Equilibrium thermodynamics and mechanism of cis-trans isomerization for diazidobis(methyldiphenylphosphine)palladium(II) and diazidobis(dimethylphenylphosphine)palladium(II)

Redfield, David; Cary, Lewis W.; Nelson, John H.

doi:10.1021/ic50143a011

Cited by 122 publications

(81 citation statements)

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“…This phenomenon, which was later also observed in the corresponding 13 C{ 1 H} NMR spectra became an important tool for geometry assignments [134]. From a practical point of view (leaving aside the theory behind it) [132,[134][135][136][137][138][139], as a result of the large 31 P-31 P coupling experienced by two phosphorus atoms in mutually trans-positions of an organometallic compound, the C atoms (and H attached to them) of the backbone can appear in the corresponding NMR spectra as "virtual triplets" and rarely as more complex spectra, because the P-P coupling constant is usually much larger than the other constants involved. Although this phenomenon can be extended to the whole molecule, in Table 7 only the ones reported for the methylene groups directly connected to phosphorus (if they are) are presented.…”

Section: Relevant Nmr-data Of Complexes Containing Trans-diphosphinesmentioning

confidence: 68%

“…The separation between the first and the third line corre-4 ν 1/2 is related to the resolving power of the spectrometer. sponds to | n J P-C + n+2 J P -C |, and it is the value usually reported (| 1 J P-C + 3 J P -C | for the carbon directly attached to P) [136,139].…”

Section: Relevant Nmr-data Of Complexes Containing Trans-diphosphinesmentioning

confidence: 74%

“…In this case, the resulting signal is also a 1:2:1 triplet when | n J H-P -n+2 J CH-P | 2 < 2 2 J P-P ν 1/2 [136]. The value of | 2 J P-H + 4 J P -H | can be directly deduced from the 1 H NMR spectra.…”

Section: Relevant Nmr-data Of Complexes Containing Trans-diphosphinesmentioning

confidence: 98%

“…In 13 C NMR spectra a spins system of type AXX (A = C; X, X = P) is attributed for the observed triplets. Strictly speaking, this signal will appear as a 1:2:1 triplet if | n J C-Pn+2 J C-P | 2 < 8 2 J P-P ν 1/2 4 (which will be the case for large 31 P-31 P trans-coupling constants and nearly null n+2 J C-P ) [136]. The separation between the first and the third line corre-4 ν 1/2 is related to the resolving power of the spectrometer.…”

Section: Relevant Nmr-data Of Complexes Containing Trans-diphosphinesmentioning

confidence: 99%

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Trans-chelating diphosphines, the elusive ligands!

Freixa

Leeuwen

2008

Coordination Chemistry Reviews

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Section: Relevant Nmr-data Of Complexes Containing Trans-diphosphinesmentioning

confidence: 68%

Section: Relevant Nmr-data Of Complexes Containing Trans-diphosphinesmentioning

confidence: 74%

Section: Relevant Nmr-data Of Complexes Containing Trans-diphosphinesmentioning

confidence: 98%

Section: Relevant Nmr-data Of Complexes Containing Trans-diphosphinesmentioning

confidence: 99%

See 2 more Smart Citations

Trans-chelating diphosphines, the elusive ligands!

Freixa

Leeuwen

2008

Coordination Chemistry Reviews

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confidence: 99%

False AA'X Spin-Spin Coupling Systems in 13C NMR: Examples Involving Phosphorus and a 20-Year-Old Mystery in Off-Resonance Decoupling

1997

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It is common in both NMR textbooks and journal articles to loosely describe certain ABX spin systems as AA′X spin systems (1)(2)(3)(4)(5). For purposes of illustration, consider the 13 CH 2 spin system of maleic anhydride shown in Figure 1. One of the AB pair of hydrogen atoms is attached to a 13 C atom, the X-nucleus in the spin system, but the other is attached to a 12 C atom, the NMR-inactive isotopomer of the Xnucleus, and so the symmetry of the molecule is broken. Rigorously, the different isotopes split the chemical shifts of the "false" AA′ pair, and the properly designated AB hydrogen atoms are chemically as well as magnetically inequivalent.In practice, however, the chemical shifts normally are indistinguishable, and many of those same textbooks and journal articles point out that while rigorously the system is ABX, for all practical purposes it can be analyzed as AA′X (1,6). The danger of all of this is that when the chemical shifts are not the same, one may fail to recognize that fact owing to the assumption that the isotopomer shift is always insignificant. Results and Discussion P ExamplesA number of authors have noted that diphosphines and transition metal complexes with two phosphine ligands represent interesting test cases of such false AA′X systems (6-8), as shown for diphos (1) in Figure 2. Here the AA′ nuclei are the 31 P atoms, and the X-nucleus is the lone 13 C atom anywhere in this molecule. Detailed descriptions of the expected appearance of AA′X systems have been published (3,4,6), and except for the few cases to be described below, the AA′X description suffices for diphosphorus compounds (2, 6, 7). Representative multiplets from 1 and 2 are shown in Figure 3 for illustration. A common feature of AA′X spectra is that each exhibits a peak at the center of a 3-or 5-line multiplet (for J AA′ ≠ 0); the relative heights of the lines are dependent on the relative values of J AA′ , J AX , and J A′X . The separation of lines 1 and 3 (Fig. 3a,b) or 2 and 4 ( Fig. 3c) is equal to |J PC + J P′C |. The coupling constant J PP′ (if relatively large) can be obtained from the outer "wings" at approximately ± J PP from the central peak (Fig. 3c), or (if relatively small) from matching the height of the central line with that in simulations of the observed spectrum (Fig. 3a). These multiplets are examples of "virtual coupling" (9), because even though the longer range coupling constant J P′C ≈ 0, lines due to the second phosphorus atom are present in the 13 C NMR spectrum caused by the strong coupling of the phosphorus atoms-hence the second phosphorus is "virtually" coupled to carbon. It is important to recognize, especially in the case of the deceptively simple "triplet", that the coupling constants cannot be extracted on the basis of familiar first-order analyses.In contrast to the AA′X patterns seen above, the multiplets due to the ipso and bridging carbon atoms of diphos exhibit split central lines in the 100.6 MHz 13 C NMR spectrum (Figure 4a,b). The spectra are readily modeled if one drops the AA′X ...

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