Synthesis and reactivity of a ruthenocene-type complex bearing an aromatic π-ligand with the heaviest group 14 element

Benchmark Study on the Calculation of 207Pb NMR Chemical Shifts

A benchmark set for the computation of 207Pb nuclear magnetic resonance (NMR) chemical shifts is presented. The PbS50 set includes conformer ensembles of 50 lead-containing molecular compounds and their experimentally measured 207Pb NMR chemical shifts. Various bonding motifs at the Pb center with up to seven bonding partners are included. Six different solvents were used in the measurements. The respective shifts lie in the range between +10745 and -5030 ppm. Several calculation settings are assessed by evaluating computed 207Pb NMR shifts for the use with different density functional approximations (DFAs), relativistic approaches, treatment of the conformational space, and levels for geometry optimization. Relativistic effects were included explicitly with the zeroth order regular approximation (ZORA), for which only the spin-orbit variant was able to yield reliable results. In total, seven GGAs and three hybrid DFAs were tested. Hybrid DFAs significantly outperform GGAs. The most accurate DFAs are mPW1PW with a mean absolute deviation (MAD) of 429 ppm and PBE0 with an MAD of 446 ppm. Conformational influences are small as most compounds are rigid, but more flexible structures still benefit from Boltzmann averaging. Including explicit relativistic treatments such as SO-ZORA in the geometry optimization does not show any significant improvement over the use of effective core potentials (ECPs).

From an Isolable Bismolyl Anion to an Yttrium-Bismolyl Complex with μ-Bridging Bismuth(I) Centers and Polar Covalent Y-Bi Bonds

The synthesis and first structural characterization of the [K(18-crown-6)] bismolyl Bitet (C4 Me4 Bi) contact ion pair (1) is presented. Notably, according to Natural Resonance Theory calculations, the Bitet anion of 1 features two types of leading mesomeric structures with localized anionic charge and two lone pairs of electrons at the BiI center, as well as delocalized anionic charge in the π-conjugated C4 Bi ring. The lone pairs at Bi enable a unique bridging coordination mode of the bismolyl ligand, as shown for the first rare earth metal bismolyl complex (Cptet 2 Y)2 (μ-η1 -Bitet )2 (2). The latter results from the salt metathesis reaction of KBitet with Cptet 2 Y(BPh4 ) (Cptet =C5 Me4 H). The Y-Bi bonding interaction in 2 of 16.6 % covalency at yttrium is remarkably large.

Fulleride-metal η5 sandwich and multi-decker sandwich complexes: A DFT prediction

The (C₆₀ CN)^- formed by the reaction of CN^- with fullerene shows high electron rich character, very similar to C₆₀ ˙^- , and it behaves as a large anion. Similar to Cp^- , the bulky anion, (C₆₀ CN)^- , acts as a strong η⁵ ligand towards transition metal centers. Previous studies on η⁵ coordination of fullerene cage are reported for pseudo fullerenes whereas the present study deals with sandwich complexes of (C₆₀ CN)^- with Fe(II), Ru(II), Cr(II), Mo(II), and Ni(II) and multi-decker sandwich complexes of CN-fullerides with Fe(II). The structural parameters of these complexes and the corresponding Cp^- complexes showed very close resemblance. Analysis of the metal-to-carbon bonding molecular orbitals showed that sandwich complex [Fe(η⁵ -(C₆₀ CN)^- )₂ ] exhibit bonding features very similar to that of ferrocene. Also, a 6-fold decrease in the band gap energy is observed for [Fe(η⁵ -(C₆₀ CN)^- )₂ ] compared to ferrocene. The energy of dissociation (ΔE) of the ligand (C₆₀ CN)^- from [Fe(η⁵ -(C₆₀ CN)^- )₂ ] is slightly lower than the ΔE of a Cp* ligand from a ferrocene derivative wherein each cyclopentadienyl unit is substituted with four tertiary butyl groups. The (C₆₀ CN)^- ligand behaved as one of the bulkiest ligands in the chemistry of sandwich complexes. Further, the coordinating ability of the dianion, (C₆₀ (CN)₂ )^2- is evaluated which showed strong coordination ability simultaneously with two metal centers leading to the formation of multi-decker sandwich and pearl-necklace type polymeric structures.

