Enforced η¹-Fluorenyl and Indenyl Coordination to Zirconium: Geometrically Constrained and Sterically Expanded Complexes Derived from the Bifunctional (FluPPh₂NAr)⁻ and (IndPPh₂NAr)⁻ Ligands

Abstract

The (FluPPh2NAr) and (IndPPh2NAr) ligands 2a–c and 4a–c (a, Ar = Ph; b, R = DIPP; c, = Mes) were readily prepared by Staudinger reactions between aryl azides and Flu/Ind diphenylphosphines, and they were coordinated to zirconium via toluene elimination. The propensity of the pendent phosphazene group to enforce low hapticity of the Flu and Ind rings in the ensuing complexes has been demonstrated experimentally and theoretically. Of particular interest, geometrically constrained and sterically expanded structures have been evidenced spectroscopically and structurally for both complexes [(FluPPh2NPh)ZrBn3] 5a and [(IndPPh2NPh)ZrBn3] 7a. In addition, the ability of the aryl substituent at nitrogen to modulate the hapticity of the Ind ring (from η1, to η2, and η3) has been substantiated, and intramolecular CH-activation reactions leading to doubly cyclometalated complexes 6c and 8c have been observed when R = Mes.

Highly Variable Zr–CH2–Ph Bond Angles in Tetrabenzylzirconium: Analysis of Benzyl Ligand Coordination Modes

“…Spectroscopically, η 1 -coordination of benzyl ligands is associated with δ H ortho > 6.5, δ C ipso ≈ 150, and 1 J C−H for the CH 2 group of ∼120 Hz, while η 2 -coordination is identified by δ H ortho < 6.5, δ C ipso ≈ 140, and 1 J C−H for the CH 2 group of ∼135 Hz. 36 In this regard, Zr(CH 2 Ph) 4 is characterized by δ H ortho = 6.38, δ C ipso = 139.5, and 1 J C−H = 135 for the CH 2 group, which support the presence of η 2 -benzyl ligands. However, while these values are in accord with the presence of some degree of η 2 -benzyl coordination in solution, they do not distinguish between a situation in which the η 2 -benzyl ligands are equivalent and one in which the molecule is fluxional, and exchange between η 2 -and η 1 -benzyl ligands is facile.…”

“…In solution, however, the benzyl ligands are chemically equivalent on the NMR time-scale, as illustrated in Figures and . Spectroscopically, η 1 -coordination of benzyl ligands is associated with δ H ortho > 6.5, δ C ipso ≈ 150, and 1 J C–H for the CH 2 group of ∼120 Hz, while η 2 -coordination is identified by δ H ortho < 6.5, δ C ipso ≈ 140, and 1 J C–H for the CH 2 group of ∼135 Hz . In this regard, Zr(CH 2 Ph) 4 is characterized by δ H ortho = 6.38, δ C ipso = 139.5, and 1 J C–H = 135 for the CH 2 group, which support the presence of η 2 -benzyl ligands.…”

Cyclopentadienylphosphazene (CpPN) Complexes of Rare-Earth Metals: Synthesis, Structural Characterization, and Hydroamination Catalysis

“…Their use in the stabilization of highly reactive alkyls of rare-earth and group 4 metals has been claimed, and a representative CpPN lutetium alkyl complex has been presented . Independently, related fluorenyl- and indenyl-phosphazene ligands (FluPN and IndPN) and their rhodium and zirconium complexes were presented by Bourissou and co-workers. Theoretical investigations of CpPN-type complexes of group 4 elements suggest them to be interesting alternatives for CpSiN-derived catalysts …”

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

“…This chemical shift is in good agreement with the iminophosphorane tautomer IndPPh 2 vNR (Ind = indenyl-1; δ P = −8.3 and −16.5 ppm for R = Ph and Dip resp.). 23 However, in contrast to C 5 Me 4 PPh 2 NHAd, 16 C 5 Me 4 HPMe 2 NR (R = SiMe 3 , Dip) 20 and IndPPh 2 vNR (R = Ph and Dip), 23 L Ad H and L Dip H show only one sharp resonance in the 31 P NMR spectra, indicating the absence of isomers. 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.…”

“…[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. The synthesis and characterization of a series of rare-earth metal constrained geometry CpPN complexes [{η 5 ,η 1 -C 5 Me 4 PMe 2 NAd}-M(CH 2 SiMe 3 ) 2 ] (M = Sc, Lu, Y, Sm, Nd, Pr, Ce) and their high catalytic activities in the intramolecular hydroamination/cyclization have been reported by us.…”