Cage substitution reactions of monocarbollide carbonyl complexes of iron: Generation of iminium groups at a boron vertex

Article abstract of DOI:10.1021/om001057x

Treatment of [N(PPh₃)₂][Fe(CO)₂(L) (η⁵-7-CB₁₀H₁₁)] (L = SMe₂, PPh₃) in SMe₂ or O(CH₂)₄ with H₂SO₄ yields the neutral charge-compensated complexes [Fe(CO)₂(L)(η⁵-9-L′-7-CB₁₀ H₁₀)] (L = SMe₂, L′ = SMe₂ (2), O(CH₂)₄ (3); L = PPh₃, L′ = SMe₂ (4), O(CH₂)₄ (5)). An X-ray crystallographic study of 2 established that one of the exopolyhedral SMe₂ groups is bonded to a boron in a β-site with respect to the carbon in the CBBBB ring coordinated to the iron atom. In contrast with these results, the salts [N(PPh₃)₂][Fe(CO)₂(L) (η⁵-7-CB₁₀H₁₁)] (L = CO, PPh₃, CNBu^t) treated with NCMe and CF₃SO₃Me afford complexes [Fe(CO)₂(L)(η⁵-9-{(E)-N(Me)=C(H)Me}-7-CB₁₀ H₁₀)] (L = CO (8), PPh₃ (9), CNBu^t (10)). An X-ray diffraction study on 8 established that the iminium group was attached to a β-B atom of the CB₄ iron-bonded ring. Compound 8 is readily hydrolyzed in the presence of a base catalyst affording [Fe(CO)₃(η⁵-9-NH₂Me-7-CB₁₀ H₁₀)] (12), and with [Na][BH₃CN] yields [Fe(CO)₃(η⁵-9-{NH(Me)Et}-7-CB₁₀ H₁₀)] (13), the structure of which was determined by X-ray diffraction. The reaction between [N(PPh₃)₂][Fe(CO)₃ (η⁵-7-CB₁₀H₁₁)] and Bu^tC≡CH gives [N(PPh₃)₂][Fe(CO)₃- (η²:η⁵-8-{(E)-C(H)=C(H)Bu^t} -7-CB₁₀H₁₀)] (14), which with NCMe in CF₃SO₃Me affords [Fe(CO)₂(η²:η⁵-8-{(E)-C(H)=C(H) Bu^t}-10-{(E)-N(Me)=C(H)Me}-7-CB₁₀H₉)] (16). The site of attachment of the exopolyhedral iminium and tert-butylvinyl substituents to the cage was established by X-ray diffraction.

Full text of DOI:10.1021/om001057x

Organometallics 2001, 20, 1597-1607
1597
Ca ge Su bstitu tion Rea ction s of Mon oca r bollid e Ca r bon yl
Com p lexes of Ir on : Gen er a tion of Im in iu m Gr ou p s a t a
Bor on Ver tex†
Andreas Franken, Shaowu Du, Paul A. J elliss,‡ J ason A. Kautz, and
F. Gordon A. Stone*
Department of Chemistry and Biochemistry, Baylor University, Waco, Texas 76798-7348
Received December 11, 2000
Treatment of [N(PPh3)2][Fe(CO)2(L)(η5-7-CB10H11)] (L ) SMe2, PPh3) in SMe2 or O(CH2)4
with H2SO4 yields the neutral charge-compensated complexes [Fe(CO)2(L)(η5-9-L′-7-CB10H10)]
(L ) SMe2, L′ ) SMe2 (2), O(CH2)4 (3); L ) PPh3, L′ ) SMe2 (4), O(CH2)4 (5)). An X-ray
crystallographic study of 2 established that one of the exopolyhedral SMe2 groups is bonded
to a boron in a â-site with respect to the carbon in the CBBBB ring coordinated to the iron
atom. In contrast with these results, the salts [N(PPh3)2][Fe(CO)2(L)(η5-7-CB10H11)] (L )
CO, PPh3, CNBut) treated with NCMe and CF3SO3Me afford complexes [Fe(CO)2(L)(η5-9-
{(E)-N(Me)dC(H)Me}-7-CB10H10)] (L ) CO (8), PPh3 (9), CNBut (10)). An X-ray diffraction
study on 8 established that the iminium group was attached to a â-B atom of the CB4 iron-
bonded ring. Compound 8 is readily hydrolyzed in the presence of a base catalyst affording
[Fe(CO)3(η5-9-NH2Me-7-CB10H10)] (12), and with [Na][BH3CN] yields [Fe(CO)3(η5-9-{NH-
(Me)Et}-7-CB10H10)] (13), the structure of which was determined by X-ray diffraction. The
reaction between [N(PPh3)2][Fe(CO)3(η5-7-CB10H11)] and ButCtCH gives [N(PPh3)2][Fe(CO)3-
(η2:η5-8-{(E)-C(H)dC(H)But}-7-CB10H10)] (14), which with NCMe in CF3SO3Me affords [Fe-
(CO)2(η2:η5-8-{(E)-C(H)dC(H)But}-10-{(E)-N(Me)dC(H)Me}-7-CB10H9)] (16). The site of
attachment of the exopolyhedral iminium and tert-butylvinyl substituents to the cage was
established by X-ray diffraction.
In tr od u ction
ubiquitous cyclopentadienide metal carbonyl complexes,
e.g., [Fe(CO)3(η5-7-CB10H11)]- versus [Fe(CO)3(η5-C5H5)]+,
yet the cyclopentadienide and monocarbollide complexes
display very different chemical behavior. The chief
In the anionic complexes [Mo(CO)4(η5-7-CB10H11)]-,
[Re(CO)3(η5-7-CB10H11)]2-, and [Fe(CO)3(η5-7-CB10H11)]-
a transition metal ion is ligated both by carbonyl groups
origin of this difference lies in the frequently adopted
3-
and a [nido-7-CB10H11
]
icosahedral cage fragment.1
3-
nonspectator role of the [η5-7-CB10H11
]
ligand, a
Their recent discovery allows detailed examination of
a class of mononuclear metal compound which has been
little studied previously.2 Hitherto the only species of
this type known were the molybdenum complexes [Mo-
(CO)3(L)(η5-7-OH-7-CB10H10)]- (L ) CO, PPh3), which
were obtained as unexpected products from reactions
between [Mo(CO)6] and [Na][nido-B10H13] and between
[Mo(CO)3(NCMe)2(PPh3)] and [NEt4]2[arachno-B10H14],
respectively.3 The chemistry of monocarbollide metal
carbonyl complexes is potentially interesting. This is
because there are electronic relationships with the
feature resulting in the formation of molecules with
unusual structures and reactivities.1
In initial studies it was observed that the compound
[N(PPh3)2][Fe(CO)3(η5-7-CB10H11)] (1a ) reacted with
donors (L) in the presence of hydride-abstracting re-
agents to yield zwitterionic complexes [Fe(CO)3(η5-9-L′-
7-CB10H10)] (L′ ) O(CH2)4, OEt2, or SMe2).1c In this
paper we report a range of new ferracarborane zwitte-
rionic molecules, isolating very unexpected products
when acetonitrile is the substrate molecule.
† The compounds described in this paper have iron atoms incorpo-
rated into closo-1-carba-2-ferradodecaborane frameworks. To relate
them to the many known iron species with η5-coordinated cyclopen-
tadienide ligands, for nomenclature purposes we treat the cages as
nido-11-vertex ligands with numbering as for an icosahedron from
which the 12th vertex has been removed.
Resu lts a n d Discu ssion
It was anticipated that the reactivity of an Fe(η5-7-
CB10H11) fragment would likely be influenced by the
donor-acceptor properties of the other ligands present.
Accordingly, in addition to studies with 1a , the com-
plexes [N(PPh3)2][Fe(CO)2(L)(η5-7-CB10H11)] (L ) PPh3
(1b), CNBut (1c), SMe2 (1d ), PMe2Ph (1e)) were also
employed. Compounds 1b and 1c were obtained from
the reactions between 1a and PPh3 and CNBut, respec-
tively, in THF (tetrahydrofuran) in the presence of Me3-
NO.1c The related complexes 1d and 1e were similarly
‡ Current address: Department of Chemistry, Saint Louis Univer-
sity, St. Louis, MO 63103-2010.
(1) (a) Blandford, I.; J effery, J . C.; J elliss, P. A.; Stone, F. G. A.
Organometallics 1998, 17, 1402. (b) J effery, J . C.; J elliss, P. A.; Rees,
L. H.; Stone, F. G. A. Organometallics 1998, 17, 2258. (c) Ellis, D. D.;
Franken, A.; J elliss, P. A.; Stone, F. G. A.; Yu, P.-Y. Organometallics
2000, 19, 1993. (d) Ellis, D. D.; Franken, A.; J elliss, P. A.; Kautz, J .
A.; Stone, F. G. A. J . Chem. Soc., Dalton Trans. 2000, 2509.
