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. 2025 Feb 24;15(8):6000-6014.
doi: 10.1039/d4ra01410c. eCollection 2025 Feb 19.

Alkyne dichotomy and hydrogen migration in binuclear cyclopentadienylmetal alkyne complexes

Huidong Li  1   2 , Jinfeng Luo  1 , Haoyu Chen  1 , Ruilin Lu  1 , Yucheng Hu  1 , Huijie Wang  1 , Yanshu Wang  1 , Qunchao Fan  1 , R Bruce King  2 , Henry F Schaefer 3rd  2
Affiliations

Alkyne dichotomy and hydrogen migration in binuclear cyclopentadienylmetal alkyne complexes

Huidong Li et al. RSC Adv. .

Abstract

The structures and energetics of the binuclear cyclopentadienylmetal alkyne systems Cp2M2C2R2 (M = Ni, Co, Fe; R = Me and NMe2) have been investigated using density functional theory. For the Cp2M2C2(NMe2)2 (M = Ni, Co, Fe) systems the relative energies of isomeric tetrahedrane Cp2M2(alkyne) structures having intact alkyne ligands and alkyne dichotomy structures Cp2M2(CNMe2)2 in which the C[triple bond, length as m-dash]C triple bond of the alkyne has broken completely to give separate Me2NC units depending on the central metal atoms. For the nickel system Cp2Ni2C2(NMe2)2 as well as the related nickel systems Cp2Ni2(MeC2NMe2) and Cp2Ni2C2Me2 the tetrahedrane structures are clearly preferred energetically consistent with the experimental syntheses of several stable Cp2Ni2(alkyne) complexes. The tetrahedrane and alkyne dichotomy structures have similar energies for the Cp2Co2C2(NMe2)2 system whereas the alkyne dichotomy structures are significantly energetically preferred for the Cp2Fe2C2(NMe2)2 system. The potential energy surfaces for the Cp2M2(MeC2NMe2) and Cp2M2C2Me2 systems (M = Co, Fe) are complicated by low-energy structures in which hydrogen migration occurs from the alkyne methyl groups to one or both alkyne carbon atoms to give Cp2M2(C3H3NMe2) and Cp2M2(C3H3Me) derivatives with bridging metalallylic ligands, Cp2M2(CH2[double bond, length as m-dash]C[double bond, length as m-dash]CHNMe2) and Cp2M2(CH2[double bond, length as m-dash]C[double bond, length as m-dash]CHMe) with bridging allene ligands, as well as Cp2M2(CH2[double bond, length as m-dash]CH-CNMe2) and Cp2M2(CH2[double bond, length as m-dash]CH-CHMe) with bridging vinylcarbene ligands. For the Cp2M2C2Me2 (M = Co, Fe) systems migration of a hydrogen atom from each methyl group to an alkyne carbon atom can give relatively low-energy Cp2M2(CH2[double bond, length as m-dash]CH-CH[double bond, length as m-dash]CH2) structures with a bridging butadiene ligand. Five transition states have been identified in a proposed mechanism for the conversion of the Cp2Co2/MeC[double bond, length as m-dash]CNMe2 system to the cobaltallylic complex Cp2Co2(C3H3NMe2) with intermediates having agostic C-H-Co interactions and an activation energy barrier sequence of 13.1, 17.0, 15.2, and 12.0 kcal mol-1.

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Conflict of interest statement

The authors declare no competing financial interests.

