Synthesis, characterisation and some reactions of alkynyl derivatives [Ni(η5-C5H5)(PPh3)C
CX]
Abstract
CCH(OEt)2] 1, to the alkynylaldehyde [Ni(η5-C5H5)(PPh3)C
CCHO] 2, in high yield. Condensation reactions of 2 with
CX] derivatives where X = CH
NNHC6H53, CH
NNHC6H3(NO2)2-2,4 4,
CH
C(CN)25, and CH
C9H5NO26. The reactivity of [Ni(η5-C5H5)(PPh3)C
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
CCH(OEt)2}{Co2(CO)6}] 7, and [{μ-η1:η1-Ni(η5-C5H5)(PPh3)C
CCHO}{Co2(CO)6}] 8, but 5, where X is the strongly electron-withdrawing CH
C(CN)2 group, does not react even after 24 h at room temperature. Furthermore, coordination of the
C) band the frequency of which
decreases along the series X = CH(OEt)2 > CH
NNHC6H5 > CH
NNHC6H3(NO2)2-2,4 > CH
C(CN)2
≈ CH
C9H5NO2; that of 2 is anomalous in that it can show two ν(C
C) bands. The
C
C
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-η1:η1-Ni(η5-C5H5)(PPh3)C
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.