The Fluxionality of Tri-iron Dodecacarbonyl

by Brian E. Mann

Department of Chemistry, The University of Sheffield, Sheffield S3 7HF, England.

e-mail b.mann@sheffield.ac.uk


The following document is supporting material for:


In the paper it is argued that the lowest energy dynamic process producing carbonyl exchange in [Fe3(CO)12] is rotation of the icosahedron of carbonyls about the S10 axis through carbonyls 6 and 10 using the numbering scheme below.

The mechanism is demonstrated using the Bürgi-Dunitz approach. This document contains a movie to demonstrate the fluxional mechanism by using the published crystal structures of [Fe3(CO)12] at 100K, [Fe3(CO)11PPh2(CH2)6PPh2Fe3(CO)11], [Fe3(CO)11{P(OMe)3], and [Fe3(CO)10{1,2-(Me2As)2C6H4}]. In order to generate each frame of the movie. the structures were processed as follows:-

  1. Non-carbonyl ligands were replaced by carbonyls using the same bond direction as in the original and placing the carbon and oxygen so that the Fe-C distance is 1.75Å, the C--O distance is 1.15Å, and the Fe--C--O bond angle is 180°.
  2. The molecule is placed so that carbons 6 and 10 form the z-axis (out of the plane of the screen).
  3. Carbons 6 and 10 and Fe2 were placed in the xz plane, so that Fe2 lies to the right of carbons 6 and 10. (The x-axis runs horizontally from left to right of the screen and the y axis runs vertically from the bottom to the top of the screen.)
  4. The structure was centred on Fe2.

There are 12 pictures making up the loop of the movie:-

Frame 1.
The structure of [Fe3(CO)12] giving a 0° rotation of the carbonyl icosahedron.
Frame 2.
The structure of one of the two identical fragments in [Fe3(CO)11PPh2(CH2)6PPh2Fe3(CO)11] giving a 6° rotation of the carbonyl icosahedron.
Frame 3.
The structure of the most strongly rotated molecule in [Fe3(CO)11{P(OMe)3}] giving an 8° rotation of the carbonyl icosahedron.
Frame 4.
The structure of [Fe3(CO)10{1,2-(Me2As)2C6H4}] giving a 18° rotation of the carbonyl icosahedron.
Frame 5.
The structure of the most strongly rotated molecule in [Fe3(CO)11{P(OMe)3}], reflected through the xy and xz planes giving a 28° rotation of the carbonyl icosahedron.
Frame 6.
The structure of one of the two identical fragments in [Fe3(CO)11PPh2(CH2)6PPh2Fe3(CO)11] reflected in the xy and xz planes giving a 30° rotation of the carbonyl icosahedron.
Frame 7.
The structure of [Fe3(CO)12] reflected in the xz plane giving a 36° rotation of the carbonyl icosahedron.
Frame 8.
The structure of one of the two identical fragments in [Fe3(CO)11PPh2(CH2)6PPh2Fe3(CO)11] reflected in the xz plane giving a 42° rotation of the carbonyl icosahedron.
Frame 9.
The structure of the most strongly rotated molecule in [Fe3(CO)11{P(OMe)3}] reflected in the xz plane giving a 44° rotation of the carbonyl icosahedron.
Frame 10.
The structure of [Fe3(CO)10{1,2-(Me2As)2C6H4}] reflected in the xz plane giving a 54° rotation of the carbonyl icosahedron.
Frame 11.
The structure of the most strongly rotated molecule in [Fe3(CO)11{P(OMe)3}] reflected in the xy plane giving a 64° rotation of the carbonyl icosahedron.
Frame 12.
The structure of one of the two identical fragments in [Fe3(CO)11PPh2(CH2)6PPh2Fe3(CO)11] reflected in the xy plane giving a 66° rotation of the carbonyl icosahedron.

Above is an in-line animated "gif" showing the rotation of the icosahedron of carbonyls around the Fe3 triangle of [Fe3(CO)12] using the frames listed above.

