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Synthetic Access to Half-Sandwich Manganese C4 Cumulenic Complexes

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journal contribution
posted on 27.09.2004, 00:00 by Koushik Venkatesan, Olivier Blacque, Thomas Fox, Montserrat Alfonso, Helmut W. Schmalle, Heinz Berke
The vinylalkynyl complexes Mn(C5H4R‘)(R‘ ‘2PCH2CH2PR‘ ‘2)(CCSnPh3C⋮CSnPh3) (5, 6) were obtained in good yields by treatment of Mn(C5H4R‘)(η6-cycloheptatriene) (R‘ = H (1a), Me (1b)) with 1 equiv of Ph3SnC⋮CC⋮CSnPh3 and R‘ ‘2PCH2CH2PR‘ ‘2 (R‘ ‘ = CH3 (dmpe), C2H5 (depe)). The theoretically characterized (DFT) C4 cumulenic species Mn(C5H4R‘)(R‘ ‘2PCH2CH2PR‘ ‘2){CCCC(SnPh3)2} (7, 8) were obtained by photolysis of the tin-substituted vinylalkynyl complexes 5 and 6. Subsequently 7 and 8 could be converted into the parent cumulenic species Mn(C5H4R‘)(R‘ ‘2PCH2CH2PR‘ ‘2){CCCC(H)2} (9, 10) by reacting complexes 7 and 8 with TBAF (5% H2O) at −40 °C. The difference in the thermodynamic stabilities between the complexes 7 and 8 and complexes 9 and 10 was traced by DFT calculations using Mn(C5H5)(dHpe){CCCC(SnMe3)2} (4-H) and Mn(C5H5)(dHpe){CCCCH2} (9-H) as model complexes. Treatment of the vinylalkynyl complex with an excess of MeOH led to the formation of a dinuclear complex with a C8 chain between two manganese centers. The cumulenic complexes and the vinylalkynyl complexes were characterized by NMR and vibrational spectroscopy and elemental analyses. An X-ray diffraction study has been performed on complex 4b.