A bis(imino)carbazolate pincer ligand stabilized mononuclear gallium(I) compound: synthesis, characterization, and reactivity

The first bis(imino)carbazolate pincer ligand supported mononuclear Ga(I) compound LGa: (3) was synthesized and fully characterized. Oxidation of 3 with elemental selenium afforded the dinuclear Ga(III) compound [LGa(μ-Se)]₂ (4) bearing two bridging Se atoms. Ligand substitution of Cr(CO)₆ with 3 under UV light irradiation afforded the gallylene-chromium complex LGa: → Cr(CO)₅ (5). In addition, the attempted synthesis of the aluminium analogue LAl: through reduction of LAlI₂ (7) only led to isolation of the dinuclear Al(III) compound (LAlI)₂ (8), most probably formed through the C-C coupling of two imino radicals.

Antimony diiminopyridine complexes

The stoichiometric reactions of antimony trichloride, trimethylsilyl trifluoromethanesulfonate, and diiminopyridine ligands lead to the formation of N,N',N''-chelated SbCl₂ cationic complexes. Methyl and phenyl substituents on the imine carbons of the ligand yielded structures with a lone pair on antimony and the hydrogen substituted variant was notably different as it forms a Menshutkin complex with meta-xylene in the solid-state.

Synthesis, properties, and catalysis of p-block complexes supported by bis(arylimino)acenaphthene ligands

Bis(arylimino)acenaphthene (Ar-BIAN) ligands have been recognized as robust scaffolds for metal complexes since the 1990 s and most of their coordination chemistry was developed with transition metals. Notably, there have been relatively few reports on complexes comprising main group elements, especially those capitalizing on the redox non-innocence of Ar-BIAN ligands supporting p-block elements. Here we present an overview of synthetic approaches to Ar-BIAN ligands and their p-block complexes using conventional solution-based methodologies and environmentally-benign mechanochemical routes. This is followed by a discussion on their catalytic properties, including comparisons to transition metal counterparts, as well as key structural and electronic properties of p-block Ar-BIAN complexes.

2,6-Bis(benzimidazol-2-yl)pyridines as more electron-rich and sterically accessible alternatives to 2,6-bis(imino)pyridine for group 13 coordination chemistry

2,6-bis(benzimidazol-2-yl)pyridines are more electron-rich yet more sterically open ligands for monovalent and trivalent group 13 elements than bis(imino)pyridines.

Electronic and Geometric Structures of Paramagnetic Diazadiene Complexes of Lithium and Sodium

The electronic and molecular structures of the lithium and sodium complexes of 1,4-bis(2,6-diisopropylphenyl)-2,3-dimethyl-1,4-diazabutadiene (Me2DADDipp) were fully characterized by using a multi-frequency electron paramagnetic resonance (EPR) spectroscopy approach and crystallography, together with density functional theory (DFT) calculations. EPR measurements, using T1 relaxation-time-filtered pulse EPR spectroscopy, revealed the diagonal elements of the A and g tensors for the metal and ligand sites. It was found that the central metals in the lithium complexes had sizable contributions to the SOMO, whereas this contribution was less strongly observed for the sodium complex. Such strong contributions were attributed to structural specifications (e.g. geometrical data and atomic size) rather than electronic effects.

Gallium Hydrides with a Radical-Anionic Ligand

The reaction of Cl₂GaH with a sodium salt of the dpp-Bian radical-anion (dpp-Bian^•-)Na (dpp-Bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) affords paramagnetic gallane (dpp-Bian^•-)Ga(Cl)H (1). Oxidation of (dpp-Bian^2-)Ga-Ga(dpp-Bian^2-) (2) with N₂O results in the dimeric oxide (dpp-Bian^•-)Ga(μ²-O)₂Ga(dpp-Bian^•-) (3). A treatment of the oxide 3 with phenylsilane affords paramagnetic gallium hydrides (dpp-Bian^•-)GaH₂ (4) and (dpp-Bian^•-)Ga{OSi(Ph)H₂}H (5) depending on the reagent's stoichiometry. The reaction of digallane 2 with benzaldehyde produces pinacolate (dpp-Bian^•-)Ga(O₂C₂H₂Ph₂) (6). In the presence of PhSiH₃, the reaction between digallane 2 and benzaldehyde (2: PhSiH₃: PhC(H)O = 1:4:4) affords compound 4. The newly prepared complexes 1, 3-6 consist of a spin-labeled diimine ligand-dpp-Bian radical-anion. The presence of the ligand-localized unpaired electron allows the use of the ESR spectroscopy for characterization of the gallium hydrides reported. The molecular structures of compounds 1, 3-6 have been determined by the single-crystal X-ray analysis.

