Syntheses, structures, and dynamic properties of M(CO)2(η3-C3H5)(L-L)(NCB H3) (M = Mo, W; L-L = dppe, bipy, en)

Article abstract of DOI:10.1016/j.jorganchem.2007.11.039

Compounds M(CO)₂(η³-C₃H₅)(L-L)(NCB H₃) (L-L = dppe, M = Mo(1), W(2); L-L = bipy, M = Mo(3), W(4); L-L = en, M = Mo(5), W(6)) were prepared and characterized. The single crystal X-ray analyses of 2-6 revealed that the cyanotrihydroborate anion bonds to the metal through a nitrogen atom, the open face of the allyl group being pointed toward the two carbonyls (endo-isomer). In compounds 2, 5, and 6, the two donor atoms of the bidentate ligand occupy equatorial and axial positions, respectively. In the solid state structures of compounds 3 and 4 both nitrogen atoms of the bipy ligand occupy equatorial positions. The NMR spectroscopy reveals a fluxional behavior of compounds 1, 2, 5, and 6 in solution. Although the fluxional behavior of compounds 5 and 6 ceased at about -40 °C, that of compound 1 could not be stopped even at -90 °C. Their low temperature conformations are consistent with their solid state structures. Both the endo- and exo-isomers coexist in solution for compounds 3 and 4.

Full text of DOI:10.1016/j.jorganchem.2007.11.039

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 537–545
www.elsevier.com/locate/jorganchem
Syntheses, structures, and dynamic properties
of M(CO)2(g3-C3H5)(L–L)(NCBH3)
(M = Mo, W; L–L = dppe, bipy, en)
a,
a
a
b
b
*
Fu-Chen Liu , Pei-Shan Yang , Chun-Yu Chen , Gene-Hsian Lee , Shie-Ming Peng
a Department of Chemistry, National Dong Hwa University, 1, Sec 2, Da Hsueh Road, Shou Feng, Hualien 974, Taiwan, ROC
b Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, ROC
Received 22 August 2007; received in revised form 17 November 2007; accepted 22 November 2007
Available online 31 December 2007
Abstract
Compounds M(CO)2(g3-C3H5)(L–L)(NCBH3) (L–L = dppe, M = Mo(1), W(2); L–L = bipy, M = Mo(3), W(4); L–L = en, M =
Mo(5), W(6)) were prepared and characterized. The single crystal X-ray analyses of 2–6 revealed that the cyanotrihydroborate anion
bonds to the metal through a nitrogen atom, the open face of the allyl group being pointed toward the two carbonyls (endo-isomer).
In compounds 2, 5, and 6, the two donor atoms of the bidentate ligand occupy equatorial and axial positions, respectively. In the solid
state structures of compounds 3 and 4 both nitrogen atoms of the bipy ligand occupy equatorial positions. The NMR spectroscopy
reveals a fluxional behavior of compounds 1, 2, 5, and 6 in solution. Although the fluxional behavior of compounds 5 and 6 ceased
at about ꢀ40 °C, that of compound 1 could not be stopped even at ꢀ90 °C. Their low temperature conformations are consistent with
their solid state structures. Both the endo- and exo-isomers coexist in solution for compounds 3 and 4.
Ó 2007 Published by Elsevier B.V.
Keywords: Allyl complex; Cyanotrihydroborate; Dynamic; Ethylenediamine
1. Introduction
the anionic ligand Xꢀ [2b,6], therefore many exceptions to
the above observation can be found in the literature [3,5,10].
In our previous work, we have compared the bonding
interaction of cyanotrihydroborate and acetonitrile ligands
in their group 6 allyl-containing metal complexes [11]. Our
results suggested that the cyanotrihydroborate anion is a
weak coordinating ligand displaying a similar, albeit a
slightly stronger interaction with the metal, than acetoni-
trile. Although many compounds of the general formula
M(CO)2(g3-allyl)(L–L)(X) have been reported, to the best
of our knowledge, the cyanotrihydroborate anion has
never been utilized as X in this type of complexes. The
cationic complexes [Mo(CO)2(g3-C3H5)(L–L)(NCCH3)]+
(L–L = dppe, bipy), having been reported recently [3], the
comparison of properties of the acetonitrile- and cya-
notrihydroborate-containing complexes can be extended
further. We have examined the cyanotrihydroborate com-
plexes containing three different bidentate ligands, namely,
There is a large number of group 6 bidentate allylic com-
plexes of general formula M(CO)2(g3-C3H5)(L–L)(X)
(M = Mo, W; L–L = bidentate ligand; X = anionic mono-
dentate ligand) [1]. The interest in this type of complexes
encompasses their conformational [2] and dynamic behav-
ior [3–5], as well as allylic alkylation [6] and their possible
catalytic properties [5,7]. It was noted that when L–L is a
rigid bidentate ligand, the complex possesses conformation
A (see Scheme 1) in the solid state and exhibits no fluxional
behavior in solution [8]. When L–L is a nonrigid bidentate
ligand, the complex possesses conformation B (B0) in the
solid state and exhibits a fluxional behavior in solution
[1c,9]. However, their conformations are also affected by
*
Corressponding author. Tel.: +886 38633601; fax: +886 38633570.
E-mail address: fcliu@mail.ndhu.edu.tw (F.-C. Liu).
0022-328X/$ - see front matter Ó 2007 Published by Elsevier B.V.
doi:10.1016/j.jorganchem.2007.11.039

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F.-C. Liu et al. / Journal of Organometallic Chemistry 693 (2008) 537–545
L
L
L
CO
CO
X
L
CO
CO
CO
CO
L
CO
CO
M
M
X
M
L
M
L
L
X
X
A
A'
B
B'
Scheme 1.
