Synthesis and reactivity of transition metal cyaphide complexes

This thesis describes the synthesis, characterisation and reactivity of a series of ruthenium cyaphide complexes featuring trans alkynyl, methyl and halide ligands, to understand how the trans ligand affects the properties of the cyaphide moiety and ultimately develop reactivity of the cyaphide moiety, seeking to engage both the phosphorus lone pair and the p-system. A series of trans-alkynyl cyaphide complexes, trans-[Ru(C=P)(C=CR)(dppe)2] were synthesised via the corresponding ?1 -phosphaalkyne complexes, trans-[Ru(P=CSiMe3)(C=CR)(dppe)2] + and the compounds characterised through NMR and infra-red spectroscopy as well as X-ray diffraction. In addition, cyclic voltammetry was undertaken to further understand the electrochemical behaviour of these complexes. Preliminary exploration into the reactivity of the ligated cyaphide was undertaken with limited success. The synthesis of the first example of a trans-[Ru(C=CR)(C=N)(dppe)2] complex was achieved to seek the comparison of the cyanide, cyaphide and alkyne ligands, albeit, further work is needed to optimise the synthetic procedure to yield pure product. The synthesis of the first trans-alkyl cyaphide complex, trans-[RuMe(dppe)2(C=P)] via its corresponding ?1 -phosphaalkyne complex, trans-[RuMe(dppe)2(P=CSiMe3)]OTf was achieved. Both the ?1 -phosphaalkyne and cyaphide complexes were characterised through NMR and infra-red spectroscopy, with the latter also being structurally characterised through X-ray diffraction. Comparable to the trans-alkynyl cyaphide complexes the initial reactivity studies to coordinate the ligated cyaphide to metal centres (Pt, Pd, Au, Ag and Rh) were unsuccessful. However, the first series of trans-halo cyaphide complexes, trans-[RuX(dppe)2(C=P)] (X = Cl, Br or I) was synthesised through the treatment of trans-{RuMe(dppe)2(C=P)] with ZnX2 (X = Cl, Br, I) in the presence of PPh3, a rare example of ruthenium demethylation using a zinc halide. The series of trans-halo cyaphide complexes had long been sought after due to the ability for post-synthetic modification, thus exploration into the reactivity of the trans-[RuBr(dppe)2(C=P)] was undertaken. Halide abstraction of trans-[RuBr(dppe)2(C=P)] led to the synthesis, isolation and characterisation of the first 5-coordinate cyaphide complex, [Ru(C=P)(dppe)2])OTF. X-ray diffraction data showed the 5-coordinate cyaphide complex to exhibit a square-based pyramidal structure with an accessible vacant coordination site trans- to the cyaphide moiety. The susceptibility to ligand addition at this site was investigated and exploited to synthesise a series of novel cyaphide complexes trans-[Ru(R)(dppe)2(C=P)]OTf, (R = C=O, C=N, F, SC=N, OC=N, P=CSiMe3, C=P, C=NCH3 and NC5H5), which have previously proven inaccessible via established routes to cyaphide complexes. The reduction chemistry of [Ru(C=P)(dppe)2]OTF was also investigated, with the reactions with LiCp and sodium naphthalenide which yielded the synthesis of the CPPC bridged dimer [(Ru(dppe)2)2(CPPC)] and the sodium bridged dimer [Ru(dppe)2(C=P)Na]2 respectively. Furthermore, the UV-vis spectra, electrochemistry and spectroelectrochemistry of a selection of the cyaphide complexes including the 5-coordiante cyaphide complex, which have been supported through DFT and TD-DFT calculations, were obtained.