The molecule is viewed along the C-6 to C-10 axis. The iron atoms are in grey, the carbons in black and the oxygens in red. Depth is indicated by the sizes of the atoms. As actual structures have been used rather than idealised structures, there is some unevenness to the motion due to distortions of the carbonyl icosahedron by the ligand(s) and/or crystal packing.


References

X-ray structures:-

CRYST1    8.110   12.680   22.171  91.88  99.64  98.16
SCALE1      0.123305  0.017681  0.022006       0.000000
SCALE2      0.000000  0.079671  0.004627       0.000000
SCALE3      0.000000  0.000000  0.045827       0.000000
ATOM      1 FE1          0      -1.922   9.503  17.446 1.000  5.41
ATOM      2 FE2          0      -3.888   7.762  17.979 1.000  4.61
ATOM      3 FE3          0      -2.593   8.741  19.942 1.000  4.97
ATOM      4  C2AA        0      -8.598   2.328  13.716 0.657  5.93
ATOM      5  O2AA        0      -9.625   1.753  13.801 0.657  7.43
ATOM      6 FE3A         0      -6.668   2.152  12.613 1.000  4.68
ATOM      7 FE2AA        0      -7.580   3.850  14.307 0.657  5.72
ATOM      8  C8AA        0      -6.499   5.118  14.872 0.657  7.08
ATOM      9  O8AA        0      -5.796   5.969  15.143 0.657  9.64
ATOM     10 FE2BB        0      -7.869   3.341  14.677 0.343  4.86
ATOM     11  C8BB        0      -6.370   4.433  15.059 0.343  7.01
ATOM     12  O8BB        0      -5.944   5.494  15.235 0.343  8.20
ATOM     13 FE1A         0      -5.562   2.279  15.061 1.000  5.55
ATOM     14  C2BB        0      -9.036   2.074  14.105 0.343  4.28
ATOM     15  O2BB        0      -9.756   1.258  13.834 0.343  7.36
ATOM     16  C1A         0      -6.311   3.950  12.360 1.000  4.99
ATOM     17  O1A         0      -5.940   4.903  11.890 1.000  7.09
ATOM     18  C4A         0      -7.005   1.399  15.709 1.000  7.08
ATOM     19  O4A         0      -7.712   0.692  16.234 1.000 10.76
ATOM     20  P1          0      -3.369   7.967  21.827 1.000  5.47
ATOM     21  P1A         0      -7.942   2.177  10.849 1.000  4.88
ATOM     22  O1          0      -2.109   5.845  19.467 1.000  5.98
ATOM     23  O2          0      -5.387   9.739  19.606 1.000  6.33
ATOM     24  O3          0      -0.065   7.221  17.386 1.000  8.69
ATOM     25  O4          0      -3.863  11.715  17.650 1.000  8.55
ATOM     26  O5          0       0.318  11.328  17.861 1.000 10.51
ATOM     27  O6          0      -2.088   9.431  14.518 1.000  9.98
ATOM     28  O7          0      -5.925   5.862  18.860 1.000  7.52
ATOM     29  O8          0      -2.776   5.966  15.917 1.000  9.11
ATOM     30  O9          0      -5.630   9.156  16.093 1.000  8.42
ATOM     31  O11         0       0.209   8.325  20.691 1.000  9.38
ATOM     32  O12         0      -2.565  11.575  20.725 1.000  9.99
ATOM     33  O13         0      -4.673   7.134  21.567 1.000  6.16
ATOM     34  O14         0      -2.483   6.896  22.579 1.000  9.48
ATOM     35  O15         0      -3.678   8.933  23.026 1.000  8.47
ATOM     36  O3A         0      -3.536   3.892  13.675 1.000  7.58
ATOM     37  O5A         0      -4.055  -0.228  14.941 1.000 10.18
ATOM     38  O6A         0      -4.574   3.146  17.667 1.000 12.41
ATOM     39  O7A         0      -9.258   5.728  13.095 1.000  8.12
ATOM     40  O9A         0      -9.095   3.717  17.010 1.000 12.69
ATOM     41  O11         0      -4.158   1.425  11.318 1.000  8.77
