η⁵–η¹ Switch in Divalent Phosphaytterbocene Complexes with Neutral Iminophosphoranyl Pincer Ligands: Solid-State Structures and Solution NMR ¹J_Yb–P Coupling Constants

Abstract

This paper reports the synthesis of a series of complexes based on the bis­(pentamethylcyclopentadienyl)­ytterbium­(II) (1; Cp*2Yb) and bis­(tetramethylphospholyl)­ytterbium­(II) (2; Tmp2Yb) fragments bearing an additional neutral bis­(methyliminophosphoranyl)­pyridine ligand (L) on which the steric demand is modulated at the phosphorus position (triethyl, L Et ; triphenyl, L Ph ; tricyclohexyl, L Cy ) to yield the original complexes Cp*2YbL Et (1-L Et ), Cp*2YbL Ph (1-L Ph ), Tmp2YbL Et (2-L Et ), Tmp2YbL Ph (2-L Ph ), and Tmp2YbL Cy (2-L Cy ), while no reaction occurs between 1 and L Cy . 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 L R differs depending on the nature of the fragments 1 and 2 and on the steric bulk of L R . The crystal structure of the divalent Tmp2Yb­(py)2 (3) is also reported for structural and spectroscopic comparisons. Interestingly, in both 2-L Et and 2-L Cy , 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 J Yb–P coupling is used to track the coordination mode of the Tmp ligand and a large difference in the 1 J Yb–P coupling constant allows the distinction between an η5 coordination mode and a dynamic η5–η1 switch.

Tuning the Stability of Pd(IV) Intermediates Using a Redox Non-innocent Ligand Combined with an Organolanthanide Fragment

“…The Cp*−Yb average distances in 3 and 4 are similar (2.305(8) and 2.29(1) Å, respectively) and are indicative of the oxidation state of the Yb center. Typical values of 2.30−2.31 Å are observed for Yb III ,18g whereas longer Cp*−Yb distances (2.43−2.50 Å) are indicative of Yb II complexes 20. They oscillate between these limiting values when the electronic ground state is multiconfigurational 18a,b.…”

f‐Block Phospholyl and Arsolyl Chemistry

“…In 2012, Labouille et al. showed that [Sm(Tmp) 2 ] reacted with pyridine to give the adduct [Sm(η 5 ‐Tmp) 2 (py) 2 ] ( 15‐Sm ); [28] the corresponding Yb II complex 15‐Yb was reported in 2015 by Nocton, Auffrant and Cheisson, together with the structures of several similar substituted Yb II bis‐phospholyl complexes coordinated by substituted pyridines, [Yb(Tmp) 2 (L R )] (L R =C 5 H 3 N(CH 2 NPR 3 ) 2 ‐2,6; R=Et, 16 ; Cy, 17 ; Ph, 18 ) [29] (Figure 7). As both [Tm(Cp ttt ) 2 ] [27] and [Sm(Cp*) 2 ] [28] reductively couple pyridine, the lack of SET chemistry of 11 and [Sm(Tmp) 2 ] towards this substrate showcases how the weaker π‐donor properties of phospholyl ligands versus Cp R makes metal centres less reducing.…”

“…The solid‐state structures of 15‐Ln for both Sm [28] and Yb [29] reveal bent metallocene‐type motifs, with two eclipsed η 5 ‐Tmp ligands with staggered C 4 P rings (Sm−P: 3.043(1) and 3.046(1) Å; Yb−P: 2.903(8) and 2.941(2) Å) and two equatorially coordinated pyridine molecules. The structures of 16 – 18 differ according to the identity of L R , with 16 and 17 containing κ 3 ‐coordinated L R ligands to enforce one η 1 ‐bound Tmp (Yb−P: 2.9723(8) Å for 16 and 3.023(1) Å for 17 ) and one η 5 ‐Tmp (Yb−P: 3.027(1) Å for 16 and 2.925(1) Å for 17 ) [29] . Only one of the iminophosphoranyl arms are bound in the κ 2 ‐L Ph ligand of 18 , thus both Tmp ligands are able to bind in an η 5 ‐fashion (Yb−P: 2.9480(8) and 2.947(1) Å).…”

Tridentate NNN Ligand Associating Amidoquinoline and Iminophosphorane: Synthesis and Coordination to Pd and Ni Centers

“…The P=N bond is also longer than in L Ph H (1.580(1) vs 1.567(1) Å) as already observed for iminophosphoranes featuring alkyl groups on the phosphorus. 6…”

“…Bochmann and coworkers reported in 2000 the coordination of bis(iminophosphoranyl)pyridine derivatives (A) to iron, cobalt, and nickel centers and used those complexes for olefin polymerization. 5 More recently we studied the coordination of the more flexible ligands B to lanthanides 6 or electron-rich Cu I centers. 7 The ligand C, exhibiting a central anionic pyrrole in place of a pyridine, was employed by the group of Hayes to stabilize rare earth complexes 8 or prepare Rh I complexes able to promote CO activation in presence of borane.…”