1,2-bis(diphenylphosphino)ethane (dppe), 2,20-bipyridine
(bipy) and 1,2-ethylenediamine (en). The bidentate ligands
dppe and bipy are routinely found in this type of com-
plexes; however, only rare examples of the en-containing
compounds M(CO)2(g3-allyl)(en)(X) (M = Mo, W, allyl =
C3H5, MeC3H4) have been reported [12].
pound possesses a pseudo-octahedral structure, with the
central atom being surrounded by an allyl group, two car-
bonyls, a cyanotrihydroborate anion, and a bidentate
ligand L–L (L–L: dppe, bipy, en). Both carbonyls are equa-
torial and cis- to each other. The allyl ligand occupies an
axial position, with its open face pointing towards the car-
bonyls (endo-isomer). The structures of bipy compounds 3
and 4 are represented by conformation A, where the bipy
ligand is trans- to the carbonyls, while those of compounds
2, 5, and 6 are represented by conformation B (and its
mirror image B0), where the bidentate ligand occupies both
an axial and an equatorial positions trans- to the allyl
group and a carbonyl, respectively. It is worth noting that
the molecular structures of dppe compound 2 and
[Mo(CO)2(g3-C3H5)(dppe)(NCCH3)]+ [3] possess the same
conformation B, while the bipy compounds 3 and 4, on the
one hand, and [Mo(CO)2(g3-C3H5)(bipy)(NCCH3)]+ [3],
on the other hand, adopt conformations A and B, respec-
tively. Our previous study suggested that electronic proper-
ties of the acetonitrile ligand are only slightly different from
those of its isoelectronic analog, cyanotrihydroborate
ligand. Nevertheless, this subtle electronic difference
resulted in a change of the preferred structure.
2. Results and discussion
2.1. Preparations and properties of M(CO)2(g3-C3H5)
(L–L)(NCBH3) (L–L = dppe, M = Mo(1), W(2);
L–L = bipy, M = Mo(3), W(4); L–L = en, M = Mo(5),
W(6))
The cyanotrihydroborate complexes M(CO)2(g3-
C3H5)(L–L)(NCBH3) (L–L = dppe, M = Mo(1), W(2);
L–L = bipy, M = Mo(3), W(4); L–L = en, M = Mo(5),
W(6)) were prepared in a two-step sequence including the
reaction of M(CO)2(g3-C3H5)(NCCH3)2Br (M = Mo, W)
with a bidentate ligand L–L (L–L = 1,2-bis(diphenylphos-
phino)ethane, dppe; 2,20-bipyridine, bipy; 1,2-ethylenedia-
mine, en) followed by a metathesis of the [Br]ꢀ ligand
with [NCBH3]ꢀ as shown in Eqs. (1) and (2). Compounds
1 and 2 decompose on short exposure to air. In contrast, a
week-long exposure of compounds 3–6 to air resulted in no
noticeable decomposition. However, as observed from
their 11B NMR spectra, compounds 3 and 4 decompose
in CH3CN and acetone, while compounds 5 and 6 decom-
pose in CH3CN, methanol, and acetone.
Tables 2–4 list the selected bond distances and bond
angles of 2–6, respectively. The cyanotrihydroborate anion
is bonded to the metal through a nitrogen atom. The cor-
responding M–N bond distances fall into the range of
˚
2.144(3)–2.2107(14) A. Compared with those found in 3
and 4, where the cyanotrihydroborate ligand is trans- to
an allyl group, longer M–N distances were observed in
2, 5, and 6, where it is trans- to a carbonyl. These M–
NCBH3 distances of 2–4 are slightly shorter than those
found for the isoelectronic compounds [Mo(CO)2(g3-
MðCOÞ2ðg3-C3H5ÞðNCCH3Þ2Br þ L–L
! MðCOÞ2ðg3-C3H5ÞðL–LÞBr þ 2CH3CN
ð1Þ
ð2Þ
ðM¼Mo;W;L–L¼dppe;bipy;enÞ
C3H5)(L–L)(NCCH3)]+ (L–L = dppe, 2.233(5) A, L–L =
˚
MðCOÞ2ðg3-C3H5ÞðL–LÞBr þ NaBH3CN
˚
bipy, 2.197(3) A) [3]. This is consistent with our previous
! MðCOÞ2ðg3-C3H5ÞðL–LÞðNCBH3Þ þ NaBr
observation that the cyanotrihydroborate anion displays
a slightly stronger interaction with a metal than acetoni-
trile [11]. The C–C–C allyl angles fall within the range
of 114.8(4)–116.4(3)°, which is consistent with other allyl
compounds [8,13]. The C–O bond distances of the tung-
sten compounds 4 and 6 are slightly longer than those
of their molybdenum analogs 3 and 5, reflecting the elec-
tron rich nature of the third row transition metal [14]. For
the carbonyl ligand trans- to a weak p-acceptor ligand
(cyanotrihydroborate in 2), or a good r-donor ligand
(en in 5 and 6) the C–O bond distance is slightly longer,
and M–CO bond distance is slightly shorter than for the
