© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 1 Nature of the Chemical Bond with applications to catalysis, materials.

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 1 Nature of the Chemical Bond with applications to catalysis, materials science, nanotechnology, surface science, bioinorganic chemistry, and energy Lecture 21 February 24, 2010 Bonds to MH + ; CH4  CH3OH catalysis William A. Goddard, III, wag@wag.caltech.eduwag@wag.caltech.edu 316 Beckman Institute, x3093 Charles and Mary Ferkel Professor of Chemistry, Materials Science, and Applied Physics, California Institute of Technology Teaching Assistants: Wei-Guang Liu wgliu@wag.caltech.edu Ted Yu

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 2 Remaining Course schedule Wednesday Feb. 24, 2pm L21, normal, TODAY Friday Feb. 26, 2pm L22, move to 115BI Friday Feb. 26, 3pm L23, move to 115BI (make up for Mar. 1) Monday, Mar. 1 no class (wag at NIST/NAS review in Maryland) Wednesday, Mar. 3 no class (wag at NIST/NAS review Maryland) Friday Mar. 5, 2pm, L24 (make up for March 3) Friday Mar 5 3pm L25 (catching up to March 5) Monday, Mar. 8 2pm L26, caught up, normal Wednesday, Mar. 10 no class (wag at conference in Chicago) Thursday Mar. 11, 2pm, L27 Last lecture (make up for Mar. 10) Final available Thursday March 11 Final due back Friday March 19

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 4 Mysteries from experiments on oxidative addition and reductive elimination of CH and CC bonds on Pd and Pt Why are Pd and Pt so different

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 11 Examine HH coupling at transition state Can simultaneously get good overlap of H with Pd sd hybrid and with the other H Thus get resonance stabilization of TS  low barrier

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 12 Examine CC coupling at transition state Can orient the CH 3 to obtain good overlap with Pd sd hybrid OR can orient the CH 3 to obtain get good overlap with the other CH 3 But CANNOT DO BOTH SIMULTANEOUSLY, thus do NOT get resonance stabilization of TS  high barier

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 13 Examine CH coupling at transition state H can overlap both CH 3 and Pd sd hybrid simultaneously but CH 3 cannot thus get ~ ½ resonance stabilization of TS

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 15 Pt goes from s 1 d 9 to d 10 upon reductive elimination thus product stability is DECREASED by 12 kcal/mol Using numbers from QM

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 16 Pd goes from s 1 d 9 to d 10 upon reductive elimination thus product stability is INCREASED by 20 kcal/mol Using numbers from QM Pd and Pt would be ~ same

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 17 Thus reductive elimination from Pd is stabilized by an extra 32 kcal/mol than for Pt due to the ATOMIC nature of the states The dramatic stabilization of the product by 35 kcal/mol reduces the barrier from ~ 41 (Pt) to ~ 10 (Pd) This converts a forbidden reaction to allowed

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 19 Examine bonding to all three rows of transition metals Use MH+ as model because a positive metal is more representative of organometallic and inorganic complexes M0 usually has two electrons in ns orbitals or else one M+ generally has one electron in ns orbitals or else zero M2+ never has electrons in ns orbitals

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 20 Ground states of neutral atoms Sc(4s)2(3d) Ti(4s)2(3d)2 V(4s)2(3d)3 Cr(4s)1(3d)5 Mn(4s)2(3d)5 Fe(4s)2(3d)6 Co(4s)2(3d)7 Ni(4s)2(3d)8 Cu(4s)1(3d)10 Sc ++ (3d)1 Ti ++ (3d)2 V ++ (3d)3 Cr ++ (3d)4 Mn ++ (3d)5 Fe ++ (3d)6 Co ++ (3d)7 Ni ++ (3d)8 Cu ++ (3d)10 Sc + (4s)1(3d)1 Ti + (4s)1(3d)2 V+V+ (4s)0(3d)3 Cr + (4s)0(3d)5 Mn + (4s)1(3d)5 Fe + (4s)1(3d)6 Co + (4s)0(3d)7 Ni + (4s)0(3d)8 Cu + (4s)0(3d)10