Iminopyridine ligand complexes of group 14 dihalides and ditriflates – neutral chelates and ion pair formation

Reaction of the chelating imino-pyridine ligand SIMPY, (SIMPY=2-(DippN=CH)-C5H4N), Dipp=2,6- i Pr2-C6H3, with germanium(II) and tin(II) halides provides the respective neutral complexes [SIMPY·EX2] (EX2: E=Ge, X=Cl, Br; E=Sn, X=Cl, Br, I). The method is readily extendable to give the tin(II) triflate complex [SIMPY·Sn(OTf)2] (OTf, triflate=CF3SO3 −). In the solid state, the neutral compounds [SIMPY·EX2] exist as monomers, in which the four-coordinate tetrel atoms feature a slightly distorted disphenoidal geometry around germanium and tin. Reaction of the tridentate imino-pyridine ligand DIMPY, (DIMPY=2,6-(DippN=CH)2-C5H3N) with Sn(OTf)2 provided access to a neutral tin(II) complex. Similar to the previously reported reactions leading to the germanium and tin chloride complexes [DIMPY·SnCl]+[SnCl3]−, and [Me2DIMPY·EX]+[EX3]− (Me2DIMPY=2,6-(DippN=C(Me))2-C5H3N, E=Ge, Sn; X=Cl), the reactions of DIMPY with GeX2·dioxane (X=Cl, Br) and SnX2 (X=Br, I) yielded Ge(II) and Sn(II) based ion pairs [DIMPY·EX]+[EX3]− (E=Ge, X=Cl, Br; E=Sn, X=Br, I) as a consequence of spontaneous dissociation of the group 14 dihalides. The tetrel atoms in the cationic parts in [DIMPY·EX]+[EX3]− are four-coordinate as one halide substituent is replaced by the coordination of a second imino donor group from the ligand. The anionic fragments adopt a pyramidally, tri-coordinate geometry. In contrast, the DIMPY tin(II) ditriflate complex crystallizes with two independent, neutral molecules per asymmetric unit, in which one of the tin centers is five- coordinate by interaction with three donor sites of the chelating bis(imino)pyridine ligand and two additional contacts towards the oxygen atoms of the triflate counter-anions. In the second crystallographically independent complex the tin atom is six-coordinate with a slightly distorted octahedral geometry via interaction with THF as an additional donor molecule. All compounds reported were studied by means of multinuclear NMR spectroscopy. In addition, the solid state structures of the complexes [SIMPY·EX2] (EX2: E=Ge, X=Cl, Br; E=Sn, X=Cl, Br, I), the ion pairs [DIMPY·EX]+[EX3]− (E=Ge, X=Cl; E=Sn, X=Br) and the tin(II) ditriflate [DIMPY·Sn(OTf)2] were authenticated by means of single-crystal X-ray diffraction analyses. Moreover, [DIMPY·Sn(OTf)2] was investigated by 119Sn Mössbauer spectroscopy.

Homolytic, Heterolytic, Mesolytic - As You Like It: Steering the Cleavage of a HC(sp3 )-C(sp3 )H Bond in Bis(1H-2,1-benzazaborole) Derivatives

