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Micro Lab Quiz 1 > organometallics test > Flashcards

organometallics test Flashcards

1
Q

what are catalysts

A

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

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2
Q

TON

A

turnover number
cat productivity
mol prod/mol cat

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3
Q

TOF

A

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

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4
Q

catalyst loading

A

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

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5
Q

active catalyst

A

collectively, the intermed’s involved in the cycle

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6
Q

catalyst resting state

A

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

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7
Q

catalysts lifetime

A

how many turnovers before decomposition

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8
Q

define chemoselectivity

A

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

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9
Q

define regioselectivity

A

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

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10
Q

define stereoselectivity

A

does one stereoisomer form preferentially
(E/Z)

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11
Q

what does catalysis rely on

A

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

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12
Q

what is fav for OA

A

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)

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13
Q

what happens for non-polar reagents (OA)

A

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

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14
Q

what happens for polar reagents (OA)

A

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)

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15
Q

what happens for medium poalr reagents (OA)

A

concerted
3c ts
cant do sn2
cis

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

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16
Q

what is fav for RE

A

1.e poor complexes

2.steric hind

3.high OS

  1. anc lig that can stab reduced state of M after lig loss
  2. HH, CH bonds = fastes (easy for H to approach for orb overlap req’d at TS)
  3. 1 row>2>3 (ML bond strength increases down triad; larger M allow L to move to optimize orb overlap)
  4. odd geom
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17
Q

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

A

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

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18
Q

what happens in sigma bond metathesis

A

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)

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19
Q

draw TS for sigma metathesis and sigma cam

A

see notes

20
Q

what is concerted metal deprotonation

A

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

21
Q

draw TS and example of CMD

A

see notes

22
Q

draw put Pd cycle

A

see notes

23
Q

what happens after an insertion rxn

A

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

24
Q

what happens w d-insertion/elim rxns?

A

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

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

25
Q

what is 1,1-insertion

A

insertion of lig’s bound by single atom

DB remains

26
Q

what is 1,2-insertion

A

attached at DB, then turns into long stretch single bond

27
Q

CO migratory insertion

A

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

28
Q

popular example of 1,2-insertion

insertion of alkene/alkyne into M-H bonds

A

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

29
Q

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

A

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

30
Q

what characterizes hydroformylation

A

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

31
Q

what are issues w hydroformylation

A

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)

32
Q

Draw Co cat cycle

A

see notes

33
Q

why add PR3 to cat cycle (Hydroformylation)

A

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

  1. increase rate of hydrog of aldehydes and alkenes

get 8:1 ratio (improved regiosel)

34
Q

why switch to Rh in hydroformylation

A

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
35
Q

draw Rh cycle

A

see notes

36
Q

metathesis

A

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

37
Q

metallation

A

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

38
Q

how to swap out L for X

A

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

39
Q

to swap L for L

A

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

40
Q

example of strong pi D

A

halides

41
Q

example of strong pi A

A

CN, CO

42
Q

what is CO

A

strong sig D and pi A

43
Q

what is PR3

A

good sig D, can act as pi A

44
Q

what is NHC

A

strong sigma D

45
Q

eta-2 H2

A

sigma D and/or pi A

Micro Lab Quiz 1 (3 decks)

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