Syntheses, Characterizations, and Coordination Chemistry of the 10-Vertex Phosphadicarbaboranes 6-R-arachno-6,8,9-PC2B7H 11 and 6-R-arachno-6,5,7-PC2B7H11

Published on Web 11/27/2003

Syntheses, Characterizations, and Coordination Chemistry of

the 10-Vertex Phosphadicarbaboranes

6-R-arachno-6,8,9-PC₂B₇H₁₁and 6-R-arachno-6,5,7-PC₂B₇H₁₁

Daewon Hong, Scott E. Rathmill, Patrick J. Carroll, and Larry G. Sneddon*

Contribution from the Department of Chemistry, UniVersity of PennsylVania,

Philadelphia, PennsylVania 19104-6323

Received August 7, 2003; E-mail: lsneddon@sas.upenn.edu

Abstract: The 10-vertex phosphadicarbaboranes, 6-R-arachno-6,8,9-PC₂B₇H₁₁(1) (R ) Ph 1a or Me 1b)

and 6-R-arachno-6,5,7-PC₂B₇H₁₁(2) (R ) Ph 2a or Me 2b) have been synthesized using in situ

dehydrohalogenation reactions of RPCl₂(R ) Ph or Me) with the arachno-4,5-C₂B₇H₁₃and arachno-4,6-

C₂B₇H₁₃carboranes, respectively. X-ray crystallographic determinations in conjunction with DFT/GIAO/

NMR calculations and NMR spectroscopic studies have established that both 1 and 2 have open cage

structures based on an icosahedron missing two vertexes. The two isomeric compounds differ in the positions

of the carbons and bridging hydrogens on the open face. Studies of the reactions of 2a with BH₃‚THF, S₈,

and hydrogen peroxide demonstrated that 2a shows strong donor properties yielding the compounds endo-

6-H₃B-exo-6-Ph-arachno-6,5,7-PC₂B₇H₁₁(3), endo-6-S-exo-6-Ph-arachno-6,5,7-PC₂B₇H₁₁(4), and endo-

6-O-exo-6-Ph-arachno-6,5,7-PC₂B₇H₁₁(5) in which the BH₃, S, and O substitutents are bonded to an electron

lone pair localized at the phosphorus endo-position. The reaction of 2a with an excess of S₈results in the

loss of a framework boron to produce the unique open-cage compound µ_7,8-{HS(Ph)P}-hypho-7,8-C₂B₆H₁₁

(6). 2a also formed the donor complexes cis-(η¹-[6-Ph-arachno-6,5,7-PC₂B₇H₁₁])₂PtBr₂(7) and trans-(η¹-

[6-Ph-arachno-6,5,7-PC₂B₇H₁₁])₂PdBr₂(8) in which the metal fragment is bonded in an η¹-fashion at the

phosphorus endo-position. In these complexes, 2a is functioning as a two-electron sigma donor to the

metals and can thus be considered as an analogue of the PR₃ligands in the classical cis-(PPh₃)₂PtBr₂and

trans-(PPh₃)₂PdBr₂coordination complexes. Although 1a did not show the donor properties exhibited by

2a, its dianion 6-Ph-6,8,9-PC₂B₇H₉(1a^2-) readily formed η⁴-coordinated complexes with late transition

2-

metals including 8-Ph-7-(Ph₃P)₂-nido-7,8,10,11-PtPC₂B₇H₉(9), 7-Ph-11-(η⁵-C₅H₅)-nido-11,7,9,10-CoPC₂B₇H₉

(10), and commo-Ni-(7-Ni-8′-Ph-nido-8′,10′,11′-PC₂B₇H₉)(7-Ni-8-Ph-nido-8,10,11-PC₂B₇H₉) (11).

Introduction

(CO)₂]-exo-6-Ph-arachno-6,7-PCB₈H₁₁and exo-6-[Mn(CO)₅]-

endo-6-Ph-arachno-6,7-PCB₈H₁₁, in which the 6-R-arachno-

6,5,7-PCB₈H₁₁anion could be considered as an anionic

While a variety of phosphacarbaboranes have been prepared

and studied,¹we have only recently reported the syntheses,

structures, and chemical reactivities of the first 10-vertex

arachno-phosphamonocarbaborane 6-R-arachno-6,7-PCB₈H₁₂

and its conjugate anion 6-R-arachno-6,7-PCB₈H₁₁

-

analogue of R₃P.

In this paper, we report the first syntheses and structural

characterizations of the 10-vertex phosphadicarbaboranes 6-R-

arachno-6,8,9-PC₂B₇H₁₁(1) and 6-R-arachno-6,5,7-PC₂B₇H₁₁

(2) along with studies that compare the reactivities and

coordination properties of these phosphadicarbaboranes with

those of the isoelectronic 6-R-arachno-6,7-PCB₈H₁₁^-phospha-

monocarbaborane anion.³

- 2

. These

studies showed that, in contrast to the properties observed for

the previously known phosphacarbaboranes, the 6-R-arachno-

-

6,7-PCB₈H₁₁anion exhibited strong donor properties arising

from a lone pair of electrons localized on the phosphorus and,

accordingly, forms many compounds, including endo-6-L-exo-

6-Ph-arachno-6,7-PCB₈H₁₁(L ) O, S, BH₃), endo-6-[CpFe-

-

Experimental Section

All manipulations were carried out using standard high-vacuum or

inert-atmosphere techniques as described by Shriver.⁴

(1) For reviews of phosphacarbaboranes, see: (a) St´ıbr, B. Collect. Czech.

Chem. Commun. 2002, 67, 843-868. (b) Todd, L. J. In ComprehensiVe

Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W.,

Eds.; Pergamon Press: New York, 1982; Vol. 1, pp 543-553. (c) Todd,

L. J. In ComprehensiVe Organometallic Chemistry; Wilkinson, G., Stone,

F. G. A., Abel, E. W., Housecroft, C. E., Eds.; Pergamon Press: New York,

1995; Vol. 1, pp 257-273.

(2) (a) Shedlow, A. M.; Kadlecek, D. E.; Clapper, J. C.; Rathmill, S. E.; Carroll,

P. J.; Sneddon, L. G. J. Am. Chem. Soc. 2003, 125, 200-211. (b) Kadlecek,

D. E.; Shedlow, A. M.; Kang, S. O.; Carroll, P. J.; Sneddon, L. G. J. Am.

Chem. Soc. 2003, 125, 212-220.

Materials. Dicholorophenylphosphine, 1,8-bis(dimethylamino)naph-

thalene (Proton Sponge, PS), sulfur powder, and HCl‚Et₂O (1.0 M Et₂O

(3) Hong, D.; Rathmill, S. E.; Kadlecek, D. E.; Sneddon, L. G. Inorg. Chem.

2000, 39, 4996-4997.

(4) Shriver, D. F.; Drezdzon, M. A. Manipulation of Air-SensitiVe Compounds,

2nd ed.; Wiley: New York, 1986.

9

16058

J. AM. CHEM. SOC. 2003, 125, 16058-16073

10-Vertex Phosphadicarbaboranes

A R T I C L E S

1

solution) were purchased from Aldrich and used as received. Dichloro-

methylphosphine, CpCo(CO)₂, (Ph₃P)₂PtCl₂, PtBr₂, and PdBr₂were

purchased from Strem and used as received. Oil dispersed NaH was

purchased from Aldrich, washed with dry hexanes under an N₂

atmosphere, and dried under high vacuum prior to use. The 1,2-

dimethoxyethane (DME), toluene, and dichloromethane were dried by

passing through an activated alumina column prior to use. HPLC grade

hexanes and chloroform were purchased from Fisher and used as

1b: HRMS (CI neg) (m/e) calcd for ¹²C₃H₁₄¹¹B₇³¹P 158.1485, found

158.1481; IR (CH₂Cl₂, NaCl, cm^-1) 2900 (w), 2650 (s), 2610 (s), 2550

(s), 2420 (s), 2350 (m), 1470 (m), 1400 (s), 1270 (m), 1100 (m), 1050

(m), 1020 (m), 980 (s), 960 (m), 920 (w), 900 (s), 880 (m).

6-Ph-arachno-6,5,7-PC₂B₇H₁₁(2a). A 0.161 g (1.4 mmol) sample

of arachno-4,6-C₂B₇H₁₃was dissolved in 20 mL of DME under an N₂

atmosphere. Then, 0.614 g (2.9 mmol) of Proton Sponge was added to

the solution at 0 °C. Stirring was continued for 1 h at room temperature,

and then 0.19 mL of PhPCl₂was added dropwise via syringe at 0 °C.

Immediately, a white precipitate formed. The mixture was brought to

room temperature and stirred for 2 h. The reaction mixture was filtered

in the glovebag, resulting in a pale yellow solution. The filtrate was

removed to a 250 mL one-piece glass vessel with a sidearm, and the

solvent was then carefully removed in vacuo, to give a mixture of white

and yellow materials visibly separated inside of the glass vessel. The

yellow material was carefully removed using dichloromethane, which

gave white solid 2a (0.140 g, 0.64 mmol, 46%). If necessary, the product

was re-extracted with toluene or hexanes. For 2a: mp 74 °C. Anal.

Calcd for C₈H₁₆B₇P‚¹/₈CH₂Cl₂: C, 42.53; H, 7.14. Found: C, 42.51;

5

6

received. The arachno-4,5-C₂B₇H₁₃and arachno-4,6-C₂B₇H₁₃were

prepared according to literature procedures.

