1,1-diboration of isocyanides with [2] borametalloarenophanes

Article abstract of DOI:10.1021/om9009813

A series of new [3]diboracarbametalloarenophanes was synthesized by reaction of [2]borametalloarenophanes or [3]diboraplatinametalloarenophanes with isocyanides and was fully characterized by multinuclear NMR spectroscopy and, in the case of [Fe{η⁵-C₅H₄B(NMe ₂)}₂C=N-t-Bu], additionally by X-ray diffraction analysis.

Full text of DOI:10.1021/om9009813

934 Organometallics 2010, 29, 934–938
DOI: 10.1021/om9009813
1,1-Diboration of Isocyanides with [2]Borametalloarenophanes
Florian Bauer, Holger Braunschweig,* and Katrin Schwab
€
Institut fu€r anorganische Chemie, Julius-Maximilians-Universitat Wurzburg, Am Hubland, 97074
€
Wu€rzburg, Germany
Received November 10, 2009
A series of new [3]diboracarbametalloarenophanes was synthesized by reaction of [2]borametallo-
arenophanes or [3]diboraplatinametalloarenophanes with isocyanides and was fully characterized by
multinuclear NMR spectroscopy and, in the case of [Fe{η5-C5H4B(NMe2)}2CdN-t-Bu], additionally by
X-ray diffraction analysis.
Introduction
as CatB-BCat (1) or PinB-BPin (2) (Figure 1) and a late-
transition-metal catalyst.3 The list of possible substrates ranges
from alkynes3a,4 to alkenes,4b,e,5 CO,5d,6 NN,7 and R,β-unsa-
turated carbonyl compounds.4f,8 It is noteworthy that in one
case an unusual 1,1-diboration of a vinylboronate was ob-
served.5l In contrast to these well-established transformations,
very little is known about the corresponding diboration of
isocyanides and only from instances where the B-B bond of
the diboration reagent is part of a strained heterocycle rather
than an acyclic diborane(4).
Paetzold et al. reported the insertion of isocyanides9 and of
the isoelectronic CO10 into the highly strained B-B bond of
tri-tert-butylazadiboriridine (3) (Figure 1). Depending on
the size of the isocyanide, monomeric or dimeric products
were isolated, whereas in the case of the smaller CO only
dimeric compounds were obtained. The postulated mecha-
nism for the formation of the latter includes initial genera-
tion of the monomeric insertion product and subsequent
intermolecular attack at one of the boron atoms by the
nucleophilic oxygen or nitrogen center (Scheme 1).
Over the past two decades transition-metal-catalyzed hydro-
boration starting from moderately reactive boranes such as
CatBH and PinBH (Cat=1,2-O2C6H4, Pin=OCMe2CMe2O)
has become a well-established protocol for the functionaliza-
tion of organic substrates.1 Likewise, the use of diboranes(4)
R2B-BR2 for the borylation or diboration of unsaturated
hydrocarbons represents a facile method for the generation
of organoboranes, many of which are key intermediates
in organic synthesis.2 This method commonly employs a
catalytic protocol involving rather stable diboranes(4) such
*To whom correspondence should be addressed. E-mail:
h.braunschweig@mail.uni-wuerzburg.de. Fax: þ49-(0)931/888-4623.
Tel: þ49-(0)931/31-85260.
(1) (a) Burgess, K.; Ohlmeyer, M. J. Chem. Rev. 1991, 91, 1179–1191.
(b) Torrent, M.; Sola, M.; Frenking, G. Chem. Rev. 2000, 100, 439–493. (c)
Braunschweig, H.; Colling, M. Coord. Chem. Rev. 2001, 223, 1–51. (d)
Crudden, C. M.; Edwards, D. Eur. J. Org. Chem. 2003, 4695–4712. (e)
Carroll, A. M.; O0Sullivan, T. P.; Guiry, P. J. Adv. Synth. Catal. 2005, 347,
609–631. (f) Vogels, C. M.; Westcott, S. A. Curr. Org. Chem. 2005, 9, 687–
699. (g) Miyaura, N. Bull. Chem. Soc. Jpn. 2008, 81, 1535–1553. (h)
Thomas, S. P.; Aggarwal, V. K. Angew. Chem., Int. Ed. 2009, 48, 1896–
1898.
A similar reactivity with respect to the insertion of CO and
isocyanides, respectively, into a B-B bond was reported
(2) (a) Marder, T. B.; Norman, N. C. Top. Catal. 1998, 5, 63–73. (b)
Matos, K.; , Burkhardt, E. R., Chim. Oggi 2005, 23, 12-13, 15; (c)
Ishiyama, T.; Miyaura, N. Pure Appl. Chem. 2006, 78, 1369–1375. (d)
Burks, H. E.; Morken, J. P. Chem. Commun. 2007, 4717–4725. (e) Tobisu,
M.; Chatani, N. Angew. Chem., Int. Ed. 2009, 48, 3565–3568. (f) Dang, L.;
Lin, Z.; Marder, T. B. Chem. Commun. 2009, 3987–3995. (g) Beletskaya, I.;
Moberg, C. Chem. Rev. 2006, 106, 2320–2354. (h) Ishiyama, T.; Miyaura, N.
