Two-electron Ligands Research Articles

Inside Cover: Reactivities of Interstitial Hydrides in a Cu11 Template: En Route to Bimetallic Clusters (Angew. Chem. Int. Ed. 2/2022)

Depending on the nature of M+ , the hydrides of the H2Cu11 reactant behave differently. In the case of M=Cu or Ag, they act as regular two-electron ligands yielding [CuH2Cu11{S2P(OiPr)2}6(C≡CPh)3]+ (Cu12H2) or [AgH2Cu14{S2P(OiPr)2}6(C≡CPh)6]+ (AgH2Cu14); in the case of M=Au, they behave as electron donors to form [AuCu11{S2P(OiPr)2}6(C≡CPh)3Cl] (AuCu11). Details of the study are presented by Jean-Yves Saillard, Chen-Wei Liu, and co-workers in their Research Article (e202113266).

Synthesis, crystal structure and catalytic activity in reductive amination of di-chlorido-(η6-p-cymene)(2'-di-cyclo-hexyl-phosphanyl-2,6-di-meth-oxy-biphen-yl-κP)ruthenium(II).

The title compound, [RuCl2(C10H14)(C26H35O2P)] (I), crystallizes in the monoclinic space group P21/c with two crystallographically independent mol-ecules (A and B) in the asymmetric unit. The geometries of both mol-ecules are very similar and distinguished only by the twist angles of the two benzene rings in the phosphine substituents [89.54 (14) and 78.36 (14)° for mol-ecules A and B, respectively]. The Ru atoms have classical pseudo-tetra-hedral piano-stool coordination environments. The conformation of each mol-ecule is stabilized by intra-molecular C-H⋯O and C-H⋯Cl hydrogen bonds and C-H⋯π inter-actions. The two mol-ecules are linked by a C-H⋯Cl hydrogen bond. In the crystal, the mol-ecules are further linked by C-H⋯ π inter-actions, forming -A-B-A-B- chains propagating along the a-axis direction. Complex I is an active catalyst for reductive amination reaction. The catalytic activity of this complex can be explained by the lability of the p-cymene ligand, which can be replaced by two-electron ligands such as CO or amine.

Activation of small molecules by a rhodium bis(phosphinite) pincer complex

Rhodium hydrido chloride pincer complex RhH(Cl)[2,6-(Buptb2PO)b2Cb6Hb3] was synthesized and used for the preparation of new complexes with labile two-electron ligands Rh(L)[2,6-(Buptb2PO)b2Cb6Hb3] (L = MeCN or S(CHb2)b4) and complexes with small molecules, such as CO, Ob2, Hb2, and Nb2.

Donor Properties of a Series of Two-Electron Ligands

A large group of two-electron donor ligands were compared and ranked with the help of DFT calculations. The following characteristics were considered: (a) C≡O stretching frequencies and distances of Ni(CO)3L, IrCl(CO)2L, and IrCp(CO)L, (b) Ir−(η2-C2H4) bond enthalpies, stretching frequencies, and distances of IrCp(η2-H2C═CH2)L, (c) enthalpies of the ligand exchange reactions IrCp(CO)L + IrCpXe(PF3) → IrCp(CO)(PF3) + IrCpXeL and Ir(III)H2CpL + Ir(I)CpXe(PF3) → Ir(III)H2Cp(PF3) + Ir(I)CpXeL, (d) Ir−(η2-H2) bond enthalpies and H−H distances of Os(η2-H2)Cl2(CO)L2. Useful trends and correlations have been established for several common ligand types.