(2) Grimes, R. N. In Comprehensive Organometallic Chemistry II;
Housecroft, C. E., Ed.; Pergamon: Oxford, 1995; Section 9 in Vol. 1
10.1021/om001057x CCC: $20.00 © 2001 American Chemical Society
Publication on Web 03/23/2001

1598 Organometallics, Vol. 20, No. 8, 2001
Ta ble 1. An a lytica l a n d P h ysica l Da ta
Franken et al.
anal./%c
compda
yield/%
ν
max(CO)b/cm-1
C
H
N
[N(PPh3)2][Fe(CO)2(SMe2)(η5 -7-CB10H11)] (1d )
[N(PPh3)2][Fe(CO)2(PMe2Ph)(η5-7-CB10H11)] (1e)
[Fe(CO)2(SMe2)(η5-9-SMe2-7-CB10H10)] (2)
[Fe(CO)2(SMe2)(η5-9-O(CH2)4-7-CB10H10)] (3)
[Fe(CO)2(PPh3)(η5-9-SMe2-7-CB10H10)] (4)
[Fe(CO)2(PPh3)(η5-9-O(CH2)4-7-CB10H10)] (5)
[Fe(CO)2(PPh3)(η5-9-NCBut-7-CB10H10)] (6)
[Fe(CO)2(PMe2Ph)(η5-9-NCMe-7-CB10H10)] (7)
[Fe(CO)3(η5-9-{(E)-N(Me)dC(H)Me}-7-CB10H10)] (8)
[Fe(CO)2(PPh3)(η5-9-{(E)-N(Me)dC(H)Me}-7-CB10H10)] (9)
[Fe(CO)2(CNBut)(η5-9-{(E)-N(Me))C(H)Me}-7-CB10H10)] (10)
[Fe(CO)2(PMe2Ph)(η5-9-{(E)-N(H)dC(H)Me}-7-CB10H10)] (11)
[Fe(CO)3(η5-9-NH2Me-7-CB10H10)] (12)
81
72
56
79
76
82
62
24
42
87
83
43
88
86
45
1993s, 1940s
1988s, 1934s
2011s, 1964s
2009s, 1956s
2009s, 1959s
2005s, 1953s
2009s, 1958s
2007s, 1957s
58.4 (58.3)
60.9 (61.4)
23.6 (23.0)
28.5 (28.7)
48.3 (48.8)
51.8 (52.1)
52.4 (53.2)
36.9 (37.1)
5.5 (5.6) 1.7 (1.7)
5.8 (5.7) 1.5 (1.5)
5.6 (6.1)
6.7 (6.4)
5.6 (5.5)
5.9 (5.8)
6.0 (5.8) 2.5 (2.4)
5.7 (5.7) 3.2 (3.3)
5.3 (5.2) 4.2 (4.3)
5.7 (5.5) 2.4 (2.3)d
6.8 (6.9) 7.3 (7.4)
6.2 (6.2) 3.2 (3.3)
5.1 (5.0) 4.8 (4.7)
5.7 (5.8) 4.2 (4.3)
2076s, 2029m, 2011m 25.7 (25.7)
2005s, 1953s
2023s, 1982se
2005s, 1952s
2078s, 2029m, 2005m 20.4 (19.9)
2078s, 2028m, 2009m 26.0 (25.5)
2003s, 1954s
49.7 (48.7)
34.4 (34.6)
37.1 (36.9)
[Fe(CO)3(η5-9-{NH(Me)Et}-7-CB10H10)] (13)
[N(PPh3)2][Fe(CO)2(η2:η5-8-{(E)-C(H)dC(H)But}-7-
CB10H10)] (14)f
[N(PPh3)2][Fe(CO)2(PPh3)(η5-8-{(E)-C(H)dC(H)But}-7-
CB10H10)] (15)
44
42
1992s, 1941s
2017s, 1964s
66.8 (67.2)
38.1 (37.8)
6.0 (5.9) 1.2 (1.3)
7.1 (7.1) 3.5 (3.7)
[Fe(CO)2(η2:η5-8-{(E)-C(H)dC(H)But}-10-{(E)-N(Me)d
C(H)Me}-7-CB10H9)] (16)
a
b
All compounds are yellow except 15 and 16 (orange). Measured in CH2Cl2; medium-intensity bands observed at ca. 2550 cm-1 in the
spectra of all compounds are due to B-H absorptions. c Calculated values are given in parentheses. Where analytically pure products
were not isolated, mass spectral data are given. Contains 0.5 molar equiv CH2Cl2, as confirmed in an 1H NMR spectrum. EI mass
d
spectrum: m/z 505.23 ([10 - 2 CO]+) (calc 505.43). e νmax(NC) ) 2177m cm-1 f EI mass spectrum: m/z 324.96 ([14]+) (calc 325.22).
.
Ch a r t 1
F igu r e 1. Structure of [Fe(CO)2(SMe2)(η5-9-SMe2-7-CB10
10)] (2), showing the crystallographic labeling scheme.
-
H
Hydrogen atoms are omitted for clarity, and thermal
ellipsoids are shown at the 40% probability level.
the CBBBB pentagonal ring coordinated to the iron
atom. However, there was no evidence from their NMR
spectra for the formation of more than one isomer. In
the molecule [Fe(CO)3(η5-9-O(CH2)4-7-CB10H10)], iso-
lated in the initial study of 1a ,1c X-ray diffraction
revealed the THF group was attached to one of the
prepared from SMe2 and PMe2Ph and were character-
ized by the data given in Tables 1-3.
Like its parent compound 1a , when the salt 1d is
dissolved in SMe2 or THF and the mixture treated with
concentrated H2SO4, the charge-compensated molecules
[Fe(CO)2(SMe2)(η5-9-L′-7-CB10H10)] (L′ ) SMe2 (2),
O(CH2)4 (3)), respectively, are formed. Similarly, com-
plex 1b in CH2Cl2 together with SMe2 or THF in the
presence of CF3SO3H yielded the species [Fe(CO)2-
(PPh3)(η5-9-L′-7-CB10H10)] (L′ ) SMe2 (4), O(CH2)4 (5)),
respectively. Data characterizing the complexes 2-5 are
given in Tables 1-3. Isomers are possible according to
whether the donor molecule is bonded to a boron vertex
located at an R- or â-site with respect to the carbon in
â-boron atoms in the CBBBB ring. From this it seemed
likely that the same regiochemistry would prevail in the
new species. To confirm this, an X-ray diffraction study
was made on 2. Selected structural parameters are
given in Table 4, and the molecule is shown in Figure
1.
It is immediately apparent that the cage SMe2 group
is attached to a boron atom situated in a â-site with
respect to the carbon in the iron-ligating CBBBB ring.
This indicates that within the cage it is the hydrogens
of the â-BH vertexes that are the most susceptible to

Iminium Groups at a Boron Vertex
Organometallics, Vol. 20, No. 8, 2001 1599
Ta ble 2. 1H a n d 13C NMR Da ta a
1H/δb
13C/δc
1d 1.83 (br s, 1 H, cage CH), 2.37 (s, 6 H, Me),
7.47-7.66 (m, 30 H, Ph)
215.2 (CO), 134.0-126.7 (Ph), 49.7 (br, cage CH), 26.8 (Me)
1e 1.02 (br s, 1 H, cage CH), 1.85 (d, 6 H, PMe,
J (PH) ) 8), 7.36-7.67 (m, 35 H, Ph)
215.1 (d, CO, J (PC) ) 24), 138.1-126.7 (Ph), 48.5 (br, cage
CH), 17.9 (d, Me, J (PC) ) 34)
213.6 (CO), 211.8 (CO), 49.2 (br, cage CH), 26.5 (SMe), 26.0
(SMe), 25.7 (SMe)
214.2 (CO), 212.0 (CO), 80.6 (OCH2), 47.1 (br cage CH), 26.5
(SMe), 25.2 (CH2)
215.7 (d, CO, J (PC) ) 29), 211.7 (d, CO, J (PC) ) 23),
134.2-128.8 (Ph), 52.9 (br, cage CH), 26.4 (SMe), 25.7 (SMe)
216.2 (d, CO, J (PC) ) 27), 212.0 (d, CO, J (PC) ) 23),
133.9-128.6 (Ph), 80.8 (OCH2), 48.7 (br, cage CH), 25.3 (CH2)
216.3 (d, CO, J (PC) ) 28), 211.1 (d, CO, J (PC) ) 22), 133.9-128.3
(Ph), 119.6 (NC), 60.6 (CMe3), 51.5 (br, cage CH), 27.0 (CMe3)
213.8 (d, CO, J (PC) ) 29), 211.8 (d, CO, J (PC) ) 24),
136.2-128.8 (Ph), 113.0 (NC), 47.5 (br, cage CH), 4.2 (Me)
2
3
4
5
6
7
1.75 (br s, 1 H, cage CH), 2.34, 2.42 (s × 2, 6 H,
Me), 2.48 (br s, 6 H, Me)
1.57 (br s, 1 H, cage CH), 2.11 (m, 4 H, CH2),
2.42 (s, 6 H, Me), 4.23 (m, 4 H, OCH2)
0.38 (br s, 1 H, cage CH), 2.63, 2.53 (s × 2, 6 H,
Me), 7.53-7.67 (m, 15 H, Ph)
0.21 (br s, 1 H, cage CH), 3.25 (m, 4 H, CH2), 4.43
(m, 4 H, OCH2), 7.44 - 7.63 (m, 15 H, Ph)
0.28 (br s, 1 H, cage CH), 1.54 (s, 9 H, But), 7.44-7.67
(m, 15 H, Ph)
0.85 (br s, 1 H, cage CH), 1.94 (d, 3 H, PMe, J (PH) ) 9), 1.98
(d, 3 H, PMe, J (PH) ) 9), 2.58 (s, 3 H, Me), 7.45-7.57
(m, 5 H, Ph)
8
9
1.83 (br s, 1 H, cage CH), 2.56 (d, 3 H, C(H)Me, J (HH)
) 6), 3.64 (s, 3 H, Me), 7.97 (vbr s, 1 H, dCH)
0.35 (br s, 1 H, cage CH), 2.65 (s, 3 H, C(H)Me), 3.72 (s,
3 H, NMe), 7.45-7.63 (m, 15 H, Ph), 7.95 (br s, 1 H, dCH)
207.0 (CO), 179.0 (CdN), 53.6 (NMe), 48.0 (br, cage CH),
21.1 (C(H)Me)
215.9 (d, CO, J (PC) ) 28), 212.0 (d, CO, J (PC) ) 24), 177.1
(CdN), 133.9-128.6 (Ph), 53.6 (NMe), 50.1 (br, cage CH),
21.1 (C(H)Me)
10 1.49 (s, 9 H, But), 1.61 (br s, 1 H, cage CH), 2.53 (s, 3 H,
C(H)Me), 3.59 (s, 3 H, NMe), 7.88 (br s, 1 H, dCH)
211.5 (CO), 211.0 (CO), 176.8 (CdN), 152.0 (CNBut), 59.0
(CMe3), 53.4 (NMe), 46.5 (br, cage CH), 30.3 (CMe3), 20.9
(C(H)Me)
11 1.30 (br s, 1 H, cage CH), 1.92 (d, 3 H, PMe, J (PH) ) 10),