ðM¼Mo;W;L-L¼dppe;bipy;enÞ
2.2. X-ray studies
The molecular structures of 2–6 were determined by sin-
gle crystal X-ray diffraction analyses; crystallographic data
and selected bond distances and angles are summarized in
Tables 1–4. The molecular structures of 2, 4, and 6 are pro-
vided in Figs. 1–3. Those for compounds 3 and 5 are
included in the supporting information due to their similar-
ity to the structures of compounds 4 and 6. Each com-

F.-C. Liu et al. / Journal of Organometallic Chemistry 693 (2008) 537–545
539
Table 1
Crystallographic data for W(CO)2(g3-C3H5)(dppe)(NCBH3) (2), Mo(CO)2(g3-C3H5)(bipy)(NCBH3) (3), W(CO)2(g3-C3H5)(bipy)(NCBH3) (4), Mo(CO)2-
(g3-C3H5)(en)(NCBH3) (5), and W(CO)2(g3-C3H5)(en)(NCBH3) (6)
Empirical formula
Formula weight
T (K)
Crystal system
Space group
C
719.19
150(1) K
Triclinic
32H32BNO2P2W
C18H16BMoN3O2
413.09
150(1)
Monoclinic
P2(1)/n
8.4094(5)
10.1503(6)
19.6128(13)
C16H16BN3O2W
476.98
150(1)
Monoclinic
P2(1)/n
8.3305(1)
10.2364(1)
19.5605(3)
C8H16BMoN3O2
292.99
150(1)
Monoclinic
C2/c
22.9600(8)
6.4545(2)
16.2120(5)
C8H16BN3O2W
380.90
150(1)
Monoclinic
C2/c
22.9047(3)
6.4328(1)
16.1151(2)
ꢀ
P1
˚
a (A)
8.2886(6)
12.1431(8)
15.1970(10)
91.998(1)
92.177(1)
106.967(1)
1460.24(17)
2
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
90.438(1)
90.8600(8)
96.024(1)
96.4307(9)
3
˚
V (A )
1674.06(18)
4
1.639
0.45 ꢁ 0.30 ꢁ 0.20
Mo Ka (0.71073)
2.08–27.50
ꢀ10 6 h 6 10
ꢀ12 6 k 6 13
ꢀ25 6 l 6 25
16,156
1667.82(4)
4
1.900
0.23 ꢁ 0.15 ꢁ 0.15
Mo Ka (0.71073)
2.08–27.50
ꢀ10 6 h 6 10
ꢀ13 6 k 6 13
ꢀ25 6 l 6 25
19,714
2389.28(13)
8
1.629
0.30 ꢁ 0.25 ꢁ 0.10
Mo Ka (0.71073)
1.78–27.50
ꢀ29 6 h 6 29
ꢀ8 6 k 6 8
ꢀ21 6 l 6 21
15,068
2359.48(6)
8
2.145
0.45 ꢁ 0.30 ꢁ 0.30
Mo Ka (0.71073)
2.08–27.50
ꢀ29 6 h 6 29
ꢀ8 6 k 6 8
ꢀ20 6 l 6 20
12,613
Z
qcalc. (g/cm3)
Crystal size (mm)
1.636
0.28 ꢁ 0.25 ꢁ 0.25
Mo Ka (0.71073)
1.34–27.50
ꢀ10 6 h 6 10
ꢀ15 6 k 6 15
ꢀ19 6 l 6 19
19,312
˚
Radiation (k, A)
2h Limits (°)
Index ranges
Reflections collected
Unique reflections
6678
3834
3834
2759
2721
Unique reflections [I > 2.0r(I)]
Completeness to h (%)
712
99.6
4.095
832
99.8
0.800
912
99.9
6.937
1184
100.0
1.082
1440
99.9
1.041
l (mmꢀ1
)
Maximum/minimum transmission
Data/restraints/parameters
Ra1 [I > 2.0r(I)]
0.4275, 0.3935
6678/0/361
0.0225
0.8564, 0.7148
3834/0/217
0.0285
0.377, 0.218
3834/0/210
0.0250
0.8995, 0.7372
2759/0/165
0.0188
0.167, 0.095
32721/0/138
0.0260
wRb2 (all data)
0.0633
0.0705
0.0533
0.0483
0.0711
Rint
Goodness-of-fit on F2
0.0314
1.104
0.0288
1.073
0.0513
1.009
0.0233
1.096
0.0668
1.041
P
P
a
R1 = kFok ꢀ jFck/ kFoj.
P
P
b
wR2 = { w(Fo2 ꢀ Fc2)2/ w(F2o)2}1/2
.
Table 2
(77.71(3)°), 5 (75.29(5)°), and 6 (75.17(12)°). All these val-
ues fall into the range reported in the literature [3,15].
3
˚
Selected bond distances (A) and bond angles (°) for W(CO)2(g -C3H5)-
(dppe)(NCBH3) (2)
Bond lengths
2.3. Infrared studies
W–C(1)
W–C(2)
W–N(1)
W–P(1)
W–P(2)
1.949(3)
1.975(3)
2.187(3)
2.5287(8)
2.5780(8)
O(1)–C(1)
O(2)–C(2)
N(1)–C(6)
B(1)–C(6)
1.173(4)
1.155(4)
1.155(4)
1.580(5)
Table 5 presents selected infrared data of compounds
1–6 and [N(CH3)4][NCBH3]. Appearance of the mBH
absorption band for each compound between 2329 and
2348 cmꢀ1 and that of the mCN absorption band between
2184 and 2196 cmꢀ1 are consistent with a M–NCBH3-
bonded complex [16]. Two carbonyl absorption bands are
observed for each compound. Since tungsten is an elec-
tron-rich third row transition metal [14], the C„O absorp-
tion bands of its complexes are found at lower frequencies
than those of related Mo complexes. This is consistent with
their solid state structures, where longer C„O bond
distances are observed for the tungsten complexes. The
infrared spectroscopy is a useful tool to differentiate the
bonding modes of the carbonyl ligand. In general, the ter-
minal M–CO carbonyl absorption occurs in the range of
1850–2120 cmꢀ1, whereas the bridging carbonyl absorption
falls into the range of 1700–1860 cmꢀ1 [17]. This general
rule could not be applied to compounds 5 and 6. As
observed in Table 5, one of the C„O absorptions
Angles
C(1)–W–C(2)
C(1)–W–N(1)
C(2)–W–N(1)
