Issue 1, 2002

Synthesis, characterisation and some reactions of alkynyl derivatives [Ni(η5-C5H5)(PPh3)C[triple bond, length as m-dash]CX]

Abstract

Oxalic acid catalyses the hydrolysis of the Ni(II) acetylide [Ni(η5-C5H5)(PPh3)C[triple bond, length as m-dash]CCH(OEt)2] 1, to the alkynylaldehyde [Ni(η5-C5H5)(PPh3)C[triple bond, length as m-dash]CCHO] 2, in high yield. Condensation reactions of 2 with phenylhydrazine and dinitrophenylhydrazine in the presence of acetic acid, and with malononitrile and 3-phenyl-5-isoxazolone (C9H7NO2) in the presence of triethylamine yield [Ni(η5-C5H5)(PPh3)C[triple bond, length as m-dash]CX] derivatives where X = CH[double bond, length as m-dash]NNHC6H53, CH[double bond, length as m-dash]NNHC6H3(NO2)2-2,4 4, CH[double bond, length as m-dash]C(CN)25, and CH[double bond, length as m-dash]C9H5NO26. The reactivity of [Ni(η5-C5H5)(PPh3)C[triple bond, length as m-dash]CX] complexes towards [Co2(CO)8] is a function of X. Thus 1 and 2, where X = CH(OEt)2 or CHO, react readily to give the bridging alkyne derivatives [{μ-η11-Ni(η5-C5H5)(PPh3)C[triple bond, length as m-dash]CCH(OEt)2}{Co2(CO)6}] 7, and [{μ-η11-Ni(η5-C5H5)(PPh3)C[triple bond, length as m-dash]CCHO}{Co2(CO)6}] 8, but 5, where X is the strongly electron-withdrawing CH[double bond, length as m-dash]C(CN)2 group, does not react even after 24 h at room temperature. Furthermore, coordination of the alkyne to a Co2(CO)6 fragment appears to inhibit the normal reactions of the group X in 7 and 8. Thus the acetal grouping in 7 does not undergo oxalic acid-catalysed hydrolysis to an aldehyde in 8, and the aldehyde function in 8 does not undergo a Knoevenagel condensation with CH2(CN)2. The IR spectra of 1, and 3–6 show a single ν(C[triple bond, length as m-dash]C) band the frequency of which decreases along the series X = CH(OEt)2 > CH[double bond, length as m-dash]NNHC6H5 > CH[double bond, length as m-dash]NNHC6H3(NO2)2-2,4 > CH[double bond, length as m-dash]C(CN)2 ≈ CH[double bond, length as m-dash]C9H5NO2; that of 2 is anomalous in that it can show two ν(C[triple bond, length as m-dash]C) bands. The UV-visible spectra of 1–6 show a strong charge transfer absorption band which increases in wavelength 1 < 3 < 2 < 4 < 5 < 6. These spectroscopic data and the 13C chemical shifts suggest that the (η5-C5H5)(Ph3P)Ni moiety is a donor and, when X is an acceptor, charge separated cumulenic mesomers such as Ni+[double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]X contribute to the description of the bonding in 1–6. This is not reflected in the molecular dimensions of 1, 2 and 5 as determined by X-ray diffraction. However, the crystal structure of [{μ-η11-Ni(η5-C5H5)(PPh3)C[triple bond, length as m-dash]CCHO}{Co2(CO)6}], 8, shows that the C2Co2 cluster core is severely distorted because of the strong donor (Ni) and acceptor (CHO) substituents on the acetylenic carbon atoms.

Graphical abstract: Synthesis, characterisation and some reactions of alkynyl derivatives [Ni(η5-C5H5)(PPh3)C [[triple bond, length as m-dash]] CX]

Supplementary files

Article information

Article type
Paper
Submitted
21 May 2001
Accepted
05 Oct 2001
First published
10 Dec 2001

J. Chem. Soc., Dalton Trans., 2002, 75-82

Synthesis, characterisation and some reactions of alkynyl derivatives [Ni(η5-C5H5)(PPh3)C[triple bond, length as m-dash]CX]

J. F. Gallagher, P. Butler, R. D. A. Hudson and A. R. Manning, J. Chem. Soc., Dalton Trans., 2002, 75 DOI: 10.1039/B104442G

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