1

Physical Measurements. NMR data are presented in Table 1. H

NMR spectra at 500.4 MHz, ¹¹B NMR spectra at 160.5 MHz, and ¹³

C

NMR at 125.8 MHz were obtained on a Bruker AM-500 spectrometer

equipped with the appropriate decoupling accessories. ³¹P NMR spectra

at 145.8 MHz were obtained on a Bruker AM-360 spectrometer. All

¹¹B chemical shifts are referenced to external BF₃‚Et₂O (0.00 ppm),

with a negative sign indicating an upfield shift. All ¹H and ¹³C chemical

shifts were measured relative to internal residual protons or carbons in

the lock solvents and are referenced to Me₄Si (0.00 ppm). All ³¹P

chemical shifts are referenced to external 85% H₃PO₄(0.0 ppm) with

a negative sign indicating an upfield shift. Infrared spectra were obtained

on a Perkin-Elmer 1430 spectrophotometer. Elemental analyses were

performed at the University of Pennsylvania microanalysis facility. Mass

spectra were recorded on a Micromass Autospec spectrometer. Melting

points were obtained on a standard melting point apparatus and are

uncorrected.

1

H, 7.53. HRMS (CI neg) (m/e) calcd for ¹²C₈H₁₆¹¹B₇³¹P 220.1641,

found 220.1640; IR (CH₂Cl₂, NaCl, cm^-1) 3150 (w, br), 2500 (s), 1450

(w), 1150 (s), 1020 (s).

6-Me-arachno-6,5,7-PC₂B₇H₁₁(2b). A 0.45 g (4.0 mmol) sample

of arachno-4,6-C₂B₇H₁₃was dissolved in 40 mL of THF under an N₂

atmosphere. Then, 1.83 g (8.5 mmol) of Proton Sponge was added to

this solution. After the solution was stirred for 1 h at room temperature,

0.40 mL of MePCl₂was added dropwise via syringe at 0 °C.

Immediately, a white precipitate formed. The mixture was brought to

room temperature and stirred for 1 h. The crude product was then

vacuum distilled at 90 °C for 3 h, to give 0.31 g (2.0 mmol, 50%) of

a pale yellow oily 2b. For 2b: Anal. Calcd: C, 22.77; H, 8.86. Found:

6-Ph-arachno-6,8,9-PC₂B₇H₁₁(1a). A 0.36 g (3.2 mmol) sample

of arachno-4,5-C₂B₇H₁₃was dissolved in 20 mL of DME under an Ar

atmosphere. A 2.05 g (9.6 mmol, 3 equiv) sample of Proton Sponge

was then added while the solution was maintained at 0 °C. The mixture

was stirred for ∼1 h at room temperature. A 0.43 mL (3.2 mmol, 1

equiv) sample of PhPCl₂was then added via syringe at 0 °C, and the

contents were allowed to warm to room temperature. A ¹¹B NMR

spectrum taken at this point was consistent with the formation of the

6-Ph-arachno-6,5,10-PC₂B₇H₁₀^-anion (vide infra). Acidification with

excess HCl‚Et₂O (1.0 M, 12 mL) at -78 °C then generated 6-Ph-

arachno-6,8,9-PC₂B₇H₁₁(1a). The solution was filtered to remove the

precipitate in an Ar-filled glovebag. The filtrate was removed to the

vacuum line, and the volatiles were evaporated in vacuo. The product

was extracted with 30 mL of toluene from the residual materials. After

toluene removal, 0.48 g (2.2 mmol, 68%) of solid 1a was obtained. If

necessary, the product was purified by flash silica gel chromatography

using hexanes/dichloromethane (4:1, v/v) as the eluent. For 1a: mp

93 °C. Anal. Calcd: C, 43.90; H, 7.37. Found: C, 44.37; H, 7.07.

1

C, 23.44; H, 9.46. LRMS (m/e) calcd for ¹²C₃H₁₄¹¹B₇³¹P 158, found

158 (seven-boron isotope pattern); IR (NaCl, neat, cm^-1) 3050 (m),

2560 (s), 2050 (w), 1500 (w), 1425 (m), 1390 (m), 1280 (m), 1200

(w), 1140 (w), 1050 (s), 970 (m), 920 (s), 880 (m), 850 (s), 810 (m),

780 (m).

Reaction of 6-Ph-arachno-6,8,9-PC₂B₇H₁₁(1a) and BH₃. A 0.5

mL sample of a THF-d₈solution containing 56 mg (0.3 mmol) of 1a

was mixed with an excess amount of BH₃‚THF (0.5 mL, 1.0 M THF)

at room temperature. No reaction was observed by NMR spectroscopy.

Reaction of 6-Ph-arachno-6,5,7-PC₂B₇H₁₁(2a) and BH₃. A 2a

THF solution (A) was prepared by dissolving 0.174 g (0.79 mmol) of

2a in 3.00 mL of freshly distilled THF. A fresh BH₃‚THF (1.0 M THF)

solution (B) was mixed with A in ratios of 0.3/0.1 (S1), 0.2/0.2 (S2),

0.2/0.3 (S3), and 0.1/0.3 (S4) (A/B, mL/mL) under an inert atmosphere

at room temperature. Immediately, endo-6-H₃B-exo-6-Ph-arachno-6,5,7-

PC₂B₇H₁₁(3) was formed. In each case, the amounts of 3 (M) and free

2a (M) were calculated by peak integrations of the -21.6 ppm (for 3)

and the -33.0 ppm (for 2a) peaks in the ¹¹B NMR spectra. These results

are summarized in Table 2.

HRMS (CI neg) (m/e) calcd for ¹²C₈H₁₆¹¹B₇³¹P 220.1650, found

1

220.1654; IR (NaCl, cm^-1) 3040 (m), 2940 (s), 2910 (s), 2860 (m),

2540 (s), 2390 (w), 2310 (w), 1730 (m), 1570 (w), 1460 (m), 1420 (s),

1350 (m), 1260 (m), 1050 (m), 950 (m), 740 (m), 680 (m).

6-Me-arachno-6,8,9-PC₂B₇H₁₁(1b). A 0.39 g (3.5 mmol) sample

of arachno-4,5-C₂B₇H₁₃was dissolved in 15 mL of DME under an Ar

atmosphere. Then, 2.22 g (10.4 mmol, 3 equiv) of Proton Sponge was

added at 0 °C. The mixture was stirred for ∼30 min at room

temperature. A 0.31 mL (3.5 mmol, 1 equiv) sample of MePCl₂was

then added via syringe at 0 °C, and the contents were allowed to warm

to room temperature. After 13 h, excess HCl‚Et₂O (1.0 M, 12 mL)

was added at -78 °C. The solution was then filtered to remove the

precipitate in an Ar-filled glovebag. The filtrate was removed to the

vacuum line, and the volatiles were evaporated in vacuo. The product

was extracted with 30 mL of toluene from the residual materials. After

toluene removal, 0.27 g (1.7 mmol, 49%) of oily 1b was obtained. If

necessary, the product was re-extracted with toluene or hexanes. For

Reaction of 6-Ph-arachno-6,8,9-PC₂B₇H₁₁(1a) and Sulfur. A 0.5

mL aliquot of CHCl₃solution containing ∼5 mg (∼0.02 mmol) of 1a

was mixed with ∼5 mg (∼0.2 mmol) of S₈at room temperature. No

reaction was observed in 3 h by ¹¹B NMR spectroscopy.

Reaction of 6-Ph-arachno-6,5,7-PC₂B₇H₁₁(2a) and Sulfur: For-

mation of endo-6-S-exo-6-Ph-arachno-6,5,7-PC₂B₇H₁₁(4). A 0.219

g (1.0 mmol) sample of 2a was reacted with 0.048 g (1.5 mmol) of

sulfur powder in 17 mL of DME at room temperature. The solution

was stirred at room temperature for 22 h. After the mixture was filtered,

the volatiles were removed in vacuo to give 0.25 g (>90% yield) of 4.

For 4: HRMS (m/e) calcd for ¹²C₈H₁₆¹¹B₇³¹P³²S 252.1362, found

252.1348; IR (CH₂Cl₂, NaCl, cm^-1) 3150 (m, br), 2500 (s), 1950 (w,

br), 1450 (w), 1440 (m, br), 1250 (m, br), 1090 (m, br), 910 (m).

1

(5) (a) Herma´nek, S.; Jel´ınek, T.; Plesek, J.; St´ıbr, B.; Fusek, J. J. Chem. Soc.,

Chem. Commun. 1987, 927-928. (b) St´ıbr, B.; Plesek, J.; Herma´nek, S.

Inorg. Synth. 1983, 22, 237-239.

(6) Garrett, P. M.; George, T. A.; Hawthorne, M. F. Inorg. Chem. 1969, 8,

2008-2009.

Reaction of 6-Ph-arachno-6,8,9-PC₂B₇H₁₁(1a) and Peroxide. A

0.5 mL sample of a THF-d₈solution containing ∼5 mg (∼0.02 mmol)

9

J. AM. CHEM. SOC. VOL. 125, NO. 51, 2003 16059

A R T I C L E S

Hong et al.

