Nuclear magnetic resonance study of ring inversion and nitrogen inversion in substituted ethylenediamine complexes of praseodymium

Abstract

A t low temperatures, ring inversion is slow on a proton n.m.r. time-scale for the Pr( [2Ho]fod),-NNN'N'tetramethylethylenediamine { [2Hg]fod = (CD,),CC( : 0)-CHC( :O)CF,CF,CF,) complex (I), and the barrier to ring inversion, Act, is 42-2 kJ mol-1 a t -38 O C; in the corresponding NNN'N'-tetramethyl-1,8-propylenediamine complex (11), interchange of N-Me groups is observed above room temperature.

Stereodynamics in Eight-Coordination; A 2D NMR Spectroscopic and Computational Study of the Exchange Process in ThCl4(Me2NCH2CH2NMe2)2

“…12 Of particular relevance to the subject matter of this Article, the inversion barrier in the eight-coordinate complex Pr(fod-d 9 ) 3 (tmed), where fod-d 9 is 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyloctane-3,5-dionate-d 9 , is ΔG ⧧ 235 K = 10.1 kcal mol −1 . 13,14 The 2:1 tmed/metal complexes of uranium and thorium, MCl 4 (tmed) 2 , are useful complexes for synthetic studies because they are soluble in aromatic and chlorinated hydrocarbon solvents; 15a ThCl 4 (tmed) 4 was used recently in the synthesis of thorium metallocene compounds. 15b,c Solubility also leads to the possibility of extraction with these organic solvents.…”

“…The initial interpretation of the 1D 1 H NMR spectrum is that (a) ring inversion of the five-membered Th-tmed ring is slow at 220 K and (b) two isomers are present at this temperature. This interpretation is supported by the less complex 13 The most important NMR spectrum is shown in Figure 3. The EXSY spectrum shows the exchange network in which each Me 2 N resonance of the major isomer can exchange into either of the chemically inequivalent Me 2 N sites in the minor isomer and vice versa.…”

“…15a NMR Spectroscopy. Experiments were conducted on a 400 MHz instrument, operating at 100.6 MHz for 13 C NMR. The temperature was measured using a sample of methanol.…”

“…The temperature was measured using a sample of methanol. 31 The 2D 13 C EXSY NMR experiment employed a standard pure-phase (TPPI) NOESY pulse sequence with 1 H decoupling throughout. The spectral width was 1055.1 Hz in both dimensions, with 393 × 1K points, 32 scans each, collected in t 1 and t 2 , respectively.…”

“…In the four-coordinate complexes [Co(tmed)(NO) 2 ] + and [Zn(tmed)Cl 2 ], Δ H ⧧ 187 K = 8.8 kcal mol –1 . Of particular relevance to the subject matter of this Article, the inversion barrier in the eight-coordinate complex Pr(fod-d 9 ) 3 (tmed), where fod- d 9 is 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyloctane-3,5-dionate- d 9 , is Δ G ⧧ 235 K = 10.1 kcal mol –1 . , …”