OSU – June – SGK1 STEVE KUKOLICH, Department of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona 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 , CHE , CHE

OSU – June – SGK2 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 STRUCTURE C) MOLECULAR STRUCTURE C 7 H 7 -Ti-C 5 H 5 (Cycloheptatriene… C 2 H 4 -M-(CO) 4 (Ethylene-M, M = Osmium, Iron) C 2 H 2 -Re-CH 3 -O 2 (Acetylene Methyl Dioxo Rhenium) C 6 H 6 -Cr-(CO) 3 (Benzene Chromium Tricarbonyl) C 4 H 6 -Fe-(CO) 3 (Butadiene Iron Tricarbonyl )     

OSU – June – SGK3 Transition Metal Complexes C 7 H 7 -Ti-C 5 H 5 C 2 H 4 -Os-(CO) 4 C 2 H 2 -Re-CH 3 -O 2

OSU – June – SGK4 C 7 H 7 -Ti-C 5 H 5  (  7 -C 7 H 7 )Ti (  5 -C 5 H 5 ) normal isotopomer reported in 2004 [i] [i]  Calculations predict a droop of the CHT hydrogens toward the titanium atom. To measure angle and other structural parameters:  Study with 13 C substitution, single-D substitution on cycloheptatriene  New Structrural Parameters obtained [ i][ i] Keck, K.S.; Tanjaroon C. and Kukolich, S. G. J. Mol. Spec. (2005) PRESENT WORK > Adam Daly, Erika Weidenschilling

OSU – June – SGK5 MOLECULAR CONSTANTS: Transitions were measured and the following B and C rotational constants were obtained and used in a structure fit

OSU – June – SGK6 A least squares fit was performed using a model with the C-C and C-H distances fixed to DFT values

OSU – June – SGK7 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), (2007)

OSU – June – SGK8  DFT-calculated rotational constants agree remarkably well with the experimental values > First transition measured ( 6 16  5 05 ) at MHz deviated only 1.5 MHz from the predicted frequency. The 4 14  3 03 transitions at ~6195 MHz observed for Os(CO)4(  2 -C 2 H 4 ). Similar 3-line patterns, arising from 3 Os isotopes ( 188 Os, 190 Os and 192 Os). were observed for most of the  K a = +1 transitions.

OSU – June – SGK9 Rotational and distortion constants obtained from the least-squares fits to determine rotational constants for 7 isotopomers. DFT calculated parameter values are also presented. Parameter C 2 H 4 Os(CO) 4 ( 192 Os) DFT a ( 192 Os) C 2 H 4 Os(CO) 4 ( 190 Os) C 2 H 4 Os(CO) 4 ( 188 Os) C 2 D 4 Os(CO) 4 ( 192 Os) 13 C axial ( 192 Os) 13 C equatorial ( 192 Os) 13 C ethylene ( 192 Os) A (MHz) (6) (5) (7) (1) (3) (10) (5) B (MHz) (3) (2) (7) (1) (2) (4) (3) C (MHz) (3) (2) (3) (2) (2) (8) (3) D J (kHz)0.037(3) (3) 0.035(1)0.037(3) b D JK (kHz)0.227(17) b D K (kHz)- 0.29(3) (3)- 0.23(4)- 0.21(1) b d1 (kHz) (2) b d2 (kHz)0.0073(8) b σ FIT (kHz) N

OSU – June – SGK10  Ethylene Iron tetracarbonyl (EtFe) * *B. J. Drouin and S. G. Kukolich, J. Am. Chem Soc. 121, (1999)  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 r z (C=C) value of 1.339(1) Å and the r 0 (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 CH 2 group and the C—C bond (  out-of-plane) is 26°. This angle is 22° for Fe(CO) 4 (C 2 H 4 ), indicating that the degree of metal (d  )  olefin (  *) back-bonding is greater for the Os complex.

OSU – June – SGK11 Acetylenemethyldioxorhenium (ACMDO), a metalacyclopropane [i] [i]  The molecular structure for ACMDO ] was obtained by measuring and analyzing the rotational spectra for 14 isotopomers. ] [i] [i] S. G. Kukolich, B. J. Drouin, O. Indris, J. J. Dannemiller, J. P. Zoller and W. A. Herrmann, J. Chem. Phys. 113, (2000) Motivation- K. Barry Sharpless developed highly efficient, enantioselective oxidation reactions using Osmium Tetroxide and Methyl Rhenium Trioxide.

OSU – June – SGK12 A, B, C’s & eqQ’s

OSU – June – SGK13 Structural parameters for ACMDO  ACETYLENE C-C BOND LENGTH Å  ETHYLENE C-C BOND LENGTH 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.

OSU – June – SGK14 Benzene Chromium Tricarbonyl Bonded Cr(CO) 3 reduces the symmetry of Benzene to C 3v 2 RESONANCE structures no longer equivalent ACTIVATES arenes toward nucleophillic attack at H sites C 3v SYMMETRIC TOP  WITH ALTERNATING C-C BOND LENGTHS, STILL A SYMMETRIC TOP - ONLY 1 MOMENT OF INERTIA from microwave spectrum  ISOTOPIC SUBSTITUTION!

OSU – June – SGK15  Experiment. view down a-axis of molecule 1,2(ortho) D 2 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) = Ǻ (0.017 Ǻ -xray, Rees &Coppens, Acta Crystallogr., Sect. B 1973, 29, 2515) ParameterE isomerS isomer A900.05(5)900.02(5) B (2) (2) C (2) (2) B - C  0.145

OSU – June – SGK16 Part of the spectrum (J = 3  4)

OSU – June – SGK17 Butadiene iron tricarbonyl  10 isotopomers measured, including 13 C and single and triple D substitutions  Increase in the butadiene C 1 - C 2 bond length (0.08 Å)  Decrease in the butadiene C 2 -C 3 bond length (-0.06 Å)

OSU – June – SGK18 Substantial structure changes  Free butadiene in a planar-trans conformation  Changes to cis  terminal CH 2 groups are rotated by 28  out of the butadiene plane  CH 2 plane is folded away from the butadiene C 1 -C 2 axis by 27   HYBRIDIZATION now looks more like sp 3 than sp 2

OSU – June – SGK19 Acknowledgements This material is based upon work supported by the National Science Foundation under Grant Nos. CHE , CHE , CHE 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.

OSU – June – SGK20 X-Ray and DFT-calculated charge densities for [Ni(  2 -CH 2 CH 2 )dbpe] reported by Scherer et al.,[1] illustrating charge redistribution for ethylene-nickel bonding, in support of the DCD model.[1] 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), [1]

OSU – June – SGK21  RESULTS H-atoms out of plane by 8º C-C bond – Free C 2 H 4  1.339Ǻ, C 3 H 6  1.54Ǻ C-C bond – GED  1.46(6) Ǻ, DFT Calculation  Ǻ J. A. C. S. 121, 4203 (1999)

OSU – June – SGK22  Experiment. view down z-axis of molecule 1,2(ortho) D 2 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 The experimental values for B-C are used to find  (C-C) = Ǻ 

OSU – June – SGK23  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, (1999)