Diphenylphosphidoboratabenzene: An anionic analogue of triphenylphosphine

Full text of DOI:10.1021/ja9615740

8176
J. Am. Chem. Soc. 1996, 118, 8176-8177
Table 1. Selected Bond Distances (Å) and Angles (deg) for (a)
Cp2ZrH(DPB)(PMe3), (b) CpFe(CO)2(DPB), and (c)
Rh(PMe3)3(DPB)
Diphenylphosphidoboratabenzene: An Anionic
Analogue of Triphenylphosphine
Diego A. Hoic, William M. Davis, and Gregory C. Fu*
(a) Cp2ZrH(DPB)(PMe3)
Department of Chemistry
Massachusetts Institute of Technology
Cambridge, Massachusetts 02139
Zr-Cp
2.506
P(1)-Zr-H
P(1)-Zr-P(2)
P(2)-Zr-H
C(17)-P(1)-C(11)
C(17)-P(1)-Zr
C(17)-P(1)-B
C(11)-P(1)-Zr
C(11)-P(1)-B
Zr-P(1)-B
58(2)
115.09(5)
57(2)
100.1(2)
111.8(2)
106.6(2)
118.5(2)
104.4(3)
114.0(2)
(average Zr-C)
Zr-P(1)
Zr-P(2)
Zr-H
P(1)-C(17)
P(1)-C(11)
P(1)-B
2.738(1)
2.657(2)
1.81(5)
1.841(5)
1.848(6)
1.966(6)
ReceiVed May 10, 1996
Stimulated by its relationship to the ubiquitous triphenylphos-
phine ligand (1),1 we have prepared2 and begun to explore the
coordination chemistry of the diphenylphosphidoboratabenzene
anion (DPB; 2). DPB may be viewed as a negatively charged,
essentially isosteric, variant of PPh3; within this context,
comparative studies of PPh3 and DPB complexes, both for a
given metal and for metals which are adjacent in the periodic
table, could lead to useful new insights into reactivity.3 In this
communication, we report the first stage of our investigation
into the chemistry of DPB, specifically, synthetic and structural
work which establishes the viability of DPB as a ligand for an
array of transition metals.
(b) CpFe(CO)2(DPB)
Fe(1)-Cp
2.097
B(1)-P(1)-Fe(1)
115.3(3)
109.0(4)
106.8(3)
104.0(3)
114.7(3)
106.4(2)
95.4(3)
(average Fe-C)
Fe(1)-P(1)
Fe(1)-C(6)
Fe(1)-C(7)
P(1)-B(1)
B(1)-P(1)-C(21)
B(1)-P(1)-C(31)
C(31)-P(1)-C(21)
C(31)-P(1)-Fe(1)
C(21)-P(1)-Fe(1)
P(1)-Fe(1)-C(6)
P(1)-Fe(1)-C(7)
C(6)-Fe(1)-C(7)
2.276(2)
1.741(10)
1.743(10)
1.967(9)
1.840(8)
1.838(8)
1.170(9)
1.167(9)
P(1)-C(21)
P(1)-C(31)
C(6)-O(2)
C(7)-O(1)
92.3(3)
94.8(4)
(c) Rh(PMe3)3(DPB)
Rh-P(1)
Rh-P(2)
Rh-P(3)
Rh-P(4)
P(1)-B
P(1)-C(1)
P(1)-C(7)
2.299(2)
2.285(2)
2.307(2)
2.306(2)
1.927(8)
1.856(8)
1.871(7)
P(1)-Rh-P(2)
96.13(7)
146.36(8)
92.59(7)
93.60(8)
148.03(8)
95.96(8)
104.2(3)
109.3(3)
105.4(3)
123.5(3)
102.8(3)
110.5(3)
P(1)-Rh-P(3)
P(1)-Rh-P(4)
P(2)-Rh-P(3)
P(2)-Rh-P(4)
P(3)-Rh-P(4)
B-P(1)-Rh
B-P(1)-C(1)
B-P(1)-C(7)
C(1)-P(1)-Rh
C(1)-P(1)-C(7)
C(7)-P(1)-Rh
A wide range of DPB adducts can be generated through
treatment of transition metal halides with potassium diphenyl-
phosphidoboratabenzene (K-DPB). For example, reaction of
Cp2ZrHCl with K-DPB in the presence of PMe3 leads to
displacement of the chloride ligand and formation of Cp2ZrH-
(DPB)(PMe3) (3; eq 1). A single-crystal X-ray diffraction study
of this complex (Figure 1a; Table 1a)4 reveals a structure very
similar to that found for Cp2ZrH(SiPh3)(PMe3).5 The P-C
bonds of the DPB ligand are ∼0.12 Å shorter than the P-B
bond, and the ligand adopts a slightly distorted tetrahedral
geometry.
2). The X-ray crystal structure of 4 (Figure 1b; Table 1b)6
displays a three-legged piano-stool geometry typical of CpFeL2X
complexes, with a nearly staggered conformation about the
Fe-P bond (dihedral angle [Cp centroid-Fe(1)-P(1)-C(31)]
) -168°).7 As in the case of zirconium complex 3, the P-C
bonds of the DPB ligand of 4 are shorter than the P-B bond
(by ∼0.13 Å).