F‐Block N‐Heterocyclic Carbene Complexes

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Macropolyhedral boron-containing cluster chemistry: The reaction of syn-B18H22 with SMe2 and I2 in monoglyme: Structure of [7-(SMe2)-syn-B18H20

The reaction of B10H14 with two-electron ligands L to give L2B10H12 is not mimicked by B18H22. Instead, an oxidizing agent is required to introduce a ligand onto the {B18} skeleton: thus deprotonation of syn-B18H22 in monoglyme followed by treatment with I2 and SMe2 gives [7-(SMe2)-syn-B18H20] (41%).☆

Synthesis of tricarbonyliron cyclohexa-2,4-dienone complexes from tosylhydrazones of acyclic dienone complexes. A novel ansa dicarbonyliron complex by intramolecular trapping of reaction intermediates of the cyclocarbonylation reaction

Cyclohexa-2,4-dienones stabilized by coordination to tricarbonyliron are obtained when tosylhydrazones of tricarbonyliron complexed dienones are submitted to the conditions of the Bamford-Stevens reaction (thermolysis in the presence of strong bases). This cyclocarbonylation reaction proceeds most likely via α-diazodiene complexes, and from there via carbenes, which react intramolecularly with a CO ligand, the coordinatively unsaturated iron species so formed being finally stabilized by an external two-electron ligand. The existence of two such hypothetical intermediates could be proven by intramolecular trapping experiments (1,3-dipolar cycloadducts 3, ansa Fe(CO) 2 complex 6, structures confirmed by X-ray diffraction).

New Ruthenium(II) Complexes Bearing N-Heterocyclic Carbenes

N-heterocyclic carbene complexes of ruthenium(II), [CpRu(L*)2Cl] (2) and [CpRu(CO)(L*)Cl] (3) (Cp = η5-C5H5; L* = 1,3-dicyclohexyl-imidazolin-2-ylidene), have been obtained in high yields by reaction of [CpRu(PR2R‘)2Cl] (R = R‘ = Ph, 1a; R = Ph, R‘ = 2-MeC6H4, 1b) and [CpRu(CO){PPh2(2-MeC6H4)}Cl] (1c), respectively, with the free carbene L*. The mixed dicarbene complex [CpRu(CPh2)(L*)Cl] (4) is prepared from [CpRu(CPh2){PPh2(2-MeC6H4)}Cl] (1d) and an equimolar amount of L*, whereas subsequent reaction of 1d with L* leads to formation of 2, along with tetraphenylethene. The reaction of [Cp*Ru(PPh3)2Cl] (1e) with L* gives the pentamethylcyclopentadienyl derivative [Cp*Ru(PPh3)(L*)Cl] (5) (Cp* = η5-C5Me5) by displacement of 1 equiv of PPh3. Complex 5 reacts in toluene with CO, pyridine (Py), and N2CHCO2Et, affording [Cp*Ru(CO)(L*)Cl] (6), [Cp*Ru(Py)(L*)Cl] (7), and the mixed dicarbene [Cp*Ru(CHCO2Et)(L*)Cl] (8), which were isolated in high yields. The molecular structure of complex 6 has been determined by an X-ray investigation, and the carbene−ruthenium distance clearly indicates a single bond (2.0951(18) Å). The N-heterocyclic carbene does not undergo substitution by other two-electron ligands.

Monosubstituierte Derivate des Halbsandwich-Komplexes Cp*Ta(CO)4 - Vergleich mit den analogen Vanadiumverbindungen Cp*V(CO)3L und Röntgenstrukturanalyse des γ-Picolin-Komplexes Cp*V(CO)3(NC5H4-Me(4)) / Monosubstituted Derivatives of the Halfsandwich Complex Cp*Ta(CO)4 - Comparison with the Analogous Vanadium Compounds Cp*V(CO)3L and X-Ray Structural Analysis of the γ-Picoline Complex Cp*V(CO)3(NC5H4-Me(4))

The photo-induced substitution of a CO ligand in Cp*Ta(CO)4 (1) has been used to prepare a series of Cp*Ta(CO)3L (2) complexes, in which the two-electron ligand L includes, e.g., isonitriles, sulfanes, cyclic ethers, phosphanes and pyridines. The complexes (2a-y) were characterized by their v(CO) frequencies and their 1H and 13C NMR spectra, and were compared - if possible - with the corresponding vanadium complex, Cp*V(CO)4 (3) and its derivatives, Cp*V(CO)3L (4). The molecular structure of the 4-picoline complex Cp*V(CO)3(NC5H4-Me(4)) (4r) has been determined by X-ray crystal structure analysis.

