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STEVE KUKOLICH, Department of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona 85721

MICROWAVE MEASUREMENTS OF STRUCTURE CHANGES FOR LIGAND MOLECULES BOUND TO TRANSITION METALS†

† This material is based on work supported by the National Science Foundation under Grant Nos. CHE-0809053, CHE-0304969, CHE-9634130.

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Structural changes on complex formation & CATALYSIS

FORMATION OF TRANSITION METAL COMPLEXES WITH SMALL ORGANIC MOLECULES CAUSES CHANGES IN:

A) REACTIVITY OF THE ORGANIC LIGANDS B) ELECTRONIC STRUCTUREC) MOLECULAR STRUCTURE

C7H7-Ti-C5H5 (Cycloheptatriene…C2H4-M-(CO)4 (Ethylene-M, M = Osmium, Iron)C2H2-Re-CH3-O2 (Acetylene Methyl Dioxo Rhenium)C6H6-Cr-(CO)3 (Benzene Chromium Tricarbonyl)C4H6-Fe-(CO)3 (Butadiene Iron Tricarbonyl)

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Transition Metal Complexes

C7H7-Ti-C5H5 C2H4-Os-(CO)4 C2H2-Re-CH3-O2

C1C2

C3C4

C5C6

C7

Ti

C8

C9C10

C11

C12

ReO1

O2

C1C2

C3

H1

H2

H5

H3

H4

b

a

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C7H7-Ti-C5H5

(7-C7H7)Ti (5-C5H5) normal isotopomer reported in 2004[i]

Calculations predict a droop of the CHT hydrogens toward the titanium atom.

To measure angle and other structural parameters:

Study with13C substitution, single-D substitution on cycloheptatriene

New Structrural Parameters obtained

[i] Keck, K.S.; Tanjaroon C. and Kukolich, S. G. J. Mol. Spec. (2005) 232 55-60. PRESENT WORK > Adam Daly, Erika Weidenschilling

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MOLECULAR CONSTANTS: Transitions were measured and the following B and C rotational constants were obtained and used in a structure fit

ISOTOPOMER MEASURED FIT VALUE DEV. No. OF LINES

12C - B 771.7891 771.8240 -0.0349 14 - C 771.7891 771.7745 0.0146 13C - C7H7 - B 769.2680 769.2427 0.0253 12 - C 766.1320 766.1463 -0.0143 13C - C5H5 - B 767.0140 767.0210 -0.0070 9 - C 765.3230 765.3072 0.0158 C7H6D - B 769.6930 769.6790 0.0140 16 - C 761.1780 761.1918 -0.0138

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Ring Parameter Value C (C7H7) R(C(center)-Ti) -1.48(1) H (C7H7) R(H(center)-Ti) -1.33 (1)

C5H5 R(C(center)-Ti)* 2.01(1)

Angle determined from the fit: 8.6˚, S. D. fit = 24 kHz * Note that C5H5 assumed planar.

A least squares fit was performed using a model with the C-C and C-H distances fixed to DFT values

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Ethylene Structure Changes on Complex Formation

Ethylene-Os: JOE TAKATS – U. ALBERTA, C. Karunatilaka, B. S. Tackett, J. Washington, and S. G. Kukolich, J. Am. Chem. Soc. 129(34), 10522-10530 (2007)

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DFT-calculated rotational constants agree remarkably well with the experimental values > First transition measured ( 616 505) at 9197.8522 MHz deviated only 1.5 MHz from the predicted frequency.

The 414 303 transitions at ~6195 MHz observed for Os(CO)4(2-C2H4). Similar 3-line patterns, arising from 3 Os isotopes (188Os, 190Os and 192Os). were observed for most of the Ka = +1 transitions.

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Rotational and distortion constants obtained from the least-squares fits to determine rotational constants for 7 isotopomers. DFT calculated parameter values are also presented. 

