_P.-Powell-auth.-Principles-of-Organometallic-Chemistry-Springer-Netherlands-1988

Organic derivatives of Group V
stibine oxides such as Ph,SbO are polymeric. Their structures thus involve formal
single bonds (Ph,Sb-0-) 11 • Other typical reactions of R,M (M = P. As. Sb)
include the addition of sulphur, selenium. halogens (X= CI. Br. I) and alkyl
halides (to give quaternary salts).
Phosphine oxides are extremely inert compounds. Me,PO is stable up to 700UC;
Ph,PO can be nitrated with a mixture of concentrated nitric and sulphuric acids
to give (3-0 2 NC 6 H 4 ),PO. Reduction to the phosphine is difficult. but can be
achieved with lithium aluminium hydride. R,PO and R,AsO form adducts
through oxygen with a wide range of Lewis acids. Typical complexes include
HgCl 2 L 2 • SnCl 4 L 2 and NiBr), 2 (L = Ph,PO or Ph,AsO). Phosphine oxides are
used to complex actinides such as uranium and plutonium in their separation by
solvent extraction.
4. 9. 3 Organo-halides
Halides R 2 MX and RMX 2 are formed by ali the elements P to Bi. In general they
ha ve pyramidal molecular structures. The rather high melting points of MeBiCl 2
(242°C) and Me 2 BiCl ( ll6rC) suggest that these compounds may be associated
in the solid state. Phosphorus forms a complete set of halides Me"PX, "
(Table 4.4). The fluorides are monomeric. volatile species. which have trigonal
bipyramidal structures. Electron diffraction studies show that the tluorine atoms
preferentially occupy the axial positions. The axial P-Fax bonds are longer than
the equatorial P-Feq· 19 F n.m.r. studies confirm these findings for Me,PF 2
Table 4.4. Organohalides of Group V elements
F
F
1 __--Me 1 /Me
Me-P' Me-p'
1 "'Me
Me
1 "Me
F
Me}.x-
Me,Px.x-
Me,AsF2
molecular
Me,As +X- Me,AsCI 2
molecular,
weak CI bridges
Me 4 Sb+x- Me,SbX2
molecular
(X=F. CI. Br. Il
no alkyls
Ph,BiXZ
molecular
(X= F. CI. Br)
F
1
_-Me
F-p"
I"Me
F
Me 2 PX 2 .X
Me 2 AsF,
probably
associated
Me 2 AsCI,
dec. 40 C
F
_-F
1
Me-P"
I"F
F
r
MePX,.X
MeAsCI 4
dec. cre
Me 2 SbCI, MeSbCI 4
dec. > 120 C dec. 1 'i C
Me 2 SbBr 1
dec.- 1 ') C
Mole-
cular
structures
cf PF 5
cf. PCI.+ PCih
AsF,
AsCI,
dec. -
'50 C
SbCI,
dec. 140 C
Autoionized.
129