ATOM     42  O12         0      -7.248  -0.661  13.153 1.000  9.82
ATOM     43  O13         0      -8.580   0.788  10.579 1.000  8.45
ATOM     44  O14A        0      -7.493   2.882   9.521 0.657  6.98
ATOM     45  O14B        0      -7.195   1.914   9.403 0.343  5.23
ATOM     46  O15         0      -9.078   3.211  10.964 1.000  9.97
ATOM     47  C1          0      -2.540   6.892  19.294 1.000  4.82
ATOM     48  C2          0      -4.472   9.109  19.339 1.000  4.87
ATOM     49  C3          0      -0.803   8.071  17.483 1.000  6.26
ATOM     50  C4          0      -3.159  10.838  17.614 1.000  6.31
ATOM     51  C5          0      -0.548  10.624  17.713 1.000  7.46
ATOM     52  C6          0      -2.032   9.476  15.645 1.000  6.96
ATOM     53  C7          0      -5.141   6.600  18.535 1.000  5.11
ATOM     54  C8          0      -3.159   6.656  16.723 1.000  6.06
ATOM     55  C9          0      -4.933   8.650  16.813 1.000  5.65
ATOM     56  C11         0      -0.860   8.476  20.371 1.000  6.40
ATOM     57  C12         0      -2.588  10.487  20.410 1.000  6.90
ATOM     58  C13         0      -5.442   6.479  22.593 1.000  7.42
ATOM     59  H13         0      -6.195   6.041  22.190 1.000  6.56
ATOM     60  H13         0      -4.889   5.828  23.031 1.000  6.56
ATOM     61  H13         0      -5.752   7.120  23.237 1.000  6.56
ATOM     62  C14         0      -1.579   7.073  23.562 1.000 12.60
ATOM     63  H14         0      -1.215   6.208  23.748 1.000  6.56
ATOM     64  H14         0      -0.908   7.651  23.218 1.000  6.56
ATOM     65  H14         0      -2.054   7.427  24.264 1.000  6.56
ATOM     66  C15         0      -4.679   9.870  23.016 1.000 11.35
ATOM     67  H15         0      -4.693  10.354  23.845 1.000  6.56
ATOM     68  H15         0      -4.529  10.482  22.291 1.000  6.56
ATOM     69  H15         0      -5.521   9.426  22.891 1.000  6.56
ATOM     70  C3A         0      -4.335   3.272  14.171 1.000  5.70
ATOM     71  C5A         0      -4.624   0.750  14.943 1.000  6.61
ATOM     72  C6A         0      -4.996   2.829  16.670 1.000  7.82
ATOM     73  C7A         0      -8.654   4.915  13.579 1.000  6.48
ATOM     74  C9A         0      -8.538   3.714  16.020 1.000  8.97
ATOM     75  C11         0      -5.143   1.706  11.825 1.000  5.79
ATOM     76  C12         0      -7.035   0.437  12.992 1.000  6.35
ATOM     77  C13         0      -9.379   0.377   9.501 1.000  7.79
ATOM     78  H13         0      -9.629  -0.542   9.617 1.000  6.56
ATOM     79  H13         0     -10.169   0.921   9.457 1.000  6.56
ATOM     80  H13         0      -8.879   0.473   8.687 1.000  6.56
ATOM     81  C14         0      -6.343   2.692   8.831 1.000 10.64
ATOM     82  H14A        0      -6.337   3.260   8.057 0.657 15.96
ATOM     83  H14A        0      -6.283   1.774   8.556 0.657 15.96
ATOM     84  H14A        0      -5.594   2.908   9.392 0.657 15.96
ATOM     85  H14B        0      -6.063   2.304   7.999 0.343 15.96
ATOM     86  H14B        0      -5.581   2.807   9.404 0.343 15.96
ATOM     87  H14B        0      -6.750   3.545   8.665 0.343 15.96
ATOM     88  C15B        0      -9.924   3.775   9.990 1.000  9.25
ATOM     89  H15B        0     -10.533   4.387  10.411 1.000  6.56
ATOM     90  H15B        0      -9.390   4.246   9.347 1.000  6.56
ATOM     91  H15B        0     -10.422   3.083   9.547 1.000  6.56

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Last updated:- 14th January, 1997