Ewa
Kober
,
Zofia
Janas
*,
Tomasz
Nerkowski
and
Lucjan B.
Jerzykiewicz
College of Chemistry, College of Wrocław, 14, F. Joliot-Curie, 50-383 Wrocław, Poland. E-mail: [email protected]
The reactions of the diaminebis(aryloxido) ligand precursors [Me2NCH2CH2N(CH2-4-R-C6H3OH)2] [R = C(CH3)2CH2C(CH3)3, H22L11; R = CH3, H22L22] with MgnBu2, ZnEt2 and AlEt3 create complexes of basic method [M2(μ-L-κ4O,N,N,O)2] (M = Mg, 1a for L1 and 1b for L2; M = Zn, 2a for L1 and 2b for L2) and [Al2(μ-L-κ3O,N,N,O)2Et2] (3 for L1) in good yields. Compounds 1a–3 have been characterised by NMR spectroscopy and ESI-MS experiments. The definitive molecular construction of 1b·CH2Cl2, 2a·H2O, 2b·CH2Cl2 and three was supplied by a single-crystal evaluation and revealed their dimeric nature with an M2O2 planar core. The L1 and L2 ligands coordinate because the dianions in a tetradentate/bridging method in 1b, 2a, 2b and in a tridentate/bridging mode in 3. The NMR spectra confirmed that the strong state of those compounds is actually retained in answer.
Introduction
A very handy methodology for the synthesis of transition steel complexes supported by diaminebis(aryloxido) ligands is thru a metathesis route that always includes important group steel derivatives e.g., Li, Na, Mg, Ca, Al in addition to Zn compounds.6 Though the zinc ion has stuffed d-orbitals however reveals many comparable properties to magnesium together with the same ionic radius, complexes of those two metals are studied collectively. To totally exploit this methodology, it’s essential to establish the construction of beginning supplies. Updated, just a few lithium compounds of the overall method [Li2(ONNO)] with diaminebis(aryloxido) ligands have been absolutely characterised.7 Additionally just a few alkaline earth steel complexes of the tripodal diaminebis(aryloxido) ligands have been reported. For the magnesium complicated the four-coordinate, mononuclear construction is postulated based mostly on the NMR research whereas the dinuclear calcium compound with formally the hexa-coordinate setting round steel ions, each within the strong state and in answer, is properly documented.8 The monomeric nature within the strong state of the zinc complexes having a four- or five-coordinate setting (relying on solvent coordination) has been established for both [Me2NCH2CH2N(CH2-2,4-tBu2-C6H2O)2]2− or [Me2NCH2CH2N(CH2-2-tBu-4-Me-C6H3O)2]2− ligands.9 Nevertheless, the asymmetrical tripodal diaminebis(aryloxido) ligands, [(C5H5N)CH2CH2N{(CH2-2-tBu-4-Me-C6H2O)(CH2-C6H4O)}]2− and [(C5H5N)CH2CH2N{(CH2-2-tBu-4-OMe-C6H2O)(CH2-C6H4O)}]2−, generate dimeric zinc complexes containing a five-coordinate setting round every steel centre.5b,e In distinction, solely monomeric aluminium complexes have been revealed which relying upon the steric properties of the phenoxy substituents and steric hindrance on the amine side-chain have totally different coordination geometries within the strong state both (distorted) trigonal bipyramidal or sq. planar.10 Along with having numerous, fascinating structural motifs, among the Li, Mg, Zn and Al compounds based mostly on the diaminebis(aryloxido) ligands have additionally been proven to be environment friendly initiators for the ring-opening polymerization (ROP) of cyclic esters akin to lactide and ε-lactone.8,10,11
Following our just lately reported work on the tripodal diaminebis(aryloxido) ligands proven in Fig. 1, which generate declinable lithium constructions in comparison with their ortho and para substituted derivatives,7d we determined to look at how a scarcity of the substituent within the ortho-position on two phenoxo rings influences the constructions of associated Mg, Zn and Al complexes within the strong state and in answer.
Herein, we report the synthesis and structural characterization of latest Mg, Zn and Al complexes based mostly on the ligand precursors offered in Fig. 1.
