Tris Complexes Research Articles

Lanthanide complexes of DOTA-nitroxide conjugates for redox imaging: spectroelectrochemistry, CEST, relaxivity, and cytotoxicity.

The lanthanide(iii) complexes (Gd, Eu, Dy, and Yb) of DOTA tris(amide) and bis(amide) derivatives (L1 and L2) featuring one redox active TEMPO arm were prepared. Ligand L2 harbours an alkyne fragment for further functionalization. The X-ray crystal structure of ligand L2 in complexation with Na+ was solved. The complexes showed in their CV one oxidation wave (0.26-0. 34 V vs. Fc+/Fc) due to an oxoammonium/nitroxide redox couple and a broad reduction corresponding to the nitroxide/hydroxylamine system. The Eu complexes demonstrated the presence of one water molecule in their coordination sphere. The nitroxide complexes were characterized by EPR spectroscopy, showing the typical 3-line pattern in the high temperature regime, which is quenched upon the addition of ascorbate (reduction into hydroxylamine). In their nitroxide form, the complexes show essentially no CEST peak. Conversely, the reduced complexes demonstrate a 12% CEST peak at 51 ppm, corresponding to the metal bound water molecule. Fast exchange precluded the CEST activity for the amide protons. All the complexes proved to be essentially non-toxic for M21 cells at concentrations up to 50 μM.

Carbene-mediated synthesis of a germanium tris(dithiolene)dianion.

While the 1 : 1 reaction of 3 with an N-heterocyclic carbene ({(Me)CN(i-Pr)}2C:) in THF resulted in ligand-substituted product 4, the corresponding 1 : 2 reaction (in the presence of H2O) gives the first structurally characterized germanium tris(dithiolene)dianion 5 as the major product and the "naked" dithiolene radical 6˙ as a minor by-product. The structure and bonding of 4 and 5 were probed by experimental and theoretical methods. Our study suggests that carbene-mediated partial hydrolysis may represent a new method to access tris(dithiolene) complexes of main-group elements.

Cerium(iv) complexes with guanidinate ligands: intense colors and anomalous electronic structures.

A series of cerium(iv) mixed-ligand guanidinate–amide complexes, {[(Me3Si)2NC(NiPr)2]xCeIV[N(SiMe3)2]3−x}+ (x = 0–3), was prepared by chemical oxidation of the corresponding cerium(iii) complexes, where x = 1 and 2 represent novel complexes. The Ce(iv) complexes exhibited a range of intense colors, including red, black, cyan, and green. Notably, increasing the number of the guanidinate ligands from zero to three resulted in significant redshift of the absorption bands from 503 nm (2.48 eV) to 785 nm (1.58 eV) in THF. X-ray absorption near edge structure (XANES) spectra indicated increasing f occupancy (nf) with more guanidinate ligands, and revealed the multiconfigurational ground states for all Ce(iv) complexes. Cyclic voltammetry experiments demonstrated less stabilization of the Ce(iv) oxidation state with more guanidinate ligands. Moreover, the Ce(iv) tris(guanidinate) complex exhibited temperature independent paramagnetism (TIP) arising from the small energy gap between the ground- and excited states with considerable magnetic moments. Computational analysis suggested that the origin of the low energy absorption bands was a charge transfer between guanidinate π orbitals that were close in energy to the unoccupied Ce 4f orbitals. However, the incorporation of sterically hindered guanidinate ligands inhibited optimal overlaps between Ce 5d and ligand N 2p orbitals. As a result, there was an overall decrease of ligand-to-metal donation and a less stabilized Ce(iv) oxidation state, while at the same time, more of the donated electron density ended up in the 4f shell. The results indicate that incorporating guanidinate ligands into Ce(iv) complexes gives rise to intense charge transfer bands and noteworthy electronic structures, providing insights into the stabilization of tetravalent lanthanide oxidation states.

