β-phosphinoethylboranes as ambiphilic ligands in nickel-methyl complexes

Article abstract of DOI:10.1021/om7010886

The ambiphilic β-phosphinoethylboranes Ph₂PCH ₂CH₂BR₂ (BR₂ = BCy₂ (1a), BBN (1b)), which feature the ethano spacer CH₂CH₂ between the Lewis acidic boryl and Lewis basic phosphino groups, were synthesized in nearly quantitative yields via the hydroboration of vinyldiphenylphosphine. Compounds 1a,b were fully characterized by elemental analysis and by NMR and IR spectroscopy. X-ray crystallographic studies of compound lb revealed infinite helical chains of the molecules connected through P ... B donor-acceptor interactions. The ability of these ambiphilic ligands to concurrently act as donors and acceptors was highlighted by their reactions with (dmpe)NiMe ₂. The zwitterionic complexes (dmpe)NiMe(Ph₂PCH ₂CH₂BCy₂Me) (2a) and (dmpe)NiMe(Ph ₂PCH₂CH₂[BBN]Me) (2b) were generated via the abstraction of one of the methyl groups, forming a borate, and intramolecular coordination of the phosphine moiety to the resulting cationic metal center. Compound 2b was characterized by X-ray crystallography. Furthermore, B(C ₆F₅)₃ abstracts the methyl group of a coordinated borate ligand to generate a free, three-coordinate borane center in [(dmpe)NiMe(1a)]⁺[MeB(C₆F₅)₃] ^- (3).

Full text of DOI:10.1021/om7010886

Organometallics 2008, 27, 1135–1139
1135
ꢀ-Phosphinoethylboranes as Ambiphilic Ligands in Nickel-Methyl
Complexes
Andreas Fischbach, Patrick R. Bazinet, Rory Waterman, and T. Don Tilley*
Department of Chemistry, UniVersity of California, Berkeley, California 94720-1460
ReceiVed October 28, 2007
The ambiphilic ꢀ-phosphinoethylboranes Ph2PCH2CH2BR2 (BR2 ) BCy2 (1a), BBN (1b)), which feature
the ethano spacer CH2CH2 between the Lewis acidic boryl and Lewis basic phosphino groups, were
synthesized in nearly quantitative yields via the hydroboration of vinyldiphenylphosphine. Compounds
1a,b were fully characterized by elemental analysis and by NMR and IR spectroscopy. X-ray
crystallographic studies of compound 1b revealed infinite helical chains of the molecules connected through
P · · · B donor–acceptor interactions. The ability of these ambiphilic ligands to concurrently act as donors
and acceptors was highlighted by their reactions with (dmpe)NiMe2. The zwitterionic complexes
(dmpe)NiMe(Ph2PCH2CH2BCy2Me) (2a) and (dmpe)NiMe(Ph2PCH2CH2[BBN]Me) (2b) were generated
via the abstraction of one of the methyl groups, forming a borate, and intramolecular coordination of the
phosphine moiety to the resulting cationic metal center. Compound 2b was characterized by X-ray
crystallography. Furthermore, B(C6F5)3 abstracts the methyl group of a coordinated borate ligand to generate
a free, three-coordinate borane center in [(dmpe)NiMe(1a)]+[MeB(C6F5)3]– (3).
Chart 1
Introduction
The elucidation of the mechanisms by which many enzymes
operate has revealed nature’s use of multifunctional catalysis
as a strategy for the optimization of chemical conversions.1 The
exploitation of the synergistic interaction of two or more reactive
centers can lead to cooperative catalytic effects on a variety of
chemical processes. In homogeneous catalysis, use of ambiphilic
ligands of the type LA-spacer-LB, with both Lewis acidic
(LA) and Lewis basic (LB) functionalities, offers the interesting
possibility of activating both the metal center and the substrate
molecule in a cooperative fashion. For example, the use of such
ambiphilic ligands was reported by Labinger and Miller in 1982
to facilitate the formation of CO insertion products.2,3 Although
relatively scarce, there have been subsequent reports on the use
of ambiphilic ligands in catalysis. The bifunctional ligand
Me2PCH2AlMe2, first synthesized by Karsch et al.,4was em-
ployed as a cocatalyst in the nickel(II)-catalyzed dehydrogena-
tive oligomerization of PhSiH3,5a and has recently been studied
as a ligand in rhodium complexes.5b Phosphino/boryl com-
pounds, featuring a variety of different spacer groups, have also
been reported as bifunctional ligands in transition-metal
chemistry.6–8
the metal center, the Lewis acidic group can interact with an
anionic ligand in the metal’s coordination sphere, abstract an
anionic ligand from the metal, or interact directly with the metal
center. Indeed, a number of such interactions have been
observed,6–10 and this supports the notion that ambiphilic ligands
can have a profound effect on the chemistry at the metal center.
We now report an efficient synthetic method for the preparation
of ꢀ-phosphinoethylboranes and their use as ambiphilic ligands
that interact with both the metal center and a second ligand (a
methyl group) in the metal’s coordination sphere.
