answers to exercises references abbreviations index atomic weights of the elements periodic table

74 Pages·2007·3.41 MB·English

ANSWERS TO EXERCISES
REFERENCES
ABBREVIATIONS
INDEX
ATOMIC WEIGHTS OF THE ELEMENTS
PERIODIC TABLE OF THE ELEMENTS
A
NSWERS TO EXERCISES
CHAPTER 1
1.1. [FeCp ]+, sandwich structure with parallel rings, [FeL X ]+, 17, 5, 3, 6;
2 4 2
[RhCl(PPh ) ], square planar, [RhL X], 16, 8, 1, 4;
3 3 3
[Ta(CH CMe ) (CHCMe )], tetrahedral, [TaX ], 10, 0, 5, 4;
2 3 3 3 5
[ScCp* (CH )], bent sandwich with CH in the equatorial plane, [ScL X ], 14, 0, 3, 7;
2 3 3 4 3
[HfCp Cl ], bent sandwich with both Cl ligands in the equatorial plane, [HfL X ],
2 2 4 4
16, 0, 4, 8;
[W(H)(CO) ]–, octahedral, [WL X]–, 18, 6, 0, 6;
5 5
[Os(NH ) ((cid:1)2-C H )]2+, octahedral, [OsL ]2+, 18, 6, 2, 6;
3 5 6 6 6
[Ir(CO)(PPh ) (Cl)], square planar, [IrL X], 16, 8, 1, 4;
3 2 3
[ReCp(O) ], pseudo-octahedral, [ReL X ], 18, 0, 7, 6;
3 2 7
[PtCl ]2–, square planar, [PtX ]2–, 16, 8, 2, 4;
4 4
[PtCl (C H )]–, square planar, [PtLX ]–, 16, 8, 2, 4;
3 2 4 3
[CoCp ], sandwich structure with parallel rings, [CoL X ], 19, 7, 2, 6;
2 4 2
[Fe((cid:1)6-C Me ) ], sandwich structure with parallel rings, [FeL ], 20, 8, 0, 6;
6 6 2 6
[AuCl(PPh )], linear, [AuLX], 14, 10, 1, 2;
3
[Fe((cid:1)4-C H )(CO) ], trigonal bipyramid (piano stool), [FeL ], 18, 8, 0, 5;
8 8 3 5
[Ru(NH ) ((cid:1)1-C H N)]2+, octahedral, [RuL ]2+, 18, 6, 2, 6;
3 5 5 5 6
[Re(CO) ((cid:1)2-phen)]+, octahedral, [(ReL ]+, 18, 6, 1, 6;
4 6
[FeCp*(CO)(PPh )(CH )]+, pseudo-octahedral (piano stool), [(FeL X ]+, 18, 6, 4, 6;
3 2 4 3
[Ru(bpy) ]2+, pseudo-octahedral, [RuL ]2+, 18, 6, 2, 6.
3 6
1.2. In the form [FeCp*((cid:1)2-dtc) ], both dithiocarbamate ligands are chelated to iron,
2
[FeL X ], 19, 5, 3, 7. In the form [FeCp*((cid:1)2-dtc)((cid:1)1-dtc)], one of the two dithio-
4 3
carbamate ligands is chelated to iron whereas the other is monodentate, [FeL X ],
3 3
17, 5, 3, 6. The two forms having respectively 19 and 17(cid:1)electrons are both to some
extent destabilized, being both one electron away (in excess and shortage
respectively) with respect to the robust 18-electron structure. The main reaction of
19-electron complexes in the absence of other substrate is to partially decoordinate
giving a 17-electron complex, and this reaction is very fast. The main reaction of
17-electron complexes in the presence of a ligand(cid:1)L (in the absence of reducing
agent) is also very fast, addition giving the 19-electron complex. Thus, the
536 OGANOMETALLIC CHEMISTRY AND CATALYSIS
dissociation of 19-electron complexes and re-association of the 17-electron complex
formed with the dissociated ligand make a rapid equilibrium between these two
species that only ends up by the reaction of either form, if any.
