organo final (unit 3) Flashcards
what is the process for carbonylation of methanol to make acetic acid
CH3OH + CO -> CH3COOH
use cat (grp 9/10 w I)
how do you make methanol
CO/H2 + het-cat
how do u make CO
CH4 + 1/2O2
List the three cats used in carbonylation
BASF - Co, I-
Monsanto - Rh, I-
Catvia - Ir, I-
as you move down, better activity and selectivity
draw out the Monsanto cycle (include names of steps, co cats, precat, TLS, complexes, and imp notes)
see notes
TLs - OA (polar, stepwise)
Rh anion makes good nu and suscept to E+ addition of Me+
what is TLS for catvia process and why/not
not OA of MeI bc much faster for Ir
-form stronger bonds to 3rd row tm
-higher nu of 3rd row tm
-pref for 3rd row tm for high os
mig insertion of CO
-formation of stronger bonds to 3rd row tm bw Ir-Me
–the E barrier changes for the M-L ligand to act as a nu to Carbonyl C
what can be done to speed up TLS for catvia process
add promoter (Ru dimer); accel negated by I- and Ru accepts I- and gives neu fac-tricarbonyl complex
-neu increases how sus co is to nu attack
-xtra co compete
these 2 things make co more E+ t/f increase rate of nu attack (intra)
–both make lead to less backbonding from M, t/f CO lig becomes more E+
see notes for process and dimer
what is the process for catalytic hydrogenation
alkene + H2 -> alkane w syn H’s
use cat
what are the cats used in hydrogenation
wilk - RhCl(PPh3)3
[Rh(dppe)(solv)2]+
[Ir(COD)(py)(PCy3)]+PF6 (crabtree)
all do H first
have labile lig’s
draw hydrogen first mech (inner or outer?)
inner
see notes
2 vac coord sites, oa H2, lig assoc, 1,2 ins (TLS), RE
draw olefin first mech (inner or outer)
inner
see notes
cats: Ru(H)Cl(PPh3)3
Cp2LaH
M-L and -H, lig sub (alkene for L), 1,2 ins and lig assoc 9L), oa H2, RE
OA and RE = hydrogenolysis
draw the cycle for hydrog of ketones(list steps, ts, imp notes)
see notes
outer
H first(attach to M and L in 4Cts)
then lig assoc of ketone (get ts w H’s)
-this ts is prochiral (if reduce it, it will become chiral)(has enentiotopic face)
(which 1 binds dets enant formed)
then dissoc?
draw cycle for hydrog of ketones using OH, not H2
see notes
outer
lig assoc of alc, then ts w it’s H’s
ketone leaves then re-assoc’s
leave w same alc SM but now enriched
overall process of hydrosilation
alkene + H-SiR3 -> alkane w h and SiR3 syn
use cat
HSiR3 = reducing agent like H2; NP and bulky
what is used in hydrosilation and what do they rely on
Pt, Rh, lanthenides
which all rely on activation of Si-H bond by M and 1,2 ins step
-use anti-mark addition - Si on least hindered end of alkene
draw the two mechs of hydrosilation for Pt and Rh
see notes
Pt: mig ins of olef into MH
Rh: mig ins of olef into SiR3
like chalk harrod
draw mech of hydrosilation for lanthanides
see notes
usu d0 t/f do sig-bond-met
start w precat (Cp2Y-Ch(TMS)2)
add H3SiR (4cts)
left w Cp2Y-H (act cat)
do lig assoc of alkene and 1,2 ins
add H3SiR (get 4cts)
spits out RH2Si -alkane
what does asymmetric mean
aka stereoselective
a rxn that yields increased amnts of 1 stereoiosomer rel to other poss’s
-rxns that reduce db’s can gen enantiomer’s when unsat’d sub is prochiral, if reduction occurs stereospecifically
what does a prochiral olefin have
enantiotopic faces
-2 enant’s form when bind to M, dep on which face approaches the M
-if Mln = achir=get enant complexes
-if Mln = enant pure L=get diast
what are some key aspects of asym hydrog of alkenes w Rh(I) cations
