Download 1 - TAMU Chemistry

CHEM462
Inorganic/Organometallic Chemistry
Fall2016
Midterm Exam: Part I (20%)
Part II (take home, 15%)
October 25, 2016
Question
Points available
I
30
II
J£ 1~
III
$ &
IV
8
v
28
VI
33
VII
35
TOTAL
150
Name:
.:f9 ,
!<ey
Points r eceived
Consider the following two structures and answer the questions relating to them:
a) Label them according to the type of divalent carbon atom ligands: Fischer Carbene or
Schrock Alkylidene (place answers on blanks below)
b) Choose the correct label for each type of the divalent carbons:
neutral, 2-electron donor; anionic, 2-electron donor; dianionic, 4-electron donor;
neutral, 4-electron donor.
c) According to your assignment for the divalent carbon ligand, give the oxidation state
of the metal and the d-electron count in each case.
d) Which divalent carbon ligand is most likely to react with PhLi? What is the product?
e) Which divalent carbon ligand is most likely to have resulted from an a -H elimination?
f) Which complex is more likely to react with BX3 to yield a carbide?
I.
,.--...
4
a)
'1~V?JdL-
4
b)
4-e.,,_ M WOV,
Ll
c)
4-
d)
1.. e)
2 f)
h.sc~-tev
dtaA1l& ntc.
)
l'Y
f\.,
)
ct
2. - e- tJ..1;nH,> ruw{Y4
c._ 0
v
)
d.(:,
~
/p~
t::e. ~cv:::= c _ pz,
+{..,(()~
or. - .etcvn ,·Yl cJ,. <Y1
-
W3-d?> X @c)4--~v--.:=:c. -1-J.
JO g) Exchange of a CO by PMe3 in the
Cr(PhC(OCH 3))(C
lex is expected to
proceed by a 1ssociative r a~ciate)
mechanism an generate the ~ r trans)
isomer? At right, sketch the expected
reaction coordinate and the structures of the
transition state and anyinterm~iate.
r 1 OJ
_.I-? ~
.... _., ......
. ,()Vk(
--r- 7 (L-~··
w
I
ef\
0
I"/
S
'-Ph
rxn coord
--~
Page 1 of6
II.
Consider Kubas ' 11z-dihydrogen complex shown right.
A) Give the oxidation state and electron count about tungsten.
,,,1
o
W j
3 \.A../..S
2 ?tZ3
:::
=
<ee
@
12-e-
-
+e~
' V{2.-t~ :: ~
cL"
t
:z.. +'- -
B) Two types of rr-backbonding are in the tungsten complex, to CO
and to the 11z-Hz ligand. Give drawings to illustrate the orbital
overlap between W and CO and betw
nd Hz.
~~~£
C) Discuss the geometrical position of ligands in this complex. That is, which
orientation of the P(i-Pr)3 ligand, cis or trans to theW- 11z -Hz, should give the "better"
interaction? Explain your reasoning and why the solid state structure is the same or
different from your conclusion.
I
!l •
L_
X"
cr
b
(-{
-\r-ans fv VJ :>._~ ~ fl1c0~ ~ - t«:k pt)yl(:t.•O"tJ ru
01"\ 2ftD\,&Je\leY l.f.l ~ 1-v Vl_ ~- H ~uJd. pu..f- ~ fwo l~ lAtJ~
2
CA~ iZ> eadt () ~. ~+~tc p)DJo le~~· 6) 81'vr.clt.t1.q 1 11.~- t-f2 ~ u.--<~~s
()'--~tttz ·n.r:, ~ H- H <r'"" ~~ fzJ.. 1"1-tM wlaert~ W"1 fk Co f¥-~ -
D) The following li~ t of physical or spectroscopic techniques were used to
characterize the Kubas complex. Choose 3 and describe what could be or was
learned from the results: i) Infrared spectroscopy in diatomic (CO) ligand region. ii)
1
H NMR spectroscopy iii) 31 P NMR spectroscopy iv) X-ray diffraction v)
Neutron diffraction (use the back of the page for your descriptions).
j) Lte. ::-/ l1 (w); £,/ped- ? bCVM-ds ,
iV 'H NmR ~0 Ct1M--. :;ee
-:-r_
_1
,. . . ~" b -
2l
III.
z.) ~ p ~
)
,,
f P-$1
lf
~tot-
H t.i
C..O""fl t,
'
V\.