Outcomes and dialogue
Key reactions to generate magnesium, zinc and aluminium sequence based mostly on the L1 and L2 ligands are proven in Scheme 1 and are based mostly on the σ-bond metathesis response between the ligand precursors and acceptable homoleptic steel alkyls. Complexes [M2(μ-L-κ4O,N,N,O)2] (M = Mg, 1a for L1 and 1b for L2; M = Zn, 2a for L1 and 2b for L2) and [Al2(μ-L-κ3O,N,N,O)2Et2] (3 for L1), have been synthesized by the easy reactions of MgnBu2, ZnEt2 and AlEt3, respectively, with the ligand precursors H22L11 or H22L22 in thf or n-hexane. Sadly, makes an attempt to isolate a chemically pure aluminium compound with an L2 ligand failed.
Compounds 1a–3 have been absolutely characterised by analytical and spectroscopic strategies. The ESI-MS spectrometry was recorded as consultant for characterization. The molecular ion peaks appeared at m/z: 1093.8 [1a + H]+, 701.4 [1b + H]+, 1173.7 [2a + H]+, 781.2 [2b + H]+, 1157.9 [3 + H]+. For 1b, 2a, 2b and three, X-ray single-crystal diffraction research have been important to unveil the nuclearity within the strong state.
As illustrated in Fig. 3–5, complexes 1b·CH2Cl2, 2a·H2O, 2b·CH2Cl2 and three have a dimeric character with an M2O2 planar core. The L1 and L2 ligands coordinate because the dianions (all of the hydroxyl teams are deprotonated) in a tetradentate/bridging method in 1b·CH2Cl2, 2a·H2O and 2b·CH2Cl2, particularly via two aryloxide oxygen atoms and two nitrogen atoms of the diamine group. Nevertheless, within the case of three a tridentate/bridging mode of the L1 ligand, via two aryloxide oxygen atoms and the tripodal nitrogen atom of the diamine group, is revealed. The steel centres in every complicated undertake the five-coordinate geometry with the τ values of 0.35 for Mg1 and 0.61 for Mg2 in 1b; 0.56 for Zn1 and Zn2 in 2a; 0.35 for Zn1 and 0.62 for Zn2 in 2b; 0.69 for each Al atoms in 3. On the premise of the τ values the coordination geometry across the steel centres in these compounds lies between a daily sq. pyramid (sqp) and a daily trigonal bipyramid (tbp).12 However, the values of the O–M–N, O–M–O and N–M–N angles seem extra acceptable for the tbp geometry and the geometry adopted by steel atoms will be accepted as a distorted trigonal bipyramid. In all constructions the bridging aryloxide oxygen and the tripodal nitrogen of the L ligand coordinate within the axial positions whereas the rest certain donor atoms are located within the equatorial websites.
The molecular constructions of 1b·CH2Cl2 and 2b·CH2Cl2 with chosen bond lengths and angles are proven in Fig. 3. The terminal Mg–O bond lengths of 1.916(2) and 1.925(2) Å fall within the common vary, and are as anticipated considerably shorter than the bridging Mg–μ-O distances of 1.995 Å (av.).13 Nevertheless, whereas the three of the Mg–μ-O bond lengths are very comparable [1.997(2), 2.005(2) and 2.006(2) Å], the fourth one (Mg2–O21) is considerably shorter by 0.03 Å. Moreover, the values of the Mg–N distances are statistically comparable (inside 3σ vary) though the tripodal nitrogen atom and that of the pendant arm within the L ligands differ of their digital properties and in consequence, within the donor talents. Nevertheless, the similarity within the M–N distances in 1b·CH2Cl2 isn’t uncommon and has been noticed within the associated five-coordinate zinc and cobalt complexes5a,b,e,9 in addition to within the monomeric six-coordinate vanadium(V) compounds.3 The identical pattern in bond parameters applies to 2b·CH2Cl2 (Fig. 3), which is nearly isostructural to 1b·CH2Cl2 and a direct comparability of the M–O and M–N distances and angles is feasible for the central N4M2O4 skeletons. It’s price noting that the M–O(terminal) bond lengths [Zn–O, 1.928(1) and 1.934(1) Å] are intently matched in these two molecules based on comparable ionic radii of Mg2+ and Zn2+, although the Zn–N distances are considerably shorter by 0.05 Å. Nevertheless the Zn–μ-O distances are notably longer by 0.03 Å than the corresponding Mg–μ-O distances in 1b·CH2Cl2, partly, it should be a mirrored image of the totally different M⋯M separation [Mg⋯Mg, 3.063(1) Å; Zn⋯Zn, 3.159(1) Å]. To our information, complicated 1b·CH2Cl2 is the primary crystallographically characterised instance of a magnesium compound bearing the diaminebis(aryloxido) ligand.
