Treatment of Ln(CH2SiMe3)3(thf)2 (Ln = Sc, Y, and Lu) with 1 equiv of CpPN-type ligands C5H4PPh2–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–PPh2N–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)–PPh2N–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–PPh2N–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)–PPh2N–C6H3 i Pr2]Lu(CH2SiMe3)2(thf), and a bis(alkyl) complex 4b, (C5Me4–PPh2N–C6H3 i Pr2)Lu(CH2SiMe3)2, were isolated. The protonolysis reaction of the IndPN-type ligands C9H7–PPh2N–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–PPh2N–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.
Synthesis of the first series of rare-earth-metal constrained geometry complexes containing the P-(1-adamantylamino)-P-dimethyl-tetramethyl-cyclopentadienylidene-phosphorane ligand C5Me4PMe2NHAd, {Cp#PN}H, was accomplished. This monoanionic chelate ligand is isoelectronically related to the classical dianionic cyclopentadienyl-silylamine ligand C5Me4HSiMe2NHtBu, {Cp # SiN}H2. The ligand stabilizes dialkyls [{Cp#PN}M(CH2SiMe3)2] (M = Sc, 1; Lu, 2; Y, 3; Sm, 4; Nd, 5; Pr, 6; Ce, 7) over the full range of group 3 and lanthanide cation radii. Results of NMR studies of these crystalline alkyls, XRD molecular structures, and a preliminary study revealing the high catalytic activity of complexes 3–6 in the intramolecular hydroamination/cyclization are reported. The catalytic experiments reveal a trend in activity Lu < Y < Sm < Nd ≤ Pr resembling the trend in rare-earth-metal radii. Interestingly they reveal a distinctive substrate-dependent first-order kinetic profile for all metals investigated. The reaction of the precatalyst 3 with 1.6 equiv of the standard substrate 2,2-dimethylpenten-4-ylamine leads to a fast and selective formation of substrate complex [{Cp#PN}Y(NHCH2CMe2CH2CHCH2)2] (8). Fast cyclization was observed only after addition of more than 2 equiv of amine substrate. A noninsertive mechanism involving a six-membered transition state by a concerted C–N bond formation and N–H bond cleavage at a 3:1 substrate to complex ratio is suggested on the basis of these findings.
The reaction of the yttrium dialkyls (C 5 H 4 − PPh 2 N−C 6 H 3 i Pr 2 )Y(CH 2 SiMe 3 ) 2 (thf) (1) with an excess of N,N′-diisopropylcarbodiimide gave the yttrium monoalkyl complex (C 5 H 4 −PPh 2 N−C 6 H 3 i Pr 2 )Y(CH 2 SiMe 3 )[ i PrN C(CH 2 SiMe 3 )−N i Pr] (2). 2 subsequently reacted with 1 equiv of PhSiH 3 to generate the CpPN/amidinate heteroleptic yttrium hydride {(C 5 H 4 −PPh 2 N−C 6 H 3 i Pr 2 )Y[ i PrNC-(CH 2 SiMe 3 )−N i Pr](μ-H)} 2 (3). Hydride 3 showed good reactivity toward various substrates containing unsaturated C− C, C−N, and N−N bonds, such as azobenzene, p-tolyacetylene, 1,4-bis(trimethylsilyl)-1,3-butanediyne, N,N′-diisopropylcarbodiimide, and 4-dimethylaminopyridine, affording the yttrium hydrazide complex 4 with a rare η 2 -Cp bonding mode, yttrium terminal alkynyl complex 5, yttrium η 3 -propargyl complex 6, yttrium amidinate complex 7, and yttrium 2-hydro-4dimethylaminopyridyl product 8, respectively.
Reactions of Cp™HPPh2 (1, diphenyl(4,4,6,6-tetramethyl-1,4,5,6-tetrahydropentalen-2-yl)phosphane) with the organic azides AdN3 and DipN3 (Ad = 1-adamantyl; Dip = 2,6-di-iso-propylphenyl) led to the formation of two novel CpPN ligands: P-amino-cyclopentadienylidene-phosphorane (Cp™PPh2NHAd; L(Ad)H) and P-cyclopentadienyl-iminophosphorane (Cp™HPPh2NDip; L(Dip)H). Both were characterized by NMR spectroscopy and X-ray structure analysis. For both compounds only one isomer was observed. Neither possesses any detectable prototropic or elementotropic isomers. Reactions of these ligands with [Lu(CH2SiMe3)3(thf)2] or with rare-earth metal halides and three equivalents of LiCH2SiMe3 produced the desired bis(alkyl) Cp™PN complexes: [{Cp™PN}M(CH2SiMe3)2] (M = Sc (1(Ad), 1(Dip)), Lu (2(Ad), 2(Dip)), Y (3(Ad), 3(Dip)), Sm (4(Ad)), Nd (5(Ad)), Pr (6(Ad)), Yb (7(Ad))). These complexes were characterized by extensive NMR studies for the diamagnetic and the paramagnetic complexes with full signal assignment. An almost mirror inverted order of the paramagnetic shifts has been observed for ytterbium complex 7(Ad) compared to 4(Ad), 5(Ad) and 6(Ad). For the assignment of the NMR signals [{η(1) : η(5)-C5Me4PMe2NAd}Yb(CH2SiMe3)2] 7 was synthesized, characterized and the (1)H NMR signals were compared to 7(Ad) and to other paramagnetic lanthanide complexes with the same ligand. 1(Ad), 2(Ad), 2(Dip), 3(Ad) and 3(Dip) were characterized by X-ray structure analysis revealing a sterically congested constrained geometry structure.
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