Organometallic Chemistry Lecture Notes 2025 PDF

# Introduction - Jan 8th 2025 - **What is Organometallic chemistry?** - The chemistry of compounds containing M-C bond. - Their bonding, properties, and reactivity. - **Consider:** - $R-C \equiv H + H_2O + R′ \longrightarrow R-C \equiv R′$ would be 2 Et together - But,...

# Introduction - Jan 8th 2025 - **What is Organometallic chemistry?** - The chemistry of compounds containing M-C bond. - Their bonding, properties, and reactivity. - **Consider:** - $R-C \equiv H + H_2O + R′ \longrightarrow R-C \equiv R′$ would be 2 Et together - But, - Electronegativity: - $C$: $2.5$ - $Cl$: $3.1$ - $O$: $3.4$ - $Mg$: $1.3$ - Therefore, $Mg$ is worse than $C$ - $Nu^−$ cuz: $C$ has $8$ from two $E^+$ (turning alkyl halide to $Nu$) - **Importance:** - C-C bond from two $E^+$ (turning alkyl halide to $Nu$) - **Electronegativity of the atoms are responsible for the reverse polarity.** - This results in a nucleophilic carbon which can attack the electrophilic ketone - As a result, Grignard reagents behave as $Nu^−$ - Invert polarity (see umpling but not) - **Important in Synthetic Chun** - A couple other reactions: - $R - Mg - Br + H_2O \longrightarrow R - H + MgBr(OH)$ Water: $ROH$ Acid: $Nitrile$ - $R - Mg - Br + CO_2 \longrightarrow [H^+] R-C(=O)_2H$ - $R-Mg-Br$ can also form $R-C \equiv N$ - $R-Mg-Br+R—C \equiv N \longrightarrow [H^+] R-C(=O)R′ + NH_3 + HO*Mg*Br$ Ketone: $Ketone$ - This also works for alkyl lithiums - $H_3C-Br + 2Li(s) \longrightarrow H_3C — Li + LiBr$ - **Transition Metals** - Not everything in D block is a TM - But all TM are in D block - **Organometallic chem is concerned w/ M-C bonds and is important for its ability to form C-C bonds between two electrophiles.** - Electronegativity of metal inverts polarity on carbons. # Definition of Transition Metal ## I do not know the order of the TMs - Sc Ti V Cr Mn Fe Co Ni Cu Zn - Y Zr Nb Mo Tc Ru Rh Pd Ag Cd - La Hf Ta W Re Os Ir Pt Au Hg - **Metal with an incomplete or empty d or f orbital in one or more of its oxidation states** - behaves more as p-block metals - In group do not count (Cd, Hg, etc.) ## Chemistry associated w/ - Compounds in complexes. - Reagents in organic chemistry - Chemistry associated with mangnetism, reactivity, etc. ## Bonding in TM complexes. - **Mostly exist as solids in their metallic form** - **But of course, metals can also form complexes. w organic & inorganic molecules as ligands** - Generally, metals are viewed as electropositive and ligands are electron donors - $M \longrightarrow L$ Covalent Bond - $ML_nL$ - **Usually has many ligands** - In OM chemistry, we are interested in Carbon based ligands - 1st reported OM complex: $[Pt(NH_3)_4]^[2+]$ Zeise's salt (1827) - Grignard reagents $R-Mg-X$ ~1900s - Ferrocene 1951 "Sandwich Compounds" # Transition Metals ## Oxidation state: Charge left on metal after all ligands dissociate - Metals are generally in their to metallic form but can form covalent bonds with electron donors - **Are elements w/ incomplete or empty ford orbital in 21 ox.