In distinction to 1b·CH2Cl2 and 2b·CH2Cl2, compound 2a crystallizes with H2O as a solvate molecule (Fig. 4). Solvating character of H2O in 2a·H2O was confirmed by profitable refinements of two hydrogen bonds O1–H11⋯O11 and O1–H12⋯O22 implicated by the distances of two.960(3) and a couple of.853(3) Å with the angles of 162 and 177°, respectively, which are near linear (180°). It’s clearly noticeable within the construction of 2a·H2O that the presence of the hydrogen bond interplay performs an necessary function within the variations between the 2 moieties of the dimer. In distinction to 1b·CH2Cl2 and 2b·CH2Cl2, each Zn atoms in 2a·H2O have equivalent τ values and in consequence the identical distortion from very best tbp geometry. The Zn–O(terminal) bond lengths of 1.941(2) and 1.947(2) Å are barely longer than the corresponding distances in 2b·CH2Cl2 on account of participation of O11 and O22 within the H-bonding with the H2O molecule. Nevertheless, neither of those distances fall exterior the vary of the Zn–O distances noticed in different five-coordinate aryloxide Zn(II) complexes [1.931–1.961 Å].5a,b,e,9,14 The bridge between Zn1 and Zn2 atoms shaped by two oxygen atoms of the L1 ligand in 2a·H2O is uneven, (Zn1–O12) 2.001(2) Å and (Zn1–O21) 2.057(2) Å and the 2 zinc(II) centres are separated by 3.160(1) Å. Curiously, the Zn–N(tripodal) distances of two.201(2) and a couple of.180(2) Å are considerably longer than the Zn–N(dimethyl sidearm) [2.145(2) and 2.143(2) Å] however similar to these in 2b·CH2Cl2.
It’s worthwhile underlining that the diaminebis(aryloxido) ligand having tert-butyl substituents in each ortho and para positions on two phenoxo rings creates monomeric four-coordinate magnesium and zinc complexes.8 The only-crystal evaluation of Zn derivatives confirmed to have a distorted trigonal-bipyramidal association across the zinc centre shaped by the donor atoms of the [Me2NCH2CH2N(CH2-2,4-tBu2-C6H2O)2]2− ligand.9 This four-coordinate Zn complicated after coordination with the tetrahydrofuran molecule varieties a five-coordinate trigonal-bipyramidal complicated.6b Nevertheless, the much less cumbersome [(C5H5N)CH2CH2N{(CH2-2-tBu-4-R-C6H2O)(CH2-C6H4O)}]2− (R = Me, OMe) ligands containing one unsubstituted phenoxo ring and the second with ortho and para substituent teams generate the dimeric zinc complexes during which the unsubstituted phenolate oxygen supplies bridging coordination and the geometry across the two Zn ions is distorted trigonal bipyramid like in compounds 1a–2b.5e
The molecular construction of [Al2(μ-L-κ3O,N,N,O)2Et2] (3) with chosen bond lengths and angles is proven in Fig. 5. The Al–O bond lengths vary from 1.766(2) to 1.995(2) Å, as anticipated the bridging is longer than the terminal, and are much like these present in different constructions of the five-coordinate aluminium aryloxides.10,15 The Al–C distances of 1.976(3) and 1.960(3) Å are appropriate with these discovered within the organoaluminium aryloxides.10b,15a,b,d–f,h,16 The Al–N bond lengths of two.118(3) and a couple of.131(3) Å are much like the Al–N(tripodal) distances [2.1083(13) and 2.153(2) Å] for monomeric, five-coordinate complexes [Al(L-κ4O,N,N,O)(OiPr)] [L = {Me2NCH2CH2N(CH2-2-tBu-4-OMe-C6H2O)2}2− or {Me2NCH2CH2N(CH2-2-tBu-4-Br-C6H2O)2}2−] and markedly shorter than the corresponding distances discovered for [Al(L-κ4O,N,N,O)X] [L = Me2NCH2CH2N(CH2-2,4-tBu2-C6H2O)2}2−; X = Me, OBn] [2.2150(16) and 2.186(4) Å].10a,b For comparability, the Al–N(tripodal) distances within the alkoxide bridged dimer [Al2(μ-L-κ4O,O,N,O)2] [L = {OCH2CH2N(CH2-2,4-Me2-C6H2O)2}3−] [2.094(1) and 2.066(1) Å] are shorter than the corresponding distances in 3.14 Notably noteworthy within the construction of three is the non-coordination mode of the nitrogen sidearm. Advanced 3 as a dimer is the primary instance amongst aluminium complexes bearing the diaminebis(aryloxido) ligands. In distinction to three, the diaminebis(aryloxido) ligands having the tert-butyl substituents in each ortho and para or the tert-butyl in ortho and the methyl in para positions of the phenoxo teams with the identical CH2CH2NMe2 in addition to the totally different amine side-chains of the ligand included CH2CH2NEt2 or pyridine create solely monomeric aluminium complexes having the trigonal-bipyramidal or square-pyramidal geometry across the steel heart.10
