The strong-field tripodal phosphine donor, [PhB(CH2P iPr2)3]-, provides access to electronically and coordinatively unsaturated transition metal complexes

Article abstract of DOI:10.1021/ic0343096

This paper introduces a sterically encumbered, strong-field tris(diisopropylphosphino)borate ligand, [PhBP^iPr₃] ([PhB^iPr₃] = [PhB(CH₂PⁱPr ₂)₃]^-), to probe aspects of its conformational and electronic characteristics within a host of complexes. To this end, the TI(I) complex, [PhB^iPr ₃]TI (1), was synthesized and characterized in the solid-state by X-ray diffraction analysis. This precursor proves to be an effective transmetallating agent, as evidenced by its reaction with the divalent halides FeCl₂ and CoX₂ (X = Cl, I) to produce the monomeric, 4-coordinate, high-spin derivatives [PhBP ^iPr₃]FeCl (2) and [PhBP^iPr]CoX (X = Cl (3), I (4)) in good yield. Complexes 2-4 were each characterized by X-ray diffraction analysis and shown to be monomeric in the solid-state. For conformational and electronic comparison within a system exhibiting higher than 4-coordination, the 16-electron ruthenium complexes {[PhBP^iPr ₃]Ru(μ-Cl)}₂ (5) and {[PhBP ₃]Ru(μ-Cl)}₂ (6) were prepared and characterized ([PhBP₃] = [PhB(CH₂PPh₂)₃] ^-). The chloride complexes 2 and 3 reacted with excess CO to afford the divalent, monocarbonyl adducts [PhBP^iPr₃] ^-) FeCl(CO) (7) and [PhBP^iPr₃]CoCl(CO) (8), respectively. Reaction of 4 with excess CO resulted in the monovalent, dicarbonyl product [PhBP^iPr₃]CO^I(CO) ₂ (9). Complexes 5 and 6 also bound CO readily, providing the octahedral, 18-electron complexes [PhBP^iPr₃]RUCl(CO) ₂ (10) and [PhBP₃] RuCl(CO)₂ (11), respectively. Dimers 5 and 6 were broken up by reaction with trimethylphosphine to produce the mono-PMe₃ adducts [PhBP^iPr ₃]RuCl(PMe₃) (12) and [PhBP₃]RuCl(PMe ₃) (13). Stoichiometric oxidation of 3 with dioxygen provided the 4-electron oxidation product [PhB(CH₂P(O)^IPr ₂)₂(CH₂PⁱPr₂)]CoCl (14), while exposure of 3 to excess oxygen results in the 6-electron oxidation product [PhB(CH₂P(O)ⁱPr₂)₃]CoCl (15). Complexes 2 and 4 were characterized via cyclic voltammetry to compare their redox behavior to their [PhBP₃] analogues. Complex 4 was also studied by SQUID magnetization and EPR spectroscopy to confirm its high-spin assignment, providing an interesting contrast to its previously described low-spin relative, [PhBP₃] CoI. The difference in spin states observed for these two systems reflects the conformational rigidity of the [PhBP^iPr3] ligand by comparison to [PhBP₃], leaving the former less able to accommodate a JT-distorted electronic ground state.

Full text of DOI:10.1021/ic0343096

Inorg. Chem. 2003, 42, 5074−5084
i
The Strong-Field Tripodal Phosphine Donor, [PhB(CH P Pr2)3]-, Provides
2
Access to Electronically and Coordinatively Unsaturated Transition
Metal Complexes
Theodore A. Betley and Jonas C. Peters*
DiVision of Chemistry and Chemical Engineering, Arnold and Mabel Beckman Laboratories of
Chemical Synthesis, California Institute of Technology, Pasadena, California 91125
Received March 21, 2003
iPr
This paper introduces a sterically encumbered, strong-field tris(diisopropylphosphino)borate ligand, [PhBP ]
3
iPr
i
([PhBP ] ) [PhB(CH PPr2)3]-), to probe aspects of its conformational and electronic characteristics within a host
3
2
iPr
of complexes. To this end, the Tl(I) complex, [PhBP ]Tl (1), was synthesized and characterized in the solid-state
3
by X-ray diffraction analysis. This precursor proves to be an effective transmetallating agent, as evidenced by its
reaction with the divalent halides FeCl2 and CoX (X ) Cl, I) to produce the monomeric, 4-coordinate, high-spin
2
iPr
iPr
derivatives [PhBP ]FeCl (2) and [PhBP ]CoX (X ) Cl (3), I (4)) in good yield. Complexes 2−4 were each
3
3
characterized by X-ray diffraction analysis and shown to be monomeric in the solid-state. For conformational and
electronic comparison within a system exhibiting higher than 4-coordination, the 16-electron ruthenium complexes
iPr
{[PhBP ]Ru(µ-Cl)}2 (5) and {[PhBP ]Ru(µ-Cl)}2 (6) were prepared and characterized ([PhBP ] ) [PhB(CH PPh ) ]-).
3
3
3
2
2 3
iPr
The chloride complexes 2 and 3 reacted with excess CO to afford the divalent, monocarbonyl adducts [PhBP ]-
FeCl(CO) (7) and [PhBP ]CoCl(CO) (8), respectively. Reaction of 4 with excess CO resulted in the monovalent,
dicarbonyl product [PhBP ]Co(CO)2 (9). Complexes 5 and 6 also bound CO readily, providing the octahedral,
18-electron complexes [PhBP ]RuCl(CO)2 (10) and [PhBP ]RuCl(CO)2 (11), respectively. Dimers 5 and 6 were
3
iPr
3
iPr
I
3
iPr
3
3
iPr
broken up by reaction with trimethylphosphine to produce the mono-PMe3 adducts [PhBP ]RuCl(PMe3) (12) and
3
[PhBP ]RuCl(PMe3) (13). Stoichiometric oxidation of 3 with dioxygen provided the 4-electron oxidation product
3
i
i
[PhB(CH P(O)Pr2)2(CH PPr2)]CoCl (14), while exposure of 3 to excess oxygen results in the 6-electron oxidation
2
2
i
product [PhB(CH P(O)Pr2)3]CoCl (15). Complexes 2 and 4 were characterized via cyclic voltammetry to compare
2
their redox behavior to their [PhBP ] analogues. Complex 4 was also studied by SQUID magnetization and EPR
3
spectroscopy to confirm its high-spin assignment, providing an interesting contrast to its previously described low-
spin relative, [PhBP ]CoI. The difference in spin states observed for these two systems reflects the conformational
3
iPr
rigidity of the [PhBP ] ligand by comparison to [PhBP ], leaving the former less able to accommodate a JT-
3
3
distorted electronic ground state.
I. Introduction
this is a very well-studied area in coordination chemistry,3
our particular interest concerns developing new, strong donor
An area of ongoing interest to our group concerns the
systematic preparation of pseudotetrahedral complexes that
feature mid-to-late 3d ions (Mn, Fe, Co, Ni, Cu).1,2 While
(3) (a) For some relevant references see: Schebler, P. J.; Mandimutsira,
B. S.; Riordan, C. G.; Liable-Sands, L. M.; Incarvito, C. D.; Rheingold,
A. L. J. Am. Chem. Soc. 2001, 123, 331. (b) Gorrell, I. B.; Parkin, G.
Inorg. Chem. 1990, 29, 2452. (c) Bunker, T. J.; Hascall, T.; Cowley,
A. R.; Rees, L. H.; O’Hare, D. Inorg. Chem. 2001, 40, 3170. (d)
Kitajima, N.; Fujisawa, K.; Moro-oka, Y. J. Am. Chem. Soc. 1990,
112, 3210. (e) Churchill, M. R.; DeBoer, B. G.; Rotella, F. J.; Salah,
O. M. A.; Bruce, M. I. Inorg. Chem. 1975, 14, 2051. (f) Belderrain,
T. R.; Parreque, M.; Carmona, E.; Gutierrez-Puebla, E.; Monge, M.
A.; Ruiz-Valero, C. Inorg. Chem. 2002, 41, 425. (g) Carrier, S. M.;
Ruggiero, C. E.; Tolman, W. B.; Jameson, G. B. J. Am. Chem. Soc.
1992, 114, 4407.
* To whom correspondence should be addressed. E-mail:
jpeters@caltech.edu.
(1) (a) Jenkins, D. M.; Di Bilio, A. J.; Allen, M. J.; Betley, T. A.; Peters,
J. C. J. Am. Chem. Soc. 2002, 124, 15336. (b) Shapiro, I. R.; Jenkins,
D. M.; Thomas, J. C.; Day, M. W.; Peters, J. C. Chem. Commun.
2001, 2152.
(2) (a) Jenkins, D. M.; Betley, T. A.; Peters, J. C. J. Am. Chem. Soc.
2002, 124, 11238. (b) Brown, S. D.; Betley, T. A.; Peters, J. C. J.
Am. Chem. Soc. 2003, 125, 322.