1.96 (d, 3 H, PMe, J (PH) ) 9), 2.22 (d, 3 H, C(H)Me, J (HH)
) 5), 7.46-7.57 (m, 5 H, Ph), 7.84 (dq, 1 H, dCH, J (HH) )
5, 20), 9.10 (d br, 1 H, NH, J (HH) ) 20)
12 1.85 (br s, 1 H, cage CH), 2.72 (s, 3 H, NMe), 4.54 (br m,
1 H, NH), 4.60 (br m, 1 H, NH)
214.3 (d, CO, J (PC) ) 29), 212.4 (d, CO, J (PC) ) 24), 176.1
(CdN), 136.6-128.8 (Ph), 47.5 (br, cage CH), 23.2
(C(H)Me), 18.5 (d, Me, J (PC) ) 34), 16.6 (d, Me, J (PC) ) 36)
207.0 (CO), 48.8 (br, cage CH), 34.4 (NMe)
13 1.30 (m, 6 H, CH2Me), 1.87 (br s, 2 H, cage CH), 2.66, 2.76
(m × 2, 8 H, NMe + CH2), 3.35, 3.48 (m × 2, 2 H, CH2), 3.97
(br m, 2 H, NH)
207.1 (CO), 52.7, 52.5 (CH2), 48.9 (br, cage CH), 40.5, 40.3
(NMe), 12.7, 12.6 (Me, CH2Me)
14 0.62 (br s, 1 H, cage CH), 1.02 (s, 9 H, But), 4.29 (d,
1 H, (C(H)But), J (HH) ) 11), 4.72 (d, 1 H, BCH, J (HH) )
11), 7.48 - 7.67 (m, 30 H, Ph)
217.1 (CO), 211.5 (CO), 134.0-126.7 (Ph), 100.6 (C(H)But),
82.0 (br, C(H)B), 58.4 (CMe3), 47.2 (br, cage CH), 33.7 (CMe3)
15 0.49 (br s, 1 H, cage CH), 1.12 (s, 9 H, But), 5.34 (d,
1 H, C(H)But, J (HH) ) 18), 5.35 (d, 1 H, C(H)B, J (HH) )
18), 7.36 - 7.65 (m, 45 H, Ph)
217.9 (d, CO, J (PC) ) 23), 213.4 (d, CO, J (PC) ) 23), 141.9
(C(H)But), 135.8-126.7 (Ph), 82.0 (br, C(H)B), 66.1 (CMe3),
55.9 (br, cage CH), 31.3 (CMe3)
16 0.08 (br s, 1 H, cage CH), 1.22 (s, 9 H, But), 2.54 (d, 3 H,
C(H)Me, J (HH) ) 6), 3.61 (s, 3 H, NMe), 3.80 (d, 1 H,
C(H)But, J (HH) ) 14), 4.77 (d, 1 H, C(H)B, J (HH) ) 14),
7.88 (br s, 1 H, C(H)Me)
213.0 (CO), 210.4 (CO), 177.5 (CdN), 111.4 (C(H)But),
85.0 (br, BCH), 65.9 (CMe3), 53.8 (NMe), 44.6 (br, cage CH),
31.0 (CMe3), 20.9 (C(H)Me)
a
b
Chemical shifts (δ) in ppm, coupling constants (J ) in hertz, measurements at ambient temperatures in CD2Cl2. Resonances for
terminal BH protons occur as broad unresolved signals in the range δ ca. -1 to 3. c 1H-decoupled chemical shifts are positive to high
frequency of SiMe4.
removal by electrophiles and are therefore likely to be
the most hydridic. The B(3)-S(1) distance of 1.921(4)
Å is perceptibly longer than those in nido-9-SMe2-7,8-
C2B9H11 (1.884(3) Å)4a and similar molecules.4b The iron-
coordinated SMe2 group (Fe-S ) 2.2842(9) Å) in 2 lies
transoid to B(3) (S(2)-Fe-B(3) ) 162.67(11)°), while the
Me groups attached to S(1) point away from the Fe-
(CO)2SMe2 moiety. This arrangement presumably serves
to reduce steric crowding.
Establishment of the molecular structure of 2 allows
ready interpretation of the NMR data (Tables 2 and 3)
for this species and also those of complexes 3-5. In the
11B{1H} NMR spectra of all the complexes one resonance
remained a singlet when a fully coupled 11B spectrum
was measured (Table 3), and this signal may therefore
be attributed to the boron nucleus of the BL′ group. In
all the 13C{1H} NMR spectra there are two resonances
for the nonequivalent CO groups, in agreement with the
asymmetry of the molecules, an unavoidable conse-
quence of substitution at a single â-boron vertex in the
CBBBB coordinating face of the carborane cage. A
diagnostic broad peak is seen in each spectrum for the
cage CH group (δ 47.1-52.9). Corresponding signals in
the 1H NMR spectra occur at δ 1.75 and 1.57 for
complexes 2 and 3 but further upfield at δ 0.38 and 0.21
for compounds 4 and 5, no doubt because of the superior
donor capacity of the ligand PMe2Ph compared with
SMe2. This results in a downfield shift of these signals,
although it is noted that this effect does not manifest
itself in the corresponding 13C{1H} chemical shifts.
Evidently in solution the Me substituents of one of the
two SMe2 groups in 2 do not undergo inversion at the S
1
atom on the NMR time scale since in the H and 13C-
(3) (a) Wegner, P. A.; Guggenberger, L. J .; Muetterties, E. L. J . Am.
Chem. Soc. 1970, 92, 3473. (b) Fontaine, X. L. R.; Greenwood, N. N.;
Kennedy, J . D.; MacKinnon, P. I.; Macpherson. I. J . Chem. Soc., Dalton
Trans. 1987, 2385.
(4) (a) Cowie, J .; Hamilton, E. J . M.; Laurie, J . C. V.; Welch, A. J .
Acta Crystallogr. 1986, C44, 1648. (b) St´ıbr, B. Chem. Rev. 1992, 92,
225.
{1H} NMR spectra there are three signals: 1H, δ 2.34,
2.42, and 2.48 (rel int 3:3:6); 13C{1H}, δ 26.5, 26.0, and
25.7. The molecules 4 and [Fe(CO)3(η5-9-SMe2-7-CB10H10)]
have no iron-ligating SMe2 groups, yet each displays in

1600 Organometallics, Vol. 20, No. 8, 2001
Ta ble 3. 11B a n d 31P NMR Da ta a
Franken et al.
11B{1H}/δb
31P{1H}/δc
1d
1e
2
5.3 (1 B), -4.4 (2 B), -5.5 (2 B), -7.8 (1 B), -13.1 (2 B), -17.4 (2 B)
6.1 (1 B), -2,9 (2 B), -6.4 (2 B), -8.5 (1 B), -12.7 (2 B), -17.7 (2 B)
5.9 (1 B), -1.5 (1 B), *-2.7 (1 B), -3.5 (1 B), -6.5 (1 B), -9.6 (1 B), -13.1 (1 B),
-15.1 (2 B), -17.7 (1 B)
*17.4 (1 B), 3.3 (1 B), -4.8 (2 B), -8.9 (2 B), -14.3 (2 B), -18.4 (1 B), -20.4 (1 B)
7.0 (1 B), *-0.5 (1 B), -0.6 (1 B), -5.2 (1 B), -6.4 (1 B), -10.0 (1 B), -12.6 (1 B),
-14.9 (1 B), -16.2 (1 B), -17.5 (1 B)
*18.4 (1 B), 4.7 (1 B), -3.1 (1 B), -6.9 (1 B), -8.3 (1 B), -9.5 (1 B), -13.4 (1 B),
-14.2 (1 B), -18.8 (1 B), -20.7 (1 B)
5.8 (2 B), -1.4 (1 B), *-4.1 (1 B), -5.9 (1 B), -8.1 (1 B), -12.7 (2 B), -17.5 (2 B)
4.7 (1 B), *-2.7 (1 B), -3.2 (1 B), -6.0 (1 B), -7.2 (1 B), -8.5 (1 B), -12.7 (2 B),
-17.6 (2 B)
10.2 (1 B), *8.3 (1 B), -1.6 (1 B), -5.8 (2 B), -7.4 (1 B), -9.6 (1 B), -10.1 (1 B),
-15.8 (2 B)
*5.6 (1 B), 5.4 (1 B), -2.2 (1 B), -5.8 (2 B), -8.7 (1 B), -12.1 (1 B), -12.7 (1 B),
-17.3 (2 B)
21.7
35.3 (Fe(PMe2Ph)), 21.7 (N(PPh3)2)
3
4
66.8
65.7
5
6
7
66.1, 65.2d
33.7
8
9
65.8
33.3
10
11
12
13
*6.1 (1 B), 5.4 (1 B), -3.1 (1 B), -6.8 (2 B), -8.5 (1 B), -12.1 (2 B), -17.4 (2 B)
*5.8 (1 B), 5.4 (1 B), -4.1 (1 B), -5.9 (1 B), -8.2 (2 B), -13.2 (2 B), -18.0 (2 B)
11.0 (1 B), *9.2 (1 B), -1.2 (1 B), -6.3 (2 B), -7.4 (1 B), -10.4 (2 B), -17.0 (2 B)
*12.6 (1 B), 11.2 (1 B), -0.6 (1 B), -6.7 (3 B), -9.6 (1 B), -10.0 (1 B), -16.7 (1 B),
-17.6 (1 B)
14
15
16
*12.6 (1 B), 7.2 (1 B), 4.8 (1 B), -3.0 (2 B), -5.7 (1 B), -13.8 (1 B), -17.0 (1 B), -18.1
(1 B), -20.8 (1 B)
6.4 (1 B), *2.4 (1 B), -1.4 (1 B), -2.5 (1 B), -6.4 (1 B), -7.7 (1 B), -9.5 (1 B), -14.7
(2 B), -17.2 (1 B)
66.8 (Fe(PPh3)), 21.7 (N(PPh3)3)
*9.5 (1 B), *3.6 (1 B), 3.5 (2 B), -3.2 (2 B), -13.5 (1 B), -17.7 (1 B), -18.9 (1 B),
-20.1 (1 B)
a
b
Chemical shifts (δ) in ppm, coupling constants (J ) in hertz, measurements at ambient temperatures in CD2Cl2. Chemical shifts (δ)
are positive to high frequency of BF3‚Et2O (external). Signals ascribed to more than one boron nucleus may result from overlapping
peaks and do not necessarily indicate symmetry equivalence. Peaks marked with an asterisk are assigned to cage-boron nuclei carrying
L substituents (see text), since they occur as singlets in fully coupled 11B spectra. c 31P{1H} chemical shifts (δ) are positive to high frequency
d
of H3PO4 (external). Weak signal, see text.