** # Coordination Number: - **How many ligands are coordinated to the same metal?** - The geometry of the metal complex is often attributed to steric factors for each ligand to spatially separate - However, we also have to consider non-bonding e- - As a result, common geometries are observed. - **Linear** - $L-M-L$ - **Trigonal Planar** - $L-M-L$ - $L$ - $L$ - **T-shaped** - $L$ - $M-L$ - $L$ - **Tetrahedral** - $L-M-L$ - $L$ - $L$ - **Square planar** - $L$ - $L-M-L$ - $L$ - **See-saw** - $L$ - $L-M-L$ - $L$ - **Trigonal bipyramidal** - $L$ - $L$ - $M$ - $L $ - $L$ - **Square pyramidal** - $L$ - $L$ - $M$ - $L$ - $L$ - **Pentagonal bipyramidal** - $ L-M-L$ - $ L-M-L$ - $ L-M-L$ - $ L-M-L$ - $ L-M-L$ ## Relevant Orbitals - $S$ - $P_z$ - $P_x$ - $P_y$ - $d_{xy}$ - $d_{yz}$ - $d_{zx}$ - $d_{x^2 - y^2}$ - $d_{z^2}$ - $d_{xyz}$ - $e_g$ - $t_{2g}$ # A LIE (CFT) - Jan 10th 2025 - **Metal complex geometry mirrors VSPER theory:** - linear, trig.plan., T-shaped, To, sq. pl., TBPY, S9. pyramidal - **On based on Sterics and non bonding e** - $t_{2g}$ A.O.s $d_{zy}$, $d_{ax}$, $d_{yx}$ & $e_g$ A.O.s $d_{zt}$, $d_{x^2 y^2}$ => **CFT splitting &** # + + + or — — — depending on Δ - High spin “paramagnetic" - low spin “diamagnetic" - $[Fe(H_2O)_6]^[3+]$ $ [Fe(CO)_6]^[2−]$ - Bonding (Aside): - **σ:** 2: Symmetric wrt bonding avis - **π:** 2: Asymetric wrt bonding axis - **δ:** - - $S + 8 P \longrightarrow $ no net overlap - $S + 0 P \longrightarrow$ Overlap! - Criteria for strong interactions - Correct symmetry (σ, τπ, δ) - Correct overlap - Similar energy # MO diagrams - [MO diagram with H and Cl] - H - $σ^∗$ <br> <br> <br> - **Dative bond:** Formally, any lewis base can be a ligand - From a simplistic pov, the donation of a lone pair from a LB to a LA does not get a charge - Another way to depict this is the use of an arrow indicating a covalent bond - **Complexes can be low or high spin based on size of a from legand field** - Bonds need correct symmetry, overlap & Similar energies between ADs to form - Dative bonds occur when Lewis bases donate 2e- to a Lewis acid (metal) # Metal-Ligand Bonding - Jan 15 2025 - $M-H$ $M\equiv O \equiv H$ $R$ - $M-CR_3$: $M\equiv O\equiv C\equiv R$ - $M-NR_3$: $M\equiv O\equiv N\equiv R$ - $R$ - $R$ - $R$ - - **Hydrides, alkyl, amines** - **σ-bonding:** no different than organic chemistry - $t_{2g}$ - $e_g$ - $a_{1g}$ - $t_{1u}$ - $t_{2u}$ - $e_g $ - $t_{1u}$ - $a_{1g}$ - $t_{2g}$ - $t_{1u}$ - $t_{2g}$ - $t_{1u}$ - - **πL-bonding:** Same basic concept as organic chemistry-but a bit more complicated - Ls many ligands can participate to πL-bonding w/ the metal as long as the appropriate orbitals are available - **πL-donors** - σ: $L$ $sp^2$ $M$ $d_σ$ - $R$ amide - $R$: $Lp$ $M$ $dτ$ - $R$ - $M$ - $M$ - $R$ - $R$ - $CI$ - $CI$ - $Alkoxide$ - $Halides$ - **Ligands (πL-bonding)** - $e_g^*$ - $t_{2g}$ - $t_{2g}$ - $a_{1g}$ - $t_{2g}$ - $Δ_o$ decreases as strength of πL- donor increases - **πL HOMO centered on metal** - **Ligand σ-bonding like in organic chemistry** - Ligands can πL-bund as long as the appropriate orbitals are free - **πL-donors (NR3, OR₂, X), Δo between $t_{2g}^∗$ and $e_g^∗$=> Δo decrease w/ increase Str.