Chem. Rec. 2004, 3, 271–280. (i) Ramirez, J.; Lillo, V.; Segarra, A. M.;
Fernandez, E. C. R. Chim. 2007, 10, 138–151. (j) Marder, T. B. In Specialist
Periodical Reports: Organometallic Chemistry; Fairlamb, I. J. S., Lynam,
J. M., Eds.; Royal Society of Chemistry: Cambridge, U.K., 2008; Vol. 34, pp
46-57.
(3) (a) Ishiyama, T.; Matsuda, N.; Miyaura, N.; Suzuki, A. J. Am.
Chem. Soc. 1993, 115, 11018–11019. (b) Baker, R. T.; Nguyen, P.; Marder,
T. B.; Westcott, S. A. Angew. Chem., Int. Ed. 1995, 34, 1336–1338.
(4) (a) Ishiyama, T.; Matsuda, N.; Murata, M.; Ozawa, F.; Suzuki,
A.; Miyaura, N. Organometallics 1996, 15, 713–720. (b) Lesley, M. J. G.;
Nguyen, P.; Taylor, N. J.; Marder, T. B.; Scott, A. J.; Clegg, W.; Norman, N. C.
Organometallics 1996, 15, 5137–5154. (c) Iverson, C. N.; Smith, M. R.III
Organometallics 1996, 15, 5155–5165. (d) Thomas, R. L.; Souza, F. E. S.;
Marder, T. B. J. Chem. Soc., Dalton Trans. 2001, 1650–1656. (e) Marder,
T. B.; Norman, N. C.; Rice, C. R. Tetrahedron Lett. 1998, 39, 155–158. (f)
Lawson, Y. G.; Lesley, M. J. G.; Norman, N. C.; Rice, C. R.; Marder, T. B.
Chem. Commun. 1997, 2051–2052. (g) Braunschweig, H.; Kupfer, T.; Lutz,
M.; Radacki, K.; Seeler, F.; Sigritz, R. Angew. Chem., Int. Ed. 2006, 45,
8048–8051.
(5) (a) Anderson, K. M.; Lesley, M. J. G.; Norman, N. C.; Orpen,
A. G.; Starbuck, J. New J. Chem. 1999, 23, 1053–1055. (b) Baker, T.;
Nguyen, P.; Marder, T. B.; Westcott, S. A. Angew. Chem., Int. Ed. 1995, 34,
1336–1338. (c) Corberan, R.; Ramirez, J.; Poyatos, M.; Peris, E.; Fernandez,
E. Tetrahedron: Asymmetry 2006, 17, 1759–1762. (d) Dang, L.; Zhao, H.;
Lin, Z.; Marder, T. B. Organometallics 2008, 27, 1178–1186. (e) Ishiyama,
T.; Yamamoto, M.; Miyaura, N. Chem. Commun. 1996, 2073–2074. (f)
Ishiyama, T.; Yamamoto, M.; Miyaura, N. Chem. Commun. 1997, 689–690.
(g) Ishiyama, T.; Momota, S.; Miyaura, N. Synlett 1999, 1790–1792. (h)
Iverson, C. N.; Smith, M. R.III Organometallics 1997, 16, 2757–2759. (i)
Lillo, V.; Fructos, M. R.; Ramirez, J.; Braga, A. A. C.; Maseras, F.; Mar Diaz-
Requejo, M.; Perez, P. J.; Fernandez, E. Chem. Eur. J. 2007, 13, 2614–2621.
(j) Mann, G.; John, K. D.; Baker, R. T. Org. Lett. 2000, 2, 2105–2108. (k)
Morgan, J. B.; Miller, S. P.; Morken, J. P. J. Am. Chem. Soc. 2003, 125,
8702–8703. (l) Nguyen, P.; Coapes, R. B.; Woodward, A. D.; Taylor, N. J.;
Burke, J. M.; Howard, J. A. K.; Marder, T. B. J. Organomet. Chem. 2002,
652, 77–85. (m) Ramirez, J.; Corberan, R.; Sanau, M.; Peris, E.; Fernandez,
E. Chem. Commun. 2005, 3056–3058. (n) Trudeau, S.; Morgan, J. B.;
Shrestha, M.; Morken, J. P. J. Org. Chem. 2005, 70, 9538–9544.
(6) (a) Laitar, D. S.; Mueller, P.; Sadighi, J. P. J. Am. Chem. Soc.
2005, 127, 17196–17197. (b) Laitar, D. S.; Tsui, E. Y.; Sadighi, J. P. J. Am.