Efficient Synthesis, Spectral, Characterization, Antimicrobial and DFT Studies of Antimony(III) Dithiocarbamates

The synthesis and characterization of novel antimony(III) dithiocarbamate complexes tris(N-furfuryl- N-propyldithiocarbamato-S,S′)antimony(III) (1) and tris(N-furfuryl-N-butyldithiocarbamato- S,S′)antimony(III) (2) have been characterized by elemental analysis, FT-IR, NMR (1H and 13C) spectra and antimicrobial studies. The characteristic thioureide (νC-N) bands occur at 1462 and 1475 cm-1 for complex 1 and 2, respectively. The theoretical calculations of the complexes have been carried out by density functional theory (DFT). The FMOs, MEP, Mulliken charge distribution and chemical activity parameters of the optimized structure have been calculated at the same level of theory. The MEP structure indicated that the positive and negative potential sites are around hydrogen atoms and electronegative atoms of the studied complexes, respectively. The Agar-well diffusion method were used to study the antimicrobial activity of the complexes against two Gram-positive bacteria (Klebsiella pneumoniae and Staphylococcus aureus), two Gram-negative bacteria (Escherichia coli and Vibrio cholera) and two fungal organisms (Candida albicans and Aspergillus niger).

Effect of cyclodextrin cavity size on the photovoltaic performance of unanchored ruthenium(II) polypyridine complex-containing dye-sensitized solar cells

We report the effect of cyclodextrin (CD) cavity size on the photovoltaic performance of dye-sensitized solar cells (DSSCs) containing inclusion complexes of tris(2,2′-bipyridyl)ruthenium(II) ([Ru(bpy)3]2 + ) in various CDs ([Ru(bpy)3]2 + / CD). The incident photon-to-current conversion efficiency (IPCE) of the [Ru(bpy)3]2 + -containing DSSC at 460 nm was calculated to be 8.1%, and this value was enhanced by the formation of [Ru(bpy)3]2 + / CD. The IPCE values of [Ru(bpy)3]2 + / α-CD-containing, [Ru(bpy)3]2 + / β-CD-containing, and [Ru(bpy)3]2 + / γ-CD-containing DSSCs were 8.8%, 8.9%, and 11.2%, respectively. It was concluded that the difference of IPCE values of [Ru(bpy)3]2 + / CD-containing DSSCs were caused by the CD cavity size, which affected the host–guest interaction between [Ru(bpy)3]2 + and the CD. These findings indicated that the cavity size of γ-CD is suitable to promote the photovoltaic conversion of DSSCs containing an unanchored photosensitizing dye with nonplanar molecular structure such as ruthenium(II) polypyridine and diimine copper(I) complexes.

La(III), Ce(III), Gd(III), and Eu(III) Complexation with Tris(hydroxymethyl)aminomethane in Aqueous Solution.

Lanthanides such as cerium(III), europium(III), and gadolinium(III) are widely used for designing fluorescent probes or magnetic resonance imaging contrasting agents for biological systems. The synthesis and study of lanthanide complexes in buffer solutions imitating biological fluids are often complicated because of a lack of data on the lanthanide interactions with buffer solution components. Therefore, Ln(III) [where Ln(III) = La(III), Ce(III), Gd(III), Eu(III)] complexation with a widely used buffer agent, tris(hydroxymethyl)aminomethane (Tris), in aqueous solution is studied using potentiometry, spectrofluorimetry, and 139La NMR spectroscopy. The stoichiometric composition of complexes is determined using mass spectrometry. The thermodynamic stability constants of Ln(III)-Tris complexes are calculated from potentiometric and spectral data; the difficulties in the study of these systems, reliability, and accuracy of the obtained constants are discussed. The possible structures of free Tris and its complexes with lanthanides(III) are optimized on the density functional theory/PBE0 level; the peculiarities of metal-ligand bonds were studied by Quantum Theory Atoms in Molecules analysis.

