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

The sigma-alkynyl complexes Ni(eta(5)-C5H5)(PPh3)-C C-R (1), Ni(eta(5)-C5H5)(PPh3)-C C-X-C-CH (2) and Ni(eta(5)-C5H5)(PPh3)C C-X-C C-Ni(eta(5)-C5H5)(PPh3) (3), reactwith 7,7,8,8-tetracyanoquinodimethaiie, TCNQ, at 30 degrees C by insertion of the alkyne C C into a C=C(CN)(2) bond to give Ni(eta(5)-C5H5)(PPh3)-C{=C6H4=C(CN)(2)}-C(=C(CN)(2))-R (4), from 1, Ni(eta(5) -C5H5)(PPh3)C{=C6H4=C(CN)(2))-C{=C(CN)(2))-X-C CH (5), from 2, and Ni(eta(5)-C5H5)(PPh3)-C(=C6H4=C(CN)(2)}-C(=C(CN)(2)}-X-C C-Ni(eta(5)-C5H5)(PPh3) (6), and Ni(eta(5)-C5H5)(PPh3)-C(=C6H4=C(CN)(2))-CI =C(CN)(2)I-X-C[=C(CN)(2)}-C (=C6H4=C(CN)(2))-Ni(eta(5)-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 (1) H; X = (a) nothing, (b) 1,4-C6H4, (C) 1,3-C6H4 and (d) 4,4'-C6H4-C6H4). The reaction is regiospecific and the other possible insertion product, R-C{=C6H4=C(CN)(2))-Cl=C(CN)(2)}-Ni(eta(5)-C5H5)(PPh3) etc., is not formed. Under the same conditions, there is no evidencefor the reaction of TCNQ with the -C CH of 2, PhC CH, 1,4-C6H4(C CH)(2) or FcC CH, or for the reaction of more than one C=C(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, H-1 NMR and C-13 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)=C6H4=C(CN)(2) and not R-C(4)=C(CN)(2). This isconsistent with tile molecular structures of 4a, 4b and 41 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 tile C=C(CN)2 plane. The molecular structures of 4a, 4b and 41 also reveal a short Ni center dot center dot center dot 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 41 is different in that it shows the same quasi reversibl oxidation at ca. I V but two reversible reductions at -0.26 and -0.47 V (vs. [Fe(eta(5)-C5Me5)(2)](+/0) 0.0 V). (C) 2007 Elsevier B.V. All rights reserved.