5074 Inorganic Chemistry, Vol. 42, No. 17, 2003
10.1021/ic0343096 CCC: $25.00 © 2003 American Chemical Society
Published on Web 06/19/2003

Strong-Field Tripodal Phosphine Donor
Scheme 1. Preparation and Solid-State Structure of [PhBPiPr3]Tl (1)a
L3 platforms that enable binding of π-acidic ligands (e.g.,
N2, CO, NO+) and also strongly π-basic ligands (e.g., O2-,
NR2-, N3-) in a fourth coordination site (i.e., L3M-X where
X is a π-acid or π-base). While later 3d systems that fulfill
the first requirement are common,3e,g,4,5 those that fulfill the
latter requirement are rare.2 The historical incompatibility
of pseudotetrahedral, later 3d ions with strongly π-basic
ligands can be attributed to the high-spin ground state
configurations that dominate this region of the periodic table.
Complexes with strongly destabilized d-orbitals containing
unpaired electrons are expected to be very reactive.
Recently, our group has shown that by using strong L3
donor ligands with a borate unit embedded within the
backbone of the ligand, 3d ions of the type L3MtE are
electronically accessible (L ) P, M ) Fe, Co; E ) NR;
d-count ) 5, 6).2 Moreover, low-spin configurations are
accessible even for d7 configurations in the absence of the
strongly π-basic fourth donor ligand (e.g., low-spin [PhBP3]-
CoI where [PhBP3] ) [PhB(CH2PPh2)3]-).1 To explore
related systems using more strongly donating tripodal phos-
phine ligands, we set to out to modify the [PhBP3] ligand
scaffold by substitution of the soft aryl phosphine donors
with harder, more electron-releasing alkyl phosphine donors.
In this context, we now describe the preparation of the
a Displacement ellipsoid (50%) representation of [PhBPiPr3]Tl (1) viewed
down the Tl-B axis. Hydrogen atoms and borate phenyl ring have been
omitted for clarity. Selected bond distances (Å) and angles (deg): Tl-P1,
2.901(1); Tl-P2, 2.921(1); Tl-P3, 2.894(1); Tl-B, 4.221(3); P1-Tl-P2,
75.25(2); P1-Tl-P3, 76.60(2); P2-Tl-P3, 77.72(2).
[PhBPiPr3][Li(TMEDA)x]. Owing to the synthetic utility we
have experienced with the thallium reagent [PhBP3]Tl,1
[PhBPiPr3][Li(TMEDA)x] was directly converted to [PhBPiPr3]-
[Tl] (1) by in situ addition of TlPF6 (58% overall yield, 31
P
1
1
NMR δ 45.8 ppm, J203 Tl-P ) 5865 Hz, J205 Tl-P ) 5913
Hz). Complex 1 proved highly unstable to protic solvents,
including water and ethanol, and also to oxidation by oxygen.
These properties contrast those of its parent complex, [PhBP3]-
Tl, which can be isolated from aqueous media under an
atmosphere of air without appreciable degradation.1b
phenyl-tris(diisopropylphosphino)borate anion, [PhBPiPr
]
3
([PhBPiPr3] ) [PhB(CH2PiPr2)3]-), and examine aspects of
its electronic and structural properties in comparison to those
of the parent [PhBP3] ligand. Studies of this type should help
us to better understand the electronic origin behind the
unusual ground state configurations we have observed in
these [PhBP3] systems thus far and will provide the impetus
to exploit these new scaffolds in small molecule activation
chemistry.
X-ray analysis confirmed a κ3-binding mode for the
phosphine ligand to a single thallium(I) ion, similar to that
of the [PhBP3] derivative. One noteworthy structural differ-
ence is that 1 is rigorously monomeric in the solid-state,
while [PhBP3][Tl] exhibits weak Tl-Tl interactions in the
solid-state.1b The isopropyl substituents of 1 form a vertical
fence around the thallium(I) center. The methyne protons
are arranged such that each bisects the methyl groups of an
adjacent isopropyl group. This interlocked pattern tightly
gears the isopropyls in a fanlike fashion that makes complex
1 chiral (Scheme 1).
IIb. Synthesis of [PhBPiPr3]M(X) and [PhBPiPr3]M(X)(L)
Complexes (M ) Fe, Co, Ru). Our present interest in the
chemistry of 1 pertains to its utility in delivering the
[PhBPiPr3] anion to transition metals. The data presented here
detail a number of iron, cobalt, and ruthenium complexes
that collectively provide the context from which to compare
steric and electronic properties between [PhBPiPr3] and
[PhBP3].
II. Results
IIa. Synthesis and Characterization of [PhBPiPr3][Tl].
Following effective methodology for the preparation of a
host of di- and tripodal borate ligands,6-8 we sought delivery
of a suitable phosphine carbanion to PhBCl2. Our attention
i
focused on the selective deprotonation of Pr2PMe using
conditions similar to those reported by Karsch for lithiating
i
tBu2PMe.9 The desired lithio reagent, Pr2PCH2Li, was
t
obtained readily by deprotonation with solid BuLi (65 °C,
12 h, 96% yield, Scheme 1). Addition of stoichiometric
TMEDA (TMEDA ) tetraethylmethylenediamine) to an
ethereal suspension of iPr2PCH2Li aided its partial dissolution
and facilitated its subsequent delivery to PhBCl2 to provide
Complex 1 underwent loss of TlX upon reaction with
either FeCl2 or CoX2 (X ) Cl, I) in THF solution to afford
the well-defined complexes [PhBPiPr3]FeCl (2), [PhBPiPr3]-
CoCl (3), and [PhBPiPr3]CoI (4) (Scheme 2). Chloride 2 was
precipitated from benzene by slow evaporation as canary-
yellow crystals that were suitable for X-ray analysis (Figure
1). Crystals were similarly obtained for aqua-colored chloride
3 and lime-green iodide 4. X-ray analysis revealed that 2, 3,
and 4 are monomeric, pseudotetrahedral species in the solid-
state (Figure 1). A detailed discussion of these crystal
structures is reserved for the Discussion subsections IIIb,c.
(4) Detrich, J. L.; Konecny, R.; Vetter, W. M.; Doren, D.; Rheingold, A.
L.; Theopold, K. H. J. Am. Chem. Soc. 1996, 118, 1703.
(5) Kisko, J. L.; Hascall, T.; Parkin, G. J. Am. Chem. Soc. 1998, 120,
1056.
(6) (a) Peters, J. C.; Feldman, J. D.; Tilley, T. D. J. Am. Chem. Soc. 1999,
121, 9871. (b) Barney, A. A.; Heyduk, A. F.; Nocera, D. G. Chem.
Commun. 1999, 23, 2379.
(7) (a) Thomas, J. C.; Peters, J. C. J. Am. Chem. Soc. 2001, 123, 5100.
(b) Betley, T. A.; Peters, J. C. Inorg. Chem. 2002, 41, 6541. (c)
Thomas, J. C.; Peters, J. C. Inorg. Chem. 2003, 42, xxxxx.
(8) (a) Ge, P.; Haggerty, B. S.; Rheingold, A. L.; Riordan, C. G. J. Am.
Chem. Soc. 1994, 116, 8406. (b) Schebler, P. J.; Riordan, C. G.; Guzei,
I. A.; Rheingold, A. L. Inorg. Chem. 1998, 37, 4754.
(9) Karsch, H. H.; Schmidbaur, H. Z. Naturforsch. 1977, 32b, 762.
Inorganic Chemistry, Vol. 42, No. 17, 2003 5075

Betley and Peters
Figure 1. Displacement ellipsoid (50%) representation of (a) [PhBPiPr3]FeCl (2), (b) [PhBPiPr3]CoCl (3), and (c) [PhBPiPr3]CoI (4). Hydrogen atoms have
been removed for clarity. Selected bond distances (Å) and angles (deg), for 2: Fe-P1 2.415(1), Fe-P2 2.431(1), Fe-P3 2.428(1), Fe-Cl 2.220(1), Fe-B
3.501(3); P1-Fe-P2 93.24(3), P1-Fe-P3 94.10(3), P2-Fe-P3 94.49(3), Cl-Fe-P1 122.12(3), Cl-Fe-P2 122.62(4), Cl-Fe-P3 122.52(3). For 3: Co-
P1 2.334(2), Co-P2 2.332(1), Co-P3 2.330(2), Co-Cl 2.196(3), Co-B 3.363(4); P1-Co-P2 97.88(3), P1-Co-P3 96.52(3), P2-Co-P3 98.19(3), Cl-
Co-P1 121.40(3), Cl-Co-P2 119.53(3), Cl-Co-P3 118.25(3). For 4: Co-P1 2.334(2), Co-P2 2.321(2), Co-P3 2.385(2), Co-I 2.540(1), Co-B 3.365(3);
P1-Co-P2 97.84(6), P1-Co-P3 97.55(6), P2-Co-P3 97.32(6), I-Co-P1 119.53(5), I-Co-P2 118.27(5), I-Co-P3 121.29(5).
Figure 2. Displacement ellipsoid (50%) representation for (a) {[PhBP3]Ru(µ-Cl)}2 (6) and (b) [PhBP3]RuCl(PMe3) (13). Hydrogen atoms are omitted for
clarity. Selected bond distances (Å) and angles (deg), for 6: Ru-Cl 2.448(1), Ru-Cl′ 2.457(1), Ru-P1 2.295(1), Ru-P2 2.221(1), Ru-P3 2.271(2),
P1-Ru-P2 90.40(2), P1-Ru-P3 86.37(2), P2-Ru-P3 86.92(2). For 13: Ru-Cl 2.427(1), Ru-P1 2.225(1), Ru-P2 2.252(2), Ru-P3 2.400(1), Ru-P4
2.381(1), P1-Ru-P2 89.90(4), P1-Ru-P3 87.86(4), P2-Ru-P3 85.93(4).