Building Block Design for Rapid Mass Transport in Quasi-Solid-State Solar Cells

Mesoscopic solar cells have rapidly emerged as a promising alternative to conventional silicon photovoltaics due to the combined benefits of low-cost, simple fabrication and competitive solar energy conversion efficiency. Recent success in low light absorption cobalt (II/III) polypyridyl complexes has led to encouraging solar energy conversion efficiencies in excess of 13%. Moreover, as one-electron redox mediators, cobalt (II/III) complexes based DSC systems also show a lower overpotential for dye regeneration and better compatibility with flexible metal substrates than iodide/tri-iodide. Such efforts open up great possibilities towards commercial applications.In contrast to the conventional organic liquid electrolytes that commonly have challenges durable encapsulation of the devices due to solvent evaporation, gel electrolytes have exhibited an impressive long-term stability, especially for outdoor applications where temperature of the DSC system can reach 80-85 oC under sunlight. Improvement on mass transport of the considerably large sized cobalt (II/III) complexes, particularly in high viscosity electrolyte, is crucial for solid-state dye-sensitized solar cells (SS-DSCs) to reach a reliable high efficiency toward practical applications.In this work, titania nanorod aggregates (TNA) with a great specific surface area and well-developed crystalline network were synthesized through a solvothermal approach and utilized as photoanode building blocks for application in cobalt (II/III) tris(2′2-bipyridine) complexes based solid-state electrolyte. An initial efficiency excess 7.1% and a long term stable efficiency of approximately 8.0% were achieved at full sun illumination by freshly assembled and aged TNA SS-DSCs, respectively. This represents dramatic enhancements of nearly 35% and 100% against the SS-DSCs prepared from two standard TiO2 nanoparticle samples – CCIC (approx. 5.9%) and Degussa P25 (approx. 4.0%), correspondingly. The TNA is characterised by a combination of mesopores within each aggregate and macro inter-aggregates voids, a high specific surface area and a great light scattering ability; such features make the aggregates superior photoanode building blocks for the application in bulky cobalt redox mediator based SS-DSCs system.

Tris(benzhydryl) and Cationic Bis(benzhydryl) Ln(III) Complexes: Exceptional Thermostability and Catalytic Activity in Olefin Hydroarylation and Hydrobenzylation with Substituted Pyridines

AbstractA series of Ln(III) tris(benzhydryl) complexes [(p‐tBu‐C6H4)2CH]3Ln (Ln=La (1), Nd (2), Y (3)) were synthesized by the salt metathesis reactions of LnHal3(THF)3.5(Ln=La, Nd, Hal=Cl; Ln=Y, Hal=I) and [(p‐tBu‐C6H4)2CH]Na. In1–3the benzhydryl ligands are linked with the metal centres inη4‐coordination mode. For diamagnetic complexes1and3a fluxional behaviour was detected in solution. Complexes1–3proved to be thermally stable: no decomposition was observed even after heating their solutions in toluene‐d8at 140 °C during 72 h. The reactions of1and2with B(C6F5)3allowed for the synthesis of base‐free cationic complexes [(p‐tBu‐C6H4)2CH]2Ln[(p‐tBu‐C6H4)2CHB(C6F5)3] (Ln=La (4), Nd (5)) which adopt the structure of a contact ion pair. Combinations of1–3and borane ((B(C6F5)3, [Me2NHPh][B(C6F5)4], [Ph3C][B(C6F5)4]) as well as4and5were found to be highly efficient, regio‐ and chemoselective catalysts for hydroarylation and hydrobenzylation of C=C bonds of a variety of substrates with substituted pyridines. These catalysts enable highly challenging transformations such as hydrobenzylation of 1,1‐disubstituted and internal C=C bonds.magnified image

Ruthenium tris(2,2′-bipyridyl) complex encapsulated in nanosized faujasite zeolite as intracellular localization tracer

Designing zeolites for medical applications is a challenging task that requires introducing new functionalities without altering the intrinsic properties such as morphology, crystallinity, colloidal stability, surface charge, and porosity. Herein, we present the encapsulation of luminescent ruthenium-tris(2,2′-bipyridyl) complex in faujasite (FAU) zeolite nanocrystals (Ru(bpy)3-FAU) and their use as an intracellular localization tracer. Upon exciting the Ru(bpy)3-FAU zeolite at 450 nm, the sample gives rise to an orange-red emission at 628 nm, thus permitting its use for cellular imaging and localization of the zeolite nanoparticles. The nanosized Ru(bpy)3-FAU zeolite is characterized in terms of size, charge, crystallinity, morphology, porosity, thermal stability, and sorption capacity. The potential toxicity of Ru(bpy)3-FAU on U251-MG glioblastoma cells was evaluated. A safe concentration (50–100 µg/ml) for the Ru(bpy)3-FAU zeolite is identified. The luminescent properties of the ruthenium complex confined in the zeolite nanocrystals allow their localization in the U251-MG cells with a main accumulation in the cytoplasm. The Ru(bpy)3-FAU nanosized zeolite is a potential candidate for biological applications for being stable, safe, capable of loading respiratory gases, and easily probed in the cells owing to its luminescent properties.