Chem. Soc. 2006, 128, 11036–11037. (c) Zhao, H.; Lin, Z.; Marder, T. B.
J. Am. Chem. Soc. 2006, 128, 15637–15643.
(7) Braunschweig, H.; Kupfer, T. J. Am. Chem. Soc. 2008, 130, 4242–
4243.
r
pubs.acs.org/Organometallics
Published on Web 01/14/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 4, 2010 935
Scheme 1. Reaction of Tri-tert-butylazadiboriridine with
Isocyanides
Figure 1. Precursors for diboration reactions.
by Siebert et al. in 1998.11 They presented corresponding
reactions of the strained 1,2-diboracyclopent(3)ene
4
(Figure 1), which led to monomeric products due to the
steric demand of the isocyanides and the boron-bound
moiety. Again, insertion of CO into the B-B bond afforded
dimeric products. While few of these dimeric species have
been structurally characterized, the constitution of the initial
insertion products was only derived from multinuclear
NMR spectroscopy in solution. The insertion of small
molecules such as alkynes in particular was also observed
for [2]silametalloarenophanes. Thus, transition-metal-
catalyzed 1,2-disilation of C-C triple bonds by [2]disila-
ferrocenophanes was first reported by Manners et al. in
1992,12 whereas our group studied the insertion of propyne
into the Si-Si bond of [2]silachromoarenophanes in 2007.13
In recent years, a number of [2]borametalloarenophanes
have been reported and their reactivity toward insertion
reactions into the B-B bond has been studied. The
[2]boraferrocenophane 5 (Figure 1), initially synthesized by
Wrackmeyer and Herberhold in 199714 and subsequently
structurally characterized,15 constitutes the first example of
these species, followed by the [2]borachromoarenophane 6
(Figure 1), which we synthesized in 2004.16 Since then,
various [2]borametalloarenophanes have been synthesized
from different transition metals such as V,17 Cr,18 and Mn.19
It was revealed that [2]borametalloarenophanes display a
certain degree of molecular strain that renders the B-B bond
very reactive, in particular with respect to oxidative addition
to low-valent transition metals: i.e., platinum. Therefore,
they have already proven ideal precursors for the functiona-
lization of organic substrates such as alkynes4g or diazo
compounds7 via transition-metal-catalyzed diboration.
(8) (a) Ito, H.; Yamanaka, H.; Tateiwa, J.; Hosomi, A. Tetrahedron
Lett. 2000, 41, 6821–6825. (b) Ali, H. A.; Goldberg, I.; Srebnik, M.
Organometallics 2001, 20, 3962–3965. (c) Takahashi, K.; Ishiyama, T.;
Miyaura, N. Chem. Lett. 2000, 982–983. (d) Takahashi, K.; Ishiyama, T.;
Miyaura, N. J. Organomet. Chem. 2001, 625, 47–53. (e) Kabalka, G. W.;
Das, B. C.; Das, S. Tetrahedron Lett. 2002, 43, 2323–2325. (f) Bell, N. J.;
Cox, A. J.; Cameron, N. R.; Evans, J. S. O.; Marder, T. B.; Duin, M. A.;
Elsevier, C. J.; Baucherel, X.; Tulloch, A. A. D.; Tooze, R. P. Chem.
Commun. 2004, 1854–1855. (g) Hirano, K.; Yorimitsu, H.; Oshima, K.
Org. Lett. 2007, 9, 5031–5033. (h) Mun, S.; Lee, J. E.; Yun, J. Org. Lett.
2006, 8, 4887–4889. (i) Lee, J. E.; Kwon, J.; Yun, J. Chem. Commun. 2008,
733–734. (j) Lee, J. E.; Yun, J. Angew. Chem., Int. Ed. 2008, 47, 145–147.
(k) Dang, L.; Lin, Z.; Marder, T. B. Organometallics 2008, 27, 4443–4454.
(l) Shiomi, T.; Adachi, T.; Toribatake, K.; Zhou, L.; Nishiyama, H. Chem.
Commun. 2009, 5987–5989. (m) Gao, M.; Thorpe, S. B.; Santos, W. L. Org.
Lett. 2009, 11, 3478–3481. (n) Chea, H.; Sim, H. S.; Yun, J. Adv. Synth.
Catal. 2009, 351, 855–858. (o) Lee, K. S.; Zhugralin, A. R.; Hoveyda, A. H.
J. Am. Chem. Soc. 2009, 131, 7253–7255.
Results and Discussion
Herein we present a series of new [3]diboracarba-
metalloarenophanes that were obtained (i) by reaction of
isocyanides with [2]borametalloarenophane and alterna-
tively (ii) from a [3]diboraplatinametalloarenophane. We
also present the first molecular structure of a monomeric
1,1-diborated isocyanide.