1.3. It is known that O can coordinate to a transition metal in a side-on mode (as
2
ethylene does), which is the case in this complex, or end-on (with an angle) as in
hemoglobin and myoglobin. In the case of the side-on coordination, the ligand is an
L(cid:1)ligand if the metal is electron poor, the length of the double O=O bond being
relatively little changed by the coordination. If, on the other hand, the metal center
has a high electron density, as inthis case, the O (cid:1)ligand undergoes an oxidative
2
addition leading to the lengthening of the O-O bond that can, at the limit, reach the
length of a single O-O bond. The metal-O species should then be formally
2
described as an IrIII metallocycle, the O (cid:1)ligand now being a peroxo X (cid:1)ligand in the
2 2
Ir-O triangle structure.
2
1.4. [CoCp ]+: organometallic 18-electron, thus stable complex.
2
[CoCp ]–: 20-electron organometallic sandwich complex (triplet state, having two
2
unpaired electrons with the same spin) isoelectronic to nickelocene (a commercial
compound). The stabilities of these two complexes are weakened by the double
occupancy of the doubly degenerate antibonding orbital (two orbitals having the
same energy are occupied by two electrons). The orbital energy level is not too
high, however, in spite of its antibonding character, which allows the isolation and
crystallization of these two reactive complexes.
[V(CO) ]+: the addition of two disadvantages, a coordination number larger than 6
7
and the cationic nature of a binary metal carbonyl leads to the non-inexistence of
this complex in spite of its 18-electron structure.
[Cr(H O) ]: non-existent as all the binary water complexes in which the metal has a
2 6
low oxidation state such as (0).
[Ni(H O) ]2+: relatively stable 20-electrons complex as [CoCp ]–, vide supra, and in
2 6 2
addition because of the ideal coordination number (6) and oxidation state (II).
[ReH ]2–: stable 18-electron complex in spite of its very high coordination number,
9
because hydrides, the only ligands present in the coordination sphere, are very
small.
[Zr(CH Ph) ]: in principle an 8-electron complex that is thermodynamically stable
2 4
but kinetically very reactive with many substrates. The stability, in spite of the very
low NVE, is due partly to the absence of (cid:2) H, and partly to the (cid:1)(cid:1)interactions
between the phenyl rings and the metal decreasing the Zr-C-Ph angle below 109°
(the value of the NVE(cid:1)=(cid:1)8, only is conventional and does not take this (cid:1)(cid:1)interactions
into account).
[Zr(CH Ph) (CO) ]: does not exist as almost all the mono- and bimetallic metal-car-
2 4 2
bonyl structures in which the metals do not have non-bonding electrons (NNBE(cid:1)=(cid:1)0)
(the M-CO bond needs (cid:1) backbonding from some filled metal d(cid:1)orbitals). There are
only exceptions in lanthanide chemistry in which the metal-CO bond is very weak
(R. Anderson’s work).
ANSWERS TO EXERCISES 537
[Cr(CO) ]2–: stable 18-electron complex as all the binary mono- or polyelectronic
5
metal-carbonyl 18-electron complexes in which the metal is at the 0, –1 or –2 oxida-
tion state.
[Cu(Cl)(PPh )]: stable; Cu, Ag and Au commonly gives complexes having the MLX
3
14-electron structure;
[Ir(CO) (PPh )(Cl)], [Pt(PPh ) ]: 16-electron complexes of noble metals of groups
2 3 3 3
9 and 10 respectively, very stable as usually the group 8-10 noble metal 16-electron
complexes are if the oxidation state is also adequate.
[ScCp* (CH )]: stable (but reactive) 14-electron complex (classic structure also
2 3
with the lanthanides, these complexes being initiators of olefin polymerization)
[NbCp (CH ) ]: stable (but reactive) 18-electron organometallic complex.
2 3 3
[FeCp*(dtc) ]+: stable 18-electron complex in spite of its odd coordination number
2
(7), because the high oxidation state (IV) is ideal in a mixed inorganic-
organometallic complex with dominant inorganic components.
1.5. The optimal stability of this type of complex corresponds to a NVE(cid:1)=(cid:1)18, the
number of electrons provided by the ambivalent, versatile ligand Ph C is 4 for two
2 2
of them and 2 for the 3rd one.
1.6. The order of decreasing thermal stability of these metallocenes is dictated by the
18-electron rule (NEV): [FeCp ] (18e)(cid:1)>(cid:1)[MnCp ] (17e) and [CoCp ]
2 2 2
(19e)(cid:1)>(cid:1)[CrCp ] (16e) and [NiCp ] (20e)(cid:1)>(cid:1)[VCp ] (15e)(cid:1)>(cid:1)[TiCp ] (14e).
