Metal Carbonyl Chemistry · PDF fileMetal Carbonyl Chemistry Here we will be talking about,...
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Metal Carbonyl Chemistry Here we will be talking about, generally, homoleptic ("all CO") complexes of first row transition metals. Discussions about hydroformylation and other carbonylation chemistry will be later. The chemistry of these metal carbonyls is possible because CO is an excellent π-acceptor, and can stablize metals with a low oxidation state and high electron density. The commercial complexes are generally stable, but are coordinatively saturated and must loose a CO ligand in order to participate. The high affinity of metals for CO means that high temps or photolytic conditions must be used. Cr(CO) 6 Mn 2 (CO) 10 Fe(CO) 5 Co 2 (CO) 8 Ni(CO) 4 precursors d 6 d 7 d 8 d 9 d 10 hν, Δ Cr(CO) 5 Fe(CO) 4 Ni(CO) 3 hν, Δ labile active species Fe 2 (CO) 9 d 8 Fe(CO) 4 Δ Many of the reactions associated with these complexes are stoichiometric. This is due to the preference of the early transition metals to be in higher oxidation states. As a result the chemistry of Fe has dominated (Fe(CO) 5 $~200/kg)
Transcript of Metal Carbonyl Chemistry · PDF fileMetal Carbonyl Chemistry Here we will be talking about,...
Metal Carbonyl Chemistry
Here we will be talking about, generally, homoleptic ("all CO") complexes of first row transition metals. Discussions about hydroformylation and other carbonylation chemistry will be later.
The chemistry of these metal carbonyls is possible because CO is an excellent π-acceptor, and can stablize metals with a low oxidation state and high electron density.
The commercial complexes are generally stable, but are coordinatively saturated and must loose a CO ligand in order to participate. The high affinity of metals for CO means that high temps or photolytic conditions must be used.
Cr(CO)6 Mn2(CO)10 Fe(CO)5 Co2(CO)8 Ni(CO)4precursorsd6 d7 d8 d9 d10
hν, Δ
Cr(CO)5 Fe(CO)4 Ni(CO)3
hν, Δ labile
active species
Fe2(CO)9
d8
Fe(CO)4
Δ
Many of the reactions associated with these complexes are stoichiometric. This is due to the preference of the early transition metals to be in higher oxidation states. As a result the chemistry of Fe has dominated (Fe(CO)5 $~200/kg)
Metal Carbonyl Chemistry
M C O M C Oδ+ δ–e–
M(CO)strong
nucleophile
E
E M CO
insertion
E C MO
X M COR
R XR XO.A.
RCMO
X
M + RCXO
O.A.
R.E.
Overview of metal carbonyl chemistry. Some of these pathways will be discussed later.
Important for Pd, Rh
Nuc
NucCMO E
MNuc
OE
NucCMO
E
E NucCEO
M +R.E.
Iron(II) Oxallyl CationsElectrohilic 3-carbon subunits for [3+N] cycloadditions
O
BrBr
+ Fe(CO)4
OFe(CO)nBr Br
must have at least one a-substitutentto stabilize allyl cation, dibromoacetonedoes not react, tetrabromoacetone does
Fe(II) oxallyl cation
J. Am. Chem. Soc. 1971, 93, 1272J. Am. Chem. Soc. 1978, 100, 1791, 1799Acc. Chem. Res. 1979, 12, 61
OFe(CO)nBr
[3+4]
OY
Y
O
stepwise reaction to givemost stable cation
[3+2]Y = Ar, NR2
O – HNR2
Me
Reactions of Vinyl Epoxides With Fe(CO)4
+ Fe(CO)4
OR1
R2
R1
R2
a. O.A.
b. Nuc attack
η3-allyl "ferrolactone"(stable, isolable)
90+ atm COΔ O
R1
R2
via 7-memberedη1-allyl ferrolactone
O
O
R2 β-lactone
γ-lactone
CANChem. Rev. 1996, 96, 423 preferred, but can depenend on substrate
O
R1
OO
Fe(CO)3
via 5-memberedη1-allyl ferrolactone
The η3-allyl ferrolactone can be present in multiple stereoisomers, but they can be separated by chromatography and carried forward to give diastereomerically pure lactones.
(R)(R)
(R)(R)(S)(S)
MeO
Et
Me
Fe2(CO)9
(R)(R) (S)(S)
O(OC)3Fe
O
Et
MeMe
(R)(R)
O(OC)3Fe
O
HH
(S)(S)
MeEt
exo cis endo cis
+dr 1:1
74% yield
Reactions of Vinyl Epoxides With Fe(CO)4
The η3-allyl ferrolactones are stable to a wide range of reaction conditions (H2O, Me3SiCN, MnO2, CuCl2, FeCl3, t-BuOOH, amine oxides, CrO3, PCC, PDC, O3, Swern, dilute acide, Et3N, cat. H2, Wittig, Tebbe, SmI2, Lewis acids). Reaction sequences can therefore be accomplished, before decomplexation. The ferrolactone is a large group that can influence stereoselective reactions.
Lactams and ketones are also possible:
R1 OO
Fe(CO)3
1. NH2Bn ZnCl2•TMEDA
2. CAN NO Bn
R1
R1
R2
Fe(CO)5hν OR1
R2
R.E. happens spontaneously
OC FeR1
COCO
CO
Collman's Regent – Na2Fe(CO)4
Disodium tetracarbonylferrate – d10, Fe(–ΙΙ) – highly nucleophilic
Fe(CO)5
Nabenzophenone
dioxane, 100 ºCNa2Fe(CO)4
Acc. Chem. Res. 1975, 8, 342
Na2Fe(CO)4R1 X
OC Fe
LCO
COCO or PR3
R1 O
Na2Fe(CO)4R1COCl
R1
OR2
I R2
R1 OH
O
O2
R1 X
O
X2
H+
R1 H
ODisplacement with Na2Fe(CO)4proceeds with inversion, and COinsertion proceeds with retention.The acyl iron complex can also bethe subject of migratory insertionreactions with olefins.
Semmelhack, Organometallics in Synthesis, Schlosser, Ed., 2002, pp 1006–1012.