Table 1. NMR Data^a

compounds

nucleus

¹¹B

δ (multiplicity, assignment, J (Hz))

6-Ph-arachno-6,8,9-PC₂B₇H₁₁(1a)^b

-5.5 (d, B2,4; J_BH163), -12.0 (d, B5; J_BH163, J_BHB24), -13.6 (d, B7; J_BH147),

-19.7 (d, B10; J_BH153, J_BHB43), -28.5 (d, B1; J_BH154), -48.4 (d, B3; J_BH159)

7.47, 7.16, 6.93 (m, 5, phenyl), 3.26 (1, BH), 3.13 (1, BH), 2.73 (1, BH), 2.39 (1, BH), 2.25 (2, BH),

1.47 (1, cage-CH), 1.08 (1, BH), 0.46 (1, cage-CH), -0.72 (1, cage-CH), -2.01 (1, BHB)

131.5 (J_CP13), 128.6, 128.0, 24.4 (C8, J_CB47), 13.2 (C9; t of d, J_CP49, J_CHendo∼160, J_CHexo∼160)

-163.5 (P6)

¹H{¹¹B}

¹³C

³¹P

Ia^c

¹¹B (calc) -4.2 (B4), -4.6 (B2), -10.8 (B5), -14.6 (B7), -22.3 (B10), -30.5 (B1), -49.5 (B3)

¹³C(calc) 132.3-142.6 (phenyl), 30.5 (C8), 14.3 (C9)

³¹P(calc)

¹¹B

-140.1 (P6)

6-Ph-arachno-6,8,9-PC₂B₇H₁₀^-(1a^-)^d

-2.7 (d, B2; J_BH∼183), -4.1 (d, B4; J_BH∼155), -17.3 (d, B5,7; J_BH141),

-18.8 (d, B10; J_BH∼136), -41.5 (d, B1,3; J_BH138)

Ia^{- c}

Ib^{- c}

¹¹B (calc) -0.7 (B2), -4.9 (B4), -10.1 (B5), -14.5 (B7), -20.2 (B10), -42.2 (B3), -43.5 (B1)

¹¹B (calc) 0.1 (B2), -1.3 (B4), -16.3 (B7), -16.7 (B5), -19.4 (B10), -42.3 (B1), -42.8 (B1)

6-Ph-arachno-6,8,9-PC₂B₇H₉^2-(1a^2-

)

¹¹B

¹¹B (calc) 6.1 (B4), -14.1 (B10), -38.7 (B1), -41.1 (B3), -42.6 (B7), -50.3 (B2), -51.2 (B5)

1.2 (1), -18.3 (1), -41.3 (1), -42.9 (2), -44.2 (2)

Ib^{2- c}

6-Me-arachno-6,8,9-PC₂B₇H₁₁(1b)^b

¹¹B

-6.0 (d, B2;J_BH157), -6.7 (d, B4; J_BH> 120, overlapped), -11.1 (d, B5; J_BH169),

-12.2 (d, B7; J_BH148), -19.9 (d, B10; J_BH146), -28.7 (d, B1; J_BH167), -48.8 (d, B3; J_BH150)

2.95 (1, BH), 2.79 (1, BH), 2.66 (1, BH), 2.20 (2, BH), 2.09 (1, BH), 1.39 (1, cage-CH),

1.03 (1, BH), 0.75 (3, CH₃), 0.38 (1, cage-CH), -0.90 (1, cage-CH), -2.15 (1, BHB)

25.5 (C8, J_CB63), 12.8 (C9, J_CP43), 7.3 (CH₃, J_CP19)

¹H{¹¹B}

¹³C{¹H}

³¹P

-184.3 (P6)

Ib^c

¹¹B (calc) -4.8 (B2), -6.6 (B4), -10.7 (B5), -11.0 (B7), -22.1 (B10), -30.3 (B1), -50.3 (B3)

¹³C(calc) 31.5 (C8), 14.4 (C9), 11.4 (C11)

³¹P(calc)

¹¹B^b

-169.5 (P6)

6-Ph-arachno-6,5,7-PC₂B₇H₁₁(2a)

-1.6 (d, B4; J_BH178), -7.4 (d, B8,10; J_BH149), -33.0 (d, B1,3,9; J_BH167), -41.6 (d, B2; J_BH149)

¹H{¹¹B}^b7.35-6.76 (5, phenyl), 2.95 (3, BH), 2.06 (2, BH), 1.97 (1, BH), 0.82 (s, 2H, cage-CH),

0.80 (1, BH), -2.98 (2, BHB)

¹³C{¹H}^e,f130.2-127.9 (phenyl), 3.2 (C5,7J_CP55)

³¹P^b

-72.5 (P6)

Va^c

¹¹B (calc) -2.3 (B4), -8.9 (B8,10), -33.6 (B5,7), -36.7 (B9), -45.7 (B2)

¹³C (calc) 146.9-132.8 (phenyl), 5.3 (C5,7)

³¹P (calc) -49.9 (P6)

6-Me-arachno-6,5,7-PC₂B₇H₁₁(2b)

¹¹B^b

-1.9 (d, B4;J_BH176), -6.9 (d, B8,10; J_BH149), -33.5 (d, B1,3,9; J_BH167), -41.9 (d, B2; J_BH148)

3.09 (1, BH), 2.56 (2, BH), 1.59 (2, BH), 1.56 (d, 3, CH₃; J_PH11), 1.37 (1, BH), 1.06 (2, cage-CH),

0.07 (1, BH), -3.23 (2, BHB)

¹H{¹¹B}^f

¹³C{¹H}^e,f18.1 (CH₃; J_CP43), 2.4 (C5,7, J_CP52)

³¹P^b

-65.2 (P6)

Vb^c

¹¹B (calc) -3.8 (B4), -8.9 (B8,10), -34.6 (B1,3), -36.5 (B9), -46.0 (B2)

¹³C(calc) 22.8 (C11), 8.0 (C5,7)

³¹P(calc)

-55.0 (P6)

-

6-Ph-arachno-6,5,10-PC₂B₇H₁₀

¹¹B{¹H}^g9.7, 1.6, -16.6, -23.7, -28.6, -41.6, -43.9

¹¹B (calc) 11.4 (B8), 0.0 (B4), -15.0 (B2), -20.4 (B7), -34.4 (B9), -36.7 (B3), -46.8 (B1)

II^-

endo-6-BH₃-exo-6-Ph-arachno-6,5,7-

PC₂B₇H₁₁(3)^d,g

¹¹B

4.4 (B4), -6.3 (B8,10), -21.6 (B1,3,4), -39.9 (BH₃), -43.7 (B2)

VI^c

¹¹B (calc) 2.5 (B4), -8.7 (B10), -8.9 (B8), -22.3 (B3), -23.0 (B1), -24.9 (B9), -44.0 (BH₃), -47.1 (B2)

endo-6-S-exo-6-Ph-arachno-6,5,7-

PC₂B₇H₁₁(4)^b

¹¹B

0.3 (d, B4; J_BH178), -7.4 (d, B8,10; J_BH150), -14.3 (d, B1,3; J_BH163), -16.5 (d, B9; J_BH151),

-44.9 (d, B2; J_BH150)

127.9-133.1 (phenyl), 15.0 (C7,8)

5.6 (P6)

¹³C{¹H}

³¹P

VII^c

¹¹B (calc) 0.0 (B4), -8.1 (B8,10), -13.0 (B1,3), -18.5 (B9), -46.7 (B2)

¹³C(calc) 131.5-150.2 (phenyl), 21.8 (C7,8)

³¹P(calc)

¹¹B

22.4 (P6)

endo-6-O-exo-6-Ph-arachno-6,5,7-

PC₂B₇H₁₁(5)^b

-0.6 (d, B4; J_BH175), -4.7 (d, B8,10; J_BH144), -12.0 (d, B1,3; J_BH163), -19.5 (d, B9; J_BH154),

-46.1 (d, B2; J_BH146)

³¹P

-18.7 (P6)

VIII^c

¹¹B (calc) -2.1 (B4), -7.1 (B8,10), -12.3 (B1,3), -21.6 (B9), -49.2 (B2)

³¹P(calc)

-18.9 (P6)

µ

_7,8-{HS(Ph)P}-hypho-7,8-C₂B₆H₁₁(6)^{b 11}B

-7.8 (d, B4,6, J_BH135), -25.3 (d, B5, J_BH144), -28.4 (d, J_BH, B2,3, 132), -54.0 (d, J_BH, B1, 141)

8.09-7.59 (phenyl), 2.37 (2, BH), 2.30 (1, BH), 1.79 (2, BH), 1.55 (SH), 1.30 (2, cage-CH),

-1.05 (1, BH), -1.49 (d, BHB, ³J_PH35), -1.83 (2, BHB)

133.8-129.2 (phenyl), 2.4 (C7,8)

¹H{¹¹B}

¹³C{¹H}

³¹P

94.4 (P9)

IX^c

¹¹B(calc) -9.3 (B4,6), -29.1 (B5), -30.1 (B2,3), -58.9 (B1)

¹³C(calc) 137.9-133.3 (phenyl), 13.7 (C7,8)

³¹P(calc)

94.0 (P9)

9

16060 J. AM. CHEM. SOC. VOL. 125, NO. 51, 2003

10-Vertex Phosphadicarbaboranes

A R T I C L E S

Table 1 (Continued)

compounds

nucleus

¹¹B

δ (multiplicity, assignment, J (Hz))

cis-(η¹-[6-Ph-arachno-6,5,7-PC₂B₇H₁₁])₂-

PtBr₂(7)^f

9.8 (d, J_BH139), 2.4 (d, J_BH150), -4.7 (br), -20.2 (br), -22.3 (br), -34.2 (br),

-42.5 (d, J_BH151)

¹H{¹¹B} 7.96-7.29 (m, phenyl), 3.39 (BH), 2.99 (BH), 2.75 (BH), 2.49 (BH), 2.14 (BH), 1.56 (BH),

1.43 (cage-CH), 1.31 (BH), 0.93 (cage-CH), -1.45 (BHB), -1.93 (BHB)

¹³C{¹H} 132.0-128.9 (phenyl), 4.6 (cage C)

³¹P

¹¹B

-5.2 (J_Pt-P3010); (-8.2, J_Pt-P3010)^h

trans-(η¹-[6-Ph-arachno-

1.7 (d, J_BH140), -4.1 (br), -20.7 (br), -23.8 (br) -23.0 (br), -41.9 (d, J_BH148)

6,5,7-PC₂B₇H₁₁])₂PdBr₂(8)^f

8-Ph-7-(Ph₃P)₂-nido-

¹¹B

-6.1 (d, J_BH∼100), -12.6 (d, J_BH∼109), -15.6 (d, J_BH143), -17.7 (br), -21.8 (br),

-37.2 (d, J_BH140)