** # Overall picture indicates that the HOMO is directly affected by M-L πL-bonding. - L-M πL-bonding increases energy - **HOMO making the metal more basic** - Therefore, πL donor ligands stabilize e- poor, high Oxidation state metals - Therefore, - **w/ a low d-count** - **Ls are common for early transition metals** - **Ls are happier in high oxidation states thanks to electropositivity** - When a metal has no d-electrons very strong ML bonding, often drawn as M=L (eg. Wonder # πL-acceptors - σ: Ln M $d_σ$ - $R$ - $R_2$ - $R$ - $M$ - $M$ - $R_2$ - $PR$ - $PR$ - $Alkene$ ($Olefin$) - $Phosphines$ - $R$ - $R$ - $R$ - $R$ - $R$ - $R$ - $R_2$ - $R$ - $R$ - $R$ - $R$ - $R$ - $R$ - $R$ - $R$ - $R$ - $R_2$ - $R_2$ - $R$ - $R$ - $R$ - $R$ - $R$ - $R$ - $R$ - $R$ - $R$ - $R$ - $R$ - $R$ - $R$: M $dτ$ $Lr^∗$ - πL: M $dτ$e*$L_d_σ^∗$ - **The rationalization of M-P backbonding is Controversial.** - The classic picture evokes a M $dτ$e P3d i inderaction. Quantum mechanics (comp . chem.) indicate that P-R orbitals play a major role. - Hybridization of phosphorus 3d and P-ROA resulting in a πL-acapting orbital has also been evoked - **πL-donors stabilize - poor metals - early TMs (high ax. states, electropositive)** - **πL-acceptors (CO, alkene, PR₃)** - **Phosphine acceptors: d-orbitals or 3d and P-R σ* orbitals** # σ-complex - $e_g^*$ = ——— = $e_g^*$ - $t_{2g}$= ——— =$t_{2g}$ - $t_{2g}$ = ——— = $t_{2g}$ - $Δ_o$ - $e_g$ - $t_{2g}$ - **Stabilizing e-nich** - **Ao increases as strength of πL-acceptor increases** # Turns non-banding d-orbitals into bonding Mos - **Centered on the metal** - The overall picture is that M-L πL-donation. (πL-backbonding) lowers the energy of the HOMO making the metal less basic (less willing to donate e-) - πL-backbonding therefore stabilizes e-rich, low oxidation state metals - L↳ very common w/ late transition metals - **The overall picture:** - $Δ_{o(3d)} >Δ_{o(4d)} >Δ_{o(5d)}$ - Strong-donor o-only strong o-donor strong πL-acceptor - $e_g = ... e_g$ - $e_g = ... e_g$ - $e_g =...t_{2g}$ - $t_{2g}$ = ... $tag$ = $t_{2g}$ - $t_{2g}$ = ... $tag$ = $t_{2g}$ - **this value is often referred to as the CF splitting**. - **Spectrochemical series** - •Colours observed of TM complexes often arise from the absorption of light that corresponds to the energy gap (4) # πL-acceptor Strength increase = increase in A - πL-backbonding stabilizes e- rich metals (late TMs at high electronegative). - Spectrochemical series gives insight on ligand type/strength # Electronic spectra can often be used to