Results and Discussion
In 1997 Schmidbaur and co-workers reported the synthesis
and structural characterization of cyclo-[(9-borabicyclo[3.3.1]-
nonanyl)butano(diphenyl)phosphine], Ph2P(CH2)4BC8H14, and
cyclo-[(9-borabicyclo[3.3.1]nonanyl)propano(diphenyl)phos-
phine], Ph2P(CH2)3BC8H14, (A and B, respectively; Chart 1).11,12
The possibility that these phosphino/boryl compounds possess
Ambiphilic ligands can interact with metal complexes in a
variety of ways. After coordination of the phosphino group to
* To whom correspondence should be addressed. E-mail: tdtilley@
berkeley.edu.
(1) Rowlands, G. J. Tetrahedron 2001, 57, 1865.
(2) (a) Labinger, J. A.; Miller, J. S. J. Am. Chem. Soc. 1982, 104, 6856.
(b) Grimmett, D. L.; Labinger, J. A.; Bonfiglio, J. N.; Masuo, S. T.; Shearin,
E.; Miller, J. S. J. Am. Chem. Soc. 1982, 104, 6858.
(3) Labinger, J. A.; Bonfiglio, J. N.; Grimmett, D. L.; Masuo, S. T.;
Shearin, E.; Miller, J. S. Organometallics 1983, 2, 733.
(4) Karsch, H. H.; Appelt, A.; Köhler, F. H.; Müller, G. Organometallics
1985, 4, 231.
(7) (a) Bontemps, S.; Gornitzka, H.; Bouhadir, G.; Miqueu, K.;
Bourissou, D. J. Am. Chem. Soc. 2006, 128, 12056. (b) Bontemps, S.;
Bouhadir, G.; Dyer, P. W.; Miqueu, K.; Bourissou, D. Inorg. Chem. 2007,
46, 5149.
(8) (a) Emslie, D. J. H.; Blackwell, J. M.; Britten, J. F.; Harrington,
L. E. Organometallics 2006, 25, 2412. (b) Oakley, S. R.; Parker, K. D.;
Emslie, D. J. H.; Vargas-Baca, I.; Robertson, C. M.; Harrington, L. E.;
Britten, J. F. Organometallics 2006, 25, 5835.
(5) (a) Fontaine, F.-G.; Zargarian, D. J. Am. Chem. Soc. 2004, 126, 8786.
(b) Thibault, M.-H.; Boudreau, S.; Drouin, F.; Sigouin, O.; Michaud, A.;
Fontaine, F.-G. Organometallics 2007, 26, 3807.
(9) Hill, A. F. Organometallics 2006, 25, 4741 and references therein.
(10) Parkin, G. Organometallics 2006, 25, 4744 and references therein.
(11) Schmidbaur, H.; Sigl, M.; Schier, A. J. Organomet. Chem. 1997,
529, 323.
(6) Bontemps, S.; Gornitzka, H.; Bouhadir, G.; Miqueu, K.; Bourissou,
D. Angew. Chem., Int. Ed. 2006, 45, 1611.
10.1021/om7010886 CCC: $40.75
2008 American Chemical Society
Publication on Web 02/29/2008

1136 Organometallics, Vol. 27, No. 6, 2008
Fischbach et al.
Table 1. Crystal Data and Data Collection Parameters of
relatively strong P-B interactions might be expected to greatly
reduce their ability to interact with organometallic species.
Therefore, the synthesis of related compounds possessing shorter
spacer groups was undertaken. Although compounds A and B
were both prepared by the rapid and quantitative hydroboration
of allyldiphenylphosphine (Ph2PCH2CHdCH2) and butenyl-
diphenylphosphine (Ph2PCH2CH2CHdCH2) with 9-borabicy-
clononane (9-BBN), attempts to prepare the ethano-bridged cyclo-
[(9-borabicyclo[3.3.1]nonanyl)ethano(diphenyl)phosphine] derivative
Ph2P(CH2)2BC8H14 (C; Chart 1) by reaction of 9-BBN with
diphenylvinylphosphine (Ph2PCHdCH2) did not produce the
desired product. Instead, the reaction gave mixtures of products
thought to contain P-B-bonded compounds generated through a
boraphosphetane intermediate (with loss of ethylene).11
Compounds 1b and 2a
1b
2a
chem formula
fw
C22H28BP
334.22
C34H58BNiP3
629.23
color/shape
cryst size (mm)
cryst syst
space group
a (Å)
colorless/fragment
0.5 × 0.5 × 0.3
tetragonal
I41/a
21.039(2)
21.039(2)
17.050(2)
90
yellow/fragment
0.16 × 0.13 × 0.09
triclinic
j
P1
10.400(2)
11.840(2)
15.520(3)
76.509(3)
88.116(3)
68.598(3)
1727.3 (5)
2
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
90
90
7547.0(13)
16
Z
A simple modification of the published hydroboration condi-
tions,11 involving aromatic solvents instead of THF, allowed
the preparation of ꢀ-phosphinoethylboranes with an ethano
spacer group separating the Lewis acidic boryl and the Lewis
basic phosphino groups. Two equivalents of diphenylvinylphos-
phine was allowed to react with freshly recrystallized, dimeric
dicyclohexylborane [Cy2B(µ-H)]2 and 9-BBN, respectively, to
produce compounds 1a,b (eq 1). The [(dicyclohexyl)boryl]eth-
yl(diphenyl)phosphine (1a) formed in a fast and quantitative
reaction (isolated yield 89%) within less than 1 h at ambient
temperature. However, slightly elevated temperatures were
required for synthesis of (9-borabicyclo[3.3.1]nonanyl)ethyl-