7,8,10,11-PtPC₂B₇H₉(9)^f

¹H{¹¹B} 7.59-6.98 (phenyl), 3.94 (1, BH), 3.10 (1, CH), 2.47 (1, BH), 2.17 (1, BH), 1.81 (1, BH),

1.67 (1, CH), 1.54 (1, BH), 0.71 (1, BH)

¹³C{¹H} 134.4-127.7 (phenyl), 54.2 (cage C), 43.6 (cage C)

³¹P

¹¹B

23.0 (J_Pt-P3596), 14.8 (J_Pt-P4218, J_PP18), 14.3 (J_Pt-P4236, J_PP17)

7-Ph-11-(η⁵-C₅H₅)-nido-

-3.4 (d, J_BH152), -7.1 (d, J_BH149), -9.0 (d, J_BH152), -15.4 (d, J_BH151, J_BP61),

-17.2 (d, J_BH151), -19.2 (d, J_BH169), -35.6 (J_BH148)

11,7,9,10-CoPC₂B₇H₉(10)^f

¹H{¹¹B} 7.64-7.42 (5, phenyl), 5.16 (5, C₅H₅), 3.68 (1, CH), 3.34 (1, BH), 3.07 (1, BH),

2.79 (1, BH), 2.40 (2, CH, BH), 1.73 (2, BH), 1.14 (1, BH)

¹³C{¹H} 133.5-129.3 (phenyl), 86.7 (C₅H₅), 59.2, 47.8 (J_CP34)

³¹P

-31.5

commo-Ni-(7-Ni-8′-Ph-8′,10′,11′-nido-PC₂B₇H₉)- ¹¹B

-3.3 (d, J_BH158), -5.5 (d, J_BH146), -12.1 (d, J_BH142), -19.4 (d, J_BH∼126, overlapped),

(7-Ni-8-Ph-8,10,11-nido-PC₂B₇H₉) (11)^f

-20.2 (d, J_BH∼158, overlapped), -30.6 (d, J_BH150)

-33.1

³¹P

^{a 1}H NMR (500.4 MHz), ¹¹B NMR (160.5 MHz), ¹³C NMR (125.8 MHz), ³¹P NMR (145.8 MHz). ^bC₆D₆. ^cDFT/GIAO (B3LYP/6-311G*). ^dTHF-d₈.

^eMeasured at -83 °C. ^fCD₂Cl₂. ^{g 11}B NMR (64.2 MHz). ^hSee text.

Table 2. Summary of ¹¹B NMR Integration Data for the Reaction

TLC (pentane/CH₂Cl₂) 2:1, v/v). For 7: mp 198-200 °C. Anal.

of 2a with BH₃‚THF

Calcd: C, 24.25; H, 4.07. Found: C, 23.30; H, 4.16. IR (CH₂Cl₂sol,

NaCl, cm^-1) 3150 (w), 2550 (s), 1480 (s), 1320 (s), 1150 (s), 1050 (s),

S1

S2

S3

S4

950 (m), 870 (s).

[3] (-21.6 ppm)

[2a] (-33.0 ppm)

0.096

0.100

6.1

0.082

0.050

3.9

0.071

0.035

3.8

0.045

0.021

3.0

trans-(η¹-[6-Ph-arachno-6,5,7-PC₂B₇H₁₁])₂PdBr₂(8). A 0.40 g

(1.45 mmol) sample of 2a was dissolved in 15 mL of DME at room

temperature. Then, 0.116 g (0.62 mmol) of PdBr₂was added. The

reaction mixture was stirred at room temperature for 21 h. Workup of

the reaction as described above yielded a mixture containing, according

to the ³¹P and ¹H NMR spectra, at least two products that were

inseparable by silica gel column chromatography. Crystals of 8 (>10

mg) trans-(η¹-[6-Ph-arachno-6,5,7-PC₂B₇H₁₁])₂PdBr₂were obtained by

crystallization from this mixture, but it was not possible to isolate other

products in sufficient quantities for characterization. For 8: Anal. Calcd

for C₁₆H₃₂B₁₄Br₂P₂Pd‚¹/₆C₆H₁₄: C, 28.4; H, 4.81. Found: C, 28.4; H,

5.03.

a

K_eq

∆G (kcal/mol)

-4.5

-3.4

-3.3

-2.7

^aK_eq) [3]_eq/[2a]_eq[BH₃‚THF]_eq.

of 1a was mixed with ∼0.05 mL of H₂O₂at room temperature.

Decomposition of 1a to borate was observed by NMR spectroscopy.

Reaction of 6-Ph-arachno-6,5,7-PC₂B₇H₁₁(2a) and Peroxide:

Formation of endo-6-O-exo-6-Ph-arachno-6,5,7-PC₂B₇H₁₁(5). A

sample (∼10 mg, ∼0.05 mmol) of 2a was dissolved in 0.5 mL of THF-

d₈containing a small amount of peroxide at room temperature.

Immediately, gas was generated, and ¹¹B and ³¹P NMR analyses

indicated the formation of endo-6-O-exo-6-Ph-arachno-6,5,7-PC₂B₇H₁₁

(5). 5 proved to be too unstable to be isolated in a pure form. For 5:

8-Ph-7-(Ph₃P)₂-nido-7,8,10,11-PtPC₂B₇H₉(9). A 0.26 g (1.2 mmol)

sample of 1a was dissolved in 10 mL of DME under an inert

atmosphere. A 1.8 mL aliquot of MeLi (1.4 M Et₂O solution) was added

dropwise at -78 °C. After 6-Ph-6,8,9-PC₂B₇H₉^2-(1a^2-) formation was

observed by ¹¹B NMR spectroscopy, 0.95 g (1.2 mmol) of (Ph₃P)₂-

PtCl₂was added to this reaction mixture at -78 °C. The mixture was

stirred at room temperature for 18 h. After the mixture was filtered,

the volatiles were removed in vacuo. The resulting dark brown species

was chromatographed on preparative TLC plates (hexanes/CH₂Cl₂)

3:2, v/v) to give 0.38 g (0.41 mmol, 34%) of yellow 9. For 9: mp

148-150 °C. Anal. Calcd: C, 56.43; H, 4.74. Found: C, 55.60; H,

4.66. IR (CH₂Cl₂sol, NaCl, cm^-1) 2890 (s), 2800 (m), 2530 (s), 1460

(s), 1420 (s), 1180 (m), 1110 (m), 1090 (m), 680 (s).

7-Ph-11-(η⁵-C₅H₅)-nido-11,7,9,10-CoPC₂B₇H₉(10). A 0.48 g (2.2

mmol) sample of 1a was dissolved in 20 mL of DME at room

temperature under an inert atmosphere. A 0.44 g (2.4 mmol) sample

of CpCo(CO)₂was then added dropwise to this solution at room

temperature. The reaction mixture was next heated at 70 °C under an

inert atmosphere for 66 h. After the solution was filtered, the solvent

was vacuum evaporated yielding a deep brown crude product (0.69 g,

2.0 mmol). After this crude product was purified by preparative TLC

(hexanes/CH₂Cl₂) 4:1, v/v), 0.11 g (0.33 mmol, 15%) of dark red 10

HRMS (CI neg) (m/e) calcd for ¹²C₈H₁₆¹¹B₇³¹P¹⁶O, 236.1590, found

236.1600.

1

Reaction of 6-Ph-arachno-6,5,7-PC₂B₇H₁₁(2a) with Excess Sul-

fur: Synthesis of µ_7,8-{HS(Ph)P}-hypho-7,8-C₂B₆H₁₁(6). A 0.28 g

(1.3 mmol) sample of 2a was reacted with 0.3 g (9.4 mmol, excess) of

sulfur powder in 10 mL of DME at room temperature. The solution

was stirred at room temperature for 8 h. After the mixture was filtered,

the volatiles were removed in vacuo. The residue was purified by

preparatory TLC (hexanes/CH₂Cl₂) 1:1, v/v) to give 0.16 g (0.67

mmol, 52%) of yellow liquid 6. For 6: HRMS (CI neg) (m/e) calcd

for ¹²C₈H₁₇¹¹B₆³¹P³²S 242.1347, found 242.1348; IR (CH₂Cl₂sol, NaCl,

1

cm^-1) 3150 (m), 2910 (m), 2540 (s), 1980 (w), 1850 (w), 1590 (w),

1480 (m), 1430 (s), 1310 (m), 1170 (m), 1100 (s), 1050 (s), 960 (m),

910 (s).

cis-(η¹-[6-Ph-arachno-6,5,7-PC₂B₇H₁₁])₂PtBr₂(7). A 0.16 g (0.73

mmol) sample of 2a was dissolved in 5 mL of DME at room

temperature. Then 0.114 g (0.32 mmol) of PtBr₂was added. The

reaction mixture was stirred at room temperature for 2.5 h. After the

mixture was filtered, the solvent was removed in vacuo. A 0.079 g

(0.10 mmol, 31%) sample of yellow 7 was obtained after preparative

9

J. AM. CHEM. SOC. VOL. 125, NO. 51, 2003 16061

A R T I C L E S

Hong et al.

was obtained. For 10: mp 190-192 °C. Anal. Calcd: C, 45.81; H,

(using the standard basis sets included) on a (4)-processor Origin 200

computer running IRIX 6.5.6. A vibrational frequency analysis was

carried out on each optimized geometry at the B3LYP/6-311G* level

with a true minimum found for each structure (i.e., possessing no

imaginary frequencies). The NMR chemical shifts were calculated at

the B3LYP/6-311G* level using the GIAO option within Gaussian 94/

98. The ¹¹B NMR GIAO chemical shifts are referenced to BF₃‚Et₂O

using an absolute shielding constant of 102.24.¹⁷The ¹³C NMR GIAO

chemical shifts are referenced to TMS using an absolute shielding

constant of 184.38 and are corrected as described previously.^16,17The

³¹P NMR GIAO chemical shifts were first referenced to PH₃using an

absolute shielding constant of 557.2396 ppm and then converted to

the H₃PO₄reference scale using the experimental value of δ(PH₃) )

