The coordination chemistry of "[BP3]NiX" platforms: Targeting low-valent nickel sources as promising candidates to L3Ni=E and L3Ni≡E linkages

Inorg. Chem. 2004, 43, 4645−4662

The Coordination Chemistry of “[BP ]NiX” Platforms: Targeting

3

Low-Valent Nickel Sources as Promising Candidates to L₃NidE and

L₃NitE Linkages

Cora E. MacBeth, J. Christopher Thomas, 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 January 15, 2004

A series of divalent, monovalent, and zerovalent nickel complexes supported by the electron-releasing, monoanionic

iPr

i

tris(phosphino)borate ligands [PhBP ] and [PhBP ] ([PhBP ] ) [PhB(CH PPh₂)₃]^-, [PhBP ] ) [PhB(CH PPr₂)₃]^-)

3

2

3

2

have been synthesized to explore fundamental aspects of their coordination chemistry. The pseudotetrahedral,

iPr

divalent halide complexes [PhBP ]NiCl (1), [PhBP ]NiI (2), and [PhBP ]NiCl (3) were prepared by the metalation

3

iPr

of [PhBP ]Tl or [PhBP ]Tl with (Ph₃P)₂NiCl₂, NiI₂, and (DME)NiCl₂(DME ) 1,2-dimethoxyethane), respectively.

3

Complex 1 is a versatile precursor to a series of complexes accessible via substitution reactions including [PhBP ]-

3

t

Ni(N ) (4), [PhBP ]Ni(OSiPh₃) (5), [PhBP ]Ni(O-p-Bu-Ph) (6), and [PhBP ]Ni(S-p-Bu-Ph) (7). Complexes 2−5 and

3

7 have been characterized by X-ray diffraction (XRD) and are pseudotetrahedral monomers in the solid state.

Complex 1 reacts readily with oxygen to form the four-electron-oxidation product, {[PhB(CH P(O)Ph₂)₂(CH PPh₂)]-

2

NiCl} (8A or 8B), which features a solid-state structure that is dependent on its method of crystallization. Chemical

reduction of 1 using Na/Hg or other potential 1-electron reductants generates a product that arises from partial

ligand degradation, [PhBP ]Ni(η²-CH PPh ) (9). The more sterically hindered chloride 3 reacts with Li(dbabh) (Hdbabh

3

2

iPr

) 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene) to provide the three-coordinate complex [κ²-PhBP ]Ni(dbabh)

3

(11), also characterized by XRD. Chemical reduction of complex 1 in the presence of L-type donors produces the

t

tetrahedral Ni(I) complexes [PhBP ]Ni(PPh₃) (12) and [PhBP ]Ni(CNBu) (13). Reduction of 3 following the addition

3

iPr

t

of PMe₃or tert-butyl isocyanide affords the Ni(I) complexes [PhBP ]Ni(PMe₃) (14) and [PhBP ]Ni(CNBu) (15),

3

respectively. The reactivity of these [PhBP ]Ni^IL and [PhBP ]Ni^IL complexes with respect to oxidative group transfer

iPr

3

reactions from organic azides and diazoalkanes is discussed. The zerovalent nitrosyl complex [PhBP ]Ni(NO) (16)

3

is prepared by the reaction of 1 with excess NO or by treating 12 with stoichiometric NO. The anionic Ni(0)

iPr

complexes [[κ²-PhBP ]Ni(CO)₂][ⁿBu₄N] (17) and [[κ²-PhBP ]Ni(CO)₂][ASN] (18) (ASN ) 5-azoniaspiro[4.4]nonane)

3

iPr

have been prepared by reacting [PhBP ]Tl or [PhBP ]Tl with (Ph₃P)₂Ni(CO)₂in the presence of R NBr. The

3

4

photolysis of 17 appears to generate a new species consistent with a zerovalent monocarbonyl complex which we

tentatively assign as {[PhBP ]Ni(CO)}{ⁿBu₄N}, although complete characterization of this complex has been difficult.

3

t

Finally, theoretical DFT calculations are presented for the hypothetical low spin complexes [PhBP ]Ni(NBu),

3

iPr

t

iPr

[PhBP ]Ni(NBu), [PhBP ]Ni(NMe), and [PhBP ]Ni(N) to consider what role electronic structure factors might

3

play with respect to the relative stability of these species.

I. Introduction

the renewed interest has been sparked by the realization that

these types of species can participate in a host of catalytic

group transfer reactions such as aziridinations,¹cyclopropa-

nations,²and oxidations.³Moreover, there is hope that new

approaches to catalytic small molecule activation and func-

tionalization reactions that exploit reactive metal fragments

from this sector of the transition block may yet be eluci-

dated.^4,5Small molecule substrates of interest might include

The fundamental coordination chemistry of mid-to-late

first row transition metal ions supported by relatively simple

ligand auxiliaries represents a mature field that has experi-

enced somewhat of a renaissance in recent years. Much of

* Author to whom correspondence should be addressed. E-mail:

jpeters@caltech.edu.

Published on Web 06/25/2004

Inorganic Chemistry, Vol. 43, No. 15, 2004 4645

MacBeth et al.

N₂, N₂O, O₂, CO₂, CO, and P₄.⁶One of the most attractive

features of the mid-to-late first row ions concerns their ability

to form metal-to-ligand multiple bond linkages that are

kinetically and thermodynamically reactive. Species of these

types (e.g., MdO, MdCR₂, MdNR, MtN) are proposed

as key intermediates in a number of catalytic reactions of

both synthetic and biocatalytic significance.^3,7

context, our group has initiated the development of pseudo-

tetrahedral “L₃MX” platforms where L₃represents the

anionic tris(phosphine) donor [PhBP₃] or [PhBP^iPr₃] ([PhBP₃]

) [PhB(CH₂PPh₂)₃]^-, [PhBP^iPr₃] ) [PhB(CH₂PⁱPr₂)₃]^-) and

M represents a first row ion such as Fe or Co, and in this

paper Ni.^14-18Our interest in the family of nickel complexes

described herein is motivated by recent findings demonstrat-

ing that “L₃Co” and “L₃Fe” complexes supported by BP₃

ligand auxiliaries (i) support later metal-to-ligand triple bond

linkages (e.g., L₃CotNR, L₃FetNR, L₃FetN) and (ii)

participate in multielectron group transfer reactions that

accept and release the multiply bonded functional unit.

Riordan’s group has moreover shown that “L₃Ni(I)” species

supported by anionic tris(thioether)borate ligands undergo

oxidative group transfer with dioxygen. For example, the

Ni(I) carbonyl supported by [PhTt^tBu] reacts with dioxygen

to form a Ni₂(µ-O)₂structure in which each nickel center

has been oxidized to Ni(III).¹⁹This structure type was first

elucidated for nickel by Hikichi and co-workers using a tris-

(pyrazolyl)borate auxiliary scaffold.²⁰

Very recently, several groups have reported the isolation

of well-defined later first row complexes that feature metal-

to-ligand multiple bond linkages. For example, using steri-

cally encumbering bis(phosphine) ligands, Hillhouse and co-

workers have shown that L₂Ni fragments are compatible with

imide (NR),⁸phosphinidene (PR),⁹and carbene (CR₂)¹⁰

functional groups (generally defined as L₂Ni^IIdE species).

These fascinating complexes, which follow on an early

observation from the Jones group that provided strong

evidence for a reactive L₂Ni^IIdS linkage,¹¹have since been

shown to undergo stoichiometric group transfer processes,

for instance to ethylene.^12,13The L₂Ni^IIdE systems owe their

appreciable stability to a combination of simple electronic

factors and to the considerable steric protection provided by

the bulky bis(phosphine) ligand and the substitution pattern

at the multiply bonded functional group. Four-coordinate

pseudotetrahedral systems that feature MdE and MtE

linkages (i.e., L₃MtE systems) are equally intriguing targets,

and a more general understanding of the electronic similari-

ties and differences that dictate the relative stability of later

first row metal MdE and MtE linkages for three-, four-,

and higher coordinate structures is clearly of interest. In this

The present report focuses on the synthesis and charac-

terization of a host of nickel complexes supported by BP₃

ligands and on theoretical and reactivity issues pertinent to

the possible construction of L₃NidE and L₃NitE linkages.

To these ends, we have prepared a series of divalent L₃NiX

(X ) I, Cl, N₃, OR, or SR) complexes, as well as mono-

and zerovalent nickel precursors. Where applicable, structural

and electronic comparisons are made between these “[PhBP₃]-

Ni” and “[PhBP^iPr₃]Ni” systems and their structurally similar

counterparts supported by other anionic and facially capping

ligand auxiliaries,^21,22or by neutral tris(phosphine) ligand

auxiliaries such as CH₃C(CH₂PPh₂)₃and PhP(CH₂PPh₂)₂.^23,24

The results presented demonstrate that tris(phosphino)borate

scaffolds effectively stabilize the lower oxidation states of

nickel (e.g., Ni⁰, Ni^I, and Ni^II) while in most cases maintain-

ing a four-coordinate pseudotetrahedral geometry. Synthetic

(1) (a) Evans, D. A.; Woerpol, K. A.; Hinman, M. M.; Faul, M. M. J.

Am. Chem. Soc. 1991, 113, 726-728. (b) Li, Z.; Quan, R. W.;

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(2) (a) Doyle, M. P.; McKervey, M. A.; Ye, T. Modern Catalytic Methods

for Organic Synthesis with Diazo Compounds; Wiley: New York,

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411-432. (c) Doyle, M. P. Chem. ReV. 1986, 86, 919-939.

(3) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles

and Applications of Organotransition Metal Chemistry, 2nd ed.;

University Science Books: Mill Valley, CA, 1987.

(14) Jenkins, D. M.; Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2002,

124, 11238-11239.

(4) Fisher, B.; Eisenberg, R. J. Am. Chem. Soc. 1980, 102, 7361-7363.

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Am. Chem. Soc. 1993, 115, 6470-6471.

(15) Brown, S. D.; Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2003,

125, 322-323.

(6) For examples, see: (a) Detrich, J. L.; Konecˇny´, R.; Vetter, W. M.;

Doren, D.; Rheingold, A. L.; Theopold, K. H. J. Am. Chem. Soc. 1996,

118, 1703-1712. (b) Cecconi, F.; Ghilardi, C. A.; Midollini, S.;

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1985, 731-733. (c) Ehses, M.; Romerosa, A.; Peruzzi, M. Top. Curr.

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Rheingold, A. L. J. Am. Chem. Soc. 1993, 115, 2075-2077. (e) Qin,

Z.; Thomas, C. M.; Lee, S.; Coates, G. W. Angew. Chem., Int. Ed.

2003, 42, 5484-5487. (f) Fox, D. J.; Bergman, R. G. J. Am. Chem.

Soc. 2003, 125, 8984-8985. (g) Holland, P. L.; Andersen, R. A.;

Bergman, R. G. J. Am. Chem. Soc. 1996, 118, 1092-1104.

(7) Bioinorganic Catalysis; Reedijk, J., Bouwman, E., Eds.; Marcel

Dekker: New York, 1999.

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10783.

(17) Brown, S. D.; Peters, J. C. J. Am. Chem. Soc. 2004, 126, 4538-4539.

(18) Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2004, 126, 6252-6254.

(19) Mandimutsira, B. S.; Yamarik, J. L.; Brunold, T. C.; Weiwei, G.;

Cramer, S. P.; Riordan, C. G. J. Am. Chem. Soc. 2001, 123, 9194-

9195.

(20) Hikichi, S.; Yoshizawa, M.; Sasakura, Y.; Akita, M.; Moro-Oka, Y.

J. Am. Chem. Soc. 1998, 120, 10567-10568.

(21) Kubiak and coworkers have examined related [PhBP₃]Ni systems:

Kubiak, C. P. et al. Private communication, 2004.

(22) For examples of Ni complexes supported by [Tp] ligands see: (a)

Gutierrez, E.; Hudson, S. A.; Monge, A.; Nicasio, M. C.; Paneque,

M. J. Organomet. Chem. 1998, 551, 215-227. (b) Shirasawa, N.;

Nguyet, T. T.; Hikichi, S.; Moro-oka, Y.; Akita, M. Organometallics

2001, 20, 3582-3598. (c) Uehara, K.; Hikichi, S.; Akita, M.; Muneta,

A. J. Chem. Soc., Dalton Trans. 2002, 3529-3538. (d) Trofimenko,

S. Scorpionates-The Coordination Chemistry of Polypyrazolylborate

Ligands; Imperial College Press: London, 1999.

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4624.

(9) Melenkivitz, R.; Mindiola, D. J.; Hillhouse, G. L. J. Am. Chem. Soc.

2002, 124, 3846-3847.

(10) Mindiola, D. J.; Hillhouse, G. L. J. Am. Chem. Soc. 2002, 124, 9976-

9977.

(11) Vicic, D. A.; Jones, W. D. J. Am. Chem. Soc. 1999, 121, 4070-4071.

(12) Waterman, R.; Hillhouse, G. L. J. Am. Chem. Soc. 2003, 125, 13350-

13351.

(23) Dapporto, P.; Fallani, G.; Sacconi, L. Inorg. Chem. 1974, 13, 2847-

2850.

(24) (a) Hou, H.; Gantzel, P. K.; Kubiak, C. P. Organometallics 2003, 22,

2817-2819. (b) Hou, H.; Gantzel, P. K.; Kubiak, C. P. J. Am. Chem.

Soc. 2003, 125, 9564-9565.

(13) Waterman, R.; Hillhouse, G. L. Organometallics 2003, 22, 5182-

5184.

4646 Inorganic Chemistry, Vol. 43, No. 15, 2004

The Coordination Chemistry of “[BP₃]NiX” Platforms

Scheme 1

access to L₃Ni^IIItE and L₃Ni^IVtE species remains a

synthetic challenge.

II. Results and Discussion

IIa. Synthesis and Characterization of Pseudotetrahe-

II

dral [PhBP₃]Ni^IIX and [PhBP^iPr]Ni X Complexes. Of

Figure 1. Displacement ellipsoid representations (50%) of (A) [PhBP₃]-

NiI (2) and (B) [PhBPⁱPr₃]NiCl (3). Hydrogen atoms and solvent molecules

have been omitted for clarity. Selected interatomic distances (Å) and angles

(deg) for 2: Ni-I, 2.498(1); Ni-P1, 2.289(2); Ni-P2, 2.265(2); Ni-P3,

2.267(2); Ni-B, 3.484(6); P1-Ni-P3, 91.52(6); P1-Ni-P2, 93.77(6); P2-

Ni-P3, 92.99(6); I-Ni-P1, 124.25(5); I-Ni-P2, 118.33(6); I-Ni-P3,

127.20(5). For 3: Ni-Cl, 2.1772(9); Ni-P1, 2.2871(8); Ni-P2, 2.2893(9);

Ni-P3, 2.2811(8); Ni-B, 3.474(3); P1-Ni-P2, 94.12(3); P2-Ni-P3,

94.97(3); P1-Ni-P3, 94.16(3); Cl-Ni-P1, 125.30(4); Cl-Ni-P2, 121.92(4);

Cl-Ni-P3, 118.94(3).

3

interest as synthetic precursors to the nickel chemistry

featured herein are the Ni(II) halides [PhBP₃]NiX and

[PhBP^iPr₃]NiX, where X ) Cl or I. Divalent complexes of

these types have already been reported for [PhBP₃]- and

[PhBP^iPr₃]-supported iron and cobalt systems,²⁵and a syn-

thetic protocol that exploits [PhBP₃]Tl or [PhBP^iPr₃]Tl as a

transmetalation reagent is equally effective for nickel. Thus,

[PhBP₃]Tl reacts with the nickel precursors (Ph₃P)₂NiCl₂or

NiI₂to eliminate TlX (X ) Cl, I) and generate the desired

green [PhBP₃]NiCl (1) and red-brown [PhBP₃]NiI (2) halide

complexes (Scheme 1) in good yield. NiCl₂could also be

used as a starting material, affording some 1 upon reaction

with [PhBP₃]Tl, but undesirable side reactions proved more

problematic. Similarly, the synthesis of the yellow-green S

) 1 complex [PhBP^iPr₃]NiCl (3) is achieved in high isolated

yield (>90%) by reaction of the starting material (DME)-

NiCl₂(DME ) 1,2-dimethoxyethane) with [PhBP^iPr₃]Tl.