(diphenyl)phosphine (1b) (isolated yield 56%). Both reactions
proceed in a nearly quantitative fashion on the basis of NMR-
scale reactions; however, the high solubility of the compounds
led to lower isolated yields. Phosphine-borane adducts, which
are possible intermediates in the reaction, were not observed in
reactions using the highly reactive [Cy2B(µ-H)]2. However,
when using 9-BBN, a broad signal in the 31P{1H} NMR
spectrum at 5.4 ppm, observable in an NMR-scale reaction at
ambient temperature after 15 min, most likely corresponds to
the intermediate [Ph2(H2CdCH)P](BBN). The formation of this
adduct is consistent with the elevated temperatures required for
the reaction to proceed. Note that the related compound
Mes2PCH2CH2B(C6F5)2 (Mes ) 2,4,6-Me3C6H2) was recently
reported.13
T (K)
108
1.177
0.146
2880
1.54–23.26
-18 e h e 23, -23
e k e 23, -18 e l
e 16
133
1.210
0.722
680
3.26–24.77
-9 e h e 12, -10
e k e 13, -17 e l
e 18
8973
5700 (all)/0.0722
352
Fcalcd (g cm-3
)
µ (mm-1
F000
θ range (deg)
data collected
)
no. of rflns collected
no. of indep rflns/Rint 2701 (all)/0.0357
no. of params refined 217
16867
R1 (obsd/all)
wR2 (obsd/all)
GOF
0.0339/0.0422
0.0788/0.0834
1.037
0.0386/0.0859
0.1571/0.1716
1.018
max/min ∆F (e Å-3
)
+0.277/-0.201
+0.94/-0.89
of elemental analysis and NMR14 and IR spectroscopy. Singlets
in the 31P{1H} NMR spectra at –8.5 (1a) and –11.5 ppm (1b)
and broad signals in the borane region of the 11B{1H} NMR
spectra at 83.0 (1a) and 86.4 ppm (1b) are indicative of three-
coordinate phosphorus and boron centers with no P-B donor–
acceptor interactions in solution. However, low-temperature
NMR experiments, performed in toluene-d8 at –80 °C, resulted
in a distinct broadening of both signals, suggesting the possibility
of some interaction between the phosphorus and boron centers.
Recrystallization of compound 1b from a toluene/THF mixture
(4:1) at –30 °C yielded colorless single crystals suitable for an
X-ray crystallographic study. Compound 1b crystallizes in the
tetragonal space group I41/a. Table 1 gives crystal data and data
collection parameters for 1b. The molecular structure of 1b does
indeed reveal the presence of P-B interactions in the solid state.
However, unlike the C3- and C4-bridged phosphinoboranes A
and B, which possess cyclic structures, compound 1b forms a
polymeric framework of infinite helical chains of 1b connected
through P · · · B donor–acceptor interactions. The asymmetric unit
is illustrated in Figure 1, and a short section of one of the helices
is shown in Figure 2.
(1)
Compounds 1a,b were isolated and purified as white solids
via crystallization from saturated hexane (1a) or toluene
solutions (1b) at –30 °C. They were fully characterized by means
Much of the metrical data for compound 1b is in agreement
with that of the corresponding C3- (B) and C4-bridged cyclic
derivatives (A).11 The P–C1 and C2–B distances of 1.834(2)
and 1.640(3) Å, respectively, show only minor differences
compared to values for the previously reported analogues (A,
1.824(1), 1.643(2) Å; B, 1.828(2), 1.628(4) Å)11 or structurally
related phosphine-borane adducts (e.g., [BH2–CH2–PPh2]2,
1.800(2), 1.645(3) Å15). The P–B bond length of 2.056(2) Å
lies between the corresponding values for B (2.029(2) Å) and
A (2.072(3) Å).11 The helical arrangement of the infinite
(12) A variety of phosphinoboranes without a spacer group between
the boron and phosphorus (R2P-BR′2), and corresponding transition-metal
complexes, have previously been reported. For example, see: (a) Paine,
R. T.; Nöth, H. Chem. ReV. 1995, 95, 343 and references therein. (b) Dorn,
H.; Singh, R. A.; Massey, J. A.; Nelson, J. M.; Jaska, C. A.; Lough, A. J.;
Manners, I. J. Am. Chem. Soc. 2000, 122, 6669. (c) Jaska, C. A.; Dorn, H.;
Lough, A. J.; Manners, I. Chem. Eur. J. 2003, 9, 271. (d) Dorn, H.; Rodezno,
J. M.;Brunnhöfer, B.; Rivard, E.; Massey, J. A.; Manners, I. Macromolecules
2003, 36, 291. In addition, Stephan and co-workers have reported interesting
properties for free phosphinoboranes with rigid spacer groups: (e) Welch,
G. C.; Cabrera, L.; Chase, P. A.; Hollink, E.; Masuda, J. D.; Wei, P. R.;
Stephan, D. W. Dalton Trans. 2007, 3407. (f) Welch, G. C.; Juan, R. R. S.;
Masuda, J. D.; Stephan, D. W. Science 2006, 314, 5802.
