Imido-supported borohydrides of titanium, vanadium and molybdenum

Article abstract of DOI:10.1002/ejic.201201351

New imido bis(borohydride) complexes [(RN=)M(PMe₃) ₂(η²-BH₄)₂] [R = Ar, M = Ti (3); R = Ar, M = V (5); R = Ar, M = Mo (6); R = Ar′, M = Mo (7); Ar = 2,6-iPr₂C₆H₃, Ar′ = 2,6-Me ₂C₆H₃] were prepared by the reaction of dichlorides [(RN=)MCl₂(PMe₃)_n] (M = Ti, n = 2; M = V, n = 2, M = Mo, n = 3) with LiBH₄ (2 equiv) in THF. Compounds 3, 5, 6 and 7 were studied by IR spectroscopy and X-ray diffraction, and an EPR spectroscopy study was performed for paramagnetic compound 5. In 3, the two borohydride units are orthogonal to each other as a result of the overlap of an antiphase combination of B-H orbitals with the empty d_xy orbital of Ti. In contrast, the d_xy orbital of the metal atom is singly occupied in 5 and fully occupied in 6 and 7, and both borohydride ligands are oriented in the same way, with the B(μ-H₂)M moieties orthogonal to the P-M-P vector. Copyright

Full text of DOI:10.1002/ejic.201201351

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DOI:10.1002/ejic.201201351
Imido-Supported Borohydrides of Titanium, Vanadium and
Molybdenum
Andrey Y. Khalimon,[a] Erik Peterson,[a] Christian Lorber,[b,c]
Lyudmila G. Kuzmina,[d] Judith A. K. Howard,[e] Art van der Est,[a]
and Georgii I. Nikonov*[a]
Keywords: Borohydrides / Imides / Titanium / Vanadium / Molybdenum
New imido bis(borohydride) complexes [(RN=)M(PMe3)2(η2-
BH4)2] [R = Ar, M = Ti (3); R = Ar, M = V (5); R = Ar, M = Mo
(6); R = ArЈ, M = Mo (7); Ar = 2,6-iPr2C6H3, ArЈ = 2,6-
Me2C6H3] were prepared by the reaction of dichlorides
[(RN=)MCl2(PMe3)n] (M = Ti, n = 2; M = V, n = 2, M = Mo, n
= 3) with LiBH4 (2 equiv) in THF. Compounds 3, 5, 6 and 7
were studied by IR spectroscopy and X-ray diffraction, and
an EPR spectroscopy study was performed for paramagnetic
compound 5. In 3, the two borohydride units are orthogonal
to each other as a result of the overlap of an antiphase combi-
nation of B–H orbitals with the empty dxy orbital of Ti. In
contrast, the dxy orbital of the metal atom is singly occupied
in 5 and fully occupied in 6 and 7, and both borohydride
ligands are oriented in the same way, with the B(μ-H2)M
moieties orthogonal to the P–M–P vector.
tion. The chemistry of imido-supported metal hydrides is
relatively undeveloped.[10] Herein we report some of our ef-
forts in preparing Group 4–6 metal hydride complexes.
Introduction
The imido ligand RN2– has received significant attention
as a useful spectator ligand owing to its isolobal relation-
ship with the ubiquitous cyclopentadienyl (Cp) ligand and
owing to the ease of tuning its electronic and steric proper-
ties by changing the imido R group.[1,2] However, the imido
ligand can be a potential reactive site, which, for instance, is
evidenced in the coupling reactions with CO2,[3] alkynes,[4]
imines[5] and silanes.[6,7] Our groups are interested in de-
veloping the catalytic chemistry of (imido)early-transition-
metal complexes,[4,6,8,9] which would circumvent the notori-
ous cost and toxicity problems pertinent to late-transition-
metal catalysts. In particular, we are interested in studying
imido-supported hydride complexes that could be precata-
lysts or reactive intermediates in catalytic reductions, such
as hydrosilylation,[9a,9b,9d,9e] hydroboration[9c] or hydrogena-
Results and Discussion
Titanium
We have recently shown that the hydride complex
[(ArN=)Mo(PMe3)3(Cl)(H)] (1, Ar = 2,6-iPr2C6H3) cataly-
ses the hydrosilylation of carbonyl substrates.[9a] By taking
into account that the covalent radius of molybdenum
(1.29 Å) is comparable to that of titanium (1.32 Å),[11] we
targeted the preparation of the corresponding titanium
complexes [(ArN=)Ti(PMe3)n(Cl)(H)], which we expected
to have interesting catalytic properties. Attempted direct
substitution of the chlorido ligand in the precursor complex
[(ArN=)Ti(PMe3)2(Cl)2] (2) for the hydrido ligand by
L-Selectride {Li[CH(CH3)CH2CH3]3BH}, a method that
worked well in the preparation of complex 1, resulted in an
intractable mixture of products. The treatment of 2 with
tBuOK followed by addition of H3SiPh also resulted in a
mixture of products, but the silane was not consumed, and
there was no evidence for the hydride complex in the NMR
spectroscopic data. In a separate set of experiments, we
found that 2 does not react with H3SiPh but reacts slowly
with tBuOK to give a mixture of unidentified products. Use
of a smaller alkoxide (LiOEt) resulted in decomposition of
the Ti complex and evolution of free phosphane.
