P-Hydrogen-Substituted 1,3,2-Diazaphospholenes:  Molecular Hydrides

Abstract

P-Hydrogen-substituted 1,3,2-diazaphospholenes 1 were prepared by an improved procedure from diazadienes and were characterized by spectroscopy and in one case by X-ray diffraction. A unique hydride-type reactivity of the P-H bonds was documented by extensive reactivity studies. Aldehydes and ketones were readily reduced to diazaphospholene derivatives of the corresponding alcohols, with alkyl-substituted ketones being converted at much lower rates than aldehydes or diaryl ketones. Reactions with the tetrachlorides of group 14 elements proceeded via hydride/chloride metathesis to give either partially chlorinated derivatives EH(n)Cl(4-n) (n = 0-3 for E = C, Si) or HCl and phosphenium salts 16c[ECl3] (for E = Ge, Sn) which were characterized by spectroscopic and X-ray diffraction studies. Tin dichloride was readily reduced to the element. Reactions of 1c with the P-chloro-diazaphospholene 3c and the salt 16c[OTf] allowed the first experimental detection of intermolecular exchange of a hydride, rather than a proton, between phosphine derivatives. Computational studies indicated that the hydride transfer between 1c and the cation 16c involves a transient H-bridged species with bonding properties similar to those of B2H7-. The preference for the formation of these bridged intermediates over P-P bonded phosphenium-phosphine adducts is attributed to the low electrophilicity of the diazaphospholenium cations and characterizes a novel reaction mode for phosphenium ions.

On the Synthesis and Addition Reactions of Chiral N-Heterocyclic Diphosphines

“…Condensation of the amine with glyoxal following a published protocol [28] gave the first chiral diazadiene 5 which was further converted to 6 in a one-pot procedure [29] via reduction to a diazadiene dianion, quenching with NEt 3 ·HCl, and base-induced condensation with PCl 3 (Scheme 2). Scheme 2.…”

“…Subsequent reaction with (cod)PdCl 2 resulted in the replacement of the 31 P{ 1 H} NMR signals of 12 by four new sets of AX patterns which display strong deshieldings (δ 31 P = 120.0 -121.0 for PN 2 and 27.6 -31.9 for P(H)Men units) and somewhat increased values of J PP (26)(27)(28)(29)(30)(31)(32)(33). Efforts to isolate individual components remained unsuccessful.…”

Recent Developments in the Chemistry of N-Heterocyclic Phosphines

“…The most widely applied precursors for the synthesis of monocyclic NHPs are a -diimines which can be converted to the target heterocycles either in a two-step reaction sequence involving two-electron reduction of the diimine to an enediamide, enediamine, or a -aminoamine and subsequent condensation with PCl 3 [18][19][20] or a dichlorophosphine RPCl 2 [21] , or via direct base-promoted reaction with PCl 3 [20,22] . The latter reaction involves addition of a P-Cl bond to each imine moiety followed by base-promoted elimination of hydrogen chloride leading to 2,4-dichloro-1,3,2-diazaphospholenes 9 (Scheme 3 ) which were isolated in moderate to good yields after crystallization.…”

“…The two-electron reduction of a -diimines to prepare the required starting materials for a subsequent condensation is usually achieved by reaction with lithium but other alkaline (Na) or alkaline earth (Mg) metals should be useful as well. The synthesis of the heterocycles 10 is either accomplished by direct metathesis of the formed metal enediamide with PCl 3 2 [19] or, alternatively, by quenching the diamide with a suitable acid to produce an enediamine or a -aminoimine, respectively, and subsequent base-induced condensation with PCl 3 or RPCl 2 [18,20] (Scheme 3 ). 1,3-Di-tert -butyl-2-chloro-1,3,2-diazaphospholene was also prepared from the reaction 2 The analogous reaction with AsCl 3 gives likewise access to As heterocycles, cf.…”

Spezifische photochemische Dehydrokupplung N‐heterocyclischer Phosphane und ihre Anwendung in der photokatalytischen Erzeugung von H2

“…Die Edukte 1a-c, [6] 1' 'a,c [16] und 3c [12] wurden wie beschriebenh ergestellt. Photolyseexperimente mit isolierten Phosphanen wurden mit 3mm Lçsungeninentgasten und absolutierten Lçsungsmitteln (THF, [D 8 ]THF,H exan)i nP yrex-NMR-Rçhrchend urchgeführt.…”