measure s directly - This feels like and ad for CFT... - $I < Br < Cl < N_3 < N < F < H < CO < NH3 < O < CH_3 <C_6H_6<CN < CO < H $ - πL-donor “low-field ligands" “weak" σ - πL-acceptors/strong “high-field ligands" # 18-Electron Rule - A stable complex is obtained when the sum of a metal's d electrons and the e- from ligands add up to 18-commonly - Similar to organic molecule octet. - What this really means is that 18 e- represents the upper limit for most complexes, as more then 18e would fill antibonding orbitals - The vast majority of stable diamagnetic organo-metallic compounds have 16 or 18 valena e due to the presina of these orbitals. - As a result, complexes w/ fewer than 18 (or 16) exist, but are unlikely to be present in high conc - Reactive, similar to a carbocation - But of course exceptions exist! # Electron Counting - •Electron counting is the process of determining the number of valenca e about a metal center in a Complex - What is important: - What metal? How many e- does it start w/ - Generally, stable metal complexes have a valence e count of 18-upper limit - 16e complexes are also common but any less is very reactive - Determined by e- counting # How many ligands are present? How are they bound? - What types of ligands? - Is there a charge on the complex? - What is the oxidation state of the metal? - $eg$ - $L(w/ charge) /Mox.$ - $Fc(CO)s$: $C≡O^*(x5)$ $Fe^2+$ - $[Fe(CO)_6]^2−$ : $C≡O^*(x4)$ $Fe^2+ $ - $PdCl_4^{2−}$: $Cl^−(x4)$ $Pd_2 ^2+ $ - $ Oxidation States$ - $Charge left on the metal after all ligands are removed in their closed shell config.$ - The D-Count - Jan 17th 2025 - $ [Ru(PPh_3)_4Cl_2]$ would be $d^6$ based on the group 8, ox. State 2 - $Ph_3P$ - $P-PPh_3$ - $PPh_3$ - $PPh_3$ - $CI$ - $Pd$ - $CI$ - $Pd(II)$ - $Sq. Pl.$ - $CO$ - $CI$ - $Oc-Ni-co$ > or $Ni-Br$ - $CO$ - $Sq. Pl.$ - $dio$ - $Ta$ - $Commonly chemists will refer to metals simply by their d-Count.$ - This is the number of valence electrons expected based on the group according to oxidation state - Effectively the no of non-bonding e on the metal in the complex - Knowing the d-count and its oxidation state will help us identify if a complex will be diamagnetic or paramagnetic. - An odd number = paramagnetic L↳ An even number could be diamagnetic NMR - Also, knowing d-counts can help us predict geometries - A common Situation is thad $d^8$ metal complexes will have 16e and be sq. planar # Types of Ligands amionic neutral - The distinction is whether or not there is a charge on the ligand when it dissociates from the metal # Electron Counting - Oxidation state: Charge on metal once ligands are remaed - Dcount can help predict paramagnetism (odd #) and geometry (d8=> 16e_ sq. pl.) - $M\longrightarrow L$ - $M$ - $L$ - $M\longrightarrow X$ - $M$ - $X$ # Examples of L-type ligands - $PR_3$ - $:NR_3$ - $C\equiv O$ - $R-N^−R'$ - $R-N^−$ - $R^−$ - $en$ - $Phosphines$ - $ Amines $ - $ Carbonyl $ - $Imines $ - $Alkenes$ - $en$ # X-type ligands - $Cl, Br, I, F$ - $C≡N$ - $H$ - $alkynyl$ - $NR_2$ - $OR' $ - $halides$ - $cyano$ - $hydridel$ - $alkyl/aryl$ - amide - alkoxide # Combination LX type ligands. - Ligands can also coordinate to metals through a combination of both types these ligands should therefore be viewed through each connection point individually - $LX types$ - $Electron Counting$ - 2 main methods: - **Ionic method:** - Ligands: $6 \times 2=12e^−$ - $Co-Cr-co$ - $Cr(0) = 6e^−$ - $I$ $Co$ $Co$ - $18e^−$ - **All ligands (X+L) contribute 2e at each connection point** - **Need to know oxidation state of the metal** - **Covalent method** - Need to know. - Number of L-type ligands de- donors - Number of X-type ligands 1e- donors - Group of the metal - **Charge (+/-e-)** - $Ph_3P$ - $CI-Pd-C1 \longrightarrow Pd^{2+} \implies d^8 \longrightarrow 16e^- - woah$ - $PPh_3$ - $CI$ - $CI-Pd-CI$ - $CI$ - $CI$ - - $Co$ - $Co$ - $Co$ - $Co$ - $CO$ - $CO$ - $Co$ - $Co$ - $#X=Ø \#L-6\implies 12e^−$ - $OC-Cr-co$ - $Co$ - $Cr(0) \longrightarrow Gr. 6\implies 6e^−$ - $CO$ - $CO$ - $18e- $ - $Charge \implies 72^− $ - $X: 4= 4e^−$ - $Pd^2+: 8e^−$ - $Pd: 10=10e^−$ - $4x: 8e^−$ - $2: 2 \implies 2e^- \implies 16e^−$ - $16e^−$ - $Ph_3P$ - $Cl$ - $Cl$ - $PPh_3$ - $Cl$ - $Cl$ - $PPh_3$ - $PPh_3$ - - $Cl$ - $Cl$ - $PPh_3$ - $...PPh_3$ # Jan 22nd 2025 - **Midterm in SC 115** “you should hit them for me” -Keske about People who insit there is only one way of doing things - Ionic: - Ligands = $5 \implies 10e^−$ - $Ru^{2+}: d^6 \implies 6e^−$ - $16e^−$ - Covalent: - $X: 2 = 2e^−$ - $L: 3 = 6e^−$ - $Ru: d^8 = 8e^−$ - $16e^−$ - $Ru^{2+}: 6e^−$ - $[Ru(p-(ym) Cl_4]2 \implies 6lig: 12e^− \implies 18e^−$ # Special Ligands for Counting. - $CI$ - $...$ - $CI$ - $ Ru $ - $CI-Ru$ - $CI$ - $ ...$ - $CI$ - - $x-type$ - $L-type$ - $↓CI$ - $Ru$ - $CI-Ru$ - $L-type$ - $x-type$ - - **Bridging ($M_2$) Cl : X-type to Ru, and L-type to Ru₂** - **Ambiden fake ($η^3$) p-(ym) 3L-type donor** - **Bridging ligands often form by necessity to fill metal orbitals** - eg - ↳ the metal will take what it can get - not picky - $CI.$ - $CI$ - $Co$ - - $R=R$ - $R$ - $R$ - $R$ - $R$ - $R$ - $R$ - $CI$ - $CI$ - $CI$ - $R=R$ - $CI $ - $[Rh(1)2Cl]_2$ - $R$ - $R$ - $H$ - $R=R$ - $H$ - $R$ - $H$ - $R$ - $14e$ - $Rh-CI$ - $H$ - $CI$ - $OC$ $Rh-CI$ - $CI$ - $OC$ - $Rh(CO)_2CI]_2$ - $OC-Rh-cl$ - $OC$ - $CI-RH$ - $CI$ - $Rh-CI$ - $H$ - $CI$ - $H$ - $CI$ - $H$ - $Hydrides EtsP-Ir-H-Ir-Pets$ - $H$ - $H$ - $Ir$ - $H$ - $Et_3P- H-Ir- PEt_3$ is rather similar to: - $H$ - $H$ - $H$ - $Ir-H$ - $H$ - $H$ - $H$ - $H$ - $H$ - $H$ - $H$ - $H$ - - **These are examples of 3 center 2-e bonds** - Little steric hinderance => effective e- sharing. - **$Ph_3P$ $OC$ $H$ $Rh$ $Rh$ $H$ $Co$ $-PPh_3$ would be 16e on each Rh via hydride bridging** - **Electrons can be counted by the ionic or covalent method** - **Bridging occurs to fill metal orbitals when needed (halides, OH, CO)** - **L-bridge to count covalently** - Lsbridges are X to one M and L to the other - Lsbest to count covalently - $PPh_3$ - $CI$ - $Pd(II): 8e^−$ - $4 lig: 8e^−$ - $Cl$ - $Pd-Cl$ - $Ph_2P-C-Cl$ - $8 + 10 = 18e^−$ - $Pd(II)$ wants to be $16e^−$ So reactive? - **Jan 24th 2025** # Hapticity (n^n) - no spaghetti - The number of contiguous conjugated atoms of a ligand which are bound to a metal. - **Allyl ($η^3$):** - $M - M^−$ - $M^−$ - $M^−$ - $M$ - $M = M$ - $ η^3$ X - $η^1$ X - $η^2$ XL - - **Acetate ($η^2$):** - $M- Ο^−$ - $M-Ο^−$ - $M$ - $η^1$ X - $η^2$ XL $η^5$ XL - - **Cyclopentadienyl ($η^5$):** - $O-M$ - $η^1$ (XL) - $η^2$ (XL) - $η^3 (XL) $ - $ η^4 (XL) $ - $η^5 (XL) $ - **Carbonyl ligands (organic):** $η^1$ - **Chelating (κ)** - **not displaying hapticity** - $Ph_3P$ - $NI$ - $PPh_3$ - $CI$ - $CI$ - **spaghetti** - $M$ - $M$ - - $R $ - $R$ - $R$ - $M$ - $M$ - $R$ - $R$ - $R$ - $κ^2$-DPPE - To be treated no differently than $PR_3$ - **Chelation in general refers to ligand's which coordinate through more than one donor atom** - $H_2$ - $N/..$ - $N$ - $H_2$ - $...$ - $H_2N$ - $... NHA$ - - $κ^2$-N,N - $H_2$ - $N/..$ - $N$ - $N$ -  $H_2$ - $ H_2N$ - $... NHA$ - $N/..$ - $N$ - $H_2$ - $ H_2 $ - **Creates a 5 member ring.** - The term chelation comes from the Greek meaning 'claw' - **Denticity is a slightly different term, which refers literally to the ligand biting the metal** - **eg. bidentate** - $Bipyridine$ - $Tetramethyl$ - $ethylene diamane$ - $EDTA $ - **most commonly up to 4x2L** # Pincer Ligands - **Actually have a formal definition- but is commonly misused** - **Hapticity:** how many conjugated atoms are contributing to dative bond. - **Chelation:** ligands who coordinate through many (not conjugated) atoms - **Pincer ligand:** 2L, X ligands that coordinate in one plane. - **Formally these are 2LX ligands which coordinate in one-plane** - $PR_3$ - $PR_2$ - $P(+Bu)_2POCOP$ - $R_2N$ - $Ir-N≡N$ - $M$ - $M$ - $M$ - $O-P(+Bu)_2$ - $O-P(+Bu)_2$ - **Metal-Metal Bonding** - **When required, metals will form bonds to other metals.** - However, this is relatively rare - The number of M-M bonds is typically determined from the assumption that metals will have 18e - $\#M-M=(18\times M-N)/2 \implies$ M= #metals, N=#valenae - $eg$ - $[Co_2(CO)_8]$ (NB. not $[Co(CO)_4]_2$ because the lowest common denominator has 2 metals - $M-M=(18\times2-34)/2=1 bond$ - $CO$ - $Co$ - $Co$ - $OC-Co-Co$ - $Co$ - $Co$ - $CO$ - $CO$ - - **Metals can form M-M bonds, #determined by assuming each M will have 18e** - **#MM=(18•M-valence e total)/2** # LIgands ## Carbonyls as Ligands - $CO$ - $CO$ - $CO$ - $CO$ - $CO$ - $CO$ - $CO$ - $CO$ - - **Carbonyl = CO** - aka the silent killer - **Carbonyl Bonding:** - 2 main synergistic effects - 1) σ- donation: from HOMO of Co to an empty orbital on M of correct symmetry - Ligand makes metal more e- rich - 2) πL-back donation: from filled orbital