A set of (3,3')-bis(1-Ph-2-R-1H-2,1-benzazaborole) compounds, in which R=tBu (Bab-tBu)₂ , R=Dipp (Bab-Dipp)₂ or R=tBu and Dipp (Bab-Dipp)(Bab-tBu), was synthesized and fully characterized using ¹ H, ¹¹ B, ¹³ C, and ¹⁵ N NMR spectroscopy as well as single-crystal X-ray diffraction analysis. The central HC(sp³ )-C(sp³ )H bond with restricted rotation at the junction of both 1H-2,1-benzazaborole rings displayed an intriguing reactivity. It was demonstrated that this bond is easily mesolytically cleaved using alkali metals to form the respective aromatic 1Ph-2R-1H-2,1-benzazaborolyl anions M⁺ (THF)_n (Bab-tBu)^- (M=Li, Na, K) and K⁺ (THF)_n (Bab-Dipp)^- . Furthermore, the central HC(sp³ )-C(sp³ )H bond of bis(1H-2,1-benzazaborole)s is also homolytically cleaved either by heating or photochemical means, giving corresponding 1Ph-2R-1H-2,1-benzazaborolyl radicals (Bab-tBu)^. and (Bab-Dipp)^. , which rapidly self-terminate. Nevertheless, their formation was unambiguously established by NMR analysis of the reaction mixtures containing products of the self-termination of the radicals after heating or irradiation. (Bab-Dipp)^. radical was also characterized using EPR spectroscopy. Importantly, it turned out that the essentially non-polarized HC(sp³ )-C(sp³ )H bond in (Bab-tBu)₂ is also cleaved heterolytically with 2 equiv of MeLi, giving the mixture of Li⁺ (SOL)_n (Bab-tBu)^- (SOL=THF or Et₂ O) and lithium methyl-substituted borate complex Li⁺ (SOL)_n (Bab-tBu-Me)^- in a diastereoselective fashion.

Synthesis, Structure, and Properties of Al((R)bpy)3 Complexes (R = t-Bu, Me): Homoleptic Main-Group Tris-bipyridyl Compounds

The neutral homoleptic tris-bpy aluminum complexes Al((R)bpy)3, where R = tBu (1) or Me (2), have been synthesized from reactions between AlX precursors (X = Cl, Br) and neutral (R)bpy ligands through an aluminum disproportion process. The crystalline compounds have been characterized by single-crystal X-ray diffraction, electrochemical experiments, EPR, magnetic susceptibility, and density functional theory (DFT) studies. The collective data show that 1 and 2 contain Al(3+) metal centers coordinated by three bipyridine (bpy(•))(1-) monoanion radicals. Electrochemical studies show that six redox states are accessible from the neutral complexes, three oxidative and three reductive, that involve oxidation or reduction of the coordinated bpy ligands to give neutral (R)bpy or (R)bpy(2-) dianions, respectively. Magnetic susceptibility measurements (4-300 K) coupled with DFT studies show strong antiferromagnetic coupling of the three unpaired electrons located on the (R)bpy ligands to give S = (1)/2 ground states with low lying S = (3)/2 excited states that are populated above 110 K (1) and 80 K (2) in the solid-state. Complex 2 shows weak 3D magnetic interactions at 19 K, which is not observed in 1 or the related [Al(bpy)3] complex.

Synthesis and structures of mononuclear and dinuclear gallium complexes with α-diimine ligands: reduction of the metal or ligand?

Reduction of the dichloro gallium(III) α-diimine complex [(L(ipr))˙(-)GaCl2] (1, L(ipr) = [(2,6-iPr2C6H3)NC(Me)]2) by different equivalents of sodium metal afforded the gallium complexes [(L(ipr))(2-)Ga(III)(μ2-Cl)2Na(THF)4] (2) and [(Na(THF)6)(+)·((L(ipr))(2-)Ga-Ga(L(ipr))(2-))˙(-)] (3). Interestingly, in complex 2 a Na(+)Cl(-) ion pair is incorporated, while compound 3 is an anionic digallium complex. Moreover, a cationic gallium complex with a tetrachlorogallium(III) counter anion, [(LGaCl2)(+)·(GaCl4)(-)] (4), was accessed from the reaction of GaCl3 with 0.5 equiv. of ligand L(ipr). In contrast, the reaction of GaCl3 with the doubly reduced anion (Na2L(2-)) of the smaller α-diimine ligands L(Me) ([(2,6-Me2C6H3)NC(Me)]2) or L(Et) ([(2,6-Et2C6H3)NC(Me)]2) yielded the Ga-Ga-bonded complexes [(L(Et))˙(-)ClGa(II)-Ga(II)Cl(L(Et))˙(-)] (5) and [(L(Me))˙(-)ClGa(II)-Ga(II)Cl(L(Me))˙(-)] (6). Here L is the neutral α-diimine ligand, L˙(-) represents the monoanion, and L(2-) is the dianionic form of the ligand. The complexes were characterized by X-ray diffraction and their electronic structures were studied by DFT computations.