The new complexes 9-12 are formed by adding the isocya-
nide to a solution of the respective [2]borametalloarenophane
(9) Luckert, S.; Eversheim, E.; Mueller, M.; Redenz-Stormanns, B.;
Englert, U.; Paetzold, P. Chem. Ber. 1995, 128, 1029–1035.
(10) Paetzold, P.; Redenz-Stormanns, B.; Boese, R. Angew. Chem.
1990, 102, 910–911.
(11) Teichmann, J.; Stock, H.; Pritzkow, H.; Siebert, W. Eur. J. Inorg.
Chem. 1998, 459–463.
(12) Finckh, W.; Tang, B. Z.; Lough, A.; Manners, I. Organometallics
1992, 11, 2904–2911.
(13) Braunschweig, H.; Kupfer, T. Organometallics 2007, 26, 4634–
4638.
€
(14) Herberhold, M.; Dorfler, U.; Wrackmeyer, B. J. Organomet.
(15) Braunschweig, H.; Seeler, F.; Sigritz, R. J. Organomet. Chem.
2007, 692, 2354–2356.
(16) Braunschweig, H.; Homberger, M.; Hu, C.; Zheng, X.; Gullo, E.;
Clentsmith, G. K. B.; Lutz, M. Organometallics 2004, 23, 1968–1970.
(17) (a) Braunschweig, H.; Lutz, M.; Radacki, K.; Schaumloeffel, A.;
Seeler, F.; Unkelbach, C. Organometallics 2006, 25, 4433–4435. (b)
Braunschweig, H.; Kaupp, M.; Adams, C. J.; Kupfer, T.; Radacki, K.;
Schinzel, S. J. Am. Chem. Soc. 2008, 130, 11376–11393.
(18) Braunschweig, H.; Lutz, M.; Radacki, K. Angew. Chem., Int. Ed.
2005, 44, 5647–5651.
(19) Braunschweig, H.; Kupfer, T.; Radacki, K. Angew. Chem., Int.
Chem. 1997, 530, 117–120.
Ed. 2007, 46, 1630–1633.

936 Organometallics, Vol. 29, No. 4, 2010
Bauer et al.
Scheme 2. Syntheses of 9-12 Starting from
[2]Borametalloarenophanes
activation of the B-B bond), as commonly observed for the
metal-mediated 1,2-diboration of alkynes. In fact, the use of
7 or 8 as diborane(4) precursors requires harsher conditions
and the reaction mixtures have to be heated to 80 °C so as to
achieve completion. This finding indicates that the release of
molecular strain, as observed for the conversion of 5 and 6
(but not in the case of 7 and 8) into the final products,
contributes to the driving force of this reaction (vide infra).
Insertion of an isocyanide with its stereochemically active
lone pair at the nitrogen center into the B-B bond of the
[2]borametallocenophanes leads to an unsymmetrical bridge
and thus a decrease of the molecular symmetry from C2v to
C1. Hence, in contrast to only two singlets for the NMe2
protons at 2.78 and 2.82 ppm found for 5, complexes 9 and 10
1
display four singlets each in the H NMR spectra between
2.57 and 2.84 ppm (9) and between 2.62 and 2.88 ppm (10).
The Cp-bound protons of 9 and 10 show eight multiplets
ranging from 4.04 to 4.38 ppm and from 4.02 to 4.38 ppm,
respectively. The protons of the t-Bu group of 9 show a
singlet at 1.44 ppm which is shifted downfield with respect to
the resonance at 0.91 ppm for t-BuNC.20 Likewise, the CH
proton of 10 can be detected at 3.31 ppm and thus appears
deshielded with respect to the corresponding signal at 2.91
ppm for CyNC,21 while the remaining protons of the cyclo-
hexyl ring show four complex multiplets between 1.35 and
2.04 ppm.
Scheme 3. Syntheses of 9-12 Starting from
[3]Diboraplatinametalloarenophanes
As discussed before in the cases of 9 and 10, the 1H NMR
spectra of 11 and 12 also exhibit four resonances for the
NMe2 protons between 2.60 and 2.83 ppm (11) and between
2.65 and 2.89 ppm (12), respectively, in contrast to only two
signals found for 6 at 2.80 and 2.84 ppm.