Recent progress in the chemistry of heavy aromatics

The aromaticity and synthetic application of "heavy benzenes", i.e., benzenes containing a heavier Group 14 element (Si, Ge, Sn, and Pb) in place of skeletal carbon, have been the targets of many theoretical and synthetic studies. Although the introduction of a sterically demanding substituent enabled us to synthesize and isolate heavy aromatic species as a stable compound by suppressing their high reactivity and tendency to polymerize, the existence of a protection group is an obstruction to the development of functional materials based on heavy aromatics. This review will delineate the most recent topics in the chemistry of heavy aromatics, i.e., the chemistry of "metallabenzenyl anions", which are the heavier Group 14 element analogs of phenyl anions stabilized by taking advantage of charge repulsion instead of steric protection.

Expanding the series of alkali metal plumbolyl complexes to Na and K

Herein we detail the straightforward and scalable synthesis of sodium and potassium complexes of the 2,5-bis(tert-butyldimethylsilyl)-3,4-diphenylplumbolyl dianion (Pbl^TBS,Ph). Their solid-state structures were found to comprise either monomeric solvates or coordination polymers depending on the alkali metal ion and crystallization medium. These complexes were readily prepared with high yields and purity compared to known routes to the dilithium congener of Pbl^TBS,Ph and are well-positioned to serve as convenient precursors for salt metathesis-type reactions leading to metal complexes of the understudied Pbl^TBS,Ph ligand.

Silole and germole complexes of lanthanum and cerium

Using dianionic metallole ligands (silole or germole) and the cyclooctatetraendiide dianion, heteroleptic lanthanide multi-decker complexes have been prepared. Due to the heteroatom of the metallole ligands intermolecular bridging between the sandwich complexes takes place. Our work highlights that different combinations of the lanthanide and heterocycle lead to different intermolecular interactions including a dimeric La-silole sandwich complex, a La-germole ladder-type polymeric species and a Ce-germole coordination polymer.

Introduction of plumbole to f-element chemistry

Herein, we present the synthesis and characterization of heteroleptic lanthanide complexes bearing a dianionic η5-plumbole ligand in their coordination sphere. The reaction proceeds via a salt elimination reaction between the dilithioplumbole ([Li(thf)]2[1,4-bis-tert-butyl-dimethylsilyl-2,3-bis-phenyl-plumbolyl] = [Li2(thf)2(η5-LPb)]) and specifically designed [Ln(η8-COTTIPS)BH4] precursors (Ln = lanthanide, La, Ce, Sm, Er; COTTIPS = 1,4-bis-triisopropylsilyl-cyclooctatetraenyl), that are capable of stabilizing a planar plumbole moiety in the coordination sphere of different trivalent lanthanide ions. In-depth ab initio calculations show that the aromaticity of the dianionic plumbole is retained upon coordination. Electron delocalization occurs from the plumbole HOMO to an orbital of mainly d-character at the lanthanide ion. The magnetic properties of the erbium congener were investigated in detail, leading to the observation of magnetic hysteresis up to 5 K (200 Oe s-1), an unequivocal proof for single molecule magnet behavior in this system. The magnetic behavior of the erbium species can be modulated by manipulating the position of the lithium cation in the complex, which directly influences the bonding metrics in the central [(η5-LPb)Er(η8-COTTIPS)]- fragment. This allowed us to assess a fundamental magneto-structural correlation in an otherwise identical inner coordination sphere.

Triple-decker complexes incorporating three distinct deck architectures

The reactivity of the dilithioplumbole ([Li₂(thf)₂(μ,η⁵-L^Pb)], L^Pb = 1,4-bis-tert-butyl-dimethylsilyl-2,3-bis-phenyl-plumbolyl) towards the reactive pnictogen precursors P₄, pentaphosphaferrocene, and pentaarsaferrocene ([Cp*Fe(η⁵-E₅)] (Cp* = η⁵-C₅Me₅, E = P, As)) is reported. The reaction with P₄ afforded a phospholyl lithium complex, via lead-phosphorus exchange, while the reactions with [Cp*Fe(η⁵-E₅)] yielded the first examples of Pb-Fe-Li heterotrimetallic triple-decker polypnictogenides with three different deck motifs.