C(1)–W–P(1)
C(2)–W–P(1)
N(1)–W–P(1)
C(1)–W–P(2)
C(2)–W–P(2)
N(1)–W–P(2)
P(1)–W–P(2)
C(9)–P(1)–W
79.75(13)
174.74(12)
97.26(12)
94.43(10)
85.81(10)
80.99(7)
99.43(10)
163.41(10)
82.19(7)
C(15)–P(1)–W
C(7)–P(1)–W
C(27)–P(2)–W
C(21)–P(2)–W
C(8)–P(2)–W
C(6)–N(1)–W
O(1)–C(1)–W
O(2)–C(2)–W
C(3)–C(4)–C(5)
N(1)–C(6)–B(1)
121.18(11)
109.36(10)
111.72(11)
122.54(11)
107.56(11)
178.2(3)
176.1(3)
175.2(3)
116.4(3)
176.4(4)
77.71(3)
113.79(11)
other carbonyl. The bidentate biting angles L–M–L
are ligand-dependent. The rigid ligand displays a smaller
biting angle. Thus the L–M–L biting angles in 3
(72.84(6)°) and 4 (72.98(10)°) are smaller than those in 2

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F.-C. Liu et al. / Journal of Organometallic Chemistry 693 (2008) 537–545
Table 3
3
3
˚
Selected bond distances (A) and bond angles (°) for Mo(CO)2(g -C3H5)(bipy)(NCBH3) (3) and W(CO)2(g -C3H5)(bipy)(NCBH3) (4)
3
4
3
4
M–C(1)
M–N(2)
O(1)–C(1)
N(1)–C(6)
B(1)–C(6)
1.970(2)
2.2392(17)
1.149(3)
1.114(3)
1.595(4)
1.958(4)
2.223(3)
1.166(4)
1.139(4)
1.583(5)
M–C(2)
M–N(1)
M–N(3)
O(2)–C(2)
1.971(2)
1.970(4)
2.144(3)
2.228(3)
1.155(4)
2.1702(19)
2.2387(17)
1.151(3)
C(1)–M–C(2)
C(2)–M–N(3)
C(2)–M–N(1)
C(1)–M–N(2)
N(3)–M–N(2)
C(6)–N(1)–M
O(2)–C(2)–M
N(1)–C(6)–B(1)
78.75(10)
167.73(8)
88.03(8)
171.28(9)
72.84(6)
175.82(17)
177.5(2)
178.6(2)
78.75(15)
170.71(12)
89.71(13)
167.26(12)
72.98(10)
176.2(3)
C(1)–M–N(3)
C(1)–M–N(1)
N(3)–M–N(1)
C(2)–M–N(2)
N(1)–M–N(2)
O(1)–C(1)–M
C(5)–C(4)–C(3)
104.04(8)
89.42(9)
80.10(6)
102.60(8)
82.04(6)
176.1(2)
116.1(3)
102.16(13)
88.29(12)
81.09(10)
104.14(12)
79.37(10)
178.2(3)
176.5(3)
178.4(3)
115.7(4)
Table 4
3
3
˚
Selected bond distances (A) and bond angles (°) for Mo(CO)2(g -C3H5)(en)(NCBH3) (5) and W(CO)2(g -C3H5)(en)(NCBH3) (6)
5
6
5
6
M–C(1)
M–N(1)
M–N(3)
O(2)–C(2)
N(1)–C(60)
N(2)–C(70)
N(3)–C(8)
C(8)–B(1)
1.9432(16)
2.2448(14)
2.2107(14)
1.152(2)
1.484(6)
1.453(6)
1.946(4)
2.238(4)
2.195(3)
1.162(5)
M–C(2)
M–N(2)
1.9604(16)
2.2945(13)
1.159(2)
1.495(4)
1.499(4)
1.964(4)
2.282(4)
1.172(5)
1.496(7)
1.477(6)
1.445(8)
O(1)–C(1)
N(1)–C(6)
N(2)–C(7)
C(6)–C(7)
C(60)–C(70)
1.499(7)
1.487(11)
1.138(2)
1.581(3)
1.147(5)
1.580(6)
C(1)–M–C(2)
C(2)–M–N(3)
C(2)–M–N(1)
C(1)–M–N(2)
N(3)–M–N(2)
C(8)–N(3)–M
O(2)–C(2)–M
N(3)–C(8)–B(1)
77.99(6)
170.30(6)
91.32(6)
166.85(6)
82.55(5)
176.11(14)
174.49(13)
178.69(19)
77.88(16)
C(1)–M–N(3)
C(1)–M–N(1)
N(3)–M–N(1)
C(2)–M–N(2)
N(1)–M–N(2)
O(1)–C(1)–M
C(5)–C(4)–C(3)
98.84(6)
92.04(6)
79.57(5)
98.46(6)
75.29(5)
99.31(15)
92.08(15)
79.06(14)
98.00(14)
75.17(12)
176.4(3)
170.15(16)
91.55(16)
166.59(14)
82.57(13)
174.7(3)
175.90(14)
115.61(16)
174.6(3)
179.1(5)
114.8(4)
Fig. 1. Molecular structure of W(CO)2(g3-C3H5)(dppe)(NCBH3) (2)
Fig. 2. Molecular structure of W(CO)2(g3-C3H5)(bipy)(NCBH3) (4)
showing 50% probability thermal ellipsoids.
showing 50% probability thermal ellipsoids.

F.-C. Liu et al. / Journal of Organometallic Chemistry 693 (2008) 537–545
541
environment [9] relative to the cyanotrihydroborate ligand.
Except for the signal of Hc, which overlaps with one of the
broad signals of the dppe backbone, compound 2 displays
1
the same pattern in its H NMR spectrum. Such a simple
proton NMR pattern is consistent with the fluxional
behavior of a typical M(CO)2(g3-C3H5)(P–P)(X) species,
for which only an averaged spectrum was observed
[1c,5,9]. This is also observed in the room temperature
31P NMR spectra of 1 and 2, each of them displaying only
a sharp singlet at 52.2 and 37.1 ppm, respectively. These
chemical shifts are consistent with those reported for
Mo(CO)2(g3-C3H5)(dppe)Cl (53.2 ppm) [9] and W(CO)2-
(g3-C7H7)(dppe)Cl (36 ppm) [12b]. The fluxional behavior
of 1 was studied by the variable-temperature 31P NMR.
As shown in Fig. 4, the signal at 52.2 ppm became broad
as the temperature was lowered, and collapsed at about
ꢀ60 °C. Upon further temperature decrease it reappeared
gradually and eventually split into three broad signals at
47.1, 48.0, and 65.9 ppm in the ratio of 1:1:0.4 at ꢀ90 °C.
Fig. 3. Molecular structure of W(CO)2(g3-C3H5)(en)(NCBH3) (6) show-
ing 50% probability thermal ellipsoids.