2 2 2 2
1.7. The splitting of these 5(cid:1)d(cid:1)orbitals into 3(cid:1)degenerate bonding levels (of identical
energy) t and 2(cid:1)degenerate antibonding e levels is represented page(cid:1)40.
2g g
Manganese has 5(cid:1)d(cid:1)electrons, one in each orbital (the semi-filling of these 5(cid:1)orbitals
stabilizes this electronic structure). The total spin(cid:1)S is 5/2 (high-spin structure,
multiplicity 2S(cid:1)+(cid:1)1: sextuplet state). μ (cid:1)=(cid:1)[5(cid:1)(5(cid:1)+(cid:1)2)]1/2(cid:1)=(cid:1)5.916(cid:1)μ . With Cp*, the
theor. B
5(cid:1)electron-releasing methyl substituents strengthen the ligand field, forcing the
electrons to pair in a low-spin state S(cid:1)=(cid:1)1/2 (doublet state: μ (cid:1)=(cid:1)[1(cid:1)(1(cid:1)+(cid:1)2)]1/2
theor.
=(cid:1)1.732(cid:1)μ ).
B
1.8. The electronic density on manganese increases as the (cid:1) acceptor character of the
ligands decreases: CO(cid:1)<(cid:1)CS(cid:1)<(cid:1)C H (cid:1)<(cid:1)THF(cid:1)<(cid:1)PPh . Detection by infrared spectros-
2 4 3
copy or cyclic voltammetry: the absorption frequency of the carbonyls and the oxi-
dation potential of the complex decrease as the electronic density increases. It is the
complex [MnCp(CO) L], L(cid:1)=(cid:1)CO, that is the most difficult to oxidize in this series.
2
1.9. Bent sandwich complex, the two carbonyls being in the equatorial plane. The two
rings are connected by a dimethylene bridge that hinders the free rotation. One of
the Cp’s is pentahapto, whereas the other Cp has to be trihapto in order to obey the
18-electron rule.
538 OGANOMETALLIC CHEMISTRY AND CATALYSIS
CHAPTER 2
2.1.
O CO
OC
C CO CO
Fe Fe Cr Cr
OC C OC
O CO
OC
CH Ph
2
CO CO
OC S CO
W W Rh Rh
OC S CO Ph3P CO
OC Ph P
CO OC 3
CH Ph
2
[FeCp(CO)(μ-CO)] : [FeL X ], 18, 6, 6; [CrCp(CO) ] : [CrL X ], 18, 4, 7;
2 4 2 3 2 5 2
[W(CO) (μ -SCH Ph)] : [WL X ], 18, 4, 7;
4 2 2 2 5 2
{[Rh(CO)(PPh )] ((cid:2)5,(cid:2)5,μ -fulvalenyl)}: [RhL X], 18, 8, 5.
3 2 2 4
2.2. 2, 3, 2.
2.3. [Re H (CO) ]: NEC(cid:1)=(cid:1)56 (localized count: counting, to simplify, H as bridging
4 4 12
1(cid:1)electron; 17 on each Re, i.e. 68 for 4 Re, minus 12 for the 6 Re-Re bonds of the
Re tetrahedron);
4
{Fe [C(CO) ]}2–: NEC(cid:1)=(cid:1)86. For the localized count, one can attribute 3 CO’s for
6 16
each of the 4 equatorial Fe’s and 2 for the 2 apical Fe’s that are formally bridged by
the C(cid:1)ligand that is doubly bonded to each of the two Fe’s. This gives 18 for each
Fe, but the 2(cid:1)electrons of the negative charges make too many for a localized count
with 18(cid:1)electrons per Fe. This count gives (6(cid:1)(cid:1)(cid:1)18)(cid:1)+(cid:1)2(cid:1)=(cid:1)110 less the 24 of the 12
formal Fe-Fe bonds of the octahedron.
[NiCp]6: NEC(cid:1)=(cid:1)90. For the localized count, one has 6(cid:1)(cid:1)(cid:1)NiL2X5, i.e. 6(cid:1)(cid:1)(cid:1)19(cid:1)=(cid:1)114
less the 24 of the 12 formal Ni-Ni bonds of the Ni octahedron.