-240 ppm.^16b

5.62. Found: C, 45.10; H, 5.72. HRMS (CI neg) (m/e) calcd for

12

C

13

¹H₁₉¹¹B₇³¹P⁵⁹Co 342.1208, found 342.1224. IR (CH₂Cl₂sol, NaCl,

cm^-1) 3080 (w), 2550 (s), 1460 (m), 1420 (m), 1400 (m), 1090 (s),

1050 (m), 1000 (s), 810 (s).

commo-Ni-(7-Ni-8′-Ph-nido-8′,10′,11′-PC₂B₇H₉)(7-Ni-8-Ph-nido-

8,10,11-PC₂B₇H₉) (11). A 0.295 g (1.35 mmol) sample of 1a was

dissolved in 15 mL of DME under an inert atmosphere. A 1.0 mL

aliquot of MeLi (1.4 M Et₂O solution) was introduced dropwise at -78

°C. To this mixture, 0.148 g (0.68 mmol) of NiBr₂was added, resulting

in an immediate color change. The reaction mixture was stirred at room

temperature for 24 h. After the precipitate was filtered off, the solvent

was removed in vacuo. After preparative TLC (hexanes/CH₂Cl₂) 4:1,

v/v), 0.034 g (R_f) 0.45, 0.069 mmol, 10%) of 11 were obtained as a

yellow solid. For 11, Anal. Calcd: C, 39.03; H, 5.73. Found: C, 39.23;

12

11

¹H₂₈³¹P₂Ni 494.2322, found

Results and Discussion

H, 5.61. HRMS (m/e) calcd for

C B

16 14

494.2308. An additional product (TLC, R_f) 0.4) of the reaction, which

according to its mass spectrum is an isomer of 11, could not be isolated

sufficiently pure for complete characterization.

Syntheses and Structural Characterizations of 6-R-arachno-

6,8,9-PC₂B₇H₁₁(1) and 6-R-arachno-6,5,7-PC₂B₇H₁₁(2). The

10-vertex phosphadicarbaboranes 6-R-arachno-6,8,9-PC₂B₇H₁₁

(1a and 1b) and 6-R-arachno-6,5,7-PC₂B₇H₁₁(2a and 2b) were

respectively synthesized by reactions of the isomeric adjacent-

carbon arachno-4,5-C₂B₇H₁₃⁵and nonadjacent-carbon arachno-

4,6-C₂B₇H₁₃carboranes with RPCl₂(R ) Ph, 1a and 2a;

R ) Me, 1b and 2b) in the presence of Proton Sponge (eqs 1

and 2).

Collection and Reduction of the Data. X-ray intensity data for 1a

(Penn 3176), 2a (Penn 3184), 7 (Penn 3183), 8 (Penn 3198), 9 (Penn

3182), 10 (Penn 3171), and 11 (Penn 3180) were collected on either a

Rigaku R-AXIS IIc or Mercury CCD (for 8) area detector employing

graphite-monochromated Mo KR radiation (λ ) 0.71069 Å). Indexing

was performed from a series of 1° oscillation images, and a crystal-

to-detector distance of 82 mm was employed, except for 8 where a

series of four 0.5° oscillation images and a 35 mm distance were used.

Oscillation images were processed to produce a listing of unaveraged

F²and σ(F²) values which were then passed to the teXsan⁷program

package for further processing and structure solution on Silicon

Graphics Indigo R4000 or O2 computers. The intensity data were

corrected for Lorentz and polarization effects. Absorption correction

data for 8 and 9 were made using REQAB⁸(minimum and maximum

transmission 0.599, 1.000 for 8; 0.748, 1.000 for 9). 8 was found to be

twinned by a rotation of 180° about the normal to 001, and twin

indexing and processing of twinned data were performed by the

TwinSolve⁹module of CrystalClear.

Solution and Refinement of the Structure. The structures were

solved by direct methods (SIR92)¹⁰except for 9 which was solved by

the Patterson method (DIRDIF).¹¹Refinements were by full-matrix least

squares based on F²using SHELXL-93.¹²All reflections were used

during refinement (F²’s that were experimentally negative were replaced

by F²) 0). Crystal and refinement data are given in Table 3. Refined

positional parameters, refined thermal parameters, bond distances, and

angles are given in the Supporting Information. Non-hydrogen atoms

were refined anisotropically. All cage hydrogen atoms were refined

isotropically. All hydrogen atoms of 1a and 11 were refined isotropi-

cally. Cage hydrogen atoms of 7 and all the hydrogen atoms of 8 were

included as constant contribution to the structure and were not refined.

All other hydrogen atoms were refined using a “riding” model. In 10,

the cyclopentadienyl ligand is rotationally disordered through two

approximately equally populated orientations. The multiplicities of the

two orientations refined to 0.49(3) and 0.51(3).

6

(1) 3 PS

(2) xs HCl

arachno-4,5-C₂B₇H₁₃+ RPCl₂

8

-3 PSH⁺Cl^-

6-R-arachno-6,8,9-PC₂B₇H₁₁

(R ) Ph, 1a; Me, 1b)

2 PS

(1)

(2)

arachno-4,6-C₂B₇H₁₃+ RPCl₂

8

-2 PSH⁺Cl^-

6-R-arachno-6,5,7-PC₂B₇H₁₁

(R ) Ph, 2a; Me, 2b)

The products were isolated as air- and moisture-sensitive

materials with typical yields ranging from 49 to 68%. The

compositions of these compounds were confirmed by elemental

analyses and/or high-resolution mass spectrometry.

(13) Yang, X.; Jiao, H.; Schleyer, P. v. R. Inorg. Chem. 1997, 36, 4897-4899

and references therein.

(14) Frisch, M, J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.; Johnson, B.

G.; Robb, M. A.; Cheeseman, J. R.; Keith, T.; Peterson, G. A.; Montgomery,

J. A.; Raghavachari, K.; Al-Laham, M. A.; Zakrzewski, V. G.; Ortiz, J.

V.; Foresman, J. B.; Cioslowski, J.; Stefanov, B. B.; Nanayakkara, A.;

Challacombe, M.; Peng, C. Y.; Ayala, P. Y.; Chen, W.; Wong, M. W.;

Andres, J. L.; Replogle, E. S.; Gomperts, R.; Martin, R. L.; Fox, D. J.;

Binkley, J. S.; Defrees, D. J.; Baker, J.; Stewart, J. P.; Head-Gordon, M.;

Gonzalez, C.; Pople, J. A. Gaussian 94, revision E.2; Gaussian, Inc.:

Pittsburgh, PA, 1995.

Computational Studies. The DFT/GIAO/NMR method,¹³using

either the Gaussian 94¹⁴or 98¹⁵program, was used in a manner similar

to that previously described.^2,16,17The geometries were fully optimized

at the B3LYP/6-311G* level within the specified symmetry constraints

(15) Frisch, M, J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M.

A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.; Stratmann,

R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin,

K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi,

R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.;

Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.;

Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz,

J. V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.;

Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,

M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;

Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-

Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 98, revision A.9;

Gaussian, Inc.: Pittsburgh, PA, 1998.

(7) Crystal Structure Analysis Package, Molecular Structure Corporation 1985,

1992.

(8) REQAB: Jacobsen, R. A. Private communication, 1994.

(9) TwinSolve: Christer Swensson, MaxLab, Lund, Sweden, private com-

munication.

(10) SIR92: Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, M.; Giaco-

vazzo, C.; Guagliardi, A.; Polidoro, G. J. Appl. Crystallogr. 1994, 27, 435.

(11) Parthasrathi, V.; Beurskens, P. T.; Slot, H. J. B. Acta Crystallogr. 1983,

A39, 860-864.

(12) Sheldrick, G. M. SHELXL-93: Program for the Refinement of Crystal

Structures; University of Go¨ttingen: Germany, 1993.

(16) (a) Bausch, J. W.; Rizzo, R. C.; Sneddon, L. G.; Wille, A. E.; Williams,

R. E. Inorg. Chem. 1996, 35, 131-135. (b) Shedlow, A. M.; Sneddon, L.

G. Inorg. Chem. 1998, 37, 5269-5277. (c) Kadlecek, D. E.; Carroll, P. J.;

Sneddon, L. G. J. Am. Chem. Soc. 2000, 122, 10868-10877.

(17) Tebben, A. J. M.S. Thesis, Villanova University, 1997.

