organometallics test

Question 1

what are catalysts

Answer 1

increase rr and not consumed in rxn

series of elementary steps that provide an alt path w a lower free E of activation for the RDS (usu have small barriers)

these series of steps: assoc of cat/sub, bond making/breaking, diss of cat/prod

Question 2

TON

Answer 2

turnover number
cat productivity
mol prod/mol cat

Question 3

TOF

Answer 3

turnover frequency
cat activity
mol prod/(mol cat x time)

Question 4

catalyst loading

Answer 4

the [] in mol% or ppm
mol of precat used/mol of lim reag

Question 5

active catalyst

Answer 5

collectively, the intermed’s involved in the cycle

Question 6

catalyst resting state

Answer 6

species present in the largest [] during catalysis (on or off cycle)

Question 7

catalysts lifetime

Answer 7

how many turnovers before decomposition

Question 8

define chemoselectivity

Answer 8

to which a variety of functional grps will a rxn occur?

Question 9

define regioselectivity

Answer 9

to which end of the alkene does addition of COH occur
(branched/linear)

Question 10

define stereoselectivity

Answer 10

does one stereoisomer form preferentially
(E/Z)

Question 11

what does catalysis rely on

Answer 11

rxns bringing subs into M’s coord sphere, cause their transformation into prods, and allow prods to leave M’s coord sphere

Question 12

what is fav for OA

Answer 12

1.e rich M (have less to lose if ox’d)

2.late TM

3.low OS

4.strong sigma-D ancil lig (NHC)

5.pi-D

6.less ster hind complexes (bc CN increased)

Question 13

what happens for non-polar reagents (OA)

Answer 13

concerted addition
via 3c ts or intermed’s
first form sigma complex then do oxidative part (fully cleave A-B)
get only cis

req open coord site and 16e or less
usu preceeded w L-diss or RE from coord sat complexes

ex) H2, alkane, silane

Question 14

what happens for polar reagents (OA)

Answer 14

stepwise (like SN2)
M acts as nu towards R+; then cat complex = E+ for X- to go to empty site
get only trans

ex) alkyl halides, pseudohalides (OTs or OMes)
—-alkyl halide reactivity: Me>1>2>3
—–I>Br>Cl>F

poss w anionic M complexes (get neu intermed)

Question 15

what happens for medium poalr reagents (OA)

Answer 15

concerted
3c ts
cant do sn2
cis

ex) CX, HX, ArX, sulfonates
ex) aniline (ArNH2), thiols (SH), OH, 1/2 phospines

Question 16

what is fav for RE

Answer 16

1.e poor complexes

2.steric hind

3.high OS

4. anc lig that can stab reduced state of M after lig loss
5. HH, CH bonds = fastes (easy for H to approach for orb overlap req’d at TS)
6. 1 row>2>3 (ML bond strength increases down triad; larger M allow L to move to optimize orb overlap)
7. odd geom

Question 17

why does RE fav odd geom’s? (draw orbs)

Answer 17

refer to notes

basically: for even , still have AB char in prod (higher E, more unstable)

for odd, have non bonding char in prod which is lower E bc orbs not sitting directly on axis

Question 18

what happens in sigma bond metathesis

Answer 18

no change in OS (key! even if looks like OA/RE)

concerted
4c ts

for d0 complexes, MC bond = very polar
—-see this for early TM
—-see this for Si, B, N, P
—–cant do OA/RE

poss for dn (usu in late M in high OS; RhIII)

Question 19

draw TS for sigma metathesis and sigma cam

Answer 19

see notes

Question 20

what is concerted metal deprotonation

Answer 20

CMD

addition of aromatic CH bond to a TM usu containing a carboxylic ligand

concerted
may look like OA/RE

may or may not change OS

TM usu acts as cat (Pd) to join 2 Ar

Question 21

draw TS and example of CMD

Answer 21

see notes

Question 22

draw put Pd cycle

Answer 22

see notes

Question 23

what happens after an insertion rxn

Answer 23

pair of X and L make 1 X lig

3/4e to 1/2 e

get vacant coord site

no change in M OS

req cis arrangement of participating lig

can come from external sources

Question 24

what happens w d-insertion/elim rxns?