Evans method measurements of 1, 2, and 3 in benzene

solution are consistent with two unpaired electrons per nickel

center. The attempted synthesis of 3 using other Ni(II)

precursors, such as (Ph₃P)₂NiCl₂and NiCl₂, again provides

some 3; however, the desired product is accompanied by

large amounts of diamagnetic impurities in each case. These

types of electron-transfer reactions would generate a reactive

borane radical that then would be expected to undergo bond

homolysis to liberate a ^•CH₂PR₂radical. The [PhBP^iPr₃] anion

is inherently more reducing than its [PhBP₃] counterpart, and,

as a result, its installation at nickel is somewhat more

sensitive.

The solid-state structures of 2 and 3 were determined by

X-ray diffraction (XRD) studies on single crystals of 2 and

3 (Figure 1). Each of the halide complexes is four-coordinate

and pseudotetrahedral, and the bond lengths and angles are

for the most part unremarkable. The iodide complex 2

features two short (2.265(2) and 2.267(2) Å) and one

modestly longer Ni-P (2.289(2) Å) bond, whereas the

chloride complex 3 exhibits three nearly equidistant bond

lengths (2.2871(8), 2.2893(9), and 2.2811(8) Å). The P-Ni-P

angles are on average slightly larger for 3 (94-95°) than

for 2 (91.5-94°). One comparison worth noting is that the

Ni-I bond length in 2 is appreciably longer (2.498(1) Å)

than the Ni-I bond length in the isostructural but cationic

Scheme 2

[L₃NiI]⁺species [(CH₃C(CH₂PPh₂)₃)NiI][As₆I₈] (2.414(4)

Å).²⁶Hence, placing a formal positive charge on the [L₃-

NiI]⁺fragment attracts the iodide anion closer to the nickel

center. While 2 can be formally described as zwitterionic

with a positive charge on the nickel unit and an anionic

charge on the borate unit, its nickel center nonetheless

appears to be appreciably less electrophilic than in the more

conventional cation [(CH₃C(CH₂PPh₂)₃)NiI]⁺. This conclu-

sion is consistent with other studies we have undertaken to

resolve electronic differences between phosphine-supported

zwitterions and their isostructural cations.²⁷In general, the

zwitterions appear to be more electron-rich by whichever

measuring stick we use as a qualitative guide.

With complex 1 in hand, we prepared a series of

complexes featuring other X-type ligands by metathetical

routes to determine what geometries would be preferred for

species of the general type [PhBP₃]NiX (Scheme 2). For

example, the yellow-green azide complex [PhBP₃]Ni(N₃) (4)

can be prepared from sodium azide and exhibits a ν(N₃)

vibration at 2060 cm^-1(KBr, C₆H₆), consistent with a

terminal azide functionality that is corroborated by its solid-

(26) Zanello, P.; Cinquantini, A.; Ghilardi, C. A.; Midollini, S.; Moneti,

S.; Orlandini, A.; Bencini, A. J. Chem. Soc., Dalton Trans. 1990,

3761-3766.

(27) (a) Thomas, J. C.; Peters, J. C. J. Am. Chem. Soc. 2003, 125, 8870-

8888. (b) Thomas, J. C.; Peters, J. C. J. Am. Chem. Soc. 2001, 123,

5100-5101.

(25) (a) Jenkins, D. M.; Di Billo, A. J.; Allen, M. J.; Betley, T. A.; Peters,

J. C. J. Am. Chem. Soc. 2002, 124, 15336-15350. (b) Betley, T. A.;

Peters, J. C. Inorg. Chem. 2003, 42, 5074-5084.

Inorganic Chemistry, Vol. 43, No. 15, 2004 4647

MacBeth et al.

Figure 2. Molecular structures of (A) [PhBP₃]Ni(N₃) (4), (B) [PhBP₃]-

Ni(OSiPh₃) (5), and (C) [PhBP₃]Ni(S-p-^tBu-Ph) (7), derived from crystal-

lographic studies. Only the L₃NiX subunit of each complex is represented.

Complete structural details can be found in the Supporting Information.

Selected interatomic distances (Å) and angles (deg) for 4: Ni-N1,

1.915(12); Ni-P1, 2.262(2); Ni-P2, 2.261(2); Ni-P3, 2.255(2); P1-Ni-

P2, 95.09(7); P1-Ni-P3, 90.80(8); P2-Ni-P3, 91.67(6); P1-Ni-N1,

126.7(4); P2-Ni-N1, 121.1(3); P3-Ni-N1, 122.4(4). For 5: Ni-O, 1.820-

(2); Ni-P1, 2.275(1); Ni-P2, 2.270(1); Ni-P3, 2.281(1); P1-Ni-P2,

89.77(3); P1-Ni-P3, 94.06(3); P2-Ni-P3, 91.65(3); P1-Ni-O, 123.59(8);

P2-Ni-O, 89.77(3); P3-Ni-O, 130.20(8); Ni-O-Si, 168.08(14). For

7: Ni-S, 2.119(1); Ni-P1, 2.189(1); Ni-P2, 2.188(1); Ni-P3, 2.244(1);

P1-Ni-P2, 89.44(3); P1-Ni-P3, 91.28(3); P2-Ni-P3, 107.87(3); P1-

Ni-S, 151.84(3); P2-Ni-S, 109.79(3); P3-Ni-S, 101.54(3).

Figure 3. Displacement ellipsoid representation (50%) of (A) [PhB(CH₂P-

(O)Ph₂)₂(CH₂PPh₂)]NiCl (8A) and (B) {[PhB(CH₂P(O)Ph₂)₂(CH₂PPh₂)]-

NiCl}₂(8B). Hydrogen atoms, phosphine phenyl rings, and solvent

molecules have been omitted for clarity. Selected bond distances (Å) and

angles (deg) for 8A: Ni-Cl, 2.210(1); Ni-O1, 1.926(2); Ni-O2, 1.958(2);

Ni-P3, 2.294(1); O1-Ni-O2, 98.79(7); O1-Ni-P3, 105.28(5); O2-Ni-

P3, 97.64(5); O1-Ni-Cl, 116.74(5); O2-Ni-Cl, 125.31(5); P3-Ni-Cl,

110.07(3). For 8B: Ni1-Cl1, 2.3543(11); Ni1-Cl2, 2.3814(12); Ni2-Cl1,

2.3311(12); Ni2-Cl2, 2.3916(11); Ni1-O1, 2.005(3); Ni1-O2, 1.989(3);

Ni2-O3, 2.006(2); Ni2-O4, 1.980(3); Ni1-P3, 2.3125(13); Ni2-P6,

2.3236(13).

are low spin and exhibit a square planar geometry.³³The

geometry of paramagnetic 7 (Evans method (C₆D₆, 298 K):

µ_eff) 3.02 µ_B) lies somewhere between a severely distorted

tetrahedral structure type and a cis-divacant octahedron. Most

striking is the dramatic variation in its three P-Ni-S bond

angles, one of which is very large (151.84(3)°) and the other

two (107.87(3)° and 109.79(3)°) of which are much closer

to those of an idealized tetrahedron. Also of note is that the

average Ni-P bond lengths of 7 (av 2.21 Å) are appreciably

shorter than for 2 (av 2.27 Å), 4 (av 2.26 Å), and 5 (av 2.28

Å). Although the solid-state structure of aryloxide 6 has not

state molecular structure.²⁸The molecular geometry of 4,

depicted in Figure 2, is monomeric and best described as

pseudotetrahedral.²⁹To our knowledge, 4 represents the only

example of a crystallographically characterized nickel azide

complex in which the azide ligand is coordinated to a single

tetrahedral or pseudotetrahedral nickel center. Other nickel

azides supported by sterically hindered tris(pyrazolyl)borate

ligands have been prepared that present tetrahedral or five-

coordinate structures in which the azide bridges two nickel

centers.³⁰

The green siloxide ([PhBP₃]Ni(OSiPh₃), 5), the purple

aryloxide ([PhBP₃]Ni(O-p-^tBu-Ph), 6), and the red arylthi-

olate ([PhBP₃]Ni(S-p-^tBu-Ph), 7) are all conveniently pre-

pared by transmetalation with thallium reagents. The mo-

lecular structures of 5 and 7 are shown in Figure 2. The

structure of 5 is related to its recently reported cobalt

congener [PhBP₃]Co(OSiPh₃).³¹The Ni-O-Si bond angle

of 168.08(14)° compares well with the Co-O-Si angle of

172.5(1)°. Perhaps structurally more interesting is the red

thiolate complex 7. A large number of nickel thiolates have

been prepared, and their chemistry is of increasing interest

due to their likely role in biocatalytic systems such as NiFe

hydrogenase.³²Four-coordinate nickel complexes that feature

a single Ni-thiolate linkage remain quite rare, and to our

knowledge all such examples that have been characterized

1

been determined, we note that its paramagnetic H NMR

resonances in benzene-d₆are very similar to those observed

for 7, suggesting that they have similar solution (and

presumably solid-state) conformations.

The divalent [PhBP₃]NiX complexes 1-7 are all quite

sensitive to dioxygen. While this reactivity has not been

studied explicitly for each case, the product of the reaction

of 1 with dioxygen has been determined. Thus, exposure of

1 to an excess of O₂in benzene results in a rapid color change

from green to purple. This color change is accompanied by

a new and intense ν(PdO) vibration in the IR spectrum (1320

cm^-1) confirming a ligand oxidation reaction. We have

observed this type of reactivity for tris(phosphino)borate-

supported Fe(II) and Co(II) systems previously.²⁵The nickel

oxidation product was isolated as purple crystals at room

temperature by vapor diffusion of petroleum ether into a

benzene solution. XRD analysis of a representative single

crystal established the monomeric and four-coordinate nickel

complex [PhB(CH₂P(O)Ph₂)₂(CH₂PPh₂)]NiCl (8A) (eq 1 and

Figure 3A), in which two of the phosphine donors have been

oxidized to their corresponding phosphine oxides. Curiously,

yellow rather than purple crystals are obtained if petroleum

(28) Nakamato, K. Infrared and Raman Spectra of Inorganic and Coor-

dination Compounds. Part B: Applications in Coordination, Orga-

nometallic, and Bioinorganic Chemistry, 5th ed.; John Wiley &

Sons: New York, 1997; pp 105-126.

(29) The structure of 4 suffers from modest disorder along its Ni-azide

bond vector, and the thermal ellipsoid of the azide N atom directly

linked to the nickel center is consequently quite large (see Supporting

Information).

(30) Trofimenko, S.; Calabrese, J. C.; Kochi, J. K.; Wolowiec, S.;

Hulsbergen, F. B.; Reedijk, J. Inorg. Chem. 1992, 31, 3943-3950.

(31) Jenkins, D. M.; Peters, J. C. J. Am. Chem. Soc. 2003, 125, 11162-

11163.

(32) (a) Volbeda, A.; Charon, M.-H.; Piras, C.; Hatchikian, E. C.; Frey,

M.; Fontescilla-Camps, J. C. Nature 1995, 373, 580-587. (b)

Sellmann, D.; Geipel, F.; Moll, M. Angew. Chem., Int. Ed. 2000, 39,

561-563.

(33) (a) Sa´nchez, G.; Ruiz, F.; Serrano, J. L.; Ram´ırez de Arellano, M. C.;

Lo´pez, G. Eur. J. Inorg. Chem. 2002, 2185-2191. (b) Clegg, W.;

Henderson, R. A. Inorg. Chem. 2002, 41, 1128-1135. (c) Tucci, G.

C.; Holm, R. H. J. Am. Chem. Soc. 1995, 117, 6489-6496. (d) Kru¨ger,

H.-J.; Holm, R. H. Inorg. Chem. 1989, 28, 1148-1155. (e) Kanatzidis,

M. G. Inorg. Chim. Acta 1990, 168, 101-103.

4648 Inorganic Chemistry, Vol. 43, No. 15, 2004

The Coordination Chemistry of “[BP₃]NiX” Platforms

appreciably lower potential (-1.44 V, Figure 4a). An

increase in the solution concentration of 3 (g1 × 10^-3M)

resulted in rapid deposition of material on the glassy carbon

electrode and the disappearance of the reduction wave. The

Ni^II/Icouple for 3 as compared to 1 (∆E_1/2) 240 mV) reflects

an appreciable difference in electron-releasing character of

the [PhBP^iPr₃] ligand relative to its [PhBP₃] counterpart. This

distinction is consistent with the cyclic voltammograms

obtained previously for the complexes [PhBP^iPr₃]FeCl and

[PhBP₃]FeCl (∆E_1/2) 322 mV).^15,25bImportant to note is

that the cyclic voltammograms for complexes 1, 2, and 3 do

not provide any evidence for an oxidation wave within the

detectable range (i.e., below ∼1.0 V).

It is interesting to compare these data to those of several

other L₃Ni^IIX systems that have been characterized electro-

chemically. For example, the cationic tripodal phosphine

system [(CH₃C(CH₂PPh₂)₃)NiX][ClO₄] has been examined

previously and shows a fully reversible Ni^II/Iredox processes

at -0.53 V (X ) Cl) and -0.43 V (X ) I) in CH₂Cl₂

solution relative to Fc/Fc⁺.^26,35The Ni^II/Icouple is thus shifted

approximately 700 mV positive on translating from the

neutral L₃Ni^IIX structure type to the isostructural but cationic

L₃Ni^IIX⁺structure type. The magnitude of the difference in

redox couples between the two systems seems large given

the zwitterionic nature of the neutral [PhBP₃]NiX system.

An appreciable difference in the degree of solvent reorga-

nization upon oxidation is to be expected, and this difference,

coupled with the increased electron-richness we expect for

zwitterionic systems supported by (phosphino)borates, sug-

gests that a relatively large difference in redox potentials is

in fact quite reasonable. Related infrared carbonyl model

studies from our lab have comparatively examined electronic

factors between zwitterions and their isostructural cations

and revealed unexpectedly large differences in ν(CO) values

between such systems, the zwitterions always giving rise to

much lower CO frequencies.^36,37,54It is also interesting to

compare Riordan’s tris(thioether)borate complex [PhTt^tBu]-

NiCl ([PhTt^tBu] ) [PhB(CH₂S^tBu)₃]^-), which features an

irreVersible Ni^II/Iredox process at -1.3 V relative to Fc/

Fc⁺in CH₂Cl₂.³⁸The irreversible nature of its one electron

reduction makes a direct comparison to the one electron

reduction potentials of the [PhBP₃]NiX systems tenuous. It

is nonetheless qualitatively interesting, and perhaps surpris-

ing, that the reduction potential for Riordan’s sulfur-

supported nickel system is approximately as low as the

phosphine-supported [PhBP₃]Ni(II) complexes 1 and 2.

The cyclic voltammetry of the [PhBP₃]NiX complexes (X

) -OSiPh₃, 5; -O-p-^tBu-Ph, 6; -S-p-^tBu-Ph, 7) was also

studied between +1.2 and - 3.0 V to examine what effect

X-type ligands of better π-donor strength might have on the

Ni(II/I) redox process and to examine whether such ligands

might better stabilize the Ni(III) oxidation state. As a point

Figure 4. Cyclic voltammograms of (a) 3, (b) 1, and (c) 2 recorded at a

scan rate of 100 mV/s in THF with Bu₄NPF₆as the supporting electrolyte.

Potentials are referenced to Fc/Fc⁺.

ether is allowed to diffuse into a toluene solution of the

oxidation product at low temperature (-40 °C). XRD

analysis of a representative yellow crystal establishes the

dimeric form of the oxidized chloride, {[PhB(CH₂P(O)-

Ph₂)₂(CH₂PPh₂)]NiCl}₂(8B), in which each of the chloride

ligands now resides in a bridging position (Figure 3B). The

structure of 8B suffers from several disordered solvent

molecules in the lattice; however, the dimeric nickel molecule

is well-defined. The two structures intimate that monomeric

8A is in equilibrium with its dimeric partner 8B and that

the equilibrium likely shifts in favor of the dimer at lower

temperatures. A similar temperature dependent monomer/

dimer equilibrium has been observed for the Ni(II) complex

dichloro[bis(3,5-dimethylpyrazolyl)methane]Ni.³⁴

excess O₂

[PhBP₃]NiCl

_benzene8

1

{[PhB(CH₂P(O)Ph₂)₂(CH₂PPh₂)]NiCl}

(1)

8A or 8B

IIb. Electrochemical Data for Divalent Complexes. The

tris(phosphino)borate ligands [PhBP₃] and [PhBP^iPr₃] ef-

fectively stabilize monovalent iron and cobalt complexes that

prove to be effective precursors for the installation of multiple

bond linkages via oxidative group transfer.^14-16To determine

the accessibility of monovalent nickel species we first studied

the cyclic voltammetry of the divalent nickel precursors.