Effects of Photosensitizers and Reaction Media on Light‐Driven Water Oxidation with Trinuclear Ruthenium Macrocycles

AbstractPhotocatalytic water oxidation is a promising process for the production of solar fuels and the elucidation of factors that influence this process is of high significance. Thus, we have studied in detail light‐driven water oxidation with a trinuclear Ru(bda) (bda: 2,2’‐bipyridine‐6,6’‐dicarboxylate) macrocycle MC3 and its highly water soluble derivative m‐CH2NMe2‐MC3 using a series of ruthenium tris(bipyridine) complexes as photosensitizers under varied reaction conditions. Our investigations showed that the catalytic activities of these Ru macrocycles are significantly affected by the choice of photosensitizer (PS) and reaction media, in addition to buffer concentration, light intensity and concentration of the sensitizer. Our steady‐state and transient spectroscopic studies revealed that the photocatalytic performance of trinuclear Ru(bda) macrocycles is not limited by their intrinsic catalytic activities but rather by the efficiency of photogeneration of oxidant PS+ and its ability to act as an oxidizing agent to the catalysts as both are strongly dependent on the choice of photosensitizer and the amount of employed organic co‐solvent.

Structural Evidence of Spin State Selection and Spin Crossover Behavior of Tripodal Schiff Base Complexes of tris(2-aminoethyl)amine and Related Tripodal Amines

A review of the tripodal Schiff base (SB) complexes of tris(2-aminoethyl)amine, Nap(CH2CH 2NH2)3 (tren), and a few closely related tripodal amines with Cr(II), Mn(III) (d4), Mn(II), Fe(III) (d5), Fe(II) (d6), and Co(II) (d7) is provided. Attention is focused on examination of key structural features, the M-Nimine, M-Namine, or M-O and M-Nap bond distances and Nimine-M-N(O) bite and C-Nap-C angles and how these values correlate with spin state selection and spin crossover (SCO) behavior. A comparison of these experimental values with density functional theory calculated values is also given. The greatest number, 132, of complexes is observed with cationic mononuclear iron(II) in a N6 donor set, Fe(II)N6. The dominance of two spin states, high spin (HS) and low spin (LS), in these systems is indicated by the bimodal distribution of histogram plots of Fe(II)-Nimine and Fe(II)-Nazole/pyridine bond distances and of Nimine–Fe(II)-Nazole/pyridine and C-Nap-C bond angles. The values of the two maxima, corresponding to LS and HS states, in each of these histograms agree closely with the theoretical values. The iron(II)-Nimine and iron(II)-Nazole/pyridine bond distances correlate well for these complexes. Examples of SCO complexes of this type are tabulated and a few of the 20 examples are discussed that exhibit interesting features. There are only a few mononuclear iron(III) cationic complexes and one is SCO. In addition, a significant number of supramolecular complexes of these ligands that exhibit SCO, intervalence, and chiral recognition are discussed. A summary is made regarding the current state of this area of research and possible new avenues to explore based on analysis of the present data.

Carbene‐Stabilized Disilicon as a Silicon‐Transfer Agent: Synthesis of a Dianionic Silicon Tris(dithiolene) Complex

AbstractReaction of carbene‐stabilized disilicon (1) with the lithium‐based dithiolene radical (2.) affords the first dianionic silicon tris(dithiolene) complex (3). Notably, the formation of 3 represents the unprecedented utilization of carbene‐stabilized disilicon (1) as a silicon‐transfer agent. The nature of 3 was probed by multinuclear NMR spectroscopy, single‐crystal X‐ray diffraction, and DFT computations.

Carbene-Stabilized Disilicon as a Silicon-Transfer Agent: Synthesis of a Dianionic Silicon Tris(dithiolene) Complex.

Reaction of carbene-stabilized disilicon (1) with the lithium-based dithiolene radical (2. ) affords the first dianionic silicon tris(dithiolene) complex (3). Notably, the formation of 3 represents the unprecedented utilization of carbene-stabilized disilicon (1) as a silicon-transfer agent. The nature of 3 was probed by multinuclear NMR spectroscopy, single-crystal X-ray diffraction, and DFT computations.