6
In conclusion, the determination of the localized NVE on each metal does not work
for any of these three diamagnetic clusters (otherwise, one would have found
NEV(cid:1)=(cid:1)18).
2.4. [Re H (CO) ]: each ReCp(H) species brings an electronic doublet to the cluster, as
4 4 12
Fe(CO) or BH also does. The analogous borane would be B H , which does not fit
3 4 4
Wade’s rule.
{Fe [C(CO) ]}2–: if the central(cid:1)C is assimilated to a doubly bonded allenic carbon
6 16
to each of the two apical Fe’s, this ligand is assimilated to 2(cid:1)CO ligands, and the
cluster is equivalent to [Fe(CO) ] 2– or B H 2– that follows Wade’s rule (closo
3 6 6 6
cluster with 6(cid:1)summits, octahedral).
ANSWERS TO EXERCISES 539
[NiCp] : each NiCp is equivalent to BH– bringing 3(cid:2)electrons to the cluster that is
6
thus equivalent to B H 6–. It is an arachno cluster with n(cid:2)=(cid:2)1/2(cid:2)(6(cid:2)+(cid:2)6(cid:2)+(cid:2)6)(cid:2)–(cid:2)3(cid:2)=(cid:2)6
6 6
summits.
2.5. The number of atoms of each layer being 10(cid:2)n2(cid:2)+(cid:2)2, the numbers of atoms of the
clusters containing 1, 2, 3, 4, 5, 6 and 7 layers are 13, 55, 147, 309, 561, 923 and
1415, respectively.
2.6. a. 6x – 14 = –2 (cid:2) x = 2;
b. (6 (cid:1) 24) + 2 = 26;
c. NEC = 26 + (14 (cid:1) 2) = 54.
CHAPTER 3
3.1. a. The reaction is endergonic (thermodynamically unfavorable): (cid:1)Go(cid:2)~(cid:2)0.1(cid:2)V
(2.3(cid:2)kcal(cid:2)·(cid:2)mol–1 or ~(cid:2)10(cid:2)kJ(cid:2)·(cid:2)mol–1);
b. The reaction is exergonic (favorable): (cid:1)Go(cid:2)~(cid:2)–(cid:2)1.8(cid:2)V
(~ –(cid:2)41(cid:2)kcal(cid:2)·(cid:2)mol–1 or ~ –(cid:2)173(cid:2)kJ(cid:2)·(cid:2)mol–1).
3.2. a. The reaction is impossible: (cid:1)Go(cid:2)=(cid:2)2(cid:2)V(cid:2)~(cid:2)46(cid:2)kcal(cid:2)·(cid:2)mol–1(cid:2)~(cid:2)190(cid:2)kJ(cid:2)·(cid:2)mol–1;
b. The photo-oxidation is favorable:
(cid:1)Go(cid:2)=(cid:2)–(cid:2)0.13(cid:2)V(cid:2)~(cid:2)–(cid:2)3(cid:2)kcal(cid:2)·(cid:2)mol–1(cid:2)~(cid:2)–(cid:2)12.5(cid:2)kJ(cid:2)·(cid:2)mol–1.
3.3. The protonation of the iron-hydride complex [FeIICp(PMe ) (H)] leads to the H
3 2 2
complex [FeIICp(PMe ) (H )]+, because the iron atom in the starting complex is
3 2 2
relatively electron poor, and the oxidation state FeII is much more favorable than
FeIV. On the other hand, the protonation of the osmium complex leads to the
protonation of OsII that is an electron-rich metal center, i.e. the oxidative addition
occurs to yield the dihydride [OsIVCp(PMe ) (H) ]+, the oxidation state OsIV being
3 2 2
much more common than FeIV.
3.4. This is the (cid:3)-bond metathesis reaction in [LuCp* CH ]; this reaction leads to the
2 3
deuteration of the methyl group bonded to lutecium.
CHAPTER 4
4.1. 1) benzene; 2) cyclohexadienyl on an external coordinated C leading to
cyclohexadiene.
4.2. Ph COH and the metal-carbene complex [FeCp(dppe)(CHCH )]+.
3 3
4.3. No, because ethylferrocene is itself very reactive towards EtCl(cid:2)+(cid:2)AlCl . It is
3
necessary to acetylate ferrocene, then to reduce the ketone by the Clemensen
method, i.e. using Zn/HCl.