Scheme 2
Reaction of 1 with RuCl2(PPh3)3 produced the rust-colored,
16-electron dimer {[PhBPiPr3]Ru(µ-Cl)}2 (5) (Scheme 2). Its
[PhBP3] analogue, {[PhBP3]Ru(µ-Cl)}2 (6), was similarly
prepared by reaction of [PhBP3]Tl with RuCl2(PPh3)3. The
solid-state structure of complex 6 was obtained (Figure 2)
and shows two 5-coordinate Ru(II) centers in an ap-
proximately square-pyramidal configuration. It is interesting
to note that related 16-electron dimers are not known for
isosteric triphos (Me(CH2PPh2)3) systems, nor for tris-
(pyrazolyl)borate analogues.10,11 In these latter cases, 18-
electron products are more typically obtained (e.g., {Me-
(CH2PPh2)3Ru}2(µ-Cl)32+, [Tp′]RuCl(PR3)2).
IIc. Magnetic Characterization of [PhBPiPr3]MX Com-
plexes (M ) Fe, Co). The complexes [PhBP3]FeCl,2b
{[PhBP3]Co(µ-Cl)}2,1a and [PhBP3]CoI1 have been described
(11) Another case of an isolated, coordinatively unsaturated ruthenium
species featuring a sterically encumbered hydrotris(3,5-diisopropyl-
pyrazolyl)borato ligand features an agostic C-H bond interaction
occupying the sixth coordination site on Ru: (a) Takahashi, Y.;
Hikichi, S.; Akita, M.; Moro-oka, Y. Organometallics 1999, 18, 2571.
Related transiently stable species that feature agostic interactions have
been studied: (b) Trimmel, G.; Slugovc, C.; Wiede, P.; Mereiter, K.;
Sapunov, V. N.; Schmid, R.; Kirchner, K. Inorg. Chem. 1997, 36,
1076. (c) Tenorio, M. A. J.; Tenorio, M. J.; Puerta, M. C.; Valerga,
P. J. Chem. Soc., Dalton Trans. 1998, 3601.
(10) (a) Rhodes, L. F.; Sorato, C.; Venanzi, L. M.; Bachechi, F. Inorg.
Chem. 1988, 27, 604. (b) Rhodes, L. F.; Venanzi, L. M.; Sorato, C.;
Albinati, A. Inorg. Chem. 1986, 25, 3335.
5076 Inorganic Chemistry, Vol. 42, No. 17, 2003

Strong-Field Tripodal Phosphine Donor
-1
Figure 3. (a) SQUID magnetization data shown as a plot of µeff (BM) versus T (K), and (b) as a plot of øm (mol/cm3) versus T (K), for [PhBPiPr3]CoI
(4).
120 mT), characteristic of a high-spin Co(II) system.12
Another signal is present in the region g ∼ 2.2 (H ) 320
mT) that features apparent hyperfine coupling due to the Co
(S ) 7/2), and possibly the P (S ) 1/2) nuclei.13,14 As expected
3
for an S ) /2 Co(II) system,1a,15 no signal was observed at
ambient temperature. By contrast, the glassy toluene EPR
spectrum of doublet [PhBP3]CoI did not feature a signal in
the region g ∼ 4.8 and afforded an isotropic signal in the
region g ∼ 2.0 even at 22 °C.1a The characteristic high-spin
signal at g ∼ 4.8 appeared only when [PhBP3]CoI was
oxidized to [PhB(CH2PPh2)(CH2P(O)Ph2)2]CoI, a rigorously
high-spin product.1a
IId. Electrochemical Comparisons between [PhBPiPr3]-
MX and [PhBP3]MX (M ) Fe, Co). To assess the relative
electron-releasing character of the [PhBPiPr3] and [PhBP3]
Figure 4. EPR spectrum of 4 in glassy toluene (4 K, X-band, 9.62 GHz).
anions, we examined the cyclic voltammetry of the respective
Fe(II) chloride and Co(II) iodide complexes. The cyclic
voltammograms for [PhBPiPr3]FeCl and [PhBP3]FeCl are
presented in Figure 5, labeled a and b, respectively. The
parent complex, [PhBP3]FeCl, shows a fully reversible FeII/I
couple at -1.23 V versus a Ag/AgNO3 electrode (Figure
5). The FeII/I couple at -1.55 V for [PhBPiPr3]FeCl (Figure
5a) appears to be only quasireversible (50 mV/s), suggesting
that some degradation or reaction of the anion [{PhBPiPr3}-
FeCl]- occurs on this time scale. The striking 322 mV shift
observed for the FeII/I couple of 2 by comparison to that of
[PhBP3]FeCl speaks to the marked increase in electron-
releasing character that occurs when six isopropyl groups
replace six phenyl groups at the phosphine donor positions.
The comparative voltammograms for the compounds
[PhBPiPr3]CoI and [PhBP3]CoI did not follow a similar trend.
elsewhere. [PhBP3]FeCl is pseudotetrahedral with an S ) 2
ground state configuration. Likewise, [PhBPiPr3]FeCl (2) is
high-spin (5.23 µB, Evans method in benzene). The compara-
tive magnetic data for the cobalt systems are more puzzling.
In benzene solution, both [PhBP3]CoCl and [PhBP3]CoI are
pseudotetrahedral and low-spin (S ) 1/2). Whereas the
chloride dimerizes in the solid-state, [PhBP3]CoI remains
monomeric and low-spin.1a By contrast, 3 and 4 are both
monomeric in the solid-state. Moreover, they are each high-
spin, both in benzene solution and in the solid-state. A
susceptibility determination using the Evans method provided
values of 4.12 and 4.02 µB for complexes 3 and 4,
respectively. To confirm its high-spin character at low
temperature, 4 was also characterized by SQUID magne-
tometry from 5 to 300 K. As can be seen from Figure 3a, 4
maintains its quartet ground state throughout this temperature
range. The Curie Law observed in this temperature range
(indicated by øm-1 vs T, Figure 3b) indicates that the 3/2 spin
state is the only state that is thermally populated.
Despite the more electron-releasing nature of the [PhBPiPr
]
3
anion by comparison to the [PhBP3] anion, it was more
(12) See ref 1a and references therein.
(13) Sealy, R.; Hyde, J. S.; Antholine, W. E. Modern Physical Methods in
Biochemistry; Neuberger, A., Van Deenen, L. L. M., Eds.; Elsevier:
New York, 1985; p 69.
The glassy toluene EPR spectrum of 4 was also collected
at 4 K, shown in Figure 4, for comparison with the spectrum
previously reported for [PhBP3]CoI.1a The spectrum for 4
shows a strong, signature signal in the region g ∼ 4.8 (H )
(14) Stelzer, O.; Sheldrick, W. S.; Subramanian, J. J. Chem. Soc., Dalton
Trans. 1976, 966.
(15) (a) Pilbrow, J. R. Transition Ion Electron Paramagnetic Resonance;
Clarendon Press: Oxford, 1990. (b) Aasa, R.; Va¨nngård, T. J. Magn.
Reson. 1975, 19, 308.
Inorganic Chemistry, Vol. 42, No. 17, 2003 5077

Betley and Peters
a similar fashion upon exposure to excess carbon monoxide
to produce [PhBPiPr3]CoCl(CO) (8) (µeff ) 2.24 µB) (Scheme
2). While the structures of 7 and 8 were not determined, we
presume each to be approximately trigonal bipyramidal, with
the chloride ligand coordinated in an equatorial position and
the CO bound axially, as is found for the structurally
characterized complex [PhBP3]CoBr(CO).17 Iodide 4 under-
went rapid reduction on CO exposure to generate the
monovalent dicarbonyl complex [PhBPiPr3]Co(CO)2 (9).
The ruthenium dimers 5 and 6 were broken up on exposure
to carbon monoxide to form the octahedral, dicarbonyl
adducts [PhBPiPr3]RuCl(CO)2 (10) and [PhBP3]RuCl(CO)2
(11), respectively. Both 5 and 6 were also broken up when
heated in the presence of trimethylphosphine to provide the
monophosphine adducts [PhBPiPr3]RuCl(PMe3) (12) and
[PhBP3]RuCl(PMe3) (13), respectively. The latter complex,
13, was examined crystallographically and shown to be
approximately trigonal-bipyramidal. Its chloride ligand oc-
cupies an axial position, and the PMe3 ligand occupies an
equatorial site (Figure 2). It is again underscored that
analogous 5-coordinate, 16-electron complexes of ruthenium
supported by tris(pyrazolyl)borate ligands are not known,
even for cases where sterically encumbering derivatives of
the ligand have been employed.11
Figure 5. Cyclic voltammetry of (a) [PhBPiPr3]FeCl (2) and (b) [PhBP3]-
FeCl in 0.4 M [TBA][PF6]/THF, scan rate ) 50 mV/s, V vs Ag/AgNO3.