[a] Chemistry Department, Brock University,
500 Glenridge Ave.,
St. Catharines, ON, L2S 3A1, Canada
E-mail: gnikonov@brocku.ca
Homepage: http://www.brocku.ca/mathematics-science/
departments-and-centres/chemistry/people/faculty/
georgii-i-nikonov
[b] CNRS, LCC (Laboratoire de Chimie de Coordination),
205, route de Narbonne, BP 44099, 31077 Toulouse Cedex 4,
France
[c] Université de Toulouse, UPS, INPT,
31077 Toulouse Cedex 4, France
[d] N. S. Kurnakov Institute of General and Inorganic Chemistry,
31 Leninskii Prosp., Moscow 119991, Russia
[e] Chemistry Department, University of Durham,
South Road, Durham DH1 3LE, UK
To prepare a masked form of the hydride, we treated
complex 2 with 1 equiv. of LiBH4. This reaction resulted in
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201201351.
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a 1:1 mixture of the starting complex 2 and the bis(boro- versus 2.4836(19) Å, respectively. In contrast, the dz2 orbital
hydride) [(ArN=)Ti(PMe3)2(η2-BH4)2] (3). When 2 equiv. of of the (ArN)Ti(PMe3)2 fragment is strongly antibonding
LiBH4 were used, complex 3 was obtained as the sole prod- with respect to the Ti–N σ-bond and hence is lying higher
uct [Equation (1)]. Complex 3 belongs to the very small in energy than dxy, which results in a weaker bonding with
class of (imido)transition-metal borohydride com- the B(1)H4 ligand. In other known borohydride complexes
pounds,[2c,2d,12–15] and is only the second example of an of titanium, the η2-coordinated BH4 ligands show Ti–B dis-
(imido)Ti borohydride that has been structurally charac- tances comparable with that in 3 {e.g., 2.37(1) Å in
terized.[15]
[Cp2Ti(η2-BH4)][18]}, whereas the η3-borohydride groups
give rise to much shorter contacts, such as 2.17(1) Å in
[CpClTi(η3-BH4)][19] and 2.265(8) Å in the imido borohyd-
ride complex [Ti(NAr){ArNC(Me)CHC(Me)CHtBu}(η3-
BH4)].[15] Similar short Ti–B contacts [2.27(1) Å] are also
observed for the B–H side-on-coordinated borohydrido li-
gand in complex [Ti(PMe3)2(BH4)3].[20]
(1)
Complex 3 was characterized by NMR and IR spec-
troscopy, and its structure was confirmed by X-ray analysis.
1
The H NMR spectrum (C6D6, 23 °C) shows iPr signals at
δ = 4.34 (sept, J = 6.9 Hz, 2 H, CHMe2) and 1.33 ppm (d,
J = 6.9 Hz, 12 H, CHMe2) and a doublet (J = 7.2 Hz, 18
H) for the PMe3 ligands at δ = 1.06 ppm. The borohydrido
ligands give rise to a broad feature in the range δ = 0.0–
1.5 ppm overlapped with the iPr and PMe3 signals. Decou-
pling from 11B leads only to a marginal sharpening of the
signal, presumably due to the exchange between the bridg-
ing and terminal hydrido ligands. The presence of phos-
phane was confirmed by a 31P NMR spectroscopic signal
at δ = –21.0 ppm. The borohydrido ligand has a typical up-
field 11B{1H} spectroscopic resonance at δ = –11.4 ppm (t,
JB,P = 85.7 Hz) showing coupling to two equivalent phos-
phanes.
The molecular structure of 3 is shown in Figure 1. The
geometry can be described as pseudo-trigonal-bipyramidal
if one considers the borohydride groups as occupying one
site each in the basal plane and two mutually trans phos-
phane ligands being in the apical positions. Since a crystal-
lographic plane of symmetry runs through the nitrogen, the
titanium and two boron atoms, the phosphane groups are
equivalent. The Ti–P distance of 2.5834(3) Å is normal. The
Ti=N distance of 1.7203(12) Å is close to the mean imido–
titanium bond of 1.722 Å (average of 339 structures in the
CCDC, in the range 1.656–1.962 Å).[8b,16] Interestingly, the
two borohydrido ligands are twisted relative to each other,
so that one of the TiH2B units lies in the TiB2N plane, and
the other is orthogonal to this plane and roughly coplanar
with the P–P axis. The phosphane ligands deviate from the
latter borohydride, so that the P(1)–Ti(1)–P(1a) bond angle
of 159.33(2)° is significantly less than straight. This differ-
ence in borohydride orientation results in an overlap with
different d orbitals of titanium and leads to different Ti–B
bond lengths. If one assumes that the z axis lies along the
Ti–N vector and that the x axis is collinear with the P–PЈ
vector, then the hydride atoms of ligand B(1) overlap with
the dz2 orbital (Scheme 1a), whereas borohydride B(2) over-
Figure 1. Molecular structure of complex 3. Hydrogen atoms ex-
–
cept for those of the BH4 ligands are omitted for clarity. Selected
bond lengths [Å] and angles [°]: Ti(1)–P(1)[P(1a)] 2.5834(3), Ti(1)–
N(1) 1.7203(12), Ti(1)–B(1) 2.4836(19), Ti(1)–B(2) 2.345(2); P(1)–
Ti(1)–P(1a) 159.33(2), B(1)–Ti(1)–B(2) 119.47(8), B(1)–Ti(1)–
P(1)[P(1a)] 81.675(11), B(2)–Ti(1)–P(1)[P(1a)] 99.408(11), N(1)–
Ti(1)–P(1)[P(1a)] 90.865(12), N(1)–Ti(1)–B(1) 131.02(6), N(1)–
Ti(1)–B(2) 109.51(7).