(14) HMQC-NMR techniques were necessary to assign all of the proton
and carbon signals.
(15) Jaska, C. A.; Lough, A. J.; Manners, I. Inorg. Chem. 2004, 43,
1090.
(13) Spies, P.; Erker, G.; Kehr, G.; Bergander, K.; Fröhlich, R.; Grimme,
S.; Stephan, D. W. Chem. Commun. 2007, 5072.

ꢀ-Phosphinoethylboranes as Ambiphilic Ligands
Organometallics, Vol. 27, No. 6, 2008 1137
(2)
31P{1H} NMR spectra of both compounds display three doublets
of doublets due to the presence of three inequivalent phosphorus
atoms coordinated to the nickel center. Another characteristic
feature of both compounds is that they display signals for two
distinct methyl groups in their 1H and 13C{1H} NMR spectra.14
Specifically, the hydrogen atoms of the abstracted methyl
groups, now bound to B, appear as broad resonances at 0.10
(2a) and –0.42 ppm (2b), due to the quadrupole moment of the
1
boron center. The H NMR shifts for the remaining Ni-CH3
groups appear as singlets at 0.23 (2a) and -0.05 ppm (2b) and
are shifted upfield with respect to those for the starting complex
(dmpe)NiMe2 (–0.31 ppm).16 In addition, sharp signals in the
11B{1H} spectra, at –14.9 (2a) and –16.3 ppm (2b), support
the proposed alkyl abstraction and the formation of borate
groups.
Figure 1. Molecular structure of compound 1b with atomic
numbering (ORTEP; 50% probability ellipsoids; hydrogen atoms
are omitted for clarity). Selected bond lengths (Å) and angles (deg):
P1 · · · B1′, 2.056(2); P1–C1, 1.834(2); C1–C2, 1.530(2); C2–B1,
1.640(3); P1–C11, 1.827(2); P1–C17, 1.836(2); B1–C3, 1.634(3);
B1–C7, 1.630(3); C1–P1–B1′, 120.0(1); C1–P1–C11, 106.7(1);
C1–P1–C17, 99.5(1); C11–P1–C17, 106.1(1); P1–C1–C2, 116.5(1);
C1–C2–B1, 118.5(2); C2–B1–P1′, 103.6(2); C2–B1–C3, 110.2(2);
C2–B1–C7, 117.0(2); C3–B1–C7, 105.0(2).
Further confirmation of the assignments of compounds 2a,b
as zwitterionic compounds was obtained from structural studies.
Crystallization of complex 2a from a toluene/THF mixture
(1:2) at –30 °C gave yellow single crystals suitable for an X-ray
diffraction structure determination. Table 1 gives crystal data
and data collection parameters for 1b. The solid-state structure
of complex 2a and the atom-numbering scheme are given in
Figure 3. Complex 2a crystallizes in the triclinic space group
j
P1 with two molecules in the formula unit. The nickel atom
exhibits a distorted-square-planar geometry (sum of angles about
Ni: 360.6°).
The ability of the ꢀ-phosphinoethylborane ligands to react
further with nickel zwitterions 2a,b was explored. Addition of
another 1 equiv of compound 1 to 2a,b did not result in a second
methyl group transfer reaction or displacement of the coordi-
nated phosphine. The signals for both the Ni-CH3 and B-CH3
groups remained clearly visible in the NMR spectra of the
reactions. Interestingly, addition of the highly Lewis acidic
compound B(C6F5)3 to 2a resulted in a methyl group transfer
from the cyclohexylborate moiety to the B(C6F5)3 molecule (eq
3). The newly formed complex (3) was identified in an NMR-
scale reaction as the only product after 10 min at ambient
temperature. The 11B{1H} NMR spectra contained two distinct
signals at 82.1 (broad) and –14.4 ppm (sharp), which were
assigned to the three-coordinate -BCy2 group (without any type
of B · · · Me interaction) and the four-coordinate, anionic borate
counteranion [MeB(C6F5)3]–, respectively.
Figure 2. Molecular structure of compound 1b: short section of
one of the P · · · B connected helices.
phosphine-borane adduct chain results in a quasi-C4 symmetry
for the {PC2B}x core, with a Pn · · · Pn+4 distance of 1.7 nm.