In the 13C NMR spectra of all new complexes the ipso
carbon atoms of the metal-bound aromatic rings could not
be detected, due to quadrupolar broadening induced by the
neighboring boron nuclei. This has already been observed in
the corresponding [4]diboradicarbametalloarenophanes.4g
However, the quaternary carbon atoms of the imine group
were detected as very broad signals between 198 and 204 ppm
in long-range 13C-1H NMR correlation experiments. As
expected and already discussed for the 1H NMR spectra, the
decrease of symmetry in the products with respect to the
starting materials 5 and 6 leads to a corresponding multitude
of resonances in the 13C NMR spectra.
in hexanes at room temperature (Scheme 2). It should be noted
that according to multinuclear NMR spectroscopy no soluble
side products are formed during these reactions, thus indicating
quantitative conversion of the starting materials. The pure
compounds can be obtained in yields of 28-55% as orange
to reddish brown crystals by cooling the respective reaction
solution to -30 °C. Nonetheless, complete removal of the
reaction solvent or concentration of the reaction solution in
vacuo has to be omitted, as it leads partially to a powdery
material of poor solubility, which probably suggests the for-
mation of an oligomeric compound, comparable to the dimeric
species depicted in Scheme 1. However, attempts to generate a
defined dimerization product of 9 or 10 by drying the reaction
mixture and redissolving the solid residue repeatedly led to
product mixtures. The aforementioned pure, crystalline com-
pounds 9-12 proved to be inert toward oligomerization in the
solid state and are readily soluble in aliphatic and aromatic
solvents. Likewise, dilute solutions of these species showed no
tendency toward aggregation at ambient temperature over a
period of several days. Compounds 9 and 10 also display a
moderate stability to air and moisture, whereas 11 and 12 tend
to undergo rapid hydrolysis.
With regard to the 11B NMR spectra, one should also
expect to see two different signals due to C1 symmetry of the
products. That is indeed the case for 9, which shows two
signals at 38.9 and 42.1 ppm, and 11, which displays two
signals at 40.0 and 43.8 ppm. However, for 10 and 12 only
one very broad signal at 40.6 and 41.1 ppm, respectively,
could be resolved. As expected, the 11B NMR resonances of
all four compounds exhibit a slight upfield shift compared to
those of the starting compounds 5 at 44.4 ppm and 6 at 46.3
ppm, as already observed in case of the [4]diboradicarba-
metalloarenophanes mentioned before.4g
Single crystals of 9 suitable for X-ray analysis were ob-
tained by crystallization from hexanes (Figure 2). The struc-
tural data prove that the isocyanide substrate is diborated in
a 1,1-fashion, in contrast to corresponding reactions with
alkynes that are diborated in a 1,2-fashion.
An alternative access to 9-12 is provided by the reaction
of [3]diboraplatinametalloarenophanes 7 and 8 (Figure 1)
with the corresponding isocyanides (Scheme 3). Surprisingly,
this reaction is not facilitated by the precoordination of the
boryl groups to the platinum center (i.e., the metal-induced
(20) Quast, H.; Meichsner, G.; Seiferling, B. Chem. Ber. 1987, 120,
217–223.
(21) Fukuda, T.; Homma, S.; Kobayashi, N. Chem. Commun. 2003,
1574–1575.

Article
Organometallics, Vol. 29, No. 4, 2010 937
of a monomeric diborated isocyanide, i.e.[Fe{η5-C5H4B-
(NMe2)}2CdN-t-Bu], was conducted.
Experimental Section
All manipulations were performed under an inert atmosphere
of argon using standard Schlenk and glovebox techniques.
Solvents were distilled from molten alkali metal, degassed,
˚
and stored over molecular sieves (4 A) under argon. Deuterated
solvents were degassed by three freeze-pump-thaw cycles
and stored under argon. [Fe{η5-C5H4B(NMe2)}2] (5),14 [Cr-
{η5-C6H5B(NMe2)}2] (6),16 [Fe{η5-C5H4B(NMe2)}2Pt(PEt3)2]
(7),4g and [Cr{η6-C6H5B(NMe2)}2Pt(PEt3)2] (8)4g were prepared
according to known methods. The isocyanides were purchased
from Aldrich and used without further purification.
Figure 2. Molecular structure of 9. Hydrogen atoms are omitted
for clarity. Thermal ellipsoids represent 50% probability. Selected
bond lengths (A) and angles (deg): C1-B1 = 1.582(5), C2-B2=
1.569(5), B1-N1=1.386(4), B2-N2=1.387(5), B1-C3=1.597(5),
B2-C3 = 1.606(5), C3-N3 = 1.291(4), N3-C4 = 1.478(4);
C1-B1-C3 = 117.3(3), C2-B2-C3 = 116.6(3), B1-C3-B2=
111.5(3), B1-C3-N3 = 115.7(3), B2-C3-N3 = 132.7(3), C3-
N3-C4 = 123.9(3), R = 5.4, δ = 176.2 (see text).
NMR experiments were performed on a Bruker Avance 200
(1H, 200.130 MHz; 11B, 64.210 MHz; 31P, 81.014 MHz) or a
Bruker Avance 500 (1H, 500.130 MHz; 11B, 160.462 MHz; 13C,
125.758 MHz). 1H NMR and 13C NMR spectra were calibrated
˚
to TMS; in the case of 11B NMR experiments BF3 OEt2 was
3
used as the external standard. Elemental analyses were per-
formed on a Vario Micro Cube elemental analyzer.
Due to the toxicity and the very unpleasant odor of the
isocyanides, all glassware was washed with HClaq./EtOH
(1:10) after use.