The query of whether or not 1b, 2a, 2b and three which, by X-ray crystallography, are dimeric with five-coordinate steel centres within the strong state, stay dimeric or cleave into four- (1b, 2a, 2b) or five-coordinate (within the case of three) monomers in answer was addressed via variable-temperature (VT) 1H NMR measurements. In response to the X-ray constructions, the C1-symmetric 1b, 2a, 2b and three ought to have 4 indicators for the methylene protons of the ArCH2N– models at room temperature. Thus, the NMR spin system of ArCH2N– for 1b, 2a, 2b and three shall be AB because of their symmetry. In reality, at room temperature the proton spectra of 1b, 2a, 2b in CDCl3 and three in C6D5CD3 exhibit 4 sharp doublets for the protons of the ArCH2N– unit (δ 4.34, 4.06, 2.86, 2.65 for 1b; 4.47, 4.28, 3.03, 2.74 for 2a; 4.57, 4.42, 3.92, 3.08 for 3; 2J = 11.8–13.8 Hz). Additionally 4 multiplets for the methylene protons of the –NCH2CH2N– group (δ 3.78, 3.09, 2.92, 2.43 for 1b; 3.11, 2.89, 2.19, 2.11 for 2a) mirror the NMR spin system AA′BB′ for 1b, 2a and 2b. The identical sample of resonances seems for 1a indicating an identical construction to 1b. Nevertheless, within the case of three, the –NCH2CH2N– group demonstrates one multiplet and one triplet in accordance with the strong state construction. Likewise, double indicators for the remainder of the protons of the L1 and CH3CH2 ligands are noticed besides the magnetically equal methyl protons of the sidearm NMe2 in 3 (δ 1.77 ppm, equally as within the ligand precursor H22L11δ 1.99 ppm). Moreover, the VT 1H NMR evaluation of 1a–3 doesn’t present any vital variations (in CDCl3 or C6D5CD3 from 233 Ok to 313 Ok), suggesting that the strong state of those compounds is actually retained in answer throughout the temperature vary studied.
In conclusion, a household of the diaminebis(aryloxido) magnesium, zinc and aluminium complexes 1a–3 of the tetradentate dianionic (ONNO) ligands, comprising totally different substituents at a place para to the phenolic oxygen atom, C(CH3)2CH2C(CH3)3 in L1 and CH3 in L2 have been ready in good yields. Their constructions have been characterised in answer by NMR spectroscopy and within the strong state by X-ray dedication apart from 1a permitting us to seek out that these substituents don’t trigger a outstanding change within the steel coordination geometry. The molecular constructions of 1b·CH2Cl2, 2a·H2O, 2b·CH2Cl2 and three revealed that the dearth of a substituent on the ortho place to the phenolic oxygen atom within the ligands L1 and L2 resulted within the creation of distinctly totally different coordination geometry round steel centres than their analogues containing each ortho and para substituents, reported within the literature. Moreover, the NMR research confirmed that the strong states of the described compounds are primarily retained in answer.
The information of the constructions of the diaminebis(aryloxido) magnesium and zinc complexes described right here allowed us to discover the artificial methodology for the preparation of heterometallic vanadium complexes, that are presently underway in our laboratory. Moreover, such well-defined complexes which stay of their strong state construction additionally in answer can be utilized because the potential initiators for the ROP of cyclic esters.
Experimental part
Basic remarks
Synthesis of [Mg2(μ-L1-κ4O,N,N,O)2] (1a)
Synthesis of [Mg2(μ-L2-κ4O,N,N,O)2]·CH2Cl2 (1b·CH2Cl2)
Synthesis of [Zn2(μ-L1-κ4O,N,N,O)2]·H2O (2a·H2O)
Synthesis of [Zn2(μ-L2-κ4O,N,N,O)2]·CH2Cl2 (2b·CH2Cl2)
Synthesis of [Al2(μ-L1-κ3O,N,N,O)2Et2] (3)
X-Ray crystallography
CCDC reference numbers: 932554 for H22L11, 874666 for 1b, 876629 for 2a, 874667 for 2b, 876628 for 3.
Acknowledgements
References – “j lorber magnesium”