Die Sammlung Simone Collinet. Simone Breton als leidenschaftliche Sammlerin des Surrealismus

A series of highly active yttrium phosphasalen initiators for the heteroselective ring-opening polymerization of <i>rac</i>-lactide are reported. The initiators are yttrium alkoxide complexes ligated by iminophosphorane analogues of the popular “salen” ligand, termed “phosphasalens”. A series of novel phosphasalens have been synthesized, with varying substituents on the phenoxide rings and ethylene, propylene, <i>rac</i>-cyclohexylene, <i>R</i>,<i>R</i>-cyclohexylene, phenylene, and 2,2-dimethylpropylene groups linking the iminophosphorane moieties. Changing the substituents on the phosphasalen ligands results in changes to the rates of polymerization (<i>k</i>_obs) and to the PLA heterotacticity (<i>P</i>_s = 0.87). Generally, the initiators have high rates, excellent polymerization control, and a tolerance to low loadings

η⁵–η¹ Switch in Divalent Phosphaytterbocene Complexes with Neutral Iminophosphoranyl Pincer Ligands: Solid-State Structures and Solution NMR ¹<i>J</i>_Yb–P Coupling Constants

This paper reports the synthesis of a series of complexes based on the bis­(pentamethylcyclopentadienyl)­ytterbium­(II) (<b>1</b>; Cp*₂Yb) and bis­(tetramethylphospholyl)­ytterbium­(II) (<b>2</b>; Tmp₂Yb) fragments bearing an additional neutral bis­(methyliminophosphoranyl)­pyridine ligand (<b>L</b>) on which the steric demand is modulated at the phosphorus position (triethyl, <b>L</b>^<b>Et</b>; triphenyl, <b>L</b>^<b>Ph</b>; tricyclohexyl, <b>L</b>^<b>Cy</b>) to yield the original complexes Cp*₂Yb<b>L</b>^<b>Et</b> (<b>1-L</b>^<b>Et</b>), Cp*₂Yb<b>L</b>^<b>Ph</b> (<b>1-L</b>^<b>Ph</b>), Tmp₂Yb<b>L</b>^<b>Et</b> (<b>2-L</b>^<b>Et</b>), Tmp₂Yb<b>L</b>^<b>Ph</b> (<b>2-L</b>^<b>Ph</b>), and Tmp₂Yb<b>L</b>^<b>Cy</b> (<b>2-L</b>^<b>Cy</b>), while no reaction occurs between <b>1</b> and <b>L</b>^<b>Cy</b>. The crystal structures of these sterically crowded complexes are reported as well as room-temperature NMR data for all the complexes. The solid-state coordination mode of <b>L</b>^<b>R</b> differs depending on the nature of the fragments <b>1</b> and <b>2</b> and on the steric bulk of <b>L</b>^<b>R</b>. The crystal structure of the divalent Tmp₂Yb­(py)₂ (<b>3</b>) is also reported for structural and spectroscopic comparisons. Interestingly, in both <b>2-L</b>^<b>Et</b> and <b>2-L</b>^<b>Cy</b>, one of the two Tmp ligands coordinates in an η¹ rather than in an η⁵ fashion, a relevant coordination mode for the study of sterically induced reductions. The behavior of those complexes in solution varies with the sterics and electronics of the ligands, as demonstrated by variable-temperature NMR experiments. In solution, the ¹<i>J</i>_Yb–P coupling is used to track the coordination mode of the Tmp ligand and a large difference in the ¹<i>J</i>_Yb–P coupling constant allows the distinction between an η⁵ coordination mode and a dynamic η⁵–η¹ switch

Nickel Complexes Featuring Iminophosphorane–Phenoxide Ligands for Catalytic Ethylene Dimerization

A series of bidentate ligands associating an iminophosphorane and a phenoxide were synthesized and coordinated to nickel­(II), leading initially to bimetallic KNi adducts. Replacement of the potassium by another metal allowed the isolation and characterization of bimetallic LiNi and AlNi complexes, while addition of one equivalent of triphenylphosphine gave access to monometallic complexes. The same type of complex was obtained with the coordination of a tridentate ligand incorporating a supplementary amine donor. These paramagnetic complexes were characterized by elemental analysis, and some of them by X-ray diffraction, evidencing a tetrahedral nickel center. They were shown to efficiently catalyze the oligomerization of ethylene in the presence of Et₂AlCl (Al/Ni = 22.5) with TOF up to 72  000 mol­(C₂H₄)/mol­(Ni)/h, giving selectively butene (more than 97%) with at best 93% of 1-C₄

Nickel Complexes Featuring Iminophosphorane–Phenoxide Ligands for Catalytic Ethylene Dimerization

A series of bidentate ligands associating an iminophosphorane and a phenoxide were synthesized and coordinated to nickel­(II), leading initially to bimetallic KNi adducts. Replacement of the potassium by another metal allowed the isolation and characterization of bimetallic LiNi and AlNi complexes, while addition of one equivalent of triphenylphosphine gave access to monometallic complexes. The same type of complex was obtained with the coordination of a tridentate ligand incorporating a supplementary amine donor. These paramagnetic complexes were characterized by elemental analysis, and some of them by X-ray diffraction, evidencing a tetrahedral nickel center. They were shown to efficiently catalyze the oligomerization of ethylene in the presence of Et₂AlCl (Al/Ni = 22.5) with TOF up to 72  000 mol­(C₂H₄)/mol­(Ni)/h, giving selectively butene (more than 97%) with at best 93% of 1-C₄

