200408-25-9

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• 198632-61-0 trans-[Ir(CO)(Ph₂PPy)2Cl] 

Relevant academic research and scientific papers

IrPd, IrHg, IrCu, and IrTl binuclear complexes bridged by the short-bite ligand 2-(diphenylphosphino)pyridine. Catalytic effect in the hydroformylation of styrene due to the monodentate P-bonded 2-(diphenylphosphino)pyridine ligands of trans-[Ir(CO)(Ph2PPy)2Cl]

The complex trans-[Ir(CO)Cl(Ph2PPy)2] (1; Ph2PPy = 2-(diphenylphosphino)pyridine) was obtained in good yield from the reaction of [Ir(p-toluidine)(CO)2Cl] with Ph2PPy. It has a square-planar geometry, as does the analogous Vaska complex, with two monodentate Ph2PPy ligands P-bonded to the iridium(I) center. Compound 1 exhibits a reactivity reminiscent of Vaska's complex; in fact, it adds SO2, halogens, HCl, and CH3I. The addition of HCl to 1 initially occurs at the pyridine nitrogen atoms of the pendant Ph2PPy and subsequently at the iridium(I) center, affording [Ir(CO)H(Cl)2(Ph2PPyH)2][Cl]2 (6). The addition of a benzene solution of[Pd(PhCN)2Cl2] to a solution of 1 in the same solvent yielded, nearly quantitatively, the IrIIPdI complex [IrPd(CO)Cl3(μ-Ph2PPy)2] (8). The reaction of 1 with HgCl2, in benzene, in a 1:1 molar ratio afforded the binuclear complex [Ir(CO)Cl2(μ-Ph2PPy)2HgCl] (9). Using a 1:2 molar ratio the product [Ir(CO)Cl2(HgCl2)(μ-Ph2PPy) 2HgCl]·2CH2Cl2 (10) was obtained. Compounds 8 and 10 were also characterized by a single-crystal X-ray diffraction analysis. The reaction of 1 with [Cu(NCCH3)4]BF4 afforded, almost quantitatively, the ionic compound [Ir(CO)Cl(μ-Ph2PPy)2Cu]BF4 (11) as an orange solid. The compound [Ir(CO)Cl(μ-Ph2PPy)2Tl]-PF6 (12) obtained from the reaction of 1 with TlPF6, shows the Ir-Tl bonding and is luminescent in frozen CH2Cl2 solution at 77 K with a lifetime of 5 ns (±10%). As opposed to analogous compounds, in the bimetallic complexes 8-12 the bridging Ph2PPy ligands assume a head-to-head structure. The aim of the work was to obtain some insight into the beneficial effect of catalytic precursors containing the pendant Ph2PPy ligand in the hydroformylation catalytic cycle. Using complex 1 as a precatalyst in the hydroformylation of styrene, at 80°C and under 80 atm of CO/H2 (1:1) pressure, the rate of the catalytic process increases significantly with respect to that observed with Vaska's complex, making clear a favorable effect of the pendant Ph2PPy ligand. However, the chemoselectivity of the process was low. A scheme of the catalytic cycle is proposed. The new aspects of the catalytic cycle are: (i) the protonation under equilibrium conditions of one of the two pyridine nitrogen atoms of the pendant Ph2PPy ligands in the reductive elimination of HCl from the dihydride-iridium(III) species formed by oxidative addition of H2 to 1 and (ii) protonolysis, by the proton coordinated to the pyridine nitrogen atom, of the acyl or σ-alkyl groups present in the intermediates formed in the reaction pathway. Unexpectedly, 11 and 12 exhibit catalytic activity comparable with that of 1. This occurs because under the experimental conditions used the Cu-N or Tl-N bonds are broken, giving 1.