540 OGANOMETALLIC CHEMISTRY AND CATALYSIS
CHAPTER 5
5.1. A 21-electron intermediate or transition state would be of much too high energy,
whereas the partial decoordination to the 17-electron species is almost barrierless.
5.2. The only selective method consists in carrying out an electrocatalytic ligand substi-
tution reaction. It is necessary to use a reducing initiator, for example the electron-
reservoir complex [FeICp(C Me )] in catalytic amount.
6 6
5.3. Electrocatalytic reaction with an oxidant such as ferrocenium as an initiator in
catalytic amount.
CHAPTER 6
6.1. a. [FeCp(CO(FcPPh )(COCH )];
2 3
b. add a catalytic amount of a reducing agent.
6.2. [ZrCp (Cl)] )(μ -C H )].
2 2 2 5 8
6.3. The phenyl complexes decompose by (cid:2)-elimination and the accessible complexes
with the other aryl ligands are stable.
6.4. [TaMe ] and [Ta(CH Ph) ] are relatively stable (thermally) because of the absence
5 2 5
of (cid:2)(cid:1)H. [Ta(CH CMe ) ] cannot be synthesized because of the steric bulk favoring
2 3 5
(cid:1)-elimination to Me C and [Ta(CH CMe ) (=CHCMe )] (see section(cid:1)5).
4 2 3 3 3
6.5. Methane is produced by (cid:1)-elimination (see section(cid:1)5) and ethane is formed by
reductive elimination of two CH ligands (see section(cid:1)3).
3
CHAPTER 7
7.1. The molecule contains both terminal and bridging carbonyl ligands (note that
these ligands are not rigidly coordinated to the metal, however; they interconvert
more slowly than the infrared time scale of 10–13(cid:1)s, the molecule being fluxional):
[FeCp(CO)(μ2-CO)] . This phenomenon is very common in polynuclear binary
2
metal carbonyls.
7.2. [FeCp(μ -CO)] .
1 2
7.3. Fluxional molecule; the carbonyl ligands rapidly “jump” from one metal to the
other via a bridging situation (μ2-CO).
7.4. [(FeCp) (μ -CO) ].
2 2 3
7.5. [FeCp(μ3-CO)] ; NEV = 18; NEC = 60.
4
ANSWERS TO EXERCISES 541
CHAPTER 8
8.1. [MoCp(CO) (CH CH )] and [MoCp (CH CH CH ) ] (NEV(cid:1)=(cid:1)18); Cr(CH Ph)
3 2 3 2 2 2 3 2 2 6
(NEV(cid:1)=(cid:1)12, no (cid:2)(cid:1)H) and [Nb(CH ) ] (NEV(cid:1)=(cid:1)10, no (cid:2)(cid:1)H are stable (moderately
3 5
for the latter); [Zr(CH CH Ph) ] (NEV(cid:1)=(cid:1)8); [Re(CH CH ) ] (NEV(cid:1)=(cid:1)12);
2 2 4 2 3 5
[TiCp (CH CH ) ] (NEV(cid:1)=(cid:1)16) and [TaPh ] (NEV(cid:1)=(cid:1)10) are unstable and
2 2 3 2 5
decompose by (cid:2)-elimination, because they have both less than 18(cid:1)valence electrons
on the metal and one H(cid:1)atom on the (cid:2)(cid:1)C(cid:1)atom.
8.2. [CH M(CO) ] CH • + •Mn(CO)
3 5 3 5
8.3. The Re complex is more stable than that of Mn for two reasons. The first one is
that the electronic density in the M-alkyl bond is higher for Re than for Mn because
of the additional electronic layer when going from Mn to Re. The second reason
is that, Re being larger than Mn, the radical Re(CO) • is less sterically stabilized
5
than Mn(CO) •; thus, its formation requires more energy. The overall result is that
5
the Re-CH bond (52(cid:1)kcal(cid:1)·(cid:1)mol–1; 217(cid:1)kJ(cid:1)·(cid:1)mol–1) is stronger than the Mn-CH bond
3 3
(36(cid:1)kcal(cid:1)·(cid:1)mol–1; 150(cid:1)kJ(cid:1)·(cid:1)mol–1) in the complexes [CH M(CO) ] (M = Mn vs. Re).
3 5
8.4. [TiPh ] is very unstable because of the fast decomposition by (cid:2)-elimination that is
4
not possible with R(cid:1)=(cid:1)CH , CH Ph and OCH giving more or less stable complexes.