Exposure of 3 in solution or in the solid-state to stoichio-
metric dioxygen led to the rapid, 4-electron oxidation of 3
to produce [PhB(CH2P(O)iPr2)2(CH2PiPr)]CoCl (14). Reac-
tion of 3 with excess dioxygen produced a 6-electron
oxidation product, the tris(phosphineoxide) complex [PhB-
(CH2P(O)iPr2)3]CoCl (15). The 4-electron oxidation product
14 is reminiscent of the only observed oxidation products
when [PhBP3]CoX complexes are exposed to excess oxygen.
The 6-electron oxidation product 15 is unique to the
[PhBPiPr3] system.1a,18 Both complexes 14 and 15 have been
characterized by X-ray analysis, and their solid-state struc-
tures are shown in Figure 7. While we have yet to pursue
the chemistry of [PhB(CH2P(O)R2)3]- ligands systematically,
it should be possible to realize their preparation, and that of
their sulfur analogues [PhB(CH2P(S)R2)3]-, independently.7c
The solid-state structure of 15 suggests that these latter ligand
classes may well be worthy of pursuit.
Figure 6. Cyclic voltammetry of (a) [PhBPiPr3]CoI (4) and (b) [PhBP3]-
CoI in 0.4 M [TBA][PF6]/THF, scan rate ) 50 mV/s, V vs Ag/AgNO3.
difficult to reduce [PhBP3]CoI than [PhBPiPr3]CoI (4) by one
electron. A reversible CoII/I couple was observed for [PhBP3]-
CoI at -965 mV, and a reversible CoII/I couple for [PhBPiPr3]-
CoI was observed at -867 mV (Figure 6). Oxidation waves
for each complex were also observed. A quasireversible wave
(50 mV/s) is observed at +439 mV for iodide 4, whereas a
fully reversible wave is observed at lower potential (-42
mV) for [PhBP3]CoI. We assign each of these waves to a
CoIII/II redox process. It is quite striking that it is so much
easier to oxidize the presumably less electron-rich iodide
complex: a difference of nearly 0.5 V! Clearly, the relative
potentials for the CoIII/II and the CoII/I redox couples in these
two complexes were unanticipated at the outset, and the
difference likely arises from their distinct electronic ground
states.
IIe. Reactivity toward CO, O2, and PMe3. Exposure of
the iron chloride 2 to excess carbon monoxide resulted in
the rapid formation of a 5-coordinate, diamagnetic mono-
carbonyl adduct, [PhBPiPr3]FeCl(CO) (7) (Scheme 2). The
5-coordinate nature of 7 is noteworthy given that exposure
of its [PhBP3] congener produces the octahedral, dicarbonyl
adduct [PhBP3]FeCl(CO)2.16 The cobalt chloride reacted in
III. Discussion
IIIa. Relative Electron-Releasing Character of [PhB-
PiPr3]. The formation of the carbonyl species 7-11 provides
an additional platform by which to compare the relative
reducing nature of the [PhBPiPr3] and [PhBP3] anions. The
difference in CO stretching frequencies of 26 cm-1 between
[PhBP3]Co(CO)(Cl)16 and 8 (see entries 3 and 2 in Table 1,
respectively) underscores the stronger electron-releasing
character of the [PhBPiPr3] anion by comparison to its [PhBP3]
(17) A series of thoroughly characterized, 5-coordinate [PhBP3]Co(II)
complexes, including [PhBP3]CoBr(CO), has been prepared and will
be reported in due course. Synthetic and characterization data for
[PhBP3]CoBr(CO) were reported in the Supporting Information of ref
1a.
(18) Oxygenation of related (triphos)Co2+ complexes did not produce
similarly isolable species. See: Hienze, K.; Huttner, G.; Zsolnai, L.
Chem. Ber. 1997, 130, 1393.
(16) Preparation and spectroscopic information included in the Supporting
Information.
5078 Inorganic Chemistry, Vol. 42, No. 17, 2003

Strong-Field Tripodal Phosphine Donor
Figure 7. Displacement ellipsoid (50%) representation of (a) [PhB(CH2P(O)iPr2)2(CH2PiPr)]CoCl (14) and (b) [PhB(CH2P(O)iPr2)3]CoCl (15). The hydrogen
atoms of each complex have been omitted for clarity. Selected bond distances (Å), for 14: Co-Cl 2.223(1), Co-O1 1.955(2), Co-O2 1.965(1), Co-P3
2.410(4). For 15: Co-Cl 2.223(1), Co-O1 1.955(2), Co-O2 1.965(1), Co-O3 1.739(2).
Table 1. Carbonyl Stretching Frequencies for (κ3-L)Co(CO)2 and
infrared data to the relative electron-releasing character of a
set of ligands. Infrared data for the cationic triphos complexes
(κ3-L)RuCl(CO)2
CO (cm-1
)
ref
[(triphos)Co(CO)2][PF6]22 and [(triphos)RuCl(CO)2][PF6]23
are presented to highlight the large difference in ν(CO)
between these cations and their neutral congeners, [PhBP3]-
Co(CO)2 and [PhBP3]RuCl(CO)2 (triphos ) CH3C(CH2-
PPh2)3). Related infrared model data for bidentate (amino)-
and (phosphine)borate systems have been catalogued else-
where.24
entry
complex
ν
1
2
3
4
5
6
7
8
[PhBPiPr3]FeCl(CO)
[PhBPiPr3]CoCl(CO)
[PhBP3]CoCl(CO)
[PhBPiPr3]Co(CO)2
[PhBP3]Co(CO)2
2020a
2010a
2036a
1990, 1904a
2008, 1932a
2011, 1949b
2016, 1939c
2033, 1972b
2030, 1972d
2028, 1974e
2045, 1993a
2059, 2008d
2068, 2021d
2071, 2011d
2076, 2043d
2
(Cp*)Co(CO)2
21
19
20
22
25
[Tp3-iPr-5Me]Co(CO)2
(Cp)Co(CO)2
9
[(triphos)Co(CO)2][PF6]
(Cp*)RuCl(CO)2
IIIb. Conformational Considerations. Of obvious con-
cern is to consider the relative steric influences exerted by
the [PhBP3] and the [PhBPiPr3] anions. [PhBPiPr3]FeCl (2)
and [PhBP3]FeCl afford an excellent and unambiguous
opportunity to consider steric and conformational charac-
teristics of the [PhBP3] and [PhBPiPr3] ligands, as they feature
the same divalent first row ion in a common electronic
configuration. Inspection of the structure of [PhBPiPr3]FeCl
(2) reveals that its Fe-P bond distances are remarkably
similar to those of the reported [PhBP3]FeCl complex2b
(complex 2, Fe-P1 2.415(1), Fe-P2 2.431(1), Fe-P3 2.428-
(1) Å; [PhBP3]FeCl, Fe-P1 2.419(1), Fe-P2 2.435(1), Fe-
P3 2.426(1) Å). Comparison of the P-Fe-P and the Cl-
Fe-P bond angles between the two iron complexes, however,
establishes 2 to be appreciably more symmetric in nature
than its [PhBP3] analogue. This detail is most obvious by
inspection of the respective Cl-Fe-P bond angles. Whereas
for 2 the three Cl-Fe-P bond angles are effectively
equivalent (122.12(3)°, 122.62(4)°, and 122.52(3)°), for
[PhBP3]FeCl one of these angles (110.60(3)°) is ca. 20 °
smaller than the other two (129.55(4)° and 129.69(4)°). It is
perhaps most instructive to consider space-filling models of
each of the iron complexes. Space-filling representations with
views down the respective Cl-Fe-B axes are shown in
Figure 8. The aryl groups in [PhBP3]FeCl are splayed in
various directions about the Fe-P core. Two of the phenyl
substituents are appreciably skewed from the molecule’s
10
11
12
13
14
15
[PhBPiPr3]RuCl(CO)2
(Cp)RuCl(CO)2
26
[PhBP3]RuCl(CO)2
[Tp]RuCl(CO)2
[(triphos)RuCl(CO)2][PF6]
27
23
a Benzene/KBr. b Cyclohexane/KBr. c Toluene/KBr. d CH2Cl2/KBr. e THF/
KBr.
relative. A similar trend is observed between dicarbonyl 9
and previously reported [PhBP3]Co(CO)2 (see entries 4 and
5). These latter two complexes provide for an interesting
comparison to other facially capping ligands. The infrared
data for the related complexes [Tp3-iPr-5Me]Co(CO)2,19 CpCo-
21
(CO)2,20 and Cp*Co(CO)2 are also recorded in Table 1
([Tp3-iPr-5Me] ) hydrotris(3-isopropyl-5-methylpyrazolyl)-
borate). Most noteworthy is that dicarbonyl 9 exhibits the
lowest carbonyl stretching frequencies of the series, surpass-
ing even that of the Cp* derivative. It is apparent that
[PhBPiPr3] is a highly electron-releasing ligand.
We examined the octahedral carbonyl complexes provided
by the Ru(II) scaffold (entries 10-15, Table 1). Like the
cobalt series, there is a strong reduction in the carbonyl
stretching frequency on moving from [PhBP3]RuCl(CO)2
(11) to [PhBPiPr3]RuCl(CO)2 (10) (entries 13 and 11 in Table
1, respectively). The more noteworthy distinction in this
series is that the Cp* system features CO vibrations that are
in fact lowest in energy, emphasizing the need to define a
specific geometric model system when trying to correlate
(22) Dapporto, P.; Midollini, S.; Sacconi, L. Inorg. Chem. 1975, 14, 1643.
