Abstract
The crystal structures of four new diphosphinated chromium Fischer amino carbenes with the compositions fac-[(P-P)(CO)3Cr=C(NR2′)(R)] (R = Me, NR2′ = pyrrolidino, P-P = dppe, 1; R = Me, NR2′ = pyrrolidino, P-P = dppp, 2; R = Me, R′ = Me, P-P = dppe, 3; R = Me, R′ = Me, P-P = dppp, 4) have been determined at 243 K. Compound 1 crystallizes in the monoclinic system, space group P21 /n with a = 12.1597(11) Å, b = 20.1556(17) Å, c = 14.0557(12) Å, β = 114.163(3)°, V = 3143.0(5) Å3, and Z = 4. Compound 2 crystallizes in the triclinic system, space group P − 1 with a = 7.4424(3) Å, b = 10.8830(5) Å, c = 20.6040(9) Å, α = 100.9880(10)°, β = 91.7650(10)°, γ = 97.6610(10)°, V = 1620.90(12) Å3, and Z = 2. Compound 3 crystallizes in the monoclinic system as a mono-solvate of d5-pyridine, space group P21 /c with a = 11.485(2) Å, b = 22.825(5) Å, c = 14.092(3) Å, β = 108.53(3)°, V = 3502.7(12) Å3, and Z = 4. Compound 4 crystallizes in the orthorhombic system, space group P2 1 2 1 2 1 with a = 8.359(3) Å, b = 15.364(6) Å, c = 23.784(9) Å, V = 3055(2) Å3, and Z = 4. Steric repulsions with the diphosphine ligand favor a conformation with the amino moiety directed away from the diphosphine backbone in 1–4.
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Notes
The syntheses, characterizations and some reactivity studies of compounds 1–3 have been published: Ref. [4].
Deuterated solvent was used as the dissolved samples were first subjected to NMR analysis. Presumably, non-deuterated pyridine could be used in its place.
Although the solutions contained an equilibrium mixture of fac and mer isomers, only the fac isomer was observed in the X-ray analyses. The mer isomer was the minor isomer in each case, and may not have crystallized out. Alternatively, crystals of the fac isomer may have been selected by happenstance.
In all of these complexes, the steric impact of the diphosphine ligand may also affect the observed bond lengths.
1H NMR results indicate that 1–3 adopt the same conformation in solution [4].
For discussion, the –CH2CH2– and –OCH(Me)– fragments of the 3-methyl-2-oxacyclopentylidenyl ligand in 7 are considered to be the alkyl and alkoxy carbene substituents, respectively.
The distance from C(5) to the more distant dppe methylene carbon is 4.315(4) Å and 4.186(3) Å in 1 and 3, respectively. The distance from the alkoxy oxygen to the more distant dppe methylene carbon is 3.855(3) Å, 3.738(2) Å, and 3.848(2) Å in 5, 6, and 7, respectively.
In 2, the distance from C(5) to either of the two methylene carbons attached to a phosphorus is essentially identical and averages 3.747(3) Å.
The analogous average distance in 2 is 3.506(3) Å.
References
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Acknowledgments
We thank the Faculty Center at California State Polytechnic University, Pomona for financial support for obtaining the X-ray diffraction analyses and the W. M. Keck Foundation Center for Molecular Structure (CMolS) at California State University, Fullerton. CMolS is a core facility of the California State University Program for Education and Research in Biotechnology (CSUPERB).
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Reinheimer, E.W., Kantardjieff, K.A., Ouyang, X. et al. Crystal Structures of Diphosphinated Chromium Fischer Amino Carbenes. J Chem Crystallogr 37, 507–515 (2007). https://doi.org/10.1007/s10870-007-9194-9
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DOI: https://doi.org/10.1007/s10870-007-9194-9