3 2 3
The order of stability is the following: CH (cid:1)<(cid:1)CH Ph(cid:1)< OCH (cid:1)<(cid:1)OPh. The complex
3 2 3
[Ti(CH ) ] is not very stable, because its NVE is very low (8). This low NVE is
3 4
compensated with R(cid:1)=(cid:1)Ph, CH Ph, OCH and OPh by an additional coordination
2 3
(attraction of the (cid:1)(cid:1)electrons of the aromatic ring for Ph, donation of the non-
bonding p(cid:1)doublet of the oxygen atom to the metal for the ligands(cid:1)OR). With OCH
3
there is the possibility of (cid:2)-elimination upon heating, but not with OPh.
8.5. The geometry around the oxygen atom in the alkoxy ligand shows a more open
angle than around the carbon atom of an alkyl ligand. This is all the more true as the
donation of one or even two oxygen p(cid:1)doublets to the metal increases the angle of
the M-O-C chain that becomes sometimes linear in the case of the donation of two
oxygen p(cid:1)doublets (bulky alkoxy). The (cid:2)(cid:1)H atoms are thus further from the metal in
an alkoxy ligand than in an alkyl ligand, and thus less easily subjected to
(cid:2)-elimination than in the alkyl ligands. Thus for instance, the complex
[TaCp*(C H ) ] very rapidly decomposes at low temperature by (cid:2)-elimination,
2 5 4
whereas [TaCp*(OMe) ] is stable at ambient temperature.
4
8.6. The equilibrium is displaced from the preferred H complex towards the dihydride
2
complex upon going down the periodic table. Indeed, the metal becomes more
electron rich upon adding electronic layers, thus more able to electronically support
two M-H bonds (oxidative addition of H ).
2
CHAPTER 9
9.1. [FeCp*(PPh3)(CO)(CH2)]+ + PMe3 [FeCp*(PPh3)(CO)(CH2PMe3)]+
[TaCp (Me)(CH )] + AlMe [TaCp (Me)+(CH AlMe )–]
2 2 3 2 2 3
542 OGANOMETALLIC CHEMISTRY AND CATALYSIS
9.2. The first complex is almost a primary carbocation, thus a very powerful and very
reactive electrophile, whereas the electron-releasing effects of the five methyl
substituents on the Cp(cid:1)ligand and the increase of electronic density resulting from
the replacement of CO by PPh decrease the positive charge on the carbenic carbon
3
in the second complex compared to that in the first one.
9.3. These reactions are of the same type, the Schrock carbene being eventually
considered as an ylid:
Me C=O + PMe CH Me C=CH + Me P=O
2 3 2 2 2 3
Me C=O + [TaCp (Me)(CH )] Me C=CH + 1/x [(-TaCp (CH )(O-)x]
2 2 2 2 2 2 3
9.4. [(MnCp(CO) ) (μ -CH )].
2 2 2 2
9.5. The three oxides are isoelectronic, but CrO 2– and MnO – are more stable than
4 4
FeO , because the FeVIII is rendered very electron poor by the very electronegative
4
oxygen atoms in the third complex due to the absence of negative charge. One
notices that the number of charges in going from CrO 2– to FeO goes along with a
4 4
shortening of the bonds (the double bond character increases).
9.6. We know that double oxidative addition of an alkene to a metal to produce a metal-
bis-carbene or triple oxidative addition of an alkyne to produce a metal-bis-carbyne
complex is not possible. Olefin insertion into a metal-hydride giving a metal-alkyl,
however, can be followed by (cid:1)-elimination to yield a hydrido-metal-carbene or
even further double (cid:1)-elimination can give a hydrido-metal-carbyne. Such a case is
known: the reaction of styrene or phenylacetylene with [Os(H)Cl L ] (L(cid:1)=(cid:1)Pi-Pr )
2 2 3
yields the carbyne complex [OsHCl (CCH Ph)L ] via the metal-carbene inter-
2 2 2
mediate. PhEt is also formed as a result of hydride consumption (K.G.(cid:1)Caulton,
J.(cid:1)Organomet. Chem. 2001, 617-618, 56).
