The reactions of some σ-alkynylnickel complexes with 7,7,8,8-tetracyanoquinodimethane

The σ-alkynyl complexes Ni(η5-C5H5)(PPh3)–Ctriple bond; length of mdashC–R (1), Ni(η5-C5H5)(PPh3)–Ctriple bond; length of mdashC–X–Ctriple bond; length of mdashCH (2) and Ni(η5-C5H5)(PPh3)–Ctriple bond; length of mdashC–X–Ctriple bond; length of mdashC–Ni(η5-C5H5)(PPh3) (3), reactwith 7,7,8,8-tetracyanoquinodimethane, TCNQ, at 30 °C by insertion of the alkyne Ctriple bond; length of mdashC into a Cdouble bond; length as m-dashC(CN)2 bond to give Ni(η5-C5H5)(PPh3)–C{double bond; length as m-dashC6H4double bond; length as m-dashC(CN)2}–C{double bond; length as m-dashC(CN)2}–R (4), from 1, Ni(η5-C5H5)(PPh3)–C{double bond; length as m-dashC6H4double bond; length as m-dashC(CN)2}–C{double bond; length as m-dashC(CN)2}–X–Ctriple bond; length of mdashCH (5), from 2, and Ni(η5-C5H5)(PPh3)–C{double bond; length as m-dashC6H4double bond; length as m-dashC(CN)2}–C{double bond; length as m-dashC(CN)2}–X–Ctriple bond; length of mdashC–Ni(η5-C5H5)(PPh3) (6),and Ni(η5-C5H5)(PPh3)–C{double bond; length as m-dashC6H4double bond; length as m-dashC(CN)2}– C{double bond; length as m-dashC(CN)2}–X–C{double bond; length as m-dashC(CN)2}–C{double bond; length as m-dashC6H4double bond; length as m-dashC(CN)2}–Ni(η5-C5H5)(PPh3) (7),from 3 {R = (a) C6H5, (b) 4-PhC6H4, (c) 4-Me2NC6H4, (d) 1-C10H7 (1-naphthyl), (e) 2-C10H7 (2-naphthyl), (f) 9-C14H9 (9-phenanthryl), (g) 9-C14H9 (9-anthryl), (h) 3-C16H9 (3-pyrenyl), (i) 1-C20H11 (1-perylenyl), (j) 2-C4H3S (2-thienyl), (k) C10H9Fe (ferrocenyl = Fc) and (l) H; X = (a) nothing, (b) 1,4-C6H4, (c) 1,3-C6H4 and (d) 4,4′-C6H4–C6H4}. The reaction is regiospecificand the other possible insertion product, R–C{double bond; length as m-dashC6H4double bond; length as m-dashC(CN)2}–C{double bond; length as m-dashC(CN)2}–Ni(η5-C5H5)(PPh3) etc., is not formed. Under the same conditions, there is no evidencefor the reaction of TCNQ with the –Ctriple bond; length of mdashCH of 2, PhCtriple bond; length of mdashCH, 1,4-C6H4(Ctriple bond; length of mdashCH)2 or FcCtriple bond; length of mdashCH, or for the reaction of more than one Cdouble bond; length as m-dashC(CN)2 of TCNQ with a Ni-alkynyl moiety. Complexes 4–7 are all air-stable, purple solids which have been characterised by elemental analysis and spectroscopy (IR, UV–Vis, 1H NMR and 13C NMR),and by X-ray diffraction for 4a, 4b and 4l. The UV–Vis spectra of 4–7 are very similar. This implies that all contain the same active chromophore which, it is suggested, is Ni–C(5)double bond; length as m-dashC6H4double bond; length as m-dashC(CN)2 and not R–C(4)double bond; length as m-dashC(CN)2. This isconsistent with the molecular structures of 4a, 4b and 4l which show that the first of these potentially chromophoric fragments is planar or close to it with an in-built potential for delocalisation, whilst in the second the aryl group R is almost orthogonal to the Cdouble bond; length as m-dashC(CN)2 plane. The molecular structures of 4a, 4b and 4l also reveal a short Ni⋯C(4) separation, indicative of a Ni → C(4) donor–acceptor interaction. The electrochemistry of 4a shows aquasi reversible oxidation at ca. 1 V and complicated reduction processes. It is typical of most 4, but 4l is different in that it shows the same quasi reversible oxidation at ca. 1 V but two reversible reductions at −0.26 and −0.47 V (vs. [Fe(η5-C5Me5)2]+/0 0.0 V).