474832-26-3Relevant academic research and scientific papers
On the mechanisms of degenerate halogen exchange in phosphorus(III) halides
Renard, Sylvie L.,Fisher, Julie,Kilner, Colin A.,Thornton-Pett, Mark,Kee, Terence P.
, p. 2921 - 2932 (2002)
Diazaphospholidine heterocycles of phosphorus(III) containing halogens or trifluoromethylsulfonate (triflate) display dynamic behaviour due to exchange of the X (Cl, OTf) groups. Full line-shape 13C{1H}-NMR simulations on (3R,8R)-1-chloro-2,9-bis(4-tert-butylbenzyl)-2,9-diaza-1-phosphabicyclo [4.0.3]nonane (4a) using the gNMR software package reveal proportionality between the rate of [P-Cl] exchange and the square of the concentration of the phosphorus compound, supportive of a second-order, bimolecular process. However, in the presence of an additional chloride ion source, a second, more rapid, process which is both first order in phosphorus compound and added chloride ion becomes competitive, consistent with a mechanism of the SN2(P) type. This tends to support the existence of parallel pathways which operate under slightly different conditions. Added nitrogen bases such as N-methylmorpholine do not affect the rate of exchange. Variable temperature full line-shape 13C{1H}-NMR analyses on both 4a and an analogue, (3R,8R)-1-chloro-2,9-bis(2,6-difluorobenzyl)-2,9-diaza-1-phosphabicyclo [4.0.3]nonane (4c), reveal isothermal exchange rates at 206 K of 22.2 and 8.0 mol L-1 s-1 (0.36 M), respectively, suggesting that the exchange is slower for 4c. Moreover, activation parameters (ΔG?, ΔH? and ΔS? of 50.6(9), 20.8(9) kJ mol-1 and -100(3) J K-1 mol-1, respectively, for 4a at 0.36 M and 55.8(1), 15.6(1) kJ mol-1 and -135(5) J K-1 mol-1, respectively, for 4c at 0.36 M) are comparable and are more consistent, especially in terms of entropy change, with a bimolecular mechanism of exchange in the absence of added chloride ion. We argue on the basis of precedence that a bimolecular mechanism proceeding via a stabilised phosphenium intermediate is most probable, since it is well known that phosphorus(III) is capable of stabilising phosphenium centers. Finally, single-crystal X-ray diffraction analysis of (3R,8R)-1-chloro-2,9-bis(4-cyanobenzyl)-2,9-diaza-1-phosphabicyclo[4.0.3] nonane (4b) reveals a fused ring system with a three-coordinate phosphorus atom in a distorted trigonal pyramidal geometry; the sum of the angles around P(1) is ca. 295°. The P-Cl, P-N and C(1)-C(2) bond lengths compare well with literature values for similar compounds; these range between 2.0-2.3, 1.6-1.7 and 1.5-1.56 A, respectively.
Electronic effects on the acidity of phosphorus(III) triflates
Renard, Sylvie L.,Kee, Terence P.
, p. 516 - 521 (2007/10/03)
A range of chiral phosphorus(III) triflates has been prepared and their donor-acceptor behaviour towards the representative donor 4-phenylpyridine investigated. Correlations between 31P-NMR shifts, relative binding strengths (Kr) and
