Micropreparation of RuH2{P(C6H5)3}4: A Transition Metal Hydride Compound

7/31/2019 Micropreparation of RuH2{P(C6H5)3}4: A Transition Metal Hydride Compound

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Form Journal of Chemical Educat ion,

Vol.76 No.1, January 1999

Art icle review by Tho Yim Peng

M20101000160


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The M-H bond plays a prominent role in

organometallic chemist ry because the metalhydrogen bond can undergo a variety of

insertion reactions such as olefin

isomerization, hydrogenation, hydrosilation,and hydroformylation.

The title compound is chosen to demonstratesome aspects of transition metal hydridechemistry.


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This inorganic laboratory experiment is

designed t o introduce inert atmosphereinorganic synthesis and to be accessible to

upper level undergraduate students.

This preparation makes use of borohydride,BH4-, to replace the chloride ligands of

dicholot ri s(triphenylphosphine)ruthenium(II),[RuCl2(PPh3)3] (Ph = C6H5).


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This starting material is prepared fromruthemium trichloride t rihydrate and

t riphenylphosphine, PPh3.

Dicholot ri s(triphenylphosphine)-ruthenium(II), [RuCl2(PPh3)3] is not air-

sensitive, requires no special handling, andcan easily be prepared in a 3-hourlaboratory.


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Preparation of hydride is done in a well-ventilated hood using argon and hydrogen as

a purge gas.

Syringe and cannula techniques areappropriate to this reaction.

The dihydride, [RuH2(PPh3)4] , can be

prepared in a second 3-hour laboratory

period.


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Hydrogenation:

Spectroscopic measurements and additionalreaction exercises are performed in a third

laboratory period.

Dihydrido-( 2-ihydrogen)tris(triphenylphosphine)ruthenium(II) is prepared by adding hydrogen.


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Each of these compounds can be readilyobtained toluene solution of [RuH2(PPh3)3] or

[RuH2(H2)(PPh3)3] wit h the appropriate ligandand characterized by IR or NMRspect roscopy.

20 minutes for an NMR tube vacuum fill cycleis a reasonable est imate.

The tet rahydride , [RuH2(H2)PPh3] , can beconverted into a variety of dihydrides simply

by losing H2 from the coordination sphere.


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Dihydrogen ligand displacement reaction:

the usual assumpt ion of subst itut ion-inertbehavior in low-spin d6 classical complexesdoes not apply in this organorutheniumcomplexes.

High trans influence of the hyride ligand.


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The 31P NMR experiment is part icularly tell ingwit h regard to the experimentalist s

technique because exposure to air causesdarkening of solution and the appearance ofa t riphenylphosphine oxide peak at -23ppm in the 31P NMR.

Further, nitrogen causes the formation of[RuH2(N2)(PPh3)3] .

NMR solution are prepared most effectivelyin a dry, degassed solvent using NMR tubessealed with valves.


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Performing the same experiment without

exogenous phosphine under hydrogenproduces [RuH2(H2)(PPh3)3] in similar yields.

[1H NMR: -7.05 (br s, Ru-H).

Slow bubbling of nit rogen or carbonmonoxide through these solut ion in an NMR

tubes for 5 min gives solution of light tan[RuH2(N2)(PPh3)3] and colourless[RuH2(CO)(PPh3)3] as confirmed by

31P {1H}

NMR.


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Micropreparation of RuH2{P(C6H5)3}4: A Transition Metal Hydride Compound