To probe the ambiphilic character of the ꢀ-phosphinoeth-
ylboranes 1, reactions of these compounds with an organome-
tallic complex were investigated. The nickel dimethyl compound
(dmpe)NiMe2 (dmpe ) bis(dimethylphosphino)ethane) was
treated with both 1a and 1b in equimolar quantities at ambient
temperature.Thisledtoformationofthezwitterionicnickel-methyl
complexes 2a,b, respectively (eq 2). The ambiphilic nature of
the ꢀ-phosphinoethylboranes is manifested in their behavior as
phosphine donors, and as Lewis acids, in the abstraction of a
methyl group from the nickel center.
(3)
Experimental Section
General Considerations. All operations were performed with
rigorous exclusion of air and water, using standard Schlenk and
drybox techniques (Vacuum Atmospheres NEXUS; <1 ppm O2,
<1 ppm H2O). Dry, oxygen-free solvents were employed through-
The identities of complexes 2a,b were established by
elemental analysis and by NMR and IR spectroscopy. The
(16) Kaschube, W.; Pörschke, K. R.; Wilke, G. J. Organomet. Chem.
1988, 355, 525.

1138 Organometallics, Vol. 27, No. 6, 2008
Fischbach et al.
Cy2BCH2). 11B{1H} NMR (benzene-d6): δ 83.0 ppm. 31P{1H}
NMR (benzene-d6): δ –8.5 ppm. Anal. Calcd for C26H36BP (mol
wt 390.35): C, 80.00; H, 9.30. Found: C, 80.29; H, 8.91.
Ph2PCH2CH2[BBN] (1b). By the procedure presented above,
vinyldiphenylphosphine (1.139 g, 5.37 mmol) and recrystallized
9-BBN (655 mg, 5.37 mmol) were combined with stirring. The
mixture was heated to 60 °C and kept for 3 h at this temperature.
Then, the solvent was removed in vacuo. The crude product was
washed with hexanes (3 × 5 mL) and dried under vacuum to give
1b as a white powder in 55.5% yield (996 mg, 2.98 mmol). IR
(Nujol, KBr): 1961 w, 1901 w, 1821 w, 1774 w, 1586 w, 1482 s,
1434 s, 1306 w, 1264 m, 1200 w, 1188 m, 1106 s, 1071 m, 1028 m,
999 w, 949 w, 896 m, 837 w, 771 w, 747 s, 699 s, 634 w, 562 w,
523 m, 502 m cm-1. 1H NMR (benzene-d6): δ 7.50 (m, 4 H, o-Ph),
7.10 (4 H, m-Ph), 7.05 (m, 2 H, p-Ph), 2.24 (m, 2 H, PCH2),
1.84–1.77 (m, 6 H, ꢀ-/γ-BBN), 1.70 (m, 2 H, R-BBN), 1.69–1.62
(m, 4 H, ꢀ-BBN), 1.55 (m, 2H, CH2B), 1.18 ppm (m, 2 H, γ-BBN).
Figure 3. Molecular structure of 2a with atomic numbering
(ORTEP; 50% probability ellipsoids; hydrogen atoms are omitted
for clarity). Selected bond lengths (Å) and angles (deg): Ni–P1,
2.195(2); Ni–P2, 2.199(1); Ni–P3, 2.17(2); Ni–C1, 1.970(4); P1–C6,
1.827(5); C6–C7, 1.550(6); C7–B, 1.662(7); B–C10, 1.659(7);
B–C81, 1.662(7); B–C91, 1.684(7); P1–Ni–P2, 102.32(5); P2–Ni–P3,
86.72(5); P3–Ni–C1, 85.8(2); C1–Ni–P1, 85.7(2); Ni–P1–C6,
107.2(2); P1–C6–C7, 110.8(3); C6–C7–B, 118.9(4); C7–B–C10,
105.2(4).
1
13C{1H} NMR (benzene-d6): δ 139.9 (d, JCP ) 15.1 Hz, ipso-
2
3
Ph), 133.2 (d, JCP ) 17.6 Hz, o-Ph), 128.7 (d, JCP ) 6.3 Hz,
m-Ph), 128.6 (p-Ph), 33.5 (ꢀ-BBN), 31.4 (vbr, R-BBN), 23.6 (γ-
1
BBN), 23.5 (vbr, CH2B), 22.9 ppm (d, JCP ) 11.3 Hz, PCH2).
11B{1H} NMR (benzene-d6): δ 86.4 ppm. 31P{1H} NMR (benzene-
d6): δ –11.5 ppm. Anal. Calcd. for C22H28BP (mol wt 334.24): C,
79.06; H, 8.44. Found: C, 79.28; H, 8.56.
