Towards multistranded molecular wires: syntheses, structures, and reactivities of tetraplatinum bis(polyynediyl) complexes with [upper bond 1 start]Pt-C(x)-Pt-(P(CH2)3P)2-Pt-C(x)-Pt-(P(CH2)3P[upper bond 1 end])2 cores (x = 4, 6, 8).
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abstract
Reactions of trans,trans-(C(6)F(5))(p-tol(3)P)(2)Pt(C[triple bond]C)(n)Pt(Pp-tol(3))(2)(C(6)F(5)) (PtC(x)Pt; x = 2n) and the 1,3-diphosphine Ph(2)P(CH(2))(3)PPh(2) (2.5 equiv) give the tetraplatinum complexes trans, trans,trans,trans-(C(6)F(5))[upper bond 1 start]Pt(C[triple bond]C)(n)Pt(C(6)F(5))(PPh(2)(CH(2))(3)Ph(2)P)(2)(C(6)F(5))Pt(C[triple bond]C)(n)Pt(C(6)F(5))(PPh(2)(CH(2))(3)Ph(2)P[upper bond 1 end])(2) ([Pt'C(x)Pt'](2); x = 4/6/8, 39%/95%/81%). Crystal structures of [Pt'C(8)Pt'](2) and two solvates of [Pt'C(6)Pt'](2) are determined. These confirm that each diphosphine spans two platinum atoms from different Pt(C[triple bond]C)(n)Pt linkages, as opposed to (1) the 1,2-diphosphine Ph(2)P(CH(2))(2)PPh(2), which under similar conditions with PtC(8)Pt affords the diplatinum bis(chelate) cis,cis-([upper bond 1 start]PPh(2)(CH(2))(2)Ph(2)P)(C(6)F(5))Pt[upper bond 1 end](C[triple bond]C)(4)[upper bond 1 start]Pt(C(6)F(5))(PPh(2)(CH(2))(2)Ph(2)P[upper bond 1 end]) (73%) or (2) alpha,omega-diphosphines with longer methylene chains, which span the platinum termini. The formulation [Pt'C(4)Pt'](2) is supported by a reaction with PEt(3) (10 equiv) to give trans,trans-(C(6)F(5))(Et(3)P)(2)Pt(C[triple bond]C)(2)Pt(PEt(3))(2)(C(6)F(5)). In [Pt'C(8)Pt'](2) and one solvate of [Pt'C(6)Pt'](2), the chains cross at 77.2 degrees-87.7 degrees 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'C(6)Pt'](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 PtC(6)Pt and PtC(8)Pt. The initially formed radical cations are proposed to undergo rapid chain-chain coupling. The new complexes decompose without melting above 185 degrees C. With [Pt'C(8)Pt'](2), IR spectra indicate the formation of a new C[triple bond]C-rich substance.
