Coordination of 1,4-Diazabutadiene Ligands to Decamethylytterbocene:  Additional Examples of Spin Coupling in Ytterbocene Complexes

Abstract

The paramagnetic 1:1 coordination complexes of (C 5 Me 5 ) 2 Yb with a series of diazabutadiene ligands, RN=C(R')C(R')=NR, where R= CMe 3 , CHMe 2 , adamantyl, p-tolyl, p-anisyl, and mesityl when R'=H, and R= p-anisyl when R'= Me, have been prepared. The complexes are paramagnetic, but their magnetic moments are less than expected for the two uncoupled spin carriers, (C 5 Me 5 ) 2 Yb(III, 4f 13 ) and the diazabutadiene radical anions (S= ½), which implies exchange coupling between the spins. The variable temperature 1 H NMR spectra show that rotation about the R-N bond is hindered and these barriers are estimated. The barriers are largely determined by steric effects but electronic effects are not unimportant.2

Thermal Dihydrogen Elimination from Cp*2Yb(4,5-diazafluorene)

“…The non-linear behavior is reminiscent of the resonances observed for Cp * 2 Yb(bipy) and its substituted derivatives. [1][2][3][4]7,14 The non-linearity is the first clue that the electronic structure of 1 is based upon intermediate-valent ytterbium, rather than divalent ytterbium, a point developed below.…”

“…Complex 1 exhibits a low magnetic moment, eff = 1.2 B at 360 K, as observed for the decamethylytterbocene adducts with various bipyridine ligands. [1][2][3][4]7 As in these adducts, when 4,5-diazafluorene is reduced by the Yb(II) center, a hole is created in the Yb(III) center (f 13 ) as the electron enters the * orbital of the ligand, and the calculated effective moment for the complex is expected to be 4.8 B at 300 K if the spins are uncorrelated ( 2 F 7/2 + 2 S). The low effective moment observed for complex 1 clearly implies that the two spins are correlated.…”

Decamethylytterbocene Complexes of Bipyridines and Diazabutadienes: Multiconfigurational Ground States and Open-Shell Singlet Formation

“…Samples were prepared as previously described, [4][5][6]26 except the compounds noted below, which were previously unknown. Preparation of Cp* 2 La(2,2′-bipyridine).…”

Radical ligand-containing single-molecule magnets

“…In these intermediate-valence compounds, the valence of ytterbium in the Cp* 2 Yb moiety is between Yb II and Yb III [328][329][330][331]. Among the complexes examined were Cp* 2 Yb(bipy-X) (X = Me, t-Bu, OMe, Ph, CO 2 Me, CO 2 Et) [316,327,328,332], Cp* 2 Yb(dad-R) (R = t-Bu, i-Pr, adamantyl, p-tolyl, p-anisyl, mesityl) [316,329], and Cp* 2 Yb(terpy) (Fig. 26) [333,334].…”