Yttrium and Lithium Complexes with Diamidophosphane Ligand Bearing 2,1,3-Benzothiazolyl Substituent: Polydentate Complexation and Reversible NH–PH Tautomery

Deprotonation of a bis(amino)phosphane H2L = PhP(HNBtd)2 bearing a heterocyclic Btd = 2,1,3-benzothiadiazol-4-yl substituents at nitrogen atoms by silylamides LiNTms2 and Y(NTms2)3 (Tms = trimethylsilylamide) results in lithium and yttrium complexes with the deprotonated HL– and L2– forms as κ2-N and κ4-N chelating ligands. A binuclear complex [LiHL]2 was crystallized from Et2O, and was shown to reversibly dissociate in thf (tetrahydrofuran) with the NH(soln)–PH(crystal) tautomeric shift; the compound [Li2L] was spectroscopically characterized. Yttrium readily forms stable bis-ligand complexes [YL2]– and [YL(HL)]. In the latter, the H atom in HL resides on phosphorus; the coordination sphere remains accessible to another ligands, and it was crystallized as [{YL(HL)}2(µ-dioxane)] species (YN8O coordination). In the former complex, the coordination sphere was saturated (YN8) by closer bound ligands; it was crystallized as a salt with [Li(thf)4]+. The monoligand complex could not be cleanly obtained in a 1:1 reaction of H2L and Y(NTms2)3, and was only crystallographically characterized as a dimer [YL(NTms)2]2. Partial oxidation of the central P atom with the formation of phosphine-oxide ligands PhP(O)(NBtd)2– was observed. They co-crystallize in the same position as non-oxidized ligands in [YL2]– and [YL(NTms2)]2 species and participate in bonding between two units in the latter. TD-DFT calculations reveal that main transitions in the visible region of electronic spectra correspond to the charge transfer bands mostly associated with the orbitals located on Btd fragments.

Scandium calix[n]arenes (n = 4, 6, 8): structural, cytotoxicity and ring opening polymerization studies

Interaction of [Sc(OR)3] (R = iPr or triflate) with p-tert-butylcalix[n]arenes, where n = 4, 6, or 8, affords a number of intriguing structural motifs, which are relatively non-toxic (cytotoxicity evaluated against cell lines HCT116 and HT-29) and a number were capable of the ring opening polymerization (ROP) of cyclohexene oxide.

Constrained geometry scandium permethylindenyl complexes for the ring-opening polymerisation of l- and rac-lactide

The synthesis and characterisation of constrained geometry scandium permethylindenyl chloride, aryloxide and borohydride complexes ^Me₂SB(^tBuN,I*)Sc(Cl)(THF) (1), ^Me₂SB(^tBuN,I*)Sc(O-2,6-ⁱPr-C₆H₃)(THF) (2), ^Me₂SB(^tBuN,I*)Sc(O-2,4-^tBu-C₆H₃)(THF) (3) and ^Me₂SB(^tBuN,I*)Sc(BH₄)(THF) (4) are reported. The activity of complexes 1-4 as initiators for the ring-opening polymerisation (ROP) of l- and rac-lactide is presented. The ROP of l- and rac-lactide using complexes 2 and 3 show first-order dependence on monomer concentration, and produced isotactic polylactide (PLA) and moderately heterotactic PLA (P_r = 0.68-0.72), respectively. Good agreement between experimental and theoretical molecular weights of PLA (M_n) and relatively narrow dispersities (M_w/M_n < 1.20) were obtained. Complex 4 showed higher activity for ROP of l- and rac-lactide than 2 or 3, with second-order dependence on monomer concentrations. However, poorly controlled molecular weights and lower heteroselectivity (P_r = 0.61-0.67) were observed. The effect of temperature and catalyst concentration for the ROP of l-lactide using 2 and 3 was also studied.

Heterobimetallic Ba/Li and Ca/Li amides and diphenylmethanide

Rare examples of stable heterobimetallic Ca/Li and Ba/Li amido polymeric species, as well as an ate Ca/Li diphenylmethanide compound stable in ethers, have been structurally characterised. Intra- and intermolecular metal⋯H–Si interactions are shown to play a key role.