1'v) X,. Y24r- OVeAAll ~~
~ pos" 'hlMA d) J( ~
~'/.C..t..ILJ f- /-f •
v) ~ J~ -Hratlt tK~ _ c.cu....
_,
1-1 •
er
~em ~ee.--> lJl.rk t-1- D C-Ot-<-p/.·vu,
<"a... rf ti4 wal ·
Give the electron count for each Mn derivative in the following equation. Show how
you derived each overall count (by giving oxidation state of Mn and d-count) .
.6. or hv
(11 1-C_,H:;)Mn(CO):; --~ (11:~-C 3 H_,JMn(C0) 4
+ ci-
~ '-e;,
&J
Hi::- 2e-
+t ,...,. &:>e-
rtn
t;"CO
+CO
-I
~3-csHs=
M.,. +-t
4 CO
~
4e-
e:
8e
6
- tz~-
Page 2 of6
IV.
v
Attempts to prepare a Kubas-type dihydrogen complex with the iridium cx{mplex
shown below resulted in a 6-coordinate complex. A) Sketch the structule of the
product. B) Give the oxidation states and electron counts about Ir in both reactant f>:.
and product. C) Discuss why should this result be different fro~ the ;~h;tudy?2
_
I,y.J..,
,PPh3
Cl - lr~ co
+
Ph P/
_
3
"'oe- ~
2.. p~3 : -1- et
V.
~
co
~ .2. e
. -
-rl CJ. ::;
ze
(
H2
_
p~
3
r:r-.L :::'/'J..v-ree-d' ·~
",D -~ w1r" ~ J.tt6W
-
Select and circle the answers for the fol
with rationale given for your answer.)
rv
I-t-
~~
--+ C- 1 Y - H
p/l
2
=
l~ -=- 2 e2 p :=.4-e-
~ ff --;: ~ :
.J-r-
fp
tze-
;.y
A) The description/parameters that best fit the forward reaction that describes COIL
0
(L = PR3) exchange in the Ni L4 complex:
Ni 0 L4 +
CO
!:;
Ni 0 L3 (CO) +
L
i) Dissociative, large positive ~H*; large neg. ~S*; a 16-electron, 3-coordinate
intermediate.
ii) Associative, small ~H*; large neg. ~S*, 18-electron, 5-coordinate intermediate.
iii)Associative, large ~H*; large positive ~S*, 16-electron, 3-coordinate intermediate.
@ .issociative, large positive ~H*; large l?ositive ~S*, 16-electron, 3-coordinate
intermediate. 'S.onq b~(~ L'Yl :f: ~ I!
4 -a:Jov-1 ~~
:>
..... ~•
l{p - ~ ~~ ~ L t.Vl(J\L~St~
v
C,.()oy(;..\.) / '
e.
) .e-k. bophL.t
B) The experiment that will yield the ~G for the reaction above, i.e.,
I
C.-;
1
Ni 0 L4 +
CO
!:;
Ni 0 L3 (CO) +
L
i) Measure rates of forward reaction at different temperatures, determine rate
~~~nstants, plot ln k vs. 1/T.
~lVleasure equilibrium product/reactant ratio; calculate: ~G = - RT InK.
C)
The experiment that will yield ~G* for the reaction above.
~easure rates of forward reaction at different temperatures, determine rate
constants, plot ln k vs. 1/T.
ii) Measure equilibrium product/reactant ratio; calculate: ~G = - RT InK.
D)
The phosphine most likely to yield the largest value for Keg and ~G for the
reaction above:
effect?)
PMe3,
P(OEt)3,
6
(Is this a steric or electronic
st~v ~~tt {)/l ~ ~j~ -v--ef? t4W
lJr
Ccl
Page 3 of6
VI.