Ta ble 4. Selected In ter n u clea r Dista n ces (Å) a n d An gles (d eg) for [F e(CO)2(SMe2)(η5-9-SMe2-7-CB10H10)] (2)
Fe-C(3)
Fe-B(5)
B(3)-S(1)
S(1)-C(5)
1.757(4)
2.142(4)
1.921(4)
1.796(4)
Fe-C(2)
Fe-B(2)
C(2)-O(2)
S(2)-C(7)
1.780(4)
2.145(4)
1.148(4)
1.802(4)
Fe-C(1)
Fe-B(4)
C(3)-O(3)
S(2)-C(6)
2.132(3)
2.183(4)
1.141(4)
1.807(4)
Fe-B(3)
Fe-S(2)
S(1)-C(4)
2.140(4)
2.2842(9)
1.793(4)
C(3)-Fe-C(2)
C(3)-Fe-B(3)
C(2)-Fe-B(5)
C(3)-Fe-B(4)
C(2)-Fe-S(2)
B(5)-Fe-S(2)
S(1)-B(3)-Fe
O(2)-C(2)-Fe
C(4)-S(1)-B(3)
C(7)-S(2)-Fe
92.7(2)
C(3)-Fe-C(1)
C(2)-Fe-B(3)
C(3)-Fe-B(2)
C(2)-Fe-B(4)
C(1)-Fe-S(2)
B(2)-Fe-S(2)
S(1)-B(3)-B(2)
O(3)-C(3)-Fe
C(5)-S(1)-B(3)
C(6)-S(2)-Fe
162.5(2)
C(2)-Fe-C(1)
104.2(2)
116.8(2)
79.8(2)
91.00(12)
162.67(11)
114.15(10)
121.4(2)
99.7(2)
90.9(2)
149.7(2)
80.8(2)
92.54(12)
81.00(11)
113.4(2)
176.4(3)
106.6(2)
111.3(2)
104.6(2)
134.5(2)
152.5(2)
92.83(9)
133.76(11)
123.0(2)
179.7(4)
104.1(2)
108.23(14)
C(3)-Fe-B(5)
C(2)-Fe-B(2)
C(3)-Fe-S(2)
B(3)-Fe-S(2)
B(4)-Fe-S(2)
S(1)-B(3)-B(4)
C(4)-S(1)-C(5)
C(7)-S(2)-C(6)
98.3(2)
their 1H and 13C{1H} NMR spectra a pair of Me
resonances. For 4 these peaks are seen at δ 2.63 and
2.53 (1H) and at δ 26.4 and 25.7 (13C{1H}), while for [Fe-
(CO)3(η5-9-SMe2-7-CB10H10)]1c they occur at δ 2.53 and
2.42 (1H) and at δ 26.4 and 25.7 (13C{1H}). From these
results it may be inferred that in all three molecules it
is the Me groups of the BSMe2 fragments that do not
invert at the S atom in solution at ambient tempera-
tures.
It was observed qualitatively that the syntheses
proceeded more readily with 1b than with 1a presum-
ably because replacement of a CO group on iron by the
better donor PPh3 enhances electron density in the cage.
Thus hydrogen atoms at the â-B sites are rendered
increasingly hydridic and so more easily abstracted by
a strong electrophile. Reaction between 1b and NCBut,
and employing in this instance CF3SO3Me as the
hydride removal reagent, also yielded a zwitterionic
molecule, [Fe(CO)2(PPh3)(η5-9-NCBut-7-CB10H10)] (6). A
similar reaction occurs using CF3SO3H, but the process
proceeds less cleanly. The 31P{1H} NMR spectrum of 6
displayed a resonance at δ 66.1, but there was also a
much weaker signal at δ 65.2, providing somewhat
tenuous evidence for the presence of a second isomer.
However the presence of this species could not be
1
detected in the H or 13C{1H} NMR spectra.
It is assumed that in the syntheses of 2-6 nucleo-
philic substitution is facilitated by removal of H- from
a â-BH vertex by H+ or Me+ with release of H2 or CH4,
although no attempt was made to identify these species.
This step would generate a site on the cage for nucleo-
philic attack by any donor present, a process first
observed by Hawthorne and co-workers5 in related
chemistry where treatment of the dianion [Fe(η5-7,8-
C2B9H11)2]2- with concentrated acid followed by addition
of a dialkyl sulfide afforded the monoanionic species [Fe-
(η5-7,8-C2B9H11)(η5-10-SR2-7,8-C2B9H10)]-. Related to
this is the synthesis of nido-8-SMe2-7-CB10H12 by treat-
ing [NMe4][nido-7-CB10H13] and SMe2 with sulfuric
(5) Hawthorne, M. F.; Warren, L. F.; Callahan, K. P.; Travers, N.
F. J . Am. Chem. Soc. 1971, 93, 2407.

Iminium Groups at a Boron Vertex
Organometallics, Vol. 20, No. 8, 2001 1601
Ta ble 5. Selected In ter n u clea r Dista n ces (Å) a n d An gles (d eg) for
[F e(CO)3(η5-9-{(E)-N(Me)dC(H)Me}-7-CB10H10)] (8)
Fe-C(4)
1.790(3)
2.150(3)
1.562(6)
1.145(4)
1.25(3)
Fe-C(3)
1.800(3)
2.185(3)
1.67(2)
1.301(10)
1.59(4)
Fe-C(2)
1.813(3)
2.188(3)
1.142(4)
1.504(12)
1.46(4)
Fe-B(5)
2.144(3)
2.199(3)
1.142(4)
1.46(2)
Fe-C(1)
Fe-B(2)
Fe-B(4)
Fe-B(3)
B(3)-N
C(4)-O(4)
N(1A)-C(5A)
B(3)-N(1A)
N-C(5)
N(1A)-C(7A)
C(2)-O(2)
N-C(7)
C(5A)-C(6A)
C(3)-O(3)
C(5)-C(6)
C(4)-Fe-C(3)
C(4)-Fe-B(5)
C(4)-Fe-C(1)
C(4)-Fe-B(2)
C(4)-Fe-B(4)
C(4)-Fe-B(3)
N-B(3)-B(4)
N(1A)-B(3)-B(2)
O(2)-C(2)-Fe
C(5)-N-C(7)
N-C(5)-C(6)
C(7A)-N(1A)-B(3)
96.35(14)
C(4)-Fe-C(2)
91.04(14)
C(3)-Fe-C(2)
90.46(14)
95.61(13)
83.27(12)
111.40(13)
139.90(14)
161.26(13)
131.9(3)
119.5(4)
179.7(3)
118.4(6)
122.5(14)
166.46(12)
122.44(13)
83.91(12)
128.00(13)
86.84(12)
116.7(3)
109.6(6)
179.4(3)
115.8(6)
126.5(7)
123(2)
C(3)-Fe-B(5)
C(3)-Fe-C(1)
C(3)-Fe-B(2)
C(3)-Fe-B(4)
C(3)-Fe-B(3)
N(1A)-B(3)-B(4)
N-B(3)-Fe
95.38(13)
140.68(13)
158.14(13)
77.82(13)
108.28(13)
140.5(6)
117.1(2)
178.0(3)
125.8(5)
114(2)
C(2)-Fe-B(5)
C(2)-Fe-C(1)
C(2)-Fe-B(2)
C(2)-Fe-B(4)
C(2)-Fe-B(3)
N-B(3)-B(2)
N(1A)-B(3)-Fe
O(4)-C(4)-Fe
C(7)-N-B(3)
C(5A)-N(1A)-B(3)
O(3)-C(3)-Fe
C(5)-N-B(3)
C(5A)-N(1A)-C(7A)
N(1A)-C(5A)-C(6A)
126(2)
acid.6 At the present time whether the initially formed
intermediates in the synthesis of 2-6 involve the
electrophile attaching itself to the iron center or to boron
remains unresolved, although recent studies of other
reactions of the compounds 1 suggest the latter. This is
because electrophilic metal-ligand fragments can be
coordinated by one or more BH vertexes without forma-
tion of metal-metal bonds.1d An interesting feature of
the synthetic methodology employed here and prev-
iously1c is that starting from the reagent 1a , it is
possible to prepare complexes in which a donor molecule
is either attached to the iron center or to the cage-boron
atom, or bonded to both. In the latter instance the donor
groups need not necessarily be the same as occurs in
3-6. This provides a route to a variety of disparate
ferracarboranes.
Reference was made earlier to the formation of 6,
where the weak donor NCBut is attached to the cage.
Very different results were obtained with acetonitrile
as the base when using the hydride-abstracting reagents
CF3SO3X (X ) Me or H). Treatment of 1a with NCMe
in the presence of CF3SO3Me did not yield a product
[Fe(CO)3(η5-9-NCMe-7-CB10H10)] akin to 6. Instead the
novel complex [Fe(CO)3(η5-9-{(E)-N(Me)dC(H)Me}-7-
CB10H10)] (8) was obtained. Similar products [Fe(CO)2-
(L)(η5-9-{(E)-N(Me)dC(H)Me}-7-CB10H10)] (L ) PPh3
(9), CNBut (10)) were obtained when 1b and 1c,
respectively, were dissolved in NCMe and treated with
CF3SO3Me. Data identifying these products are given
in Tables 1-3, but their nature only became well
established after X-ray diffraction studies had been
carried out on compound 8. Selected structural param-
eters are listed in Table 5, and the molecule is shown
F igu r e 2. Structure of [Fe(CO)3(η5-9-{(E)-N(Me)dC(H)-
Me}-7-CB10H10)] (8), showing the crystallographic labeling
scheme. Hydrogen atoms are omitted for clarity, and
thermal ellipsoids are shown at the 40% probability level.
arachno-6-SB9H11 where an arachno-6-SB9H11 cage
bears an endo-oriented ketiminium substituent bound
to a low-connectivity boron vertex.7 Because of the closo
nature of the ferracarborane moiety in 8, the iminium
substituent is strictly exo. The nitrogen atom in endo-
9-N(H)dC(Me)But-arachno-6-SB9H11, however, acts as
a two-electron donor, as it does in complex 8, and the
B-N bond length (1.542(5) Å) is correspondingly similar
to that in 8. The CdN iminium bond (1.284(4) Å) is also
comparable in length with that observed in complex 8,
confirming that it lies within the double-bond range.