A Fluxional α-Carbonyl Diazoalkane Complex of Copper Relevant to Catalytic Cyclopropanation

The neutral copper(I) ethylene complex [tBu2P(NSiMe3)2-κ2N]Cu(η2-C2H4) (1) reacts with diazophenanthrone (2), yielding an equilibrium mixture of 1 and 2 with free ethylene and the novel diazoalkane copper(III) complex 3, which represents a stabilized analogue of early intermediates in the mechanism of copper-catalyzed cyclopropanation reactions of electron-rich olefins with α-carbonyl diazoalkanes. Its X-ray structure determination displays square-planar coordination of the formally d8 copper(III) center with a κO:κN-bound diazophenanthrone. The geometry of the coordinated diazoalkane ligand can be directly compared to that of uncomplexed, cocrystallized diazophenanthrone, indicating a formal two-electron ligand reduction upon coordination. LT NMR spectroscopy reveals facile rotation of the diazoalkane ligand in solution even at temperatures below −110 °C. DFT calculations (B3LYP) on the model [H2P(NH)2-κ2N]Cu(N2CHCHO-κN:κO) (4) help to understand the bonding and fluxionality in 3 and predict a small liga...

The NMR-Spectroscopic and X-ray Crystal-Structural Characterization of Two Cp*Ir Halfsandwich Complexes Containing the 1,2-Dicarba-closo-dodecaborane-1,2-diselenolato Ligand

The reaction of [Cp*IrCl2]2 with dilithium 1,2-ortho-carborane-1,2-diselenolate 3 leads to the green 16-electron diselenolene complex [Cp*Ir{Se2C2(B10H10)}] (4) which takes up two-electron ligands such as trimethylphosphane to give the 18-electron diselenolate derivative [Cp*Ir(PMe3){Se2C2(B10H10)}] (5). The molecular structures of 4 and 5 were determined by X-ray crystal structure analysis. The 77Se-nuclear shielding in 4 is lower by almost 500 ppm relative to that in 5.

The NMR-Spectroscopic and X-ray Crystal-Structural Characterization of Two Cp*Ir Halfsandwich Complexes Containing the 1,2-Dicarba-closo-dodecaborane-1,2-diselenolato Ligand

The reaction of [Cp*IrCl2]2 with dilithium 1,2-ortho-carborane-1,2-diselenolate 3 leads to the green 16-electron diselenolene complex [Cp*Ir{Se2C2(B10H10)}] (4) which takes up two-electron ligands such as trimethylphosphane to give the 18-electron diselenolate derivative [Cp*Ir(PMe3){Se2C2(B10H10)}] (5). The molecular structures of 4 and 5 were determined by X-ray crystal structure analysis. The 77Se-nuclear shielding in 4 is lower by almost 500 ppm relative to that in 5.

Synthesis of Rhenium Complexes That Contain the [(C6F5NCH2CH2)3N]3- Ligand

The reaction between [Et4N]2[ReOCl5] and (C6F5NHCH2CH2)3N (H3[N3NF]) in CH3CN at room temperature in the presence of NEt3 yielded air stable, emerald green, diamagnetic [(C6F5NCH2CH2)2NCH2CH2NHC6F5]Re(O)Cl (1). The reaction between 1 and Ta(CH-t-Bu)(THF)2Br3 gave paramagnetic [N3NF]ReBr (2). An X-ray structure of a sample of 2 showed it to be analogous to that of [N3NF]MoCl. Reduction of 2 by methyllithium (or more conveniently by Mg) in the presence of a variety of two-electron ligands gave complexes of the type [N3NF]Re(L) (L = H2, ethylene, propylene, CO, N2, phosphines, pyridine, tetrahydrothiophene, acetonitrile, or silanes). An X-ray structure of [N3NF]Re(ethylene) showed η2-ethylene to be bound in the apical “pocket” with its C−C axis lying in one of the Nax−Re−Neq planes. Protonation of the PMe3 complex gave an authentic hydrido phosphine complex, {[N3NF]Re(H)(PMe3)}+, but protonation of other phosphine complexes gave species in which coupling between H and P is relatively large (∼60 Hz) and there...