Short answer questions:
a) The species with highest v(CO) stretching frequency:
CO
~
or
or
Ni(C0) 4
b)
or
Ni(C0)3 PF3
c) The species with highest v(NO) stretching frequency:
NO
or
or
d) The species with longest N - 0 distance:
NO
or
or
e) The molecule with highest average v(CO):
2
Fe(C0)4 =; Fe(C0)4(YJ -CHz=CHz); Fe(C0)4(YJ 2 -CF2 =CF2);
or~
f) The orientation of ethylene in Fe(C0)4(YJ 2 -CH2 =CH2):
Cli)face on and parallel to the x/y plane;
ii) face on and perpendicular to the x/y plane;
iii) side on and parallel to the z axis; iv) side on and perpendicular to the z-axis.
(if you don't understand "face on" or "side on", ask.)
g) The MCO anion with fastest rate of reaction with Mel :
5
(YJ -CsHs)Fe(CO)z-
~
5
(YJ -CsHs)Cr(CO)J-
h) The metal carbonyl most likely to have a multiple metal-metal bond.
i) The molecule with greatest number of v(CO)IR absorption bands.
Mo(C0)6 ; trans-(Ph3 P):Mo(C0) 4 ; cis-(Me 3P)zMo(C0)4; trans-Mo(( diphos )z(CO)z.
j) The molecule with only one v(CO IR absorption band:
~
rans-(Ph3 P)Mo(CO ; cis-(Me3 P) 2Mo(C0)4; trans-Mo((diphos)z(CO)z.
k) The ligand least likely to be a pi-acceptor:
co
Page 4 of6
VII. The following diagrams are energy levels in the frontier molecular orbitals (FMO's)
of organometallic complexes. They correspond mainly to d-orbitals (or are largely of
d-orbital character).
A. Underneath each diagram above (i, ii, iii, iv), place geometry labels: Oh, Td, Sq.
Planar, metallocene
B. Assign the following molecules to the appropriate energy level diagrams, i - iv,
give oxidation state of the M and the number of d electrons. Assign metal d
electrons to the FMOs using the splitting diagrams above as guides:
0st~
RhCl(PPh3 ) 3
.
(j ~ oC'~ ~-L,
Cr(C0)6
(9h)dji)
Ni(C0)4
(It)(>{ 6"1i)
•
)
I(
---
t
I
/'
1-) ((:_-
l~ a1.JtJ v'e-
0 be~
7
iztj ~
(TJ -CsHs)zV
-1(0
t;
+
6;~~- e4
-+-2-J~e
5
(p
)
-
e;t~
1
·)
t- 2 3e- +(-.._;_Z~ _ _ _ _ _ _ }
e_:Lj
I
"')
-r'?--)
<;;'
oe
-
cl
"'2-
{)
u..,5
a,j
2._
{,.1
ellA..
0
ctu
"2...
J.. -z_ \.t~
c2..ex.~
-
:Jcr':J
----Page 5 of6
C. Consider the conversion of metallocene to a bent metallocene. Which d-arbital
labels goes on the highest FMO in the diagram at left (the e 1g *)and why is it seen
to split and lower (stabilized) in the diagram at right, i.e., as the bend occurs?
(Note: this question merely tests your understanding of Crystal Field splitting.)
-6
e,.,e': ~
Oz
-7
-;;
"'
~ /~'a,
~
-e
w
-9
o,.,o;
~ b2
-10
e2;,e~
- II
M
~
lo,
4:ao=·-~
~so=·---.I.
J 40"
~-.L.I
I2o·
c;Ybt.f-d .ewe\
I
e- ~
~ o,111 a ~ p-n$cvL D'f ~l:J JJC:.,
, f? OA .~ beu_t( (!)c~; .
;:::'t>!,lo,:\-ztls aAR.. 1"0 11'!($"f- Ye_~_/ ~ , R-iM d.<vt:J- li-t~
{f)
ey:
1
...h1-~ ~ ~-uat
tL:
'U e1 ~ C() n~ · ~ ,_ _ _, ~ ~ ,_,.,vu.~Jnf¥, .
~
D. "Short answer questiOns about methllocend :
'v1..-v•
a) The paramagnetic metallocene(s).
b) The metallocene with largest average M -C bond distance.
c) The oxidation state of the nickels ~in the triple decker [(TJ -CsHs)3Nht
-3
-t--1(none of these)
+1
+1.5
0
5
d) Circle the molecule that is not a bent metallocene:
CpzTi(CO)z
CpzTiCh
[CpzTi]z
CpzFeH+
C§~ zFe(CO)V
Page 6 of6