A possible pathway for the formation of compounds
8-10 is shown in Scheme 1. It is proposed that in an
initial step NCMe is methylated at the nitrogen atom
by CF3SO3Me, giving the N-methylnitrilium cation
[MeNtCMe]+. The formation of N-methylnitrilium salts
from nitriles and methyl triflate is well established.8 The
cation [MeNtCMe]+ could then abstract H- from a cage
BH vertex to give an imine molecule. It is suggested
that the tricarbonylferracarborane moiety should exert
in Figure 2. Atom B(3), lying in a â-site in the CBBBB
ring coordinated to the iron atom, carries an N(Me)d
C(H)Me iminium substituent. Although the pendant
iminium group was disordered with the N and dC
atoms occupying two sites in an approximately 3:1 ratio,
it was evident that the Me substituents had a transoid
arrangement (B(3)-N ) 1.562(6), C(5)-N ) 1.301(10)
Å, torsion angle C(7)-N-C(5)-C(6) ) 175.0(8)° for the
major component; B(3)-N(1A) ) 1.67(2), C(5A)-N(1A)
) 1.25(3) Å, torsion angle C(7A)-N(1A)-C(5A)-C(6A)
) 168(2)° for the minor component). Comparison can
be made with the structure of endo-9-N(H)dC(Me)But-
(7) Ku¨pper, S.; Carroll, P. J .; Sneddon, L. G. Inorg. Chem. 1992,
31, 4921.
(8) (a) Alder, R. W.; Phillips, J . G. E. In Encyclopedia of Reagents
for Organic Synthesis; Paquette, L. A., Ed.; Wiley: Chichester, 1995;
Vol. 5, p 3617. (b) Booth, B. L.; J ibodu, K. O.; Proenc¸a, M. F. J . Chem.
Soc., Chem. Commun. 1980, 1151.
(6) Quintana W.; Sneddon, L. G. Inorg. Chem. 1990, 29, 3242.

1602 Organometallics, Vol. 20, No. 8, 2001
Franken et al.
[Fe(CO)2(PMe2Ph)(η5-9-{(E)-N(H)dC(H)Me}-7-CB10
Sch em e 1. P ossible Mech a n ism of F or m a tion of
-
Com p lexes 8-10
H10)] (11). Data characterizing these compounds are
given in Tables 1-3. Evidently formation of 7 and 11
must proceed by two competing pathways. The replace-
ment of a CO group in 1a by PMe2Ph to afford the
precursor 1e increases the electron density of the
system, thus enhancing the hydridic nature of the cage-
BH and thereby allowing in one pathway removal of H-
by H+ and coordination of NCMe to give compound 7.
In the alternative pathway affording complex 11 the
reagent CF3SO3H protonates NCMe to give [HNt
CMe]+, which then reacts according to the steps in
Scheme 1 to yield 11. Since compounds 7 and 11 are
formed in a ratio of about 1:2, protonation of NCMe is
apparently the preferred route.
The presence in 11 of the (E)-N(H)dC(H)Me group is
clearly revealed in the 1H NMR spectrum (Table 2).
Resonances for this moiety are seen in a 3:1:1 intensity
ratio at δ 2.22 (d, Me, J (HH) 5 Hz), 7.84 (dq, dCH,
J (HH) 5, 20 Hz), and 9.10 (d, NH, J (HH) 20 Hz). The
J (HH) coupling of 20 Hz is diagnostic for the H atoms
in a (E)-N(H)dC(H)Me configuration.9 Other signals in
1
the H NMR spectrum are as expected. In the 13C{1H}
NMR spectrum the asymmetry of the molecule results
in two resonances (δ 214.3 and 212.4) for the non-
equivalent CO groups, each a doublet due to 31P-13C
coupling (J (PC) ) 29 and 24 Hz, respectively). There is
a signal at δ 176.1 for the CdN carbon and a broad peak
at δ 47.5 for the cage CH group. A resonance at δ 5.8 in
the 11B{1H} NMR spectrum (Table 3) remains a singlet
in a fully coupled 11B spectrum and can therefore be
assigned to the boron atom bonded to the imine mol-
ecule.
Since the complexes 8-11 are, as far as we are aware,
the first molecules known where an imine group is
substituted on boron in a metallacarborane cage, inves-
tigation of some simple reactions was merited. The
functionality of the imine group is relevant to general
interest in derivatization of carborane frameworks.10
Formally the â-boron-appended [-N(Me)dC(H)Me]+
group carries a positive charge. There are two canonical
forms for the cationic fragment with the charge residing
either on the N atom or on the C atom to which it is
attached, the former naturally being favored. It would
be anticipated therefore that the imine group would
react with nucleophiles such as OH- or H- at the carbon
center, and this was confirmed by experiment. Com-
pound 8 in THF is hydrolyzed by traces of water to yield
the complex [Fe(CO)3(η5-9-NH2Me-7-CB10H10)] (12). This
process is catalyzed by PMe3 or amines, with the former
giving a cleaner product. It is suggested that the
reaction proceeds by the pathway shown in Scheme 2.
Data for compound 12 (Tables 1-3) are in complete
accord with its formulation.
some regiochemical control over this process and neces-
sarily yield the Z-isomer. The nitrogen atom of the imine
so formed then coordinates to the vacant site created
on the â-B vertex to give product 8. As stated the Me
groups are, however, trans in 8 and there was no
evidence from NMR spectroscopy for the presence of any
cis isomer in the crude product mixture. The E-forms
of imines are more stable than the Z-configurations, and
this must favor an evidently facile rearrangement of
Z-N(Me)dC(H)Me into E-N(Me)dC(H)Me shown in
Scheme 1, although geometric isomerization of the
iminium group after it has been bound to the carborane
cage cannot be ruled out.
The formation of compounds 8-10 instead of NCMe
adducts [Fe(CO)2(L)(η5-9-NCMe-7-CB10H10)] is evidently
due to the reagent CF3SO3Me reacting preferentially
with NCMe rather than abstracting H- from the cage.
This is in contrast with the result when the reactants
are 1b, NCBut, and CF3SO3Me, since as described
above, the complex [Fe(CO)2(PPh3)(η5-9-NCBut-7-CB10-
The [-N(Me)dC(H)Me]+ group in 8 was also readily
reduced by [Na][BH3CN], the reagent of choice for
reducing imines and iminium salts.11 The product
obtained from 8 was the complex [Fe(CO)3(η5-9-{NH-
H
10)] (6) is formed. No isolable cage-substitution product
was obtained by treating 1a and NCBut with CF3SO3-
Me. These results suggest that NCBut is not as readily
methylated as NCMe8b and that 1b has a more hydridic
â-BH site than 1a .
(9) J ackman, L. M.; Sternhell, S. Applications of Nuclear Magnetic
Resonance Spectroscopy to Organic Chemistry; Pergamon Press: Ox-
ford, 1969.
(10) Grimes, R. N. Coord. Chem. Rev. 2000, 200-202, 773. Grimes,
R. N. In Contemporary Boron Chemistry; Davidson, M., Hughes, A.
K., Marder, T. B., Wade, K., Eds.; Royal Society of Chemistry:
Cambridge, 2000; pp 283-290.
Interestingly, no reaction occurred when mixtures of
1a and NCMe were treated with CF3SO3H, there being
no products formed akin to 6 or 8. However, complex
1e did react under these conditions, affording a mixture
of [Fe(CO)2(PMe2Ph)(η5-9-NCMe-7-CB10H10)] (7) and

Iminium Groups at a Boron Vertex
Organometallics, Vol. 20, No. 8, 2001 1603
Ta ble 6. Selected In ter n u clea r Dista n ces (Å) a n d An gles (d eg) for [F e(CO)3(η5-9-{NH(Me)Et}-7-CB10H10)]
(13)
Fe-C(4)
Fe-B(5)
B(3)-N
N-C(5)
1.759(4)
2.145(4)
1.585(4)
1.474(4)
Fe-C(2)
Fe-B(2)
C(2)-O(2)
N-C(7)
1.784(4)
2.159(4)
1.138(4)
1.487(4)
Fe-C(3)
Fe-B(3)
C(3)-O(3)
N-H(1a)
1.801(4)
2.184(3)
1.127(4)
0.86
Fe-C(1)
Fe-B(4)
C(4)-O(4)
2.130(3)
2.185(3)
1.140(4)
C(4)-Fe-C(2)
C(4)-Fe-C(1)
C(4)-Fe-B(5)
C(4)-Fe-B(2)
C(4)-Fe-B(3)
C(4)-Fe-B(4)
N-B(3)-B(8)
N-B(3)-B(4)
O(3)-C(3)-Fe
C(5)-N-B(3)
H(1a)-N-C(5)
94.3(2)
C(4)-Fe-C(3)
C(2)-Fe-C(1)
C(2)-Fe-B(5)
C(2)-Fe-B(2)
C(2)-Fe-B(3)
C(2)-Fe-B(4)
N-B(3)-B(7)
N-B(3)-Fe
89.5(2)
C(2)-Fe-C(3)
91.2(2)
91.73(14)
82.0(2)
159.92(14)
113.0(2)
138.3(2)
92.90(14)
79.91(14)
113.2(2)
126.1(3)
178.3(3)
115.8(2)
98
105.7(2)
151.7(2)
80.6(2)
103.2(2)
150.7(2)
111.2(3)
121.2(2)
178.5(3)
115.7(3)
104
C(3)-Fe-C(1)
C(3)-Fe-B(5)
C(3)-Fe-B(2)
C(3)-Fe-B(3)
C(3)-Fe-B(4)
N-B(3)-B(2)
O(2)-C(2)-Fe
C(5)-N-C(7)
N-C(5)-C(6)
H(1a)-N-B(3)
131.7(2)
165.2(2)
117.3(2)
123.7(3)
178.8(4)
113.4(3)
115.5(3)
107
O(4)-C(4)-Fe
C(7)-N-B(3)
H(1a)-N-C(7)
Sch em e 2. P Me3-Ca ta lyzed Hyd r olysis of
Com p lex 8
F igu r e 3. Structure of [Fe(CO)3(η5-9-{NH(Me)Et}-7-
CB10H10)] (13), showing the crystallographic labeling scheme.
