Carbyne-carbyne coupling at a single metal center. Synthesis structure of bis(diethylamino)acetylene complexes of molybdenum(II) and tungsten(II)

Alexander Constantin Filippou, Christian Völkl, Walter Grünleitner, Paul Kiprof

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A high-yield synthesis of MoII and WII bis(diethylamino)acetylene complexes starting from M(CO)6 (1, 2) is reported. This begins with the stepwise transformation of M(CO)6 to the MII isocyanide complexes M(CO)2(CNR)3(Br)2 (7a-8b) (7: M Mo; 8: M W; a: R Et; b: R tBu). Complexes 7a-8b react with Et2NCCNEt2 to give the cationic alkyne complexes mer-[Br(CO)(RNC)3M(η2-Et2NCCNEt2)]Br (9a-10b) (9: M Mo; 10: M W). Thermal decarbonylation of 9a-10b with RNC affords the carbonyl-free derivatives trans-[Br(RNC)4M(η2-Et2NCCNEt2)]Br (11a-12b) (11: M Mo; 12: M W). Complexes 11a and 12a can be also obtained from the homoleptic isocyanide complexes M(CNEt)6 (13: M Mo; 14: M W) by a sequence of reactions resulting in coupling of two ethyl isocyanide ligands to give a bis(diethylamino)acetylene ligand. This sequence is initiated by the regioselective ethylation of M(CNEt)6 with one equivalent of [Et3O]BF4 to give the diethylaminocarbyne complexes [(EtNC)5MCNEt2]BF4 (15: M Mo; 16: M W). Addition of another equivalent [Et3O]BF4 to 15 and 16 results in the formation of the bis-diethylaminocarbyne complexes [(EtNC)4M(CNEt2)2(BF4)2 (17: M Mo; 18: M W). On treatment with [NEt4]Br these undergo a carbyne-carbyne coupling reaction to give the alkyne complexes 11a and 12a, respectively. Spectroscopic data for the novel transition-metal complexes of bis(diethylamino)acetylene 9a-12b indicate substantial bond delocalization in the metal-alkyne fragment and restricted rotation of the diethylamino groups around the Calkyne-N bonds. The alkyne ligand acts as a four-electron donor and allows the metal center to achieve a closed-shell configuration. These observations are supported by the results of a single-crystal X-ray diffraction study of the complex trans-[Br(tBuNC)4W(η2-Et2NCCNEt2)]PF6 (12b′), obtained from 12b and TIPF6.

Original languageEnglish (US)
Pages (from-to)201-223
Number of pages23
JournalJournal of Organometallic Chemistry
Issue number2
StatePublished - Aug 11 1992

Bibliographical note

Funding Information:
We thank Professor W.A. Herrmann for providing institute facilities, the Volkswagen and Leonhard-Lorenz Foundation for financial support, M. Barth and U. Graf for elemental analyses, J. Riede for assistance in the single crystal X-ray

Copyright 2014 Elsevier B.V., All rights reserved.


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