(23) Siegl, W. O.; Lapporte, S. J.; Collman, J. P. Inorg. Chem. 1973, 12,
674.
(24) For example, see refs 7b,c. Also see: (a) Thomas, J. C.; Peters, J. C.
J. Am. Chem. Soc., in press. (b) Betley, T. A.; Peters, J. C. Angew.
Chem., Int. Ed. 2003, 42, 2385.
(19) Detrich, J. L.; Reinaud, O. M.; Rheingold, A. L.; Theopold, K. H. J.
Am. Chem. Soc. 1995, 117, 11745.
(20) King, R. B.; Bisnette, M. B. J. Organomet. Chem. 1967, 8, 287.
(21) King, R. B.; Bisnette, M. B. J. Organomet. Chem. 1973, 56, 345.
Inorganic Chemistry, Vol. 42, No. 17, 2003 5079

Betley and Peters
previously suggested that the unusual low-spin configuration
of [PhBP3]CoI arises from its strong donor strength, coupled
with a pronounced axial distortion along the Co-I bond
vector away from tetrahedral bond angles.1a The axial
distortion in [PhBP3]CoI affords average P-Co-P angles
that approach 90°. These angles serve to minimize antibond-
ing overlap between the σ donor orbitals of the phosphines,
2
and the central torus lobe of a dz type orbital at the cobalt
center (note: the z-axis is placed along the Co-I vector;
see Figure 10). These factors are consequences of the ligand-
field and geometric constraints dictated by the [PhBP3]
ligand. The donor strength provided by [PhBPiPr3] should
be even stronger than for [PhBP3], as suggested from the
carbonyl model complexes discussed above, and from the
electrochemical data described for the iron complexes
[PhBPiPr3]FeCl (2) and [PhBP3]FeCl. It was to be expected
that the monomeric [PhBPiPr3]CoX halides 3 and 4 would
exhibit low-spin configurations by analogy to their mono-
meric [PhBP3]CoX cousins. This turns out not to be the case.
The [PhBPiPr3]CoX complexes are rigorously high-spin,
presenting somewhat of a paradox that we think can be
explained by considering the ability of the two tripodal ligand
sets to geometrically accommodate a Jahn-Teller distortion.
Figure 8. Space-filling models of (a) [PhBP3]FeCl and (b) [PhBPiPr3]FeCl
(2) generated from X-ray crystal structures.
vertical axis, while the larger isopropyl units of 2 maintain
a rigid, parallel orientation to the Fe-Cl axis. The isopropyl
groups of 2 are far more tightly packed and closely
interlocked to apparently minimize energetically unfavorable
steric interactions. The two space-filling models persuasively
suggest that the [PhBPiPr3] ligand is conformationally much
more rigid than its [PhBP3] analogue. While this conclusion
should perhaps be regarded as intuitively obvious, its
emphasis is important with respect to the explanation we
provide for the distinctly different spin states observed for
the divalent cobalt halides of each ligand type.
IIIc. Consideration of the Different Spin States Ob-
served for [PhBP3]CoI and [PhBPiPr3]CoI. We have
Figure 9. Structural representations of the immediate coordination sphere of (A) [PhBP3]CoI, (B) [PhBPiPr3]CoCl (3), and (C) [PhBPiPr3]CoI (4) to aid the
discussion presented in section IIIb,c.
Figure 10. Qualitative orbital correlation diagram that illustrates the origin and nature of the JT-distortion observed in the solid-state structure of [PhBP3]-
CoI, but not in the structures of [PhBPiPr3]CoCl (3) and [PhBPiPr3]CoI (4).
5080 Inorganic Chemistry, Vol. 42, No. 17, 2003

Strong-Field Tripodal Phosphine Donor
To aid consideration of the following arguments, the core
atoms of the previously reported structure of [PhBP3]CoI
are shown alongside those of 3 and 4 in Figure 9.
might also contribute, such as a decreased π-acidity in the
[PhBPiPr3] ligand versus the [PhBP3] ligand, but a steric
explanation seems most plausible. In the absence of steric
consequences, we would have expected the high-lying pair
of orbitals that are π* in character with respect to the
phosphine donors to be more strongly destabilized in the
[PhBPiPr3]CoX system, which would render it even more
likely to accommodate a low-spin ground state. The differ-
ence in energy between the high- and low-spin ground states
in these pseudotetrahedral d7 systems is presumably small
(i.e., between ca. 100 and 1000 cm-1). This is a reasonable
supposition, especially given that the low-spin [PhBP3]CoX
complexes are unique with respect to their doublet configu-
rations, and that structurally related high-spin systems are
also accessible. Theopold and Doren have provided support
to these assertions by theoretically examining a [Tp]CoI
model system that, while having an experimentally observed
high-spin state, is theoretically predicted to have a low-spin
state that is very close in energy.4 The consequence of these
collective assertions is that it should be possible to prepare
pseudotetrahedral cobalt(II) species that exhibit spin-
crossover. Efforts to elucidate such a species are now under
way.
The high, nearly ideal 3-fold symmetry of [PhBPiPr3]CoCl
(3) is consistent with its high-spin electronic configuration.
The structure reveals three virtually equivalent Co-P bond
lengths (Co-P1 2.334(2), Co-P2 2.332(1), Co-P3 2.330-
(2) Å). Its three X-Co-P angles (average Cl-Co-P )
119.7°) and its three P-Co-P angles (average ) 97.5°) also
display very little variance. The same may in general be said
of high-spin [PhBPiPr3]CoI (4). While in the latter complex
there is a slightly more notable spread in the Co-P bond
distances (Co-P1 2.334(2), Co-P2 2.321(2), Co-P3 2.385-
(2) Å), once again the variance in its three X-Co-P and
P-Co-P bond angles is trivial, and the average of each is
analogous to that for the chloride (average I-Co-P )
119.7°; P-Co-P ) 97.6°). The variance in these angles and
in the Co-P bond lengths observed for the parent iodide,
[PhBP3]CoI, is much more striking. The average of its
P-Co-P angles (92.2°) is on average 5° smaller than for
the high-spin systems, and a large variation in the I-Co-P
bond angles (118°, 129°, and 124°) is also observed. The
smaller average P-Co-P angle observed in [PhBP3]CoI
likely reflects its ability to accommodate the low-spin
configuration. The closer these angles are to 90°, the smaller
the overlap of the phosphine donor ligands with the central
Experimental Section
All manipulations were carried out using standard Schlenk or
glovebox techniques under a dinitrogen atmosphere. Unless oth-
erwise noted, solvents were deoxygenated and dried by thorough
sparging with N2 gas followed by passage through an activated
alumina column. Nonhalogenated solvents were typically tested with
a standard purple solution of sodium benzophenone ketyl in
tetrahydrofuran in order to confirm effective oxygen and moisture
removal. The reagents TlPF6, CoI2, CoCl2, FeCl2, and iPr2PCl were
purchased from commercial vendors and used without further
purification (metal reagents from Strem Chemicals; phosphine from
Aldrich). The RuII precursor RuCl2(PPh3)3 was synthesized as
described previously.28 PhBCl2 was purchased from Aldrich and
distilled under N2 prior to use. [PhBP3]Tl was prepared as previously
described.1b Deuterated solvents were degassed and stored over
activated 3-Å molecular sieves prior to use. Elemental analyses
were carried out at Desert Analytics, Tucson, Arizona. NMR spectra
were recorded at ambient temperature on Varian Mercury 300 MHz,
Joel 400 MHz, and Inova 500 MHz spectrometers, unless otherwise
noted. 1H and 13C NMR chemical shifts were referenced to residual
solvent. 31P NMR, 11B NMR, and 19F NMR chemical shifts are
reported relative to an external standard of 85% H3PO4, neat BF3‚
Et2O, and neat CFCl3, respectively. IR spectra were recorded on a
Bio-Rad Excalibur FTS 3000 spectrometer controlled by Win-IR
Pro software. MS data for samples were obtained by injection of a
hydrocarbon solution into a Hewlett-Packard 1100MSD mass
spectrometer (ES+) or an Agilent 5973 mass selective detector (EI).
UV-vis measurements were taken on a Hewlett-Packard 8452A
diode array spectrometer using a quartz crystal cell with a Teflon
2
torus of the 3dz type orbital. The doublet ground state of
[PhBP3]CoI also requires that it accommodate a Jahn-Teller
distortion. This is reflected in its asymmetric solid-state
structure. Two short (P1 and P2) and one elongated (P3)
Co-P bonds manifest a gentle distortion akin to an e-
vibrational mode under 3-fold symmetry that serves to
stabilize a cobalt-based orbital that is antibonding with
respect to a phosphine donor and that houses a single
unpaired electron. A lobal representation of this orbital is
shown to the right in Figure 10. The three I-Co-P angles
of [PhBP3]CoI also highlight its overall asymmetry. If we
assume that the doublet state of [PhBP3]CoI is not too far in
energy from its higher lying quartet state, accommodating a
JT-distortion would seem to require that the [PhBP3] ligand
be able to adjust its conformation with little energetic cost.
As is suggested from the conformational description of the
iron chloride complexes, different conformations of the
[PhBP3] ligand would seem energetically easy to accom-
modate.