Answer 24

opp of insertion
gen cis arrangement of X and L lig
concerted

ex) LnM-N=N-Ar -> LnM-Ar + N2

Question 25

what is 1,1-insertion

Answer 25

insertion of lig's bound by single atom DB remains

Question 26

what is 1,2-insertion

Answer 26

attached at DB, then turns into long stretch single bond

Question 27

CO migratory insertion

Answer 27

what: CO is inserted into MR or MAr bond to get M-acyl complexes how: the new CO comes in, the Me migrates and joins w CO already in complex that is cis to it (intramolecular) proof: d-insertion/elim rxns show that the Me migrates (not the CO); get 2:1 ration of cis of label and Me key notes: no trans prod or rearrangment of 5 coord intermed (t/f under kinetic control) variations: 1. incoming L trap reagent ----PR3, THF, CH3CN 2. X grps have tend for mig insertion -----R= alkyl>aryl>acyl>H -----X =alkoxo, amido, silyl

Question 28

popular example of 1,2-insertion insertion of alkene/alkyne into M-H bonds

Answer 28

key step in M-cat'd olefin polymerization LnM-R + CH2=CH2 -> LnM-Ch2-CH2-R usu for early TM/e def M usu fav cat complexes (over neu bc more e def) M-C insertion = therm fav rel to M-H if have HMLn v CH3MLn; pref one w H bc less bulky/easier to get to TS

Question 29

variations of 1,2-ins w alkene/kyne into MH bonds

Answer 29

L: ketones, imines insert into MH aldehydes, imines insert in MC x: alkenes insert into MN, MO, MB, MSi or rev rxn: B elim for alkoxo. amido lig

Question 30

what characterizes hydroformylation

Answer 30

used for long chain alkene substrates HCo(CO) forms at high temp and pp of H2 ----high press of CO(g) prevents formation of inactive u-CO Co clusters ----can now be seen for shorter chains

Question 31

what are issues w hydroformylation

Answer 31

chemosel - cat=high act for alkene hydrogentaion -----solution: PCO is increased rel to PH2 to supress this but affects all setps w vac coordn sites that add CO instead of H2 regio - 4:1 lin:branched (low)\ cat volitility (easily lost) cat sep (air and acid added to destroy cat and pull into aq layer)

Question 32

Draw Co cat cycle

Answer 32

see notes

Question 33

why add PR3 to cat cycle (Hydroformylation)

Answer 33

it means higher MW and its strongly donating 1.volatility of cat decreases 2. strengthens Co-CO bonds, lowers CO press ----PR3 = e D helps CO strengthen interaction ----good P->M D ability, allowing more M-CO backbonding 3. increase rate of hydrog of aldehydes and alkenes get 8:1 ratio (improved regiosel)

Question 34

why switch to Rh in hydroformylation

Answer 34

also add more PPh3 ---want sweet spot of amnt: H(Rh)(CO)(PPh3)3//16e 1. higher act, selectivity, stability under milder conditions 2. keeps good [] of active species and addresses the slow decomp of PPh3 overtime

Question 35

draw Rh cycle

Answer 35

see notes

Question 36

metathesis

Answer 36

M-X form salt no OS change use polar reagent w R- source install X

Question 37

metallation

Answer 37

M-alkyl, M-amido w CH acid form weaker acid no OS change install X

Question 38

how to swap out L for X

Answer 38

1) deprot of coord'd L ligand 2) nu addition to a coord'd L

Question 39

to swap L for L

Answer 39

1) lig sub 2) metal-reduction-ligation (reduce M-salt in presence of L)

Question 40

example of strong pi D

Answer 40

halides

Question 41

example of strong pi A

Answer 41

CN, CO

Question 42

what is CO

Answer 42

strong sig D and pi A

Question 43

what is PR3

Answer 43

good sig D, can act as pi A

Question 44

what is NHC

Answer 44

strong sigma D

Question 45

eta-2 H2

Answer 45

sigma D and/or pi A