On the Nature and Incidence of β-Agostic Interactions in Ethyl Derivatives of Early Transition Metals: Ethyltitanium Trichloride and Related Compounds

In light of the structures and spectroscopic properties of the ethyltitanium compounds EtTiCl 3 (1), and EtTiCl3(dmpe) (dmpe ) Me2PCH2CH2PMe2 )( 2), extensive DFT calculations have been carried out to explore the structures, energetics, potential energy surfaces, and spectroscopic properties not only of these but also of related ethyl derivatives of early transition metals, M. The analysis has sought to assess the true nature of so-called ‚-agostic interactions in these systems and how such interactions depend on the atomic number, coordination number, valence electron (VE) count, and net charge of M. The calculations reproduce well the experimentally determined properties of 1 and 2. Analysis of wave functions indicates that, where significant ‚-interactions occur, the M-CR bonding electrons are delocalized over the entire ethyl group, the marked reduction of the MCC valence angle allowing the metal atom to establish covalent bonding interactions with the ‚-C atom and, perhaps to a lesser extent, with its appended proximal H atom. A ‚-agostic alkyl group may be considered a two-electron ligand, and the main contribution to the stabilization arises from Ti‚‚‚C‚ bonding. Barriers to conformational change of the M-Et unit depend inter alia on the space available in the coordination sphere of the central M atom, with rearrangement of the ethyl group to accommodate significant ‚-interaction being opposed by interligand repulsion. Such interaction is found not in 1, but in its dmpe adduct 2 because the increase in coordination number is offset by elongation of the Ti-C and Ti-Cl bonds and by the extra pliability of the EtTiCl3 moiety resulting from complexation by the dmpe ligand.

Group 5 Metallocene Complexes as Models for Metal-Mediated Hydroboration: Synthesis of a Reactive Borane Adduct, endo-Cp*2Nb(H2BO2C6H4), via Hydroboration of Coordinated Olefins

The olefin complexes Cp*2M(CH2CH(R))(H) (R = H (1), CH3 (2); M = Nb (a), Ta (b)) react cleanly with catecholborane (HBCat) and HBO2C6H3-4-tBu (HBCat‘) to give Cp*2M(H2BCat) (M = Nb (5a), Ta (5b)) and Cp*2M(H2BCat‘) (M = Nb (6a), Ta (6b)) and the anti-Markovnikov hydroboration products CatBCH2CH2R and Cat‘BCH2CH2R. Compounds 2a and 2b react with DBCat‘ (DBO2C6H3-4-tBu) to afford the deuterated analogs Cp*2M(D2BCat‘) (M = Nb (6a), Ta (6b)) where the deuterium label is incorporated exclusively in the metal complex. The hydride resonances in 6a exhibit large perturbations in chemical shift when deuterium is incorporated. On the basis of this isotopic labeling experiment, a mechanism is proposed where HBCat reacts with the 16-electron alkyl intermediates, Cp*2MCH2CH2R (R = H (3), Me (4)), via σ-bond metathesis or oxidative-addition/reductive-elimination sequences, to generate the alkylboranes and an intermediate hydride, Cp*2MH, that is trapped by additional borane to give Cp*2M(H2BCat) (5a and 5b). The solid-state structures for Cp*2Nb(η2-H2BO2C6H3-3-tBu) (16) and Cp2*Nb(η2-BH4) (17) were determined by X-ray diffraction. The metal−boron distances in these two compounds are identical within experimental error. While related group 5 catecholateboryl compounds have pronounced boryl character, the structural parameters for the hydride and boryl ligands in 16 are consistent with formulation as either a borohydride complex or a borane adduct of “Cp*2NbH”. In contrast to other group 5 boryl complexes, 6a reacts readily with various two-electron ligands with elimination of HBCat‘. For example, H2 reacts reversibly to form Cp*2NbH3 and HBCat‘, while “BH3” and CO react irreversibly to yield Cp*Nb(BH4) and Cp*2Nb(H)(CO) with elimination of HBCat‘, respectively. Ethylene and propylene react at 40 °C to regenerate 1a and 2a, with elimination of HBCat‘. When excess olefin is present, the liberated borane is converted to CatBCH2CH2R. Solutions of 1a and 2a catalyze olefin hydroboration under mild conditions. Relationships between the reactivity of 1a and 2a and other early metal and lanthanide catalysts are discussed.

