The phosphorus ligands are arranged almost tetrahedrally around the metal atoms, with the hydrogen ligands occupying the faces of the tetrahedra. 2 • In the initial stages of this work, various substituents were explored at the site of the ethyl group in an attempt to improve the binding ability of the ligand.
SECTION I
XPERIM:ENTAL
The stopcock of the pump is then closed and nitrogen pressure is established on both sides of the filter. The mother liquor is separated and reduced in volume to obtain more product. The crystals are washed several times with cold ethanol and dried under vacuum.
2 ( 0.02 mol), and the flask is heated on an oil bath~ The color of the mixture begins to lighten immediately (even before it: is hot) 9 and the solid gradually dissolves. The filtrate is allowed to stand under nitrogen at room temperature for several hours. The mother liquor is drawn off with a syringe and the almost colorless.
SPECTRA
Crystal structure calculations were performed using CRYM system programs on a 1Br computer. The weighting function used was w = 1/a- where er is the standard deviation of the intensity.
SECTION II
DIHYDRIDOTETRP.KIS (DIETHYLPHENYLPHOSPHONITE) IRON(II)
INTRODUCTION
The results of the present work indicate that such an assignment cannot be made on the basis of n.rn.r. or dipole moment data all. In the case of phosphine or carbonyl ligands converted to a hydride, the weakening of the transo bond can apparently be compensated.
With all these atoms included in the calculation input of the structure factor R. At this point in the refinement, the poor quality of the higher angle data was noted.
It is clear that carbon-carbon distars are unrealistic, especially in the case of ethoxy groups. As might be expected, the average of the relatively rigid phenylcarbon-carbon distances is only 0.02 R shorter than the usual 1.39.
EOUATORIAL PLANE
ATOM DEVIATION
Alternatively, the configuration of the complex could be considered as a highly distorted octahedron. In view of the general tendency towards tetrahedraal coordination of the non-hydrogen ligands in complexes of this type. Comparison of the v ib rats of this molecule with those of the very similar HCo((c.
Be caused by the large distance between the n mole vertices and the bulk of the phosphonium ligands.
DISCUSSION OF THE SPECTRAL PROPERTIES OF
The assignment of the symmetric quintet to a t rans isomer is more difficult to evaluate. In the present case, however, soma assumptions must be ba ma de in view of the steric problems of having four phosphonite ligands in the same plane. The authors concluded that the four phosphorus ligands in the "trans" isomer us undergo rapid intra-amolecular exchange.
As mentioned in the introduction, there seems to be an additional way of distinguishing between cis and trans.
VII VI II
XIII XIV
- two adjacent edges, C) two non-adja cent edges, D) a face and an adjacent edge~ and E) a face and a non-adjacent
In the following discussion, this configuration is used as a basis for examining possible hydride positions. Rapid rearrangement of the hydrides from face to edge and edge to face around tetrahedra of phosphorus atoms would produce an apparent equivalence of the phosphorus atoms and lead to a quintet in the high field p. The rearrangements of the phosphorus atoms during this process are much smaller than those required to produce the same effect in the C species.
This may account for the predominance of bit nate ligands in the complex s, which appear to have trans (C) configurations.
SECT ION III
INTRODUCTI ON
As in the case of the corresponding iron complex, several recrystallizations were needed to obtain it. A structure factor calculation with positional and thermal (estimated isotropic) parameters for all non-hydrogen atoms gave an R value of. The positional parameters of the thG phosphonium hydrogens were then calculated according to the known geometries of the atoms.
Correspondence of the Unit Cells and Atoms of the Iron and Cobalt Complexes.
Since the phosphorus ligand configuration would probably be different for the two species, we must expect large anisotropic thermal parameters for the atoms of the molecule. A comparison of the root-mean-square amplitudes of vibrations of the principal ellipsoidal axes for the two complexes (Tables 4 and 12. Although the phosphorus atoms are disposed n e ar ed tetrahedrally approximately the cobalt t atoms~ the general configuration appears to be t ha t of a trigonal bipyramid.
TRble 12. Continued
- Co(N 2)(PPh3) 3 2085 cm -1 54 H Co(PhP(OEt)z)z,, 2017
The parameters of the ligand atoms were found to be quite similar to those of the iron complex. As an example ~ it is assumed that all the 0-C bond distances are equivalent, the standard deviation of . The deviations of the carbon atoms from the least-squares planes of the four phenyl rings are given in table 13.