1
The variable-temperature H NMR spectra of 1 were also
acquired; however, several broad signals were observed at
ꢀ90 °C. A trigonal twist rearrangement has been proposed
(1800 cmꢀ1 for 5 and 1781 cmꢀ1 for 6) is significantly below
the range generally accepted for the terminal carbonyl. This
result may be attributed to the asymmetric coordination of
the en ligand, which is a good r-donor but a poor p-accep-
tor. The carbonyl trans- to the nitrogen atom of the en
ligand displays a significant p-back bonding effect, resulting
in a weaker absorption band. In DME solution, where fast
conformational exchange takes place (vide infra), this car-
bonyl absorption band displays a significant blue shift of
about 50 cmꢀ1, accompanied by a slight red shift of the
other C„O absorption band for each compound.
2.4. NMR studies
The 11B NMR signals of compounds 1–6 appear in the
range of ꢀ42.9 to ꢀ44.2 ppm as broad quartets (JB–H
=
90 Hz). This is very close to the signals of NaBH3CN
(ꢀ43.5 ppm, JB–H = 89 Hz) [18] and other N-bonded cya-
notrihydroborate compounds [11,16a,16b,19].
1
The H NMR spectra of compounds 1 and 2 are rela-
tively simple. The allyl ligand hydrogens of compound 1
appear at 1.97 (Ha), 3.66 (Hs), and 3.80 (Hc) ppm. Two
broad signals at 2.32 and 2.77 ppm assigned to the methy-
lene groups of dppe correspond to two different kinds of
Fig. 4. Variable temperature 31P NMR spectra of Mo(CO)2(g3-
C3H5)(dppe)(NCBH3) (1).
Table 5
Selected Infrared data of compounds [Mo(CO)2(g3-C3H5)(dppe)(NCBH3)] (1), [W(CO)2(g3-C3H5)(dppe)(NCBH3)] (2), [Mo(CO)2(g3-C3H5)(bi-
py)(NCBH3)] (3), [W(CO)2(g3-C3H5)(bipy)(NCBH3)] (4), [Mo(CO)2(g3-C3H5)(en)(NCBH3)] (5), [W(CO)2(g3-C3H5)(en)(NCBH3)] (6), and
[N(CH3)4][NCBH3]
Compounds
mCO
mCN
mBH (cmꢀ1
)
1
1945(vs)
1933(vs)
1945(vs)
1935(vs)
1944(vs)
1937(vs)
1863(vs)
1 1844(vs)
1861(vs)
1846(vs)
1800(vs)
1781(vs)
2204(vw)
2203(vw)
2215(vw)
2214(vw)
2218(vw)
2218(vw)
2230(w)
2184(m)
2185(m)
2194 (m)
2194(m)
2196(s)
2329(m)
2338(m)
2347(m)
2348(m)
2344(s)
2277(vw)
2267(vw)
2301(w)
2294(vw)
2266(m)
1114(m)
1114(m)
1117(m)
1118(m)
1113(s)
2
3
4
5
6
2194(m)
2172(s)
2346(m)
2339(s)
2260(vw)
2301(s, sh)
1110(s)
1132(m)
[N(CH3)4][NCBH3]

542
F.-C. Liu et al. / Journal of Organometallic Chemistry 693 (2008) 537–545
[12b] for this type of compound. The mechanism involves
rotation of the triangular face formed by the cyanotrihyd-
roborate and two phosphorus atoms with respect to the
face formed by the allyl and two carbonyls. Both the 31P
and 1H NMR spectroscopy observations suggest a fast
rotation to occur at room temperature. The rearrangement
involves three isomers: A, B, and B0. It is possible that the
broad signal at 65.9 ppm is due to conformation A, where
both phosphorous atoms are in the equatorial positions.
The two phosphorous atoms in B, and B0 are in different
environments; however, since the 31P NMR is not able to
distinguish these two isomers, they display the same
chemical shifts. Thus, at low temperature the asymmetric
conformations consistent with the solid state structures of
compounds predominate. The low temperature NMR
study has also suggested compound Mo(CO)2(g3-C3H5)-
(dppe)(X) (X = halide) [9] to exist as conformation B (B0).
For compound 3 two isomers coexist in solution in a 3:2
The 1H NMR spectra of 5 and 6 display broad signals at
room temperature. Their assignments are based on the
1
1H–1H COSY and H–13C HMQC 2D NMR studies at
ꢀ40 °C. In solution, both compounds adopt asymmetric
conformation B (B0) at low temperature, which is consis-
tent with their solid state structures. The variable-tempera-
1
ture H NMR spectra of 5 are shown in Fig. 5. A static
state is obtained at about ꢀ40 °C. As the temperature
increased, the signals broadened at first and collapsed later
at about 30 °C. As the temperature increased further, the
signals sharpened; however, a fast rotation has not been
reached yet at 60 °C. Compared with the fluxional behavior
observed for 1, the rotation energy barriers for these two
compounds containing en ligand are higher.
3. Experimental
3.1. General procedures
1
ratio. Their NMR signals were assigned through H–1H
1
COSY and H–13C HMQC 2D NMR studies. As three
All manipulations were carried out on a standard high
vacuum line or in a drybox under an atmosphere of nitro-
gen. Unless otherwise noted, reagents were used as obtained
from the commercial suppliers, and solvents were dried
and freshly distilled prior to use. Mo(CO)2(g3-C3H5)-
(CH3CN)2Br and W(CO)2(g3-C3H5)(CH3CN)2Br were pre-
pared by the literature procedures [20]. Elemental analyses
were recorded on a Hitachi 270-30 spectrometer. Proton
spectra (d(TMS) = 0.00 ppm) were recorded either on a
Bruker Avance DPX300 or a Varian Unity Inova 600 spec-
trometer operating at 300.130 and 599.948 MHz, respec-
tively. 11B spectra (externally referenced to BF3 ꢂ OEt2
(d 0.00 ppm)) were recorded on the same instruments oper-
ating at 96.293 and 192.481 MHz, respectively. Infrared
spectra were recorded on a Jasco FT/IR-460 Plus spectrom-
eter with 2 cmꢀ1 resolution.
allyl group signals were found for each isomer, these
isomers were assigned to A and A0. A recent theoretical cal-
culation has suggested conformations A and A0 of
[Mo(CO)2(g3-C3H5)(bipy)(NCCH3)]+ to be in equilibrium
in solution [3]. The structure of the only isomer found for
compound 4 has been assigned to conformation A.