Inspection of the structure of 4 reveals it to be distinctly
more symmetric in nature. Foremost, the Co-I bond is
noticeably lengthened in 4 (2.540(1) Å) from that observed
for [PhBP3]CoI (2.474 Å) due to its expanded high-spin
radius. The I-Co-P bond angles of 4 are virtually indis-
tinguishable from 3 and, ignoring the PhB-backbone, nearly
an ideal 3-fold axis runs through the Co-I bond vector of
4, evidenced by its nearly identical P-Co-P bond angles.
We suggest that the ability of the [PhBP3] ligand to
conformationally accommodate a JT-distorted doublet state,
a distortion that would likely be energetically more expensive
for the bulkier [PhBPiPr3] system, is the key difference that
gives rise to their different spin states. Other differences
(25) Fagan, P. J.; Mahoney, W. S.; Calabrese, J. C.; Williams, I. D.
Organometallics 1990, 9, 1843.
(26) Brown, D. A.; Lyons, H. J.; Sane, R. T. Inorg. Chim. Acta. 1970, 4,
621.
(27) Tenorio, M. A. J.; Tenorio, M. J.; Puerta, M. C.; Valerga, P. J. Chem.
Soc., Dalton Trans. 1998, 3601.
(28) Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Synth. 1970,
12, 237.
Inorganic Chemistry, Vol. 42, No. 17, 2003 5081

Betley and Peters
Table 2. X-ray Diffraction Experimental Details for [PhBPiPr3]Tl (1), [PhBPiPr3]FeCl (2), [PhBPiPr3]CoCl (3), [PhBPiPr3]CoI (4), {[PhBP3]Ru(µ-Cl)}2
(6), [PhBP3]RuCl(PMe3) (13), and Crystal Sample for 14 and 15
1
2
3
4
6
13
14 and 15
chemical formula
C27H53BP3Tl
C33H59BClFeP3
C27H53BClCoP3
C27H53BCoIP3
C98H98B2Cl2-
O2P6Ru2
1788.24
-177
C48H50BCl-
P4Ru
898.14
C27H53BCl-
CoO2P3
610.51
fw
685.78
-177
650.82
-177
0.71073
9.4852(8)
11.6854(10)
32.866(3)
90
90
90
3642.8(5)
P212121
4
575.79
-177
667.28
-177
0.71073
46.165(3)
12.2340(8)
34.353(2)
90
90
90
19402(2)
Cmca
28
T (°C)
λ (Å)
a (Å)
b (Å)
c (Å)
-177
-177
0.71073
9.1981(7)
9.9374(7)
17.5546(13)
79.070(1)
80.225(1)
79.997(1)
1535.9(2)
P1h
0.71073
9.5545(10)
9.8481(10)
17.4990(18)
78.387(2)
81.246(2)
82.425(2)
1585.3(3)
P1h
0.71073
13.0430(11)
13.1103(11)
13.5126(11)
71.899(1)
67.271(1)
82.508(1)
2025.6(3)
P1h
0.71073
19.215(3)
12.2280(19)
20.500(3)
90
0.71073
11.7012(10)
12.4231(11)
13.0885(12)
73.695(2)
71.296(2)
63.149(2)
1586.9(2)
P1h
R (deg)
â (deg)
γ (deg)
V (Å3)
space group
Z
107.805(2)
90
4586.0(12)
P21/c
2
2
1
4
2
D
calcd (g/cm3)
µ (cm-1
R1, wR2a
(I > 2σ(I))
1.483
5.427
0.0274, 0.0612
1.187
6.390
0.0492, 0.0844
1.206
7.91
0.0464, 0.0934
1.371
16.48
0.0602, 0.1217
1.466
6.110
0.0302, 0.0671
1.423
5.780
0.0516, 0.0909
1.278
7.99
0.0488, 0.1225
)
2
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|, wR2 ) {∑[w(Fo - Fc )2]/∑[w(Fo )2]}1/2
.
cap. X-ray diffraction studies were carried out in the Beckman
Institute Crystallographic Facility on a Bruker Smart 1000 CCD
diffractometer.
working in the TE102 mode. Variable temperature measurements
were conducted with an Oxford continuous-flow helium cryostat
(temperature range 3.6-300 K). Accurate frequency values were
provided by a frequency counter built in the microwave bridge.
Solution spectra were acquired in toluene for all of the complexes.
Sample preparation was performed under a nitrogen atmosphere.
X-ray Crystallography Procedures. X-ray quality crystals were
grown as indicated in the experimental procedures per individual
complex. The crystals were mounted on a glass fiber with Paratone
N oil. Structures were determined using direct methods with
standard Fourier techniques using the Bruker AXS software
package. In some cases, Patterson maps were used in place of the
direct methods procedure. Table 2 includes the X-ray diffraction
experimental details, while the full crystallographic tables are
included in the Supporting Information.
Magnetic Measurements. Measurements were recorded using
a Quantum Designs SQUID magnetometer running MPMSR2
software (Magnetic Property Measurement System Revision 2).
Data were recorded at 5000 G. Samples were suspended in the
magnetometer in plastic straws sealed under nitrogen with Lilly
No. 4 gel caps. Loaded samples were centered within the magne-
tometer using the DC centering scan at 35 K and 5000 gauss. Data
were acquired at 2-10 K (one data point/2 K), 10-60 K (one data
point/5 K), 60-310 K (one data point/10 K).
øM
mG
øm )
(1)
(2)
[PhBPiPr3]Tl, (1). Preparation of iPr2PMe. iPr2PCl (24 g, 0.157
mol) was diluted with diethyl ether (250 mL) in a 500 mL Schlenk
flask. The ether solution was cooled to -78 °C in a dry ice/acetone
bath. To this solution, MeLi (112.3 mL, 0.157 mol) was added via
syringe over a period of 40 min. White precipitate formed
immediately. The reaction was stirred for 14 h and allowed to warm
to room temperature over this time period. The precipitate was
filtered on a sintered-glass frit. The volatiles from the supernatant
were removed in vacuo, which resulted in further precipitation of
LiCl salts. The resulting liquid was diluted in petroleum ether and
filtered through Celite on a sintered-glass frit to remove salt. This
process was repeated three times, and the volatiles were then
removed in vacuo to afford spectroscopically pure iPr2PMe (20.13
g, 97%).
µeff
)
7.997ø T
x
m
The magnetic susceptibility was adjusted for diamagnetic
contributions using the constitutive corrections of Pascal’s constants
and a fixed temperature independent paramagnetism (TIP) crudely
set to 2 × 10-4 cm3 mol-1 29
.
The molar magnetic susceptibility
(øm) was calculated by converting the calculated magnetic suscep-
tibility (ø) (or magnetization) obtained from the magnetometer to
a molar susceptibility using the multiplication factor [molecular
weight (M)]/[sample weight (m) × field strength (G)]). Curie-
-1
Weiss behavior was verified by a plot of øm versus T (Figure
3b). Data were analyzed using eqs 1 and 2. Average magnetic
moments were taken from the average of magnetic moments from
the ranges indicated in the Experimental Section for each complex.
The Weiss constant (ø) was taken as the x-intercept of the plot of
ø m-1 versus T. Error bars were established at 95% confidence using
regression analysis or taking two standard deviations from the mean.
Solution magnetic moments were measured by the Evans method
and were adjusted for diamagnetic contributions using the constitu-
tive corrections of Pascal’s constants.
t
Lithiation of MePiPr2.7c Solid BuLi (7.28 g, 0.113 mol) was
i
added to neat quantity of Pr2PMe (15.0 g, 0.113 mol) to form a
homogeneous solution in a 50 mL round-bottom Schlenk flask. The
reaction was heated to 60 °C for 10 h under a slow purge of nitrogen
through a bubbler. The white solid was washed with petroleum
ether (1 × 25 mL) and collected on a sintered glass frit (15.05 g,
96%; purity ascertained by 31P{1H} NMR in THF: δ 22.4 ppm).
Preparation of [PhBPiPr3]Tl. In a 250 mL Schlenk flask, solid
iPr2PCH2Li (6.5 g, 0.047 mol) was suspended in diethyl ether to
which 1 equiv of TMEDA was added in one portion (5.47 g, 0.047
mol). The flask was sealed with a septum and cooled to -78 °C in
Averaged g-factors can be extracted from the susceptibility data,
assuming zero orbital contributions, using the following equation:
Ng2â2
3kT
øm )
(S(S + 1))
EPR Measurements. X-band EPR spectra were obtained on a
Bruker EMX spectrometer equipped with a rectangular cavity
(29) Kahn, O. Molecular Magnetism; VCH Publishers: New York, 1993;
pp 1-10.
5082 Inorganic Chemistry, Vol. 42, No. 17, 2003

Strong-Field Tripodal Phosphine Donor
a dry ice/acetone bath. A toluene solution (15 mL) of PhBCl2 (2.49
g, 0.016 mol) was added dropwise to the ether solution over a period
of 5 min. Salt precipitation was evident within a few minutes after
the borane was added. The solution was allowed to warm to room
temperature over a period of 10 h, at which time the solution was
filtered through Celite on a sintered glass frit to remove the
precipitate. Formation of the product was evident by 31P NMR,
which showed a single broad resonance at 4 ppm. Solid TlPF6 (5.48
g, 0.016 mol) was dissolved in THF and added to the ether solution.
