One-Pot and Step-by-Step N-Assisted C(Ph)-H Activation in 2-(4-Bromophenyl)imidazol[1,2-a]pyridine: Synthesis of a New C,N-Cyclometalated Compound [{Pt(C(boolean AND)N)(mu-Cl)}(2)] as Precursor of Luminescent Platinum(II) Compounds

 
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One-Pot and Step-by-Step N-Assisted C(Ph)-H Activation in 2-(4-Bromophenyl)imidazol[1,2-a]pyridine: Synthesis of a New C,N-Cyclometalated Compound [{Pt(C(boolean AND)N)(mu-Cl)}(2)] as Precursor of Luminescent Platinum(II) Compounds (EN)

Fornies, J. (EN)

Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας (EL)
Fornies, J. (EN)

The activation of a C(ph)-H bond in the phenyl ring of 2-(4-bromophenyl)imidazol[1,2-a]pyridine (HC(boolean AND)N) by [{Pt(eta(3)-C(4)H(7))(mu-Cl)}(2)](eta(3)-C(4)H(7) = eta(3)-2-methylallyl) renders the new cyclometalated complex [Ppt(C(boolean AND)N)(mu-Cl)}(2)] (2) with high yield and selectivity. Complex 2 can be achieved directly in a one-pot reaction or step by step through the intermediate [Pt(eta(3)-C(4)H(7))Cl(HC(boolean AND)N-kappa N)] (1). Compound I could be isolated and fully characterized. The X-ray structure shows the coordination of HCA(boolean AND)N through only the N and the existence of a weak Pt center dot center dot center dot H-C hydrogen bridging bond (Pt center dot center dot center dot H1 = 2.78 angstrom, Pt center dot center dot center dot Cl = 3.365(3) angstrom, Pt-Hl-Cl = 120.9 degrees). Hence, the formation of this intermediate could be considered the first step in the cyclometalation process. The mononuclear complexes [PtCl(C(boolean AND)N)L] (L = tht (3), PPh(3) (4), CN-Xyl (5), CN-(t)Bu (6)) were obtained by cleavage of the bridging system in [{Pt(C(boolean AND)N)mu-Cl)}(2)] (2) by the neutral ligands, L. The resulting geometry (trans C, Cl) is that expected from the electronic preferences, taking into account the degree of transphobia (T) of pairs of trans ligands, T[C(C(boolean AND)N)/L(CI)] < T[C(C(boolean AND)N)/L(S, P, C)]. Complexes [PtCI(C(boolean AND)N)L] (L = CN-Xyl (5), CN-(t)Bu (6)) containing two strong-field ligands, a C(C)boolean AND N sigma-abonded and an isocyanide ligand, are luminescent. TD-DFT calculations were performed for the singlet ground state, S(0), as well as for the first triplet excited state of 6 in both the gas phase and solution. Calculations indicate that the lowest-lying absorption involves mainly (1)IL (C(boolean AND)N) mixed with a small contribution of (1)MLCT/(1)L'LCT (L = C(boolean AND)N; L' = Cl) transitions. Complex 5 exhibits "luminescent thermochromism" in the solid state; at 77 K it shows a green phosphorescence band assigned to (3)IL transitions located on the C(boolean AND)N group of monomer species, while at 298 K an orange-red emission is observed, being tentatively assigned to excited states of emissive aggregates ((3)MMLCT/(3)pi-pi*). However complex 6 shows phosphorescence only at 77 K both in Solution and in the solid state with the emissions arising from (3)IL and 3L'MLCT excited states of monomer species. (EN)

metal-carbon bonds (EN)

Πανεπιστήμιο Ιωαννίνων (EL)
University of Ioannina (EN)

Organometallics (EN)

Αγγλική γλώσσα

2010

<Go to ISI>://000275410300013



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