Scheme 1. Selected orbital interactions in 3 for the interaction of
the borohydride ligands with the titanium atom.
Attempts to convert complex 3 into an active hydride
laps with the dxy orbital (Scheme 1b).[17] Because the empty form were unsuccessful. Complex 3 does not undergo BH3
dxy orbital of Ti is not shared with any other ligand, the abstraction with added PMe3, nor does it react with PhSiH3
Ti–B(2) bond is shorter than the Ti–B(1) bond, 2.345(2) in the absence or presence of phosphane.
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Vanadium
the Ti–B distance to the borohydrido ligand in 3 that has
the same orientation. These structural features can be ex-
plained by the single occupancy of the dxy orbital shown in
Scheme 1b. Two phosphane ligands of 5 are related by a
crystallographic symmetry plane. The V–P bond is
2.4782(5) Å, a value slightly lower than that in the related
[V(=NAr)Cl2(PMe2Ph)2] [2.489(2) and 2.517(2) Å].[17] The
V=N imido bond of 1.6835(15) Å is in the expected
range;[17,23,24] however, it is shorter than the Ti=N bond in
3 [1.7203(12) Å], despite the ionic radius of five-coordinate
vanadium(IV) being marginally larger than the ionic radius
of titanium(IV), 0.53 versus 0.51 Å, respectively.[25] We be-
lieve that the difference in the imido–metal bond lengths in
3 and 5 may reflect the different orientation of the borohyd-
rido ligands.
Similar to the titanium complex, reaction of [(ArN=)-
V(PMe3)2(Cl)2] (4, Ar 2,6-iPr2C6H3) with LiBH4
(2 equiv.) leads to the bis(borohydride) [(ArN=)V(PMe3)2-
(η2-BH4)2] (5), [Equation (2)]. Complex 5 has a d1 configu-
ration and thus is EPR-active.
=
(2)
The room-temperature EPR spectrum of 5 is shown in
Figure 2 along with its simulation. The spectrum is similar
to that of the previously reported rare example of a (imido)-
bis(phosphane)VIV complex[21] and consists of eight over-
lapping 1:2:1 triplets. The pattern arises from coupling to
the I = 7/2 51V nucleus and two equivalent I = 1/2 31P nu-
clei. The simulation yields giso = 1.977, Aiso(51V) =
216 MHz (7.71 mT) and Aiso(31P) = 98.3 MHz (3.51 mT).
Hyperfine splittings from the imido nitrogen atom and
hydrido protons are too small to be resolved.
Figure 3. Molecular structure of complex 5. Hydrogen atoms ex-
cept for BH4– ligands are omitted for clarity. Selected bond lengths
[Å] and angles [°]: V(1)–N(1) 1.6835(15), V(1)–P(1)[P(1a)]
2.4782(5), V(1)–B(1) 2.432(2), V(1)–B(2) 2.419(3); P(1)–V(1)–P(1a)
172.50(2), B(1)–V(1)–B(2) 119.24(9), B(1)–V(1)–P(1)[P(1a)]
86.571(13), B(2)–V(1)–P(1)[P(1a)] 90.352(13), N(1)–V(1)–B(1)
123.88(8), N(1)–V(1)–B(2) 116.88(9), N(1)–V(1)–P(1)[P(1a)]
93.170(11).
Figure 2. Room-temperature EPR spectrum of 5 and its simulation.
Molybdenum
Borohydrides [(ArN=)Mo(PMe3)2(η2-BH4)2] (6) and
[(ArЈN=)Mo(PMe3)2(η2-BH4)2] (7, ArЈ = 2,6-Me2C6H3)
were prepared by the addition of LiBH4 (2 equiv) in THF
to the dichloride precursors [(RN=)Mo(Cl)2(PMe3)3] [R =
ArЈ and Ar, respectively; Equation (3)].