These studies were performed in THF using [ⁿBu₄N][PF₆]

(0.35 M) as the supporting electrolyte. All data were

referenced to Fc/Fc⁺as an internal standard using Ag/AgNO₃

as the reference electrode.

Figure 4 compares the first reduction process observed

for the halide complexes 1, 2, and 3. Each process is assigned

as a one-electron reduction of L₃Ni^IIX to [L₃Ni^IX]^-. A fully

reversible reduction process is observed for the chloride

complex 1 at -1.20 V (Figure 4b). The Ni^II/Icouple shifts

to -1.12 V (Figure 4c) upon replacement of chloride by the

weaker field iodide ligand in 2. The cyclic voltammetry of

3 shows a quasi-reversible redox process (100 mV/s) at an

(35) The authors report potentials versus SCE and corrected these values

relative to Fc/Fc⁺.

(36) Betley, T. A.; Peters, J. C. Inorg. Chem. 2003, 42, 5074-5084.

(37) Betley, T. A.; Peters, J. C. Angew. Chem., Int. Ed. 2003, 42, 2385-

2389.

(38) Schebler, P. J.; Riordan, C. G.; Guzei, I. A.; Rheingold, A. L. Inorg.

Chem. 1998, 37, 4754-4755.

(34) Reedijk, J.; Verbiest, J. Transition Met. Chem. 1978, 3, 51-52.

Inorganic Chemistry, Vol. 43, No. 15, 2004 4649

MacBeth et al.

Scheme 3

of rather soft tris(thioether)borate ligands to stabilize Ni(I).

For example, the reduction of [PhTt^tBu]NiCl by methyllithium

under a blanket of CO produces the Ni(I) species [PhTt^tBu]-

Ni(CO).³⁹Ni(I) complexes species supported by betadiketim-

inate ligands have also been reported recently.⁴⁰

The direct reduction of chloride 2 by Na/Hg in THF led

to the generation of a diamagnetic red organometallic,

[PhBP₃]Ni(η²-CH₂PPh₂) (9), rather than the anticipated

[PhBP₃]Ni^ICl^-anion suggested by the cyclic voltammetry

of 2. The same product was formed when other strong

reductants were examined, including sodium mirror and

potassium graphite. Complex 9 can be synthesized indepen-

dently in high yield by the direct reaction of 1 with Ph₂-

PCH₂Li(TMEDA) (Scheme 3), and it appears to be a

thermodynamic sink within the [PhBP₃]Ni system. For

instance, when potentially reducing nucleophiles, such as

alkyllithiums or lithium amides, are added to chloride 2 at

low temperature (-78 °C), complex 9 is invariably generated

as the dominant reaction product. Riordan’s [PhTt^tBu]NiCl

system was reported to behave in a similar fashion in the

presence of alkyllithiums without a trapping ligand such as

CO or PMe₃available.³⁹An obvious unanswered question

for both systems concerns whether (i) a bona fide Ni^II-alkyl

(or Ni^II-amide) is generated but is inherently unstable within

these pseudotetrahedral borate-based systems and somehow

degrades to 9 or (ii) outer-sphere electron transfer occurs as

a first step to generate L₃Ni^I-Cl^-, which is unstable to

chloride loss and subsequent degradation to 9. At present

we can only conclude that complexes 1 and 2 are sensitive

to reducing conditions, and that borate ligand degradation

can occur even at low temperatures to produce 9. Degradation

processes are less problematic when a donor ligand trap is

used (vide infra).

Figure 5. Cyclic voltammograms of (a) 5, (b) 6, and (c) 7 recorded at a

scan rate of 100 mV/s. Potentials are referenced to Fc/Fc⁺.

of reference, we have previously reported that the complex

[PhBP₃]Co(OSiPh₃) exhibits fully reversible Co^III/IIand Co^II/I

redox processes, but that its iodide counterpart [PhBP₃]CoI

exhibits only a single reversible redox couple (Co^II/I) along

with an irreversible Co^III/IIoxidation wave.^25b,31Reversible

Ni^II/Ireduction processes are observed for each of the

complexes 5, 6, and 7 (Figure 5). The siloxide complex 5

exhibits the most negative potential at -1.47 V (Figure 5a).

Like its cobalt relative, complex 5 also exhibits an oxidation

wave at higher potential (0.350 V), but in this case the

process is irreversible. Its irreversibility suggests that the

putative [Ni^III-OSiPh₃]⁺species generated decays rapidly

under these conditions. A similar set of observations was

made for the aryloxide complex 6. It exhibits a single and

reversible reduction process (Ni^II/I) at -1.36 V (Figure 5b),

and an irreversible oxidation event at 0.240 V, suggesting

that complex 6 is both easier to reduce and easier to oxidize

than the siloxide complex 5. The arylthiolate complex 7

displays the most readily accessible Ni^II/Iredox couple (-1.12

V, Figure 5c). Perhaps more interesting is that 7 also shows

a second reduction event at -2.56 V. This latter process is

irreversible, and while we suspect that it corresponds to a

Ni^I/0redox change, it may also represent a reduction event

at the arylthiolate ligand. As discussed below, the Ni(0) state

is more readily accessible within these BP₃Ni systems when

π-acidic ligands are coordinated to the fourth binding site.

Finally, an irreversible oxidation event is observed at 0.170

V for 7, establishing that it is more easily oxidized than either

5 or 6. Considered collectively, these electrochemical data

establish that monovalent nickel is readily accessible within

these BP₃Ni platforms, but that the stabilization of a trivalent

nickel state is likely to require more strongly π-donating

X-type ligands.

A reaction worthy of particular comment is that between

CoCp₂and 1 in the presence of [ⁿBu₄N][PF₆]. The crude

product of this reaction is a new paramagnetic species (¹H

NMR) that is tentatively formulated as the one electron

reduced complex {[PhBP₃]Ni^ICl}{ⁿBu₄N}. This species is

very unstable in solution and has not been isolated in

analytically pure form. Solution degradation occurs to

produce a mixture of both paramagnetic and diamagnetic

products even at low temperatures (-40 °C). Nonetheless,

its assignment is consistent with the following observation:

rapid reoxidation of the crude product using [Fc][PF₆]

regenerates the starting nickel halide 1 in ∼85% yield (¹H

NMR).

IIc. Chemical Reduction of [PhBP₃]NiX and [PhBP^iPr₃]-

NiCl Precursors. Given the electrochemical stability of

monovalent nickel within these P₃NiX platforms, it was of

interest to investigate the preparation of Ni(I) complexes for

subsequent group transfer studies. Efforts to prepare and

study the reactivity patterns of molecular Ni(I) species have

only recently been pursued in a systematic fashion. For

instance, Hillhouse and co-workers have prepared a series

of L₂Ni^IX complexes that feature halides, pseudohalides, and

alkyls as the X-type ligand using relatively soft phosphine

donor ligands.^8-10Riordan’s group has moreover made use

The related reduction chemistry of [PhBP^iPr₃]NiCl (3) with

a variety of typical reductants, for example, Na/Hg, sodium

(39) 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, 331-332.

(40) Holland, P. L.; Cundari, T. R.; Perez, L. L.; Eckert, N. A.; Lachicotte,

R. J. J. Am. Chem. Soc. 2002, 124, 14416-14424.

4650 Inorganic Chemistry, Vol. 43, No. 15, 2004

The Coordination Chemistry of “[BP₃]NiX” Platforms

Scheme 4

diisopropylphenyl)}, also suggests the formation of three

coordinate Ni^II-NR₂structures. These products are likewise

diamagnetic and give highly colored solutions (red and

purple, respectively). It appears that the [PhBP^iPr₃]Ni^II

scaffold is more resistant to outer-sphere reduction and

thereby allows cleaner substitution to occur at the Ni(II) state.

However, the pseudotetrahedral geometry is compromised

by dechelation of one phosphine donor.

Figure 6. Displacement ellipsoid representation (50%) of [κ²-PhBPⁱPr₃]-

Ni(dbabh) (11). Hydrogen atoms have been omitted for clarity. Selected

distances (Å) and angles (deg): P1-Ni, 2.1475(7); P2-Ni, 2.1317(7);

N-Ni, 1.748(2); P1-Ni-P2, 93.38(3); P1-Ni-N, 136.86(7); P2-Ni-N,

129.65(7).

naphthalenide, potassium graphite, Mg⁰, and (9,10-dihydro-

9,10-anthracenediyl)tris(tetrahydrofuran)magnesium, was also

surveyed. These reactions did not result in the formation of

the degradation product [PhBP^iPr₃]Ni(η²-CH₂PⁱPr₂) (10),

which was synthesized independently by reaction of 3 with

LiCH₂PⁱPr₂in THF (Scheme 3). Ill-defined product mixtures

resulted instead.

IId. Synthesis and Characterization of [PhBP₃]Ni^IL and

[PhBP^iPr₃]Ni^IL Complexes. The presence of a suitable L-

type trapping ligand can stabilize the Ni(I) state to give syn-

thetically useful precursors (Scheme 4). For example, the

reduction of 1 in the presence of PPh₃by KC₈yields [PhBP₃]-

Ni(PPh₃) (12) in good yield. PMe₃is also an effective trap.

The core structure of 12 is shown in Figure 7. Similarly, the

reduction of 1 by sodium amalgam in the presence of ^tBuNC

results in the formation of [PhBP₃]Ni(CN^tBu) (13). It is ob-

The [PhBP^iPr₃] anion lowers the reduction potential of the

divalent nickel state considerably as observed in our elec-

trochemical studies, and we therefore suspected that [PhBP^iPr₃]-

NiCl might give rise to cleaner substitution chemistry with

potentially reducing nucleophiles rather than problematic

redox chemistry. The reactivity of 3 was therefore explored

with a host of lithiated amines. One example concerns the

lithium amide Li(dbabh) (Hdbabh ) 2,3:5,6-dibenzo-7-

azabicyclo[2.2.1]hepta-2,5-diene),⁴¹chosen as a possible

N-atom transfer reagent (vide infra). The reaction between

3 and Li(dbabh) at low temperature results in an inky green-

brown solution from which the three-coordinate nickel(II)

complex [κ²-PhBP^iPr₃]Ni(dbabh) (11) can be isolated. The

three coordinate nature of 11 in solution is strongly suggested

by its NMR data, which shows a diamagnetic product.

Interestingly, only one phosphine environment is evident by

t

served that the addition of BuNC to 1 prior to addition of

the reductant causes an immediate color change from green

to purple. NMR spectra of the purple reaction mixture (¹H

and ³¹P{¹H}) show the formation of a diamagnetic interme-

diate prior to reduction, presumably “[κ²-PhBP₃]Ni(Cl)

(CN^tBu)”. Complexes 12 and 13 are paramagnetic and

exhibit solution magnetic moments of 1.91 µ_Band 1.74 µ_B,

respectively. Complex 13 exhibits an intense ν(CN) band in

its IR spectrum at 2094 cm^-1(KBr, C₆H₆) suggesting that

the isocyanide ligand is terminal.²⁸This is corroborated by

its solid-state molecular structure (Figure 7).

The [PhBP^iPr₃]NiCl (3) precursor can be similarly reduced

to form P₃Ni^IL complexes (Scheme 4). Reduction of 3 using

a sodium/mercury amalgam in the presence of excess PMe₃

(5 equiv) results in the formation of analytically pure bright

yellow [PhBP^iPr₃]Ni(PMe₃) (14). Yellow 14 is also formed

in good yield from the reaction of the Ni(0) precursor Ni-

(PMe₃)₄with [PhBP^iPr₃]Tl. This reaction proceeds with

concomitant reduction of Tl(I) to Tl(0), evident by the

precipitation of thallium metal from solution. Crystals of 14

were obtained from this latter reaction by crystallization from

diethyl ether at -30 °C. XRD analysis showed that the

crystals contained a 95:5 mixture of 14 and [PhBP^iPr₃]Tl.

The presence of a small amount of [PhBP^iPr₃]Tl in the crystals

was also visible from their ³¹P{¹H} NMR spectrum and by

the presence of a well-refined peak in the difference Fourier

map attributable to the presence of thallium (see Supporting

Information for refinement details). The molecular structure

of 14, depicted in Figure 7, shows a four-coordinate and

pseudotetrahedral Ni(I) center very similar to that for 12.

Measurement of the magnetic moment of analytically pure

14 by the method of Evans in benzene solution provides µ_eff

) 1.82 µ_B, consistent with one unpaired electron for the d⁹

electronic configuration. A [PhBP^iPr₃]-ligated Ni(I) isocyanide

complex has also been prepared by a similar method.

1

both H NMR and ³¹P{¹H} NMR spectroscopy, indicative

that the phosphine ligands of 11 are in rapid exchange.

Definitive assignment of the structure of 11 is provided by

its solid-state molecular structure (Figure 6). As can be seen,

the amide ligand adopts a conformation such that its available

π-orbital lies in the P₂Ni plane. This conformation is similar

t

to a related (dtbpe)Ni-NR₂species (dtbpe ) Bu₂PCH₂-

CH₂P^tBu₂) prepared by the Hillhouse group.⁸When compar-

ing 11 to other Ni-amide complexes, it is interesting to note

that most of their Ni-N distances range from 1.82 to 1.93

Å,⁴²approximately 0.1 Å longer than that observed for 11.

The Ni-N distance of 11 (1.748(2) Å) is quite similar,

however, to that reported for [(dtbpe)Ni-NH{2,6-

(CHMe₂)₂C₆H₃}][PF₆] (1.768(14) Å).⁸The short Ni-N bond

length suggests a significant π-interaction, consistent with

the orientation of the amide ligand. The dechelation of one

phosphine ligand in 11 is likely favored due to this

π-interaction. In addition to Li(dbabh), the reaction between

3 and lithium anilides, such as Li(NHPh) and Li{NH(2,6-

(41) Mindiola, D. J.; Cummins, C. C. Angew. Chem., Int. Ed. 1998, 37,

945-947.

(42) See ref 8 and references therein.

Inorganic Chemistry, Vol. 43, No. 15, 2004 4651

MacBeth et al.

Figure 7. Molecular structures of (A) [PhBP₃]Ni(PPh₃) (12), (B) [PhBP₃]Ni(CN^tBu) (13), (C) [PhBP^iPr₃]Ni(PMe₃) (14), (D) [PhBP^iPr₃]Ni(CN^tBu) (15), and

(E) [PhBP₃]NiNO (16), derived from crystallographic studies. Only the L₃NiX subunit of each complex is represented. Complete structural details can be

found in the Supporting Information. Selected interatomic distances (Å) and angles (deg) for 12: Ni-P1, 2.28(2); Ni-P2, 2.28(2); Ni-P3, 2.27 (2); Ni-P4,

2.25(2); Ni-B, 3.44(9); P1-Ni-P4, 120.1(8); P2-Ni-P4, 122.1(8); P3-Ni-P4, 123.0(8); P1-Ni-P2, 95.6(8); P2-Ni-P3, 96.8(8); P1-Ni-P3, 92.2(8).

For 13: Ni-C46, 1.861(2); Ni-P1, 2.229(1); Ni-P2, 2.216(1); Ni-P3, 2.252(1); P1-Ni-P2, 91.86(2); P1-Ni-P3, 95.00(2); P2-Ni-P3, 94.58(2); P1-

Ni-C46, 125.59(6); P2-Ni-C46, 107.38(6); P3-Ni-C46, 131.77(6). For 14: Ni-P1, 2.2533(5); Ni-P2, 2.2764(5); Ni-P3, 2.2873(5); Ni-P4, 2.2631(5);

Ni-B, 3.436(2); P1-Ni-P4, 118.67(2); P2-Ni-P4, 121.90(2); P3-Ni-P4, 123.43(2); P1-Ni-P2, 92.76(2); P2-Ni-P3, 98.24(2); P3-Ni-P1, 94.74(2).

For 15: Ni-C28, 1.864(2); Ni-P1, 2.2403(5); Ni-P2, 2.2749(6); Ni-P3, 2.2562(6); Ni-B, 3.431(2); P1-Ni-P2, 96.83(2); P1-Ni-P3, 93.50(2); P2-

Ni-P3, 96.42(2); P1-Ni-C28, 104.56(6); P2-Ni-C28, 124.37(7); P3-Ni-C28, 131.79(7). For 16: Ni-N, 1.624(3); N-O, 1.183(3); Ni-P1, 2.232(1);

Ni-P2, 2.215(1); Ni-P3, 2.234(1); O-N-Ni, 176.0(3); P1-Ni-P2, 92.54(3); P1-Ni-P3, 95.42(3); P2-Ni-P3, 91.74(3); P1-Ni-N, 124.68(9); P2-

Ni-N, 119.84(9); P3-Ni-N, 124.01(9).