As expected, the degree of molecular strain in 9 is less
pronounced than in the starting material 5, due to the
extension of the bridge from two to three atoms. Thus, the
tilt angle R, which describes the mutual inclination of the
metal-bound cyclopentadienyl rings, is reduced from 12.8°
for 5 to 5.4°. This value is comparable to that of 5.0° found
for the [3]diboraplatinaferrocenophane 7, which is also
characterized by a bridging unit consisting of three atoms.4g
Likewise, the angle centroid(1)-Fe-centroid(2) of 176.2° is
enlarged in comparison to that of 5 (170.1°), thus resembling
the corresponding value of 7 (175.7°) and indicating an
almost nonstrained, ferrocene-like geometry. The cyclo-
pentadienyl rings exhibit a slightly staggered conformation,
as indicated by a torsion angle Cp centroid(1)-C1-C2-Cp
centroid(2) of 12.2° that falls between the corresponding
values for 5 (16.0°) and 7 (6.0°). The B-C-B bridge adopts a
folded conformation: i.e., the N1 and N2 atoms are situated
opposite to the C3 center with respect to the plane defined by
Synthesis of [Fe{η5-C5H4B(NMe2)}2CdN-t-Bu] (9). (a) To a
stirred solution of 100 mg (0.340 mmol) of [Fe{η5-C5H4B-
(NMe2)}2] (5) in 5 mL of hexanes was added 39 μL (28.3 mg) of
t-BuNC via syringe. In doing so, the color of the solution changed
from orange-redtoorange. Thesolutionwasfilteredandcooledto
-30 °C for 3 d. The precipitate was isolated by decanting the
cooled mother liquor, predried under a stream of argon, and
subsequently dried in vacuo. The product was isolated as an
orange powdery solid (53 mg, 0.139 mmol, 41%) and analyzed
by multinuclear NMR spectroscopy. Single crystals suitable for
X-ray diffraction analysis were obtained by redissolving the solid
in hexanes and allowing the solvent to evaporate slowly.
(b) A 20 mg portion (0.028 mmol) of [Fe{η5-C5H4B-
(NMe2)}2Pt(PEt3)2] (7) was dissolved in 0.5 mL of benzene-d6,
and a drop of t-BuNC was added. The solution was heated to
80 °C, and the reaction progress was monitored by NMR
spectroscopy. The color of the solution thereby changed from
orange-red to orange. After 1 h no signals for 7 could be observed.
1H NMR (500.130 MHz, C6D6): δ 1.44 (s, C(CH3)3, 9H), 2.57
(s, NCH3, 3H), 2.61 (s, NCH3, 3H), 2.64 (s, NCH3, 3H), 2.84 (s,
NCH3, 3H), 4.04 (m, C5H4, 1H), 4.08 (m, C5H4, 1H), 4.18 (m,
C5H4, 1H), 4.20 (m, C5H4, 1H), 4.29 (m, C5H4, 1H), 4.30 (m,
C5H4, 1H), 4.33 (m, C5H4, 1H), 4.38 ppm (m, C5H4, 1H).
11B{1H} NMR (160.462 MHz, C6D6): δ 38.9 (br), 42.1 ppm
(br). 13C{1H} NMR (125.758 MHz, C6D6): δ 30.3 (C(CH3)3),
39.6 (NCH3), 40.5 (NCH3), 40.7 (NCH3), 41.7 (NCH3), 61.5
(C(CH3)3), 69.9 (C5H4), 70.5 (C5H4), 70.7 (C5H4), 71.4 (C5H4),
71.6 (C5H4), 72.0 (C5H4), 74.4 (C5H4), 76.6 (C5H4), 199 ppm
(B2CN-t-Bu). Anal. Calcd for C19H29B2FeN3 (376.92): C, 60.54;
H, 7.75; N, 11.15. Found: C, 60.44; H, 7.57; N, 10.58.
˚
B1, Fe, and B2. The C-N bond length of 1.291(4) A and
the C3-N3-C4 angle of 123.9(3)° lie in the expected range
for a corresponding imine double bond.22 The overall geo-
metry of the cyclopentadienyl rings is normal, and likewise,
the atoms B1, B2, and C3 display the expected planar
coordination, as indicated by angle sums of 359.9, 359.0,
and 359.9°, respectively.
Conclusions
Synthesis of [Fe{η5-C5H4B(NMe2)}2CdNCy] (10). (a) A 100
mg portion (0.340 mmol) of 5 was dissolved in 5 mL of hexanes.
When 42 μL (37.2 mg) of CyNC was added via syringe, the color
of the solution changed from orange-red to orange. The solution
was filtered and cooled to -30 °C for 3 d. The cooled mother
liquor was decanted, and the formed solid was predried under a
stream of argon and then dried in vacuo. The product was
isolated as an orange-red solid (75 mg, 0.187 mmol, 55%) and
analyzed by multinuclear NMR spectroscopy.