Transmetalation Reactions of Aromatic Dilithionickelole: Synthesis of Heterobimetallic Complexes Featuring Metalloles as Diene Ligands

The aromatic metallole dianions are important metallaaromatic compounds because of their various reactivities and extensive synthetic applications. Herein we report the reactions of dilithionickelole with MgCl₂ , EtAlCl₂ , Cp*ScCl₂ , Cp*LuCl₂ and Pt(COD)Cl₂ (COD=1,5-cyclooctadiene) affording a series of Ni/M heterobimetallic complexes of the general formula (η⁴ -C₄ R₄ M)Ni(COD), in which the metalloles act as diene ligands, as suggested by single-crystal X-ray, NMR and theoretical analyses. In these reactions, two electrons of the nickelole dianion transferred to Ni, representing different reactivity compared with main-group metallole dianions.

Yttrium germole dianion complexes with Y-Ge bonds

The reactions of dipotassium 3,4-dimethyl-2,5-bis(trimethylsilyl)-germole dianion K2[1] with YCl3 and Cp*YCl2 (Cp* = cyclopentadienyl) in THF at room temperature afforded the dianion salt [(K-cryptand-222)2][1-YCl3] (K2[2]) and the dimeric complex [1-Y-Cp*]2 (3), respectively. While the polymeric complex {[(1)2-Y-K(toluene)]2}n (4) was obtained from the reaction of K2[1] and half molar equivalent of YCl3(THF)3.5 in toluene at 80 °C. The germole dianions in complexes 3 and 4 feature η5/η1 coordination interactions with the yttrium atoms. They represent the first examples of rare earth (RE) complexes containing RE-Ge bonds other than the RE-GeR3 structural type.

Direct amidation of metallaaromatics: access to N-functionalized osmapentalynes via a 1,5-bromoamidated intermediate

The direct C–H amidation or imidation of metallaaromatics with N-bromoamides or imides has been achieved under mild conditions and leads to the formation of a family of N-functionalized metallapentalyne derivatives. A unique 1,5-bromoamidated species has been identified, and can be viewed as a σ^H-adduct intermediate in a nucleophilic aromatic substitution. The 1,5-addition of both electrophilic and nucleophilic moieties into the metallaaromatic framework demonstrates a novel pathway in contrast to the typical radical process of arene C–H amidation involving N-haloamide reagents.

The direct C–H amidation of metallapentalyne has been achieved under mild conditions in which key 1,5-bromoamidated intermediates was determined.

Metal-metal multiple bond formation induced by σ-acceptor Lewis acid ligands

The reaction of [Cp*Ru(μ-NHPh)]2 (Cp* = η5-C5Me5) with Lewis acids of the type MX2 (M = Zn, Sn, Pb; X = Cl, OTf) affords Ru2 → M donor-acceptor adducts characterized as π complexes of a Ru[double bond, length as m-dash]Ru double bond with M(ii) Lewis acids. The results illustrate for the first time the ability of σ-acceptor Lewis acid ligands to induce the formation of a metal-metal multiple bond via stabilizing dative interactions.

Metallaaromatic Chemistry: History and Development

Since the prediction of the existence of metallabenzenes in 1979, metallaaromatic chemistry has developed rapidly, due to its importance in both experimental and theoretical fields. Now six major types of metallaromatic compounds, metallabenzenes, metallabenzynes, heterometallaaromatics, dianion metalloles, metallapentalenes and metallapentalynes (also termed carbolongs), and spiro metalloles, have been reported and extensively studied. Their parent organic analogues may be aromatic, non-aromatic, or even anti-aromatic. These unique systems not only enrich the large family of aromatics, but they also broaden our understanding and extend the concept of aromaticity. This review provides a comprehensive overview of metallaaromatic chemistry. We have focused on not only the six major classes of metallaaromatics, including the main-group-metal-based metallaaromatics, but also other types, such as metallacyclobutadienes and metallacyclopropenes. The structures, synthetic methods, and reactivities are described, their applications are covered, and the challenges and future prospects of the area are discussed. The criteria commonly used to judge the aromaticity of metallaaromatics are presented.