Homoligand Tris-o-Dioxolene Complexes. Peculiarities of the Molecular Structures and Magnetic Properties

Metal tris-o-dioxolene (o-quinone, o-semiquinone, and catecholate) complexes represent an interesting and vivid model system for the demonstration of a relationship between the structure and magnetic properties when considering a series of objects of the same type. After publishing the reviews [1, 2], the metal tris-o-dioxolene complexes containing the symmetric 3,6-di-tert-butyl-o-benzoquinone derivatives with substituents in positions 4 and 5 are described in a number of works. In addition, some earlier unpublished structures of the complexes of this type are reviewed. The substituents in the lateral chains enhance the steric protection of the metal center and, as a consequence, result in the formation of coordination polyhedra uncharacteristic of the tris(dioxolene) complexes, such as a trigonal prism. In turn, the distortion of the structure affects the magnetic properties of the complexes. Only the complexes with the derivatives of sterically hindered o-quinones, 3,5- and 3,6-di-tert-butyl-o-benzoquinones, are considered in the present review. On the one hand, bulky tert-butyl groups prevent the formation of direct intermolecular contacts and, on the other hand, prevent organic reactions to occur at the benzoquinone cycle.

Heteroleptic Ruthenium(II) Complexes with Bathophenanthroline and Bathophenanthroline Disulfonate Disodium Salt as Fluorescent Dyes for In-Gel Protein Staining.

The in-gel detection of proteins for various proteomic experiments is commonly done with the fluorescent RuII tris(bathophenanthroline disulfonate) complex (Ru(BPS)3), which is more cost-effective compared to commercial Ru-based formulations but requires tedious procedures for its preparation and strongly acidic staining conditions. Herein, we report the synthesis and characterization of heteroleptic RuII complexes Ru(BPS)2(BP) and Ru(BPS)(BP)2 containing bathophenanthroline (BP) and bathophenanthroline disulfonate disodium salt (BPS) in comparison with Ru(BPS)3. It was shown by fluorescent and UV-vis measurements that novel RuII complexes were excitable in both UV and visible light, close to emission bands of classical lasers, which is important for successful in-gel protein detection. Novel fluorescent dyes demonstrated improved protein detection in comparison with commercially available SYPRO Ruby staining solution. In addition, unlike commonly used staining protocols, staining with Ru(BPS)(BP)2 can be performed at nearly neutral pH, thereby reducing artificial post-translational modifications (PTMs).

Luminescence from a highly asymmetric nine-coordinate tricapped trigonal prismatic Sm(III) complex

The nine-coordinate complexes of tris(dibenzoylmetanato)La(III) and Sm(III) with tptz were synthesized and thoroughly characterized. The 1H NMR spectrum of [La(dbm)3(tptz)]∙CH3CN is consistent with the coordination of three dbm and one tptz. The tricapped trigonal prism geometry of [Sm(dbm)3(tptz)]∙CH3CN complex is revealed by single crystal X-ray diffraction analysis. The shape 2.1v analysis authenticates the tricapped trigonal prism geometry of [Sm(dbm)3(tptz)]∙CH3CN complex. The Sm(III) is coordinatively saturated by the coordination of six oxygen atoms from dbm units and two pyridyl and one triazine nitrogen atoms from tptz moiety. The steady-state and time resolved photoluminescence of the solid [Sm(dbm)3(tptz)]∙CH3CN and its PMMA hybrid films of different concentration are investigated and discussed. The complex has only one emitting center since the decay times are fitted by mono-exponential function. The higher PL intensity of 4G5/2 → 6H7/2 (ΔJ = 1, magnetic-dipole transition) transition compared to 4G5/2 → 6H9/2 (ΔJ = 2, electric-dipole transition), in the case of 3% (w/w) PMMA hybrid film is the result of strong vibrionic coupling. Although the PL intensity of two transition are different even then the decay times of the transition are roughly similar in magnitude. The stark splitting of electric-dipole 4G5/2 → 6H9/2 transition in the spectrum of 3% film is interesting and leads to believe a strong coupling between states of f-electrons and electric fields of the surrounding ligands.

Electrocatalytic Hydrogen Evolution and Oxidation with Rhenium Tris(thiolate) Complexes: A Competition between Rhenium and Sulfur for Electrons and Protons

Recent electrochemical experiments reveal that the rhenium-tris(thiolate) [ReL3] (L = DPPBT = diphenylphosphinobenzenethiolate, a noninnocent ligand) complex catalytically reduces protons and oxidi...

