Phosphoranes bond lengths

Structure, Bonding and Ligand Reorganisation. - An X-ray analysis of the monocyclic phosphorane (2) reveals a tbp structure with the hydrogen in an axial position and an H-P bond length of... 

The authors also prepared other compounds, such as the phosphorane 123 with a seven-membered ring, and homologues of 122 in which X is replaced by a biphenylene moiety similar to that in 120. When X in 122 is replaced by CH2, XRD gives the bond lengths as PO = 1.617(4), PN = 1.887(6) A. The important geometrical modifications brought about by methylation of the N atom are thus revealed. 

The first x-ray structure of a P(V)-P(V) derivative, the dimeric cyclen phosphorane [(NCH2CH2) P]2 (6) above, shows a normal P-P single bond length (2.264(2) A). 

Synthesis and Characterisation of Phosphonium Ylides. - We start this section with a phosphanylidene-o -phosphorane (14) which, although not strictly an ylide, has a P-P bond which displays many of the properties of more conventional phosphonium ylides. A crystal structure of (14) revealed a P-P bond length of 2.084(2) A, which is similar to those found in other phos-phanylidene-o( -phosphoranes and is certainly shorter than a typical P-P single bond ca. 2.22 A), indicative of multiple bond character. Compound (14) undergoes reactions with electrophiles (Scheme 1) which demonstrate its nucleophilic... 

PCC and CCC bond angles (126.6 and 127.7°) involving the a- and /S-carbon atoms of the allyl group of (191) are considerably increased compared to sp angles. It has been concluded that the ylide character cannot be estimated from the P—C bond length on the basis of complete ylene structure for methylenetriphenylphosphorane. Studies are also reported for the imino-phosphorane (193), (194), monoclinic triphenylphosphine oxide, the... 

X-Ray analysis has shown that although the chemical shift of the phosphorane (79) is + 66.9p.p.m. and the geometry around the phosphorus is approximately trigonal bipyramidal, the PO bond length is 2.14 A. Contributions to the structure by the dipolar species (80) and... 

The reaction of phosphaalkyne 9a with trialkylaluminum (ratio 4 1) in diethyl ether instead of in rt-hexane follows a completely different course phosphaalkyne cyclotetramerization with incorporation of one equivalent of trialkylaluminum provides the polycyclic compound 81 (74%) [64). X-ray crystallography revealed that the molecule possesses symmetry the bond lengths in the phosphonium-phosphorane structural element (81A) are indicative of a delocalization of the positive charge according to 81B. The X o -phosphorus atom is easily recognized by its low-field position in the P-NMR spectrum (6 = 208.0, /(P,P) = 320.6 Hz, V(P,P) = 10.8 Hz) [64]. 

The geometries at the phosphorus atoms in the p-bromophenyl- and. W-toluene-p-suIphonyl- iminotriphenylphosphoranes are very similar. P-C(aryl) distances lie in the range 1.79—1.82 A, and the P=N bonds are 1.567 and 1.579 A. A rather abnormal situation occurs in the crystal structure of bis(triphenylphosphoranylidene)methane (or hexaphenylcarbodi-phosphorane), in which the P=C=P angle is not only bent, but has different values, of 131 and 145°, in the two crystallographically independent molecules (Figure 3). The P=C bond lengths of 1.624 A, by comparison with P=0 values, must represent double bonds. The bonding at the carbon atom is thus difficult to rationalize, but may be connected with use of the phosphorus cf-orbitals. 

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