2,5-Bis-trimethylsilyl substituted boroles

This manuscript includes a comprehensive study of the synthesis and spectroscopic features of 2,5-disilyl boroles.

A Dimeric η1 ,η5 -Germole Dianion Bridged Titanium(III) Complex with a Multicenter Ti-Ge-Ge-Ti Bond

Dimeric germole dianion bridged Ti^III and Zr^IV complexes have been synthesized. In these complexes, the germole dianion adopts a formal η¹ ,η⁵ coordination to the two metal centers. The bonding situation in these bridged dimers is dominated by a covalent Ge-Ge interaction that results, for example, in a strong antiferromagnetic coupling of the d¹ Ti centers.

Transition-Metal Complexes Featuring Dianionic Heavy Group 14 Element Aromatic Ligands

The synthesis of dilithio-stannoles and -plumboles, dianionic aromatic compounds containing tin and lead atoms in their π-skeletons, opened a new field of transition-metal chemistry. Since the discovery of ferrocene (Cp₂Fe), which is composed of anionic aromatic ligands (Cp: cyclopentadienyl) and Fe(II), ferrocene-type sandwich complexes have long played important roles in many fields of chemistry. During the last few decades, the electronic and structural properties of the Cp ligand have been modified by introducing electron-donating, electron-withdrawing, and sterically encumbered substituents on the skeletal carbon atoms to obtain desirable properties of the resulting sandwich complexes. In terms of modifying the Cp ligand, we focused our attention on introducing a heavy group 14 atom into the π-skeleton. This idea was originally inspired by a question of whether or not aromaticity was retained after the replacement of a skeletal carbon atom by a heavy group 14 atom. After we succeeded in the synthesis of aromatic dilithio-stannoles and -plumboles, revealing that the concept of conventional aromaticity was expanded to lead-containing π-systems, we undertook the present project on applying these dianionic aromatic heavy Cp analogues as ligands for transition-metal complexes. The combination of a stannole and Cp*Ru units accomplished the creation of a neutral triple-decker complex and an anionic ruthenocene, which was not be accessible using Cp and its related ligands that are composed of only carbon atoms. The anionic ruthenocene reacted with electrophiles to afford ruthenocene-type sandwich complexes, and the structures of the stannole skeletons were highly dependent on the substituents on the tin atoms, in sharp contrast to the planar Cp ligand. The dianionic plumbole ligand was also found to function as an η⁵-coordinating ligand in an anionic ruthenocene, which is noteworthy in terms of incorporating the heaviest group 14 atom into a π-ligand to produce a ferrocene-type sandwich complex. The anionic ruthenocene bearing the plumbole ligand reacted with electrophiles to afford ruthenocene-type plumbole complexes, which have oxidation potentials lower than those of the corresponding tin analogues, demonstrating the effect of introduction of a lead atom heavier than a tin atom. In the reactions of dilithiostannoles with group 4 metals, the resulting complexes were found to have exotic electronic structures that cannot be constructed by the Cp ligand. The transition-metal complexes derived from dilithio-stannoles and -plumbole therefore exhibit remarkable differences as well as similarities to the traditional Cp-based transition-metal complexes. These results spotlight the introduction of heavy group 14 atoms into carbon-based π-skeletons, which can perturb the electronic properties of conventional transition-metal complexes and open a new chemistry of transition-metal complexes.

Ru-Complexes of an anionic germabenzenyl ligand

Complexation of germabenzenylpotassium [KGeC₅(t-Bu)H₄] with [Cp*RuCl]₄ resulted in the formation of two types of ruthenium complexes having unique coordination modes.