alkene 1st
subs may have D grp that can bind to Rh to help ensure alkene anchored to bind to correct place
act cat = [Rh(solv)2(diphos)]+
chirophos = used to make an alpha aa deriv; has c2 sym
chiral and chelating phos’s used to make hydrog enantiosel
draw cycle for asym hyd of alkenes w Rh(I) cations
see notes
cat precursor (w COD; add 2H2 + 2S to get rid of octane)
lig assoc
OA H2
lig assoc and ins
lig sub
which product gets formed when using [(chirophos)]Rh]+
more stable and abundant interm gives minor prod enant
-poss bc fast interconversion bw diast’s
explain the curtin-hammett principle
when competing rxn paths start from rapidly interconverting isomers, the product ratio is det’d by rel deltaGTSsymbol (ie rates/rate constants/barriers) leading from isomers to products
have plot E x rxn coord
in middle can interconvert bc small barrier when alkene approaches
-facile and fast eq
can go L or R but OS of H2 is going to be lower E for one of the ways which will be fav’d
–less stable isomer reacts faster t/f leads to major product (lower E barrier)
what is overall rxn for pd cross coupling
alkene - X (w sp2C) + R-M+ -> alkene - R + MX
-for CC bond formation
-subs = aryl, vinyl, pseudohalide which act as cat nu (R)
-main grp (M) = Mg, Zn, Sn, B, Si
pd = usu cat
draw the cycle used for suzuki-miyaura, stille, hyiyama, negishi, kumada
suz- B
stil-Sn (tin)
hiy - Si
neg - Zn
Kum-Mg
see notes
get to reduced Pd 0, then lose L to get 1-2 L in act cat
ArX OA
Transmetallation
RE Ar-nu
draw cycle for mizoroki-heck
use when other’s arent present
see notes (2 cycles)
Ar-X + alkene -> Ar -alkene + HXbase
use Pd cat and base
Ar grp ends up on least sub’d
same as other mech’s but do 1,2 ins, then Bh elim and RE of baseHX
xtra notes ab suzuki-miyaura
B(OH)2
also use base
-hard like OH or F which is needed to facilitate cross coupling
i)4 coord anion [ArB(OH)3]- may transfer Ar gpr faster than ArB(OH)2
ii) OH- replaces Pd-X, so Pd-OH participates more easily in transmet.
rel rates of OA: arI>arbr>arcl and artf>Arots
what is the overall process for olefin metathesis
2 alkene (2R1 and 2R2) -> 2 alkenes (allR1 and all R2)
use cat (usu alkylidenes like schrock carbenes- M=CR2)
-can use grubbs which still have schrock aspect but also bulky lig and/or strong sigma donor’s like PCy3 or NHC’s
–5 coord sq pyram
lose ethylene = DF
what transformations are possible w olefin met
RCM, ROM, cross met (two alkenes merged to 1), acyclic diene metath
mech of olefin met
see notes
metal d-orbs in M=C bonds allows transformation of 2+2cycloadd (usu forbidden for C=C bonds)
start w alkylidene, lig assoc of alkene and 2+2 cycladd, 2+2 cycloadd and lig dissoc, repeat for second alkene
synthesis of schrock carbene
alpha - elim from dialkyl precursor
see notes
Justify why OA is not RDS when using Ir in hydrogenation
- Ir is larger than Rh and less charge dense t/f better nu for E+ Me t/f increases RDS
- 3rd row TM create stronger M-L bonds
-stronger bond being form lowers TS E (thermo feat) - TM’s in higher OS are more common for heavier TM’s (comp’d to lighter)
-rationalized by charge-density argument (higher charge spread over larger radius)
what are examples of additives in Pd cross coupling
bases (K2CO3)
M-halides (CuCN)
what makes an alkene more susceptible to nu attack
EWG (like H or CN or COOR)
how to make organo borane
2 methods (see notes)
