Phosphorus atoms, nonequivalence

On the basis of the deconvolution, the ABCX pattern was assigned to originate from the three complexed nonequivalent phosphorus atoms of monocyclic 1,3-diphenylphosphinopropane 3-(diphenylphosphino)-propyldiphenylphosphinerhodium(I) carbonyl hydride. 

The solution and solid P-31 NMR spectra of the prophos ligand are presented in Figure 10. As seen from this figure, the expected nonequivalence of the phosphorus atoms was observed in both spectra. The signals in the solid-state spectrum showed increased shielding relative to the solution spectrum. The solution spectrum also revealed a P-P coupling (/P P = 20.5 Hz). 

The 119Sn NMR spectrum of the adduct PhSnCl3 (EtO)2POCH2CH2PO(OEt)2 at —90 °C consists of a triplet at —557 ppm and a doublet of doublets at —551 ppm with approximately 5 1 relative intensities. These resonances were attributed to isomers of the hexacoordinate complex301,1056. The first isomer has two equivalent phosphorus atoms in the tin coordination sphere and consists of cis-fac octahedra in accordance with the preferred cis -bridging behavior of the ethylene-diphosphonate ligand. The second isomer with nonequivalent phosphorus atoms consists of cis-mer octahedra125. 

In 10, there are two remote stereogenic centers at phosphorus and it was isolated as an almost equimolecular mixture of the two sets of diastereoisomers, that is, (RR/SS) and (RS/SR). In each chiral diastereoisomer, the phosphorus atoms are nonequivalent and four distinct 31P resonances were obtained almost in a 1 1 1 1 ratio <1997J(P2)1445>. The kinetics of the thermal decomposition of 11 in dibutyl phthalate was studied. The high rate of decomposition was probably determined by mutual steric influence of the bulky dinitromethylene moieties <2006RJC499>. 

A -Dioxaphospholanes show no inversion at the phosphorus atom, which can be seen in the nonequivalence of the CFj groups (273). A -Dioxaphospholanes 73 can be oxidized with halogens to form A -dioxaphospholanes 74 (228). Exchange of the halogens in 73a-c with suitable reaction partners (e.g., LiNHj) yields substituted A -phospholanes [e.g., 73g (265)] (see also Section III,A,2). 

In order to model the square planar rhodium(I) complex we need to realize that the positions trans to the diphosphine may not be equivalent, since the diphosphine is chiral. Consider the [(diphosphine)Rh(norbornadiene)] as a model for the solvento species. In order to distinguish between the nonequivalent phosphorus atoms, we label them and P ,. Each olefin is 90° from one phosphorus atom... 

H n.m.r. spectra of complexes of unsymmetrical acetylenes and phosphines show coupling to two nonequivalent phosphorus atoms showing that the square planar environment is maintained in solution 3>. However rotation of both ethylene and acetylene in zerovalent complexes has been predicted 115T... 

Figure 10.6 shows three possible isomers for 4. Isomer II (Cs symmetry) can be ruled out on the basis of steric arguments as the size of the oligosilyl substituents is too large. In isomer III, all seven phosphorus atoms are nonequivalent and hence seven resonances would be expected. For isomer I (Cs symmetry) with two pairs of equivalent phosphorus atoms, five resonances with an intensity ratio I I I 2 2 would be expected, in accordance with observation. There is no evidence for the formation of isomer III. The formation of the anion upon reaction of 1 with tert-BuOK proceeds with a simultaneous inversion of one of the phosphorus atoms. 

Addition of 2 equiv of PPh3 to Pd°(dba)2 in THF or DMF generates a palladium(0) complex Pd°(dba)(PPh3)2 (Eq. 1 of Scheme 3) in which the dba ligand behaves as an 17 -ligand leading to two nonequivalent phosphorus atoms characterized by P NMR spectroscopy. 

Coordination of the BF ion lowers the 7 symmetry of [BF4] and makes the fluorine atoms nonequivalent. Therefore the IR spectra showthree instead of one viiB-F absorptions(Tables I and II) the low-temperature FNMR spectra show two distinct fluorine resonances, a high-iield quartet (which may be split by coupling to the phosphorus in the PRj substituted compounds and a doublet at lower field, close to the resonance of free [BF4] the P NMR spectrum shows at low temperature a pseudodoublet, produced by coupling with the coordinated fluorine (Tables I and II). Compounds MoCp(CO)2(PR3)(FBp3) are obtained as cis and trans isomers. In WCp(CO)2 [P(OPh)3] (FBF3) total isomerization from the pure ds hydride to the pure trans-BF compound could be followed via NMR. ... 

This is still more difficult to do in the case of the diphosphine ligands with backbone chirality, when all four substituents on the phosphorus atoms are phenyls. The conformation of the chelate cycle (fixed by the backbone substituents) makes these foin phenyls pairwise nonequivalent... 

The oxidation of (171) with (172) gave the zwitterionic compound (173) that was analyzed by X-ray crystallography and shown to contain both and atoms and a P-H bond. The P H NMR data on (173) in CDCI3 showed a high field doublet of triplets at —134.2 ppm, characteristic of hexacoordinate phosphorus with the splitting pattern due to one nonequivalent and two equivalent fluorines. 

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