Phosphazene-Functionalized Cyclopentadienyl and Its Derivatives Ligated Rare-Earth Metal Alkyl Complexes: Synthesis, Structures, and Catalysis on Ethylene Polymerization

Abstract

Treatment of Ln(CH2SiMe3)3(thf)2 (Ln = Sc, Y, and Lu) with 1 equiv of CpPN-type ligands C5H4PPh2–NH–C6H3R2 (R = Me, L1(Me); R = i Pr, L1( i Pr)) at room temperature readily generated the corresponding CpPN-type bis(alkyl) complexes 1 and 2a–2c. Addition of 3 equiv of LiCH2SiMe3 to a mixture of L1( i Pr) and LnCl3(thf)2 (Ln = Sm and Nd) also afforded the CpPN-type bis(alkyl) complexes 2d and 2e. The Cp moiety bonds to the central metal in a classical η5 mode in all CpPN-type complexes 1 and 2. In contrast, the CpMePN-type ligands C5Me4H–PPh2N–C6H3R2 (R = Me, L2(Me); R = i Pr, L2( i Pr)) behaved differently. L2(Me) did not react with Sc(CH2SiMe3)3(thf)2. Similarly, L2( i Pr) was also inert to Sc(CH2SiMe3)3(thf)2 even at 50 °C. When the central metal was changed to yttrium, however, the equimolar reaction between Y(CH2SiMe3)3(thf)2 and L2( i Pr) in the presence of LiCl afforded two bis(alkyl) complexes 3a and 3b. In the main product 3a, [C5HMe3(η3-CH2)–PPh2N–C6H3 i Pr2]Y(CH2SiMe3)2(thf), the ligand bonds to the Y3+ ion in a rare η3-allyl/κ-N mode, whereas in 3b, (C5Me4–PPh2N–C6H3 i Pr2)Y(CH2SiMe3)2(LiCl)(thf), the Cp ring coordinates to the Y3+ ion in an η5 mode, and a LiCl unit is located between the Y3+ ion and the nitrogen atom. When the central metal was changed to lutetium, a bis(alkyl) complex 4a, [C5HMe3(η3-CH2)–PPh2N–C6H3 i Pr2]Lu(CH2SiMe3)2(thf), and a bis(alkyl) complex 4b, (C5Me4–PPh2N–C6H3 i Pr2)Lu(CH2SiMe3)2, were isolated. The protonolysis reaction of the IndPN-type ligands C9H7–PPh2N–C6H3R2 (R = Me, L3(Me); R = Et, L3(Et); R = i Pr, L3( i Pr)) with Ln(CH2SiMe3)3(thf)2 (Ln = Sc, Y, and Lu) generated the IndPN-type bis(alkyl) complexes 5a–5c, 6, and 7a–7c, selectively, where the Ind moiety tends to adopt an η3-bonding fashion. The more bulky FluPN-type ligands C13H9–PPh2N–C6H4R (R = H, L4(H); R = Me, L4(Me)) were treated with Ln(CH2SiMe3)3(thf)2 (Ln = Sc and Lu) to afford the FluPN-type bis(alkyl) complexes 8 and 9a and 9b, where the Flu moiety has a rare η1-bonding mode. Complexes 1–9 were fully characterized by 1H, 13C, and 31P NMR; X-ray; and elemental analyses. Upon activation with AlR3 and [Ph3C][B(C6F5)4], the scandium complexes showed good to high catalytic activity for ethylene polymerization. The effects of the sterics and electronics of the ligand, the loading and the type of AlR3, the polymerization temperature, and the polymerization time on the catalytic activity were also discussed.

Rare‐Earth‐Metal Alkylaluminates Supported by N‐Donor‐Functionalized Cyclopentadienyl Ligands: CH Bond Activation and Performance in Isoprene Polymerization

“…described heteroscorpionate‐supported scandium and yttrium complexes (Scheme , B )9 and Hou and co‐workers reported the methylene‐bridged binuclear complex [({C 5 Me 4 C 6 H 4 NMe(μ ‐ CH 2 )}Sc(CH 2 SiMe 3 )) 2 ] (Scheme , C ) 4a. More recently, pyridyl‐methylene‐ and phosphazene‐functionalized cyclopentadienyl complexes were exploited by Cui and co‐workers10 and Sundermeyer and co‐workers11 for the polymerization of styrene and ethylene (Scheme , D and E ), respectively. Anilinyl‐ (Scheme , C ) and pyridinyl‐functionalized cyclopentadienyl ligands were also recently applied to the synthesis of half‐sandwich bis(allyl) complexes 12…”

Tetrahydropentalenyl-phosphazene constrained geometry complexes of rare-earth metal alkyls

“…Recently, we also observed only one tautomer in C 5 Me 4 HPR 2 NC 6 H 3 R′ 2 (R = Me, R′ = iPr; R = Ph, R′ = Me, iPr) at thermodynamic equilibrium. 18 The resonance of the NH-proton in L Ad H at δ H = 2.05 ppm appears as a doublet ( 2 J HP = 5.0 Hz). It does not correlate with any carbon atom in the molecule according to the HMQC correlation spectrum.…”

“…Despite the sterically demanding Cp-moiety 1 Ad -3 Ad , 2 Dip and 3 Dip reveal that the Cp ring coordinates to the metal centre in a typical η 5 mode, while IndPN adopt an η 3 -bonding fashion and the more bulky FluPN-type ligands have a rare η 1 -bonding mode. 18 In the solid state, all complexes adopt mononuclear structures, in which the metal atoms reveal a pseudo-tetrahedral coordination by the η 5 -bonded C5-ring and the nitrogen atom of the CpPN-ligand together with two σbonded alkyl groups. The pseudo-tetrahedral environment around the metal centre can be shown by comparison of the C CH2SiMe3 -M-N1, C CH2SiMe3 -M-N1, C CH2SiMe3 -M-C CH2SiMe3 bond angles, which are all very close to 109°.…”

“…There are also some complexes bearing monoanionic ligands which are isoelectronically related to the classical dianionic CpSiN ligand system such as CpSiNP (D), 13 CpSiNIm (E) 14 and the cyclopentadienyl-phosphazenes (CpPN) (F) that is the focus of our current investigation. [15][16][17][18][19] Previously we reported a general and convenient synthetic protocol for a large variety of CpPN type ligands, 20 and their use in the stabilization of highly reactive alkyls of rare-earth and group 4 metals has been claimed. 21 Independently, related fluorenyl-and indenyl-phosphazene ligands (FluPN and IndPN) and their rhodium 22 and zirconium 23 complexes were presented by Bourissou and co-workers.…”

“…CpPN ligands, with less steric bulkiness of the Cp-ring, lead to the coordination of THF, while IndPN adopt a η 3 -bonding fashion and the more bulky FluPN-type ligands display a η 1 -bonding mode. 18 Moreover, the reactivity toward various substrates was recently studied and, among others, CpPN amidinate, hydride and terminal imido complexes were synthesized, characterized and their reactivity was probed. 19 These current developments reveal that CpPN type complexes appear to be a promising class of catalysts.…”