SYNTHESIS OF THE 17-ELECTRON CATIONS [FEL(L')(NO)(2)](- STRUCTURE ANDBONDING IN 4-CO-ORDINATE METAL DINITROSYLS, AND IMPLICATIONS FOR THE IDENTITY OF PARAMAGNETIC IRON DINITROSYL COMPLEX CATALYSTS() (L,L'=PPH(3), OPPH(3)) )
Fl. Atkinson et al., SYNTHESIS OF THE 17-ELECTRON CATIONS [FEL(L')(NO)(2)](- STRUCTURE ANDBONDING IN 4-CO-ORDINATE METAL DINITROSYLS, AND IMPLICATIONS FOR THE IDENTITY OF PARAMAGNETIC IRON DINITROSYL COMPLEX CATALYSTS() (L,L'=PPH(3), OPPH(3)) ), Journal of the Chemical Society. Dalton transactions, (17), 1996, pp. 3491-3502
The complex [FeL(2)(NO)(2)] (L = PEt(3) 1a, L = PPh(3) 1b or L(2) = dp
pe 1c) prepared from [{Fe(mu-I)(NO)(2)}(2)] and PPh(3) or Ph(2)PCH(2)C
H(2)PPh(2) (dppe) {in the presence and absence of [Co(cp)(2)] (cp = et
a(5)-C5H5) respectively} undergo one-electron oxidation at a platinum
electrode in CH2Cl2. The complex [{Fe(mu-dppm)(NO)(2)}(2)] 2, prepared
from [{Fe(mu-I)(NO)(2)}(2)] and Ph(2)PCH(2)PPh(2) (dppm) in the prese
nce of [Co(cp)(2)], undergoes two sequential one-electron oxidations.
Complex 1b with [Fe(cp)(2)](+) gave 1b(+), X-ray studies of which show
a distorted tetrahedral geometry with near C-2 upsilon symmetry. Oxid
ation of 1b leads to substantial lengthening of the Fe-P bonds and cha
nges in the P-Fe-P and N-Fe-N angles. These changes are consistent wit
h significant Fe-P pi-bonding character in the singly occupied molecul
ar orbital of 1b(+). Cation 1b(+) reacts with halide ions, giving [FeX
(PPh(3))(NO)(2)] (X = Cl or I) and then [FeX(2)(NO)(2)](-), and with O
PPh(3) to give [Fe(OPPh(3))(PPh(3))(NO)(2)](+) 3(+). X-Ray studies on
the last, as its [PF6](-) salt, show a distorted tetrahedral geometry;
the co-ordination angles at iron approach trigonal bipyramidal with t
he PPh(3) ligand in one apical site and the other apical site vacant.
The complex [Fe(OPPh(3))(2)(NO)(2)](+) 4(+) resulted from the reaction
between [{Fe(mu-I)(NO)(2)}(2)] and OPPh(3) in the presence of TlPF6.
An analysis of the ESR spectra of the paramagnetic cations 1b(+), 3(+)
and 4(+), together with extended-Huckel MO calculations on models of
1b(+) and 3(+), suggest that the complex catalysts formed from [{Fe(mu
-Cl)(NO)(2)}(2)] and Ag+ or Tl+ are also four-co-ordinate 17-electron
radicals. A crystallographic database study of four-co-ordinate dinitr
osyl complexes of iron and other metals confirms that the N-Fe-N and O
... Fe ... O angles are linearly related. Consideration of these geom
etric effects, and those resulting from oxidation of 1b, in the light
of a model proposed by Summerville and Hoffmann provides insight into
the bonding in these and related species.