ParameterC2H4Os(CO)4

(192Os)

DFT a

(192Os)

C2H4Os(CO)4

(190Os)

C2H4Os(CO)4

(188Os)

C2D4Os(CO)4

(192Os)

13C axial(192Os)

13C equatorial

(192Os)

13C ethylene(192Os)

A (MHz) 929.3256(6) 930.85 929.3328(5) 929.3407(7) 881.4489(1) 929.2751(3) 923.1201(10) 920.6996(5)

B (MHz) 755.1707(3) 754.62 755.1689(2) 755.1666(7) 744.4294(1) 750.9077(2) 753.9757(4) 754.9994(3)

C (MHz) 752.7446(3) 752.56 752.7494(2) 752.7545(3) 724.3714(2) 748.4802(2) 749.8525(8) 747.2494(3)

DJ (kHz) 0.037(3) 0.05 0.033(3) 0.033(3) 0.035(1) 0.037(3)b 0.037(3)b 0.037(3)b

DJK (kHz) 0.227(17) 0.21 0.227b 0.227b 0.227b 0.227b 0.227b 0.227b

DK (kHz) - 0.29(3) - 0.24 - 0.24(3) - 0.23(4) - 0.21(1) - 0.29b - 0.29b - 0.29b

d1 (kHz) - 0.002(2) - 0.002 - 0.002b - 0.002b - 0.002b - 0.002b - 0.002b - 0.002b

d2 (kHz) 0.0073(8) - 0.0066 0.0073b 0.0073b 0.0073b 0.0073b 0.0073b 0.0073b

σFIT (kHz) 4.7 - 3.2 3.6 3.3 2.5 5.7 3.4

N 42 - 24 18 27 8 7 9

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Ethylene Iron tetracarbonyl (EtFe)*

*B. J. Drouin and S. G. Kukolich, J. Am. Chem Soc. 121, 4023-4030 (1999)

OH

C

H

O

C

C

C

O

C

H

H

C

O

o1.073 A

1.812 A

o

2.097 Ao

Fe

1.144 A

1.152 Ao

o

110.9

o

The deformation of the ethylene ligand upon coordination to osmium is large, well-determined. The experimental ethylene C—C bond length of 1.43 Å for the complex falls between the free ethylene average rz (C=C) value of 1.339(1) Å and the r0(C—C) bond length of 1.534(2) Å for ethane. The C—C bond length for the Fe congener is 1.421(7) Å.

The angle between the plane of the CH2 group and the C—C bond (out-of-plane) is 26°. This angle is 22° for Fe(CO)4(C2H4), indicating that the degree of metal (d) olefin (*) back-bonding is greater for the Os complex.

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Acetylenemethyldioxorhenium (ACMDO),

a metalacyclopropane [i]

The molecular structure for ACMDO] was obtained by measuring and analyzing the rotational spectra for 14 isotopomers.

[i] S. G. Kukolich, B. J. Drouin, O. Indris, J. J.

Dannemiller, J. P. Zoller and W. A. Herrmann, J. Chem. Phys. 113, 7891-7900 (2000)

ReO1

O2

C1C2

C3

H1

H2

H5

H3

H4

b

a

Motivation-K. Barry Sharpless developed highly efficient, enantioselective oxidation reactions using Osmium Tetroxide and Methyl Rhenium Trioxide.

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A, B, C’s & eqQ’s

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Structural parameters for ACMDO

H5

H1

C3

H2

C1

Re

C2

H4

O1

z

2.116 A

1.710 A

2.043 A2.067 A

81.9

100.8

146 1471.294 A

1.072 A1.075 A

ACETYLENE C-C BOND LENGTH 1.207 Å ETHYLENE C-C BOND LENGTH 1.339 Å

The C-C bond length is increased by 0.08 Å to 1.29 Å. The H-C-C interbond angles are reduced from 180 to 146, and 147.

The experimental structural parameters indicate that this compound is better described as a metallacyclopropene rather than as an 2-type, -bonded complex.

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Benzene Chromium Tricarbonyl• Bonded Cr(CO)3

reduces the symmetry of Benzene to C3v

• 2 RESONANCE structures no longer equivalent

• ACTIVATES arenes toward nucleophillic attack at H sites

C3v SYMMETRIC TOP WITH ALTERNATING C-C BOND

LENGTHS, STILL A SYMMETRIC TOP - ONLY 1 MOMENT OF INERTIA from microwave spectrum ISOTOPIC SUBSTITUTION!