9

16062 J. AM. CHEM. SOC. VOL. 125, NO. 51, 2003

10-Vertex Phosphadicarbaboranes

A R T I C L E S

Table 3. Crystallographic Data Collection and Structure Refinement Information

1a

2a

7

8

PdC₁₆B₁₄H₃₂P₂Br₂

703.92

empirical formula

formula weight

crystal class

space group

Z

a, Å

b, Å

C₈B₇H₁₆P

Pt₂C₃₅B₂₈H₆₇P₄Br₄

1624.27

218.85

orthorhombic

Pbca

8

12.5579(1)

15.6169(2)

12.6071(1)

triclinic

P1h

4

triclinic

P1h

2

15.5744(3)

18.3360(3)

11.3806(2)

102.285(1)

109.983(1)

78.590(1)

monoclinic

P2₁/n (#14)

2

8.6301(7)

8.5428(7)

19.166(2)

11.0280(2)

11.0406(3)

10.7862(2)

107.620(1)

91.338(2)

95.646(1)

1243.64(5)

1.80

c, Å

R, deg

â, deg

92.095(3)

γ, deg

V, Å³

2472.45(4)

1.81

2956.54(9)

75.68

1412.1(2)

36.08

µ, cm^-1

crystal size, mm³

0.32 × 0.30 × 0.26

0.23 × 0.15 × 0.14

0.26 × 0.20 × 0.06

0.32 × 0.12 × 0.06

D

_calc, g/cm³

1.176

1.169

1.825

1.656

F(000)

2θ angle, deg

hkl collected

912

456

1546

688

5.22-50.68

-15 e h e 15

-18 e k e18

-15 e l e 15

13 524

2257 (R_int) 0.0393)

2129 (F > 4σ)

2257

5.08-50.7

-13 e h e 13

-13 e k e 13

-12 e l e 12

10 088

4190 (R_int) 0.0296)

3781 (F > 4σ)

4190

5.04-54.96

-20 e h e 20

-23 e k e 23

-14 e l e 14

30 754

12 376 (R_int) 0.0515)

11 206 (F > 4σ)

12 376

5.1-55.1

-10 e h e 10

-10 e k e 10

-21 e l e 23

8710

8221 (F > 4σ)

8710

no. of reflns measured

no. of unique reflns

no. of observed reflns

no. of reflns used

in refinement

no. parameters

213

417

659

161

R^aindices (F > 4σ)

R₁) 0.0685

wR₂) 0.1519

R₁) 0.0740

wR₂) 0.1548

1.316

R₁) 0.0485

wR₂) 0.1080

R₁) 0.0553

wR₂) 0.1123

1.102

R₁) 0.0550

wR₂) 0.1407

R₁) 0.0614

wR₂) 0.1476

1.130

R₁) 0.0852

wR₂) 0.2261

R₁) 0.0898

wR₂) 0.2320

1.217

R^aindices (all data)

GOF ^b

final difference peaks, e/Å³

+0.200, -0.215

+0.186, -0.296

+1.912, -2.278

+4.315, -1.811

9

10

11

empirical formula

formula weight

crystal class

space group

Z

a, Å

b, Å

PtC₅₃B₇H₅₃P₃

1053.62

triclinic

P1h

2

12.9520(3)

18.3819(4)

11.2556(3)

92.702(2)

114.316(1)

81.214(2)

2413.01(10)

30.43

CoC₁₃B₇H₁₉P

340.85

orthorhombic

Pbcn

NiC₁₆B₁₄H₂₈P₂

492.37

monoclinic

P2₁/c

4

13.0466(2)

10.5141(2)

17.7492(2)

8

23.4553(2)

7.9746(1)

17.2053(2)

c, Å

R, deg

â, deg

90.271(1)

γ, deg

V, Å³

3218.19(6)

11.50

2434.69(7)

9.34

µ, cm^-1

crystal size, mm³

0.32 × 0.22 × 0.07

0.32 × 0.25 × 0.08

0.42 × 0.26 × 0.24

D

_calc, g/cm³

1.450

1.407

1.343

F(000)

2θ angle, deg

hkl collected

1058

1392

1008

5.26-54.96

-16 e h e 15

-23 e k e 23

-14 e l e 14

25 744

10 157 (R_int) 0.0382)

9610 (F > 4σ)

10 157

5.04-50.7

-25 e h e 28

-9 e k e 9

-20 e l e 18

18 897

2940 (R_int) 0.0352)

2829 (F > 4σ)

2940

5.48-50.68

-15 e h e 15

-12 e k e 12

-21 e l e 20

19 738

4230 (R_int) 0.0284)

4080 (F > 4σ)

4230

no. of reflns measured

no. of unique reflns

no. of observed reflns

no. of reflns used

in refinement

no. parameters

614

266

410

R^aindices (F > 4σ)

R₁) 0.0499

wR₂) 0.1372

R₁) 0.0527

wR₂) 0.1425

1.113

R₁) 0.0373

wR₂) 0.0873

R₁) 0.0398

wR₂) 0.0889

1.180

R₁) 0.0361

wR₂) 0.0897

R₁) 0.0379

wR₂) 0.0909

1.090

R^aindices (all data)

GOF ^b

final difference peaks, e/Å³

+1.956, -2.061

+0.302, -0.308

+0.255, -0.462

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

.

^bGOF ) {∑w(F_o- F_c)²/(n - p)}^1/2, where n ) no. of reflections and p ) no. of

2

parameters refined.

If, as in other phosphapolyboranes,^1,18the RP unit is a

four-electron donor to the cage, then 1 and 2 each have 26

skeletal electrons and should adopt a 10-vertex arachno-

geometry (n + 3 skeletal electron pairs),¹⁹based on an icosa-

hedron minus two vertexes. As diagramed in Figure 1, depend-

ing on how insertion of the RP unit into the skeletal framework

of the arachno-4,5-C₂B₇H₁₃and arachno-4,6-C₂B₇H₁₃occurs,

(18) (a) Getman, T. D.; Deng, H.-B.; Hsu, L.-Y.; Shore, S. G. Inorg. Chem.

1989, 28, 3612-3616. (b) Jutzi, P.; Wegener, D.; Hursthouse, M. J.

Organomet. Chem. 1991, 418, 277-289.

9

J. AM. CHEM. SOC. VOL. 125, NO. 51, 2003 16063

A R T I C L E S

Hong et al.

Figure 2. DFT calculated optimized geometries and relative energies for

isomeric 6-R-arachno-PC₂B₇H₁₁structures.

framework.^16a,20Only slightly higher in energy (0.2 kcal/mol)

is the 6-Me-arachno-6,7,9-PC₂B₇H₁₁isomer (IV), which also

has the phosphorus and one carbon located in the low-coordinate

6- and 9-position but has the second carbon in the facial

7-position adjacent to the phosphorus rather than the carbon-

adjacent 8-position in I. In the 6-Me-arachno-6,5,10-PC₂B₇H₁₁

(II) and 6-Me-arachno-6,5,7-PC₂B₇H₁₁(V) isomers, the phos-

phorus is again in the 6-position, but the carbon atoms in each

compound are located in unfavorable higher-coordinate positions

(C5, C10 and C5, C7, respectively). The higher energy of the

V structure (17.4 kcal/mol), where P6 is connected to two

carbons and one boron, compared to that of II (16.6 kcal/mol),

where P6 is connected to two borons and one carbon, is

consistent with the tendency of the most electron-rich hetero-

atoms in a cage to favor bonding interactions with electron-

poor neighbors.^16a,20As expected based on the unfavorable

location of one of the carbons in the high-coordinate 4-position

of the cage skeleton, the 6-R-arachno-6,4,7-PC₂B₇H₁₁(III)

isomer was found to be of highest energy (29.5 kcal/mol).

Single-crystal X-ray diffraction determinations (Figure 3a and

b) established that compound 1a adopts the thermodynamically

favored 6-Ph-arachno-6,8,9-PC₂B₇H₁₁structure (Ph derivative

of I), while 2a adopts the higher energy 6-Ph-arachno-6,5,7-

PC₂B₇H₁₁structure (Ph derivative of V). The phosphorus atoms

in both compounds are located in the low-coordinate 6-position,

but the carbon and the bridge and/or endo-hydrogen atoms in

the two isomers are found in different locations. In 1a, one

carbon is present in the favored low-coordinate 9-position, while

Figure 1. Possible geometric isomers of 6-R-arachno-PC₂B₇H₁₁derived

from arachno-4,5-C₂B₇H₁₃and arachno-4,6-C₂B₇H₁₃.

a number of different geometric isomers could result. Thus,

for the arachno-4,5-C₂B₇H₁₃carborane, three isomers are

possible resulting from insertion at the B7-B8-B9, C5-B6-

B7, or B9-C4-C5 positions to respectively yield the 6-R-

arachno-6,8,9-PC₂B₇H₁₁(I), 6-R-arachno-6,5,10-PC₂B₇H₁₁(II),

or 6-R-arachno-6,4,7-PC₂B₇H₁₁(III) isomers. Because of the

C_ssymmetry of the arachno-4,6-C₂B₇H₁₃carborane, only two

isomeric products are possible. Thus, insertion at either C6-

B7-B8 or B8-B9-C4 yields the two enantiomeric forms of

the same 6-R-arachno-6,7,9-PC₂B₇H₁₁geometric isomer (IV),

whereas insertion at the position spanning C4-B5-C6 yields

the C_s-symmetric 6-R-arachno-6,5,7-PC₂B₇H₁₁(V).

Density functional theory (DFT) calculations at the B3LYP/

6-311G* level for the five isomers yielded the optimized

molecular geometries shown in Figure 2. The 6-Me-arachno-

6,8,9-PC₂B₇H₁₁(I) structure is of lowest energy, in agreement

with the known tendency of electron-rich heteroatoms, such as

phosphorus and carbon, to favor the lowest-coordinate positions

(i.e., the 6- and 9-position) on the open face of a polyhedral

(19) (a) Williams, R. E. Inorg. Chem. 1971, 10, 210-214. (b) Wade, K. AdV.

Inorg. Chem. Radiochem. 1976, 18, 1-66. (c) Williams, R. E. Chem. ReV.

1992, 92, 177-207. (d) Rudolph, R. W.; Thompson, D. A. Inorg. Chem.

1974, 13, 2779-2782. (d) Williams, R. E. In Electron Deficient Boron

and Carbon Clusters; Olah, G. A., Wade, K., Williams, R. E., Eds.;

Wiley: New York, 1991; pp 11-93.

(20) Williams, R. E. AdV. Inorg. Chem. Radiochem. 1976, 18, 67-142.

9

16064 J. AM. CHEM. SOC. VOL. 125, NO. 51, 2003

10-Vertex Phosphadicarbaboranes

A R T I C L E S

the other carbon is found in the adjacent higher-coordinate

8-position. There is an endo-hydrogen at the C9 carbon and a

hydrogen bridging the B5-B10 edge. In 2a, the two carbons

are nonadjacent and are situated in the higher-coordinate cage

positions adjacent to the phosphorus, with bridge-hydrogens

present at the B9-B8 and B9-B10 edges. The observed bond

distances and angles fall into the normal ranges; however, there

are some differences between the two compounds that can be

related to their different donor properties. As discussed later,

in contrast to 1a, 2a shows donor properties consistent with a

lone pair of electrons localized at the endo-P6 position.