Cationic cluster formation versus disproportionation of low-valent indium and gallium complexes of 2,2'-bipyridine

Group 13 M^I compounds often disproportionate into M⁰ and M^III. Here, however, we show that the reaction of the M^I salt of the weakly coordinating alkoxyaluminate [Ga^I(C₆H₅F)₂]⁺[Al(OR^F)₄]⁻ (R^F=C(CF₃)₃) with 2,2'-bipyridine (bipy) yields the paramagnetic and distorted octahedral [Ga(bipy)₃]^2+•{[Al(OR^F)₄]⁻}₂ complex salt. While the latter appears to be a Ga^II compound, both, EPR and DFT investigations assign a ligand-centred [Ga^III{(bipy)₃}^•]²⁺ radical dication. Surprisingly, the application of the heavier homologue [^In^I(C₆H₅F)₂]⁺[Al(OR^F)₄]⁻ leads to aggregation and formation of the homonuclear cationic triangular and rhombic [In₃(bipy)₆]³⁺, [In₃(bipy)₅]³⁺ and [In₄(bipy)₆]⁴⁺ metal atom clusters. Typically, such clusters are formed under strongly reductive conditions. Analysing the unexpected redox-neutral cationic cluster formation, DFT studies suggest a stepwise formation of the clusters, possibly via their triplet state and further investigations attribute the overall driving force of the reactions to the strong In−In bonds and the high lattice enthalpies of the resultant ligand stabilized [M₃]³⁺{[Al(OR^F)₄]⁻}₃ and [M₄]⁴⁺{[Al(OR^F)₄]⁻}₄ salts.

Group 13 metals such as gallium and indium with oxidation states of +I tend to disproportionate into more stable 0 and +III states. Here, the authors report that with a 2,2'-bipyridine ligand Ga(+I) forms a paramagnetic mononuclear Ga(+III) complex, whereas the indium analogue aggregates forming cationic clusters retaining the +I state.

Titanium and zirconium complexes of the N,N'-bis(2,6-diisopropylphenyl)-1,4-diaza-butadiene ligand: syntheses, structures and uses in catalytic hydrosilylation reactions

We report here a number of dianionic 1,4-diaza-1,3-butadiene complexes of titanium and zirconium synthesised by a salt metathesis reaction. The reaction of either CpTiCl3 or Cp2TiCl2 with the dilithium salt of N,N'-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene [; abbreviated (Dipp)2DADLi2] afforded the mono-cyclopentadienyl titanium complex [η(5)-CpTi((Dipp)2DAD)Cl] () bearing a dianionic ene-diamide ligand, while the analogous reaction of zirconocene dichloride (Cp2ZrCl2) with the dilithium salt gave the bis-cyclopentadienyl zirconium complex [Cp2Zr{(Dipp)2DAD}] (). The metal dichloride complexes [Ti((Dipp)2DAD)Cl2] () and [{(Dipp)2DADZrCl(μ-Cl)}2(κ(3)-Cl)(Li)(OEt2)2] () were obtained by the reaction of and anhydrous metal tetrachloride in a 1 : 1 molar ratio in diethyl ether at room temperature. Meanwhile, the homoleptic titanium complex [Ti{((Dipp)2DAD)}2] () was isolated in good yield by the treatment of with TiCl4 in a 1 : 2 molar ratio in diethyl ether. The complexes and were further reacted with neosilyl lithium to afford mono- and bis-alkyl complexes of titanium [η(5)-CpTi{(Dipp)2DAD}(CH2SiMe3)] () and zirconium [Zr{(Dipp)2DAD}(CH2SiMe3)2] () respectively. Molecular structures of the complexes , , and in the solid states were confirmed by single crystal X-ray diffraction analysis. The solid state structures of all the complexes reveal that the metal ions are chelated through the amido-nitrogen atoms and the olefinic carbons of the [(Dipp)2DAD](2-) moiety, satisfying the σ(2),π coordination mode. Compound was used as a catalyst for the intermolecular hydrosilylation reaction of a number of olefins, and moderate activity of catalyst was observed.

Moilanen J, Roemmele TL, Boeré RT, Konu J, Tuononen HM. Group 13 complexes of dipyridylmethane, a forgotten ligand in coordination chemistry

A comprehensive study of the coordination properties of dipyridylmethane (dpma) was performed. The preparation of metal complexes of the type [(dpma)₂MCl₂]⁺, [(dpma)MCl₂]⁺, (M = Al, Ga), (dpma)InCl₃ and (dpma)(BCl₃)₂ is described along with their characterization.