3.2. X-ray structure determination
Suitable crystals of 2–6 were mounted and sealed inside
glass capillaries under nitrogen. Crystallographic data col-
lections were carried out on a Nonius KappaCCD diffrac-
tometer with graphite-monochromated Mo Ka radiation
˚
(k = 0.71073 A) at 150(1) K. Unit cell parameters were
retrieved and refined using DENZO-SMN [21] software on
all reflections. Data reduction was performed with the
DENZO-SMN [21] software. An empirical absorption was
based on the symmetry-equivalent reflections and was
applied to the data using SORTAV [22] program. The struc-
ture was solved using the SHELXS-97 [23] program and
refined using SHELXL-97 [24] program by full-matrix least-
squares on F2 values. All nonhydrogen atoms in each
structure were located and refined anisotropically. The
hydrogen atoms on the boron atoms in 2 were located
and refined isotropically and other hydrogen atoms were
fixed at calculated positions and refined using a riding
mode. Crystallographic data of 2–6 are summarized in
Tables 1–4.
Fig. 5. Variable temperature 1H NMR spectra of Mo(CO)2(g3-C3H5)(en)-
(NCBH3) (5).

F.-C. Liu et al. / Journal of Organometallic Chemistry 693 (2008) 537–545
543
3.3. Preparation of complexes
1435(s), 1420(w), 1408(w), 1396(vw), 1382(vw), 1334(vw),
1309(vw), 1266(vw), 1187(vw), 1158(vw), 1114(m), 1097(m),
1071(vw), 1027(vw), 999(vw), 955(vw), 872(vw), 825(w),
743(m), 703(s), 692(s), 677(w), 653(w), 624(vw), 616(vw),
598(vw), 568(vw), 544(m), 526(m), 515(m), 485(w), 472(w),
456(vw), 441(vw), 431(w), 423(w), 418(vw), 413(vw), and
401(w) cmꢀ1. Anal. Calc. for C32H32BNO2P2W: N, 1.95; C,
53.44; H, 4.48. Found: N, 1.96; C, 53.33; H, 4.45%.
3.3.1. Mo(CO)2(g3-C3H5)(dppe)(NCBH3) (1)
Mo(CO)2(g3-C3H5)(NCCH3)2Br (360.2 mg, 1.00 mmol)
and 1,2-bis(diphenylphosphino)ethane (dppe) (402.5 mg,
1.01 mmol) were placed in a 50 mL flask. After degassing,
about 25 mL of CH2Cl2 was transferred into the flask at
ꢀ78 °C. The system was warmed to room temperature
and stirred for 2 h resulting in a red solution. A solution
of sodium cyanotrihydroborate (63.1 mg, 1.00 mmol) in
3.0 mL of methanol was added dropwise to the red solution.
The reaction mixture was stirred for additional 9 h chang-
ing color to orange-red with precipitation. The solvent
was removed under a dynamic vacuum, and the resulting
orange-red solid was extracted several times with 20.0 mL
portions of CH2Cl2. The CH2Cl2 extracts were combined
and stripped off the solvent in vacuo. The resulting red solid
was dissolved in CH2Cl2 and layered with CH3OH for crys-
tallization. The product was isolated as orange-red crystals
(520.3 mg, 82.4%). 11B NMR (CH2Cl2): d ꢀ43.6 ppm (br, q,
JB–H = 90 Hz). 31P NMR (CH2Cl2): d 52.2 ppm (s). 1H
NMR (CDCl3): d 7.36–7.79 (m, 20H, Ph), 3.80 (m, 1H,
Hc), 3.66 (br, m, 2H, Hs), 2.77 (m, 2H, PCH2CH2P), 2.32
(m, 2H, PCH2CH2P), 1.97 (d, JH–H = 10.8 Hz, 2H, Ha),
and 0.29 ppm (br, 3H, BH3). 13C NMR (CDCl3): d 223.22
(CO), 133.16, 132.11, 131.20, 130.83, 129.10 (C6H5), 87.11
(Cc), 60.08 (Ct), 26.50, and 26.27 ppm (PCH2CH2P). IR
(KBr): 3079(vw), 3059(w), 3023(vw), 3002(vw), 2968(vw),
2923(vw), 2329(m), 2277(vw), 2204(vw), 2184(m), 1945(vs),
1863(vs), 1587(vw), 1575(vw), 1483(m), 1469(vw), 1459(vw),
1435(s), 1410(w), 1398(vw), 1389(vw), 1334(vw), 1308(vw),
1261(vw), 1234(vw), 1187(vw), 1163(vw), 1114(m), 1071(m),
1025(m), 999(w), 968(vw), 925(vw), 874(w), 853(vw),
823(w), 746(m), 694(s), 678(m), 654(w), 615(vw), 597(w),
564(vw), 529(s), 515(m), 481(m), 462(w), 446(vw), 432(w),
and 418(m) cmꢀ1. Anal. Calc. for C32H32BNO2P2Mo: N,
2.22; C, 60.88; H, 5.11. Found: N, 2.24; C, 60.67; H, 5.07%.