The molecular structure of 5 is shown in Figure 3. Al-
though the overall appearance is similar to that of complex
3, there is an essential structural difference. Namely, both
borohydride moieties are oriented in the same way so that
the VH2B units are orthogonal to the VNP2 plane, with two
bridging ligands from opposite borohydride groups lying
trans to each other and two other bridging hydrido ligands
trans to the imido ligand. As a result, the V–H(bridge)
bonds are very different: 1.856 and 1.857 Å for the mutually
trans hydrido ligands and 1.999 and 2.048 Å for the hydrido
ligands trans to imido. The two V–B distances in 5 are very
close: 2.432(2) and 2.419(3) Å[22] and are comparable with
(3)
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The higher solubility of derivative 6 in nonpolar solvents
allowed for its easy extraction with hexanes to furnish, after
filtration and removal of volatiles, the compound in 51%
isolated yield. Complex 7 was isolated in 67% yield by
means of extraction with toluene and recrystallization from
Et2O. Both 6 and 7 were characterized by NMR and IR
1
spectroscopy, and X-ray analyses. The H NMR spectra of
6 and 7 show broad resonances for the BH4 groups at δ =
–0.02 and –0.03 ppm, respectively. Lowering the tempera-
ture allowed for observation of separate signals for the
bridging and terminal hydrido ligands at δ = –5.43 (br. s, 2
H, B–Hbridge) and –1.16 ppm (br. s, 2 H, B–Hterm) for 6 and
at δ = –5.38 (br. s, 2 H, B–Hbridge) and –1.10 ppm (br. s, 2
H, B–Hterm) for 7. 31P NMR spectra for both 6 and 7 do
not show any significant temperature dependence and fea-
ture a singlet for two equivalent trans-PMe3 groups at δ =
1.1 and 1.9 ppm, respectively. As for related compounds 3
and 5, IR spectra show multiple bands in the B–H region,
in accord with the presence of two η2-coordinated boro-
hydrido ligands: 1950, 1969, 2013, 2102, 2266, 2378, and
2405 cm–1 for 6 and 2111, 2189, 2269, 2371, and 2395 cm–1
for 7.[26] In the large variety of structurally charac-
terized molybdenum, and Group 6 in general, boro-
hydride complexes,[27] compounds 6 and 7 are only the sec-
ond and third examples, respectively, of (imido)Mo boro-
hydrides.[14]
The molecular structure of 6 is shown in Figure 4. The
structure of its ArЈ analogue 7 is very similar and is given
in the Supporting Information. Complex 6 is isostructural
with vanadium complex 5, with both borohydride groups
orthogonal to the MoNP2 plane and one bridging hydrido
atom of each Mo(μ-H)2B unit lying trans to the imido
group. The trans-PMe3 ligands are coplanar with the other
two hydrido ligands of two Mo(μ-H)2B groups. The Mo(1)–
Figure 4. Molecular structure of complex 6. Hydrogen atoms ex-
–
cept for the BH4 ligands are omitted for clarity. Selected bond
lengths [Å] and angles [°]: Mo(1)–N(1) 1.7434(15), Mo(1)–P(1)
2.4918(5), Mo(1)–P(2) 2.4905(5), Mo(1)–B(1) 2.468(2), Mo(1)–B(2)
2.481(2);
P(1)–Mo(1)–P(2)
162.586(17),
B(1)–Mo(1)–B(2)
124.07(9), B(1)–Mo(1)–P(1) 85.50(5), B(1)–Mo(1)–P(2) 87.06(5),
B(2)–Mo(1)–P(1) 85.13(6), B(2)–Mo(1)–P(2) 86.05(6), N(1)–
Mo(1)–B(1) 115.94(7), N(1)–Mo(1)–B(2) 119.99(8), N(1)–Mo(1)–
P(1) 99.64(5), N(1)–Mo(1)–P(2) 97.77(5).
Conclusion
Newimidobis(borohydride)complexes[(RN=)M(PMe3)2-
(η2-BH4)2] [R = Ar, M = Ti (3); R = Ar, M = V (5); R =
Ar, M = Mo (6); R = ArЈ, M = Mo (7); Ar = 2,6-iPr2C6H3,
ArЈ = 2,6-Me2C6H3] can be easily prepared by treating the
dichloride precursors with 2 equiv. of LiBH4 in THF. X-ray
studies of 3, 5, 6 and 7 showed mutual trans disposition of
two borohydride groups and two phosphane ligands in all
four structures. However, the geometry of 3 is different from
the others in that one BH2Ti unit is orthogonal to the other
BH2Ti unit. We attribute the difference to the overlap of an
antiphase combination of B–H bonding orbitals with the
empty dxy orbital of the titanium atom. In contrast, dxy is
half-full or full in the other three compounds and is not
available for bonding. Complexes 3, 6 and 7 are surprisingly
stable and do not undergo abstraction of the BH3 unit upon
addition of phosphane.