(dmpe)NiMe(Ph2PCH2CH2BCy2Me) (2a). In a drybox, (dmpe)N-
iMe216 (126.2 mg, 0.53 mmol) was dissolved in 8 mL of a toluene/
THF mixture (1:1). A solution of 206.2 mg of Ph2PCH2CH2BCy2
(0.53 mmol) in 4 mL of toluene was slowly added with stirring at
ambient temperature. The mixture was stirred at ambient temper-
ature for 3 h. Then, the solvents were removed in vacuo, and the
residue was washed with toluene (1 × 3 mL) and hexanes (3 × 3
mL) and dried under vacuum to give 264.7 mg (0.42 mmol, 79%)
of analytically pure 5a as a light yellow powder. Crystallization
from toluene/THF mixtures (1:2) at –30 °C gave single crystals
suitable for an X-ray structure determination. IR (Nujol, KBr):
1586 w, 1463 s, 1328 w, 1301 m, 1285 m, 1260 m, 1240 s, 1227 m,
1197 m, 1175 m, 1161 m, 1147 w, 1118 m, 1100 s, 1070 m,
1022 m, 987 m, 876 m, 852 w, 829 m, 797 m, 737 s, 698 s, 655 m,
522 m, 512 m cm-1. 1H NMR (400.1 MHz, dichloromethane-d2):
δ 7.59 (m, 4 H, o-Ph), 7.36 (m, 6 H, m-Ph, p-Ph), 2.43 (m, 2 H,
PCH2CH2B), 1.75–1.40 (br m, 18 H, Cyꢀ, Cyγ, Cyδ, PCH2CH2B,
PMe2), 1.25–0.80 (br m, 18 H, CyR, Cyꢀ, Cyγ, Cyδ, PMe2), 0.60
(br, 2 H, PCH2CH2P), 0.11 (br, 2 H, PCH2CH2P), –0.07 (s, 3 H,
NiMe), –0.75 ppm (br s, 3 H, BMe). 1H NMR (400.1 MHz,
benzene-d6): δ 7.58 (m, 4 H, o-Ph), 7.01 (m, 4 H, m-Ph), 6.95 (m,
2 H, p-Ph), 2.90 (m, 2 H, PCH2CH2B), 2.50–2.15 (m, 10 H, Cyꢀ,
Cyγ, Cyδ), 1.90–1.65 (m, 10 H, Cyꢀ, Cyγ, Cyδ), 1.08 (m, 2 H,
PCH2CH2B), 0.99 (m, 2 H, CyR), 0.91 (m, 10 H, PCH2CH2P,
PMe2), 0.56 (m, 6 H, PMe2), 0.23 (s, 3 H, NiMe), 0.10 (br s, 3 H,
BMe). 13C{1H} NMR (100.6 MHz, dichloromethane-d2): δ 137.0
out. Removal of thiophenes from benzene and toluene was
accomplished by washing each with H2SO4 and saturated NaHCO3
followed by drying over MgSO4. Olefin impurities were removed
from pentane by treatment with concentrated H2SO4, 0.5 N KMnO4
in 3 M H2SO4, saturated NaHCO3, and then the drying agent
MgSO4. All solvents were distilled from sodium benzophenone
ketyl and stored under nitrogen. Benzene-d6 (Cambridge Isotope
Laboratories Inc.) was purified by vacuum distillation from Na/K
alloy. Dichloromethane-d2 (Cambridge Isotope Laboratories Inc.)
was purified by vacuum distillation from CaH2. All other chemicals
were obtained from Aldrich and used without further purification.
All NMR spectra were recorded at room temperature in benzene-
d6 or dichloromethane-d2 unless otherwise noted, using a Bruker
AM-400 spectrometer (FT, 400.1 MHz 1H; 128.4 MHz 11B; 100.6
MHz 13C; 162.0 MHz 31P), a Bruker AMX-400 spectrometer (FT,
400.1 MHz 1H; 376.5 MHz 19F) or a Bruker DRX-500 spectrometer
(FT, 500.1 MHz 1H, 160.5 MHz 11B; 125.8 MHz 13C; 202.5 MHz
31P). Spectra were referenced to the residual nondeuterated solvent
for 1H and 13C or to external standard samples (BF3 · OEt2 for 11B,
85% H3PO4 for 31P, C6F6 for 19F). Infrared spectra were recorded
as Nujol mulls using a Mattson FT-IR spectrometer at a resolution
of 4 cm–1. Elemental analyses (CHN) were performed by the
microanalytical laboratory at the University of California, Berkeley.
Ph2PCH2CH2BCy2 (1a). At ambient temperature a solution of
2.506 g of vinyldiphenylphosphine (11.81 mmol) in 5 mL of toluene
was added to a suspension of 2.103 g of dicyclohexylborane (11.81
mmol) in 10 mL of toluene with stirring. A colorless solution
formed within 1 min. After the mixture was stirred for 2 h at
ambient temperature, the solvent was removed in vacuo. The sticky
crude product was redissolved in 15 mL of hexanes and crystallized
during ca. 14 h at –30 °C to give 1a as a colorless solid (3.922 g,
10.05 mmol, 85%). A second crop of crystals (195 mg, 0.50 mmol,
4.2%) was obtained from the concentrated mother liquid. IR (Nujol,
KBr): 1946 w, 1880 w, 1806 w, 1587 w, 1304 s, 1262 m, 1227 m,
1142 m, 1094 m, 1027 m, 976 m, 957 m, 890 w, 841 w, 737 s,
2
(br, ipso-Ph), 132.9 (d, JCP ) 8.8 Hz, o-Ph), 130.1 (p-Ph), 128.9
3
(d, JCP ) 5.9 Hz, m-Ph), 36.8 (m, PCH2CH2P), 32.8 (Cyꢀ), 32.7
(Cyꢀ), 31.3 (Cyγ), 29.6 (Cyδ), 26.6 (m, PCH2CH2P), 24.7 (d, 1JCP
) 19.0 Hz, PCH2CH2B), 12.2 (d, 1JCP ) 23.4 Hz, PMe2), 12.1 (d,
1JCP ) 29.2 Hz, PMe2), 5.9 (br m, BMe), 0.2 ppm (br m, NiMe).