Reduction of C,N-chelated chloroborane: straightforward formation of the unprecedented 1H-2,1-benzazaborolyl potassium salt

Reduction of C,N-chelated chloroborane [2-(CH=NtBu)C6H4]BPhCl () with the potassium metal afforded (3,3')-bis(1-Ph-2-tBu-1H-2,1-benzazaborole) (2). Compound 2 is formed via C-C reductive coupling reaction. Subsequent reduction of 2 with two equivalents of the potassium metal produced orange crystals of 1Ph-2tBu-1H-2,1-benzazaborolyl (Bab) potassium salt K(THF)(Bab) (3). Compound 3 is able to react with simple electrophiles (MeI or Me3SiCl) resulting in the formation of substituted 1H-2,1-benzazaboroles.

Masking of Lewis acidity trends in the solid-state structures of trichlorido- and tribromido(2,2':6',2''-terpyridine-κ(3)N,N',N'')gallium(III)

The molecular structures of trichlorido(2,2':6',2''-terpyridine-κ(3)N,N',N'')gallium(III), [GaCl3(C15H11N3)], and tribromido(2,2':6',2''-terpyridine-κ(3)N,N',N'')gallium(III), [GaBr3(C15H11N3)], are isostructural, with the Ga(III) atom displaying an octahedral geometry. It is shown that the Ga-N distances in the two complexes are the same within experimental error, in contrast to expected bond lengthening in the bromide complex due to the lower Lewis acidity of GaBr3. Thus, masking of the Lewis acidity trends in the solid state is observed not only for complexes of group 13 metal halides with monodentate ligands but for complexes with the polydentate 2,2':6',2''-terpyridine donor as well.

Unusual formation of a N-heterocyclic germylene via homolytic cleavage of a C–C bond

A N-heterocyclic germylene has been synthesized via an unusual homolytic cleavage of a C–C bond under reductive conditions.

Electronic structure of 2,2'-bipyridine organotransition-metal complexes. Establishing the ligand oxidation level by density functional theoretical calculations

A density functional theoretical (DFT) study (B3LYP) has been carried out on 20 organometallic complexes containing η(5)- and/or η(3)-coordinated cyclopentadienyl anions (Cp(-)) and 2,2'-bipyridine (bpy) ligand(s) at varying oxidation levels, i.e., as the neutral ligand (bpy(0)), as the π-radical monoanion (bpy(•-))(-), or as the diamagnetic dianion (bpy(2-))(2-). The molecular and electronic structures of these species in their ground states and, in some cases, their first excited states have been calculated using broken-symmetry methodology. The results are compared with experimental structural and spectroscopic data (where available) in order to validate the DFT computational approach. The following electron-transfer series and complexes have been studied: [(Cp)(2)V(bpy)](0,+,2+) (1-3), [(Cp)(2)Ti(bpy)](-,0,+,2+) (4-7), [(Cp)(2)Ti(biquinoline)](0,+) (8 and 9), [(Cp*)(2)Ti(bpy)](0) (10) (Cp* = pentamethylcyclopentadienyl anion), [Cp*Co(bpy)](0,+) (11 and 12), [Cp*Co(bpy)Cl](+,0) (13 and 14), [Fe(toluene)(bpy)](0) (15), [Cp*Ru(bpy)](-) (16), [(Cp)(2)Zr(bpy)](0) (17), and [Mn(CO)(3)(bpy)](-) (18). In order to test the predictive power of our computations, we have also calculated the molecular and electronic structures of two complexes, A and B, namely, the diamagnetic dimer [Cp*Sc(bpy)(μ-Cl)](2) (A) and the paramagnetic (at 25 °C) mononuclear species [(η(5)-C(5)H(4)(CH(2))(2)N(CH(3))(2))Sc((m)bpy)(2)] (B). The crystallographically observed intramolecular π-π interaction of two N,N'-coordinated π-radical anions in A leading to an S = 0 ground state is reliably reproduced. Similarly, the small singlet-triplet gap of ~600 cm(-1) between two antiferromagnetically coupled (bpy(•-))(-) ligands in B, two ferromagnetically coupled radical anions in the triplet excited state of B, and the structures of A and B is reproduced. Therefore, we are confident that we can present computationally obtained, detailed electronic structures for complexes 1-18. We show that N,N'-coordinated neutral bpy(0) ligands behave as very weak π acceptors (if at all), whereas the (bpy(2-))(2-) dianions are strong π-donor ligands.