Towards multistranded molecular wires: Syntheses, structures, and reactivities of tetraplatinum bis(polyynediyl) complexes with Pt-Cx-Pt-(P(CH2)3P)2-Pt-Cx-Pt-(P(CH2)3P)2 cores (x = 4, 6, 8)

Reactions of trans,trans-(C6F5)(p-tol3P)2Pt(CC)nPt(Pp-tol3)2(C6F5) (PtCxPt; x = 2n) and the 1,3-diphosphine Ph2P(CH2)3PPh2 (2.5 equiv) give the tetraplatinum complexes trans, trans,trans,trans-(C6F5)Pt(CC)nPt(C6F5)(PPh2(CH2)3Ph2P)2(C6F5)Pt(CC)nPt(C6F5)(PPh2(CH2)3Ph2P)2 ([Pt′CxPt′]2; x = 4/6/8, 39%/95%/81%). Crystal structures of [Pt′C8Pt′]2 and two solvates of [Pt′C6Pt′]2 are determined. These confirm that each diphosphine spans two platinum atoms from different Pt(CC)nPt linkages, as opposed to (1) the 1,2-diphosphine Ph2P(CH2)2PPh2, which under similar conditions with PtC8Pt affords the diplatinum bis(chelate) cis,cis-(PPh2(CH2)2Ph2P)(C6F5)Pt(CC)4Pt(C6F5)(PPh2(CH2)2Ph2P) (73%) or (2) α,ω-diphosphines with longer methylene chains, which span the platinum termini. The formulation [Pt′C4Pt′]2 is supported by a reaction with PEt3 (10 equiv) to give trans,trans-(C6F5)(Et3P)2Pt(CC)2Pt(PEt3)2(C6F5). In [Pt′C8Pt′]2 and one solvate of [Pt′C6Pt′]2, the chains cross at 77.2°–87.7° angles, with the closest interchain carbon–carbon distances (3.27–3.61 A) less than the sum of the van-der-Waals radii. In the other solvate of [Pt′C6Pt′]2, the chains are essentially parallel, and the separation is much greater (4.96 A). UV-visible spectra show no special electronic interactions. However, cyclic voltammograms indicate irreversible oxidations, in contrast to the partially reversible oxidations of PtC6Pt and PtC8Pt. The initially formed radical cations are proposed to undergo rapid chain–chain coupling. The new complexes decompose without melting above 185 °C. With [Pt′C8Pt′]2, IR spectra indicate the formation of a new CC-rich substance.