The synthesis and oxidation of some cyclophosphazanes
The reactions of a series of cyclic and acyclic phosph(])azanes
with diborane and borane adducts were investigated in an attempt to establish
the most reactive nucleophilic sites in the phosph(31t)azanes and to gain
information relating conformation and reactivity.
Tris (dim ethyl amino) phosphine, P(NMe2)3, reacted with triethylamine
-borane, Et3NBH3, to produce the monoborane adduct, (Me2N[()M3Pe2BNH)32.P ]R2eNaMcetio n
of diborane, B2H6, with the acyclic phosph(7I[)azanes, gave
a diborane adduct. In similar reactions of B2H6 with a series of phosph(I)azanes
= Me, Et and Pr' the products rapidly decomposed, but evidence
was obtained for the formation of a monoborane adduct where R= Me and Et. In
all cases where an acyclic phosphazane-borane adduct was obtained it was
established that the BH3 group was bonded to the phosphorus atom.
Analogous reactions with cyclodiphosph(=)azanes have shown that
BH3 groups bond to the P2N2 ring through the phosphorus atoms. The reactions
of cis and trans (Me2NPNBut)2 with 1 mole equivalent of Et3NBH3 produced only
cis Me2N(BH3)PNBut. P(NMe2)NBut , with 2 mole equivalents of Et3NBH3 a bis
borane adduct was obtained, the proportion of the geometrical isomers produced
being dependent on the temperature of the reaction.
The reaction of (Me2NPNBut)2 with excess diborane, B2H6, proceeded
with overall retention of configuration. Analogous reactions using (MeOPNBut)
gave a bis borane adduct, similar to those above but (MeOPNBut)2 was less
reactive than (Me2NPNBut)2"
An attempted reaction between (C1PNBut)2
and Et3NBH3 failed to
produce a borane adduct, but when the reaction was repeated using tetrabydrofuran-
borane, THF. BH3, the monoborane adduct , C1(BH )pNBu t NBut
Over a period of several weeks cis-Me 2N(BH3)PNButP-(NMe2)NBut disproportionated
to cis-(Me 2NPNBut)2 and cis-(Me 2N(BH3)PNBut)2"
Nmr data indicates that the reaction of (XPNBut)2 (X = Cl or We2)
and 1 mole equivalent of chlorine gave a product which is either XPNBXNB t
or the ionic salt XPNBuF+C1 me2NBut Cl . When the reaction was repeated
using (C1PNBut)2 and excess chlorine, ring cleavage occured, the only
identifiable product being Cl2P(0)I PCl2N(H)But. (ClPNBut)2 and bromine
resulted mainly in the formation of decomposition products.
Reaction of C1PNButPC1NR (R = Me, Et) with excess of dry chlorine
surprisingly gave a zwitterionic product, C12PNBuP C14NR (R = Me, Et).
The reaction of ClPNButPClNEt with 1 mole equivalent of bromine gave either
C1PNButPC1Br2NEt or C1PNButP+BrXNEt Y (X and Y= Cl or Br). When the
reaction was repeated with 2 mole equivalents or excess bromine, a
zwitterionic product was obtained.
By contrast, the reaction of (C1PNPh)2 and excess chlorine
resulted in the simple oxidation product, (C13PNPh)2.
Reactions of excess chlorine with a series of acyclic phosph(M)azane
of the type (C12P)2N. R (R = Me, Et and Prn ) gave cyclodiphosph(Y)azanes,
(Cl3PNR)2 (R = Me, Et, and Prn). These reactions have been shown to proceed
via two intermediate. compounds, the first is still unidentified but the
second has been identified by nmr as the hitherto unknown monomeric species
Cl3P=NR (R = Me, Et, and Prn), and C13P=NBut.
When the reactions were repeated with bromine the products again
included (C13PNR)2, though small quantities of (BrCl2PNR)2, (Br2C1PNR)2
(Br3PNR)2 were found in small traces along with PC13, PC12Br, and PC1Br2.
The formation of phosph(IIL)azanes by the reaction of PC13
with EtNH3C1 in refluxing sym-tetrachloroethane has been reinvestigated.
It was found that different major products (C12P)2NEt, (C1PNEt)3 and
P4(NEt)5C12 could be obtained by suitable variation of the stoichiometry,
However, when the reactions were repeated using McNH3Cl instead of
EtNH3C1, only (C12P)2NMe could be obtained. When (C12P)2NR (R - Me or
Et) was heated, (C1PNR)3 (R = Me or Et) and PC13 were produced along
with decomposition products. The reverse reaction was also possible;
refluxing a solution containing PC13 and p4(NEt)5Cl2 gave (C1PNEt)3
and3in turn, (C12P)2NEt.
A series of derivatives of (C1PNEt)3 were prepared,
(Me2NPNEt)3 was obtained only as a trans isomer while (MeOPNEt)
3 were present as a mixture of cis and trans isomers.
Conformational information for these rings was difficult to establish.
The ring compound (C1PNEt)3 was also reacted with a series of monoamines
H2NR (R = Et, Pri, and But) to produce a trans substituted product,
(R(H)NPNEt)3 (R = Et, Pri, and But), and a fused ring compound,
The ratio of the two types of products varied with the size of R, the
larger R the more the fused ring compound was favoured. This proportion
of products, as detected by
nmr, was also affected by heating
which favoured the fused ring compound. An adamantane like cage molecule
P4(IEt)6 was also identified.
Fluoro-, alkylamino- and alkoxy- derivatives of'p4(NEt)5Cl2
were prepared by reaction with SbF3, Me2NH, Et2NH, C5H10NH, NeOH and
ButOH. In all cases two isomers were formed, termed 'symmetric' and
'asymmetric' (these terms are based on consideration of the 31p
spectra and the resulting structural assignments of the terminal
The reaction of P4(NEt)5C12 with a series of monoamines
RNH2 (R = Et, But and H) led to the formation of a series of compounds
P4(NR)5(NR') (R = Et, R' = But or H) with an adamantane-like cage
structure. In the reaction of P4(NEt)5C12 with EtNH2 an intermediate
with a direct P -P bond was tentatively identified.
Oxidation reactions using So, Sen, Tea and BuL00H were VV
carried out on (ClPNEt)
3 and P4(NEt)5C12 and their derivatives. The
reaction of (Me2NPNEt)3 and (MeOPNEt)
3 with sulphur and selenium gave
the oxidation products (Me2N(X)PNEt)3 (X =S or Se), and (Me0(Y)PNEt)3
(Y =S or Se). In all cases only a trans isomer was obtained regardless
of the structure of the starting material. The reaction of (C1PNEt)3
with three moles of Me2SO gave only a small amount of the trans monoand
di-o7yr derivatives, Cl(0)PNEt. P(C1)NEt. P(Cl)NEt and
Cl(0)PNEt. P(Cl)(0)NEt. P(Cl)NEt respectively. Dithio-derivatives
2)2S2 and P4(NEt)5(NC5H10)2S2 were also made by reaction
with elemental sulphur. Only one isomer was obtained in each case,
possibly containing the sulphur atoms bonded to terminal phosphorus
atoms. Reactions with elemental Se8 mainly produced decomposition
The oxide, p4(NEt)5c120, as a mixture of two isomers, was
produced by the reaction of Me2SO on P4(NEt)5C12 and it was also
found as an impurity in a number of reactions.