Kinetic and Thermodynamic Kinetic and Thermodynamic Studies of Gaseous Metallo-Studies of Gaseous Metallo-

Organic ComplexesOrganic Complexes

Jason Dee, Darrin BellertJason Dee, Darrin BellertBaylor UniversityBaylor University

June 25, 2009June 25, 2009

OutlineOutline

What we doWhat we do

How we do itHow we do it

What we learn from itWhat we learn from it

What we doWhat we do

A major goal of our research is to obtain rate A major goal of our research is to obtain rate constants of unimolecular decomposition of mass-constants of unimolecular decomposition of mass-selected metallo-organic ionic complexes via laser-selected metallo-organic ionic complexes via laser-driven photodissociationdriven photodissociation

Investigate bond rupture dynamics and conditions Investigate bond rupture dynamics and conditions required to open various dissociative pathways in required to open various dissociative pathways in metal catalyzed systemsmetal catalyzed systems

Custom built Custom built molecular beam molecular beam apparatusapparatus

Orthogonal Orthogonal ExtractionExtraction

Hemispherical Hemispherical energy analyzer energy analyzer tuned to tuned to transmit the full transmit the full kinetic energy of kinetic energy of molecular beammolecular beam

Voltage tuned to Voltage tuned to transmit solely transmit solely “daughter” ions “daughter” ions produced produced following following photodissociatiophotodissociationn

Mass Spectra of Mass Spectra of NiNi++Acetaldehyde Clusters Acetaldehyde Clusters

GeneratedGenerated

Daughter fragments produced through Daughter fragments produced through photodissociation of Niphotodissociation of Ni++AcetaldehydeAcetaldehyde

onTransmissiDaughteronTransmissiParentComplexParentMass

forVoltageSectorforVoltageSectorIonDaughterMass

Possible mechanism for Possible mechanism for decarbonylation of decarbonylation of NiNi++AcetaldehydeAcetaldehyde

Left trace ~ NiLeft trace ~ Ni++ isertion into a C-H isertion into a C-H bond followed by bond followed by a methide shifta methide shift

Right trace ~ NiRight trace ~ Ni++ insertion into a C-insertion into a C-C bond followed C bond followed by a hydride shiftby a hydride shift

How we measure rate How we measure rate constantsconstants

Intersect Intersect molecular beam molecular beam with laser before with laser before extractionextraction

Sector to Sector to transmit only transmit only ions with ions with appropriate appropriate “daughter” “daughter” kinetic energykinetic energy

Parent complex Parent complex must dissociate must dissociate after exiting the after exiting the acceleration gridacceleration grid

What we were What we were anticipating…anticipating…

Laser must have Laser must have sufficient energy to sufficient energy to couple to couple to dissociative statedissociative state

There is a time delay There is a time delay after laser excitation after laser excitation before dissociative before dissociative fragments are fragments are detected detected

Plot ln [Int] vs time Plot ln [Int] vs time to obtain rate to obtain rate constantconstant

Don’t draw your line before plotting your

points…

What we are actually What we are actually acquiringacquiring

y A e d tA

ke e

A

ke

ekt

t

t

k t k t t k tk t

i

f

i i i

00 0 1 1

yk

eA ek

k

'.1 5 0

At =A0e-kT

NiNi++AldAld→ Ni→ Ni++COCO

Two representative Two representative plots of plots of decarbonylation of decarbonylation of Ni+AcetaldehydeNi+Acetaldehyde Top~18000 cmTop~18000 cm-1-1

Bottom~16,000 cmBottom~16,000 cm-1-1

Two Different Two Different Pathways Pathways Observed with Observed with different rate different rate constantsconstants

Kinetic Scans of KetonesKinetic Scans of Ketones

Rate constants Rate constants acquired after acquired after deuterization of deuterization of Acetone were Acetone were ~5x greater than ~5x greater than those of normal those of normal acetoneacetone Vanessa Vanessa

Castleberry’s talk Castleberry’s talk on Friday (FB05)on Friday (FB05)

Comparing NiComparing Ni++Ald to NiAld to Ni++AcAcInternal energy Internal energy

(cm(cm-1-1))k(E) (µsk(E) (µs-1-1))

1880018800 0.113 ± 0.0050.113 ± 0.005

1800018000 0.087 ± 0.0030.087 ± 0.003

1640016400 0.059 ± 0.0020.059 ± 0.002

1610016100 0.058 ± 0.0030.058 ± 0.003

1560015600 0.055 ± 0.0030.055 ± 0.003

C-C insertion C-H insertion

Internal energy (cm-1)

k(E) (µs-1) k(E) (µs-1)

18,200 0.480 ± 0.002 0.100 ± 0.002

17,800 0.359 ± 0.002 0.095 ± 0.002

16,800 0.331 ± 0.002 0.085 ± 0.003

16,400 0.255 ± 0.003 0.076 ± 0.004

15,800 0.183 ± 0.005 0.052 ± 0.006

15,600 0.106 ± 0.008 0.050 ± 0.007

15,100 --------- ---------

Ni+Ac→Ni+CO

Ni+Ald→Ni+CO

What we learned from itWhat we learned from it

Molecular Migration appears to be rate-Molecular Migration appears to be rate-limiting step in simple ketoneslimiting step in simple ketones

From the NiFrom the Ni++Ald studiesAld studies NiNi++ insertion into either a C-H or C-C sigma insertion into either a C-H or C-C sigma

bond is possiblebond is possible Isomerization Step appears to be rate limiting Isomerization Step appears to be rate limiting

step though further studies are neededstep though further studies are needed At lower energies, C-C insertion followed by a At lower energies, C-C insertion followed by a

hydride shift appears to predominatehydride shift appears to predominate Rate Constants dependent on energy of photon Rate Constants dependent on energy of photon

beambeam

AcknowldgementsAcknowldgements

Baylor UniversityBaylor University Petroleum Research Fund (PRF)Petroleum Research Fund (PRF) Dr. Darrin BellertDr. Darrin Bellert

Bellert Research GroupBellert Research Group Vanessa CastleberryVanessa Castleberry Otsmar VillarealOtsmar Villareal Ivanna LaborenIvanna Laboren Sarah FreySarah Frey

Any Questions?Any Questions?

Or post-doc positions…Or post-doc positions…

How cold is our molecular How cold is our molecular beam?beam?

Fit experimental Fit experimental data to Maxwell-data to Maxwell-Boltzmann Boltzmann distribution of distribution of velocitiesvelocities

Top~Pure He Top~Pure He expansion with Niexpansion with Ni T = 12.2 KT = 12.2 K M = 8.6M = 8.6

Bottom~AcetaldehyBottom~Acetaldehyde doped He de doped He expansionexpansion T = 0.32 KT = 0.32 K M = 63M = 63

P v vm v x u

kT x( ) exp

( ( ) )

( )

3

2

2