Addition of excess (ca. 5 equiv) ^tBuNC to 3 in THF solution

results in the initial formation of a red, likely square planar

Ni(II) complex, [κ²-PhBP^iPr₃]Ni(Cl)(CN^tBu) (19). Assignment

of this species is based upon its ³¹P{¹H} NMR spectrum (δ

62.7 (br d), 47.7 (br d), 3.2 (br s)). Removal of the reaction

volatiles followed by redissolution in THF and subsequent

reduction using sodium/mercury amalgam provides the

yellow Ni(I) complex [PhBP^iPr₃]Ni(CN^tBu) (15) in good

yield. Attempts to reduce 3 in the presence of excess CN^t-

Bu result in the formation of an increased number of side

Figure 8. Cyclic voltammograms of (a) 15 and (b) 14 recorded at a scan

rate of 50 mV/s. Potentials are referenced to Fc/Fc⁺.

products, presumably due to the competitive reduction of

isocyanide. Complex 15 is more readily prepared in high

yield by the reaction of 14 with excess (ca. 5 equiv) CN^tBu,

which substitutes PMe₃. The solution magnetic moment of

15 as determined by the Evans method is 1.68 µ_B. Examina-

tion of the IR spectrum of 15 provides a ν(CN) stretching

frequency of 2056 cm^-1(KBr, THF). The increased electron-

releasing character of [PhBP^iPr₃] versus [PhBP₃] is quite

striking from the ν(CN) vibrations recorded for 15 and 13,

the former being shifted to lower energy by 38 cm^-1. The

relatively similar solid-state structures of 15 and 13 are

evident in Figure 7. Hence, this electronic comparison is a

good qualitative benchmark for the [PhBP^iPr₃] and [PhBP₃]

anions. To the best of our knowledge, complexes 13 and 15

are the only structurally characterized, mononuclear Ni(I)

isocyanide complexes.

cyanide ligand. Both complexes show reduction processes,

presumably to Ni(0), at quite low potentials.

On the basis of these electrochemical observations, we

studied the independent chemical reduction of [PhBP^iPr₃]Ni-

(PMe₃) (14). As suggested from the formation of 14 by the

reaction between [PhBP^iPr₃]Tl and Ni(PMe₃)₄, the putative

Ni(0) anion {[PhBP^iPr₃]Ni(PMe₃)}^-(20) is generated at very

low potential. Anionic {[PhBP^iPr₃]Ni(PMe₃)}^-appears to be

accessible by reduction of 14 with strong alkali metal

reductants, such as Na/Hg or KC₈, in THF solution.

1

Examination of the H NMR spectra of such reduction

reactions shows complete consumption of paramagnetic 14

and the presence of broadened diamagnetic resonances

consistent with a fluxional Ni(0) anion. In THF solution,

these complexes have limited stability and ultimately reoxi-

dize to Ni(I) 14.

The reduction chemistry of neutral [PhBP^iPr₃]Ni(CN^tBu)

15 was also studied. Chemical reduction of 15 using strong

reductants (e.g., KC₈, Na/Hg) results in its complete con-

sumption and the formation of a diamagnetic species (¹H

NMR). The solution infrared spectrum of this product shows

a dramatically shifted ν(CN) vibration (1982 cm^-1, compared

with 2056 cm^-1for 15), indicating the presence of the Ni-

(0) anion {[PhBP^iPr₃]Ni(CN^tBu)}^-(21). This species is

kinetically unstable in benzene or THF solution and gradually

decays to regenerate the Ni(I) species 15 as the predominant

IIe. Access to the Ni(0) State. With Ni(I) complexes in

hand, we studied their proclivity to undergo redox events

by electrochemical methods. The cyclic voltammetry of the

Ni(I) complexes 14 and 15 was studied in THF solution.

The cyclic voltammetry of 14 shows a reversible reduction

to Ni(0) at -1945 mV (Figure 8b). An irreversible oxidation

event occurs at -503 mV. 15 gives rise to a low reduction

potential for the Ni^I/0couple (-1848 mV) (Figure 8a), and

an irreversible oxidation event (-396 mV). The shift to more

positive potentials for both the oxidation and reduction

processes for 15 as compared to 14 reflects the exchange of

an electron-donating phosphine ligand for a π-acidic iso-

4652 Inorganic Chemistry, Vol. 43, No. 15, 2004

The Coordination Chemistry of “[BP₃]NiX” Platforms

product. Whether some type of disproportionation reaction

or reaction with solvent occurs is presently unclear. The

degradation process to regenerate 15 is quite clean, suggest-

ing the involvement of some external electron acceptor such

as THF solvent.

is achieved by reaction of [PhBP^iPr₃]Tl with (Ph₃P)₂Ni(CO)₂

in the presence of ASNBr (ASN ) 5-azoniaspiro[4.4]nonane)

in THF solution. The substitution reaction is much slower

in the latter case, but proceeds in reasonable yield after a

period of 3 days at room temperature to form [[κ²-PhBP^iPr₃]-

Ni(CO)₂][ASN] (18). Attempts to accelerate the reaction via

mild heating (50 °C) result in extensive decomposition of

the starting material to unidentified products. Complex 18

displays a characteristic infrared spectrum (2004 (sym) and

1878 cm^-1(antisym); KBr, THF) and ³¹P{¹H} NMR

spectrum (δ 51.1 (s, 2P), 4.8 (s, 1P)). Photolysis of 17 under

a sparge of N₂appears to affect replacement of one of the

CO ligands by the remaining phosphine donor to produce

the κ³species {[PhBP₃]Ni(CO)}{ⁿBu₄N} (22). A single sharp

resonance is observed in the ³¹P{¹H} NMR spectrum for 22

at 25.3 ppm, and a single ν(CO) vibration is observed at

1869 cm^-1(KBr, THF). This value is comparable but

appreciably lower than the ν(CO) value of 1890 cm^-1(Nujol)

reported for the neutral Ni(0) complex (triphos)Ni(CO).⁴⁸

We were surprised to find that attempts to oxidize 17 and

18 by [Fc][PF₆] to give well-defined Ni(I) monocarbonyl

products instead led to multiple products as determined by

IR and NMR spectroscopy. Given the stability of Riordan’s

[PhTt^tBu]Ni^I(CO) and related Ni(I) carbonyls,³⁹we suspect

overoxidation to be problematic. Gentler oxidants may yet

prove synthetically effective.

Synthetic access to other zerovalent nickel species sup-

ported by these phosphine anions is possible.⁴³For example,

treatment of 1 with NO gas generates the diamagnetic nitrosyl

product [PhBP₃]Ni(NO) (16) as a crystalline red product (eq

2). This complex is formally an 18-electron species and is

isolobal to its well-known relatives CpNi(NO)⁴⁴and Cp*Ni-

(NO).⁴⁵The solid-state structure of 16 (Figure 7) shows a

pseudotetrahedral nickel complex with a nearly linear Ni-

N-O bond angle (176.0(3)°) and a very short Ni-N bond

distance of 1.624(3) Å. Complex 16 also exhibits a rather

low ν(NO) vibration at 1737 cm^-1(KBr, C₆H₆), considerably

lower than observed for the tris(thioether)borate system

[PhTt^tBu]Ni(NO) (1785 cm^-1, CH₂Cl₂)³⁸and the Cp* system

Cp*Ni(NO) (1787 cm^-1, Nujol).⁴⁶Another structurally

related example is Sacconi’s four-coordinate nickel nitrosyl

[(κ³(P)-np₃)Ni(NO)][BPh₄] (np₃) N(CH₂CH₂PPh₂)₃).⁴⁷The

average of the P-Ni bond distances in [(κ³(P)-np₃)Ni(NO)]-

[BPh₄] is 2.293(6) Å, and its Ni-NO bond distance is 1.59(2)

Å. Thus, all of the Ni-ligand linkages contract for the cation

[(np₃)Ni(NO)]⁺by comparison to 16. Cationic [(κ³(P)-np₃)-

Ni(NO)][BPh₄] displays a ν(NO) at 1755 cm^-1(Nujol),

intermediate between those for 16 and [PhTt^tBu]Ni(NO) or

Cp*Ni(NO). The remarkably low ν(NO) frequency recorded

for 16 indicates a very large degree of π-back-bonding and

is perhaps suggestive that the NidNdO resonance contribu-

tor is meaningful. The N-O bond distance of 1.183(3) Å is

nonetheless similar to those recorded in the other structures.

IIf. Synthetic Attempts To Generate NidE/NitE Link-

ages. One of the primary goals of this study was to assess

the propensity of the low valent nickel precursors described

herein to mediate oxidative group transfer processes that

install NidE/NitE multiple bond linkages at a pseudotet-

rahedral nickel center. We have canvassed numerous reac-

tions that might have led to such species, but to date have

not isolated or spectroscopically verified well-defined ex-

amples of L₃NidE/L₃NitE. It is nonetheless informative

to briefly summarize these attempts.

NO

8

[PhBP ]Ni(NO)

1 or 12

(2)

3

16

Access to Ni(0) carbonyl complexes was achieved by

reaction of either of the tris(phosphino)borate ligands with

(Ph₃P)₂Ni(CO)₂. Thus, the anionic complex [[κ²-PhBP₃]Ni-

(CO)₂][ⁿBu₄N] (17) is synthesized cleanly by the reaction

between [PhBP₃]Tl and (Ph₃P)₂Ni(CO)₂in the presence of

[ⁿBu₄N][Br] in THF over a period of 12 h. Its ³¹P{¹H} NMR

spectrum shows two distinct resonances at 29.2 and -9.46

ppm (2:1 ratio) that correspond to its coordinated and

dissociated phosphine donors, respectively. The solution IR

spectrum of this complex (KBr, THF) shows symmetric and

antisymmetric ν(CO) vibrations at 1994 and 1913 cm^-1.

Synthesis of the analogous [PhBP^iPr₃]-containing complex

One of the more interesting target molecules whose

stability we sought to evaluate concerns the tetravalent L₃-

Ni^IVtN. This hypothetical d⁶unit would be both isolobal

and isoelectronic to remarkably stable d⁶L₃Co^IIItNR species

that our lab has prepared previously.^14,16It would moreover

be structurally related to a recently reported d⁴L₃Fe^IVtN

system.¹⁸Various routes were canvassed to generate a

putative Ni^IVtN species, and two are most worthy of

comment. Photolysis of the divalent azide 4 precursor might

effect N₂expulsion and thus nitride transfer to nickel to

produce “[PhBP₃]Ni^IVtN”. We find, however, that the azide

ligand remains intact even under extended photolysis (Hg

lamp) in THF at room temperature. Extended heating of 4

results in a mixture of diamagnetic and paramagnetic

products, but there was no spectroscopic evidence to suggest

that any of these products correspond to a nitride functional

group (bridging or terminal). Another plausible route to the

terminal nitride concerns a two-electron oxidative N-atom

transfer from the dbabh amide to Ni(II). Precedence for this

type of transformation has been provided by Mindiola and

(43) For relevant reviews on the synthesis of transition metal nitrosyl

complexes see: (a) Mingos, M. D.; Sherman, D. J. AdV. Inorg. Chem.

1989, 34, 293-377. (b) Richter-Addo, G. B.; Legzdins, P. Metal

Nitrosyls; Oxford University Press: New York, 1992; pp 34-78.

(44) Crichton, O.; Rest, A. J. J. Chem. Soc., Dalton Trans. 1977, 986-

993.

(45) Schneider, J. J.; Goddard, R.; Krueger, C. Organometallics 1991, 10,

665-670.

(46) (a) Fomitchev, D. V.; Furlani, T. R.; Coppens, P. Inorg. Chem. 1998,

37, 1519-1526. (b) Green, J. C.; Underwood, C. J. Organomet. Chem.

1997, 528, 91-94.

(47) Di Vaira, M.; Ghilardi, C. A.; Sacconi, L. Inorg. Chem. 1976, 15,

1555-1561.

(48) Bianchini, C.; Mealli, C.; Meli, A.; Scapacci, G. Organometallics 1983,

2, 141-143.

Inorganic Chemistry, Vol. 43, No. 15, 2004 4653

MacBeth et al.

Cummins in the synthesis of a Cr^VItN nitride,⁴¹and more

recently by our lab in the generation of [PhBP^iPr₃]Fe^IVtN.¹⁸

As described above, the reaction between Li(dbabh) and 3

installs the required Ni^II-N amide linkage, but the thermo-

dynamically stable product is the trigonal planar three-

coordinate Ni^IIspecies 11 rather than the four-coordinate

complex. We had hoped that the [PhBP^iPr₃] ligand might be

sufficiently electron-releasing to induce the loss of anthracene

with concomitant nitride transfer to generate the Ni^IVtN

subunit. Dechelation of a phosphine arm occurs instead to

give a relatively stable amide. Complex 11 is quite stable at

room temperature in solution, and while its thermolysis at

slightly elevated temperature does produce a new diamag-

of unidentified diamagnetic species. The absence of new

paramagnetic species in the product profile suggests that

terminal Ni^IIIdCR₂species are not present.

Finally, we note that the reactivity of the Ni(0) species

{[PhBP^iPr₃]NiL}^-20 and 21 to group transfer was also

canvassed. These species were generated in situ by reduction

of their Ni(I) precursors using sodium/mercury amalgam.

Quantitative consumption of the Ni(I) species is confirmed

by ¹H NMR spectroscopy, and subsequent addition of 2 equiv

of an organic azide or diazoalkane leads in each case to rapid

re-formation (<1 h) of the Ni(I) precursor (either 14 or 15)

in high yield. We suspect that the highly reducing Ni(0)^-

species are acting as electron-transfer reagents and affecting

radical reduction of the organic substrate. A more systematic

analysis of the organic products of these reactions was not

undertaken.

1

netic species, the H NMR spectrum of the species defini-

tively shows the presence of an intact dbabh ligand, evident

from the signature bridgehead proton resonance (ca. 5.4

ppm). A definitive structural assignment for this thermolysis

product has not yet been made.

IIg. Theoretical Considerations. We undertook the

theoretical analysis of several hypothetical nickel complexes

featuring a multiply bonded linkage to explore the feasibility

of such species from an electronic structure perspective. To

contextualize these results, it is instructive to first consider

the L₂NidE fragments of Hillhouse and co-workers which

are already known to give rise to isolable NidE complexes.

Bonding considerations for these complexes have been

addressed previously.⁴⁹Figure 9A shows lobal representa-

tions of the frontier orbitals of an L₂MdE fragment as

derived from the classic text of Albright, Burdett, and

Whangbo.⁵⁰The LUMO orbital is of b₂symmetry (under

C_2V) and is π* in character. The much lower lying, filled

MdE π-bonding orbital is not shown. As the transition is

made from the L₂MdE fragment to the pseudotetrahedral

L₃M-E structure under idealized 3-fold symmetry, the M-E

linkage is more appropriately described as a bona fide triple

bond (MtE) for a d⁶configuration (Figure 9B).^14,49,51For

higher d-count configurations (d⁷or d⁸) of similar geometry

the formal bond order is lowered because the e-set is both

σ* (with respect to the phosphines) and π* (with respect to

the multiply bonded ligand) in character. The extent to which

such configurations might be expected to be stable invariably

depends on how energetically destabilized the upper π*

orbitals can lie while still housing an unpaired electron. The

previously reported complexes [PhBP₃]CoI^14,52and [PhBP₃]-

Co(OSiPh₃)³¹provide well-defined examples of pseudotet-

rahedral d⁷species with ²E ground state configurations that

serve as electronic models for the hypothetical S ) ¹/₂[BP₃]-

Ni^III(NR) systems under present consideration. An obvious

issue concerns the extent to which the imide ligand,

conventionally thought to be quite strongly π-donating, will

By analogy to the previously reported reactions of [BP₃]-

M^IL precursors (where [BP₃] ) [PhBP₃] and [PhBP^iPr₃], M

) Fe and Co, L ) PR₃) with aryl and alkyl azide (RN₃)

substrates to generate M^IIItNR imides,^14,15it was of obvious

interest to canvass similar reactions with the low valent nickel

precursors described herein. To this end, we surveyed a

number of reactions that might have facilitated two-electron

group transfer reactivity to install a NidNR linkage. The

reaction of 12, 13, 14, and 15 with 2 equiv of an organic

azide (typical organic azides used: p-tolyl azide, tert-butyl

azide, 1-adamantyl azide, tosyl azide, and trimethylsilyl

azide) in each case produces a mixture of paramagnetic and

diamagnetic species that is relatively ill-defined. The phos-

phine-capped Ni(I) complexes react relatively quickly at

room temperature (hours). By contrast, the Ni(I) isocyanide

complexes reacted much more slowly. In these latter cases,

starting material is still present even after several days at

room temperature. Attempts to accelerate the rate of these

reactions by heating reaction mixtures of 13 and 15 in the

presence of azide substrates did lead to more rapid consump-

tion of the nickel precursors, but also to an even greater range

of spectroscopically detectable species. A major organic

product of the reaction between 12 and 2 equiv of p-tolyl

1

azide is p-tolyl-NdPPh₃(identified by H NMR and GC/

MS), but it is unclear whether this product is formed by a

nickel-mediated reaction that proceeds through an insipient

“Ni^IIIdN-p-tolyl” fragment or by the direct reaction between

dissociated PPh₃and p-tolyl azide. The reaction between 13

and p-tolyl azide generates only a small amount of the

carbodiimide p-tolyl-NdCdN^tBu (¹H NMR, GC/MS).