(b) A 20 mg (0.028 mmol) portion of 7 was dissolved in 0.5 mL
of benzene-d6, and 1 drop of CyNC was added. The solution was
heated to 80 °C, and the reaction progress was monitored by
NMR spectroscopy. The color of the solution changed thereby
from orange-red to orange. After 1 h no signals for 7 could be
observed.
To conclude, we have described the four new, fully chara-
cterized [3]diboracarbametalloarenophanes [M{ηn-CnHn-1
B(NMe2)}2CdNR] (M=Fe, n=5, R=t-Bu, Cy; M=Cr,
n=6, R=t-Bu, Cy). These new species were synthesized by
two different ways: i.e., by 1,1-diboration of the isocyanide
RNC (R = t-Bu, Cy) with a [2]borametalloarenophane
[M{ηn-CnHn-1B(NMe2)}2] (M=Fe, n=5; M=Cr, n=6)
or a [3]diboraplatinametalloarenophane [M{ηn-CnHn-1B-
(NMe2)}2Pt(PEt3)2] (M = Fe, n = 5; M = Cr, n = 6).
In addition to that, the first X-ray diffraction study
(22) Ruiz-Valero, C.; Gutierrez-Puebla, E.; Monge, A. Acta Crystal-
logr., Sect. C: Cryst. Struct. Commun. 1983, C39, 793–794.

938 Organometallics, Vol. 29, No. 4, 2010
Bauer et al.
1H NMR (500.130 MHz, C6D6): δ 1.35-1.49 (m, CyCH , 3H),
(b) A 20 mg portion (0.027 mmol) of 8 was dissolved in 0.5 mL
of benzene-d6, and a drop of CyNC (excess) was added. The
solution was heated to 80 °C, and the reaction progress was
monitored by NMR spectroscopy. The color of the solution
changed thereby from dark red to red. After 1 h no signals for 8
could be observed.
2
1.65 (m, CyCH , 1H), 1.90 (m, CyCH , 1H), 1.93-2.04 (m, CyCH
,
2
2
2
6H), 2.62 (s, NCH3, 3H), 2.65 (s, NCH3, 3H), 2.67 (s, NCH3,
3H), 2.88 (s, NCH3, 3H), 3.31 (m, CyCH, 1H), 4.02 (m, C5H4,
1H), 4.05 (m, C5H4, 1H), 4.22 (m, C5H4, 2H), 4.28 (m, C5H4,
2H), 4.36 (m, C5H4, 1H), 4.38 ppm (m, C5H4, 1H). 11B{1H}
NMR (160.462 MHz, C6D6): δ 40.6 ppm (vbr). 13C{1H} NMR
(125.758 MHz, C6D6): δ 25.0 (CyCH ), 25.0 (CyCH ), 26.6
1H NMR (500.130 MHz, C6D6): δ 1.35-1.48 (m, CyCH , 3H),
2
1.64 (m, CyCH , 1H), 1.86-2.14 (m, CH2 Cy, 6H), 2.65 (s, NCH3,
2
2
2
(CyCH ), 34.3 (CyCH ), 35.8 (CyCH ), 39.9 (NCH3), 40.4
3H), 2.70 (s, NCH3, 3H), 2.70 (s, NCH3, 3H), 2.89 (s, NCH3,
3H), 3.41 (m, CyCH, 1H), 4.20 (m, C6H5, 1H), 4.30 (m, C6H5,
1H), 4.42 (m, C6H5, 6H), 4.55 (m, C6H5, 1H), 4.75 ppm (m,
C6H5, 1H). 11B{1H} NMR (160.462 MHz, C6D6): δ 41.1 ppm
(vbr). 13C{1H} NMR (125.758 MHz, C6D6): δ 25.0 (C6H11), 25.2
(C6H11), 26.6 (C6H11), 34.2 (C6H11), 36.2 (C6H11), 40.0 (NCH3),
40.5 (NCH3), 40.5 (NCH3), 41.8 (NCH3), 71.1 (C6H11 CH),
75.3 (C6H5), 75.6 (C6H5), 76.3 (C6H5), 76.5 (C6H5), 76.6
(C6H5), 76.6 (C6H5), 76.7 (C6H5), 77.5 (C6H5), 78.4 (C6H5),
79.9 (C6H5), 201 ppm (vbr, B2CNCy). Anal. Calcd for
C23H33B2CrN3 (415.15): C, 64.97; H, 7.82; N, 9.89. Found: C,
64.02; H, 7.82; N, 9.89.
