Zhu, Yun (2023-06). Macrocyclic Dibridgehead Diphosphines That Turn Themselves Inside Out and Their Platinum Adducts: A Tour Through Three Oxidation States. Doctoral Dissertation.
Thesis
The broad field of molecular rotors is highly relevant to several types of molecular machines and chemists have had an ongoing interest in the sub-nanoscale miniaturization of various macroscopic devices. Two classes of metal complexes with the general formula cis/transPt(Cl)2 (P((CH2 )n )3P) have been intensively studied by Gladysz et al., which are often termed "gyroscope like" (trans) or "parachute like" (cis) due to their structural similarity to their corresponding macroscopic counterparts. Research on the reactivities and structures is of potential interest, as structure alterations can optimize the dynamic behaviors of such molecules, thereby influencing their performance as molecular rotors. Thus, a comprehensive study of the syntheses, structures, and reactivities of various platinum complexes and related phosphine ligands is detailed in this dissertation. The research on the substitution chemistry of the square planer gyroscope like dichloride complexes trans-Pt(Cl)2 (P((CH2 )n )3P) is first elaborated in chapter 2. Normally, isomerization to the cis configuration occurs upon reactions with alkyl lithium reagents to give the dialkyl complexes cis-Pt(R)2 (P((CH2 )n )3P) (R = Me, Et). These subsequently react with HCl to generate trans-Pt(Cl)(R)(P((CH2 )n )3P). In the case of R = Me, cis-Pt(Cl)(Me)(P((CH2 )n )3P) is isolated, which easily converts to its trans isomer over silica gel or at elevated temperature. A series of thermolyses experiments and DFT calculations indicate that the trans/gyroscope complexes have lower energies than cis/parachute complexes, except for dialkyl complexes which have comparable energies. Chapter 3 turns attention to a closely related field of macrocyclic dibridgehead diphosphines P((CH2 )n )3P), which are prepared by demetalation of cis/trans-Pt(Cl)2 ((P((CH2 )n )3P) with a nucleophile MC?X, in certain cases in decent yields. These ligand frameworks demonstrated high flexibility with extensive conformational manifolds and coordination modes. Apparent configurational isomerizations between in,in/out,out and in,out/out,in species are showcased, and the homeomorphic isomerizations within each manifold are further characterized by variable temperature NMR data. Studies on octahedral platinum(IV) complexes are described in chapter 4. The gyroscope like platinum(IV) tetrahalide complexes trans-Pt(X)4 (P((CH2 )n )3P) (X = Cl, Br) are obtained by treating the square planar platinum(II) dihalide complexes trans-Pt(X)2 (P((CH2 )n )3P) with excess X2 . Their crystal structures are compared to those of Pt(II) precursors. In one exploratory attempt, trans-Pt(Me)4 (P((CH2 )n )3P) was isolated in a reaction of trans-Pt(Br)2 (P((CH2 )n )3P) with MeMgBr, as verified crystallographically. The cis parachute isomer was obtained by treatment of the free dibridgehead diphosphine P((CH2 )14)3P with the PtMe4 source Pt2Me8 (u-SMe2 )2 . Chapter 5 of this dissertation deals with an ongoing pursuit of the platinum(0) complex trans-Pt(P((CH2 )14)3P), which has been generated by the reaction of trans-Pt(Cl)2 (P((CH2 )14)3P) and C8K in C6D6 or diethyl ether. The NMR data (31P{1H} chemical shift and JPPt) closely resembles similar trans-Pt(PR3 )2 species in the literature. Treatments of this transient species with MeI and H2 afford the corresponding platinum(II) oxidative addition products, as evidenced by 31P{1H} and 1H NMR. Moreover, additions of ethylene and diphenylacetylene give 1:1 ? adducts, believed to have trigonal geometries based upon similar literature compounds.