We also surveyed the reaction between the Ni^I-L precur-

sors and diazoalkanes as potential two-electron carbene

transfer reagents. For example, we studied the reactivity of

14 and 15 in the presence of 2 equiv of Ph₂CN₂, Mes₂CN₂,

ethyl diazoacetate, and trimethylsilyldiazomethane in benzene

solution. Similar to the observations noted above, 14 is

consumed more rapidly (hours) than 15 (days) at ambient

temperature for each substrate except Mes₂CN₂, which does

not react over a period of several days at room temperature.

The resulting product mixtures invariably contain a variety

(49) (a) Albright, T. A.; Hoffmann, R.; Tse, Y.; D’Ottavio, T. J. Am. Chem.

Soc. 1979, 101, 3812-3821. (b) Albright, T. A.; Hoffmann, R.;

Thibeault, J. C.; Thorn, D. L. J. Am. Chem. Soc. 1979, 101, 3801-

3812. (c) Glueck, D. S.; Wu, J.; Hollander, F. J.; Bergman, R. G. J.

Am. Chem. Soc. 1991, 113, 2041-2054. (d) Cundari, T. R. J. Am.

Chem. Soc. 1992, 114, 7879-7888.

(50) Adapted from: Albright, T. A.; Burdett, J. K.; Whangbo, M.-H. Orbital

Interactions in Chemistry; Wiley & Sons: New York, 1985; pp 365,

383.

(51) Glueck, D. S.; Green, J. C.; Michelman, R. I.; Wright, I. N.

Organometallics 1992, 11, 4221-4225.

4654 Inorganic Chemistry, Vol. 43, No. 15, 2004

The Coordination Chemistry of “[BP₃]NiX” Platforms

Figure 9. Qualitative molecular orbital diagrams for trigonal planar and pseudotetrahedral complexes containing NidE linkages. Idealized point groups

and coordinate axes are indicated.

Table 1. Experimental and Calculated Bond Lengths and Angles for 14

and 16

14

exptl

calcd

16

exptl

calcd

Bond Lengths (Å)

Ni-P4

Ni-P1

Ni-P2

Ni-P3

2.263

2.276

2.287

2.253

2.358

2.396

2.379

2.384

Ni-N

1.624

2.232

2.215

2.234

1.665

2.309

2.316

2.315

Ni-P1

Ni-P2

Ni-P3

Angles (deg)

P4-Ni-P1

P4-Ni-P2

P4-Ni-P3

P1-Ni-P2

P1-Ni-P3

P2-Ni-P3

121.90

123.43

118.67

98.24

92.76

94.74

122.45

124.66

117.44

97.50

92.17

95.12

N-Ni-P1

N-Ni-P2

N-Ni-P3

P1-Ni-P2

P1-Ni-P3

P2-Ni-P3

Ni-N-O

124.68

119.84

124.01

92.54

95.42

91.74

176.0

123.43

125.67

122.58

91.54

92.93

91.29

177.9

Figure 10. DFT optimized (Jaguar 5.0: B3LYP/LACVP**) molecular

structures for (A) [PhBP^iPr₃]Ni(PMe₃) (optimized as a doublet ground state)

and (B) [PhBP₃]Ni(NO) (optimized as a singlet ground state). Hydrogen

atoms have been omitted for clarity.

destabilize such a system by raising the energy of the high-

lying unpaired electrons for d⁷or d⁸configurations.

imaginary frequencies through vibrational frequency calcula-

tions. No imaginary frequencies were located.

Figure 9B,C provides qualitative MO splitting diagrams

that we can use to describe the electronic structure of putative

d⁶L₃Ni^IVtE and d⁷L₃Ni^IIIdE species. To examine the

electronic structure of these structure types more thoroughly,

we have calculated hypothetical structures (DFT) for a series

of [PhBP₃] and [PhBP^iPr₃] nickel complexes. To establish a

reasonable degree of confidence in the theoretical methods

used, we first performed geometry optimizations for the

synthetically isolable and structurally characterized com-

plexes [PhBP₃]Ni(NO) (16) and [PhBP^iPr₃]Ni(PMe₃) (14).

Using the Jaguar computational package (B3LYP/LACVP**),

geometry optimizations were performed starting from the

crystallographically determined coordinates of complexes 16

and 14 as the initial starting point in each case. As shown in

Figure 10 and Table 1, the geometry optimized structures

for 16 and 14 compare favorably with the experimentally

determined solid-state structures. The most significant struc-

tural distinction worth noting is that the Ni-P bond distances

are on average ∼0.1 Å longer in the DFT determined

structures by comparison to the observed distances. As an

additional check, the geometry of the optimized structure of

[PhBP₃]Ni(NO) was evaluated for the correct number of

We next examined the theoretical structures of several

hypothetical Ni^IIIimides (Jaguar 5.0: B3LYP/LACVP**).

As a starting point geometry for the theoretical optimization

of S ) ¹/₂[PhBP₃]Ni(N^tBu), [PhBP^iPr₃]Ni(N^tBu), and [PhBP^iPr₃]-

Ni(NMe), we incorporated the x,y,z coordinates for the L₃-

Ni-N framework from crystallographically determined

coordinates for S ) 0 [PhBP^iPr₃]CotNR and [PhBP₃]Cot

NR structures.^14,16The DFT-minimized structure for [PhBP₃]-

Ni(N^tBu) is shown in Figure 11A. The complex features a

rather short Ni-N bond distance (1.690 Å, Table 2) that is

nonetheless appreciably longer (∼0.04 Å) than the Co-N

and Fe-N bond distances observed for [PhBP₃]CotNR and

[PhBP₃]FetNR imide species, respectively.^14-16This dif-

ference may be a manifestation of the attenuated Ni-N

π-bond order in [PhBP₃]Ni(N^tBu). Also of note from the

structure is the significant variation in the three Ni-P bond

distances. One Ni-P distance is significantly longer than

the other two (2.429 Å vs 2.277 and 2.343 Å). The Ni-

N-C imide angle is remarkably linear (179.28°). A similar

overall geometry is obtained for the optimized structure of

[PhBP^iPr₃]Ni(N^tBu) (Figure 11B). In this latter structure,

Inorganic Chemistry, Vol. 43, No. 15, 2004 4655

MacBeth et al.

Figure 11. DFT optimized (Jaguar 5.0: B3LYP/LACVP**) molecular

structures for (A) [PhBP₃]Ni(N^tBu), (B) [PhBP^iPr₃]Ni(N^tBu), and (C)

[PhBP^iPr₃]Ni(NMe). Each geometry assumes a doublet ground state.

Hydrogen atoms have been omitted for clarity.

Figure 12. Starting point (A) and DFT optimized (Jaguar 5.0: B3LYP/

LACVP**) geometry (B) for S ) 0 [PhBP^iPr₃]Ni(N). Hydrogen atoms have

been omitted for clarity.

¹/₂d⁷nickel imide species suggest that L₃NidNR may indeed

be synthetically viable targets if (i) the L₃ligand scaffold

employed is sufficiently flexible to accommodate the an-

ticipated distortion and (ii) bimolecular degradation pathways

are not kinetically problematic.

Table 2. Bond Lengths and Angles of DFT Optimized Structures for

[PhBP₃]Ni(N^tBu), [PhBP^iPr₃]Ni(N^tBu), and ([PhBP^iPr₃]Ni(NMe)

[PhBP₃]Ni(N^tBu) [PhBP^iPr₃]Ni(N^tBu) [PhBP^iPr₃]Ni(NMe)

Bond Lengths (Å)

Ni-N

1.690

2.429

2.343

2.277

1.687

2.519

2.301

2.303

1.692

2.378

2.368

2.320

Ni-P1

Ni-P2

Ni-P3

The other structure type of interest to us concerns the

hypothetical nickel nitride species [PhBP^iPr₃]Ni^IVtN. As

mentioned above, this d⁶species is formally isolobal and

isoelectronic with the surprisingly stable d⁶cobalt imides

that we have described previously.^14,16However, there is an

important distinction to be drawn between the relative

d-orbital splitting energies between L₃MtNR and L₃MtN

structure types due to the rehybridization at nitrogen that

occurs. As we have recently suggested, the d orbital of a₁

symmetry in the d⁴complex [PhBP^iPr₃]Fe^IVtN is highly

Angles (deg)

Ni-N-C

179.28

89.85

88.81

176.90

90.70

92.25

156.99

94.93

91.90

P1-Ni-P2

P2-Ni-P3

P1-Ni-P3

N-Ni-P1

N-Ni-P2

N-Ni-P3

89.45

90.78

91.26

122.33

126.35

128.38

119.83

124.54

128.40

111.46

114.04

142.75

however, the elongated Ni-P bond distance is extremely

elongated (2.519 Å). The elongation observed for one of the

Ni-P bonds in [PhBP^iPr₃]Ni(N^tBu) and [PhBP₃]Ni(N^tBu) is

fully consistent with the presence of a single electron in an

orbital that is σ* with respect to a N-P bond vector, as

illustrated in Figure 9C. The distorted geometries we have

previously reported for the structurally characterized low spin

d⁷[PhBP₃]CoI and [PhBP₃]CoOSiPh₃species provide ex-

perimental verification that this type of elongation is to be

reasonably anticipated for such configurations.^25,31That the

DFT-minimized structure of [PhBP^iPr₃]Ni(N^tBu) reveals such

a pronounced distortion relative to [PhBP₃]Ni(N^tBu) most

likely reflects the respective σ donor character of the two

borate auxiliaries. To probe whether steric factors might also

be significantly contributing to the structure observed, the

methyl imido complex [PhBP^iPr₃]Ni^III(NMe) was examined.

As can be seen in Figure 11C, replacement of the tert-butyl

group in [PhBP^iPr₃]Ni(N^tBu) for a methyl group in [PhBP^iPr₃]-

Ni(NMe) results in a dramatic distortion of the imido ligand.

The Ni-N-C angle is now quite bent (156.99°). Moreover,

in the [PhBPⁱPr₃]Ni(NMe) structure the three Ni-P bond

distances show comparatively little variation. Thus, stabiliza-

tion of the d⁷imide configuration is observed to occur by

one of two processes. For a sterically encumbering imide,

elongation of one Ni-P bond vector appears to be favored.

For an imide that is less bulky, a severe bend in the imide

functionality appears to be more energetically favorable such

that a new geometry, better described as trigonal pyramidal

with the imide ligand occupying an equatorial position, is

obtained. Collectively, the DFT data obtained for these S )

2

destabilized due to a strong σ* interaction between d_zand

the nitride σ donor.¹⁸The addition of two electrons to the

frontier orbital diagram of [PhBP^iPr₃]Fe^IVtN, which is pro-

vided by replacing the iron center by nickel, provides the

electronic configuration (e)⁴(a₁)²(e)⁰. Two electrons are there-

fore expected to lie at high energy for [PhBP^iPr₃]Ni^IVtN,

perhaps helping to explain why this species is not generated

from [κ²-PhBP^iPr₃]Ni(dbabh) (11) by loss of anthracene upon

heating, whereas a similar synthetic strategy is quite effective

for the case of iron. Thus, the electronic situation is quite

distinct between a hypothetical [PhBP^iPr₃]Ni^IVtN species and

the known d⁶BP₃CotNR systems. In the latter species, the

2

a₁orbital of d_zparentage is nearly degenerate with the

nonbonding e-set.¹⁴

The consequences of electronic destabilization in [PhBP^iPr₃]-

NitN are manifest in its DFT-minimized structure. The

starting and final geometries of this calculation are shown

in Figure 12A,B. As can be seen, the nitride group inserts

in a Ni-P bond in the optimized structure to afford a

complex that is better viewed as a diamagnetic Ni(II)

complex with one phosphinimato and two phosphine link-

ages. Whether this product is kinetically (or even thermo-

dynamically) reasonable is unclear. In solution, bimolecular

pathways to other structures, such as Ni^IV₂N₂and Ni^I-N₂-

Ni^I, might dominate. Regardless, the overall picture that

begins to emerge is the following: for pseudotetrahedral

structure types L₃NitE, imide (NR^2-), and perhaps related

carbyne (CR^3-) functionalities are more likely to electroni-

cally stabilize tetravalent nickel than terminal oxo or nitrido

functionalities.

4656 Inorganic Chemistry, Vol. 43, No. 15, 2004

The Coordination Chemistry of “[BP₃]NiX” Platforms

TlOSiPh₃,⁵⁷KC₈,⁵⁸Li-NH-2,6-ⁱPr-Ph,⁸and lithium(dbabh)⁴¹were

prepared according to literature methods. Deuterated solvents were

purchased from Cambridge Isotopes Laboratories, Inc., and were

degassed and stored over activated 3-Å molecular sieves prior to

use. All other reagents and solvents were purchased from com-

mercial vendors and used without further purification unless

otherwise noted. CAUTION: Thallium reagents are extremely toxic

and should be handled and disposed of with care.

Conclusions

We have described synthetic entry to the chemistry of

“[PhBP₃]Ni” and “[PhBP^iPr₃]Ni” systems. Most all of the

complexes that have been prepared, for which the formal

oxidation states Ni(0), Ni(I), and Ni(II) have been assigned,

give rise to pseudotetrahedral geometries. For the divalent

nickel complexes [PhBP₃]Ni^IIX in particular, small perturba-

tions of the pseudotetrahedral geometry are observed that

that depend on the nature of the X-type ligand employed.

The unusual Ni(II) thiolate complex [PhBP₃]Ni(S-p-^tBu-Ph)

(7) is perhaps most distinct in this regard as it adopts a

geometry that lies somewhere between that of a tetrahedron

and a cis-divacant octahedron. The [PhBP^iPr₃]-containing Ni-

(II) complex [κ²-PhBP^iPr₃]Ni(dbabh) (11) is in principle a

precursor to a nickel(IV) nitride species but fails to evolve

anthracene. Why this is the case is in part explained by

theoretical considerations that suggest that a d⁶L₃NitN

would feature a pair of electrons lying in a highly destabilized

σ* orbital. A general characteristic of the Ni(II) systems

described is that access to pseudotetrahedral L₃Ni^IIX com-

plexes where X represents a strong-field ligand, such as an

alkyl or an amide, is problematic. This characteristic is also

true of Riordan’s tris(thioether)borate system [PhTt^tBu]Ni^IIX.³⁸

When an amide can be installed, as for 11, the structure type

observed is three-coordinate trigonal planar. Electrochemical

interrogation of the Ni(II) and Ni(I) complexes has revealed

that reversible 1-electron Ni^II/Iand Ni^I/0redox couples are

accessible at fairly low potentials. Perhaps most striking is

that the Ni^III/IIredox process is irreversible in all cases we

have examined, even for ligands that are potentially good

π-donors such as alkoxides and thiolates. This situation

stands in contrast to related BP₃Fe and BP₃Co systems we

have described, where the trivalent state is quite readily

accessible. Whereas we had hoped that access to trivalent

nickel might be possible by turning to dianionic imide and

carbene functionalities in the fourth site (L₃Ni^IIIdNR or L₃-

Ni^IIIdCR₂), the successful synthesis of such species has thus

far eluded us. Simple MO considerations and DFT calcula-

tions nonetheless suggest that these types of complexes may

be electronically accessible. We suspect that our inability to

isolate well-defined examples of these types of species is

due to synthetic nuances that we have yet to fully appreciate.

