides under selective extrusion of one PPh₃ moiety to give borane adducts of a novel zwitterionic phosphonio‐1, 2, 4‐diazaphospholide. Both the Et₃B adduct 2b and the free zwitterionic heterocycle 3 , which was liberated by further reaction of 2b with NEt₃, were characterized by spectroscopic data and 2b , as well, by a single crystal X‐ray diffraction study. The comparison of the structural data with those of a neutral 1, 2, 4‐diazaphosphole and a lithium‐1, 2, 4‐diazaphospholide which was formed by deprotonation of the parent 1, 2, 4‐diazaphosphole 4a discloses trends in endocyclic bonding distances which can be rationalized in terms of a charge dependent shift in the π‐electron distribution. First studies of the co‐ordination properties reveal for both 2b and 4a a marked preference to bind two M(CO)₅‐fragments (M = Cr, W) via the lone‐pairs of the phosphorus and one nitrogen atom; mononuclear complexes with P‐co‐ordinated heterocycles are formed as intermediates. A single crystal X‐ray diffraction study of the dinuclear complex [Cr₂(CO)₁₀(μ₂‐C₂H₃N₂P‐κP, κN)] ( 10a ) together with spectroscopic studies (including ¹⁸³W NMR studies of tungsten complexes) suggests that M→L back donation is more efficient for P‐ than for N‐bound metal fragments. No evidence for π‐co‐ordination of the 1, 2, 4‐diazaphosphole ring to a Cr(CO)₃ fragment was obtained.     

POSSIBLE HYDRIDE AND METHIDE TRANSFER REACTIONS: REACTIONS OF Fe(CO)4R−(R = H,CH3) AND W(CO)5R− (R = H,CH3, Cl,Br, I) WITH METAL CARBONYL CATIONS

Abstract

Reactions of metal carbonyl cations (M(CO)₆ ⁺, M = Mn, Re) with hydride-, methide- or halide-containing metal carbonyl anions (Fe(CO)₄R^?, R = H, Me; W(CO)₅R^?, R = H, Me, Cl, Br, I) produce products that indicate several mechanisms are operative. Reactions of the halo-tungsten complexes produce neutral, solvated tungsten complexes, W(CO)₅(CH₃CN) and W(CO)₄(CH₃CN)₂ and M(CO)₅X in a reaction that appears to be initiated by decomposition of W(CO)₅X^?. In contrast, the tungsten hydride and methide complexes react, predominantly, by transfer of the hydride or methide to a carbonyl of the cation at a much faster rate. The iron hydride and methide complexes react by iron-based nucleophilicity involving a two-electron process.     

Zur kenntnis der chemie der metallcarbonyle und der cyanokomplexe in flüssigem ammoniak : XXXIII. Über die darstellung neuer carbamoylcarbonyl-komplexe aus bekannten und neuen kationischen carbonylverbindungen des mangans und rheniums

The covalent carbamoyl carbonyl compounds Re(CO)₅COHN₂, cis-M(CO)₄(L)CONH₂, M(CO)₃(L)₂CONH₂ and M(CO)₃(D)CONH₂ (M = Mn, Re; L = PPh₃, PEt₃; D = bipy, phen) are formed by reactions of the cationic complexes [Re(CO)₆]⁺, [M(CO)₅L]⁺, [M(CO)₄L₂]⁺ and [M(CO)₄D]⁺ (M = Mn, Re; L = PPh₃, PEt₃; D = bipy, phen) with liquid NH₃ with concomitant deprotonation: [M(CO)_6?nL_n]⁺ + 2 NH₃ → M(CO)_5?nL_nCONH₂ + NH₄⁺ (n = 0, 1, 2) and [M(CO)₄D]⁺ + 2 NH₃ → M(CO)₃(D)CONH₂ + NH₄⁺ The stability of the above-mentioned carbamoyl carbonyl complexes increases from the penta- to the tetra- to the tri-carbonyl derivatives. In all cases the rhenium compounds are much more stable than the corresponding manganese complexes. Whereas the carbamoyl compound Re(CO)₄(PEt₃)CONH₂ can be isolated by reaction of [Re(CO)₅PEt₃]⁺ with NH₃, the corresponding manganese complex undergoes Hofmann degradation of amides even at ?70°C to form HMn(CO)₄PEt₃ and NH₄NCO. The IR and some mass and ¹H NMR spectra of the new hexacoordinated carbamoyl carbonyl complexes are discussed and the reactions of these compounds with liquid NH₃, HCl and CH₃OH are described.     