Except for H(1a), hydrogen atoms are omitted for clarity,
and thermal ellipsoids are shown at the 40% probability
level.
eomeric pairs of enantiomers. Additonally the methyl-
ene protons of the NEt group are diastereotopic. Thus
peaks for the NH(Me)(Et) fragment are duplicated,
giving theoretically two resonances for the NMe protons
and four for the methylene protons. Alas due to some
overlap of poorly resolved signals, not all are fully
identified with multiplets at δ 2.66, 2.76, 3.35, and 3.48
for all these protons. The signals due to the CH2Me (δ
1.30) and NH (3.97) protons are also broad but clearly
integrate to six and two hydrogens, respectively. Fur-
thermore, the broad resonance resulting from the cage
CH group also accounts for two protons by integration.
The 13C{1H} NMR spectrum is less cluttered, with two
resonances each for the CH2Me (δ 52.7 and 52.5), NMe
(40.5 and 40.3), and CH2Me (12.7 and 12.6) groups. The
transmittance of the effects of this diastereomeric
asymmetry to the cage CH proton is less evident, with
one signal observed at δ 48.9, albeit broad, and even
less so to the Fe(CO)3 groups, with just one resonance
at δ 207.1. The 11B{1H} NMR spectrum (Table 3) shows
a resonance at δ 12.6, which remained a singlet in a
fully coupled 11B spectrum, a feature diagnostic for a
cage boron carrying an exopolyhedral substituent other
than hydrogen.
(Me)Et}-7-CB10H10)] (13), the nature of which was
established by a single-crystal X-ray diffraction study.
The molecule is shown in Figure 3, and selected
structural parameters are listed in Table 6. The pres-
ence of the NH(Me)Et group attached to a â-boron atom
in the pentagonal CBBBB ring ligating the iron is
clearly evident (B(3)-N ) 1.585(4) Å). Atom H(1A) was
located in a difference Fourier synthesis. The N atom
is a chiral center which, coupled with the planar
chirality imposed by substitution at one of the â-B
vertexes in the CBBBB ring, gives rise to two diaster-
(11) Hutchins R. O. In Comprehensive Organic Synthesis; Trost, B.
M., Fleming, I., Eds.; Pergamon (Elsevier): Oxford, 1991; Vol. 8,
Section 1.2.
We have previously shown that reactions between the
ruthenacarborane [Ru(CO)2(THF)(η5-7,8-C2B9H11)] and

1604 Organometallics, Vol. 20, No. 8, 2001
Franken et al.
alkynes RCtCH result in insertion of the organic
moiety into a cage BH to yield products containing R-
or â-B-(E)-C(H)dC(H)R groups.12 The likely pathway
for the process involves initial displacement of THF from
the precursor to give a Ru(η2-RCtCH) complex, which
rearranges into RudCdC(H)R. The vinylidene moiety
then inserts into a BH bond. It was of interest therefore
to determine if 1a would react in a similar manner with
an alkyne of the type RCtCH.
Treatment of 1a in THF with ButCtCH, in the
presence of Me3NO, which was added to facilitate
removal of a CO molecule, afforded a product formulated
as [N(PPh3)2][Fe(CO)2(η2:η5-n-{(E)-C(H)dC(H)But}-7-
CB10H10)] (14, with n ) 8 or 9), a species closely related
to the neutral dicarbollide ruthenium compound [Ru-
(CO)2(η2:η5-n-{(E)-C(H)dC(H)But}-7,8-C2B9H10)] (iso-
mers, n ) 9 and 10).12 Careful examination of the NMR
spectra of the salt 14 revealed that only one isomer was
formed, but the data did not permit a distinction to be
made between attachment of the (E)-C(H)dC(H)But
group to a B atom in an R (n ) 8) site and attachment
in a â (n ) 9) site with respect to the carbon in the
F igu r e 4. Structure of [Fe(CO)2(η2:η5-8-{(E)-C(H)dC(H)-
But}-10-{(E)-N(Me)dC(H)Me}-7-CB10H9)] (16), showing the
crystallographic labeling scheme. Except for H(5a) and
H(4a), hydrogen atoms are omitted for clarity, and thermal
ellipsoids are shown at the 40% probability level.
metal-coordinated CBBBB ring. Moreover, compound
14 was invariably formed contaminated with the
salts [N(PPh3)2][closo-2-CB10H11] and [N(PPh3)2][nido-
7-CB10H13]. Repeated chromatography of the mixture
failed to yield a satisfactory microanalytical sample.
However, a mass spectrum showed the molecular ion
[14]+ (Table 1), and NMR data (Tables 2 and 3)
established the presence of a B-C(H)dC(H)But group
Ch a r t 2
1
(11B{1H} NMR spectrum: δ 12.6). The H-1H coupling
constant (J (HH) ) 11 Hz) for the alkenyl protons
B-C(H)dC(H)But in the 1H NMR spectrum is some-
what smaller than that expected for a trans configura-
tion and almost suggestive of a cis arrangement of this
fragment. These isomers had not been previously ob-
served in the ruthenacarborane work,12 and clearly
firmer structural verification was required.
A derivative of complex 14 was prepared by reaction
with PPh3. The product obtained, [N(PPh3)2][Fe(CO)2-
(PPh3)(η5-n-{(E)-C(H)dC(H)But}-7-CB10H10)] (15), could
be isolated pure and was characterized by microanalysis
and by its NMR spectra (Tables 1-3), although again
the site of attachment (n ) 8 or 9) of the B-C(H)dC(H)-
1
But group to the cage system was unresolved. The H
NMR spectral data were, however, more conclusive with
regard to the configuration of the η2-alkenyl group. With
a
1H-1H coupling constant for the B-C(H)dC(H)But
protons J (HH) ) 18 Hz, the trans arrangement would
seem to be confirmed, as geometric isomerization during
the reaction with PPh3 is extremely unlikely. Conver-
sion of 14 into 15 occurs with a lifting of the η2
coordination of the B-(E)-C(H)dC(H)But moiety to the
iron, a reaction step previously observed in reactions
with dicarbollide ruthenium species.12
The site of attachment of the (E)-C(H)dC(H)But group
to the cage system in 14 and 15 was resolved by a single-
crystal X-ray diffraction study on the molecule [Fe(CO)2-
(η2:η5-8-{(E)-C(H)dC(H)But}-10-{(E)-N(Me)dC(H)Me}-
7-CB10H9)] (16). This complex was prepared by treating
compound 14 in NCMe with CF3SO3Me. The structure
is shown in Figure 4, and selected bond distances and
angles are given in Table 7. The (E)-C(H)dC(H)But
group is bonded to an R-boron vertex (B(2)-C(4) )
1.527(5) Å), from which it may reasonably be inferred
that it is also bonded in this manner in complexes 14
and 15. The trans arrangements of both the η2-alkenyl
(torsion angle B(2)-C(4)-C(5)-C(6) 171.9(3)°) and
the iminium (torsion angle C(11)-C(10)-N-C(12)
178.6(6)°) fragments are confirmed. The alkenyl hydro-
gen atoms H(4a) and H(5a) were located from difference
1
Fourier syntheses and displayed a 14 Hz H-1H cou-
pling in the 1H NMR spectrum (Table 2), which is within
the limits for trans-alkenyl protons.9 The η2 ligation of
the iron by the double bond of the vinyl group (C(4)-
C(5) ) 1.386(5) Å, Fe-C(4) ) 2.129(3) Å, Fe-C(5) )
2.289(3) Å) is similar to that found by X-ray diffraction
(12) Anderson, S.; Mullica, D. F.; Sappenfield, E. L.; Stone, F. G. A.
Organometallics 1996, 15, 1676.