Physical Methods. Elemental analyses were performed by Desert

Analytics, Tucson, AZ. A Varian Mercury-300 spectrometer was

1

used to record H, ³¹P{¹H}, and ¹³C{¹H} spectra at room temper-

ature unless otherwise noted. ¹H and ¹³C{¹H} chemical shifts were

referenced to residual solvent. ³¹P{¹H} NMR are reported relative

to an external standard of 85% H₃PO₄(0 ppm). Abbreviations for

reported signal multiplicities are as follows: s, singlet; d, doublet;

t, triplet; q, quartet; m, multiplet; br, broad. IR spectra were recorded

on a Bio-Rad Excalibur FTS 3000 spectrometer controlled by Win-

IR Pro software using a KBr solution cell. Solution magnetic

moments were measured at 298 K in C₆D₆following the Evans

method.⁵⁹MS data were obtained by injection of a hydrocarbon

solution onto a Hewlett-Packard 1100MSD mass spectrometer

(ES⁺) or an Agilent 5973 mass selective detector (EI). UV-vis

measurements were recorded on a Varian Cary 50 Bio Spectro-

photometer controlled by Cary WinUV software. All measurements

were recorded using a quartz cell fitted with a Teflon cap. X-ray

diffraction studies (Table 3) were carried out in the Beckman

Institute Crystallographic Facility on a Bruker Smart 1000 CCD

diffractometer. Cyclic voltammetry measurements were recorded

using a BAS CV 100W (Bioanalytical Systems Inc., West Lafayette,

IN) using a glassy carbon working electrode, a platinum wire

auxiliary electrode, and an Ag/AgNO₃nonaqueous reference

electrode filled with THF and Bu₄NPF₆. All electrochemical

measurements are referenced to Fc/Fc⁺as an internal standard and

can be corrected to SCE by adding 0.56 V to reported potential.⁶⁰

Computational Methods. All calculations were performed using

the hybrid DFT functional B3LYP as implemented in the Jaguar

5.0 program package.⁶¹This DFT functional utilizes the Becke

three-parameter functional⁶²(B3) combined with the correlation

functional of Lee, Yang, and Parr⁶³(LYP). The Ni was described

using the LACVP basis set with the valence double-ú contraction

of the basis functions, LACVP**. All electrons were used for the

other elements using Pople’s⁶⁴6-31G** basis set. Input coordinates

were derived as described in the text from crystallographically

determined structures. Spin states and molecular charges were

explicitly stated, and no molecular symmetry was imposed. Default

values for geometry and SCF iteration cutoffs were used, and all

(55) Blicke, F. F.; Hotelling, E. B. J. Am. Chem. Soc. 1954, 76, 5099-

5103.

Experimental Section

(56) Jazdzewski, B. A.; Holland, P. L.; Pink, M.; Young, V. G., Jr.; Spencer,

D. J. E.; Tolman, W. B. Inorg. Chem. 2001, 40, 6097-6107.

(57) Harvey, S.; Lappert, M. F.; Raston, C. L.; Skelton, B. W.; Srivastava,

G.; White, A. H. J. Chem. Soc., Chem. Commun. 1988, 17, 1216-

1217.

All manipulations were carried out using standard Schlenk or

glovebox techniques under a nitrogen atmosphere. Petroleum ether,

benzene, toluene, diethyl ether, THF, dichloromethane, and aceto-

nitrile were deoxygenated and dried by sparging with N₂gas and

passage through an activated alumina column. Hydrocarbon and

ethereal solvents were tested with a standard purple solution of

sodium benzophenone ketyl in tetrahydrofuran to ensure dioxygen

and water removal. The compounds [PhBP₃]Tl,⁵²[PhBP^iPr₃]Tl,^25b

Ph₂PCH₂Li(TMEDA),^{53 i}Pr₂PCH₂Li,⁵⁴ASNBr,⁵⁵Tl-O-p-^tBu-Ph,⁵⁶

(58) Schwindt, M.; Lejon, T.; Hegedus, L. Organometallics 1990, 9, 2814-

2819.

(59) (a) Evans, D. F. J. Chem. Soc. 1959, 2003-2005. (b) Sur, S. K. J.

Magn. Reson. 1989, 82, 169-173.

(60) For information regarding correcting redox potenials vs Fc⁺/Fc in

various solvents see: Connelly, N. G.; Geiger, W. E. Chem. ReV. 1996,

96, 877-910.

(61) Jaguar 5.0, Schrodinger, LLC, Portland, Oregon, 2002.

(62) Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652.

(63) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1988, 37, 785-789.

(64) (a) Hariharan, P. C.; Pople, J. A. Chem. Phys. Lett. 1972, 16, 217-

219. (b) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.

Gordon, M. S.; DeFrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77,

3654-3665.

(52) Shapiro, I. R.; Jenkins, D. M.; Thomas, J. C.; Day, M. W.; Peters, J.

C. Chem. Commun. 2001, 2152-2153.

(53) (a) Peterson, D. J. J. Organomet. Chem. 1967, 8, 199-208. (b) Schore,

N. E.; Benner, L. S.; Labelle, B. E. Inorg. Chem. 1981, 20, 3200-

3208.

(54) Thomas, J. C.; Peters, J. C. Inorg. Chem. 2003, 42, 5055-5073.

Inorganic Chemistry, Vol. 43, No. 15, 2004 4657

MacBeth et al.

Table 3. X-ray Diffraction Experimental Details for 2-5, 7, 8A,B, and 11-16

2

3

4

5

7

chem formula

C₄₅H₄₁BINiP₃‚

0.5C₆H₆

871.14 + 39.05

-177

0.71073

22.502(3)

12.694(2)

29.393(7)

90

90.418(12)

90

8396(3)

P2₁/c

C₂₇H₅₃BClNiP₃

0.84C₄₅H₄₁BN₃NiP₃‚

0.16C₄₅H₄₁BClNiP₃

821.69

C₆₃H₅₆BNiOP₃Si‚

1.5C₆H₆

1136.76

-177

0.71703

C₅₅H₅₄BNiP₃S

fw

575.57

-177

0.71073

9.4015(8)

11.5998(10)

29.392(3)

90

3205.4(5)

P2₁2₁2₁

4

909.47

-177

0.71703

38.222(2)

38.2222(2)

12.5712(9)

90

T (°C)

λ (Å)

a (Å)

b (Å)

c (Å)

R (deg)

â (deg)

γ (deg)

V (Å³)

space group

Z

-177

0.71073

40.37(3)

12.887(15)

16.067(12)

90

13.1627(14)

14.3575(15)

17.2349(18)

101.988(2)

112.185(2)

90.580(2)

2936.1(5)

P1h

111.48(6)

90

7779(13)

C2/c

90

18366.0(19)

I₁/a

16

1.316

6.10

8

2

D

_calcd(g/cm³)

1.440

13.45

0.0494, 0.0824

1.193

8.52

0.0392, 0.0717

1.403

7.29

0.0489, 0.0708

1.286

4.78

0.0556, 0.0823

µ (cm^-1)

R1, wR2^a(I > 2σ(I))

0.0523, 0.0649

8A

8B

11

12

chem formula

C₄₅H₄₁BClNiO₂P₃‚

C₆H₆

C₉₀H₈₂B₂Cl₂Ni₂O₄P₆

‚2C₇H₈‚C₆H₆‚

CH₂Cl_1.5

C₄₁H₆₃BNNiP₃

C₆₃H₅₆BNiP₄‚C_9.95

fw

888.76

-177

0.71703

16.2376(12)

16.4690(13)

17.7364(14)

90

113.379(1)

90

4353.6(6)

P2₁/c

1952.89

-177

0.71703

24.8113(15)

13.9514(8)

30.9581(19)

90

112.5030(10)

90

9900.3

P2₁/n

4

732.35

-177

0.71703

12.0312(10)

26.359(2)

12.9206(11)

90

99.150(2)

90

4045.4(6)

P2₁/n

1006.52 + 119.15

-177

0.71073

19.9842(13)

17.8132(11)

33.699(2)

90

T (°C)

λ (Å)

a (Å)

b (Å)

c (Å)

R (deg)

â (deg)

γ (deg)

V (Å³)

space group

Z

90

11996.4(13)

Pbca

8

1.247

4.73

4

D

_calcd(g/cm³)

1.356

6.58

0.0506, 0.0774

1.310

6.25

0.0697, 0.1129

1.202

6.27

0.0513, 0.0943

µ (cm^-1)

R1, wR2^a(I > 2σ(I))

0.0573, 0.0951

13

14

15

16

chem formula

C₅₀H₅₀BNiP₃

0.95C₃₀H₆₂BNiP₄‚

0.05C₂₇H₅₃BP₃Tl

619.37

C₃₂H₆₂BNNiP₃

C₄₅H₄₁BNNiOP₃

fw

T (°C)

λ (Å)

a (Å)

b (Å)

c (Å)

R (deg)

â (deg)

γ (deg)

V (Å³)

space group

Z

827.34

-177

623.26

-177

774.22

-177

0.71073

39.395(4)

12.9396(13)

16.1218(16)

90

110.668(2)

90

7682.2(13)

C2/c

-177

0.71703

12.3572(10)

13.6104(11)

15.1576(12)

75.775(1)

70.824(1)

66.409(1)

2187.3(3)

P1h

0.71703

9.6258(5)

21.6538(12)

16.8244(9)

90

0.71703

9.6300(7)

12.2632(9)

15.4425(11)

87.053(1)

80.119(1)

84.968(1)

1788.5(2)

P1h

93.871(2)

90

3498.8(3)

P2₁/c

2

4

2

8

D_calcd(g/cm³)

µ (cm^-1)

R1, wR2^a(I > 2σ(I))

1.256

5.88

0.0411, 0.0669

1.176

9.35

0.0534, 0.0925

1.157

6.97

0.0410, 0.0876

1.339

6.67

0.0492, 0.0717

2

^aR1 ) ∑||F_o| - ∑||F_c||/∑|F_o|, wR2 ) {∑|w(F_o- F_c)²|/∑|w(F_o)²}^1/2

.

structures converged under these criteria. The geometry of the

optimized structure of [PhBP₃]Ni(NO) was evaluated for the correct

number of imaginary frequencies through vibrational frequency

calculations using the analytic Hessian. Zero imaginary frequencies

correspond to a local minimum, whereas one imaginary frequency

corresponds to a transition structure. No imaginary frequencies were

found for [PhBP₃]Ni(NO). Further frequency calculations were

precluded due to the impractical time requirements necessary to

complete frequency calculations on molecules with so many non-

hydrogen atoms.

suspension of (Ph₃P)₂NiCl₂(0.230 g, 0.352 mmol) in benzene (10.0

mL). The reaction mixture was stirred at room temperature for 24

h and filtered through a Celite pad. The dark green filtrate was

concentrated under reduced pressure to dryness to yield a dark green

solid. The resulting solid was isolated on a medium porosity frit

and washed three times with 4 mL portions of petroleum ether.

The solid was then redissolved in benzene (10 mL) and filtered

again through a Celite pad. Vapor diffusion of petroleum ether into

the resulting green filtrate yielded analytically pure, green crystalline

product (0.225 g, 82.0%). A second crop yielded an additional 0.192

1

Synthesis of [PhBP₃]NiCl (1). A benzene solution (30 mL) of

[PhBP₃]Tl (0.313 g, 0.352 mmol) was added dropwise to a stirring

g, 12%. H NMR (300 MHz, C₆D₆): δ 26.1 (s), 8.3 (s), 7.6 (s),

7.5 (s), 1.22 (s), 0.89 (s), -6.8 (br s), -9.9 (s). UV-vis (C₆H₆)

4658 Inorganic Chemistry, Vol. 43, No. 15, 2004

The Coordination Chemistry of “[BP₃]NiX” Platforms

_max, nm (ꢀ): 434 (3332). µ_eff(C₆D₆, 298 K): 2.91 µ_B. Anal. Calcd

λ

to dryness under reduced pressure to yield a bright purple solid.

The solid was extracted with benzene (3 mL) and filtered through

a Celite pad. Vapor diffusion of petroleum ether into the benzene

solution afforded the product as purple crystals (0.152 g, 76%). ¹H

NMR (300 MHz, C₆D₆): δ 43.1 (br s), 23.9 (s), 4.3 (s), 3.6 (s),

2.7 (s), 0.3 (s), -4.3 (br s), -8.2 (s). UV-vis (C₆H₆) λ_max, nm (ꢀ):

707 (1116), 524 (2437), 417 (3020). µ_eff(C₆D₆, 298 K): 2.87 µ_B.

Anal. Calcd for C₅₅H₅₄BNiOP₃: C, 73.94; H, 6.09. Found: C,

73.67; H, 5.81.

for C₄₅H₄₁BClNiP₃: C, 69.32; H, 5.30. Found: C, 69.54; H, 5.69.

Synthesis of [PhBP₃]NiI (2). A benzene solution (30 mL) of

[PhBP₃]Tl (0.561 g, 0.631 mmol) was added dropwise to a stirring

suspension of NiI₂(0.394 g, 1.26 mmol) in benzene (20 mL). The

reaction mixture was stirred at room temperature for 24 h and

filtered through a Celite pad. The resulting red-brown filtrate was

concentrated under reduced pressure to 50% of original volume

and filtered again through a Celite pad. Vapor diffusion of petroleum

ether into the resulting red-brown filtrate produced brown, crystal-

line needles of the analytically pure product (0.472 g, 86%).¹H

NMR (300 MHz, C₆D₆): δ 26.6 (s), 8.7 (s), 8.3 (s), 7.8 (s), 1.20

(s), 0.84 (s), -6.9 (br s), -11.07 (s). UV-vis (C₆H₆) λ_max, nm (ꢀ):

705 (556), 446 (5612), 329 (7437). µ_eff(C₆D₆, 298 K): 2.87 µ_B.

Anal. Calcd for C₄₅H₄₁BINiP₃: C, 62.04; H, 4.74. Found: C, 61.81;

H, 4.93.

Synthesis of [PhBP^iPr₃]NiCl (3). In a 50 mL round-bottom flask,

(DME)NiCl₂(283.2 mg, 1.289 mmol) was suspended in THF (15

mL). A THF solution (20 mL) of [PhBP^iPr₃]Tl (882.0 mg, 1.286

mmol) was added dropwise over 10 min with vigorous stirring.

After completion of the addition, the reaction mixture was stirred

for 25 min and then filtered over Celite on a sintered glass frit.

The solids and Celite were washed with benzene (10 mL). The

combined filtrates were concentrated to dryness under reduced

pressure. The resultant green-brown material was dissolved in

benzene (10 mL) and filtered. Lyophilization of the filtrate provided

green solid [PhBP^iPr₃]NiCl (716.8 mg, 96.8%). Crystals of 3 were

grown from a concentrated solution in diethyl ether at -30 °C. ¹H

NMR (300 MHz, C₆D₆): δ 37.1 (br s), 7.2-7.4 (m), 2.5 (br). µ_eff

(C₆D₆, 298 K): 2.97 µ_B. UV-vis (C₆H₆) λ_max, nm (ꢀ): 720 (330),

425 (3450), 385 (3340). Anal. Calcd for C₂₇H₅₃BClNiP₃: C, 56.34;

H, 9.28. Found: C, 56.29; H, 8.92.

Synthesis of [PhBP₃]Ni(N₃) (4). A solution of 1 (0.171 g, 0.219

mmol) in THF (4 mL) was added to a stirring suspension of NaN₃

(1.43 g, 21.9 mmol) in THF (10 mL) at room temperature. After

being stirred for 18 h, the yellow-green reaction mixture was filtered

through a Celite pad and then evaporated to dryness under reduced

pressure. The resulting solid was then extracted into benzene (3

mL) and filtered again through a Celite pad. Vapor diffusion of

petroleum ether into the resulting yellow-green filtrate yielded

yellow-green crystalline product (0.152 g, 88%).¹H NMR (300

MHz, C₆D₆): δ 25.4 (s), 8.02 (s), 7.5 (s), 7.4 (s), 1.25 (s), 0.47 (s),

-6.6 (br s), -9.7 (s). UV-vis (C₆H₆) λ_max, nm (ꢀ): 698 (310),

463 (3143), 328 (6285). µ_eff(C₆D₆, 298 K): 2.86 µ_B. IR: (C₆H₆)

ν(N₃) ) 2060 cm^-1. Anal. Calcd for C₄₅H₄₁BN₃NiP₃: C, 68.74;

H, 5.26; N, 5.34. Found: C, 68.37; H, 4.96; N, 4.93.