3.3.3. Mo(CO)2 (g3-C3H5)(bipy)(NCBH3) (3)
In a dry box, 361.1 mg (1.00 mmol) of Mo(CO)2-
(g3-C3H5)(NCCH3)2Br and 158.3 mg (1.01 mmol) of 2,20-
bipyridine were added into a 50 mL flask. The flask was
evacuated and about 25 mL of CH2Cl2 was transferred into
the flask. After stirring for 1 h a red-purple solution was
obtained. A solution of sodium cyanotrihydroborate
(62.4 mg, 0.99 mmol) in 3.0 mL of methanol was added
dropwise to this red-purple solution. This reaction mixture
was stirred for additional 8 h changing color to red with
precipitation. The solvent was removed in vacuo, and the
resulting red solid was extracted several times with
20.0 mL portions of DME. The combined DME extracts
were concentrated and layered with hexane for crystalliza-
tion. The product was isolated as red crystals (253.6 mg,
65% yield). 11B NMR (CH2Cl2): d ꢀ44.2 ppm (br, q, JB–H
=
91 Hz). 1H NMR (CD2Cl2): isomer A, d 8.88–7.68 (m, bipy),
3.31 (d, JH–H = 6.0 Hz, Hs), 3.11 (m, Hc), 1.60 (d, JH–H
=
9.6 Hz, Ha), and 0.12 ppm (br, BH3). isomer B, d 9.10-
7.79 (m, bipy), 3.88 (m, Hc), 3.59 (br, Hs), 1.54 (m, Ha),
and 0.01 ppm (br, BH3). 13C NMR (CD2Cl2): isomer A, d
224.08 (CO), 153.66, 152.34, 139.45, 126.62, 122.62 (bipy),
73.65 (Cc), and 57.41 ppm (Ct). isomer B, 224.08 (CO),
153.66, 152.32, 138.53, 126.82, 122.73 (bipy), 71.57 (Cc),
and 57.41 ppm (Ct). IR (KBr): 3106(vw), 3081(vw),
3069(vw), 3026(vw), 3004(vw), 2960(vw), 2920(vw),
2856(vw), 2357(m), 2347(m), 2301(w), 2215(vw), 2194(m),
2039(vw), 2017(vw), 1945(vs), 1861(vs), 1600(m), 1470(vw),
1457(w), 1441(m), 1424(w), 1419(vw), 1364(vw), 1339(vw),
1311(w), 1260(w), 1248(vw), 1226(vw), 1173(vw), 1151(vw),
1145(vw), 1117(m), 1103(w), 1072(w), 1046(vw), 1024(w),
865(vw), 852(vw), 818(vw), 802(w), 760(s), 733(m),
669(vw), 648(vw), 630(vw), 603(vw), 575(vw), 569(vw),
555(vw), 545(vw), 513(vw), 510(w), and 504(vw) cmꢀ1. Anal.
Calc. for C16H16BN3O2Mo: N, 10.80; C, 49.39; H, 4.14.
Found: N, 10.60; C, 48.71; H, 4.21%.
3.3.2. W(CO)2(g3-C3H5)(dppe)(NCBH3) (2)
A procedure similar to the one described for the prepara-
tion of 1 was used. The reaction of W(CO)2(g3-C3H5)-
(NCCH3)2Br (448.0 mg, 1.01 mmol) with 1,2-bis(diphenyl-
phosphino)ethane (400.7 mg, 1.01 mmol) and sodium
cyanotrihydroborate (63.1 mg, 1.00 mmol) followed by lay-
ering the CH2Cl2 solution of the product with methanol
produced 562.7 mg (78.2% yield) of 2 as orange-red crystals.
11B NMR (CH2Cl2): d ꢀ43.6 ppm (br, q, JB–H = 86 Hz). 31
P
3.3.4. W(CO)2(g3-C3H5)(bipy)(NCBH3) (4)
1
NMR (CH2Cl2): d 37.1 ppm (s, JW–P = 202 Hz). H NMR
(CDCl3): d 7.38–7.82 (m, 20H, Ph), 3.40 (br, s, 2H, Hs),
2.82 (m, 3H, PCH2CH2P, Hc), 2.32 (m, 2H, PCH2CH2P),
A procedure similar to the one described for the
preparation of 3 was used. The reaction of W(CO)2(g3-
C3H5)(NCCH3)2Br (447.3 mg, 1.00 mmol) with 2,20-bipyri-
dine (156.6 mg, 1.00 mmol) and NaBH3CN (62.6 mg,
1.00 mmol) afforded 332.5 mg (70% yield) of red crystals
of 4 isolated from a hexane/DME solution. 11B NMR
(DME): d ꢀ44.0 ppm (br, q, JB–H = 91 Hz). 1H NMR
(CD2Cl2): d 8.95–7.64 (m, bipy), 3.14 (d, JH–H = 6.6 Hz,
Hs), 2.27 (m, Hc), 1.86 (d, JH–H = 8.4 Hz, Ha), and 0.10
ppm (br, BH3). 13C NMR (CD2Cl2): d 216.64 (CO),
1.89 (d, JH–H = 9.9 Hz, 2H, H ), and 0.29 ppm (br, 3H,
a
BH3). 13C NMR (CDCl3): d 213.25 (CO), 133.50, 133.43,
131.90, 130.98, 130.66, 129.15 (C6H5), 75.74 (Cc), 51.31
(Ct), 27.23, and 26.70 ppm (PCH2CH2P). IR (KBr):
3080(vw), 3061(w), 3026(vw), 3004(vw), 2990(vw),
2944(vw), 2923(vw), 2338(m), 2267(vw), 2203(vw),
2185(m), 1933(vs), 1844(vs), 1586(vw), 1574(vw), 1484(w),

544
F.-C. Liu et al. / Journal of Organometallic Chemistry 693 (2008) 537–545
154.64, 152.69, 139.57, 127.35, 122.93 (bipy), 66.58 (Cc),
and 49.39 ppm (Ct). IR (KBr): 3111(vw), 3085(vw),
3058(vw), 2975(vw), 2869(w), 2364(m), 2348(m), 2294(vw),
2214(vw), 2194(m), 1935(vs), 1846(vs), 1635(vw), 1601(m),
1559(vw), 1490(vw), 1469(m), 1442(m), 1418(w), 1383(w),
1311(w), 1281(vw), 1260(vw), 1242(vw), 1222(vw),
1143(m), 1127(m), 1118(m), 1072(w), 1047(w), 1020(w),
821(w), 805(vw), 801(vw), 760(s), 747(w), 734(m), 541(w),
457(w), 445(w), and 426(w) cmꢀ1. Anal. Calc. for
C16H16BN3O2W: N, 8.81; C, 40.29; H, 3.38. Found: N,
8.71; C, 39.95; H, 3.41%.