A monoanionic NNNN-type macrocyclic ligand for electropositive metal centers

The coordination of a mono(amido) triamine macrocyclic ligand Me₃TACD derived from cyclen (1,4,7,10-tetraazacyclododecane or [12]aneN₄) toward electropositive metal centers is surveyed. This NNNN-type monoanionic macrocyclic ligand is capable of stabilizing a variety of metal coordination environments that are commonly not amenable to stable coordination spheres. Metal complexes supported by Me₃TACD include hydrides, hydrocarbyls, silyls, and amides. Protection of one hemisphere of a large metal center allows, as in the case of metallocene scaffolds for early transition metals, deaggregation and control of reactivity.

Facile ring-opening of THF at a lithium center induced by a pendant Si-H bond and BPh3

The macrocyclic polyamine 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane [LH = (Me₃TACD)H] formed adducts with tetramethyl-silazides [M{N(SiHMe₂)₂}] (M = Li, Na, K) of light alkali metals. Upon heating, intramolecular dehydrocoupling occurred to give [M{(L)SiMe₂N(SiHMe₂)}]. BPh₃ induced facile ring-opening of THF when reacted with [Li{(L)SiMe₂N(SiHMe₂)}].

Unexpected alkane elimination from cationic group 13 dialkyls in a reaction with a macrocyclic polyamine

A macrocyclic polyamine 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane, (Me₃TACD)H formed thermally stable adducts with MR₃ (M = Al, In) but released RH from reactions with [MR₂]⁺.

Synthesis and characterization of dinuclear rare-earth complexes supported by amine-bridged bis(phenolate) ligands and their catalytic activity for the ring-opening polymerization of l-lactide

Reactions of amine-bridged bis(phenolate) protio-ligands N,N-bis(3,5-di-tert-butyl-2-hydroxybenzyl)aminoacetic acid (L(1)-H3) and N,N-bis[3,5-bis(α,α'-dimethylbenzyl)-2-hydroxybenzyl]aminoacetic acid (L(2)-H3), with 1 equiv. M[N(SiMe3)2]3 (M = La, Nd, Sm, Gd, Y) in THF at room temperature yielded the neutral rare-earth complexes [M2(L)2(THF)4] (L = L(1), M = La (), Nd (), Sm (), Gd (), Y (); L = L(2), M = La (), Nd (), Sm (), Gd (), Y ()). All of these complexes were characterized by single-crystal X-ray diffraction, elemental analysis and in the case of yttrium and lanthanum complexes, (1)H NMR spectroscopy. The molecular structure of revealed dinuclear species in which the eight-coordinate lanthanum centers were bonded to two oxygen atoms of two THF molecules, to three oxygen atoms and one nitrogen atom of one L(1) ligand, and two oxygen atoms of the carboxyl group of another. Complexes were also dinuclear species containing seven-coordinate metal centers similar to , albeit with bonding to one rather than two carboxyl group oxygens of another ligand. Further treatment of with excess benzyl alcohol provided dinuclear complex [La2(L(1))2(BnOH)6] (), in which each lanthanum ion is eight-coordinate, bonded to three oxygen atoms and one nitrogen atom of one ligand, three oxygen atoms of three BnOH molecules, as well as one oxygen atom of bridging carboxyl group of the other ligand. In the presence of BnOH, complexes efficiently catalyzed the ring-opening polymerization of l-lactide in a controlled manner and gave polymers with relatively narrow molecular weight distributions. The kinetic and mechanistic studies associated with the ROP of l-lactide using /BnOH initiating system have been performed.

