Calcium Complexes of Noninnocent α-Diimine Ligands

A 2,2'-bipyridyl calcium complex: synthesis, structure and reactivity studies

A 2,2'-bipyridyl calcium complex based on a tridentate ligand [CH₃C(N-2,6-ⁱPr₂C₆H₃)CHC(CH₃)NCH₂CH₂N(CH₃)₂]Ca(bipy)(THF) (1) was prepared by the reduction of {[CH₃C(N-2,6-ⁱPr₂C₆H₃)CHC(CH₃)NCH₂CH₂N(CH₃)₂]CaI(THF)}₂ with potassium graphite in the presence of 2,2'-bipyridine (bipy). Complex 1 is a good Ca(I)synthon, as shown by its reactivity with I₂, PhCH₂SSCH₂Ph, PhCH₂SeSeCH₂Ph and 9-fluorenone, yielding the calcium iodide complex [CH₃C(N-2,6-ⁱPr₂C₆H₃)CHC(CH₃)NCH₂CH₂N(CH₃)₂]CaI(bipy) (2), calcium thiolate [CH₃C(N-2,6-ⁱPr₂C₆H₃)CHC(CH₃)NCH₂CH₂N(CH₃)₂]Ca(SCH₂Ph)(bipy) (3), calcium selenolate [CH₃C(N-2,6-ⁱPr₂C₆H₃)CHC(CH₃)NCH₂CH₂N(CH₃)₂]Ca(SeCH₂Ph)(bipy) (4), and calcium ketyl complex [CH₃C(N-2,6-ⁱPr₂C₆H₃)CHC(CH₃)NCH₂CH₂N(CH₃)₂]Ca[O-(9-C₁₃H₈˙)](bipy)·2THF (5·2THF), respectively. In addition, reactions of complex 5 with CS₂, CH₂CHCH₂Br and PhCH₂Br give the corresponding dimeric bis(thiolate) complex {[S₂CC(CMe(NAr))C(Me)NCH₂CH₂NMe₂]Ca(DME)}₂ (6), dimeric calcium bromide complex {[(9-CH₂CHCH₂-C₁₃H₈-9)-O]CaBr(THF)(bipy)}₂ (7) and {[(9-C₆H₅CH₂-C₁₃H₈-9)-O]CaBr[O-(9-C₁₃H₈)](bipy)}₂ (8). These results demonstrated that the calcium ketyl complex 5 can also be employed as a single-electron transfer reagent. All the new compounds were characterized by various spectroscopic methods, and their solid-state structures were further confirmed by single-crystal X-ray diffraction analyses.

Main-group metal complexes of α-diimine ligands: structure, bonding and reactivity

α-Diimine ligands, in particular 1,4-diazabutadiene (dad) and bis(iminoacenaphthene) (bian) derivatives, have been widely used for coordination with various metals, including main-group, transition, and lanthanide and actinide metals. In addition to their tunable steric and electronic properties, the dad and bian ligands are redox-active and can readily accept one or two electrons, converting into the radical-anionic (L˙^-) or dianionic (enediamido, L^2-) form, respectively. This non-innocence brings about rich electronic structures and properties of the ligands and complexes thereof. For example, the dad ligands in their three redox levels can effectively stabilize a series of metal centers in different oxidation states, including low-valent metals. Moreover, these ligands can serve as electron reservoirs and can participate in reactions toward other molecules with or without metals. Therefore, such ligands are extremely useful in the areas of low-valent complexes and small molecule activation. Herein, we will discuss the use of dad (and bian) ligands in the stabilization of metal-metal-bonded compounds, in particular those of main-group metals, as well as small molecule activation by these (low-valent) metal coordination species where the non-innocence of the ligands plays a key role.

Transformation of carbodiimides to guanidine derivatives facilitated by gallylenes

The reductive coupling of carbodiimides RN[double bond, length as m-dash]C[double bond, length as m-dash]NR (R = 2,6-iPr2C6H3, Cy, iPr) by using [(dpp-bian)GaNa(dme)2] (1); [(dpp-dad)GaNa(thf)3] (2a) and [(dpp-dad)GaK(thf)4Ga(dpp-dad)][K(thf)6] (2b) led to the guanidinate derivatives [(dpp-bian)Ga(NCy)2C[double bond, length as m-dash]NCy][Na(thf)2] (3); [LGaN(R)C(RN)N(R)C(RN)][M] L = dpp-bian, M = Na(dme)2, R = iPr, (4a); L = dpp-dad, M = Na(thf)3, R = iPr, (4b); R = Cy, (4c); M = K(thf)4, (4d); L = dpp-bian, M = Na(dme)2, R = Cy, (4e) and [(dpp-dad)Ga(2,6-iPr2C6H3N)2C][Na(thf)2] (5).

Synthesis and structures of mono- and di-nuclear aluminium and zinc complexes bearing α-diimine and related ligands, and their use in the ring opening polymerization of cyclic esters

Multi-metallic complexes (of Al, Zn) derived from imine-based ligands effectively operate as catalysts for the ring opening polymerization (ROP) of ε-caprolactone (ε-CL), δ-valerolactone (δ-VL) and co-polymerization thereof.

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.

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.

Aluminium salalen complexes based on 1,2-diaminocyclohexane and their exploitation for the polymerisation of rac-lactide

In this paper nine various salalen ligands have been prepared and characterised. The steric and electronic effects of both the salen and salan fragments have been varied in a systematic fashion to ascertain how this affects the selectivity for the ROP of rac-lactide. These were complexed to AlMe3 to generate pseudo trigonal bypyramidal metal centred complexes. Upon addition of benzyl alcohol the active initiator can be easily prepared. The complexes were screened for the ROP of rac-lactide in solution and melt conditions. PLA with narrow molecular weight distributions (PDIs range from 1.07-1.67) could be isolated with moderate degrees of tacticity. Significantly it was found that chloro groups on the imine fragment increased the degree of heterotactic enchainment in the polymer. The kinetics for one series of salalen-Al complexes was also investigated.