Organometallic Chemistry

Transcription

1 rganometallic hemistry igands in rganometallic hemistry 2 Electron Donors 4 Electron Donor 6 Electron Donors ferrocene chromium hexacarbonyl H H halide ions dicarbonyldiiodorhodium(1+) Zeise s salt P 3, phosphines cyclopentadienide ion 16 & 18 Valence Electron ule. A. Tolman, hem. Soc. ev., 1972, 1, 337 Diamagnetic organometallic compounds of the transition metals may exist in significant concentration at moderate temperatures only if the metal s valence shell contains 16 or 18 valence electrons. 16 & 18 Valence Electron ule. A. Tolman, hem. Soc. ev., 1972, 1, 337 rganometallic reactions, including catalytic ones, proceed by elementrary steps involving only intermediates with 16 or 18 metal valence electrons. 16 & 18 Valence Electron ule chromium hexacarbonyl r 0 = d 6 = 6 e- 6 = 6 x 2 e- = 12 e- Total = 18 valence electrons 18 valence electrons lead to maximum bonding. l bonding molecular orbitals are filled. Bonding in oordination ompounds onsider r(nh 3 ) 6 3+ r 3+ = 3 valence electrons 6 NH 3 ligands = 12 valence electrons TTA valence electrons = 15 rdinary coordination compounds do not generally have 18 (or 16) valence electrons. 1

2 Bonding in M omplexes igand to metal! bonding M Electron flow tal to ligand π bonding M electron flow Electron flow from filled M d orbitals into π antibonding ligand orbitals. This SYNEGY leads to stronger bonding than either sigma or pi bonding alone. M Stabilization by π Acceptor igands Screen 22.7 of hemnow D-M Bonding in tal arbonyls M- bonding illustrates why M compounds of trans metals always use low-valent metals (< +2) (usually 0 or +1). M ---> π* bonding leads to stabilization. ow valence state of M means effective nuclear charge of M is low, so M--> charge flow is possible. r() 6 White solid tal arbonyls () 5 olorless liquid Ni() 4 olorless liquid r,, and Ni have even number of d electrons tal arbonyls tal-lefin omplexes Pt 2+ has 8 valence e- 2e per - Zeise s salt 2e- donated by π electrons of ligand Mn 2 () 10 Yellow solid o 2 () 8 ed solid Mn and o have DD number of d electrons 2

3 tal-aromatic omplexes 6 π electrons of donated by 6 H 6 ligand tal-aromatic omplexes 6 π electrons of donated by 5 H 5 ligand r has 6 valence e- 2+ has 6 valence e- Dibenzenechromium rrocene rrocene hemistry H 3/ 3 H 3 16 & 18 Valence Electron ule. A. Tolman, hem. Soc. ev., 1972, 1, 337 xidation + Bui HH/HN2 i H2N2 p 2 undergoes electrophilic substitution much more rapidly than benzene. rganometallic reactions, including catalytic ones, proceed by elementrary steps involving only intermediates with 16 or 18 metal valence electrons. A hodium atalyst eactions & atalysis Ir()(PPh 3 ) 2 Total valence electrons? dicarbonyldiiodorhodium(1+) Vaska s compound 3

4 xidative Addition & eductive Elimination rganometallic hemistry Problem 12 xidative addition + H 3I Ir Ir+ 16 valence e- S4 I Ir - H 3I W W()6 Na,Hg W() 3 Na5 H5 W frequencies frequencies 1744 and 1894 cm and 2010 cm-1 eductive elimination Ir3+ 18 valence e- = PPh3, triphenylphosphine Infrared Spectroscopy of tal arbonyls Bands for stretch. Uncomplexed is at 2140 cm -1 Number of bands depends on symmetry. Frequency depends on other ligands. tal kyls and Aryls Grignard reagents X + Mg in ether -----> MgX Structure is more complex than MgX. rganomercury compounds Hg + 2 Na + 2 X ---> Hg Na ompounds like Hg(H 3)2 are EXTEMEY toxic rganolithium compounds 2 i (dispersion) + ---> li + i Usually done in pet. Ether, benzene, or cyclohexane i can be used to transfer groups to other compounds X3: X =, Br, I or 221 pm pm In liquid and gas phase 3 is dimer. Br3 and I 3 are dimers in all phases. eplace with alkyl or aryl groups ---> organoaluminum compounds (3)2 196 pm sp3 Terminal and bridging groups exchange positions rapidly at room temperature enter, 2-Electron Bond 123 2e- spread over 3 orbitals 215 pm 4

5 rganosilanes, 4 Si Si + H 3 over u catalyst at >200 Si 3 25% 3 Si 3 65% 3 Si 5% This is the origin of silicone polymers 2 Si 2 H 2 Si Si n 5