B(1) and Mo(1)–B(2) distances in
6 [2.468(2) and
2.481(2) Å, respectively] are very similar and lie at the
longer end of the previously characterized molybdenum
borohydride compounds: [Mo0(CO)4(η2-BH4)]– [Mo–B
2.41(2) Å],[27a]
trans-[MoII(PMe3)4H(η2-BH4)]
[Mo–B
2.468(12) Å],[27b] [Mo0(η7,η1-C7H6-2-C6H4PiPr2)(η2-BH4)]
(Mo–B 2.358 Å),[27c] [Mo0(η-C7H7)(PCy3)(η2-BH4)] (Mo–B
2.379 Å)[27d] and [MoV(NAr)2(PMe3)2(η2-BH4)] (1) [Mo–B
2.461(3) Å].[14] The Mo(1)–N(1)–C(7) linkage is approxi-
mately linear [176.7(1)°], which suggests that the ArN2– li-
gand acts as a six-electron donor to the metal atom.[16] The
Mo=N bond of 1.7434(15) Å comes at the shorter end of
(imido)Mo distances [range 1.745(4)–1.780(3) Å] in com-
plexes featuring the same NAr substituent.[28]
Complexes 6 and 7 turned out to be surprisingly robust.
Like 3 and 5 they are inert towards a variety of Lewis bases.
Thus, treatment with NEt3 or PMe3 did not show any sig-
nificant reaction even upon heating up to 50 °C. Even more
remarkably, no reaction was observed in the case of
alcohols (ethanol and ethylene glycol) and water! Heating
of compound 7 up to 100 °C in the presence of an excess
amount of water gave only a slow decomposition of the
complex by partial hydrolysis of the Mo=NAr bond and
formation of ArNH2.
Experimental Section
General: All manipulations were carried out by using conventional
inert gas glovebox and Schlenk techniques. Dry solvents were ob-
tained by using Grubbs-type purification columns. NMR spectra
were obtained with Bruker DPX-300 and Bruker DPX-600 instru-
ments (1H: 300 and 600 MHz; 13C: 75.5 and 151 MHz; 29Si: 59.6
and 119.2 MHz; 31P: 121.5 and 243 MHz, 11B: 96.3 and
192.6 MHz). EPR spectra were collected by using a Bruker Elexsys
E580 instrument operating in continuous-wave (cw) mode. The
simulation of the EPR spectra were carried out by using Easy-
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Spin.[29] IR spectra were measured with a Perkin–Elmer 1600 FTIR
spectrometer. Elemental analyses were performed in “ANALEST”
laboratories (University of Toronto) by using a Perkin–Elmer
Model 2400II CHN analyzer with a Perkin–Elmer AD-6 autobal-
ance or at the Service de Microanalyses du LCC-CNRS. PMe3 was
purchased from Strem, and C6D6 was from Cambridge Isotope
Laboratories. All other chemicals were obtained from Aldrich.
{V(NAr)Cl2}n was prepared according to a known procedure.[18]
cm–1. C18H43B2NP2V (408.057): calcd. C 52.98, H 10.62, N 3.43;
found C 48.2, H 8.04, N 3.95.[31]
Preparation of [(ArN=)Mo(PMe3)2(η2-BH4)2] (6): A solution of
LiBH4 in THF (2.0 m, 4.2 mL, 8.4 mmol) was added at room tem-
perature to
a solution of [(ArN=)Mo(Cl)2(PMe3)3] (2.38 g,
4.2 mmol) in THF (100 mL). The reaction mixture was stirred over-
night. During this time the colour changed from green to brown.
All volatiles were removed under vacuum, and the residue was ex-
tracted with hexanes (150 mL). The solvent was removed under
reduced pressure to give a fine yellow powder (1.07 g, 51%). 1H
NMR (300 MHz, [D8]toluene, 25 °C): δ = –0.02 (br. s, η2-BH4),
Preparation of [(ArN=)VCl2(PMe3)2] (4): PMe3 (0.192 mg,
2.524 mmol) was added to a solution of {V(NAr)Cl2}n (0.250 g,
0.841 mmol) in toluene (1 mL). The solution was shaken for a few
minutes and left at room temperature for 6 h for crystallization.
The first crop of red crystals of 4 (0.125 g) was separated by fil-
tration. Slow addition of pentane to the filtrate afforded a second
crop of 4 (0.120 mg). The crystals were washed with pentane (3ϫ
2 mL) and dried under vacuum. The combined yield was 0.245 g
(65%). EPR (toluene, 20 °C): g = 1.990, Aiso(51V) = 7.8 mT,
Aiso(31P) = 5.8 mT. C18H35Cl2NP2V (449.27): calcd. C 48.12, H
7.85, N 3.12; found C 48.30, H 7.96, N 3.17.
