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-(Di
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- 作者：Giancarlo Franciò ; Rosario Scopelliti ; Carmela Grazia Arena ; Giuseppe Bruno ; Dario Drommi ; and Felice Faraone
- 刊名：Organometallics
- 出版年：1998
- 出版时间：February 2, 1998
- 年：1998
- 卷：17
- 期：3
- 页码：338 - 347
- 全文大小：234K
- 年卷期：v.17,no.3(February 2, 1998)
- ISSN：1520-6041
文摘
The complextrans-[Ir(CO)Cl(Ph2PPy)2](1; Ph2PPy =2-(diphenylphosphino)pyridine) wasobtained in good yield from the reaction of[Ir(p-toluidine)(CO)2Cl] withPh2PPy. It has asquare-planar geometry, as does the analogous Vaska complex, with twomonodentate Ph2PPyligands P-bonded to the iridium(I) center. Compound1 exhibits a reactivity reminiscent ofVaska's complex; in fact, it adds SO2, halogens, HCl, andCH3I. The addition of HCl to 1initially occurs at the pyridine nitrogen atoms of the pendantPh2PPy and subsequently atthe iridium(I) center, affording[Ir(CO)H(Cl)2(Ph2PPyH)2][Cl]2(6). The addition of a benzenesolution of [Pd(PhCN)2Cl2] to a solutionof 1 in the same solvent yielded, nearlyquantitatively,the IrIIPdI complex[IrPd(CO)Cl3(
-Ph2PPy)2](8). The reaction of 1 withHgCl2, in benzene,in a 1:1 molar ratio afforded the binuclear complex[Ir(CO)Cl2(-Ph2PPy)2HgCl](9). Usinga 1:2 molar ratio the product[Ir(CO)Cl2(HgCl2)(-Ph2PPy)2HgCl]·2CH2Cl2(10) was obtained.Compounds 8 and 10 were also characterizedby a single-crystal X-ray diffraction analysis.The reaction of 1 with[Cu(NCCH3)4]BF4afforded, almost quantitatively, the ionic compound[Ir(CO)Cl(-Ph2PPy)2Cu]BF4(11) as an orange solid. The compound[Ir(CO)Cl(-Ph2PPy)2Tl]PF6 (12) obtained from the reaction of1 with TlPF6, shows the Ir-Tl bonding andisluminescent in frozen CH2Cl2 solution at77 K with a lifetime of 5 ns (±10%). As opposedto analogous compounds, in the bimetallic complexes8-12 the bridging Ph2PPyligandsassume a head-to-head structure. The aim of the work was to obtainsome insight into thebeneficial effect of catalytic precursors containing the pendantPh2PPy ligand in thehydroformylation catalytic cycle. Using complex 1 as aprecatalyst in the hydroformylationof styrene, at 80 
C and under 80 atm of CO/H2 (1:1)pressure, the rate of the catalyticprocess increases significantly with respect to that observed withVaska's complex, makingclear a favorable effect of the pendant Ph2PPy ligand.However, the chemoselectivity of theprocess was low. A scheme of the catalytic cycle is proposed.The new aspects of the catalyticcycle are: (i) the protonation under equilibrium conditions of one ofthe two pyridine nitrogenatoms of the pendant Ph2PPy ligands in the reductiveelimination of HCl from the dihydride-iridium(III) species formed by oxidative addition of H2to 1 and (ii) protonolysis, by the protoncoordinated to the pyridine nitrogen atom, of the acyl or 
-alkylgroups present in theintermediates formed in the reaction pathway. Unexpectedly,11 and 12 exhibit catalyticactivity comparable with that of 1. This occurs becauseunder the experimental conditionsused the Cu-N or Tl-N bonds are broken, giving 1.
-Ph2PPy)2](8). The reaction of 1 withHgCl2, in benzene,in a 1:1 molar ratio afforded the binuclear complex[Ir(CO)Cl2(-Ph2PPy)2HgCl](9). Usinga 1:2 molar ratio the product[Ir(CO)Cl2(HgCl2)(-Ph2PPy)2HgCl]·2CH2Cl2(10) was obtained.Compounds 8 and 10 were also characterizedby a single-crystal X-ray diffraction analysis.The reaction of 1 with[Cu(NCCH3)4]BF4afforded, almost quantitatively, the ionic compound[Ir(CO)Cl(-Ph2PPy)2Cu]BF4(11) as an orange solid. The compound[Ir(CO)Cl(-Ph2PPy)2Tl]PF6 (12) obtained from the reaction of1 with TlPF6, shows the Ir-Tl bonding andisluminescent in frozen CH2Cl2 solution at77 K with a lifetime of 5 ns (±10%). As opposedto analogous compounds, in the bimetallic complexes8-12 the bridging Ph2PPyligandsassume a head-to-head structure. The aim of the work was to obtainsome insight into thebeneficial effect of catalytic precursors containing the pendantPh2PPy ligand in thehydroformylation catalytic cycle. Using complex 1 as aprecatalyst in the hydroformylationof styrene, at 80 C and under 80 atm of CO/H2 (1:1)pressure, the rate of the catalyticprocess increases significantly with respect to that observed withVaska's complex, makingclear a favorable effect of the pendant Ph2PPy ligand.However, the chemoselectivity of theprocess was low. A scheme of the catalytic cycle is proposed.The new aspects of the catalyticcycle are: (i) the protonation under equilibrium conditions of one ofthe two pyridine nitrogenatoms of the pendant Ph2PPy ligands in the reductiveelimination of HCl from the dihydride-iridium(III) species formed by oxidative addition of H2to 1 and (ii) protonolysis, by the protoncoordinated to the pyridine nitrogen atom, of the acyl or -alkylgroups present in theintermediates formed in the reaction pathway. Unexpectedly,11 and 12 exhibit catalyticactivity comparable with that of 1. This occurs becauseunder the experimental conditionsused the Cu-N or Tl-N bonds are broken, giving 1.