Reaction Behavior of Decacarbonyldimetalates(2‐) (M = Cr and Mo) towards the Nitrosyl Carbonyls of Iron and Cobalt

The reaction of the nitrosyl carbonyl complexes [Fe(NO)₂(CO)₂] and [Co(NO)(CO)₃] with the decacarbonyldimetalates [M₂(CO)₁₀]^2– (M = Cr and Mo) in THF as the solvent at room temperature was investigated. Thereby a substitution of one nitrosyl ligand towards carbon monoxide was observed in each case. Both reactions afforded the known metalate complexes [Fe(NO)(CO)₃]^– and [Co(CO)₄]^–, respectively. These species were isolated as their corresponding PPN salts [PPN⁺ = bis(triphenylphosphane)iminium cation] in nearly quantitative yields. The products were unambiguously identified by their IR spectroscopic and elemental analytic data as well as by their characteristic colors and melting points.     

Structure and stability of B+13 clusters

The structures and energies of B⁺₁₃, observed experimentally to be an unusually abundant species among cationic boron clusters, have been studied systematically with B3LYP/6–31G* density functional theory. The most thermodynamically stable B⁺₁₂ and B⁺₁₃ clusters are confirmed to have planar or quasiplanar rather than globular structures. However, the computed dissociation energies of the 3-dimensional B⁺₁₃ clusters are much closer to the experimental values than those of the planar or quasiplanar structures. Hence, planar and 3-dimensional B⁺₁₃ may both exist. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 203–214, 1998     

First‐Row Transition‐Metal–Diborane and –Borylene Complexes

A combined experimental and quantum chemical study of Group 7 borane, trimetallic triply bridged borylene and boride complexes has been undertaken. Treatment of [{Cp*CoCl}₂] (Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl) with LiBH₄ ? thf at ?78 °C, followed by room‐temperature reaction with three equivalents of [Mn₂(CO)₁₀] yielded a manganese hexahydridodiborate compound [{(OC)₄Mn}(η⁶‐B₂H₆){Mn(CO)₃}₂(μ‐H)] ( 1 ) and a triply bridged borylene complex [(μ₃‐BH)(Cp*Co)₂(μ‐CO)(μ‐H)₂MnH(CO)₃] ( 2 ). In a similar fashion, [Re₂(CO)₁₀] generated [(μ₃‐BH)(Cp*Co)₂(μ‐CO)(μ‐H)₂ReH(CO)₃] ( 3 ) and [(μ₃‐BH)(Cp*Co)₂(μ‐CO)₂(μ‐H)Co(CO)₃] ( 4 ) in modest yields. In contrast, [Ru₃(CO)₁₂] under similar reaction conditions yielded a heterometallic semi‐interstitial boride cluster [(Cp*Co)(μ‐H)₃Ru₃(CO)₉B] ( 5 ). The solid‐state X‐ray structure of compound 1 shows a significantly shorter boron–boron bond length. The detailed spectroscopic data of 1 and the unusual structural and bonding features have been described. All the complexes have been characterized by using ¹H, ¹¹B, ¹³C NMR spectroscopy, mass spectrometry, and X‐ray diffraction analysis. The DFT computations were used to shed light on the bonding and electronic structures of these new compounds. The study reveals a dominant B?H?Mn, a weak B?B?Mn interaction, and an enhanced B?B bonding in 1 .