The presence of only one ligand hydrogen atom in this complex greatly simplifies the discussion of.
Consideration of the energies of the bands in Table 15 shows that the metal-hydrogen bands are comparable in energy to the bands in the c-dihydride complexes. There are three bands present in the infrared spectrum of DCo((C 6H5 ) P(OC2H5)2)4 which are not served in that of. Such reactivity is surprising since the iron dihydride has no detectable effect on iig Cl.
Movement of the hydrogen across the edge positions will be relatively difficult in such a situation (see Section II) and the intramolecular re-. oc2H5)2)4 the phosphorus ligands can be moved further.
The authors therefore concluded that the hydrogen atom was protected from reaction by one or more of the phenyl groups. 4 will act as an acid in the presence of triethylamine (the test used for acidity. 4 readily forms the anion Co(PF 3) 4 - in the presence of triethylamine; however, this complex is not prepared in the presence of NaBH.
4 • All currently available evidence indicates that only PF is a phosphorus ligand.
SECTION IV
SUMMARY
The prevailing theme throughout this work has been the tetrahedral arrangement of the phosphonite ligands around the metal a to m. The question may well arise as to the necessity of speaking of the hydride complexes as fundamentally distorted tetrahedra rather than distorted oct a hedra. The relative low energy of one of the iro bands indicated that a species approaching a t trans isomer (L H-Fe-H somewhat less than 180 0 ) was.
The A arrangement is the only configuration that does not require one of the hydrides to occupy an energetically unfavorable edge.
APPENDIX I
IC2 10.I IOl
Derived from difference Fourier map
APPENDIX II
ADDITIONAL STRUCTUR.~.L DATA FOR
TION S
It also appears because the w-receptivity (or whatever unknown mechanism gives the acceptability (or whatever unknown mechanism gives the appearance of T-acceptance) increases with the electronegativity of the phosphorus substituents. Researching all of the aforementioned complexes would be a major undertaking; it is likely , that experimental difficulties will preclude the investigation of some compounds.Phosphorus compounds were chosen in this case because of the large variety of known complexes suitable for this type of study.
The chemical shifts are certainly not large (8 ) P, and it may be that such a dete:cmi nation is actually beyond the ca:;:i similairties of the ESCA system.
PR OPOSITIO N 2
The disorder of the chains relative to each other is observed in oscillation photographs (camera axis parallel to the chains) as diffuse bands instead of the odd numbered layer lines. One of the obvious choices to consider is the perchlorate anion and a perchlorate complex. An examination of oscillation photographs of this complex reveals no sign of the previously observed low line bands.
It now appears that in the case of non-bridged species (such as Magnus's green salt, (Pt(NH. 3) 4)(PtC14))P that the usual spectral features are not due to any metal -metal bonding ~ but to perturbations of energy states from the close presence of cation and anion (12).
5 ) 2 PcH
Although hydride complexes of many transition metals are now known and in many cases are under extensive investigation, hydride complexes of nickel have previously received Although there are likely several reasons for this apparent neglect, the most obvious is the very small number of known stable nickel hydride complexes. As with the other transition metals, phosphine ligands tend to stabilize hydride complexes to a.
2 P- (C6H5)2)2Ni has been shown to yield the cation
Bridging hydrogen atoms are not unknown in transition metal complexes and some structural work has been carried out (7,8i9); the hydrogen atom position is fixed in the structure deter-. In view of the similar borohydride complex reported (5), it seems very possible that the low temperature n.m.r spectrum will still be consistent with the hydrogen-bridged structure. In addition, it is suggested that the unit cells and space groups of the complexes are determined.
It may be advantageous to use a more asymmetric form of the phosphorus ligand if the symmetry of the cell is too high.
PROPOS ITI ON 4
The acetonitrile ligands are quite labile and should be easily replaced by the stronger bonding CNO- ligands
- In order to have an internal check on the trans influ- ence , the system should be structured such that there are
Such an analysis, similar to that performed for cyanide complexes (16), would provide a better idea of the nature of the binding in the fulminate ligand. Although much work has been done investigating the trans effects of various ligands (mostly in relation to platinum(ll)), very little structural information is available on the trans influence of the ligands. There is a need for a systematic study, similar to the kinetic studies conducted on trans.
For the proposed work, we would like to investigate the trans influence of several different ligands on a single trans ligand.