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 22 Exchange energies: Get 6*5/2=15 exchange terms 5Ksd + 10 Kdd Responsible for Hund’s rule Ksd Kdd Mn+4.819.8 Tc+8.315.3 Re+11.914.1 kcal/mol Form bond to H, must lose half the exchange stabilization for the orbital bonded to the H A [(d 1  )(d 2  )(d 3  )(d 4  )(d 5  )(s  )] Mn+: s 1 d 5 For high spin (S=3) A {(d 1  )(d 2  )(d 3  )(d 4  )(sd b  )[(sd b )H+H(sd b )](  )} sd b is  half the time and  half the time

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 24 Size of atomic orbitals, M + Valence s similar for all three rows, 5s biggest Big decrease from La(an 57) to Hf(an 72 Valence d very small for 3d

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 25 Charge transfer in MH + bonds electropositive electronegative 1 st row all electropositive 2 nd row: Ru,Rh,Pd electronegative 3 rd row: Pt, Au, Hg electronegative

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 49 Catalyst Challenges for the Selective Chemistry needed for Sustainable Development Enormous experimental efforts have been invested in solving these problems but better solutions are needed more quickly I claim that Theory and Modeling are poised to provide guidance to achieve these goals much more quickly Challenge: improved catalysts for industrial applications including Low temperature conversion of methane to fuels and organic feedstocks High selectivity and activity for converting alkanes to organic feedstocks Fuel cell cathode catalysts for the oxygen reduction reaction (ORR) with decreased overpotential, much less Pt, and insensitive to deactivation Fuel cell anode catalysts capable of operating with a variety of fuels but insensitive to CO and to deactivation A methane fuel cell (CH 4 + H 2 O  CO 2 + power [8 (H+ and e-)] Efficient catalysts for photovoltaic production of energy and H 2 Efficient catalysts for storing and recovering hydrogen Catalysts for high performance Li ion and F ion batteries

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 50 Propane ammoxidation - structure of new phases in Mixed Metal Oxide (Mitsubishi, BP) catalysts: MoVNbTaTeOx TUESDAY butane  MA over VOPO and ODH over V 2 O 5 Fuel Cell cathode electrocatalysis: nonPt and CoPt,NiPt alloys Direct methanol fuel cell: PtRu-RuOHy at anode CuSi x catalysis of MeCl to Si(Me) 2 Cl 2 and role additives Organometallic Catalysts CH 4 to liquids: Pt, Ir, Os, Re, Rh, Ru TODAY Pd-mediated activation of molecular oxygen Mechanism of the Wacker reaction in aqueous solution Single Site Polymerization catalysts for polar monomers Projects in Catalysis: First establish mechanism then use mechanism to design improved catalyst

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 51 Role of Theory in Developing Catalysts 1. Establish Mechanism of current catalysts: Use QM to predict all plausible reaction paths, Determine transition states (TS) and stable reaction intermediates (RI) Calculate vibrational frequencies (vf) to prove TS (one negative curvature) and RI Use frequencies to calculate entropy, Cp. Use QM and Poisson-Boltzmann to get free solvation energy. Get free energy at reaction temperatures G = E elec + ZPE + H vib (T) + H lib (T) –TS vib – TS lib + G solv Use to estimate rates This provides the conceptual framework to interpret experiments 2. Validation: Predict new experiments to test mechanism 3. Lead discovery: Combinatorial Computational Rapid Prototyping In silico search for new lead candidates for Ligands, Metals, Solvents 4. Experiments: optimize best predicted ligands and reaction conditions. Continue theory and simulation in collaboration with experiments Critical to new role of theory: accuracy and reliability for novel systems Must trust the theory well enough to do only 1 to 10% of the systems Focus experiments on these 1% to 10% predicted to be best