Consistent with this observation, the B4-P6-C11 (87.04(10)°),

C5-P6-C11 (106.44(11)°), C7-P6-C11 (105.08(10)°), and

C5-P6-C7 (86.18(10)°) bond angles in 2a are considerably

more acute than the comparable B4-P6-C11 (97.50(13)°),

B5-P6-C11 (113.05(14)°), B7-P6-C11 (113.6(2)°), and B5-

P6-B7 (95.7(2)°) angles in 1a, suggesting that in 2a the P6-

C11 bond is being repelled by the P6 lone pair. In 2a, the P6-

C11 (1.839(2) Å) and P6-B4 (2.208(3) Å) bond distances are

also significantly longer than the comparable distances in 1a

(P6-C11 (1.820(3) Å) and P6-B4 (2.050(3) Å) probably as a

result of the shorter P6-C5 (1.885(2) Å) and P6-C7 (1.888(2)

Å) bonds in 2a relative to the P6-B5 (1.986(4) Å) and P6-B7

(1.984(4) Å) bonds in 1a.

Figure 3. (a) ORTEP drawing of 6-Ph-arachno-6,8,9-PC₂B₇H₁₁(1a).

Selected bond distances (Å) and angles (deg): B5-P6, 1.986(4); P6-B7,

1.984(4); B7-C8, 1.721(6); C8-C9, 1.660(8); C9-B10, 1.660(7); B10-

B5, 1.714(5); P6-C11, 1.820(3); P6-B4, 2.050(3); B4-P6-C11, 97.50(13);

B5-P6-C11, 113.05(14); B7-P6-C11, 113.6(2); B5-P6-B7, 95.7(2).

(b) ORTEP drawing of 6-Ph-arachno-6,5,7-PC₂B₇H₁₁(2a). Selected bond

distances (Å) and angles (deg): C5-P6, 1.885(2); P6-C7, 1.888(2); C7-

B8, 1.635(4); B8-B9, 1.825(5); B9-B10, 1.830(5); B10-C5; 1.636(4);

P6-C11, 1.839(2); P6-B4, 2.208(3); B4-P6-C11, 87.04(10); C5-P6-

C11, 106.44(11); C7-P6-C11, 105.08(10); C5-P6-C7, 86.18(10).

The spectroscopic properties for compounds 1a,b and 2a,b

are consistent with both the crystallographically determined

structures and with the results of the DFT/GIAO chemical shift

calculations (Table 1). Thus, the ¹¹B NMR spectral patterns of

1a,b indicate C₁cage-symmetry, while those of 2a,b indicate

C_Ssymmetry, with the DFT/GIAO calculated values and

assignments for structures I and V closely matching those

experimentally determined in the two-dimensional COSY ¹¹B-

¹¹B NMR studies of 1a and 2a (Table 1). Likewise, in the 1a

¹¹B NMR spectra, the resonances near -12 and -20 ppm clearly

show bridge-hydrogen couplings consistent with their calculated

assignments to the B5 and B10 borons.

2b) being consistent with the adjacent positions of the carbon

(C5,7) and phosphorus (P6) atoms. The ¹³C NMR spectra of

1a and 1b showed the expected two cage-carbon resonances,

one of which appeared as a triplet of doublets and the other as

a doublet, consistent with the C9-H₂and C8-H cage units,

respectively. Surprisingly, given its location on the opposite side

of the cage from the P6 atom, the C9-carbon exhibited

1

In addition to their respective Ph or Me resonances, the H

NMR spectra of 1a and 1b show the expected seven terminal

BH, an intensity-one bridge-hydrogen, and three cage-CH

resonances with one of the cage-CH resonances in both

compounds occurring at the high field (-0.72 ppm, 1a; -0.90

ppm, 1b) characteristic of an endo-hydrogen of a cage-CH₂

group.²¹The ¹H NMR spectra of 2a and 2b showed, in addition

to their terminal BH and respective phenyl or methyl resonances,

intensity-two bridge-hydrogen and cage-CH resonances.

¹³C-³¹

significant carbon-phosphorus coupling (J

_P49 Hz, 1a and

2

1

43 Hz, 1b). These values are close to normal J_CPor J_CP

coupling values,²³such as discussed above for the ¹J_CPcoupling

value found for phosphorus-adjacent C5,7-carbons in com-

pounds 2a,b. An examination of the crystallographically deter-

mined structure of 1a shown in Figure 3 reveals that the P6-

H9 distance (2.49(4) Å) is shorter that the van der Waals radii

of phosphorus and hydrogen (3.1 Å). As shown in Figure 4a,

DFT calculations on Ia also showed that there is significant

interaction of electrons localized at the endo-P6 position and

the endo-C9-H hydrogen in the HOMO. This suggests an

intramolecular C9-H9-P6 hydrogen-bonding interaction in

The calculated ¹³C and ³¹P chemical shifts for I and V (and

their Ph-analogues) match well with the experimentally deter-

¹³C-³¹

mined values for 1a,b and 2a,b. The J

values observed

P

in these compounds deserve special comment. The room

temperature ¹H-decoupled ¹³C NMR spectra of 2a,b contained

a single resonance with a multiplet structure arising from both

boron and phosphorus coupling. When the temperature was

lowered to -83°C to thermally decouple ¹¹B interactions,²²this

resonance resolved into a sharp doublet with the magnitude of

¹³C9-³¹P6

1a,b as the mechanism for the J

coupling observed in

the ¹³C NMR spectra of these compounds.

When the progress of the reaction given in eq 2 was

monitored by ¹¹B NMR spectroscopy, no intermediate species

were observed. However, when the reaction in eq 1 leading to

1a was monitored, an intermediate anionic species was observed

after addition of PhPCl₂and excess Proton Sponge. The ¹¹B

NMR spectrum of this intermediate anion is in good agreement

¹³C-³¹

the phosphorus-carbon coupling (J

_P55 Hz, 2a and 52 Hz,

(21) Kang, S. O.; Furst, G. T.; Sneddon, L. G. Inorg. Chem. 1989, 28, 2339-

2347 and references therein.

(22) (a) Wrackmeyer, B. In Progress in NMR Spectroscopy; Emsley, J. W.,

Feeney, J., Sutcliffe, L. H., Eds.; Pergamon: New York, 1979; Vol. 12,

pp 227-259. (b) Gragg, B. R.; Layton, W. J.; Niedenzu, K. J. Organomet.

Chem. 1977, 132, 29-36.

(23) Quin, L. D. In Phosphorus-31 NMR Spectroscopy in Stereochemical

Anaylsis; Verkade, J. G.; Quin, L. D., Eds.; VCH: New York, 1987; Chapter

12.

9

J. AM. CHEM. SOC. VOL. 125, NO. 51, 2003 16065

A R T I C L E S

Hong et al.

Figure 6. Possible reaction steps leading to the formation of 6-R-arachno-

6,8,9-PC₂B₇H₁₁(1).

-

Reaction of the resulting arachno-4,5-C₂B₇H₁₂anion with

RPCl₂would then reasonably result in the formation of 5-RPCl-

arachno-4,5-C₂B₇H₁₂(A, Figure 6), in which the RPCl- group

is substituted at C5. A subsequent B6-B7 bridge-hydrogen

deprotonation-dehydrohalogenation involving a second equiva-

lent of Proton Sponge would result in phosphorus cage insertion

to yield B, which, in the presence of the of excess Proton

Figure 4. HOMO density surfaces for (a) 6-Ph-arachno-6,8,9-PC₂B₇H₁₁

(Ia) and (b) 6-Ph-arachno-6,5,7-PC₂B₇H₁₁(Va).

-

Sponge, would deprotonate to the 6-R-arachno-6,5,10-PC₂B₇H₁₀

anion (C) (having structure II^-) that was observed by ¹¹B NMR

spectroscopy. Acidification of C (II^-) then results in cage

rearrangement to generate the final product 1 (with structure

I).

Deprotonation of the arachno-4,6-C₂B₇H₁₃carborane has also

been previously shown to occur at the endo-C4-H to produce

-

the arachno-4,6-C₂B₇H₁₂anion having the negative charge

largely localized on the C4 carbon.²⁵A metathesis reaction of

this anion with RPCl₂could then yield a 4-RPCl-arachno-4,6-

C₂B₇H₁₂derivative D (Figure 7). Deprotonation of the acidic

endo-C6-H of D by an additional equivalent of Proton Sponge,

followed by dehydrohalogenation, then leads in a straightforward

manner to the structure (V) observed for 6-R-arachno-6,5,7-

PC₂B₇H₁₁(2) having the phosphorus inserted between the two

carbons.

Even though the DFT calculations show that structure V is

considerably higher in energy, the isomerization of 2 to 1 (with

the more stable structure I) was not observed even after being

heated at 90 °C in DME for 2 days.

Reactions of 6-R-arachno-6,8,9-PC₂B₇H₁₁(1) and 6-R-

arachno-6,5,7-PC₂B₇H₁₁(2) with BH₃‚THF, S₈, and H₂O₂.