Coordinatively Unsaturated Cp*Ru Alkoxo Complexes. 16.1Addition Products Cp*Ru(acac)L and Solution Equilibria1

With [Cp*Ru(OMe)]2 (1) as starting material, a number of 2,4-pentanedionato complexes Cp*Ru(2,4-pentanedionate) were prepared. The solid-state structure of Cp*Ru(1-phenyl-2,4-pentanedionate) (3) was elucidated by X-ray crystallography, and the complex was found to be a dimer in the solid state, as previously established for Cp*Ru(2,4-pentanedionate) (2). The molecular weight of 3 in benzene indicates a dimer (3-3) in solution as well. Low-temperature 1H NMR spectroscopy reveals a process involving dissociation of the dimer into monomers associated with an inversion of the pentanedionate ligand at Ru. The activation energy (Ea = 43.5 ± 0.7 kJ/mol, toluene-d8) reflects the enthalpy of dissociation of the dimer. All dimers are easily cleaved with two-electron ligands L, resulting in the mononuclear complexes Cp*Ru(2,4-pentanedionate)L. Besides isolable complexes with L = phosphine, phosphite, and CO, labile adducts of the same composition with σ-S and N donor ligands (L = methyl p-tolyl sulfoxide, ethyl meth...

Titanium Complexes of Chelating Bis(phenolato) Ligands with Long Titanium−Sulfur Bonds. A Novel Type of Ancillary Ligand for Olefin Polymerization Catalysts

The sulfide-linked bis(phenol) tbmpH2 (tbmp = 2,2‘-thiobis(6-tert-butyl-4-methylphenolato)) gives a series of titanium complexes of the formula [Ti(tbmp)X2]2 or [Ti(tbmp)(L)X2] (L = two-electron ligand, X = one-electron ligand). The molecular structures of [Ti(tbmp)(OiPr)2]2 and of [Ti(tbmp){C6H4(CH2NMe2)-2}Cl] were determined by single-crystal X-ray structural analyses. An unusually long titanium−sulfur bond of ∼270 pm is observed in both complexes which contain a six-coordinate titanium center. Variable-temperature NMR spectroscopy shows a fluxional coordination of the chelating aryl group in [Ti(tbmp){C6H4(CH2NMe2)-2}Cl].

Reversible Formation of Raftlike Organoimidotetrarhodium Clusters by the Migration of RhL Fragments

The formation of three new metal-metal bonds results from the addition of CO to the tetranuclear complex 1. This process invovles the migration of the Rh center coordinatated to the arene ligand in 1 to the open edge of the Rh3 core to give the complex 2. The reaction is reversible, and thus the Rh center hops from one site to the other by addition or removal of a two-electron ligand  1,5-cyclooctadiene.

