Isolation of the "Open Form" of Cyclenphosphorane by Deprotonation and Reaction with Electrophilic Reagents

Ab Initio Study of Cyclenphosphorane: The Molecular Structures of Phosphorus(III) and Phosphorus(V) Tautomers

“…Table gives the optimized geometrical parameters for the open form 2b and the X-ray crystal data 4b for the (cyclen)P unit in Mes 2 B(cyclen)P. The conformations of eight-membered rings of four open form conformers are all quite different from one another, while the geometries of two five-membered rings around the P atom are almost the same. These four conformers can be described as a chair-boat form, a crown form, a boat-boat form, and a boat-chair form in 2a , 2b , 2c , and 2d , respectively 4a. In the open form conformer 2c , we can expect that an axial N 4 atom is involved in a transannular interaction with the phosphorus atom through its lone pair electrons 4a.…”

“…These four conformers can be described as a chair-boat form, a crown form, a boat-boat form, and a boat-chair form in 2a , 2b , 2c , and 2d , respectively 4a. In the open form conformer 2c , we can expect that an axial N 4 atom is involved in a transannular interaction with the phosphorus atom through its lone pair electrons 4a. Since the distance between both atoms is about 2.6 Å at all RHF levels, which is well within the sum of the van der Waals radii, the open form conformer 2c may not be a genuine tricoordinate tautomer.…”

“…Previous spectral characterizations 1,3 indicate that pentacoordination is rather preferable to tricoordination for the phosphorus atom in (cyclen)PH. It seems that this stabilization of a pentacoordinate tautomer is caused by the constraint of polycyclic tetraamine rings around the phosphorus atom. 3e, The tricoordinate tautomer, called the “open form”, is isolated only in certain metal complexes. 2f,4a, Recently, the isolation of an open form without complexation to a metal, that is, Mes 2 B(cyclen)P, has also been reported 4b. The structure of pentacoordinate (cyclen)PH, called the “closed form”, can have either trigonal bipyramidal (tbp) or square pyramidal (sp) geometry, which is consistent with the previous NMR spectral data 1a…”

Crystal structure of bis(mesityl)(pyrrol-1-yl)borane

“…The N-B bond is 1.4425 (15) A ˚long. This is ca 0.04 A longer than in similar compounds where the nitrogen atom is attached to two sp 3 carbon atoms [ROCRAD (two molecules; Morawitz et al, 2008), TAYYAV (Araki et al, 2012), UWUFID (Smith et al, 2016), YOMKAM (Khasnis et al, 1995); T 173 K, N-B range 1.388 (2)-1.412 (3) A ˚, average 1.40 A ˚] and where the nitrogen lone pair is fully available for donation to boron. Compared to the molecular geometry of pyrrole itself, as determined by X-ray crystallography at 103 K (Goddard et al, 1997) and by calculation at the B3LYP-631G * level (Lee & Boo, 1996), the most notable difference is in the increase of the two N-C bond lengths to 1.4005 ( 14) and 1.3981 (14) A ˚from 1.365 (2) A ˚(experimental) and 1.376 A (calculated) (Table 1).…”