Figures

Fig. 1
Fig. 1. Structures of some experimentally known alkyne metal complexes.
Fig. 2
Fig. 2. Products formed by hydrogen migration from Mn2(CO)8(MeC2NEt2) structurally characterized by X-ray crystallography.
Fig. 3
Fig. 3. The tetrahedrane and alkyne dichotomy structures for the Cp2M2C2RR′ derivatives.
Fig. 4
Fig. 4. The optimized low-energy Cp2Ni2C2(NMe2)2 structures. The symmetry of the structure is indicated in parentheses in the first line. The numbers in parentheses in the second line are the relative emergies (ΔE in kcal mol−1) predicted by M06-L/def2-TZVP method.
Fig. 5
Fig. 5. The optimized low-energy Cp2Co2C2(NMe2)2 structures. The symmetry of the structure is indicated in parentheses in the first line. The numbers in parentheses in the second are the relative energies (ΔE in kcal mol−1) predicted by M06-L/def2-TZVP method.
Fig. 6
Fig. 6. The reaction pathway between the singlet tetrahedrane and dichotomy Cp2Co2C2(NMe2)2 isomers 2N–Co–3S and 2N–Co–1s, respectively, showing the low energy barrier of ∼6.0 kcal mol−1. The numbers in parentheses are the relative energies predicted by M06-L/def2-TZVP method.
Fig. 7
Fig. 7. The optimized low-energy Cp2Fe2C2(NMe2)2 structures. The symmetry of the structure is indicated in parentheses in the first line. The numbers in parentheses in the second line are the relative energies (ΔE in kcal mol−1) predicted by M06-L/def2-TZVP method.
Fig. 8
Fig. 8. Structure types formed by hydrogen migration from methyl groups in methylalkynes (a to d); an observed sandwich-type structure (e).
Fig. 9
Fig. 9. The optimized low-energy Cp2Ni2(MeC2NMe2) structures. The symmetry of the structure is indicated in parentheses in the first line. The numbers in parentheses in the second line are the relative energies (ΔE in kcal mol−1) predicted by M06-L/def2-TZVP method.
Fig. 10
Fig. 10. The optimized low-energy Cp2Co2(MeC2NMe2) structures. The symmetry of the structure is indicated in parentheses in the first line. The numbers in parentheses in the second line are the relative energies (ΔE in kcal mol−1) predicted by M06-L/def2-TZVP method.
Fig. 11
Fig. 11. The optimized low-energy Cp2Fe2(MeC2NMe2) structures. The symmetry of the structure is indicated in parentheses in the first line. The numbers in parentheses in the second line are the relative energies (ΔE in kcal mol−1) predicted by M06-L/def2-TZVP method.
Fig. 12
Fig. 12. The optimized low-energy Cp2Ni2C2Me2 structures. The symmetry of the structure is indicated in parentheses in the first line. The numbers in parentheses in the second line are the relative energies (ΔE in kcal mol−1) predicted by M06-L/def2-TZVP method.
Fig. 13
Fig. 13. The optimized low-energy Cp2Co2C2Me2 structures. The symmetry of the structure is indicated in parentheses in the first line. The numbers in parentheses in the second line are the relative energies (ΔE in kcal mol−1) predicted by M06-L/def2-TZVP method. Four of the other seven low-energy Cp2Fe2C2Me2 structures, namely 0N–Fe–3T, 0N–Fe–4T, 0N–Fe–7S, and 0N–Fe–8S, have bridging ferrallylic ligands with the three higher energy structures clearly having agostic hydrogen C–H–Fe interactions. A bridging butadiene unit with one agostic C–H–Fe interaction is found in 0N–Fe–6T and a bridging methylallene ligand is found in 0N–Fe–10T.
Fig. 14
Fig. 14. The optimized low-energy Cp2Fe2C2Me2 structures. The symmetry of the structure is indicated in parentheses in the first line. The numbers in parentheses in the second line are the relative energies (ΔE in kcal mol−1) predicted by M06-L/def2-TZVP method.
Fig. 15
Fig. 15. QTAIM analysis of the singlet Cp2Fe2C2(NMe2)2 structures.
Fig. 16
Fig. 16. Proposed hydrogen migration path for the Cp2Co2(MeC2NMe2) system predicted by the M06-L/def2-TZVP method.
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References

    1. Greenfield H. Sternberg H. W. Friedel R. A. Wotiz J. H. Markby R. Wender I. Acetylenic dicobalt hexacarbonyls—organometallic compounds derived from alkynes and dicobalt octacarbonyl. J. Am. Chem. Soc. 1956;78:120–124.
    1. Dickson R. S. Fraser P. J. Compounds derived from alkynes and carbonyl complexes of cobalt. Adv. Organomet. Chem. 1974;12:323–377.
    1. Went M. J. Synthesis and reactions of polynuclear cobalt alkyne complexes. Adv. Organomet. Chem. 1997;41:69–125.
    1. Gibson S. E. Mainolfi N. The intermolecular Pauson–Khand reaction. Angew. Chem., Int. Ed. 2005;44:3022–3037. - PubMed
    1. Nicholas K. M. Chemistry and synthetic utility of cobalt-complexed propargyl cations. Acc. Chem. Res. 1987;20:207–214.