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J. G. Rudick CHE 322: Organic Chemistry IIA Spring 2017 Lecture 15 (2/24/17) Electron Counting for Transition-Metal Complexes Chapter 18 in Loudon, M.; Parise, J. Organic Chemistry, 6th Ed. W. H. Freeman: New York, NY, 2016 Prof. Jon Rudick Office Hours: CHEM 775 Mondays 1:30–2:30p Tuesdays 1:30–2:30p Thursdays 2:30p–3:30p 1 J. G. Rudick Transition-Metal Complexes 2 Spring 2017 J. G. Rudick Transition-Metal Complexes Spring 2017 The 18-electron rule: transition metals like to have 18 valence electrons The valence orbitals of transition metals include one s-orbital, five d-orbitals, and three p-orbitals that can hold up to 18 electrons Ti: [Ar] 4s2 3d2 Cr: [Ar] 3d5 4s1 Mo: [Kr] 5s1 4d5 Fe: [Ar] 4s2 3d6 Ru: [Kr] 5s1 4d7 Ni: [Ar] 4s2 3d8 Pd: [Kr] 4d10 The 18-electron rule is analogous to the “octet rule” for main group elements 3 J. G. Rudick L L halides hydride acetate cyanide alkyl vinyl aryl Transition-Metal Complexes X-Type Ligands L L L M L L L L M X L Cl–, Br–, I–, F– H– O + Spring 2017 X (can be a bidentate ligand that doneate 4e– and –1q) R O NC– R 3C – R Ar – These ligands donate 2e– and a negative charge (–1q) 4 J. G. Rudick Transition-Metal Complexes Spring 2017 L-Type Ligands L L L L M L ML5 + L L amines :NR3 (R = H, alkyl) carbon monoxide :C≡O: (usually through carbon) phosphines :PR3 (R = H, alkyl, aryl) water (aquo) H2O: (bonds through 1 lone pair) acetonitrile H3C–C≡N: Neutral (0q) ligands that donate 2e– 5 J. G. Rudick Transition-Metal Complexes Spring 2017 Some ligands use electrons in π-orbitals to bind metals Alkenes donate 2e– and no charge (0q): L-Type Ligand L L ML5 + L M L L Benzenes donate 6e– (or 4e– or 2e–) and no charge (0q) L3-Type ligand M L L L Cyclopentadienyl anion (Cp) donates 6e– and –1 charge (–1q) M L 6 L L L2X-Type ligand J. G. Rudick Transition-Metal Complexes Spring 2017 Nickel tetracarbonyl: Ni(CO)4 O Ni O O O Ni: [Ar] 4s2 3d8 Ni(0) has 10 valence electrons C O each CO donates the lone pair (2e–) from C Counting all of the electrons involved in bonds to Ni (8e–) and the non-bonding electrons on Ni (10e–) we conclude that Ni(CO)4 is an 18-electron complex 7 J. G. Rudick Clicker Question #1 Spring 2017 (Pre-lecture Quiz Question) CO CO OC Cr CO OC CO Cr: [Ar] 3d5 4s1 Cr(0) has 6 valence electrons each CO donates the lone pair (2e–) from C C O What is the total electron count on the metal in Cr(CO)6 (i.e., chromium hexacarbonyl)? A. 6 B. 12 C. 16 D. 18 8 J. G. Rudick PPh3 Pd Ph3P PPh3 PPh3 Clicker Question #2 Pd: [Kr] P 4d10 Ph Ph Ph Spring 2017 Pd(0) has 10 valence electrons each PR3 donates the lone pair (2e–) from P What is the total electron count on the metal in Pd(PPh3)4 (i.e., palladium tetrakis(triphenylphosphine)? A. 6 B. 12 C. 16 D. 18 9 J. G. Rudick Transition-Metal Complexes Spring 2017 Palladium tetrakis(triphenylphosphine): Pd(PPh3)4 PPh3 Pd Ph3P PPh3 PPh3 Pd: [Kr] P 4d10 Ph Ph Ph Pd(0) has 10 valence electrons each PR3 donates the lone pair (2e–) from P Counting all of the electrons involved in bonds to Pd (8e–) and the non-bonding electrons on Pd (10e–) we conclude that Pd(PPh3)4 is an 18-electron complex 10 J. G. Rudick Transition-Metal Complexes Spring 2017 Cis-platin: Pt(NH3)2Cl2 Cl Cl NH3 Pt NH3 For the complex to be neutral (i.e., 0 charge), the metal must be Pt(II) (i.e., Pt2+) H N H H L-type ligand (2e–, 0q) X-type ligand (2e–, –1q) Cl Pt(II) has (10 – 2 =) 8 valence electrons Counting all of the electrons involved in bonds to Pt (8e–) and the non-bonding electrons on Pt(II) (8e–) we conclude that cis-platin is an 16-electron complex 11 J. G. Rudick Clicker Question Spring 2017 (Pre-lecture Quiz Question) #3 What is the oxidation state of the metal in PdCl2(PPh3)2? Cl Ph3P Pd PPh3 Cl A. –2 B. 0 C. +2 D. +4 #4 Palladium(II) has how many valence electrons? (What is the dn count for Pd in the complex?) A. 8 B. 10 C. 16 D. 18 #5 What is the total electron count on the metal in PdCl2(PPh3)2? A. 