Synthesis of [PhBP₃]Ni(OSiPh₃) (5). A solution of TlOSiPh₃

(0.0551 g, 0.115 mmol) in THF (2 mL) was added to a stirring

solution of 1 (0.0897 g, 0.115 mmol) in benzene (4 mL). A white

precipitate formed immediately. The reaction mixture was stirred

for 2 h, filtered through a Celite pad, and evaporated to dryness

under reduced pressure to yield a green solid. The green solid was

extracted with benzene (2 mL) and filtered through a Celite pad.

Vapor diffusion of petroleum ether into the filtrate provided bright

green crystals of the analytically pure product (0.0984 g, 77%). ¹H

NMR (300 MHz, C₆D₆): δ 24.3 (s), 8.7 (s), 7.4 (s), 6.9 (s), 1.39

(s), 0.92 (s), -4.6 (br s), -8.3 (s). UV-vis (C₆H₆) λ_max, nm (ꢀ):

693 (353), 404 (3546). µ_eff(C₆D₆, 298 K): 2.95 µ_B. Anal. Calcd

for C₇₀H₆₄BNiOP₃Si: C, 75.62; H, 5.80. Found: C, 76.02; H, 5.60.

Synthesis of [PhBP₃]Ni(O-p-^tBu-Ph) (6). A solution of Tl(O-

4-^tBu-Ph) (0.0794 g, 0.225 mmol) in THF (4 mL) was added

dropwise to a stirring solution of 1 (0.175 g, 0.225 mmol) in THF

(5 mL). The reaction mixture was stirred for 3 h and concentrated

Synthesis of Tl(S-p-^tBu-Ph). 4-tert-Butylthiophenol (0.4418 g,

2.66 mmol) was dissolved in petroleum ether (10 mL). The colorless

solution was then treated with Tl(OCH₂CH₃) (0.663 g, 2.66 mmol)

as a petroleum ether solution (5 mL). The reaction mixture was

stirred for 2 h, and the bright yellow solid that precipitated was

collected on a medium porosity glass frit and washed with petroleum

ether (15 mL) yielding yellow Tl(S-p-^tBu-Ph) (0.812 g, 83%). Anal.

Calcd for C₁₀H₁₃STl: C, 32.49; H, 3.54. Found: C, 32.58; H, 3.73.

Synthesis of [PhBP₃]Ni(S-p-^tBu-Ph) (7). A solution of Tl(S-

4-^tBu-Ph) (0.0509 g, 0.138 mmol) in THF (3 mL) was added

dropwise to a stirring solution of 1 (0.107 g, 0.138 mmol) in THF

(4 mL). The reaction mixture was stirred for 3 h and concentrated

to dryness under reduced pressure to yield a dark red solid. The

solid was extracted with benzene (3 mL) and filtered through a

Celite pad. Vapor diffusion of petroleum ether into the benzene

solution yielded the product as red crystals (0.101 g, 81%). ¹H NMR

(300 MHz, C₆D₆): δ 33.4 (br s), 22.8 (s), 8.6 (s), 2.8 (s), 2.7 (s),

0.3 (s), -4.9 (br s), -8.4 (s). UV-vis (C₆H₆) λ_max, nm (ꢀ): 680

(778), 470 (3442). µ_eff(C₆D₆, 298 K): 3.02 µ_B. Anal. Calcd for

C₅₅H₅₄BNiOP₃: C, 72.63; H, 5.98. Found: C, 72.54; H, 5.65.

Synthesis of [PhB(CH₂P(O)Ph₂)₂(CH₂PPh₂)]NiCl (8A). A

solution of 1 (0.0850 g, 0.109 mmol) in benzene (4 mL) was treated

with O₂gas (8.0 mL, 0.327 mmol) with stirring at room temperature.

The color of the reaction mixture changed from bright green to

purple over the course of 6 h. Volatiles were removed under reduced

pressure to yield a dark purple solid. This solid was extracted into

toluene and filtered through a Celite pad. The filtrate was layered

with petroleum ether and stored at -40 °C to afford the bright

yellow crystalline product (0.0712 g, 80%).

{[PhB(CH₂P(O)Ph₂)₂(CH₂PPh₂)]Ni(µ-Cl)}₂(8B). 8B was pre-

pared as above with the following exception: The dark purple solid

was extracted into benzene and filtered through a Celite pad. Slow

diffusion of petroleum ether into the benzene solution at room

temperature yielded the product as bright purple crystals (0.0782

mg, 94%).¹H NMR (300 MHz, C₆D₆): δ 19.2 (s), 9.6 (s), 8.4 (s),

8.1 (s), 7.8 (s), 5.8 (s), -0.68 (br s), -2.4 (s), -9.9 (s), -15.3 (s).

UV-vis (C₆H₆) λ_max, nm (ꢀ): 901 (323), 505 (634). Anal. Calcd

for C₉₀H₈₂Cl₂B₂Ni₂O₄P₆‚2C₇H₈‚C₆H₆‚CH₂Cl_1.5: C, 68.67; H, 5.31.

Found: C, 68.58; H, 5.15.

Synthesis of [PhBP₃]Ni(η²-CH₂-PPh₂) (9). Method A. A 0.21%

Na/Hg amalgam was prepared by dissolving metallic sodium (8.1

mg, 0.36 mmol) in mercury (3.70 g). A THF solution (10 mL) of

2 (0.307 g, 0.352 mmol) was added dropwise to a stirring

suspension of the amalgam in THF (5 mL). The reaction mixture

was stirred for 24 h, during which the color changed from red-

brown to bright red. The THF solution was decanted away from

the Hg and removed under reduced pressure to yield a bright red

solid. This solid was extracted into toluene (3 mL) and filtered

through a Celite pad. The resulting deep red filtrate was stored at

-40 °C overnight and afforded red crystalline product (139 mg,

42%). Method B. A solution of 1 (0.114 g, 0.146 mmol) in toluene

(4.0 mL) was cooled to -78 °C. A toluene solution (2 mL) of Ph₂-

PCH₂Li(TMEDA) (0.047 g, 0.146 mmol) was cooled to -78 °C

and added dropwise to the solution of 1. The reaction mixture was

Inorganic Chemistry, Vol. 43, No. 15, 2004 4659

MacBeth et al.

allowed to warm to room temperature over a 6 h period, during

which the color changed from dark green to blood red. The reaction

mixture was filtered through a Celite pad, and the red filtrate was

layered with petroleum ether and stored at -40 °C overnight to

afford a red microcrystalline product. The product was isolated on

a medium porosity frit and washed twice with 2 mL portions of

a yellow solid. This solid was extracted into benzene and filtered

through a Celite pad. Slow diffusion of petroleum ether into the

yellow filtrate produced yellow crystals of the product (0.711 g,

95%). H NMR (300 MHz, C₆D₆): δ 42.3 (s), 26.1 (s), 11.7 (s),

9.1 (s), 8.6 (s), 8.0 (s), 7.7 (br s), 6.3 (br), 5.1 (s), 0.60 (br), 0.30

1

(s), -9.9 (s). µ_eff(C₆D₆, 298K): 1.91 µ_B. UV-vis (C₆H₆) λ_max

,

1

diethyl ether (0.109 g, 80%). H NMR (300 MHz, C₆D₆): δ 8.16

nm (ꢀ): 443 (1927). Anal. Calcd for C₆₄H₅₈NiP₄: C, 75.32; H,

(d, 2H, J ) 7.2 Hz), 7.66 (t, 2H, J ) 7.2 Hz), 7.44 (m, 5H), 7.24

(m, 12H), 6.89 (m, 24H), 1.90 (br, 6H), 1.60 (q, 2H, J ) 7.80 Hz).

¹³C{¹H} NMR (75.4 MHz, C₆D₆): δ 167.1 (m), 141.3 (m), 133.4

(d, J_P-C) 12.1 Hz), 132.5 (m), 132.1(s), 129.8 (d, J_P-C) 3.5

Hz), 128.8 (s), 128.6 (s), 125.1(s), 30.1 (br), -9.5 (m). ³¹P{¹H}

NMR (121.4 MHz, C₆D₆): δ 22.28 (d, 3P, ²J_P-P) 53 Hz), 29.20

(q, 1P, J_P-P) 53 Hz). UV-vis (C₆H₆) λ_max, nm (ꢀ): 544 (882),

435 (2670). Anal. Calcd for C₅₈H₅₃BNiOP₄: C, 73.84; H, 5.66;.

Found: C, 73.49; H, 5.45.

Synthesis of [PhBP^iPr₃]Ni(η²-CH₂PⁱPr₂) (10). A THF solution

(2 mL) of ⁱPr₂PCH₂Li (23.3 mg, 0.169 mmol) was added dropwise

to a stirring THF solution (2 mL) of 3 (95.9 mg, 0.167 mmol).

The color of the reaction changed from pale green to yellow. After

30 min, volatiles were removed under reduced pressure. The solids

were extracted with benzene (1 mL) and filtered. Volatiles were

removed under reduced pressure, providing yellow 10 (103.1 mg,

92.0%). Attempts to obtain satisfactory elemental analysis for this

compound have not been successful thus far. ¹H NMR (300 MHz,

5.73. Found: C, 75.38; H, 5.91.

Synthesis of [PhBP₃]Ni(CN^tBu) (13). A 0.23 wt % amalgam

was prepared by dissolving sodium (2.7 mg, 0.118 mmol) in

mercury (1.18 g). Liquid ^tBuNC (9.8 mg, 0.118 mmol) was added

to a THF solution (3 mL) of 1 (0.0916 g, 0.118 mmol) to produce

an immediate color change from dark green to purple. This solution

was then added dropwise to the stirring amalgam, and the reaction

mixture was stirred for 12 h. Over this time period the reaction

mixture changed from purple to burgundy. The burgundy solution

was decanted away from the amalgam and dried under reduced

pressure to yield a solid. The solid was extracted into benzene and

filtered through a pad of Celite. Vapor diffusion of petroleum ether

into the filtrate yielded red block crystals of the product (0.0761 g,

78%). ¹H NMR (300 MHz, C₆D₆): δ 12.52 (s), 8.9 (s), 7.9 (s), 7.7

(s), 0.47 (s), -6.6 (br s), -9.7 (s). UV-vis (C₆H₆) λ_max, nm (ꢀ):

1059 (224), 443 (1409), 342 (8580). µ_eff(C₆D₆, 298 K): 1.74 µ_B.

IR (C₆H₆, KBr), cm^-1, ν(CN): 2094. Anal. Calcd for C₅₀H₅₀-

BNNiP₃: C, 72.58; H, 6.09; N, 1.69. Found: C, 72.29; H, 6.07;

N, 1.30.

Synthesis of [PhBP^iPr₃]Ni(PMe₃) (14). In a 20 mL vial, [PhB-

(CH₂PⁱPr₂)₃]NiCl (227.7 mg, 395.6 µmol) was dissolved in THF

(8 mL). Neat PMe₃(614 µL, 5.93 mmol) was added to the solution,

causing the reaction mixture to become dark red. After 10 min,

the homogeneous reaction mixture was transferred to a vial

containing a stirbar and sodium/mercury amalgam (0.378% w/w,

2.4022 g, 395 µmol of sodium atoms). The reaction mixture was

stirred vigorously for 4 h, during which time the color became

yellow-orange. The reaction mixture was filtered over Celite on

glass fiber filter paper, and the Celite was washed with benzene [3

× 2 mL]. The combined filtrates were concentrated to dryness under

reduced pressure, providing analytically pure yellow-orange solid

14 (239.4 mg, 98.4%). Crystals of 14 were grown from a diethyl

2

3

C₆D₆): δ 8.01 (br d, 2H, J_H-H) 6.6 Hz), 7.49 (t, 2H, J_H-H

)

3

7.5 Hz), 7.26 (t, 1H, J_H-H) 7.5 Hz), 1.84 (br m, 6H), 1.13 (m,

36H), 0.75 (m, 12H), -0.28 (s, 2H). ¹³C{¹H} NMR (75.4 MHz,

C₆D₆): δ 165.6 (q, ¹J_B-C) 47 Hz), 132.93, 126.77, 123.39, 26.33

(br), 21.08, 20.85, 20.35 (d, J_P-C) 6.4 Hz), 19.87 (d, J_P-C) 5.1

Hz), 19.71, 19.51 (d, J_P-C) 7.4 Hz), -12.84 (doublet of quartets,

¹J_P-C) 15.9 Hz, J_P-C) 5.8 Hz). ³¹P{¹H} NMR (121.4 MHz,

2

C₆D₆): δ 49 (br, 3P), -18.2 (q, 1P, ¹J_P-P) 41 Hz). ¹¹B{¹H} NMR

(128.3 MHz, C₆D₆): δ -15.7.

Synthesis of [K²-PhBP^iPr₃]Ni(dbabh) (11). A diethyl ether

suspension (2 mL) of Hdbabh⁴¹(11.4 mg, 59.0 µmol) was frozen

in a liquid nitrogen cooled well. To the stirring, thawing suspension

was added a hexanes solution of n-butyllithium (1.6 M, 40 µL, 64

µmol). The reaction mixture was stirred and warmed at room

temperature for 30 min. The resulting solution and a diethyl ether

solution of 3 (33.9 mg, 58.9 µmol) were frozen in a liquid nitrogen

cooled well. The two solutions were thawed, and the thawing

solution of 3 was added to the thawing solution of [Li][dbabh].

The yellow-green reaction mixture was stirred and warmed. As the

mixture warmed, a color change to inky green brown occurred.

After 45 min of warming, the volatiles were removed under reduced

pressure. The dark solids were extracted with petroleum ether (3

mL) and filtered. Crystals were obtained from the petroleum ether

solution by cooling to -30 °C for several days. The crystals were

1

ether/petroleum ether mixture at -30 °C. H NMR (300 MHz,

C₆D₆): δ 35.3 (br s, 6H), 16.5 (br s, 9H), 11.0 (br s, 6H), 10.1 (br

s, 18H), 9.0 (s, 2H), 8.0 (t, 2H, J ) 7.2 Hz), 7.7 (t, 1H, J ) 7.5

Hz), -0.3 (br s, 18H). µ_eff(C₆D₆, 298 K): 1.82 µ_B. UV-vis (C₆H₆)

λ_max, nm (ꢀ): 430 (1240). Anal. Calcd for C₃₀H₆₂BNiP₄: C, 58.47;

H, 10.14. Found: C, 58.50; H, 10.30.

Alternative Synthesis. Solid yellow (COD)₂Ni (49.5 mg, 180

µmol) was dissolved in petroleum ether (3 mL). Neat PMe₃(75

µL, 725 µmol) was added with stirring. After 1 h, a benzene solution

(3 mL) of [PhBP^iPr₃]Tl (123.5 mg, 180.1 µmol) was added to the

pale yellow reaction mixture. Upon addition, the reaction mixture

darkened. Over 48 h, gray solids precipitated from solution.

Volatiles were removed from the reaction mixture under reduced

pressure. The solids were extracted with petroleum ether (10 mL)

and filtered. Crystallization of the petroleum ether solution at -30

°C over 3 days provided yellow crystals of 14. Analysis of the

1

analyzed as 11 (26.4 mg, 61.3%). H NMR (300 MHz, C₆D₆): δ

3

7.75 (d, 2H, J_H-H) 7.5 Hz), 7.41 (t, 2H, J_H-H) 7.5 Hz), 7.21

3

(t, 1H, J_H-H) 7.2 Hz), 6.98 (dd, 4H, J_H-H) 1.8, 2.7 Hz), 6.72

(dd, 4H, J_H-H) 1.8, 3.0 Hz), 5.44 (s), 1.57 (septet, 6H, J ) 7.5

Hz), 1.18 (d, 18H, J ) 7.3 Hz), 1.1 (br m), 0.82 (d, 18H, J ) 7.5

Hz). ³¹P{¹H} NMR (121.4 MHz, C₆D₆): δ 58 (br). Anal. Calcd

for C₄₁H₆₃BNNiP₃: C, 67.24; H, 8.67; N, 1.91. Found: C, 67.18;

H, 8.83; N, 1.48.