[CpFe(CO)2(PPh3)]+ and CpFe(CO)2(PPh2) are isoelectronic
with complex 4.8,9 Comparison of the C-O stretching frequen-
cies (Table 2) suggests that the iron atom of [CpFe(CO)2-
(PPh3)]+ is the least electron-rich and that of CpFe(CO)2(PPh2)
is the most electron-rich. It is important to note that the
diphenylphosphido group is unique among the three phosphorus
ligands in that it bears a “lone pair” which can contribute
electron density to the metal. The IR data as well as the Fe-
We have also established that the iodide of CpFe(CO)2I is
readily substituted by DPB, producing CpFe(CO)2(DPB) (4, eq
(1) For a review of phosphine complexes of transition metals, see: Dias,
P. B.; de Piedade, M. E. M.; Simoes, J. A. M. Coord. Chem. ReV. 1994,
135, 737-807.
(2) Qiao, S.; Hoic, D. A.; Fu, G. C. J. Am. Chem. Soc. 1996, 118, 6329-
6330.
(3) This general approach has proved to be extremely interesting in early
transition metal metallocene chemistry. For examples and leading references,
see: (a) Crowther, D. J.; Baenziger, N. C.; Jordan, R. F. J. Am. Chem. Soc.
1991, 113, 1455-1457. (b) Quan, R. W.; Bazan, G. C.; Kiely, A. F.;
Schaefer, W. P.; Bercaw, J. E. J. Am. Chem. Soc. 1994, 116, 4489-4490.
(4) Data for compound 3: A wheat-colored plate (0.08 × 0.09 × 0.39
mm; grown from toluene/reaction-mixture at -35 °C for three weeks) was
mounted with a glass fiber on a Siemens SMART/CCD three circle
diffractometer (ø fixed at 54.78°). Data collection was done at -120 °C
using Mo KR radiation. The crystal was found to be monoclinic, belonging
to the space group P21/c. The cell constants are a ) 9.1017(6) Å, b )
17.6952(12) Å, c ) 17.8481(12) Å, â ) 104.2750(10)°, V ) 2785.8(3)
Å3, Z ) 4, Fcalc ) 1.334 g/cm3. 10 886 reflections were collected, of which
3977 were unique (Rint ) 0.0550). Solution was done by direct methods.
The final refinement by full-matrix least-squares was done on F2 (3971
data, 312 parameters) and yielded R1 ) 0.0641 and wR2 ) 0.1104 (for
data with I > 2σ(I)); GOF ) 1.411. All computations were handled by the
Siemens software package (SMART, SAINT, SHELXTL).
(6) Data for compound 4: Orange plate (0.28 × 0.12 × 0.07 mm; from
pentane/toluene/THF at -35 °C). Monoclinic, C2/c, a ) 17.1939(14) Å, b
) 15.0376(13) Å, c ) 15.9249(13) Å, â ) 92.5420(10), V ) 4113.4(6)
Å3, Z ) 8, Fcalc ) 1.415 g/cm3. 5705 reflections, 1914 unique (Rint
0.0713). The final refinement (1898 data, 262 parameters) yielded R1
0.0649 and wR2 ) 0.1389 for data with I > 2σ(I); GOF ) 1.290.
)
)
(7) For a discussion, see: Brunner, H.; Hammer, B.; Kruger, C.;
Angermund, K.; Bernal, I. Organometallics 1985, 4, 1063-1068.
(8) (a) [CpFe(CO)2PPh3]Cl‚3H2O: Riley, P. E.; Davis, R. E. Organo-
metallics 1983, 2, 286-292. See also: Davison, A.; Green, M. L. H.;
Wilkinson, G. J. Chem. Soc. 1961, 3172-3177. (b) [CpFe(CO)2PPh3]+-
[(NC)2CC(CN)C(CN)2]-: Sim, G. A.; Woodhouse, D. I.; Knox, G. R. J.
Chem. Soc., Dalton Trans. 1979, 629-635. (c) [CpFe(CO)2PPh3]PF6: Janik,
T. S.; Krajkowski, L. M.; Churchill, M. R. J. Chem. Cryst. 1995, 25, 751-
754. [CpFe(CO)2PPh3]Cl‚3H2O, [CpFe(CO)2PPh3]+[(NC)2CC(CN)C(CN)2]-,
and [CpFe(CO)2PPh3]PF6 differ by less than 0.01 Å for all of the bond
distances reported in Table 2.
(5) Kreutzer, K. A.; Fisher, R. A.; Davis, W. M.; Spaltenstein, E.;
Buchwald, S. L. Organometallics 1991, 10, 4031-4035.
(9) CpFe(CO)2(PPh2): Burckett-St. Laurent, J. C. T. R.; Haines, R. J.;
Nolte, C. R.; Steen, N. D. C. T. Inorg. Chem. 1980, 19, 577-587.