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 52 Design Criteria for a Good Catalyst Factors for which Theory can provide essential optimization: Low barrier for rate-determining step (normally insertion) Higher barriers for catalyst poisoning than for propagation Affinity for complexing the monomer strongly enough for stability but not so strong as to slow subsequent insertion Large barriers for termination pathways Ability to control of Regioselectivity Ability to control branching, tacticity For copolymers: comparable monomer affinities/insertion rate: Factors that are more difficult to address theoretically: Stability under reaction conditions Ease of synthesis Cost Ability to form active catalyst from precursor plus co-catalyst

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 53 Has theory ever contributed to catalysis development? Case study: New catalysts for low temperature activation of CH 4 and functionalization to form liquids (CH 3 OH) Over last 30 years quantum mechanics (QM) theory has played an increased role in analyzing and interpreting experimental results on catalytic systems But has QM led to new catalysts before experiment and can we count on the results from theory to focus experiments on only a few systems?

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 54 Motivation: The enormous stranded methane gas reserves, huge opportunity for new technology World Gas (CH 4 ) Reserves are estimated at 5000-6000 tcf  equivalent to 600 billion barrels of liquid fuel, comparable to total petroleum reserves To transport as gas is too expensive, must transform to liquid, e.g. CH 3 OH Current technology: high temperature (800C) Sasol process, requires huge capital investments ($billion) Much of remaining methane is associated gas that must be flared as the petroleum is removed Required: Low temperature (250C) process to selectively convert CH 4 to CH 3 OH and other liquids

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 55 (NH 3 ) 2 PtCl 2 TOF: 1x10 -2 s -1 t ½ = 15 min Rate ok, but decompose far too fast. Why? (NH 3 ) 2 PtCl 2 TOF: 1x10 -2 s -1 t ½ = 15 min Rate ok, but decompose far too fast. Why? (bpim)PtCl 2 TOF: 1x10 -3 s -1 t ½ = >200 hours Not decompose but rate 10 times too slow Also poisoned by H2O product How improve rate and eliminate poisoning (bpim)PtCl 2 TOF: 1x10 -3 s -1 t ½ = >200 hours Not decompose but rate 10 times too slow Also poisoned by H2O product How improve rate and eliminate poisoning Experimental discovery: Periana et al., Science, 1998 Catalytica: Many $$$ trying to solve these problems experimentally, failed, cancelled project. Periana came to USC, teamed up with Goddard, Chevron funded. Found success Two Platinum compounds (out of laaarge number examined) catalyze conversion of methane to methylbisulfate in fuming sulphuric acid (102%) CH 4 + H 2 SO 4 + SO 3  CH 3 OSO 3 H + H 2 O + SO 2 CH 3 OSO 3 H + H 2 O  CH 3 OH + H 2 SO 4 SO 2 + ½O 2  SO 3

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 56 Quantum Mechanics for Organometallic reactions Density Functional Theory (B3LYP or M06) Includes Generalized Gradient Approximation (nonlocal) exact exchange (hybrid). M06 has KE functional Basis Set: Gaussian functions C,H, N, O, S: All electron, 6-31G**(+) or cc-pVTZ(-f) Triple zeta basis for C,N,O,H (includes diffuse functions) Metals: Pt, Ir, etc : Replace (1s) through (4f) shells with Nonlocal PsuedoPotentials Thus for Pt treat 18 electrons explicitly [(5s) 2 (5p) 6 (5d) 9 (6s) 1 ] Basis set: LACVP**(+) (polarization + diffuse functions) We have used this level of theory for studying reaction mechanisms of over 20 organometallic reaction systems. Always find good agreement with experimental observations, but seldom is there a clear-cut experimental measurement for comparison. Periodic 2D slabs: Sequest with PBE DFT using Psuedopotentials and Gaussian basis sets based on PBE DFT More recently M06