3
2
1.16 (d, JH,H = 6.9 Hz, 12 H, 4 CH3, ArN), 1.33 (vt, JH,P
=
3
7.8 Hz, 18 H, 2 PMe3), 3.91 (sept, JH,H = 6.9 Hz, 2 H, 2 CH,
ArN), 6.88 (d, JH,H = 7.8 Hz, 2 H, m-H, ArN), 7.00 (t, JH,H
3
3
=
6.9 Hz, 1 H, p-H, ArN) ppm. 1H NMR (600 MHz, [D8]toluene,
–44 °C): δ = –5.43 (br. s, 2 H, Mo-H-B), –1.16 (br. s, 2 H, Mo-H-
B), 3.60 (br. s, 4 H, BH2) ppm. 31P{1H} NMR (121.5 MHz, [D8]-
toluene, 25 °C): δ = 1.1 (s, 2 PMe3) ppm. 13C NMR (75.5 MHz,
1
[D8]toluene, 25 °C): δ = 16.0 (vt, JC,P = 24.9 Hz, PMe3), 23.4 (s, 2
CH3, ArN), 27.8 (s, 2 CH, ArN), 123.7 (s, m-C, ArN), 127.1 (s, p-
Preparation of [(ArN=)TiCl2(PMe3)2] (2): This compound was pre-
pared by using the same procedure as that described above for 4,
C, ArN), 146.4 (s, o-C, ArN), 153.1 (s, i-C, ArN) ppm. 11B NMR
1
(192.6 MHz, [D8]toluene, 22 °C): δ = –15.84 (quint, JB,H
=
[30]
but starting from {Ti(NAr)Cl2}n
(0.500 g) and PMe3 (0.388 g,
80.9 Hz, 2 BH ) ppm. IR (Nujol): ν = 1950 (weak), 1969 (w), 2013
˜
4
1
3 equiv.). Yield 550 g (72%). H NMR (C6D6, 300 MHz, 25 °C): δ
= 7.01 (d, J = 7.5 Hz, 2 H, m-Ar), 6.86 (d, J = 7.6 Hz, 2 H, p-Ar),
4.63 (sept, J = 6.7 Hz, 2 H, CHMe2), 1.44 (d, J = 6.9 Hz, 12 H,
CHMe2), 1.05 (app t, J = 3.6 Hz, 18 H, PMe3) ppm. 31P{1H} NMR
(w), 2102 (m), 2266 (m), 2378 (s), 2405 (s) cm–1. C18H43B2MoNP2
(453.050): calcd. C 47.72, H 9.57, N 3.09; found C 47.82, H 9.78,
N 2.95.
Preparation of [(ArЈN=)Mo(PMe3)2(η2-BH4)2] (7): A solution of
LiBH4 (2.5 mL, 2.0 m) in THF was added at room temperature to
a solution of [(ArЈN=)Mo(Cl)2(PMe3)3] (0.300 g, 0.58 mmol) and
PMe3 (0.12 mL, 1.17 mmol) in THF (50 mL). After addition of
LiBH4, the colour of the reaction mixture turned from green to
yellow-green and then, after 30 min of stirring, to yellow. The reac-
tion mixture was stirred for an additional 4 h. All volatiles were
pumped off, and the residue was extracted with toluene (50 mL).
The solvent was removed under reduced pressure to give a yellow
solid, which was then recrystallized at –30 °C from a solution in
diethyl ether (0.155 g, 67%). 1H NMR (300 MHz, [D8]toluene,
(C6D6, 121.5 MHz, 25 °C):
δ =
–25.6 ppm. 13C{1H} NMR
(75.5 MHz, C6D6, 23 °C): δ = 158.4 (i-C, ArN), 145.5 (o-C, ArN),
124.2 (p-C, ArN), 123.0 (m-C, ArN), 28.5 (CH, ArN), 24.8 (CH3,
ArN), 13.6 (PMe3) ppm. C18H35Cl2NP2Ti (446.20): calcd. C 48.45,
H 7.91, N 3.14; found C 48.48, H 7.95, N 3.26.
Preparation of [(ArN=)Ti(PMe3)2(η2-BH4)2] (3): Toluene (10 mL)
was added to a dry mixture of [(ArN=)TiCl2(PMe3)2] (0.100 g,
0.224 mmol) and LiBH4 (0.224 g, 0.448 mmol). The colour
changed to orange-yellow. The mixture was stirred overnight. The
solution in toluene was filtered, and all volatiles were removed un-
2
24 °C): δ = –0.03 (br. s, η2-BH4), 1.27 (vt, JH,P = 7.5 Hz, 18 H, 2
der vacuum to give
a yellow-brown compound (0.065 g,
0.160 mmol, 72%). Recrystallization from diethyl ether afforded
well-formed red crystals. 1H NMR (C6D6, 300 MHz, 23 °C): δ =
6.98 (d, J = 7.5 Hz, 2 H, m-Ar), 6.85 (d, J = 7.5 Hz, 2 H, p-Ar),
4.34 (sept, J = 6.9 Hz, 2 H, CHMe2), 1.33 (d, J = 6.9 Hz, 12 H,
CHMe2), 1.06 (d, J = 7.2 Hz, 18 H, PMe3), 0.5–1.5 (BH4) ppm.
31P NMR (C6D6, 121.5 MHz, 23 °C): δ = –21.0 ppm. 11B{1H}
NMR (C6D6, 96.3 MHz, 23 °C): δ = –11.4 (t, JB,P = 85.7 Hz) ppm.
