Heteroatom functionalised metal-carbon chains
Creators: name: Onn, Chee Sheng
Publisher: name: The Australian National University
Year: 2021

description: This thesis explores synthesis and reactivity of tungsten complexes featuring carbon chains that connect multiple metal centres with heteroatom incorporated either within or at the termini of such chains. Alkynylselenolatoalkylidynes have a selenium atom that bridges a metal carbyne and an alkynyl motif. This presents many potential reactive sites - tungsten-carbyne, C-Se, alkynyl CC bonds and potentially the alkynyl terminus. The reaction of [W(CBr)(CO)2(Tp*)] (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) with lithium alkynylselenolates furnishes the alkynylselenolatoalkylidyne complexes [W(CSeCCR)(CO)2(Tp*)]. Desilylation of the SiMe3 complex furnishes the parent alkyne complex [W(CSeCCH)(CO)2(Tp*)], which may be further derivatized by deprotonation. These syntheses are explored in Chapter 2. Chapter 3 explores the reactivity of tungsten-carbyne in alkynylselenolatoalkylidynes with gold(I) reagents, which were proven to have high proclivity to coordinate onto metal carbynes. The desilylation of [W(CSeCCSiMe3)(CO)2(Tp*)] in the presence of a electrophilic metal precursors yields the corresponding metalled alkynylselenolatoalkylidynes featuring Au(I), Hg(II), Pt(II) and Ir(I). Similar attempts with palladium(II) bisphosphine dichloride instead afforded a mixed-valent inter-metallic Pd0/PdII bonded isoselenocarbonyl dimeric species, which has lost the alkynyl motif. A one-pot reaction of the appropriate molar equivalents of [W(CSe)(CO)2(Tp*)][NEt4], [Pd2(dba)3] as the Pd0 source, [PdCl2(COD)] as the PdII source and the requisite phosphines PR3 (PR3 = PPh3, PCy3) furnishes derivatives of the mixed-valent metal complexes. Alternatively, treatment of an equivalent of the salt and an equivalent of [PdCl2(PR3)2] (PR3 = PPh3, PCy3, PPh2Cy) surprisingly yields the same complexes. This one-pot strategy similarly enables access to Pt0 dative bonded to PdII derivatives by using [Pt(nbe)3] as the Pt0 source. Chapter 5 explores phosphorus functionalized metal-carbon chains, phosphoniocarbynes in particular. Reacting equimolar amount of bis(diphenylphosphino)methane with [W(CBr)(CO)2(Tp*)] and NaPF6 furnishes a novel phosphoniocarbyne that features a free phosphine terminus, [W(CPPh2CH2PPh2)(CO)2(Tp*)][PF6]. This complex undergoes similar metallation with [AuCl(SMe2)], [CuCl(SMe2)] and [Pt(nbe)3] to afford the heterometallic bridged derivatives, with the terminal phosphine coordinating to Au(I), Cu(I) and Pt(0) in tandem. The labile norbonene ligand in the lattermost is readily replaced by isonitriles, CO and selective terminal alkynes to afford the coordinated complexes with retention of the metallocyclopropene and the pentacyclic platinum-phosphine frameworks. The phosphoniocarbyne also chalcogenates readily at the terminal phosphine. With electron-deficient metal derivatives, the phosphoniocarbyne forms only P-coordinated complexes. Chapter 6 details some preliminary work on synthesis of silicon functionalized carbynes that feature Si-H bonds, the presence of which was targeted to achieve Si-H activation reactions. However, only simple metalation studies have worked successfully. Successive treatment of [W(CBr)(CO)2(Tp*)] with nBuLi and R2SiHCl affords the silylcarbyne complexes [W(CSiHR2)(CO)2(Tp*)] (R = Me, Ph). The treatment of the lithiocarbyne with half an equivalent of RSiHCl2 and a third equivalent of SiHCl3 to furnish the corresponding di- and tri-substituted silylcarbyne complexes, [{(Tp*)(CO)2WC}2SiHR] (R = Me, Ph) and [{(Tp*)(CO)2WC}3SiH] respectively. Preliminary Si-H activation studies have been unsuccessful, but addition of gold(I) across the carbyne moiety could be achieved exclusively, retaining the Si-H bond present throughout all of the aforementioned complexes. This enables time-efficient 2D-NMR correlation studies (29Si-1H HSQC and 29Si-1H HMBC) to obtain silicon resonances.