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 57 Calculate Solvent Accessible Surface of the solute by rolling a sphere of radius R solv over the surface formed by the vdW radii of the atoms. Calculate electrostatic field of the solute based on electron density from the orbitals Calculate the polarization in the solvent due to the electrostatic field of the solute (need dielectric constant  ) This leads to Reaction Field that acts back on solute atoms, which in turn changes the orbitals. Iterated until self- consistent. Calculate solvent forces on solute atoms Use these forces to determine optimum geometry of solute in solution. Can treat solvent stabilized zwitterions Difficult to describe weakly bound solvent molecules interacting with solute (low frequency, many local minima) Short cut: Optimize structure in the gas phase and do single point solvation calculation. Some calculations done this way Extremely important for these systems (pH from -10 to +30) in very highly polar solvents: accuracy of predicting Solvation effects in QM Solvent:  = 99 R solv = 2.205 A Implementation in Jaguar (Schrodinger Inc): pK organics to ~0.2 units, solvation to ~1 kcal/mol (pH from -20 to +20) The Poisson-Boltzmann Continuum Model in Jaguar/Schrödinger is extremely accurate

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 58 6.9 (6.7) -3.89 (-52.35) 6.1 (6.0) -3.98 (-55.11) 5.8 (5.8) - 4.96 (-49.64) 5.3 (5.3) -3.90 (-57.94) 5.0 (4.9) - 4.80 (-51.84) pKa: Jaguar (experiment) E_sol: zero (H+) Comparison of Jaguar pK with experiment

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 59 First Step: Nature of (Bpym)PtCl 2 catalyst Is H + on the Catalytica Pt catalyst in fuming H 2 SO 4 (pH~-10)? In acidic media (bpym)PtCl 2 has one proton  H kcal/mol  G kcal/mol)

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 60 Most favorable species (bpym)PtCl 2 is stable due to chelation and presence of backside protonation sites Why is (Bpym)PtCl 2 Stable? Mixing Pt metal with bpym in H 2 SO 4 dissolves the metal to form the catalyst, thus quite stable Energetics are  G in kcal/mol

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 61 (NH 3 ) 2 PtCl 2 quickly protonated to form NH 4 +, losing the NH 3 ligands, leading to precipitation of inorganic Pt. (NH 3 ) 2 PtCl 2 quickly protonated to form NH 4 +, losing the NH 3 ligands, leading to precipitation of inorganic Pt. Why is (NH 3 ) 2 PtCl 2 catalyst unstable? Most favorable species

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 62 To discuss kinetics of C-H activation for (NH 3 ) 2 Pt Cl 2 and (bpym)PtCl 2 Need to consider the mechanism Mechanisms for CH activation Electrophilic addition Sigma metathesis (2 s + 2 s ) Oxidative addition Form 2 new bonds in TS Concerted, keep 2 bonds in TS Stabilize Occupied Orb. in TS

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 63  H(sol, 0K) kcal/mol Electrophilic addition Oxidative addition Start CH 4 complex CH 3 complex  -bond metathesis Use QM to determine mechanism: C-H activation step. Requires high accuracy (big basis, good DFT) 3. Electrophilic Addition wins (bpym)PtCl 2 2. Rate determining step is CH 4 ligand association NOT CH activation! 1. Form Ion-Pair intermediate Theory led to new mechanism, formation of ion pair intermediate, proved with D/H exchange

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 64 C-H Activation Step for (bpymH + )Pt(Cl)(OSO 3 H) Solution Phase QM (Jaguar) Oxidative addition Start CH 4 complex Form Ion-Pair intermediate CH 3 complex Electrophilic substitution RDS is CH 4 ligand association NOT CH activation! Differential of 33.1-32.4=0.7 kcal/mol confirmed with detailed H/D exchange experiments

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 65 Theory based mechanism: Catalytic Cycle Adding CH 4 leads to ion pair with displaced anion After first turnover, the catalyst is (bpym) PtCl(OSO 3 H) not (bpym)PtCl 2 Start here 1 st turnover Catalytic step

