Research on Diplatinum Polyyne Complexes: Atropisomerism and Bottom-Up Syntheses of Graphene
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Major objectives of this dissertation pay attention to synthesis, probe the feasibility of a new type of inorganic atropisomerism of diplatinum ethynediyl and butadiynediyl complexes, and explore the feasibility of Diels-Alder functionalization of polyyne chains to achieve graphene-like structures. Reaction of trans-(C6F5)(Me2PhP)(p-tol3P)Pt(Cl) and trans-(C6F5)(Me2PhP)(p-tol3P)Pt(C≡CSiEt3) (cat. n-Bu4NF/CuCl, HNEt2, –45 °C) gives a series of PtC≡CPtcomplexes in which the two phosphine ligands have been scrambled. Preparative TLC affords the target complex trans,trans-(C6F5)(p-tol3P)(Me2PhP)Pt(C≡C)Pt(PPhMe2)(Pp-tol3)(C6F5) (2.3%). The crystal structure of trans,trans-(C6F5)(p-tol3P)(Me2PhP)Pt(C≡C)Pt(PPhMe2)(Pp-tol3)(C6F5) is determined, shows much congestion about the PtC≡CPt linkage. Low temperature ^1H NMR spectra of trans,trans-(C6F5)(p-tol3P)(Me2PhP)Pt(C≡C)Pt(PPhMe2)(Pp-tol3)(C6F5) are recorded. However, nodecoalescence is observed (CD2Cl2/–95 °C; CDFCl2/–100 °C); this suggests that interconversion of the putative atropisomers remains rapid on the NMR time scale at < –95 °C. Cross couplings of trans-(C6F5)(R2PhP)(p-tol3P)Pt(Cl) (Pt'Cl-a-c, R = a/Me, b/p-t-BuC6H4, c/p-MeOC6H4, d/n-Pr) and trans-(C6F5)(R2PhP)(p-tol3P)Pt(C≡C)2H(Pt'C4H-a-c) (cat. CuI, HNEt2) give mixtures of diplatinum butadiynyl complexes in which the two phosphine ligands scramble over all four positions (PtC4Pt, PtC4Pt'-a-c, PtC4Pt"-a-c, Pt'C4Pt'-a-c, Pt'C4Pt"-a-c, Pt"C4Pt"-b; 27-2% each). A modified coupling recipe is tested with Pt'Cl-b,d and Pt'C4H-b,d (t-BuOK, KPF6, cat. CuCl), and gives Pt'C4Pt'-b,d (21-76%) with traces of scrambling. The crystal structures of Pt'C4Pt'-a-d are determined, and the endgroup/endgroup interactions analyzed. Low temperature NMR spectra do not reveal any dynamic processes. Reactions of PtC4H or PtC6TES and the 1,4-dihydro-2,3-benzoxathiin-3-oxide in refluxing toluene are investigated. Mass spectrometric data give evidence for 1:1 aromatized cycloadducts. A similar reaction of PtC8Pt and 1,3-dihydrobenzo[c]thiophene-2,2-dioxide in 1,2,4-trichlorobenzene (160 °C) affords 1:1, 1:2, and 1:3 aromatized cycloadducts, as assayed by mass spectrometry. These reactions are viewed as possible initial steps in bottom up syntheses of graphene, but appear to lack generality in diplatinum homologs with longer sp carbon chains. Other types of cycloadditions are attempted with B10H12·2[S(CH3)2] (TESC4TES, TESC8TES, PtC8Pt; refluxing toluene, o-carborane targets) and the cyclotrimerization catalyst [CpCo(CO)(dimethyl fumarate)] (PtC4H, TESC8TES, PtC6Pt, PtC8Pt; reluxing toluene, dark/ambient lighting, arene targets). However, no tractable products could be isolated, and in most cases the platinum containing reactant was recovered. These data suggest that the polyynes investigated are less reactive in various cycloaddition processes than many simple organic alkynes.
variable temperature NMR
sp carbon chains
Zhang, Tianyi (2017). Research on Diplatinum Polyyne Complexes: Atropisomerism and Bottom-Up Syntheses of Graphene. Doctoral dissertation, Texas A & M University. Available electronically from