Iminium Groups at a Boron Vertex
Organometallics, Vol. 20, No. 8, 2001 1605
Ta ble 7. Selected In ter n u clea r Dista n ces (Å) a n d An gles (d eg) for
[F e(CO)2(η2: η5-8-{(E)-C(H)dC(H)Bu t}-10-{(E)-N(Me)dC(H)Me}-7-CB10H9)] (16)
Fe-C(3)
Fe-C(4)
Fe-C(5)
C(3)-O(3)
N-C(10)
1.753(4)
2.129(3)
2.289(3)
1.144(4)
1.278(6)
Fe-C(2)
1.776(4)
2.148(4)
1.527(5)
0.96
Fe-B(2)
Fe-B(4)
B(4)-N
2.034(4)
2.181(4)
1.559(5)
1.386(5)
Fe-C(1)
2.121(3)
2.190(3)
1.149(5)
0.91
Fe-B(5)
Fe-B(3)
B(2)-C(4)
C(4)-H(4A)
N-C(12)
C(2)-O(2)
C(5)-H(5A)
C(4)-C(5)
1.467(6)
C(3)-Fe-C(2)
C(3)-Fe-C(1)
C(2)-Fe-C(4)
C(3)-Fe-B(5)
C(3)-Fe-B(4)
C(3)-Fe-B(3)
C(3)-Fe-C(5)
C(1)-Fe-C(5)
B(4)-Fe-C(5)
N-B(4)-B(3)
O(2)-C(2)-Fe
H(4A)-C(4)-C(5)
H(5A)-C(5)-C(4)
C(5)-C(4)-Fe
C(4)-C(5)-Fe
C(10)-N-B(4)
91.7(2)
C(3)-Fe-B(2)
C(2)-Fe-C(1)
B(2)-Fe-C(4)
C(2)-Fe-B(5)
C(2)-Fe-B(4)
C(2)-Fe-B(3)
C(2)-Fe-C(5)
C(4)-Fe-C(5)
B(3)-Fe-C(5)
N-B(4)-B(5)
O(3)-C(3)-Fe
H(4A)-C(4)-B(2)
H(5A)-C(5)-C(6)
B(2)-C(4)-Fe
C(6)-C(5)-Fe
C(12)-N-B(4)
122.8(2)
C(2)-Fe-B(2)
142.1(2)
167.3(2)
122.7(2)
129.7(2)
88.7(2)
83.9(2)
103.3(2)
83.50(14)
156.48(14)
127.2(3)
177.9(4)
117
99.6(2)
43.0(2)
84.4(2)
113.8(2)
161.5(2)
86.4(2)
36.27(13)
112.09(14)
119.5(3)
176.4(4)
118
C(3)-Fe-C(4)
C(1)-Fe-C(4)
C(4)-Fe-B(5)
C(4)-Fe-B(4)
C(4)-Fe-B(3)
B(2)-Fe-C(5)
B(5)-Fe-C(5)
C(4)-B(2)-Fe
N-B(4)-Fe
100.1(2)
78.81(14)
123.9(2)
122.3(2)
75.82(14)
71.73(14)
126.4(2)
71.8(2)
117.2(3)
121.6(4)
111
C(5)-C(4)-B(2)
H(4A)-C(4)-Fe
H(5A)-C(5)-Fe
C(4)-C(5)-C(6)
C(10)-N-C(12)
N-C(10)-C(11)
119
112
97
78.2(2)
65.6(2)
128.2(4)
65.2(2)
128.5(3)
115.2(3)
124.9(4)
116.6(4)
128.8(5)
with the dicarbollide ruthenium species [Ru(CO)2(η2:η5-
9-{(E)-C(H)dC(H)But}-7,8-C2B9H10)].12
7-CB10H13] was synthesized from 7-NMe3-nido-7-CB10H12 ac-
cording to the method of Knoth et al.13 The complex [N(PPh3)2]-
[Fe(CO)3(η5-7-CB10H11)] was prepared according to literature
methods.1c
Con clu sion s
Syn th esis of [N(P P h 3)2][F e(CO)2(L)(η5-7-CB10H11)] (L )
SMe2, P Me2P h ). (i) Compound 1a (0.40 g, 0.50 mmol) was
dissolved in SMe2 (10 mL), and Me3NO (0.15 g, 2.00 mmol)
was added. The mixture was stirred for 24 h, solvent removed
in vacuo, and the residue treated with CH2Cl2 (15 mL). After
filtration through a Celite plug, ca. 2 g of silica gel was added
to the filtrate. Solvent was removed in vacuo, affording a
yellow brownish powder, which was transferred to the top of
a chromatography column. Elution with pure CH2Cl2 gave a
yellow fraction. Removal of solvent in vacuo yielded yellow
microcrystals of [N(PPh3)2][Fe(CO)2(SMe2)(η5-7-CB10H11)] (1d )
(0.34 g).
The substituent on the cage in the charge-compen-
sated complexes 2-6 formally reduces the charge on the
3-
[nido-7-CB10H11
]
ligands present in their precursors
from -3 to -2. This allows the design of new ferracar-
borane reagents of FeII for further syntheses and the
preparation of new complexes with different combina-
tions of functional groups ligating the iron. The syn-
thesis of the iminium derivatives 8-11 using the
reagents CF3SO3X (X ) Me or H) makes possible further
derivatization of the cage system by reactions at the
iminium group. There is a definite trend in these
substitutions for attack and replacement of a â-B-H
(ii) The compound [N(PPh3)2][Fe(CO)2(PMe2Ph)(η5-7-CB10H11)]
(1e) (0.33 g) was similarly obtained from 1a (0.40 g, 0.50 mmol)
and PMe2Ph (0.35 g, 5.00 mmol).
Syn th esis of [F e(CO)2(SMe2)(η5-9-L′-7-CB10H10)] (L′ )
SMe2, O(CH2)4). (i) Compound 1d (0.42 g, 0.50 mmol) was
dissolved in SMe2 (20 mL) and concentrated H2SO4 (0.50 mL)
added. After stirring for 24 h solvent was removed in vacuo,
and the residue treated with CH2Cl2 (15 mL). After filtration
through a Celite plug, ca. 2 g of silica gel was added to the
filtrate. Solvent was removed in vacuo affording a yellow
powder, which was transferred to the top of a chromatography
column. Elution with a mixture of CH2Cl2-petroleum ether
(3:2) gave a yellow fraction. Removal of solvent in vacuo gave
yellow microcrystals of [Fe(CO)2(SMe2)(η5-9-SMe2-7-CB10H10)]
(2) (0.10 g).
(ii) Compound 1d (0.42 g, 0.50 mmol) in THF (20 mL) was
stirred with concentrated H2SO4 (0.50 mL) for 24 h. The
remaining THF was removed in vacuo, and the residue
(polymerized THF and product) was treated with CH2Cl2 (15
mL). After filtration through a Celite plug and removal of
solvent yellow microcrystals of [Fe(CO)2(SMe2)(η5-9-O(CH2)4-
7-CB10H10)] (3) (0.15 g) were obtained.
bond in the CBBBB ring. The reactions result from a
direct hydride abstraction by X+ from CF3SO3X, and the
cause may be due to a subtle increase in polarity of the
â-Bδ+-Hδ- bonds over the adjacent R-Bδ+-Hδ- bonds.
However, when the substitution reaction proceeds via
a vinylidene insertion of a dCdC(H)But group (i.e.,
hydroboration, as in the formation of complex 14),
R-B-H bonds in the CBBBB ring are apparently
favored. Thus the mechanism of hydroboration may be
less dependent on the polarity of the B-H bonds. The
products formed from the hydride abstraction may
therefore be more kinetically controlled, while the
distribution for hydroboration is more dependent on the
frontier orbital energies; that is, control is thermo-
dynamic.
Exp er im en ta l Section
Syn th esis of [F e(CO)2(P P h 3)(η5-9-L′-7-CB10H10)] (L )
SMe2, O(CH2)4 a n d NCBu t). (i) Compound 1b (0.53 g, 0.50
mmol) was dissolved in CH2Cl2-SMe2 (20 mL, 1:1), and CF3-
SO3H (0.25 mL) was added. After stirring (24 h), solvent was
removed in vacuo and the residue treated with CH2Cl2 (15 mL).
After filtration through a Celite plug, ca. 2 g of silica gel was
added to the filtrate. Solvent was removed in vacuo, affording
Gen er a l Con sid er a tion s. All reactions were carried out
under an atmosphere of dry nitrogen using Schlenk line
techniques. Solvents were distilled from appropriate drying
agents under nitrogen prior to use. Petroleum ether refers to
that fraction of boiling point 40-60 °C. Chromatography
columns (ca. 15 cm in length and ca. 2 cm in diameter) were
packed with silica gel (Acros, 60-200 mesh). NMR spectra
were recorded at the following frequencies: 1H 360.13, 13C
90.56, 31P 145.78, and 11B 115.5 MHz. The salt [NHMe3][nido-
(13) Knoth, W. H.; Little, J . L.; Lawrence, J . R.; Todd, L. J . Inorg.
Synth. 1968, 11, 33.

1606 Organometallics, Vol. 20, No. 8, 2001
Ta ble 8. Da ta for X-r a y Cr ysta l Str u ctu r e An a lyses
Franken et al.
2
8
13
16
cryst dimens (mm)
formula
Mr
0.54 × 0.13 × 0.10
C7H22B10FeO2S2
366.32
0.52 × 0.49 × 0.24
C7H17B10FeNO3
327.17
0.36 × 0.30 × 0.20
C7H19B10FeNO3
329.18
0.70 × 0.36 × 0.29
C12H27B10FeNO2
381.30
cryst color, shape
cryst syst
space group
a (Å)
b (Å)
c (Å)
amber needles
orthorhombic
P212121
6.7065(14)
14.0124(11)
18.680(2)
yellow prisms
monoclinic
P21/c
13.2967(13)
8.978(3)
13.820(3)
109.755(11)
1553
pale-yellow prisms
monoclinic
P21/c
12.325(2)
7.6538(10)
17.502(2)
106.856(14)
1580
orange blocks
orthorhombic
P212121
9.3727(13)
12.8796(8)
16.719(2)
â (deg)
V (Å3)
1755
2018
Z
d
4
4
4
4
calcd (g cm-3
)
1.386
10.89
752
1.400
9.70
664
1.384
9.53
672
1.255
7.52
792
µ(Mo KR) (cm-1
F(000) (e)
)
T (K)
2θ range (deg)
no. of reflns coll (excld stds)
no. of unique reflns
no. of obsd reflns
183(2)
3.6-50.0
3478
3071
2741
183(2)
3.2-50.0
2795
2671
2437
293(2)
3.4-45.0
2171
2059
1771
293(2)
4.0-50.0
2166
2140
1998
refln limits: h, k, l
0 to 7; 0 to 16;
-22 to 22
200
0 to 15; 0 to 10;
-16 to 15
236
0 to 13; 0 to 8;
-18 to 18
202
0 to 11; 0 to 15;
-1 to 19
245
no. of params refined
final residuals wR2 (R1)
all dataa
0.0720 (0.0330)b
0.0936 (0.0399)
0.0838 (0.0335)
0.0817 (0.0311)c
weighting factorsa
a ) 0.0324,
b ) 0.3544
1.040
a ) 0.0336,
b ) 1.0333
1.207
a ) 0.0398,
b ) 1.4400
1.038
a ) 0.0454,
b ) 0.9491
1.056
goodness of fit on F2
final electron density diff
0.232, -0.216
0.352, -0.264
0.336, -0.324
0.293, -0.408
features (max/min)/e Å-3
a
2
Refinement was block full-matrix least-squares on all F2 data: wR2 ) [∑{w(Fo - Fc2)2}/∑w(Fo2)2]1/2 where w-1 ) [σ2(Fo2) + (aP)2
+
bP] where P ) [max(Fo2,0) + 2Fc2]/3. The value in parentheses is given for comparison with refinements based on Fo with a typical
threshold of Fo > 4σ(Fo) and R1 ) ∑||Fo| - | Fc||/∑|Fo| and w-1 ) [σ 2(Fo) + g(Fo2)]. Flack parameter ) 0.47(2). c Flack parameter )
b
0.03(3).
a yellow powder, which was transferred to the top of a
chromatography column. Elution with CH2Cl2-petroleum
ether (3:2) afforded a pale yellow fraction. Removal of solvent
in vacuo gave pale yellow microcrystals of [Fe(CO)2(PPh3)(η5-
9-SMe2-7-CB10H10)] (4) (0.22 g).
yellow microcrystals of [Fe(CO)2(PPh3)(η5-9-{(E)-N(Me)dC(H)-
Me}-7-CB10H10)] (9) (0.24 g).
