sp Carbon Chains Surrounded by sp³Carbon Double Helices:  Coordination-Driven Self-Assembly of Wirelike Pt(C⋮C)_nPt Moieties That Are Spanned by Two P(CH₂)_mP Linkages

Abstract

Reactions of trans,trans-(C6F5)(p-tol3P)2Pt(CC)4Pt(Pp-tol3)2(C6F5) and diphosphines Ar2P(CH2)mPAr2 yield trans,trans-(C6F5)(Ar2P(CH2)mPAr2)Pt(CC)4Pt(Ar2P(CH2)mPAr2)(C6F5), in which the platinum atoms are spanned via an sp and two sp3 carbon chains (Ar/m = 3, Ph/14, 87%; 4, p-tol/14, 91%; 5, p-C6H4-t-Bu/14, 77%; 7, Ph/10, 80%; 8, Ph/11, 80%; 9, Ph/12, 36%; only oligomers form for m > 14). Crystal structures of 3-5 show that the sp3 chains adopt chiral double-helical conformations that shield the sp chain at approximately the van der Waals distance, with both enantiomers in the unit cell. The platinum square planes define angles of 196.6 degrees -189.9 degrees or more than a half twist. Crystal structures of 7-9, which have shorter sp3 chains, exhibit nonhelical conformations. Reaction of the corresponding Pt(CC)6Pt complex and Ph2P(CH2)18PPh2 gives an analogous adduct (27%). The crystal structure shows two independent molecules, one helical and the other not. Low-temperature NMR data suggest that the enantiomeric helical conformations of 3-5 rapidly interconvert in solution. Cyclic voltammograms of 3-5 show more reversible oxidations than model compounds lacking bridging sp3 chains. These are the only double-helical molecules that do not feature bonding interactions between the helix strands, or covalent bonds to templates dispersed throughout the strands, or any type of encoding. The driving force for helix formation is analyzed.

A Synthetic Breakthrough into an Unanticipated Stability Regime: A Series of Isolable Complexes in which C6, C8, C10, C12, C16, C20, C24, and C28 Polyynediyl Chains Span Two Platinum Atoms

“…Indeed, chromatography gave the deep red tetracosadodecaynediyl complex PtC 24 Pt in 36 % yield, along with 38 % of recovered PtC 12 Si. A similar reaction of PtC 14 Si at 0 8C gave the deep red octacosatetradecaynediyl complex PtC 28 Pt in 51 % yield, shattering existing length records for C x complexes.…”

“…No attempts were made to detect the intermediates PtC 8 H and PtC 10 H; which are certain to be extremely labile. To our knowledge, PtC 14 Si and PtC 16 Si feature the longest sp carbon chains with a single transitionmetal endgroup. Key spectroscopic data for PtC x Si are summarized in Tables 1-3, including that of the previously reported complex PtC 4 Si.…”

“…Species with cumulenic bridges are much less stable. [8] Of the polyynediyl complexes, only those with {FeA C H T U N G T R E N N U N G (h 5 -C 5 Me 5 )(CO) 2 }, [9] {RuA C H T U N G T R E N N U N G (h 5 -C 5 R 5 )(L) 2 } or {Ru(L')(L) 4 } n + , [10] {ReA C H T U N G T R E N N U N G (h 5 -C 5 Me 5 )(NO)A C H T U N G T R E N N U N G (PPh 3 )}, [11] {Ru 2 (2-anilinopyridinate) 4 }, [12] {PtA C H T U N G T R E N N U N G (C 6 F 5 ){PA C H T U N G T R E N N U N G (p-tol) 3 } 2 }, [13] and {PtA C H T U N G T R E N N U N G (C 6 F 5 )A C H T U N G T R E N N U N G (RAr 2 P) 2 } [14] endgroups have been extended to long chain lengths, beyond four triple bonds (! C 10 ).…”

Insulated molecular wires: inhibiting orthogonal contacts in metal complex based molecular junctions

“…1a). [74][75][76][77][78][79] Fig . 1 Representative sketches of different insulating strategies for metal-complex based molecular wires: (a) helical alkyl chains arranged around a conjugated chain (bold line); (b) fluorous alkyl chains selfassembled around a conjugated chain; (c) encapsulation of a conjugated chain in a rotaxane-like structure; (d) protection of the ancillary ligands on the metal complex by alkyloxy side-chains; (e) single molecule conductance can be determined by placing the molecule within a junction represented here by an STM tip and a conducting substrate.…”

Refining the Interpretation of Near‐Infrared Band Shapes in a Polyynediyl Molecular Wire

“…In contrast, the transition dipole moment of the higher-energy transition, which correlates with the shoulder in the experimental spectrum (Figure 1 To test the quantum-chemically predicted importance of rotamers for the shape of the NIR band of mixed-valence systems a conformationally restricted diynediyl complex comparable to 1 was required. Gladysz and colleagues have used a,w-bis(phosphines) in constructing "insulated" molecular wire models based on polyynediyl complexes, [23] providing a conceptual basis for the work which follows. The pseudo-macrocyclic complex [{RuCp} 2 Figure 4) was prepared in 33 % yield by phosphine exchange of 1 with 1,5-bis(diphenylphosphino)-pentane ( Figure 5) and crystallographically characterised.…”