13C{1H} NMR (100.6 MHz, benzene-d6): δ 137.1 (br, ipso-Ph),
132.6 (o-Ph), 129.5 (p-Ph), 128.6 (m-Ph), 37.1 (vbr, CyR), 33.3
(Cyꢀ), 33.2 (Cyꢀ), 31.7 (Cyγ), 30.0 (Cyδ), 27.8 (br, PCH2CH2P),
26.3 (vbr, PCH2CH2B), 25.7 (vbr, PCH2CH2P), 25.3 (br, 27.8 (br,
PCH2CH2B), 11.5 (d, 1JCP ) 23.1 Hz, PCH3), 11.1 (d, 1JCP ) 42.3
Hz, PCH3), 8.6 (vbr, NiMe), 1.1 ppm (vbr, BCH3). 11B{1H} NMR
(128.4 MHz, dichloromethane-d2): δ –15.7 ppm. 11B{1H} NMR
(128.4 MHz, benzene-d6): δ –14.9 ppm. 31P{1H} NMR (162.0
MHz, dichloromethane-d6): δ 40.0 (br, trans-Pdmpe), 30.8 (br), 28.8
ppm (cis-Pdmpe). 31P{1H} NMR (162.0 MHz, benzene-d6): δ 38.7
1
3
696 s, 505 w cm-1. H NMR (benzene-d6): δ 7.52 (t, JHH ) 7.6
Hz, 4 H, o-Ph), 7.13–7.03 (m, 6 H, m-/p-Ph), 2.12 (m, 2 H, PCH2),
1.70 (m, 6 H, ꢀ-/δ-Cy), 1.50 (m, 4 H, γ-Cy), 1.45–1.36 (m, 4 H,
R-Cy, PCH2CH2B), 1.33–1.15 (m, 6 H, ꢀ-/δ-Cy), 1.07 (m, 4 H,
1
γ-Cy). 13C{1H} NMR (benzene-d6): δ 140.0 (d, JCP ) 16.1 Hz,
2
3
ipso-Ph), 133.3 (d, JCP ) 18.1 Hz, o-Ph), 128.7 (d, JCP ) 6.2
Hz, m-Ph), 128.7 (p-Ph), 36.1 (vbr, R-Cy), 27.8 (ꢀ-Cy), 27.4 (γ-
2
2
(dd, JPP ) 255.6 Hz, JPP ) 15.9 Hz, trans-Pdmpe), 31.6 (br d,
1
2
2
Cy), 27.3 (δ-Cy), 22.1 (d, JCP ) 14.1 Hz, PCH2), 20.1 (vbr,
2JPP ) 255.6 Hz, PPh2), 27.9 ppm (dd, JPP ) 33.7 Hz, JPP
)

ꢀ-Phosphinoethylboranes as Ambiphilic Ligands
Organometallics, Vol. 27, No. 6, 2008 1139
15.9 Hz, cis-Pdmpe). Anal. Calcd for C34H58BNiP3 (mol wt 629.25):
C, 64.90; H, 9.29. Found: C, 64.94; H, 9.52.
Hz, cis-Pdmpe). Anal. Calcd for C30H50BNiP3 (mol wt 573.14): C,
62.87; H, 8.79. Found: C, 63.02; H, 8.90.
(dmpe)NiMe(Ph2PCH2CH2[BBN]Me)(2b).Inadrybox,(dmpe)N-
iMe2 (130.8 mg, 0.55 mmol) was dissolved in 15 mL of a toluene/
THF mixture (3:1) and the resulting solution was stirred at ambient
temperature. Solid Ph2PCH2CH2BBN (183.0 mg, 0.55 mmol) was
slowly added, and the brownish mixture was stirred for 3 h. The
yellow precipitate was separated, washed with toluene (1 × 3 mL)
and hexanes (4 × 3 mL), and dried under vacuum to give 129.6
mg (0.23 mmol, 41%) of analytically pure 5b as a yellow powder.