1H, NH2), 3.96 (m, 1H, NH2), 3.76 (m, 1H, NH2), 2.93
(m, 1H, Hs), 2.86 (m, 2H, Hc, en), 2.79 (m, 1H, en), 2.75
(m, 1H, Hs), 2.64 (m, 1H, en), 2.53 (m, 1H, en), 1.21 (d,
JH–H = 9.0 Hz, 1H, Ha), 1.00 (d, JH–H = 8.4 Hz, 1H, Ha),
and 0.36 ppm (br, q, 3H, BH3). 13C NMR (d8-
THF, ꢀ40°C): d 218.66, 218.58 (CO), 128.97 (CN), 61.22
(Cc), 48.19, 47.74 (Ct), 45.28, and 43.71 ppm (en). IR
(KBr): 3337(vw), 3325(m), 3313(w), 3274(w), 3260(vw),
3146(vw), 3062(vw), 2983(vw), 2960(vw), 2894(vw),
2358(m), 2346(m), 2260(vw), 2251(vw), 2238(vw), 2218
(vw), 2194(m), 1937(vs), 1781(vs), 1580(m), 1458(w),
1316(vw), 1287(w), 1261(w), 1158(w), 1110(s), 1086(m),
1049(s), 1029(m), 1008(m), 961(vw), 932(vw), 905(vw),
872(vw), 817(w), 810(w), and 803(w) cmꢀ1. IR (DME,
3.3.5. Mo(CO)2(g3-C3H5)(en)(NCBH3) (5)
In a drybox a solution of 1,2-ethylenediamine (61.2 mg,
1.02 mmol) in 3.0 mL CH2Cl2 was added dropwise into a
solution of Mo(CO)2(g3-C3H5)(NCCH3)2Br (362.4 mg,
1.01 mmol) in 20 mL CH2Cl2. The system was stirred for
2 h furnishing a yellow solution. A solution of sodium cya-
notrihydroborate (62.7 mg, 0.99 mmol) in 3.0 mL of meth-
anol was added dropwise to this yellow solution. After
stirring for 12 h the solvents were removed under a
dynamic vacuum. The resulting yellow solid was extracted
several times with 20 mL portions of DME. The extracts
were combined, concentrated, and layered with hexane
for crystallization. The product was obtained as yellow
crystals (182.2 mg, 62%). 11B NMR (DME): d ꢀ42.9 ppm
m
CO): 1932 and 1837 cmꢀ1. Anal. Calc. for C8H16BN2O3W:
N, 11.03; C, 25.23; H, 4.23. Found: N, 11.10; C, 25.21; H,
4.25%.
Acknowledgement
This work was supported by the National Science Coun-
cil of the ROC through Grant NSC 95-2113-M-259-011.
Appendix A. Supplementary material
CCDC 657170, 657171, 657172, 657173, and 657174
contains the supplementary crystallographic data for 2, 3,
4, 5, and 6. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif. Supplementary data
associated with this article can be found, in the online ver-
sion, at doi:10.1016/j.jorganchem.2007.11.039.
1
(br, q, JB–H = 89 Hz). H NMR (d8-THF, ꢀ40°C): d 5.85
(m, 1H, NH2), 3.98 (m, 1H, NH2), 3.70 (m, 2H, NH2,
Hc), 3.35 (m, 1H, NH2), 3.16 (m, 1H, Hs), 2.99 (m, 1H,
Hs), 2.79 (m, 1H, en), 2.65 (m, 1H, en), 2.50 (m, 2H, en),
1.11 (d, JH–H = 9.6 Hz, 1H, Ha), 0.89 (d, JH–H = 9.6 Hz,
1H, Ha), and 0.33 ppm (br, q, 3H, BH3). 13C NMR (d8-
THF, ꢀ40 °C): d 226.21, 226.07 (CO), 129.09 (CN), 69.94
(Cc), 56.49, 55.79 (Ct), 44.83, and 43.22 ppm (en). IR
(KBr): 3340(m), 3330(m), 3279(m), 3265(m), 3152(vw),
3069(w), 3043(vw), 3006(w), 2990(w), 2976(m), 2954(m),
2920(w), 2893(w), 2344(s), 2266(m), 2240(m), 2218(vw),
2196(s), 2147(w), 1944(vs), 1800(vs), 1583(m), 1578(s),
1558(w), 1539(w), 1472(w), 1457(m), 1399(vw), 1381(w),
1362(vw), 1315(w), 1284(m), 1261(vw), 1234(vw),
1146(m), 1134(m), 1122(m), 1113(s), 1105(m), 1081(m),
1044(s), 1027(m), 1009(m), 979(w), 954(w), 931(w),
919(w), 856(w), 844(w), 634(w), 613(vw), 587(vw),
575(m), 556(m), 503(m), 492(m), and 468(m) cmꢀ1. IR
(DME, mCO): 1941 and 1849 cmꢀ1. Anal. Calc. for
C8H16BN3O2Mo: N, 14.35; C, 32.80; H, 5.50. Found: N,
14.14; C, 32.39; H, 5.55%.
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3.3.6. W(CO)2(g3-C3H5)(en)(NCBH3) (6)
A procedure similar to the one described for the
preparation of 5 was used. The reaction of W(CO)2(g3-
C3H5)(NCCH3)2Br (447.9 mg, 1.00 mmol) with 1,2-ethy-
lenediamine (60.5 mg, 1.01 mmol) and NaBH3CN
(62.3 mg, 1.01 mmol) furnished 3226.4 mg (59% yield) of
yellow crystals isolated from a hexane/DME solution. 11B
NMR (DME): d ꢀ43.1 ppm (br, q, JB–H = 90 Hz). 1H
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