Excited-State Relaxation in Luminescent Molybdenum(0) Complexes with Isocyanide Chelate Ligands

Diisocyanide ligands with a m-terphenyl backbone provide access to Mo0 complexes exhibiting the same type of metal-to-ligand charge transfer (MLCT) luminescence as the well-known class of isoelectronic RuII polypyridines. The luminescence quantum yields and lifetimes of the homoleptic tris(diisocyanide) Mo0 complexes depend strongly on whether methyl- or tert-butyl substituents are placed in α-position to the isocyanide groups. The bulkier tert-butyl substituents lead to a molecular structure in which the three individual diisocyanides ligated to one Mo0 center are interlocked more strongly into one another than the ligands with the sterically less demanding methyl substituents. This rigidification limits the distortion of the complex in the emissive excited-state, causing a decrease of the nonradiative relaxation rate by one order of magnitude. Compared to RuII polypyridines, the molecular distortions in the luminescent 3MLCT state relative to the electronic ground state seem to be smaller in the Mo0 complexes, presumably due to delocalization of the MLCT-excited electron over greater portions of the ligands. Temperature-dependent studies indicate that thermally activated nonradiative relaxation via metal-centered excited states is more significant in these homoleptic Mo0 tris(diisocyanide) complexes than in [Ru(2,2′-bipyridine)3]2+.

Facile amidation of esters with aromatic amines promoted by lanthanide tris (amide) complexes

The development of catalysts capable of catalyzing amidation of esters with amines to construct amides under mild conditions is of great importance. Compared to aliphatic amines, the direct catalytic amidation of esters with less nucleophilic aromatic amines is rather difficult. Employing simple lanthanide tris (amide) complexes Ln[N (SiMe3)2]3(μ‐Cl)Li (THF)3 as the catalysts, it was found a broad range of aromatic amines and esters were efficiently converted into various amides in good yields under mild conditions. A plausible mechanism for this transformation was experimentally supported as starting from an amide exchange reaction between the lanthanide tris (amide) complex and the substrate amine.

Unexpected Coordination Complexes of the Metal Tris-silylamides M{N(SiMe3)2}3 (M = Ti, V).

The synthesis, molecular structures, and spectroscopic details of a series of isocyanide and nitrile complexes of the early first-row transition-metal tris(silyl)amides M{N(SiMe3)2}3 (M = Ti, V) are reported. Previously, first-row transition-metal tris(silyl)amides were generally thought to be incapable of forming complexes with Lewis bases due to their excessive steric crowding. However, it is now shown that simple treatment of the base-free trisamides with 2 equiv of an isocyanide or nitrile base at room temperature results in the formation of the trigonal bipyramidal complexes Ti{N(SiMe3)2}3(1-AdNC)2 (1), Ti{N(SiMe3)2}3(CyNC)2 (2), Ti{N(SiMe3)2}3(ButNC)2 (3), Ti{N(SiMe3)2}3(PhCN)2 (4), V{N(SiMe3)2}3(1-AdNC)2 (5), V{N(SiMe3)2}3(CyNC)2 (6), V{N(SiMe3)2}3(ButNC)2 (7), and V{N(SiMe3)2}3(PhCN)2 (8), which incorporate two donor ligands (1-AdNC = 1-adamantyl isocyanide, CyNC = cyclohexyl isocyanide, ButNC = tert-butyl isocyanide, PhCN = benzonitrile). All complexes display a characteristic increase in the frequency of the multiple bonded C-N stretching mode which is observed to be in the range of 2170-2190 cm-1 for the isocyanide complexes 1-3 and 5-7 and at 2250 cm-1 for the nitrile complex 8. This effect was not observed for the titanium nitrile complex 4, suggesting weak binding of the donor to titanium. Paramagnetic 1H NMR studies showed these complexes to have detectable, though extremely broadened, signals attributable to the trimethylsilyl groups of the amide ligands (δ = ca. 2.8 ppm for titanium isocyanide complexes, ca. 4.5-4.7 ppm for vanadium isocyanide complexes). A variable-temperature 1H NMR study showed that in solution these complexes exist as mixtures of the five-coordinate species and a putative four-coordinate species coordinating a single Lewis basic ligand. Electronic spectroscopy indicated that the vanadium complexes 5-8 bind the Lewis bases more strongly than the corresponding titanium complexes, where the spectra of complexes 1-4 are essentially identical to the base-free Ti{N(SiMe3)2}3 at the temperatures and concentrations studied. In contrast to these results, no corresponding complexes were detected for the metal silylamides M{N(SiMe3)2}3 (M = Cr, Mn, Fe, or Co) when treated with the isocyanide or nitrile bases.