1

crystals by H NMR and ³¹P{¹H} NMR spectroscopy showed the

presence of [PhB(CH₂PⁱPr₂)₃]Ni(PMe₃) and [PhB(CH₂PⁱPr₂)₃]Tl,

1

Synthesis of [PhBP₃]Ni(PPh₃) (12). Solid PPh₃(0.191 g, 0.727

mmol) was added to a stirring solution of 1 (0.567 g, 0.727 mmol)

in THF (7 mL). A THF solution (3 mL) of KC₈(0.108 g, 0.799

mmol) was added to the reaction mixture and stirred for 12 h. Over

this time period the color changed from bright green to bright

yellow. All volatiles were removed under reduced pressure to yield

in a 95:5 ratio. H NMR (300 MHz, C₆D₆): δ 35.3 (br s, 6H),

16.5 (br s, 9H), 11.0 (br s, 6H), 10.1 (br s, 18H), 9.0 (s, 2H),

8.0 (t, 2H, J ) 7.2 Hz), 7.7 (t, 1H, J ) 7.5 Hz), 7.1-7.3 (m, [PhB-

(CH₂PⁱPr₂)₃]Tl), 1.90 (br, [PhB(CH₂PⁱPr₂)₃]Tl), 1.21 (br, [PhB-

(CH₂PⁱPr₂)₃]Tl), 1.07 (m, [PhB(CH₂PⁱPr₂)₃]Tl), -0.3 (br s, 18H).

³¹P{¹H} NMR (121.4 MHz, C₆D₆): δ 45.35 (d, ¹J_Tl-P) 5910 Hz).

4660 Inorganic Chemistry, Vol. 43, No. 15, 2004

The Coordination Chemistry of “[BP₃]NiX” Platforms

Synthesis of [PhBP^iPr₃]Ni(CN^tBu) (15). To a benzene solution

(3 mL) of 14 (91.3 mg, 148 µmol) was added dropwise a benzene

solution (2 mL) of CN^tBu (67.7 mg, 814 µmol). The reaction

mixture darkened to orange-red. The reaction mixture was stirred

for 20 min. The solution was filtered and concentrated to dryness

under reduced pressure. The resulting orange-red material was

dissolved in toluene (1 mL), and concentrated to dryness under

reduced pressure. The toluene evaporation procedure was repeated

twice more, providing yellow-orange solid 15 (78.7 mg, 85.4%).

Crystals of 15 were grown from a diethyl ether/petroleum ether

solution at -30 °C. ¹H NMR (300 MHz, C₆D₆): δ 47.9 (br s, 6H),

12.6 (br s, 6H), 11.3 (br s, 18H), 8.8 (s, 2H), 7.8 (s, 2H), 7.6 (t,

1H, J ) 7.5 Hz), 3.0 (s, 9H), 0.3 (br s, 18H). µ_eff(C₆D₆, 298 K):

1.68 µ_B. UV-vis (C₆H₆) λ_max, nm (ꢀ): 430 (1560). IR (THF, KBr)

cm^-1, ν(CN): 2056. Anal. Calcd for C₃₂H₆₂BNNiP₃: C, 61.67; H,

10.03; N, 2.25. Found: C, 61.39; H, 10.35; N, 2.00.

Celite pad. All volatiles were removed under reduced pressure to

yield a pale yellow solid. The solid was isolated on a medium

porosity frit and washed twice with 2 mL portions of EtOH.

Dissolving the solid in THF and layering with diethyl ether afforded

crystalline product (0.272 g, 83%). ¹H NMR (300 MHz, C₆D₆): δ

8.15 (t, 2H, J ) 8.0 Hz), 8.0 (m, 4H), 7.69 (d, 2H, J ) 6.3 Hz),

7.55 (m, 6H), 7.27 (t, 2H, J ) 6.0 Hz), 7.06 (m, 17H), 2.79 (br,

8H, [ⁿBu₄N]), 2.61 (br, 6H), 1.16 (br, 16H, [ⁿBu₄N]), 0.882 (br,

12H, [ⁿBu₄N]). ¹³C{¹H} NMR (75.4 MHz, acetone-d₆): δ 206.2

(t, J_P-C) 2.1 Hz), 149.0 (m), 138.6 (m), 134.5 (s), 134.3 (s), 134.0

(d, J ) 4.5 Hz), 133.5 (s), 132.8 (s), 132.6 (s), 130.1 (s), 129.8 (s),

129.1 (d, J ) 3.7 Hz), 129.0 (s), 128.2-127.1 (overlapping

resonances), 126.6 (s), 59.5 (t, J_C-N) 2.9 Hz), 24.6 (s), 20.5 (s),

15.7 (br), 13.5 (s). ³¹P{¹H} NMR (121.4 MHz, C₆D₆): δ 29.2 (s),

-9.46 (br). IR (THF, KBr), cm^-1, ν(CO): 1994, 1913. Anal. Calcd

for C₆₃H₇₇BNNiO₂P₃: C, 72.57; H, 7.44; N, 1.34. Found: C, 72.21;

H, 7.06; N, 1.47.

Alternative Synthesis. Solid green 3 (81.0 mg, 141 µmol) was

dissolved in THF (3 mL). Neat CN^tBu (40 µL, 660 µmol) was

added and the reaction mixture was stirred, forming a golden orange

solution. After 20 min, the ³¹P{¹H} NMR spectrum was examined.

³¹P{¹H} NMR (121.4 MHz, THF): δ 62.7 (br d), 47.7 (br d), 3.2

(br s). Volatiles were removed under reduced pressure. The resultant

solids were dissolved in THF (2 mL) and added to a sodium/

mercury amalgam (0.378% w/w, 859.0 mg, 141.2 µmol of sodium

atoms), followed by washing with additional THF (3 mL). The

reaction mixture was stirred vigorously for 3 h. The reaction mixture

was filtered, providing an orange-yellow solution. Volatiles were

removed under reduced pressure. The resultant solids were washed

with petroleum ether [3 × 0.5 mL], removing an orange-red

supernatant and leaving yellow solids. The solids were dried under

reduced pressure, providing 15 (51.3 mg, 58.4%).

Synthesis of [[K²-PhBP^iPr₃]Ni(CO)₂][ASN] (18). Solid [PhBP^iPr₃]-

Tl (317.1 mg, 0.4625 mmol), (Ph₃P)₂Ni(CO)₂(296.2 mg, 0.4633

mmol), and ASNBr (96.1 mg, 0.466 mmol) were combined in THF

(7 mL) and stirred in the dark. Monitoring of the reaction mixture

by ³¹P{¹H} NMR showed that all of the [PhBP^iPr₃]Tl had been

consumed after 4 days. Volatiles were removed under reduced

pressure, and benzene (1 mL) was added to the resulting sticky

solids. A yellow oil separated, and the benzene was decanted. This

procedure was repeated three times, the yellow oil being isolated

each time. The yellow oil was placed under reduced pressure for

several hours, providing sticky yellow solids. The solids were taken

up in a mixture of THF and diethyl ether (2:1), and stored at -30

°C for 24 h. A small amount of white precipitate formed, which

was removed by filtration. This precipitation process was repeated

again. The resulting solution was concentrated to dryness under

reduced pressure, to provide sticky yellow solids whose spectro-

Synthesis of [PhBP₃]Ni(NO) (16). Method A. A solution of

12 (0.645 g, 0.641 mmol) in benzene (15 mL) was stirred under 1

atm of NO gas for 2 h. The color of the reaction mixture changed

from bright yellow to dark red over this time period. The reaction

mixture was concentrated to dryness under reduced pressure to yield

a red solid. This solid was extracted into benzene (4 mL) and filtered

through a Celite pad. Vapor diffusion of petroleum ether into the

red filtrate yielded red crystalline product (0.452 g, 91%). Method

B. A solution of 1 (0.215 g, 0.276 mmol) in benzene (4 mL) was

treated with NO gas (13.6 mL, 0.552 mmol) and stirred for 2 h.

Over this time period the reaction mixture changed from dark green

to dark red. The solution was concentrated under reduced pressure

to 50% of its original volume and filtered through a Celite pad.

Vapor diffusion of petroleum ether into the red filtrate yielded

1

scopic properties were consistent with 18 (129.3 mg, 38.7%). H

NMR (300 MHz, THF-d₈): δ 7.44 (br s, 2H), 6.87 (t, 2H, J ) 7.5

Hz), 6.67 (t, 1H, J ) 7.5 Hz), 3.49 (m, 8H), 2.19 (m, 8H), 1.91

(septet, 2H, J ) 7.2 Hz), 1.64 (m, 4H), 1.18 (dd, 12H, J ) 6.5, 7.2

Hz), 1.08 (m, 4H), 0.97 (m, 12H), 0.77 (dd, 12H, J ) 6.2, 7.5 Hz),

0.28 (br, 2H). ¹³C{¹H} NMR (75.4 MHz, THF-d₈): δ 208.16 (t,

²J_P-C) 1.6 Hz), 169.08 (q, ¹J_B-C) 50 Hz), 133.66, 126.11, 122.20,

1

63.86 (t, J_N-C) 3.2 Hz), 28.23, 27.30, 24.92 (d), 23.03, 21.23

(d), 20.71 (d), 20.45 (d), 20.10 (br), 19.81 (br), 19.73 (d). ³¹P{¹H}

NMR (121.4 MHz, THF-d₈): δ 51.13 (s, 2P), 4.80 (s, 1P). ¹¹B-

{¹H} NMR (128.3 MHz, THF-d₈): δ -15.0. IR (THF, KBr) cm^-1

ν(CO): 2004, 1878.

,

1

crystalline dark red product (0.193 g, 90%). H NMR (300 MHz,

Photolysis of [K²-PhBP₃]Ni(CO)₂][ⁿBu₄N]. A THF (10 mL)

solution of 17 (0.1274 g, 0.122 mmol) was transferred to a

photolysis cell equipped with an N₂inlet line and a gas outlet line

connected to a mineral oil bubbler. The solution was photolyzed

with a mercury lamp for 8 h. The solution was evaporated to dryness

to yield a pale yellow solid. This solid was extracted into benzene

solution and filtered through a Celite pad. Attempts to crystallize

by slow evaporation of a benzene solution or slow diffusion of

petroleum ether into a THF solution both yielded a yellow oil

containing {[PhBP₃]Ni(CO)}{ⁿBu₄N} (22) and a paramagnetic

impurity. ¹H NMR (300 MHz, C₆D₆): δ 8.28 (t, J ) 8.15 Hz, 2H),

8.03 (m, 6H), 7.63 (m, 6H), 7.49 (m, 1H), 7.06 (m, 9H), 6.75 (m,

13H) (br, 8H, [ⁿBu₄N]), 1.49 (br, 6H), 1.16 (br, 16H, [ⁿBu₄N]),

0.882 (b, 12H, [ⁿBu₄N]). ³¹P{¹H} NMR (121.4 MHz, C₆D₆): δ

25.33. IR: (THF, KBr) cm^-1, ν(CO): 1869.

C₆D₆): δ 8.01 (d, 2H, J ) 6.6 Hz), 7.76 (m, 7H), 7.55 (m, 12H),

7.02 (t, 6H, J ) 7.2 Hz), 6.78 (d, 15H, J ) 6.6 Hz), 1.50 (br, 6H).

¹³C NMR (C₆D₆, 75.4 MHz, 25 °C): δ 138.3 (m), 132.2-131.0

(overlapping resonances), 131.8 (dd, J ) 4.3, 7.8 Hz) 131.4 (s),

129.5 (s), 129.3 (s), 128.3 (s), 124.9(s), 18.3 (br). ³¹P{¹H} NMR

(121.4 MHz, C₆D₆): δ 37.3. UV-vis (C₆H₆) λ_max, nm (ꢀ): 913

(159), 433 (2206), 350 (2059). µ_eff(C₆D₆, 298K): 2.86 µ_B. IR

(C₆H₆, KBr), cm^-1, ν(NO): 1737. Anal. Calcd for C₄₅H₄₁-

BNNiOP₃: C, 69.81; H, 5.34; N, 1.81. Found: C, 70.21; H, 5.18;

N, 1.53.

Synthesis of [K²-PhBP₃]Ni(CO)₂][ⁿBu₄N] (17). A benzene

solution (3 mL) of [PhBP₃]Tl (0.276 g, 0.313 mmol) was added

dropwise to a stirring benzene solution (3 mL) of (PPh₃)₂Ni(CO)₂

(0.200 g, 0.313 mmol). After stirring for 1 h, a THF solution (3

mL) of [ⁿBu₄N][Br] (0.101 g, 0.313 mmol) was added to the

reaction mixture and a white precipitate formed immediately. The

reaction mixture was stirred for 12 h and was filtered through a

Reactivity of 1 with Methyllithium. A diethyl ether (6 mL)

solution of 1 (0.0831 g, 0.106 mmol) was cooled to -78 °C. A

solution of methyllithium (1.6 M in hexanes, 1.71 mL, 0.106 mmol)

Inorganic Chemistry, Vol. 43, No. 15, 2004 4661

MacBeth et al.

was added dropwise to this solution. The solution was warmed

slowly to room temperature over the course of 4 h. During this

time the color of the reaction mixture went from dark green to

blood red. The solution was filtered through a pad of Celite to

remove insoluble material. All volatiles were remove under reduced

pressure to yield a dark-red solid. When extracted into benzene

and analyzed by ¹H and ³¹P{¹H} NMR, the reaction mixture

exhibited the diamagnetic resonances of complex 9.

was added p-tolyl azide (29.3 mg, 0.22 mmol) drowise as a benzene

solution (2 mL). After 15 min, the color changed from bright yellow

to dark brown. The reaction mixture was stirred for 24 h, and all

solvent was removed under reduced pressure. The only identifiable

product in this reaction was p-tolyl-NdPPh_3.¹H NMR (300 MHz,

C₆D₆): δ 7.81 (m, 4H), 7.04 (m, 15H), 2.20 (s, 3H). ³¹P{¹H} NMR

(121.4 MHz, C₆D₆): δ -1.17 (s). ESI/MS (m/z): 368.1 (p-tolyl-

NdPPh₃+ H⁺).

Reactivity of 1 with Lithium Amides. A procedure similar to

that reported for the reactions of 1 with methyllithium was followed.

In all procedures, the lithium amides were added cold (-78 °C) to

1. The solutions became dark red upon warming to room temper-

ature. The products exhibited the same spectral signatures as

complex 9.

Reaction of 1 with CoCp₂. A THF (5 mL) solution of CoCp₂

(5 mL) was added dropwise to a (THF) solution of 1 (0.1889 g,

0.242 mmol). The reaction mixture was stirred for 1.5 h. [ⁿBu₄N]-

[Br] (0.0939 g, 0.242 mmol) was then introduced as a THF solution

(3 mL), and the reaction mixture was stirred for an additional hour.

The THF solution was filtered through a Celite pad to remove

insoluble material, and the resulting red-brown solution was

concentrated to dryness. The red-brown solid was collected on a

medium porosity frit and washed with Et₂O. Crude ¹H NMR (300

MHz, C₆D₆): δ 21.5 (br), 12.2 (m), 11.8 (m), 8.4 (m), -3.6 (br)

-5.8 (br), -47.6 (br). Attempts to recrystallize this product led to

a mixture of diamagnetic and paramagnetic products.

Acknowledgment. We acknowledge the DOE (PECASE)

and the NSF (CHE-0132216) for financial support of this

work. Larry Henling, Smith Nielsen, and Eric Peters provided

technical assistance. We are grateful to Professors Peter T.

Wolczanski and Daniel Rabinovich for providing insightful

discussions. We also thank Professor Clifford Kubiak for

disclosing results prior to publication. The Beckman Institute

Senior Research Fellows Program (CEM), the Moore Foun-

dation (J.C.T.), the NSF (J.C.T.), and the DOD (T.A.B.) are

each acknowledged for fellowship support.

Supporting Information Available: CIFs and tables of crystal-

lographic data for complexes 2-5, 7, 8A,B, and 11-16, including

fully labeled thermal ellipsoid plots, crystallographic details, atomic

coordinates, equivalent isotropic displacement parameters, aniso-

tropic displacement parameters, and interatomic distances and

angles. This material is available free of charge via the Internet at

http://pubs.acs.org.

Reaction of 12 with p-Tolyl Azide. Complex 12 (0.1103 g,

0.110 mmol) was dissolved in benzene. To this reaction mixture

IC049936P

4662 Inorganic Chemistry, Vol. 43, No. 15, 2004

Article Doi

The coordination chemistry of "[BP3]NiX" platforms: Targeting low-valent nickel sources as promising candidates to L3Ni=E and L3Ni≡E linkages

DOI: 10.1021/ic049936p

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Article abstract of DOI:10.1021/ic049936p

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