Dissociation of 2,4-Bis(2,4,6-tri-tert-butylphenyl)-cyclo-1,3-dipnicta-2,4-diazanes (pnict = P, As, Sb) Imposed by Substituent Steric Strain:  A Cyclobutane/Olefin Analogy

Abstract

Three 2,4-bis(Mes)-cyclo-1,3-dipnicta-2,4-diazanes, 2PnX, have been synthesized as 1,3-dichloro- (Pn = As; X = Cl) or 1,3-bis(triflato)- (Pn = P, Sb; X = OTf) derivatives (Mes = 2,4,6-tri-tert-butylphenyl; OTf = triflato = trifluoromethanesulfonoxy). The compounds have been structurally characterized as cyclodimers, but spectroscopic characterization of melts and solutions indicates facile dissociation of the diphosphadiazane 2POTf derivative to give the corresponding iminophosphine 1POTf and of the diarsadiazane 2AsCl derivative to give the corresponding iminoarsine 1AsCl. 1,3-Bis(triflato)-2,4-bis(Mes)-cyclo-1,3-distiba-2,4-diazane (2SbOTf) does not dissociate in the melt or in solution. The presence of the sterically bulky Mes substituent does not preclude association of N-Pn olefin analogues to give single bonded cyclobutane analogues. The facile dissociation of 2POTf and isolation of 1POTf implicates a relatively high degree of substituent steric strain in the dimer. In comparison, dissociation of 2AsCl is only apparent in the melt and in solution, likely the result of the lower substituent strain in the larger N(2)As(2) framework. The largest N(2)Pn(2) framework in 2SbOTf provides sufficient space for the Mes substituents, and the monomer is not observed under the conditions examined.

On the equilibrium between monomeric and dimeric iminochlorophosphanes R–N=P–Cl

“…This trend can be attributed to less stable E=N double bonds and decreasing steric strain within the E 2 N 2 ring. Experimentally known is the stable monomeric Mes*-N=P-Cl [20,21], while the heavier arsenic analog forms a dimer in the solid state [41]. The arsenic dimer was first described by Burford et al, and the authors already speculated on the reversible dissociation, which was experimentally proven by temperature dependent 1 H NMR experiments displaying a dimer/monomer ratio of 1:1.7 [42,43].…”

Tetrazarsoles—A New Class of Binary Arsenic–Nitrogen Heterocycles

“…The dimer was first described by Burford et al, and the authors speculated on its reversible dissociation. [5] The white crystalline dimer 1 readily dissolves in CH 2 Cl 2 , but the initially colorless solution slowly turns red, the color of the monomeric species. To derive thermochemical data for the dimer-monomer equilibrium, 1 H NMR spectra were collected between 233 and 298 K, yielding a value of 2.2 kJ mol À1 for the enthalpy of monomerization.…”

“…In contrast to the well-known iminophosphanes, [10] little is known about the corresponding compounds containing As = N bonds. [5,9,11] The first fully characterized compound with an As = N bond (d(AsÀN) = 1.714(7) and 1.745(7) ) was N,N'-bis(2,4,6-tritert-butylphenyl)amino-iminoarsane, prepared by Lappert et al in 1986. [12] The GaÀN bond length of 1.964(2) is in the typical range for GaCl 3 adducts (1.990(4) in 5).…”

Tieftemperatur‐Isolierung des bicyclischen Phosphinophosphoniumsalzes [Mes*2P4Cl][GaCl4]

“…B. A), [4][5][6][7][8] grçßeren Ringsystemen durchC ycloadditionsreaktionen sowie Ringerweiterung [4,9,10] oder auch kationischen Spezies durch Abstraktion von Halogenen (C). [11][12][13][14][15] Infolgedessen interessieren wir uns momentan für die Chemie analoger Ringsysteme,d ie ausschließlich aus Phosphor aufgebaut sind (d. h. [XP(m-PR)] 2 ), um mçgliche Reaktionswege zu vergleichbaren, neuen Phosphorspezies aufzufinden.…”