Distortion Pathways of Transition Metal Coordination Polyhedra Induced by Chelating Topology

A continuous shape measures analysis of the coordination polyhedra of a host of transition metal complexes with bi- and multidentate ligands discloses the distortion pathway associated with each particular topology of the chelate rings formed. The basic parameter that controls the degree of distortion is the metal-donor atom bond distance that induces nonideal bond angles due to the rigidity of the ligands. Thus, the degree of distortion within each family of complexes depends on the atomic size, on which the high- or low-spin state has a large effect. Special attention is therefore paid to several spin-crossover systems and to the enhanced distortions that go along with the transition from low- to high-spin state affected by temperature, light, or pressure. Several families of complexes show deviations from the expected distortion pathways in the high-spin state that can be associated to the onset of intermolecular interactions such as secondary coordination of counterions or solvent molecules. Also, significant displacement of counterions in an extended solid may result from the changes in metal-ligand bond distances when ligands are involved in intermolecular hydrogen bonding.

Synthesis and characterization of group 4 metal alkoxide complexes containing imine based bis-bidentate ligands: effective catalysts for the ring opening polymerization of lactides, epoxides and polymerization of ethylene

A series of group 4 complexes containing imine based bis-bidentate ligands were synthesized and used as catalysts for various polymerizations.

Zwitterionic group 4 aminophenolate catalysts for the polymerization of lactides and ethylene

A series of group 4 metal chloride complexes based on aminophenol ligands were synthesized and characterized by conventional spectroscopic techniques, elemental analysis and X-ray crystallography.

Potassium, zinc, and magnesium complexes of a bulky OOO-tridentate bis(phenolate) ligand: synthesis, structures, and studies of cyclic ester polymerisation

Reaction of the OOO-coordinating tridentate bis(phenolate) protio-ligand 2,2'-{oxybis(methylene)}bis{4,6-di(1-methyl-1-phenylethyl)phenol} (L(O3)-H2), with 1 equiv. of KN(SiMe3)2 in toluene or THF yielded [K(L(O3)-H)] (1) or [K(L(O3)-H)(THF)] (2), respectively. Single-crystal X-ray diffraction studies of 1 and 2 revealed mononuclear structures with the phenyl rings of the bulky ligand displaying stabilising π-interactions to the potassium centre. L(O3)-H2 also reacts with 1 equiv. of ZnEt2 or Mg(n)Bu2 to give [M2(L(O3))2] (M = Zn (3) or Mg (4)) in good yield. The molecular structures of complex 3 and 4 reveal dinuclear species in which the metal centres are tetra-coordinated to the three oxygen atoms of one L(O3) ligand, and to the bridging oxygen atom of one phenolate group of another. Complexes 1-4 are catalysts for ring-opening polymerisation of ε-caprolactone and L- and rac-lactide in the presence of benzyl alcohol (BnOH) and also other initiators to give the corresponding polyesters. Kinetic studies for the ROP of ε-caprolactone using 3 and BnOH gives an unusual rate expression R(p) = -d[CL]/dt = k(p)[BnOH]0[3]0(0.5) for which a tentative kinetic model is proposed.

Synthesis and characterization of multi-alkali-metal tetraphenolates and application in ring-opening polymerization of lactide

A series of alkali metal complexes supported by two bulky tetraphenols were synthesized and characterized. The reactions of α,α,α',α'-tetra(3,5-di-tert-butyl-2-hydroxyphenyl)-p-xylene(para-tetraphenol) with (n)BuLi, sodium, and KSi(NMe(2))(3) gave bimetallic complexes 1, 2, and 3, respectively. Treatments of the α,α,α',α'-tetra(3,5-di-tert-butyl-2-hydroxyphenyl)-m-xylene(meta-tetraphenol) with 2 or 4 equiv of (n)BuLi afforded complexes 4 or 5, while the reactions of meta-tetraphenol with sodium and KSi(NMe(2))(3) gave only trimetallic complexes 6 and 7 for the additional p-π interaction. Complexes 1-7 were all characterized by single-crystal X-ray diffraction techniques. In the presence of benzyl alcohol, all complexes are active catalysts for the ring-opening polymerization of L-lactide. Comparatively, bimetallic complexes 1, 2, and 3 are more efficient catalysts because of their symmetric structures, in which complex 3 presents as a rare highly active potassium catalyst for the ring-opening polymerization of lactide, leading to polymers with good molecular weight control and narrow molecular weight distributions.