An X-ray structure determination of the title compound shows that the co-ordination about the cobalt atom is approximately trigonal bipyramidal; n.m.r. data indicate that the complex is non-rigid in solution

Gray, Harry B.

Marsh, R. E.

Orio, A. A.

Titus, D. D.

English

Caltech Authors - Main

322 CHEMICAL COMMUNICATIONS, 1971 
The Crystal and Molecular Structure of Hydridotetrakis(diethy1 
phenylphosphonite)cobalt( I)? 
By D. D. TITUS, A. A. ORIO,$ R. E. MARSH, and HARRY B. GRAY* 
(Adhw Amos Noyes Laboratory of Chemical Physics, California I'titute of Technotogy, Pasadena, California 91 109) 
Summary An X-ray structure determination of the title 
compound shows that the co-ordination about the 
cobalt atom is approximately trigonal bipyramidal ; 
n.m.r. data indicate that the complex is non-rigid in 
solution. 
THE syntheses and n.m.r. spectra of HCo[(PhO),P141 and 
HCo[ (EtO) rP]> have been reported. Although HCo- 
[(EtO) ,PI4 has been assigned a square-pyramidal con- 
figuration on the basis of a temperature-independent high- 
field quintetJ2 the possibility of a distorted trigonal bipyra- 
midal structure with a very low intramolecular rearrange- 
ment barrier is attractive.1 We have found the latter 
possibility in the case of an analogous complex, HCo[(Ph)- 
P(OEt),],, and report its preparation and structural 
characterization. 
A mixture of cobaltous chloride, diethyl phenylphos- 
phonite, and ethanol was treated with a concentrated 
ethanolic solution of sodium borohydride. After filtration, 
orange-yellow holohedral prisms separated from the solu- 
tion (80% yield). 
In the i.r. spectrum v(C0-H) is observed as a weak band 
at 2017cm-l (Nujol mull). At  room temperature, the 
high-field n.m.r. spectrum (methylcyclohexane solution) 
consists of a quintet (T 24.5) with intensity ratios 
1 : 4 : 6 : 4 : 1. At - 55O, however, only a single broad band 
is observed (7 24.5). The change in the spectrum at low 
temperature is consistent with a non-rigid model forthe 
molecule. 
Crystal data: HCo[(Ph)P(OEt),],; M = 850; triclinic; 
a = 11.932(2); 6 = 12.841(2); c = 17.680(2) A; a = 95.50- 
= 1.25; 2 = 2; space group P1. 
Intensities of 4294 independent reflections were recorded 
on a Datex-automated General Electric diffractometer, 
using Co-K, radiation, The non-hydrogen atoms were 
located by Patterson and Fourier techniques, and least- 
squares refinements of the atomic parameters were carried 
out with all atoms vibrating anisotropically. The ethyl 
and phenyl hydrogen atoms were then positioned according 
to their known geometries. A difference Fourier map was 
calculated and the ligand hydrogen atom was observed as 
the most prominent feature of the map (0.36 e-/A3), 1.54 A 
from the cobalt atom. Positional parameters for the 
ligand hydrogen atom were refined in two subsequent 
cycles of least-squares refinement, yielding a position 
somewhat closer to the cobalt atom (Co-H 1-38 A). As 
X-ray studies classically yield short bond lengths when 
hydrogen atoms are involved, the true internuclear distance 
is probably closer to the 1-54 A distance derived from the 
difference Fourier parameters. At  the end of the refine- 
ment, R stood at 0.050. 
(1); = 89*75(1); y = 123*09(1)O; U = 2255 f 1 A3, Dc - 
t This research was supported by the National Science Foundation. 
$ On leave of absence from the Istituto di Chimica Generale, University of Padova. 
CHEMICAL COMMUNICATIONS, 197 1 323 
The inner co-ordination sphere about the cobalt atom is 
Selected bond distances and 
The approximately tetrahedral disposition of the four 
represented in the Figure. phosphorus ligands suggests strongly that the barrier to 
angles are given in the Table. The configuration of the intramolecular rearrangement via a tetrahedral COP, 
transition state would be extremely low. Presumably, in 
the transition state the hydrogen could tunnel between 
triangular face (edge) positions. The n.m.r. data require 
the barrier to be lower for HCo[phO),P], and HCo[(EtO),- 
PI4 than it is for HCo[(Ph)P(OEt),],, which implies that the 
solution ground-state COP, geometries of the former two 
complexes are closer to a tetrahedral configuration. 
TABLE 
I 
FIGURE. The inner co-ordination sphere of the cobaEt atom in 
[(Ph)P(O%I4* 
ligands about the cobalt atom is roughly trigonal bipyra- 
midal, with the cobalt atom positioned 0.492 k out of the 
equatorid plane defined by P( l), P(2), and P( 3). Although 
the four phosphorus atoms are arranged nearly tetrahedrally 
the hydride ligand occupies a specific co-ordination site. 
A recent X-ray study of HCo(PF,), failed to give the 
hydrogen atom position, although a slight distortion of the 
COP, structure from tetrahedral symmetry indicates that 
in this case also the hydrogen atom occupies a specific 
co-ordination site., These observations are of interest in 
view of the fact that in X-ray structural studies of HRh- 
(PPh,),' and HRh(PPh,) JAsPh,)b a specific co-ordination 
position for the hydrogen atom could not be established. 
Bond distances Bond angles 
Co-P(1) 2*116(2) A P(l)-Co-P(2) 124.1( 1)' 
C0-P(2) 2*103(2) P(l)-Co-P(3) 116-4(1) 
C0-P(3) 2*126(1) P(l)-Co-P(4) 97.8(1) 
C0-P(4) 2*128(1) P(2)-C+P(3) 104*5(1) 
CO-H 1*38(54)s P(2)-Co-P(4) 108*4(1) 
P(3)-Co-P(4) 104.9(1) 
P(4)-Co-H 173*6(2*0) 
8 See text. 
There appear to be significant differences in the cobalt- 
phosphorus bond distances for HCo[(Ph)P(OEt),],, as was 
also noted previously in the case of HCo(N,)(PPh,),.6 The 
Co-P bond distances in the present work are 0-06 to 0.10 A 
shorter than those in HCo(N,)(PPh,),, consistent with the 
greater --bonding capabilities of the (Ph)P(OEt) ligand. 
The v-acceptor character of (Ph)P(OEt) 2, however, does not 
appear to match that of PF,; the average Co-P distance in 
HCo(PF,), has been founds to be 2.052(5) k. 
(Received, December 7th, 1970; Corn. 2119.) 
J. J. Levison and S. D. Robinson, J .  Chem. SOC. (A) ,  1970,96. 
W. Kruse and R. H. AtaUa, Chem. Comm., 1968, 921. 
* B. A. Frenz and J. A. Ibers, Inorg. Chem., 1970.9, 2403. 
R. W. Baker and P. Pauling, Chem. Comm., 1969,1495. 
5 R. W. Baker, B. Ilmaier, P. J. Pauling, and R. S. Nyholm, Chem. Comm., 1970,1077. 
6 B. R. Davis, N. C. Payne, and J. A. Ibers, Inorg. Chem., 1969,8,2719. 


The crystal and molecular structure of Hydridotetrakis(diethyl phenylphosphonite)cobalt(I)

http://authors.library.caltech.edu/33186/1/TITcc71.pdf

The crystal and molecular structure of Hydridotetrakis(diethyl phenylphosphonite)cobalt(I)

Abstract

Similar works

Full text

Available Versions

Caltech Authors - Main