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 66 L 2 PtCl 2 – Water Inhibition Theory: Complexation of water to activated catalyst is 7 kcal/mol exothermic, making barrier 7 kcal/mol higher. Product formation  0 Thus inhibition is a ground state effect Challenge: since H 2 O is a product of the reaction, must make the catalyst less attractive to H 2 O but still attractive to CH 4 Theory: Complexation of water to activated catalyst is 7 kcal/mol exothermic, making barrier 7 kcal/mol higher. Product formation  0 Thus inhibition is a ground state effect Challenge: since H 2 O is a product of the reaction, must make the catalyst less attractive to H 2 O but still attractive to CH 4 Experimental Observation: Reaction strongly inhibited by water, shuts off as solvent goes from 102% to 96% Is this because of interaction of water with reactant, catalysis, transition state or product? Experimental Observation: Reaction strongly inhibited by water, shuts off as solvent goes from 102% to 96% Is this because of interaction of water with reactant, catalysis, transition state or product? Barrier 33.1 kcal/mol Barrier 39.9 kcal/mol

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 67 Quantum Mechanical Rapid Prototyping QMRP: computational analogue of combinatorial chemistry Three criteria for CH 4 activation: 1.Thermodynamic Criterion: Energy cost for formation of R-CH 3 must be less than 10 kcal mol -1. Fast to calculate because need only minimize stable M-CH 3 Reaction Intermediate 2.Poisoning Criterion: Species must be resistant to poisoning from water (i.e. water complexation is endothermic) Fast to calculate because minimize only M-H 2 O intermediate. 3.Kinetic Criterion: Barrier to product formation must be less than 35 kcal mol -1. Test for minimized M-(CH 4 ). Barrier only a few kcal/mol higher. Slower to calculate because of weakly bound anion and CH 4, but minimize only intermediate. 4.Do real barriers only when  3 is less than 35 kcal/mol Small set systems for lab experiment Muller, Philipp, Goddard Topics in Catalysis 2003, 23, 81 Many cases of Metal, ligand, solvent 1234exper pilot

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 71 QMRP: Os II NCN and Pt IV NNN ligands, reject (NCN)Pt(IV)  E(A-C) too high for (NCN)Os(II), but acceptable for (NCN)Pt(IV) (NCN)Os(II)

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 72 (NCN)Ir(III) system passes QM-RP tests 1 and 3, but is not resistant to water (test 2) QMRP: Ir III NCN, passes 1,3, fails 2, reject

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 73 (NNN)Ir(I) picked as focal point for more detailed studies (NNN)Ir(I) system passes all three tests! QMRP: Ir I NNN, passes 1,2,3 examine further (NNN)Ir(I)

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 74 +H 3 O + -H 2 O + H 2 O 0.0-32.7-28.7 4.6 Ir(I) not compatible with acidic media – protonation to Ir(III) predicted to be rapid and irreversible. QMRP: further examination of Ir I NNN. Not stable in acid media, reject Oxidation state of IrI too low move to IrIII

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 75 0.0 18.6 2.0 -H 2 O -OH - Solvated in (H 2 O) Even though (NCN)Ir I Cl failed QC-RP tests, could (NCN)Ir III (OH) 2 be viable? Very slight water inhibition, low ligand lability, Both good Very slight water inhibition, low ligand lability, Both good QMRP: Ir III NCN

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 76 20.1 10.6 ? +CH 4 46.1 ? Unfavorable to have covalent Ir-CH 3 bond trans to Ir-Ph bond Oxidative addition Thermodynamically Inaccessible. Thus reject Unfavorable to have covalent Ir-CH 3 bond trans to Ir-Ph bond Oxidative addition Thermodynamically Inaccessible. Thus reject Solvated (H 2 O) QMRP: Further examine Ir III - NCN

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 77 0.0 20.6 8.0 -H 2 O -OH - Solvated (H2O) Eliminate trans-effect by switching ligand central C to N Get some water inhibition, but low ligand lability Continue Eliminate trans-effect by switching ligand central C to N Get some water inhibition, but low ligand lability Continue Switch from Ir III NCN to Ir III NNC

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 78 0.0 28.9 8.0 -H 2 O -9.0 CH 4 activation by Sigma bond metathesis - Neutral species - Kinetically accessible with total barrier of 28.9 kcal/mol CH 4 activation by Sigma bond metathesis - Neutral species - Kinetically accessible with total barrier of 28.9 kcal/mol Solvated (H2O) Further examine Ir III NNC Passes Test