IR (Nujol, KBr): 1428 m, 1280 w, 1259 m, 1176 w, 1144 w,
1101 w, 1060 w, 1010 w, 941 s, 901 m, 841 w, 817 w, 796 w,
NMR-Scale Reaction of (dmpe)NiMe(Ph2PCH2CH2BCy2Me)
with B(C6F5)3 (3). In a drybox, a solution of 12.6 mg of 5a (20
µmol) in 0.5 mL of benzene-d6 was added to 10.2 mg of B(C6F5)3
(20 µmol). A few drops of THF were added to completely dissolve
the brownish mixture, which was then transferred into a 5 mm
Wilmad NMR tube equipped with a J. Young Teflon valve seal.
Proton, boron, fluorine, and phosphorus NMR spectroscopy con-
firmed the clean formation of one new product. 1H NMR (benzene-
d6): δ 7.31 (m, 4 H, o-Ph), 7.10 (m, 6 H, m-Ph, p-Ph), 2.28 (m, 2
H, PCH2CH2B), 1.74 (m, 4 H, Cy), 1.50–0.90 (br m, 10 H, Cy,
PCH2CH2B, PCH2CH2P), 0.83 (d, 2JHP ) 9.6 Hz, 6 H, PMe2), 0.34
741 m, 655 w, 521 m, 487 m cm-1 1H NMR (400.1 MHz,
.
2
(d, JHP ) 8.4 Hz, 6 H, PMe2), –0.04 (m, 3 H, NiMe). 11B{1H}
dichloromethane-d2): δ 7.60 (m, 4 H, o-Ph), 7.36 (m, 6 H, m-Ph,
p-Ph), 2.4 (m, 2 H, PCH2CH2B), 2.07–1.85 (br m, 4 H, BBNꢀ),
NMR (benzene-d6): δ 82.1 (vbr, BCy2), –14.4 ppm (MeB(C6F5)3).
1.85–1.60 (br m, 6 H, BBNγ, BBNR, PCH2CH2B), 1.52 (d, 2JHP
9.2 Hz, 6 H, PMe2), 1.47 (m, 6 H, BBNꢀ, BBNγ), 0.93 (d, 2JHP
)
)
19F{1H} NMR (376.5 MHz, benzene-d6): δ –130.8 (d), –163.4 (t),
2
–165.8 ppm (t). 31P{1H} NMR (benzene-d6): δ 41.0 (dd, JPP
)
257.5 Hz, JPP ) 17.8 Hz, trans-Pdmpe), 29.3 (dd, JPP ) 257.5
2
2
8.0 Hz, 6 H, PMe2), 0.77 (br, 2 H, PCH2CH2P), 0.17 (br, 2 H,
PCH2CH2P), –0.05 (br d, 3 H, NiMe), –0.42 ppm (br, 3 H,
MeBBN). 13C{1H} NMR (100.6 MHz, dichloromethane-d2): δ
137.1 (d, 1JCP ) 34.2 Hz, ipso-Ph), 132.9 (d, 2JCP ) 9.1 Hz, o-Ph),
2
2
2
Hz, JPP ) 30.8 Hz, PPh2), 27.7 ppm (dd, JPP ) 29.3 Hz, JPP
)
17.8 Hz, cis-Pdmpe).
3
130.1 (p-Ph), 128.9 (d, JCP ) 8.0 Hz, m-Ph), 34.0 (BBNꢀ), 33.8
Acknowledgment. This work was supported by the
Director, Office of Energy Research, Office of Basic Energy
Sciences, Chemical Sciences Division, of the U.S. Depart-
ment of Energy under Contract No. DE-AC03-76SF00098.
A.F. thanks the Deutsche Forschungsgemeinschaft for a
postdoctoral scholarship.
(BBNꢀ), 29.5 (m, PCH2CH2P), 28.8 (br m, PCH2CH2B), 28.0 (m,
PCH2CH2P), 27.8 (BBNγ), 27.4 (BBNγ), 26.7 (vbr, BBNR), 23.2
(d, 1JCP ) 18.1 Hz, PCH2CH2B), 12.3 (d, 1JCP ) 21.1 Hz, PMe2),
11.9 (d, 1JCP ) 28.2 Hz, PMe2), 9.8 (br m, MeBBN), 1.0 ppm (br
m, NiMe). 11B{1H} NMR (128.4 MHz, dichloromethane-d2): δ
–17.3 ppm. 11B{1H} NMR (128.4 MHz, benzene-d6): δ –16.3 ppm.
31P{1H} NMR (162.0 MHz, dichloromethane-d2): δ 40.4 (br d, 2JPP
Supporting Information Available: CIF files giving crystal-
lographic data for 1b and 2a. This material is available free of
charge via the Internet at http://pubs.acs.org.
2
) 244 Hz, trans-Pdmpe), 30.3 (br d, JPP ) 244 Hz, PPh2), 28.8
ppm (br, cis-Pdmpe). 31P{1H} NMR (162.0 MHz, benzene-d6): δ
38.5 (dd, 2JPP ) 256 Hz, 2JPP ) 16.2 Hz, trans-Pdmpe), 31.3 (br d,
2JPP ) 256 Hz, PPh2), 27.8 ppm (dd, 2JPP ) 34.0 Hz, 2JPP ) 16.2
OM7010886