PMe3), 2.23 (s, 6 H, 2 CH3, ArЈN), 6.54 (m, 2 H, m-H, ArЈN),
6.80 (m, 1 H, p-H, ArЈN) ppm. 1H NMR (600.2 MHz, [D8]toluene,
2
22 °C): δ = –0.01 (br. s, η2-BH4), 1.27 (vt, JH,P = 7.5 Hz, 18 H, 2
3
PMe3), 2.23 (s, 6 H, 2 CH3, ArЈN), 6.71 (d, JH,H = 7.5 Hz, 2 H,
3
m-H, ArЈN), 6.80 (t, JH,H = 7.5 Hz, 1 H, p-H, ArЈN) ppm. 1H
NMR (600.2 MHz, [D8]toluene, –79 °C): δ = –5.38 (br. s, 2 H, η2-
BH4, bridge), –1.10 (br. s, 2 H, η2-BH4, bridge), 1.16 (br. s, 18 H,
2 PMe3), 2.30 (br. s, 6 H, 2 CH3, ArЈN), 3.60 (br. s, 2 H, 2 BH,
term.), 3.79 (br. s, 2 H, 2 BH, term.), 6.62 (m, 2 H, m-H, ArЈN),
6.80 (m, 1 H, p-H, ArЈN) ppm. 31P{1H} NMR (121.5 MHz, C6D6,
24 °C): δ = 1.9 (s, PMe3) ppm. 31P{1H} NMR (243 MHz, [D8]-
toluene, 22 °C): δ = 2.1 (s, PMe3) ppm. 11B NMR (96.3 MHz,
C6D6, 22 °C): δ = –15.8 (br. m, 2 η2-BH4) ppm. 11B NMR
1
13C NMR (C6D6, 23 °C): δ = 14.3 (d, JC,P = 16.6 Hz, PMe3), 24.0
(s, CH3, Ar), 27.4 (s, CH, Ar), 122.4 (s, m-Ar), 123.5 (s, p-Ar), 144.5
(s, o-Ar), 155.5 (s, i-C, Ar) ppm. IR (Nujol): ν = 2469, 2401, 2370,
˜
2249, 2116, 2042, 1951 (BH4) cm–1. C18H43B2NP2Ti (404.982):
calcd. C 53.38, H 10.7, N 3.46; found C 51.49, H 10.16, N 3.82.[31]
Preparation of [(ArN=)V(PMe3)2(η2-BH4)2] (5): A 2 m solution of
LiBH4 in THF (0.23 mL, 0.464 mmol) was added to a solution of
[(ArN=)VCl2(PMe3)2] (0.122 g, 0.232 mmol) in diethyl ether
(20 mL) precooled to 0 °C. The pale-brown mixture was stirred for
40 min and warmed to room temperature. The solution was fil-
tered, and the precipitate was washed with diethyl ether (5 mL).
Volatiles were removed from combined fractions, and the residue
was extracted with hexane (7 mL). Keeping the solution at –30 °C
produced crystals. The cold solution was decanted, and the crystals
were dried under vacuum (0.0183 g, 0.045 mmol, 19%). Hexane
was removed under vacuum, and the residue was dissolved in di-
ethyl ether cooled to –30 °C to give crystals suitable for X-ray
(96.3 MHz, [D8]toluene, –78 °C): δ = –16.4 (br. s, 2 η2-BH4) ppm.
1
13C NMR (75.5 MHz, [D8]toluene, 24 °C): δ = 16.2 (vt, JC,P
=
24.2 Hz, 2 PMe3), 19.6 (s, 2 CH3, ArЈN), 126.0 (s, p-C, ArЈN), 128.8
(s, m-C, ArЈN), 136.1 (s, o-C, ArЈN), 156.0 (s, i-C, ArЈN) ppm. 13C
1
NMR (151 MHz, [D8]toluene, –80 °C): δ = 15.3 (vt, JC,P
=
24.1 Hz, 2 PMe3), 20.1 (s, 2 CH3, ArЈN), 126.0 (s, p-C, ArЈN), 129.1
(s, m-C, ArЈN), 136.0 (s, o-C, ArЈN), 155.7 (s, i-C, ArЈN) ppm. IR
(Nujol): ν = 2111 (m), 2189 (w), 2269 (m), 2371 (s), 2395 (s) cm–1.
˜
C14H35B2MoNP2 (396.944): calcd. C 42.36, H 8.89, N 3.53; found
C 42.42, H 9.27, N 3.43.
X-ray Diffraction Analysis: Single crystals of 3, 5, 6 and 7 were
analysis. IR (Nujol): ν = 2401, 2388, 2362, 2231, 2168, 2110 (BH )
grown from solutions in Et2O by cooling to –30 °C. The crystals
˜
4
Eur. J. Inorg. Chem. 0000, 0–0
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I21351
/KAP1
Date: 04-02-13 15:29:34
Pages: 8
www.eurjic.org
FULL PAPER
Table 1. Crystal and structure refinement data for 3, 5, 6 and 7.