8 B. 14 C. 16 D. 18 12 J. G. Rudick Transition-Metal Complexes Spring 2017 Dichlorobis(triphenylphosphine)palladium(II): PdCl2(PPh3)2 Ph P L-type ligand (2e–, 0q) Ph Ph Cl Ph3P Pd PPh3 Cl Cl X-type ligand (2e–, –1q) Pd2+ has (10 – 2 =) 8 valence electrons For the complex to be neutral (i.e., 0 charge), the metal must be Pd(II) (i.e., Pd2+) Counting all of the electrons involved in bonds to Pd (8e–) and the non-bonding electrons on Pd(II) (8e–) we conclude that PdCl2(PPh3)2 is a 16-electron complex 13 J. G. Rudick Clicker Question #6 What is the oxidation state of the metal in [Rh(CO)2I2]–? CO I Rh CO I Spring 2017 A. –2 B. –1 C. +1 D. +2 #7 Rhodium(I) has how many valence electrons? (What A. 7 is the dn count for Rh in the complex?) B. 8 C. 9 D. 10 #8 What is the total electron count on the metal in [Rh(CO)2I2]–? 14 A. 15 B. 16 C. 17 D. 18 J. G. Rudick Transition-Metal Complexes Spring 2017 [Rh(CO)2I2]– This is an anionic complex CO I Rh CO I C O I L-type ligand (2e–, 0q) X-type ligand (2e–, –1q) Rh1+ has (9 – 1 =) 8 valence electrons For the complex to be anionic (i.e., –1 charge), the metal must be Rh(I) (i.e., Rh1+) Counting all of the electrons involved in bonds to Rh (8e–) and the non-bonding electrons on Rh(I) (8e–) we conclude that [Rh(CO)2I2]– is a 16-electron complex 15 J. G. Rudick Clicker Question Spring 2017 #9 What is the oxidation state of the metal in Cl2Ru(=CHPh)(PCy3)2? PCy3 Cl Ru Cl Ph PCy3 #10 Ruthenium(IV) has how many valence electrons? (What is the dn count for Ru in the complex?) A. +4 B. +2 C. –2 D. –4 #11 What is the total electron count on the metal in Cl2Ru(=CHPh)(PCy3)2? A. 18 B. 16 C. 14 D. 12 16 A. 0 B. 4 C. 8 D. 12 J. G. Rudick Transition-Metal Complexes Spring 2017 Grubbs 1st-Generation Catalyst: Cl2Ru(=CHPh)(PCy3)2 (J. Am. Chem. Soc. 1996, 118, 100–110) PCy3 Cl Ru Cl Ph PCy3 CHR X2-type ligand (4e–, –2q) PCy3 L-type ligand (2e–, 0q) Cl X-type ligand (2e–, –1q) Ru4+ has (8 – 4 =) 4 valence electrons For the complex to be neutral (i.e., 0 charge), the metal must be Ru(IV) (i.e., Ru4+) Counting all of the electrons involved in bonds to Ru (12e–) and the non-bonding electrons on Ru(IV) (4e–) we conclude that Cl2Ru(=CHPh)(PCy3)2 is a 16-electron complex 17 J. G. Rudick Clicker Question Spring 2017 #12 What is the oxidation state of the metal in ZrCp2HCl A. –4 (a.k.a., Schwartz’s reagent)? B. –2 C. +2 D. +4 Zr H Cl #13 Zirconium(IV) has how many valence electrons? (What is the dn count for Zr in the complex?) A. 0 B. 1 C. 2 D. 4 #14 What is the total electron count on the metal in ZrCp2HCl (a.k.a., Schwartz’s reagent)? A. 12 B. 14 C. 16 D. 18 18 J. G. Rudick Transition-Metal Complexes Spring 2017 Schwartz’s Reagent: ZpCp2HCl (Chem. Commun. 1969, 1105; J. Am. Chem. Soc. 1974, 96, 8115–8116) L2X-type ligand (6e–, –1q) Zr H Cl Cl , H X-type ligand (2e–, –1q) Zr4+ has (4 – 4 =) 0 valence electrons For the complex to be neutral (i.e., 0 charge), the metal must be Zr(IV) (i.e., Zr4+) Counting all of the electrons involved in bonds to Zr (8e–) and the non-bonding electrons on Zr(IV) (0e–) we conclude that ZrCp2HCl is a 16-electron complex 19 J. G. Rudick Clicker Question Spring 2017 Pre-lecture Quiz Question #15 What is the oxidation state of the metal in NiCl2(PPh3)2? Cl Ph3P Ni PPh3 Cl A. –2 B. 0 C. +2 D. +4 #16 Nickel(II) has how many valence electrons? (What is the dn count for Ni in the complex?) A. 8 B. 10 C. 16 D. 18 #17 What is the total electron count on the metal in NiCl2(PPh3)2? A. 8 B. 10 C. 16 D. 18 20 J. G. Rudick Transition-Metal Complexes Spring 2017 Dichlorobis(triphenylphosphine)nickel(II): NiCl2(PPh3)2 Cl Ph3P Ni PPh3 Cl PPh3 L-type ligand (2e–, 0q) Cl X-type ligand (2e–, –1q) Ni2+ has (10 – 2 =) 8 valence electrons For the complex to be neutral (i.e., 0 charge), the metal must be Ni(II) (i.e., Ni2+) Counting all of the electrons involved in bonds to Ni (8e–) and the non-bonding electrons on Ni(II) (8e–) we conclude that NiCl2(PPh3)2 is a 16-electron complex 21