A. Organometallic Mechanisms Oxidation State: The oxidation state of a metal is defined as the charge left on the metal after all ligands have been removed in their natural, closed-shell configuration. This is a formalism and not a physical property! d-Electron Configuration: position in the periodic table minus oxidation state. 18-Electron Rule: In mononuclear, diamagnetic complexes, the total number of electrons never exceeds 18 (noble gas configuration). The total number of electrons is equal to the sum of d-electrons plus those contributed by the ligands. 18 electrons = coordinatively saturated < 18 electrons = coordinatively unsaturated. Organometallic Mechanisms Oxidation State: The oxidation state of a metal is defined as the charge left on the metal after all ligands have been removed in their natural, closed-shell configuration. This is a formalism and not a physical property! d-Electron Configuration: position in the periodic table minus oxidation state. 18-Electron Rule: In mononuclear, diamagnetic complexes, the total number of electrons never exceeds 18 (noble gas configuration). The total number of electrons is equal to the sum of d-electrons plus those contributed by the ligands. 18 electrons = coordinatively saturated < 18 electrons = coordinatively unsaturated. Cl for each Pd: Ox. state Pd Pd , Cl Cl bridging by lone Pd(II) pairs on Cl; d: 10 (4d10 5s0) - 2 = 8 each Cl acts as a 2-electron, mono electron count: negative ligands to one of the Pd's, - and a 2-electron : 4e neutral donor ligand like PPh to the other 3 - Cl : 2e - Cl : 2e 8e- + d8 = 16e- unsaturated Ox. State: 2 Cp-, 1 H-, 1 Cl- H → Zr(IV) Zr Cl d: 4 (4d25s2) - 4 = 0 electron count: 2 Cp-: 12 H- : 2 Cl- : 2 Zr : 0 16 e-, unsaturated Bonding considerations donation: M or vacant σ dsp hybrid π backdonation: M filled d orbital π∗ for M-CO: M C O σ−donor dspn acceptor Structure • saturated (18 e-) complexes: - tetracoordinate: Ni(CO)4, Pd(PPh3)4 are tetrahedral - pentacoordinate: Fe(CO)5 is trigonal bipyramidal - hexacoordinate: Cr(CO)6 is octahedral z y • unsaturated complexes have high dx2-y2; 16e- prefers square planar x Basic reaction mechanisms - ligand substitution: M-L + Lʼ → M-Lʼ + L can be associative, dissociative, or radical chain. L M X + - + - + - trans-effect: kinetic effect of a ligand on the role of substitution at the position trans to itself in a square or octahedral complex (ground-state weakening of bond). L → M, repels negative charge to trans-position. Nu Lc Lc X Nu Lc X L Pt Pt + Nu- Pt t Lt Lc X Lt Lc Lc L Nu Lc Nu c - Pt Pt + X L L Lt Lc t c X - oxidative addition: Br -L -L Ph [Ph3P]4Pd [Ph3P]3Pd [Ph3P]2Pd 16 e- 14 e- strong σ-donor (+II) Br Br L2Pd L2Pd H H Ph Ph 16 e- 16 e- agostic (2e-/3-center bond) interactions - reductive elimination: the major way in which transition metals are used to form C,C- and C,H-bonds! Ph P Me -L Ph P Me Me PPh3 3 3 Pd Pd Pd Ph P-Pd Ph P 3 Ph3P 3 - 14e- 12e Ph cis! Ph ? Ph +L Ph - migratory insertion: Cp O Cp Cp CO C Zr Cp Zr Cp R Zr Cp R R Cl Cl Cl O 16e- 18e- - 16e .