9.7. Thermolysis of [Cp Zr(NHAr) ] generates ArNH and the catalyst [Cp Zr=NAr]
2 2 2 2
that reacts with the alkyne to provide the azazirconacyclobutene. Addition of
ArNH yields the bis-amino-Zr intermediate resulting from (cid:2)-bond methathesis,
2
then reductive elimination gives the hydroamination product and the catalyst
(R.G.(cid:1)Bergman et al., J.(cid:1)Am. Chem. Soc. 1992, 114, 1708; A.L. Odon et al., J.(cid:1)Am.
Chem. Soc. 2004, 126, 1794).
CHAPTER 10
10.1. In the first two cases, the positive charge or the electron-withdrawing ligands
decreases the electron density on the metal, favoring the true olefin complex. In the
3rd case, the electron-releasing character of the ligands and the electron-rich metal
(3rd row, located on the right of the periodic table) provoke the oxidative addition to
the platinacyclopropane complex. In the 4th example, the ancillary electron-
releasing ligand and the very electron poor olefin (four fluorine substituents) favor
the oxidative addition to the nickelacyclopropane.
ANSWERS TO EXERCISES 543
10.2. a. [WCp(CO) ] + [Cp Fe]+PF – + C H
3 2 2 6 2 4
b. [WCp(CO) Cl] + AgBF + C H
3 4 2 4
10.3. Syn (Me at the outside) and anti (Me inside).
10.4. The reaction starts by the substitution of two CO(cid:1)ligands by the diene to give
[Fe(CO) ((cid:1)4-diene)], then continues by the substitution of a 3rd CO(cid:1)ligand and the
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intramolecular oxidative addition of the endo C-H bond leading to [FeCp(CO) H]. It
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ends by the dimerization with formation of the Fe-Fe bond and the loss of H . This
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last step is not mechanistically clear-cut, but it could be taken into account by par-
tial decoordination of the Cp(cid:1)ring (from (cid:1)5- to (cid:1)3-), coordination of the Fe-H bond
of another molecule on the vacant site and binuclear reductive elimination of H .
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10.5. The fragment Cr(CO) is not sufficiently activating to carry out this type of reaction.
3
On the other hand, with the isoelectronic fragment Mn(CO) +, the electron-
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withdrawing effect is considerably stronger because of the positive charge, which
makes the reaction possible in spite of the low availability of the nitrogen doublet
that is engaged in the conjugation with the aromatic ring.
CHAPTER 11
11.1.(cid:1)[FeCp ]+ is a 17-electron d5 FeIII complex: (a )1; S = 1/2; μ = 1.73 μ
2 1g theor B
(cid:1) [CoCp ]– is a 20-electron d8 CoI complex: (e* )2; S = 1; μ = 2.83 μ
2 1g theor B
(cid:1) [Co(C Me ) ]+ is 19-electron CoI d7 complex (e* )1; S = 1/2; μ = 1.73 μ
6 6 2 1g theor B
11.2. The variations of the numbers of electrons concern the d(cid:1)metal orbitals. The metal is
protected from the point of view of the reactivity by the cage of ligands, especially
when these ligands are permethylated. The metal orbitals being of higher energy
with the 2nd and 3rd row, the electron deficiencies and excesses then concern ligands
whose radical reactivity is high even when they are permethylated.
11.3. The decaisopropylmetallocenes of the first row of transition metals (Fe, Co+, etc.)
cannot exist because of the steric bulk (mutual hindrance of the two rings that are
too close to each other). On the other hand, the larger size of the elements of the 2nd
and 3rd row of transition metals than with that of the 1st row metals locates the two
Cp rings sufficiently remote from each other, and decaisopropylrhodocenium can be
synthesized from decamethylrhodocenium (PF – salts) by reaction of excess KOH
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and CH I.
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11.4. Ferrocene first reacts with CO (cid:1)+(cid:1)AlCl to undergo carboxylation of one ring. Then
2 3
AlCl complexes the free ring (the more electron-rich one), provoking the
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weakening of the Fe-Cp bond, then its cleavage and substitution by the arene ring.
The cation formed is insensitive towards electrophiles.
11.5. In the first case, the fulvene form is more stable due to the coordination of the exo-
cyclic double bond, because the iron center reaches NVE(cid:1)=(cid:1)18 in this way, whereas,
in the second example, the p(cid:1)orbital of the exocyclic carbon and the d(cid:1)orbitals of iron
push each other away (the metal orbitals are all filled, the metal having NVE(cid:1)=(cid:1)18).