SYNTHESIS AND REACTIVITY OF NITRIDORUTHENIUM(VI) COMPLEXES OF WEAKLY COORDINATING LIGANDS

Abstract Neutral, trialkylruthenium complexes Ru(N)R3L (R = CH3, CH2SiMe3; L = pyridine, 2,6-lutidine, 4-picoline, PMe3, CNCMe3) were prepared by the reaction of [Ru(N)R4]− salts with HBF4 and the ligand, L. The molecular structure of Ru(N)(CH2SiMe33 (py) was determined by X-ray diffraction. Crystals of Ru(N)(CH2SiMe3)3(py) are monoclinic in space group. P21/n with a = 14.551(5) Å, b = 9.113(4) Å, c = 19.801(5) Å, α = γ = 90°, β = 109.27(2), Z = 4, R = 0.032 and R w = 0.039. The neutral dialkyl complex, Ru(N)R2Cl, is in equilibrium with the dimer and adds a variety of neutral, two-electron ligands. Cationic complexes [Ru(N)R2L2][BF]4] (R = CH3, CH2SiMe3;L = NCCH3, pyridine) were prepared by the reactions of Ru(N)R3L with HBF4 and additional ligand. The addition of concentrated HNO3(aq) to [Ru(NO)R4]− gave the nitrato complexes [Ru(N)R2(ONO2)2]−. The complexes [Ru(N)R2L2][BF4] react with water to form the μ-hydroxo dimers, {Ru(N)R2(μ-OH)}2. The molecular structure of {Ru(N)(CH)2SiMe3)2(μ-OH)} was determined by X-ray diffraction. Crystals of {Ru(N)(CH)]2SiMe3)2(μ-OH)} are monoclinic in space group P21/a with a = 11.510(8) Å, b = 20.440(8) Å, c = 12.858(4) Å, α = γ = 90°, β = 109.04, Z = 4, R = 0.027 and R w = 0.029. The acetonitrile complex, [Ru(N)(CH2SiMe3)2(NCMe)2][BF4], is a catalyst for the polymerization of ethylene.

Neue Untersuchungen zu zwei alten Sandwich-Verbindungen: Cyclopentadienyl-mangan-benzol und Cyclopentadienyl-mangan-biphenyl

The sandwich complexes CpMn(C 6H 6) ( 1) and CpMn(C 6H 6-Ph) ( 2) have been characterized by X-ray structure analyses. The description of 1 involved a model of disordered ring ligands; the distance between the ring centers (327 pm) has been found to be intermediate between the ring-ring distances of ferrocene (332 pm) and dibenzenechromium (323 pm). In 2 the manganese atom stands closer to the center of the six-membered (154.6 pm) than to that of the five-membered ring (174.8 pm); the planes of the two phenyl moieties of the biphenyl ligand are twisted by 24.4° in the crystal. Displacement of the benzene ring in 1 by the two-electron ligands L  CO, PMe 3 and P(OMe) 3 gives halfsandwich compounds CpMnL 3 ( 3a- c). The metallation of 1 by nbutyl-lithium in the presence of tetramethylethylenediamine (tmeda) leads to a 1,1′-dilithiated intermediate (C 5H 4Li)Mn(C 6H 5Li) ( 4) which, after reaction with trimethylelement chlorides, Me 3ECl (E  Si, Ge, Sn, Pb), or diorganyl dichalcogenides, MeEEMe and PhEEPh (E  S, Se), gives 1,1′-disubstituted derivatives of 1. The new sandwich compounds (C 5H 4-R)Mn(C 6H 6-R′) (R  R′  SiMe 3, ( 5a), GeMe 3 ( 5b), SnMe 3 ( 5c), PbMe 3 ( 5d), SMe ( 6a) and SeMe ( 6b)) have been studied in benzene solution by 1H, 13C, 29Si, 77Se, 119Sn and 207Pb NMR spectroscopy, and the NMR data have been compared with those of the corresponding ferrocene derivatives, Fe(C 5H 4-R) 2.