2
2
2
(NCH3), 40.6 (NCH3), 41.6 (NCH3), 70.0 (C5H4), 70.0 (C5H4),
70.5 (C5H4), 71.0 (CyCH), 71.2 (C5H4), 71.4 (C5H4), 71.9 (C5H4),
74.4 (C5H4), 75.6 (C5H4), 203 ppm (vbr, B2CNCy). Anal. Calcd
for C21H31B2FeN3 (402.96): C, 62.59; H, 7.75; N, 10.43. Found:
C, 62.58; H, 7.77; N, 10.31.
Synthesis of [Cr{η6-C6H5B(NMe2)}2CdN-t-Bu] (11). (a) To a
stirred solution of 100 mg (0.316 mmol) of [Cr{η5-C6H5B-
(NMe2)}2] (6) in 5 mL of hexanes was added 36 μL (26.3 mg)
of t-BuNC via syringe. In doing so, the color of the solution
changed from red to orange-red. The solution was filtered and
cooled to -30 °C for 3 d. The cooled mother liquor was
decanted, and the precipitate was first dried under a stream of
argon and then in vacuo, yielding the product as a reddish
brown powdery solid (39 mg, 0.098 mmol, 31%) that was
analyzed by multinuclear NMR spectroscopy.
Crystal Structure Determination. The crystal data of 9 were
collected on a Bruker D8 diffractometer with an Apex CCD area
detector and graphite-monochromated Mo KR radiation. The
structure was solved using direct methods, refined with the Shelx
software package,23 and expanded using Fourier techniques. All
non-hydrogen atoms were refined anisotropically. Hydrogen
atoms were assigned idealized positions and were included in
structure factor calculations.
(b) A 20 mg portion (0.027 mmol) of [Cr{η6-C6H5B-
(NMe2)}2Pt(PEt3)2] (8) was dissolved in 0.5 mL of benzene-d6,
and 1 drop of t-BuNC was added. The solution was then heated
to 80 °C, and the reaction progress was monitored by NMR
spectroscopy. The color of the solution changed thereby from
dark red to red. After 1 h no signals for 8 could be observed.
1H NMR (500.130 MHz, C6D6): δ 1.45 (s, C(CH3)3, 9H), 2.60
(s, NCH3, 3H), 2.62 (s, NCH3, 3H), 2.69 (s, NCH3, 3H), 2.83 (s,
NCH3, 3H), 4.23 (m, C6H5, 2H), 4.40 (m, C6H5, 6H), 4.56 ppm
(m, C6H5, 2H). 11B{1H} NMR (160.462 MHz, C6D6): δ 40.0
(br), 43.8 ppm (br). 13C{1H} NMR (125.758 MHz, C6D6): δ 30.4
(C(CH3)3), 39.6 (NCH3), 40.5 (NCH3), 41.0 (NCH3), 42.0
(NCH3), 61.7 (C(CH3)3), 75.3 (C6H5), 76.4 (C6H5), 76.4
(C6H5), 76.5 (C6H5), 76.7 (C6H5), 76.8 (C6H5), 76.9 (C6H5),
77.6 (C6H5), 78.0 (C6H5), 81.0 (C6H5), 197 ppm (B2CN-t-Bu).
Anal. Calcd for C21H31B2CrN3 (399.11): C, 63.19; H, 7.83; N,
10.53. Found: C, 62.66; H, 7.74; N, 10.15.
Crystal data for 9: C19H29B2FeN3, Mr=376.92, yellow plate,
0.24 ꢀ 0.15 ꢀ 0.03 mm3, monoclinic, space group P21/n, a=
˚
˚
˚
9.8191(10) A, b=20.866(2) A, c=9.8839(10) A, β=106.474(2)°,
V=1941.9(3) A , Z=4, Fcalcd=1.289 g cm-3, μ=0.782 mm-1
,
3
˚
F(000)=800, T=168(2) K, R1=0.0843, wR2=0.1304, 3873
independent reflections (2θ e 52.34°), 233 parameters.
Crystallographic data have been deposited with the
Cambridge Crystallographic Data Center as supplementary
publication no. CCDC-753234. These data can be obtained free
of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgment. We thank the Deutsche Forschun-
gsgemeinschaft (DFG) and the Fonds der chemischen
Industrie (FCI) for financial support.
Synthesis of [Cr{η6-C6H5B(NMe2)}2CdNCy] (12). (a) A 100
mg portion (0.316 mmol) of 6 was dissolved in 5 mL of hexanes,
and 39 μL (34.5 mg) of CyNC was added via syringe, whereupon
the color of the solution changed from red to orange-red.
The solution was filtered and cooled to -30 °C for 3 d. The
cooled mother liquor was decanted, and the precipitate was
predried under a stream of argon and afterward dried in vacuo.
The product was isolated as a dark red solid in a yield of 38 mg
(0.088 mmol, 28%) and analyzed by multinuclear NMR
spectroscopy.
Supporting Information Available: A CIF file giving crystal-
lographic data for compound 9. This material is available free of
charge via the Internet at http://pubs.acs.org.
(23) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
2008, A64, 112–122.