Phosphasalen Yttrium Complexes: Highly Active and Stereoselective Initiators for Lactide Polymerization

Preparation and characterization of three yttrium alkoxide complexes with new phosphasalen ligands are reported. The phosphasalens are analogues of the well-known salen ligands but with iminophosphorane donors replacing the imine functionality. The three yttrium alkoxide complexes show mono- and dinuclear structures in the solid state, depending on the substituents on the ligand. The new ligands and complexes are characterized using multinuclear NMR spectroscopy, mass spectrometry, elemental analysis, and single-crystal X-ray diffraction experiments. The complexes are all rapid initiators for lactide polymerization; they show excellent polymerization control on addition of exogeneous alcohol. The mononuclear complex shows extremely rapid rates and a high degree of stereocontrol in <i>rac</i>-lactide polymerization, yielding heterotactic PLA (<i>P</i>_s of 0.9). The phosphasalens are, therefore, excellent ligands for lactide ring-opening polymerization catalysis showing superior rates and stereocontrol versus salen ligands, which may be related to their excellent donating ability and the high degrees of steric protection they can confer

Phosphasalen Yttrium Complexes: Highly Active and Stereoselective Initiators for Lactide Polymerization

Preparation and characterization of three yttrium alkoxide complexes with new phosphasalen ligands are reported. The phosphasalens are analogues of the well-known salen ligands but with iminophosphorane donors replacing the imine functionality. The three yttrium alkoxide complexes show mono- and dinuclear structures in the solid state, depending on the substituents on the ligand. The new ligands and complexes are characterized using multinuclear NMR spectroscopy, mass spectrometry, elemental analysis, and single-crystal X-ray diffraction experiments. The complexes are all rapid initiators for lactide polymerization; they show excellent polymerization control on addition of exogeneous alcohol. The mononuclear complex shows extremely rapid rates and a high degree of stereocontrol in <i>rac</i>-lactide polymerization, yielding heterotactic PLA (<i>P</i>_s of 0.9). The phosphasalens are, therefore, excellent ligands for lactide ring-opening polymerization catalysis showing superior rates and stereocontrol versus salen ligands, which may be related to their excellent donating ability and the high degrees of steric protection they can confer

Yttrium Phosphasalen Initiators for <i>rac</i>-Lactide Polymerization: Excellent Rates and High Iso-Selectivities

Highly active yttrium phosphasalen initiators for the stereocontrolled ring-opening polymerization of <i>rac</i>-lactide are reported. The initiators are coordinated by a new class of ancillary ligand: an iminophosphorane derivative of the popular “salen” ligand, termed “phosphasalen”. Changing the phosphasalen structure enables access to high iso-selectivities (<i>P</i>_i = 0.84) or hetero-selectivities (<i>P</i>_s = 0.87). The initiators also show very high rates, excellent polymerization control, and tolerance to low loadings; furthermore, no chiral auxiliaries/ligands are needed for the stereocontrol. The combination of such high rates with high iso-selectivities is very unusual

Yttrium Phosphasalen Initiators for <i>rac</i>-Lactide Polymerization: Excellent Rates and High Iso-Selectivities

Highly active yttrium phosphasalen initiators for the stereocontrolled ring-opening polymerization of <i>rac</i>-lactide are reported. The initiators are coordinated by a new class of ancillary ligand: an iminophosphorane derivative of the popular “salen” ligand, termed “phosphasalen”. Changing the phosphasalen structure enables access to high iso-selectivities (<i>P</i>_i = 0.84) or hetero-selectivities (<i>P</i>_s = 0.87). The initiators also show very high rates, excellent polymerization control, and tolerance to low loadings; furthermore, no chiral auxiliaries/ligands are needed for the stereocontrol. The combination of such high rates with high iso-selectivities is very unusual

Synthesis and Characterization of Bidentate Rare-Earth Iminophosphorane <i>o</i>-Aryl Complexes and Their Behavior As Catalysts for the Polymerization of 1,3-Butadiene

<i>O</i>-Aryllithium complexes are easily prepared from stable aminophosphonium salts, and their coordination to rare-earth metals was studied. The ligand to metal ratio in the formed complexes was shown to depend exclusively on the substituent on the nitrogen atom of the ligand. Aryllithium derivatives <b>3a</b> and <b>3b</b>, exhibiting bulky groups (SiMe₃ and ^<i>t</i>Bu, respectively), gave monocoordinated yttrium complexes <b>4a-</b>Y and <b>4b-</b>Y. On the other hand, with aryllithium <b>3a</b>, possessing an <i></i>isopropyl at nitrogen, complexes of Y^III, Nd^III, and Gd^III with a 2:1 ligand to metal ratio could be obtained. Finally with less hindered ligands such as <b>6c</b>, featuring an <i>n</i>-butyl substituent, triscoordinated Y, Nd, and La complexes were accessible. X-ray crystal structures have been obtained with all three stoichiometries. These complexes were employed as catalyst precursors for 1,3-butadiene polymerization using various activators. Yttrium complexes were found ineffective, but some neodymium complexes achieved highly selective polymerization of 1,3-butadiene, giving up to 95% of 1,4-<i>cis</i>-polybutadiene albeit with mild activity