(iii) Similarly compound 1c (0.43 g, 0.50 mmol) in NCMe
(10 mL) with CF3SO3Me (0.25 mL) yielded pale yellow
microcrystals of [Fe(CO)2(CNBut)(η5-9-{(E)-N(Me)dC(H)Me}-
7-CB10H10)] (10) (0.16 g).
(ii) Similarly 1b (0.53 g, 0.50 mmol) in CH2Cl2-THF (20
mL, 1:1) with CF3SO3H (0.25 mL) yielded pale yellow micro-
crystals of [Fe(CO)2(PPh3)(η5-9-O(CH2)4-7-CB10H10)] (5) (0.23
g).
R ea ct ion s of [F e(CO)3(η5-9-{(E)-N(Me)dC(H )Me}-7-
CB10H10)] (8). (i) Compound 8 (0.16 g, 0.50 mmol) was
dissolved in THF (10 mL), and a PMe3 solution in THF (1.0
M, 2 mL) was added. After stirring for 24 h the solvent was
removed in vacuo, and the residue taken up in CH2Cl2 (15 mL).
Following filtration through a Celite plug, ca. 2 g of silica gel
was added to the filtrate. Solvent was removed in vacuo,
affording a yellow powder, which was transferred to a chro-
matography column. Elution with a mixture of CH2Cl2-NCMe
(24:1) gave a pale yellow fraction. Removal of solvent in vacuo
yielded pale yellow microcrystals of [Fe(CO)3(η5-9-NH2Me-7-
CB10H10)] (12) (0.13 g).
(ii) Similarly, compound 8 (0.16 g, 0.50 mmol) with [Na]-
[BH3CN] (0.06 g, 0.63 mmol) in MeOH (10 mL) yielded pale
yellow microcrystals of [Fe(CO)3(η5-9-{NH(Me)Et}-7-CB10H10)]
(13) (0.14 g) following chromatographic purification eluting
with neat CH2Cl2.
(iii) Compound 1b (0.53 g, 0.50 mmol) in CH2Cl2-NCBut
(10 mL, 4:1) with CF3SO3Me (0.25 mL) yielded pale yellow
microcrystals of [Fe(CO)2(PPh3)(η5-9-NCBut-7-CB10H10)] (6)
(0.18 g).
Syn th esis of [F e(CO)2(P Me2P h )(η5-9-L′-7-CB10H10)] (L′
) NCMe, (E)-N(H)dC(H)Me). Compound 1e (0.46 g, 0.50
mmol) was dissolved in NCMe (10 mL), and CF3SO3H (0.25
mL) was added. After stirring for 24 h, solvent was removed
in vacuo, and the residue was taken up in CH2Cl2 (15 mL).
After filtration through a Celite plug, ca. 2 g of silica gel was
added to the filtrate. Solvent was removed in vacuo, affording
a yellow powder, which was transferred to the top of a
chromatography column. Elution with a mixture of CH2Cl2-
petroleum ether (4:1) gave a pale yellow fraction. Removal of
solvent in vacuo yielded pale yellow microcrystals of [Fe(CO)2-
(PMe2Ph)(η5-9-NCMe-7-CB10H10)] (7) (0.05 g). Further elution
with neat CH2Cl2 removed a yellow fraction. Removal of
solvent in vacuo yielded yellow microcrystals of [Fe(CO)2(PMe2-
Ph)(η5-9-{(E)-N(H)dC(H)Me}-7-CB10H10)] (11) (0.09 g).
Syn th esis of [F e(CO)2(L)(η5-9-{(E)-N(Me)dC(H)Me}-7-
CB10H10)] (L ) CO, CNBu t, P P h 3). (i) Compound 1a (0.40 g,
0.50 mmol) was dissolved in NCMe (10 mL), and CF3SO3Me
(0.25 mL) was added. Using a procedure similar to that which
gave 11, but eluting the chromatography column with CH2-
Cl2-petroleum ether (3:2), afforded pale yellow microcrystals
of [Fe(CO)3(η5-9-{(E)-N(Me)dC(H)Me}-7-CB10H10)] (8) (0.07 g).
(ii) Compound 1b (0.53 g, 0.50 mmol) in CH2Cl2-NCMe (20
mL, 1:1) with CF3SO3Me (0.25 mL) similarly yielded pale
Syn th esis of [N(P P h 3)2][F e(CO)2(η2:η5-8-{(E)-C(H)dC-
(H)Bu t}-7-CB10H10)]. A sample of 1a (0.40 g, 0.50 mmol) was
dissolved in THF (10 mL), and ButCtCH (0.5 mL) and Me3-
NO (0.15 g, 2 mmol) were added and the mixture was stirred
for 24 h. Using a workup method similar to that which gave
compound 12, but eluting the chromatography column with
neat CH2Cl2, gave deep yellow microcrystals of [N(PPh3)2][Fe-
(CO)2(η2:η5-8-{(E)-C(H)dC(H)But}-7-CB10H10)] (14) (0.19 g).
The product is always contaminated with the salts [N(PPh3)2]-
[closo-2-CB10H11] (0.17 g, 51%) and [N(PPh3)2][nido-7-CB10H13
]
(0.01 g, 4%). The yield calculation is based on the relative peak
integrals in the NMR spectra.
Syn th esis of [N(P P h 3)2][F e(CO)2(P P h 3)(η5-8-{(E)-C(H)d
C(H)Bu t}-7-CB10H10)]. Compound 14 (0.43 g of the crude

Iminium Groups at a Boron Vertex
Organometallics, Vol. 20, No. 8, 2001 1607
material) was dissolved in THF (10 mL), and PPh3 (0.52 g,
2.00 mmol) was added. After stirring for 24 h, the solvent was
removed in vacuo, and the residue was treated with CH2Cl2
(15 mL). Following filtration through a Celite plug, ca. 2 g of
silica gel was added to the filtrate. Solvent was removed in
vacuo, affording a yellow powder, which was transferred to a
chromatography column (15 cm). Elution with a neat CH2Cl2
and removal of solvent in vacuo yielded yellow microcrystals
were made by full-matrix least-squares on all F2 data using
SHELXL-97.15 Anisotropic thermal parameters were included
for all non-hydrogen atoms. For all structures, cage carbon
atoms were assigned by comparison of the bond lengths to
adjacent boron atoms in conjunction with the magnitudes of
their isotropic thermal parameters. With the exception of H(1a)
in 13 along with H(4), H(5a), and H(10a) in 16, all hydrogen
atoms were included in calculated positions and allowed to ride
on their parent boron or carbon atoms with fixed isotropic
thermal parameters (Uiso ) 1.2Uiso of the parent atom or Uiso
) 1.5Uiso for methyl protons). The remaining hydrogens, H(1a)
in 13 and H(4a), H(5a), and H(10a) in 16, were located in
difference Fourier syntheses. The positional parameters of
these hydrogens were allowed to refine while their isotropic
thermal parameters were constrained to 1.2Uiso of the parent
nitrogen or carbon atoms. The pendant iminium group in
compound 8 was disordered over two distinct sites in 73:27
and 52:48% ratios, respectively. The absolute configurations
of compounds 2 and 16 were determined by examination of
the appropriate Flack parameters (Table 8, footnotes b and
c).16 All calculations were carried out on Dell PC computers.
of [N(PPh3)2][Fe(CO)2(PPh3)(η5-8-{(E)-C(H)dC(H)But}-7-CB10
10)] (15) (0.25 g).
Syn th esis of [F e(CO)2(η2:η5-8-{(E)-C(H)dC(H)Bu t}-10-
-
H
{(E)-N(Me)dC(H)Me}-7-CB10H9)]. Using the same procedure
as that described for the synthesis of 8, compound 14 (0.22 g,
0.25 mmol) in NCMe (10 mL) with CF3SO3Me (0.25 mL)
yielded deep yellow microcrystals of [Fe(CO)2(η2:η5-8-{(E)-
C(H)dC(H)But}-10-{(E)-N(Me)dC(H)Me}-7-CB10H9)] (16) (0.04
g).
Cr ysta l Str u ctu r e Deter m in a tion s a n d Refin em en ts.
Experimental data for 2, 8, 13, and 16 are shown in Table 8.
Diffracted intensities were collected on an Enraf-Nonius
CAD-4 diffractometer using graphite-monochromated Mo KR
X-radiation operating in the ω-1/3θ (13), ω-2/3θ (8), ω-4/3θ (16),
and ω-5/3θ (2) scan modes. Final unit cell dimensions were
determined from the setting angles of 25 accurately centered
reflections. Crystal stability during the data collection was
monitored by measuring the intensities of three standard
reflections every 2 h. Low-temperature data (183 K) were
collected at a varied rate of 4.13-5.17 deg min-1 in ω with a
scan range of 1.05 + 0.34 tan θ for 2 and a constant speed of
5.17 deg min-1 in ω with a scan range of 1.40 + 0.34 tan θ for
8. Room-temperature data were collected at a constant speed
of 5.17 deg min-1 in ω with a scan range of 1.25 + 0.34 tan θ
for 13 and 16. The data were corrected for Lorentz, polariza-
tion, and X-ray absorption effects, the last using a numerical
method based on the measurements of crystal faces.
Ack n ow led gm en t. We thank Professor Roger Alder
for helpful discussions in connection with the work
involving nitriles and the Robert A. Welch Foundation
for support (Grant AA-1201).
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates and U values, bond lengths and angles, and
anisotropic thermal parameters and ORTEP diagrams for 2,
8, 13, and 16 in CIF format. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM001057X
(14) SHELXTL version 5.03, Bruker AXS: Madison, WI, 1995.
(15) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen: Go¨t-
tingen, Germany, 1997.
The structures were solved by direct methods, and succes-
sive difference Fourier syntheses were used to locate all non-
hydrogen atoms using SHELXTL version 5.03.14 Refinements
(16) Flack, H. D. Acta Crystallogr. 1983, A39, 876.