Some formation of thallium metal was evident along with the
precipitation of salts upon the addition of the TlPF6 solution. The
precipitate was collected on a glass frit. Petroleum ether (25 mL)
was added to the supernatant, and the solution was cooled to -33
°C overnight, which resulted in the precipitation of a white
crystalline solid. The supernatant was decanted, and the solids were
washed with acetonitrile (35 mL). The remaining solids were
dissolved in a mixture of toluene (3 mL) and petroleum ether (3
mL). The solution was recrystallized by cooling to -33 °C
MHz): δ 41.6 (bs), 24.1 (bs), 12.8 (s), 9.03 (s), 7.23 (s), 5.86 (s),
3.24 (bs). UV-vis (C6H6) λmax, nm (ꢀ): 660 (676), 745 (1630).
Evans Method (C6D6): 4.10 µB. Anal. Calcd for C27H53BCoIP3:
C, 48.60; H, 8.01. Found: C, 47.84; H, 7.91.
{[PhBPiPr3]Ru(µ-Cl)}2 (5). A solution of 1 (80 mg, 0.12 mmol)
in 2 mL of THF was added to a stirring solution of RuCl2(PPh3)3
(140 mg, 0.12 mmol) in THF (5 mL) at room temperature. After
stirring for 4 h, the brown solution was filtered through a sintered-
glass frit to remove insolubles. The volatiles were removed in vacuo
to yield a brown solid. The solid was dissolved in CH2Cl2 and
filtered through a Celite plug to remove TlCl. A red-brown solid
was precipitated by vapor diffusion of petroleum ether into CH2-
Cl2, affording analytically pure material (112 mg, 78%). 1H NMR
(C6D6, 300 MHz): δ 7.81 (m, 2H), 7.45 (t, J ) 7.6 Hz, 2H), 7.28
(m, 1H), 2.68 (bs, 6H), 1.65 (m, 18H), 1.18 (m, 6H). 31P{1H} NMR
(C6D6, 121.4 MHz): δ 47.5. 13C{1H} NMR (C6D6, 75.409 MHz):
δ 157, 132, 127, 124, 25 (m), 20, 15 (m). 11B{1H} NMR (C6D6,
128.3 MHz): δ -7.2. Anal. Calcd for C54H106B2Cl2P6Ru2: C,
52.48; H, 8.64. Found: C, 52.38; H, 8.66.
1
overnight, affording analytically pure material (6.2 g, 58%). H
NMR (C6D6, 300 MHz): δ 7.97 (m, 2H, Ho BPh), 7.59 (t, 2H, Hm
BPh), 7.31 (t, 1H, Hp BPh), 1.89 (septet, 6H, P(CH(CH3)2)), 1.20
(m, 6H, B(CH2PiPr2)), 1.05 (dd, 36H, P(CH(CH3)2). 13C{1H} NMR
(C6D6, 75.409 MHz): δ 158 (m, Cipso BPh), 132 (s, Co BPh), 128
(s, Cm BPh), 124 (s, Cp BPh), 24.2 (dd, P(CH(CH3)2)), 20.6 (s,
P(CH(CH3)2), 15 (m, B(CH2PiPr2)). 31P{1H} NMR (C6D6, 121.4
MHz): δ 24.3 (dd, 1J203Tl-P ) 5865 Hz, 1J205Tl-P ) 5913 Hz). 11B-
{1H} NMR (C6D6, 128.3 MHz): δ -13. Anal. Calcd for C27H53-
BP3Tl: C, 47.28; H, 7.79. Found: C, 47.23; H, 7.68.
{[PhBP3]Ru(µ-Cl)}2 (6). A solution of [BP3][Tl] (40 mg, 0.045
mmol) in 2 mL of THF was added to a stirring solution of RuCl2-
(PPh3)3 (55 mg, 0.045 mmol) in THF (2 mL) at room temperature.
After stirring for 4 h, the solution was filtered through a Celite
plug to remove insolubles. Vapor diffusion of petroleum ether into
the crude THF solution precipitated brown crystals, affording
analytically pure material (38 mg, 97%). A suitable crystal was
1
selected for X-ray analysis. H NMR (CDCl3, 300 MHz, 25 °C):
δ 7.86 (d, J ) 6.6 Hz, 2 H), 7.54 (t, J ) 8.4 Hz, 11H), 7.42 (t, J
) 7.5 Hz, 2H), 7.31 (t, J ) 7.5 Hz, 2H), 7.02 (m, 18H), 1.63 (m,
6H). 31P{1H} NMR (CDCl3, 121.4 MHz, 25 °C): δ 64 (s). 11B-
{1H} NMR (CDCl3, 128.3 MHz): δ 10.7 (s). Anal. Calcd for
C90H82B2Cl2P6Ru2: C, 65.75; H, 5.03. Found: C, 65.72; H, 5.12.
[PhBPiPr3]FeCl(CO) (7). A solution of 2 (20 mg, 0.035 mmol)
in benzene (1 mL) was sparged with CO gas for 1 min while stirring
vigorously at room temperature. The color changed from canary-
yellow to a gold hue immediately upon introduction of the CO gas.
After stirring for 0.5 h, the resulting golden solution was evaporated
to dryness in vacuo to afford analytically pure material (20.2 mg,
[PhBPiPr3]FeCl (2). A solution of 1 (30.3 mg, 0.044 mmol) in
THF (1 mL) was added to a stirring suspension of FeCl2 (5.6 mg,
0.044 mmol) in THF (2 mL) at room temperature. After stirring
for 2 h, the resulting canary-yellow solution was filtered through a
Celite pad and then evaporated to dryness in vacuo. The yellow
solids were dissolved in benzene (2 mL) and filtered again through
a Celite pad. Slow evaporation of the benzene solution afforded
analytically pure, crystalline product (21.9 mg, 87%). Suitable
1
crystals were selected for an X-ray diffraction study. H NMR
(C6D6, 300 MHz): δ 42.5 (s), 20.0 (s), 18.5 (s), 4.16 (bs), 2.03
(bs), -17.6 (bs), -36.3 (bs). UV-vis (C6H6) λmax, nm (ꢀ): 422
(550). Evans Method (C6D6): 5.23 µB. Anal. Calcd for C27H53-
BClFeP3: C, 56.62; H, 9.33. Found: C, 56.22; H, 9.32.
1
98%). H NMR (C6D6, 300 MHz): δ 7.83 (m, 2H), 7.55 (t, J )
7.8 Hz, 2H), 7.31 (m, 1H), 2.71 (bs, 1H), 2.08 (bs, 1H), 1.75 (m,
1H), 1.55 (dq, J ) 6.6, 35 Hz, 5H), 1.18 (m, 8H), 0.87 (dd, J )
7.2, 12 Hz, 3H), 0.60 (m, 2H), 0.29 (s, 1H). 31P{1H} NMR (C6D6,
121.4 MHz): δ 67.5 (t, J ) 50.3 Hz, 1P), 41.9 (d, J ) 50 Hz, 2P).
11B{1H} NMR (C6D6, 128.3 MHz): δ -7.2. IR: (C6H6/KBr) νCO
) 2020 cm-1. Anal. Calcd for C28H53BClFeOP3: C, 55.98; H, 8.89.
Found: C, 56.02; H, 8.78.
[PhBPiPr3]CoCl (3). A solution of 1 (51.3 mg, 0.075 mmol) in
THF (1 mL) was added to a stirring suspension of CoCl2 (9.7 mg,
0.075 mmol) in THF (2 mL) at room temperature. After stirring
for 2 h, the resulting aqua-green solution was filtered through a
Celite pad and then evaporated to dryness in vacuo. The aqua-
green solids were dissolved in benzene (2 mL) and filtered again
through a Celite pad. Slow evaporation of the benzene solution
afforded analytically pure, crystalline product (38.3 mg, 89%).
[PhBPiPr3]CoCl(CO) (8). A solution of 3 (19.5 mg, 0.034 mmol)
in benzene (1 mL) was sparged with CO gas for 1 min while stirring
vigorously at room temperature. The color changes from aqua-green
to an intense green immediately upon introduction of the CO gas.
After stirring for 0.5 h, the resulting green solution was evaporated
to dryness in vacuo to afford analytically pure material (20.3 mg,
1
Suitable crystals were selected for an X-ray diffraction study. H
NMR (C6D6, 300 MHz): δ 40.5 (bs), 24.7 (bs), 11.7 (s), 8.68 (s),
6.91 (s), 3.64 (bs). UV-vis (C6H6) λmax, nm (ꢀ): 610 (1140), 720
(1350). Evans Method (C6D6): 4.12 µB. Anal. Calcd for C27H53-
BClCoP3: C, 56.32; H, 9.28. Found: C, 56.29; H, 9.45.
[PhBPiPr3]CoI (4). A solution of 1 (50.0 mg, 0.073 mmol) in
THF (1 mL) was added to a stirring suspension of CoI2 (22.0 mg,
0.073 mmol) in THF (2 mL) at room temperature. After stirring
for 2 h, the resulting green solution was filtered through a Celite
pad and then evaporated to dryness in vacuo. The green solids were
dissolved in benzene (2 mL) and filtered again through a Celite
pad. Slow evaporation of the benzene solution afforded analytically
pure crystalline product (44.7 mg, 92%). Suitable crystals were
selected for an X-ray diffraction study. 1H NMR (C6D6, 300
1
99%). H NMR (C6D6, 300 MHz): δ 24.8 (bs), 12.1 (s), 8.68 (s),
6.91 (s), 3.64 (bs), -0.86 (s). Evans Method (C6D6): 2.24 µB. IR:
(C6H6/KBr) νCO ) 2010 cm-1. Anal. Calcd for C28H53BClCoOP3:
C, 55.69; H, 8.85. Found: C, 55.66; H, 8.89.