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Experiment.

view down a-axis of molecule

• 1,2(ortho) D2 substituted Benzene

• C-C bond with D’s can be E(eclipsed), or S(staggered) W.R.T. CO ligand

• For E, distance between D’s is SHORTER, for S – LONGER than normal

• Now we have ASYMMETRIC top, same A, but different B, C

Experimental values for B-C are used to find (C-C) = 0.016 Ǻ(0.017 Ǻ -xray, Rees &Coppens, Acta Crystallogr., Sect. B 1973, 29, 2515)

Parameter E isomer S isomer

A 900.05(5) 900.02(5)

B 723.9167(2) 723.8423(2)

C 717.8598(2) 717.9305(2)

B - C 6.057 5.912

0.145

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Part of the spectrum (J = 3 4)

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Butadiene iron tricarbonyl

10 isotopomers measured, including 13C and single and triple D substitutions

Increase in the butadiene C1-C2 bond length (0.08 Å)

Decrease in the butadiene C2-C3 bond length (-0.06 Å)

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Substantial structure changes

Free butadiene in a planar-trans conformation

Changes to cisterminal CH2 groups are rotated by 28 out of the butadiene plane CH2 plane is folded away from the butadiene C1-C2 axis by 27HYBRIDIZATION now looks more like sp3 than sp2

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Acknowledgements

This material is based upon work supported by the National Science Foundation under Grant Nos. CHE-0809053, CHE-0304969, CHE-9634130. This support from the National Science Foundation is gratefully acknowledged

Adam Daly, Erika Weidenschilling, Kristen Keck, Chakree Tanjaroon, Chandana Karunatilaka, Brandon Tackett, John Washington, Brian Drouin, Oliver Indris, J. P. Zoller, Shane Sickafoose, Jennifer Dannemiller, Mark Roehrig, Giles Henderson (EIU), Wolfgang Herrmann (T.U.M), Joe Takats (Alberta)

•Department of Chemistry and Biochemistry, U. of Arizona.

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X-Ray and DFT-calculated charge densities for [Ni(2-CH2CH2)dbpe] reported by Scherer et al.,[1] illustrating charge redistribution for ethylene-nickel bonding, in support of the DCD model.

x) y)Above, X-ray(x), and DFT(y)

charge density plots. Right, DFT-calculated,

donation and back- donation contributions to bonding

[1] Scherer, Wolfgang; Eickerling, Georg; Shorokhov, Dmitry; Gullo, Emanuel; McGrady, G. Sean; Sirsch, Peter. New Journal of Chemistry 2006, 30(3), 309-312.

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RESULTS

• H-atoms out of plane by 8º

• C-C bond – Free C2H4 1.339Ǻ, C3H6 1.54Ǻ

• C-C bond – GED 1.46(6) Ǻ, DFT Calculation 1.4186Ǻ• J. A. C. S. 121, 4203 (1999)

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Experiment.

view down z-axis of molecule

• 1,2(ortho) D2 substituted Benzene

• C-C bond with D’s can be E(eclipsed), or S(staggered) W.R.T. CO ligand

• For E, distance between D’s is SHORTER, for S – LONGER than normal

• Now we have ASYMMETRIC top, same A, but different B, C

Parameter E isomer S isomer A (MHz) 900.05(5) 900.02(5) B (MHz) 723.9167(2) 723.8423(2) C (MHz) 7 17.8598(2) 717.9305(2) DJ (kHz) 0.046(2) 0.048(2) DJK (kHz ) -0.10(6) -0.11(5)

The experimental values for B-C are used to find (C-C) = 0.016 Ǻ

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Ethylene Iron tetracarbonyl (EtFe)*

• Olefin activation on metal catalysts is used in synthesis. Accepted mechanisms involve metalocyclopropane intermediates.

• Simplest “stable” olefin-iron complex

• Example of a “one-on-one” complex → EASIER TO STUDY.

*B. J. Drouin and S. G. Kukolich, J. Am. Chem Soc. 121, 4023-4030 (1999)

OH

C

H

O

C

C

C

O

C

H

H

C

O

o1.073 A

1.812 A

o

2.097 Ao

Fe

1.144 A

1.152 Ao

o

110.9

o