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 79 -9.0 44.3 -7.0 -1.3 Reductive Elimination to form CH 3 OH Kinetically inaccessible Reductive Elimination to form CH 3 OH Kinetically inaccessible Maybe problem is that Ir III -> Ir I unfavorable Need to Oxidize to Ir V prior to functionalization? Maybe problem is that Ir III -> Ir I unfavorable Need to Oxidize to Ir V prior to functionalization? Solvated (H 2 O) Examine Functionalization for Ir III - NNC

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 80 Oxidize with N 2 O prior to Functionalization Ir III - NNC -9.0 24.5 -7.4 -19.8 -OH - +N 2 O -N 2 Solvated (H 2 O) Passes Test Oxidation by N 2 O Kinetically accessible Oxidation by N 2 O Kinetically accessible

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 81 8.3 -2.1 -11.2 -19.8 -65.9 Thus reductive elimination from Ir V Is kinetically accessible Thus reductive elimination from Ir V Is kinetically accessible Solvated (H 2 O) Re-examine Functionalization for Ir III NNC Passes Test

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 82 A solution Ir III – NNC 0.0 28.9 8.0 -H2O-H2O -9.0 +CH 4 -9.0 24.5 -7.4 -19.8 -OH - +N 2 O -N 2 8.3 -2.1 -11.2 -19.8 -65.9 CH activation Oxidation Functionalization CH 4  CH 3 OH To avoid H 2 O poisoning, work in strong base instead of strong acid. Use lower oxidation states, e.g. Ir III and Ir I QM  optimum ligands (Goddard) 2003 Tested experimentally (Periana) 2009 It works Experimental ligand Predicted: Muller, Philipp, Goddard Topics in Catalysis 2003, 23, 81

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 83 Experimental Synthesis of Ir III NNC system Experimental realization of catalytic CH 4 hydroxylation predicted for an iridium NNC pincer complex, demonstrating thermal, protic, and oxidant stability; Young, KJH; Oxgaard, J; Ess, DH; Meier SK, Stewart T, Goddard WA, Periana RA; Chem. Comm., (22): 3270-3272 (2009)

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 84 Xray of Ir III NNC Thermal ellipsoid plot of 1-TFA with 50% probability. Hydrogens, and benzene co-solvent removed for clarity. bond lengths (Å): bond angles (deg): bond lengths (Å): Ir(1)-N(2) 2.017(6), Ir(1)-C(16) 2.078(8), Ir(1)-C(27) 2.174(9), Ir(1)- N(1) 2.164(6), Ir(1)-C(29) 2.081(11), Ir(1)-O(1) 2.207(6). bond angles (deg): N(2)-Ir(1)-C(16) 78.7(3), N(2)-Ir(1)-C(27) 161.0(3), N(2)-Ir(1)-N(1) 76.8(2), C(16)-Ir(1)-N(1) 155.4(3), C(27)-Ir(1)-N(1) 84.2(3), C(29)-Ir(1)-O(1) 171.1(5). Experimental realization of catalytic CH 4 hydroxylation predicted for an iridium NNC pincer complex, demonstrating thermal, protic, and oxidant stability; Young, KJH; Oxgaard, J; Ess, DH; Meier SK, Stewart T, Goddard WA, Periana RA; Chem. Comm., (22): 3270-3272 (2009)

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 85 Final step: QM for Experimental Ligand enthalpy solvent corrections in kcal mol -1 (453K) for HTFA (  = 8.42 radius = 2.479 Å). Chem. Comm., (22): 3270-3272 (2009) Message: it took 2 years of experiments to synthesize the desired ligand and incorporate the Ir in the correct ox. state. Periana persisted only because he was confident it would work. Not practical to do this for the 1000’s of cases examined in QMRP

© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 1 Nature of the Chemical Bond with applications to catalysis, materials.

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© copyright 2010 William A. Goddard III, all rights reservedCh120a-Goddard-L21 1 Nature of the Chemical Bond with applications to catalysis, materials.

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