3
5
6
7
Empirical formula
Formula mass
T [K]
C18H43B2NP2Ti
404.99
123(2)
C18H43B2NP2V
408.3
123(2)
C18H43B2MoNP2
453.03
123(2)
C14H35B2MoNP2
396.93
120(2)
λ [Å]
0.71073
0.71073
0.71073
0.71073
Crystal system
Space group
a [Å]
b [Å]
c [Å]
orthorhombic
Pnma
19.1641(8)
13.8042(6)
9.4761(4)
90
2506.86(18)
4
1.073
orthorhombic
Pnma
18.8898(19)
13.9170(14)
9.5429(10)
90
2508.7(4)
4
1.080
orthorhombic
P2(1)2(1)2(1)
11.6885(3)
12.1854(3)
18.0303(4)
90
2568.04(11)
4
1.172
monoclinic
P12(1)/n1
8.192(4)
19.071(8)
13.840(6)
92.615(10)
2159.9(17)
4
β [°]
V [Å3]
Z
ρcalcd. [gcm–3]
1.221
0.747
μ [mm–1]
0.470
0.524
0.637
F(000)
880
884
960
832
Crystal size [mm]
θ range collected data [°]
Index ranges [°]
0.38ϫ0.32ϫ0.26
2.13 to 29.98
–24ՅhՅ26
–19ՅkՅ19
–12ՅlՅ13
21671
0.38ϫ0.34ϫ0.24
2.16 to29.00
–25ՅhՅ25
–18ՅkՅ18
–13ՅlՅ13
24791
0.34ϫ0.28ϫ0.22
2.02 to 29.97
–15ՅhՅ16
–14ՅkՅ16
–24ՅlՅ24
25298
0.22ϫ0.12ϫ0.04
1.82 to 27.00
–10ՅhՅ10
–22ՅkՅ24
–17ՅlՅ17
11303
Reflections collected
Independent reflections
Absorption correction
Max. transmission
3790 [R(int) = 0.0325] 3457 [R(int) = 0.0460] 7044 [R(int) = 0.0374] 4698 [R(int) = 0.1311]
multiscan
0.8875
multiscan
0.8845
multiscan
0.8726
multiscan
0.9707
Min. transmission
0.8416
3790/0/153
1.024
R1: 0.0306,
wR2: 0.0811
R1: 0.0432,
wR2: 0.0856
–
0.8257
3457/0/153
0.980
R1: 0.0358,
wR2: 0.1068
R1: 0.0483,
wR2: 0.1147
–
0.8127
7044/0/389
1.022
R1: 0.0240,
wR2:0.0474
R1: 0.0287,
wR2:0.0485
0.00(2)
0.8528
4698/0/198
0.887
R1: 0.0950,
wR2: 0.2081
R1: 0.1721,
wR2: 0.2425
–
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [IՆ2σ(I)]
R indices (all data)
Absolute structure parameter
Largest difference peak/hole [eÅ–3] 0.384/–0.434
0.444/–0.386
0.562/–0.247
5.045/–1.268
were coated with perfluorated oil and mounted on a Bruker
SMART diffractometer. Data collection by using an ω-scan tech-
nique was performed. Data reduction was carried out by using
SAINT software.[32] Absorption correction based on measurements
of equivalent reflections was applied.[33] The structures were solved
by direct methods and refined by full-matrix least-squares pro-
cedures on F2 (Table 1).[34] CCDC-909414 (3), -909415 (5), -909416
(6) and -909417 (7) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
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Acknowledgments
This work was supported by the Natural Science and Engineering
Research Council of Canada (NSERC) Discovery Grants to
G. I. N. and A. v. d. E., NSERC Undergraduate Student Research
Award (USRA) to E. P., the Ontario Graduate Scholarship (OGS)
to A. Y. K., the Russian Foundation for Basic Research (RFBR)
grant to L. G. K., and the Centre National de la Recherche Sci-
entifique (CNRS) grant to C. L. G. I. N. thanks the Canadian
Foundation for Innovation and the Ontario Innovation Trust (CFI/
OIT) for a generous equipment grant. We also thank the University
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Eur. J. Inorg. Chem. 0000, 0–0
6
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I21351
/KAP1
Date: 04-02-13 15:29:34
Pages: 8
www.eurjic.org
FULL PAPER
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[24]
The mean imido–vanadium bond is 1.666 Å, calculated for 258
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Received: November 8, 2012
Published Online: ᭿
Eur. J. Inorg. Chem. 0000, 0–0
7
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I21351
/KAP1
Date: 04-02-13 15:29:34
Pages: 8
www.eurjic.org
FULL PAPER
Borohydrides
A. Y. Khalimon, E. Peterson, C. Lorber,
L. G. Kuzmina, J. A. K. Howard,
A. van der Est, G. I. Nikonov* .......... 1–8
Imido-Supported Borohydrides of Tita-
nium, Vanadium and Molybdenum
Treatment of (imido)Ti, -V and -Mo di-
chloride complexes with LiBH4 gives imido
bis(borohydride) complexes, which have
been studied by NMR and EPR spec-
troscopy, and X-ray diffraction.
Keywords: Borohydrides / Imides / Tita-
nium / Vanadium / Molybdenum
Eur. J. Inorg. Chem. 0000, 0–0
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