S0002-7863(96)01574-0 CCC: $12.00 © 1996 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 118, No. 34, 1996 8177
Table 2. Comparison of [CpFe(CO)2(PPh3)]Cl.3H2O,8
CpFe(CO)2(DPB), and CpFe(CO)2(PPh2)9
av bond
distances (Å)
ν (CO) (cm-1
)
Fe-(CO) C-O
[CpFe(CO)2(PPh3)]Cl‚3H2O 2025, 2070 (Nujol) 1.771
1.139
1.168
CpFe(CO)2(DPB)
1982, 2024 (KBr)
1989, 2035
1.742
(CH2Cl2)
1966, 2015
CpFe(CO)2(PPh2)
not available
(cyclohexane)
between cis phosphorus ligands ranging from 92 to 96° and
angles between trans phosphorus ligands of 146° and 148° (P-
Rh-P).11 The Rh-P bond distance for the PMe3 group trans
to DPB is 2.307(2) Å, and the Rh-P bond distances for the
PMe3 groups cis to DPB are 2.285(2) and 2.306(2) Å. The
P-C bonds of the DPB ligand of Rh(PMe3)3(DPB) are only
∼0.06 Å shorter than the P-B bond, about half the difference
found for 3 and 4, possibly reflecting the lower Lewis acidity
of the rhodium center.12
In conclusion, we have established that a range of complexes
containing DPB, a new anionic ligand, can be synthesized via
substitution reactions of transition metal halides. It is worth
noting that the chemistry of K-DPB differs from that of its
nitrogen analogue, potassium diphenylamidoboratabenzene,
which does not afford an η1 adduct in any of the reactions
described above.13,14 Given the structural similarity of PPh3
(1) and DPB (2), we anticipate that studies comparing the
reactivity of complexes which bear these ligands may prove to
be particularly interesting. The development of a chiral variant
of DPB is also underway.15
Acknowledgment. Support has been provided by the American
Cancer Society, the Camille and Henry Dreyfus Foundation, and the
National Science Foundation (Young Investigator Award, with funding
from DuPont, Hoechst Celanese, Merck, Pfizer, Procter & Gamble,
Rohm & Haas, and Upjohn). Acknowledgment is made to the donors
of the Petroleum Research Fund, administered by the ACS, for partial
support of this research.
Supporting Information Available: A listing of experimental
procedures and compound characterization data (31 pages). See any
current masthead page for ordering and Internet access instructions.
JA9615740
Figure 1. ORTEP illustrations, with thermal ellipsoids drawn at the
35% probability level, of transition metal complexes of DPB: (a) Cp2-
ZrH(DPB)(PMe3), (b) CpFe(CO)2(DPB), and (c) Rh(PMe3)3(DPB).
(11) For a closely related structure, see: Thorn, D. L.; Harlow, R. L.
Inorg. Chem. 1990, 29, 2017-2019.
(12) A preliminary reactivity study indicates that treatment of complex
5 with H2 results in the formation of two rhodium hydride species. Further
investigations are underway.
(CO) and C-O bond distances (Table 2) indicate that the DPB
ligand donates significantly more electron density to iron than
does the PPh3 ligand.
Finally, we have determined that treatment of Rh(PMe3)3Cl
with K-DPB generates Rh(PMe3)3(DPB) (5; eq 3). A single-
crystal X-ray diffraction study of complex 5 (Figure 1c; Table
1c)10 reveals a distorted square planar geometry, with angles
(13) DPB adducts 3-5 are the first boratabenzene complexes in which
the ligand is σ-bound, rather than π-bound, to the metal. For leading
references to π-bound boratabenzene complexes, see: (a) Herberich, G. E.
In ComprehensiVe Organometallic Chemistry II; Abel, E. W.; Stone, F. G.
A.; Wilkinson, G., Eds.; Pergamon: New York, 1995; Vol. 1, Chapter 5.
(b) Herberich, G. E.; Ohst, H. AdV. Organomet. Chem. 1986, 25, 199-
236. (c) Bazan, G. C.; Rodriguez, G.; Ashe, A. J., III; Al-Ahmad, S.; Muller,
C. J. Am. Chem. Soc. 1996, 118, 2291-2292.
(10) Data for compound 5: Dark red prisms (0.22 × 0.22 × 0.13 mm;
from pentane/THF at room temperature). Monoclinic, P21/n, a ) 9.4031-
(8) Å, b ) 17.692(2) Å, c ) 17.672(2) Å, â ) 95.6350(10), V ) 2925.8(4)
(14) (η6-C5H5BNPh2)Rh(PMe3)2 is formed cleanly upon treatment of
Rh(PMe3)3Cl with potassium diphenylamidoboratabenzene.
(15) Examples of anionic η1 ligands in which the ligating atom is both
stereogenic and configurationally stable are rare. See: Brunner, H.;
Zettlmeier, W. Handbook of EnantioselectiVe Catalysis; VCH: New York,
1993; Vol. 2.
Å3, Z ) 4, Fcalc ) 1.344 g/cm3. 7705 reflections, 2710 unique (Rint
0.1446). The final refinement (2640 data, 290 parameters) yielded R1
0.0572 and wR2 ) 0.1000 for data with I > 2σ(I); GOF ) 1.166.
)
)