[PhBPiPr3]Co(CO)2 (9). A solution of 4 (9.1 mg, 0.014 mmol)
in benzene (1 mL) was sparged with CO gas for 1 min while stirring
vigorously at room temperature. The color changes from green to
an intense lime-green immediately upon introduction of the CO
gas. After stirring for 0.5 h, the resulting green solution was
evaporated to dryness in vacuo. The lime-green solids were
dissolved in a mixture of benzene (1 mL) and petroleum ether (1
Inorganic Chemistry, Vol. 42, No. 17, 2003 5083

Betley and Peters
mL) and filtered through a Celite pad. The volatiles were then
removed in vacuo to afford analytically pure material (7.4 mg, 92%).
1H NMR (C6D6, 300 MHz): δ 7.92 (m, 2H), 7.80 (m, 2H), 7.44
(m, 1H), 2.55 (m, 6H), 1.86 (m, J ) 7.2 Hz, 18H), 0.86 (m, 6H).
13C{1H} NMR (C6D6, 75.409 MHz): δ 182, 156, 130, 127, 123,
24.4 (m), 19, 16 (m). 31P{1H} NMR (CDCl3, 121.4 MHz, 25 °C):
δ 56. IR: (C6H6/KBr) νCO ) 1990, 1904 cm-1. Anal. Calcd for
C29H53BCoO2P3: C, 58.40; H, 8.96. Found: C, 58.21; H, 8.99.
[PhBPiPr3]RuCl(CO)2 (10). To a solution of 5 (40 mg, 0.032
mmol) in 5 mL THF was added 1 atm of CO gas (through a septum
in a 20 mL vial) at room temperature. The vial was stirred at room
temperature until the solution color changed from red-brown to a
pale yellow, at which point the excess CO gas was removed via an
Ar purge. The solution was filtered through a Celite plug in air to
remove insolubles. The solution was then evaporated to dryness in
vacuo to afford analytically pure material (40 mg, 92%). 1H NMR
(C6D6, 300 MHz): δ 7.80 (m, 2H), 7.60 (t, J ) 7.2 Hz, 2H), 7.30
(m, 1H), 3.01 (bs, 1H), 2.28 (bs, 1H), 1.78 (m, 1H), 1.65 (dq, J )
6.6, 35 Hz, 6H), 1.18 (m, 8H), 0.90 (dd, J ) 7.2, 12 Hz, 3H), 0.60
(m, 2H). 31P{1H} NMR (C6D6, 121.4 MHz): δ 56 (t, J ) 46 Hz,
1P), 35 (d, J ) 48 Hz, 2P). 11B{1H} NMR (C6D6, 128.3 MHz): δ
-9.2. IR: (CH2Cl2/KBr) νCO ) 2045, 1993 cm-1. Anal. Calcd for
C29H53BClO2P3Ru: C, 51.68; H, 7.93. Found: C, 51.25; H, 7.91.
[PhBP3]RuCl(CO)2 (11). To a solution of 6 (40 mg, 0.024
mmol) in 5 mL of THF was added 1 atm of CO gas (through a
septum in a 20 mL vial) at room temperature. The vial was stirred
until the solution color changed from yellow-brown to colorless,
at which point the excess CO gas was removed via an Ar purge.
The solution was filtered through a Celite plug in air to remove
insolubles. The solution was then evaporated to dryness in vacuo
to afford analytically pure material (41 mg, 96%). 1H NMR (CDCl3,
300 MHz): δ 7.86 (d, J ) 6.6 Hz, 2 H), 7.47 (m, 16H), 7.00 (m,
18H), 1.98 (m, 4H), 1.82 (bs, 2H). 31P{1H} NMR (CDCl3, 121.4
MHz, 25 °C): δ 39.9 (t, J ) 32 Hz), 11.3 (d, J ) 32 Hz). IR:
(CH2Cl2/KBr) νCO ) 2068, 2021 cm-1. Anal. Calcd for C47H41-
BClO2P3Ru: C, 64.29; H, 4.71. Found: C, 64.25; H, 4.58.
[PhBPiPr3]RuCl(PMe3) (12). To a solution of 5 (40 mg, 0.032
mmol) in 5 mL of toluene was added an excess of PMe3 (10 mg,
0.13 mmol). After stirring for 4 h at 50 °C, the volatiles were
removed in vacuo to afford a brick-red oil. Red-brown solids were
precipitated by cooling the toluene solution at -33 °C overnight,
affording analytically pure material (40.8 mg, 91%). 1H NMR
(C6D6, 300 MHz): δ 7.74 (m, 2H), 7.45 (t, J ) 7.6 Hz, 2H), 7.28
(m, 1H), 2.68 (bs, 6H), 1.65 (m, 18H), 1.18 (m, 6H), 0.72 (b, 9H).
31P{1H} NMR (C6D6, 121.4 MHz): δ 44 (very broad), -4.4 (q, J
) 77 Hz). 13C{1H} NMR (C6D6, 75.409 MHz): δ 157, 132, 127,
124, 24 (m), 20, 18 (m), 15 (m). Anal. Calcd for C30H62BClP4Ru:
C, 51.92; H, 9.00. Found: C, 50.96; H, 8.99.
0.13 mmol). After stirring for 4 h at 50 °C, the volatiles were
removed in vacuo to afford a brick-red solid. Crystals were afforded
by vapor diffusion of petroleum ether into THF, providing
analytically pure material (38.4 mg, 88%). A crystal was selected
1
for an X-ray diffraction study. H NMR (CDCl3, 300 MHz): δ
7.84 (d, J ) 6.6 Hz, 2 H), 7.53 (t, J ) 8.4 Hz, 11H), 7.47 (t, J )
7.5 Hz, 2H), 7.23 (t, J ) 7.5 Hz, 2H), 6.95-7.07 (m, 18H), 1.63
(m, 6H), 0.67 (bs, 9H). 31P{1H} NMR (CDCl3, 121.4 MHz): δ 54
(bm), 2.50 (q, J ) 74.8 Hz). 11B{1H} NMR (CDCl3, 128.3 MHz):
δ 10.8 (s). Anal. Calcd for C48H50BClP4Ru: C, 64.19; H, 5.61.
Found: C, 64.22; H, 5.60.
[PhB(CH2P(O)iPr2)2(CH2PiPr2)]CoCl (14). Dioxygen (1 mL,
0.045 mmol) was added via syringe to a solution of 3 (25.7 mg,
0.045 mmol) in benzene (1 mL), and then, the mixture was stirred
vigorously at room temperature. The color changes from aqua-green
to an intense blue. After stirring for 2 h, the resulting blue solution
was evaporated to dryness. Crystals were afforded by slow
evaporation of a benzene solution affording analytically pure
material (24.0 mg, 87%). 1H NMR (C6D6, 300 MHz): δ 24.5, 11.7,
8.72, 6.92, 3.6 (b), 0.88, -0.66. Evans Method (C6D6): 4.23 µB.
Anal. Calcd for C27H53BClCoO2P3: C, 53.35; H, 8.79. Found: C,
52.69; H, 8.86.
[PhB(CH2P(O)iPr2)3]CoCl (15). Dioxygen (3 mL, 0.135 mmol)
was added via syringe to a solution of 3 (25.7 mg, 0.045 mmol) in
benzene (1 mL) and then stirred vigorously at room temperature.
The color changes from aqua-green to an intense blue. After stirring
for 6 h, the resulting blue solution was evaporated to dryness to
afford analytically pure material (24.2 mg, 86%). 1H NMR (C6D6,
300 MHz): δ 24.8, 12.1, 8.25, 6.86, 3.55 (b), 0.68, -0.99. Evans
Method (C6D6): 4.24 µB. Anal. Calcd for C27H53BClCoO3P3: C,
51.98; H, 8.56. Found: C, 51.33; H, 8.54.
Crystals of 14 and 15 were grown by letting a concentrated
solution of 3 to stand for 12 h at room temperature under an
atmosphere of air. While the majority of the species formed was
14 (81%), a small fraction (19%) of the tris(phosphineoxide) 15
was also formed and cocrystallized.
Acknowledgment. We acknowledge the Dreyfus Foun-
dation and the ACS Petroleum Research Fund for financial
support. T.A.B. thanks the Department of Defense for a
graduate research fellowship. J.C.P. is grateful for a Camille-
Dreyfus Teacher Scholar Award.
Supporting Information Available: Complete crystallographic
tables and special refinement details for complexes 1, 2, 3, 4, 6,
13, 14, and 15. This material is available free of charge via the
Internet at http://pubs.acs.org.
[PhBP3]RuCl(PMe3) (13). To a solution of 6 (40 mg, 0.024
mmol) in 5 mL toluene was added an excess of PMe3 (10 mg,
IC0343096
5084 Inorganic Chemistry, Vol. 42, No. 17, 2003