The insertion of electron-rich elements, such as phosphorus, into

a boron cluster normally results in the formation of a compound

having a formal lone pair of electrons associated with the

heteroatom. Because of the extensive electron delocalization in

Figure 5. DFT optimized geometry II^-for the 6-R-arachno-6,5,10-

PC₂B₇H₁₀^-anion. Selected bond distances (Å) and angles (deg): P6-B4,

2.162; C5-P6, 1.891; P6-B7, 2.015; P6-C11, 1.904; C5-C10, 1.526;

C5-P6-B7, 90.1; B4-P6-C11, 88.1; C5-P6-C11, 102.9; B7-P6-C11,

112.7.

with the DFT/GIAO calculated chemical shifts (Table 1) for

-

that of the 6-R-arachno-6,5,10-PC₂B₇H₁₀anion (II^-, Figure

5). Protonation of this anion would then be expected to produce

neutral 6-R-arachno-6,5,10-PC₂B₇H₁₁having structure II shown

in Figure 2. However, owing to its unfavorable carbon locations,

II is 16.6 kcal/mol higher in energy than I, and indeed, it was

-

found that when the intermediate 6-R-arachno-6,5,10-PC₂B₇H₁₀

(with structure II^-) was protonated with HCl‚OEt₂, 6-R-

arachno-6,8,9-PC₂B₇H₁₁(1) with structure I, rather than II, was

produced.

The formation of the structures established for 6-R-arachno-

6,8,9-PC₂B₇H₁₁(1, Figure 3a) and 6-R-arachno-6,5,7-PC₂B₇-

H11 (2, Figure 3b) by the reactions given in eqs 1 and 2 can be

envisioned to have resulted from a series of substitution/

dehydrohalogenation steps.^16bInitial deprotonation of arachno-

4,5-C₂B₇H₁₃has been shown to occur at the endo-C5-H.²⁴

(24) Jel`ınek, T.; Holub, J.; St´ıbr, B.; Fontaine, X. L. R.; Kennedy, J. D. Collect.

Czech. Chem. Commun. 1994, 59, 1584-1595.

(25) (a) Tebbe, F. N.; Garrett, P. M.; Hawthorne, M. F. J. Am. Chem. Soc. 1968,

90, 869-879. (b) Kadlecek, D. E.; Hong, D.; Carroll, P. J.; Sneddon, L.

G. In preparation.

9

16066 J. AM. CHEM. SOC. VOL. 125, NO. 51, 2003

10-Vertex Phosphadicarbaboranes

A R T I C L E S

Figure 7. Possible reaction steps leading to the formation of 6-R-arachno-

6,5,7-PC₂B₇H₁₁(2).

polyhedral boron clusters, these heteroatom lone pairs are

usually delocalized and have low Lewis basicity.¹However, we

have recently found that the 10-vertex phosphamonocarbaborane

Figure 8. ¹¹B{¹H} NMR spectrum (64.2 MHz) for the reaction of 2a with

BH₃‚THF, with species marked as 3 (b); 2a (3); BH₃‚THF (a); and BH₃

group of 3 (b).

-

anion exo-6-R-arachno-6,7-PCB₈H₁₁shows strong donor

properties arising from a phosphorus-localized lone pair of

electrons.²The 6-R-arachno-6,8,9-PC₂B₇H₁₁(1) and 6-R-

arachno-6,5,7-PC₂B₇H₁₁(2) phosphadicarbaboranes are iso-

The calculated P6-BH₃bond distance in 3 of 1.959 Å is

longer than that found for Ph₃P‚BH₃(1.93(1) and 1.90(2) Å)²⁶

-

electronic with the exo-6-R-arachno-6,7-PCB₈H₁₁anion and

but shorter than the corresponding P-BH₃distance of 1.988 Å

have similar 10-vertex arachno-structures in which their phos-

phorus atoms occupy the 6-position in the cage. DFT calcula-

tions on the HOMO density surfaces (Figure 4) revealed that

both Ia (1a) and Va (2a) have significant electron density

localized at their endo-phosphorus positions. These observations

prompted our investigations of the reactions of 1a and 2a with

Lewis acids to see if they would exhibit donor properties.

It was found that 1a does not react with BH₃‚THF, but when

2a was mixed with BH₃‚THF in THF, an equilibrium mixture

containing both 2a and endo-6-H₃B-exo-6-Ph-arachno-6,5,7-

PC₂B₇H₁₁(3) was immediately established (eq 3).

- 2a

calculated for endo-6-BH₃-exo-6-Ph-arachno-6,7-PCB₈H₁₁

.

As mentioned above, in addition to forming a complex with

-

BH₃, the exo-6-R-arachno-6,7-PCB₈H₁₁anion was found to

react with S₈and O₂to form the endo-6-S-exo-6-Ph-arachno-

-

6,7-PCB₈H₁₁^-and endo-6-O-exo-6-Ph-arachno-6,7-PCB₈H₁₁

adducts.^2aIn contrast, the 6-Ph-arachno-6,8,9-PC₂B₇H₁₁(1a)

did not react with S₈and was completely decomposed to borates

by hydrogen peroxide. However, in its reactions with S₈and

hydrogen peroxide, 6-Ph-arachno-6,5,7-PC₂B₇H₁₁(2a) formed

endo-6-S-exo-6-Ph-arachno-6,5,7-PC₂B₇H₁₁(4, eq 4) and endo-

6-O-exo-6-Ph-arachno-6,5,7-PC₂B₇H₁₁(5, eq 5).

¹/₈S₈

₁₁+ BH ‚THF y^-THF

z

6-Ph-arachno-6,5,7-PC₂B₇H₁₁

6-Ph-arachno-6,5,7-PC₂B₇H

8

3

2a

endo-6-H₃B-exo-6-Ph-arachno-6,5,7-PC₂B₇H₁₁

(3)

endo-6-S-exo-6-Ph-arachno-6,5,7-PC₂B₇H₁₁

(4)

3

4

H₂O₂

6-Ph-arachno-6,5,7-PC₂B₇H₁₁

2a

3 could not be isolated in a pure form since, upon vacuum

removal of solvent, complete dissociation of the BH₃occurred

and only free 2a was observed. However, Figure 8 shows a

¹H-decoupled ¹¹B NMR spectrum taken for the reaction of 2a

and BH₃‚THF where the peaks of free 2a (∇) and the new 3

(b) are marked accordingly. The GIAO calculated shifts for

the DFT optimized geometry VI shown in Figure 9a with the

BH₃bound at the endo-P6 position are in excellent agreement

with the ¹¹B NMR spectrum observed for 3. Although the

relative ratio of 3 to 2a increased as the amount of initial

BH₃‚THF was increased, complete formation of 3 could not be

reached even in the presence of a large excess of BH₃‚THF.

Based on integrations of the relative peak intensities of the

-21.6 ppm peak of 3 and the -33.0 ppm peak of 2a in a series

of equilibrium mixtures of 2a, 3, and BH₃‚THF (Table 2), the

equilibrium constant K_eqwas obtained as ∼4 at room temper-

ature in THF solution (K_eq) [3]/[2a][BH₃‚THF]), and ∆G was

crudely estimated as -3 kJ/mol.

8

endo-6-O-exo-6-Ph-arachno-6,5,7-PC₂B₇H₁₁

(5)

5

The ¹¹B NMR spectra of 4 and 5 are quite similar, each

showing five boron resonances at similar chemical shift values

in 1:2:2:1:1 intensity ratios indicating C_ssymmetry. The GIAO

calculated chemical shifts for the DFT optimized geometries

VII and VIII (Figure 9b and c) are in good accordance with

the experimental data for 4 and 5 (Table 1). In both 4 (VII)

and 5 (VIII), the sulfur and the oxygen atoms are located at

the endo-P6 position with bridge-hydrogens at the B8-B9 and

B9-B10 edges. The calculated values of the P6-S (1.970 Å)

distance in VII, and the P6-O distance (1.495 Å) in VIII are

(26) There are two independent molecules in the unit cell; see: Huffman, J. C.;

Skupinski, W. A.; Caulton, K. G. Cryst. Struct. Commun. 1982, 11, 1435-

1440.

9

J. AM. CHEM. SOC. VOL. 125, NO. 51, 2003 16067

A R T I C L E S

Hong et al.

Figure 10. DFT calculated optimized geometry IX for µ_7,8-{HS(Ph)P}-

hypho-7,8-C₂B₆H₁₁(6). Selected bond distances (Å) and angles (deg): P9-

C7, 1.774; P9-C8, 1.770; P9-S10, 2.144; P9-C11, 1.823; B2-C7, 1.627;

B6-C7, 1.604; B5-B6, 1.790; B5-B4, 1.790; B4-C8, 1.600; B3-C8,

1.620; C7-P9-C8, 104.3; C7-P9-S10, 114.2; C8-P9-S10, 114.6; S10-

P9-C11, 100.3; B2-C7-P9, 105.5; B3-B2-C7, 107.8; B2-B3-C8,

107.6; B3-C8-P9, 105.7; B4-C8-P9, 116.4; B6-C7-P9, 117.1.

While the reaction of 2a with 1 equiv of sulfur afforded 4,

in the presence of a large excess of S₈, 2a yielded 6 (eq 6).

xs S₈

6-Ph-arachno-6,5,7-PC₂B₇H₁₁

_-B8

2a

µ_7,8-{HS(Ph)P}-hypho-7,8-C₂B₆H₁₁

(6)

6

Compound 6 was obtained as a yellow oil in 52% yield, and

its composition was established by high-resolution mass spec-

troscopy. In its ¹¹B NMR spectrum, 6 exhibited a C_s-symmetric

pattern of four resonances in 2:1:2:1 ratios consistent with the

loss of one cage-boron atom from 2a. The resonance at -25.3

ppm showed an additional fine-structure characteristic of

coupling to two bridge-hydrogens. In its ¹H NMR spectrum, 6

showed two different sets of bridge-hydrogens in a 2:1 intensity

ratio with the intensity-one resonance exhibiting coupling (³J_PH

) 35 Hz) to the phosphorus. The ¹³C NMR spectrum of 6

showed one broad cage-carbon resonance. The single resonance

observed in the ³¹P NMR spectrum was found in a chemical

shift region significantly downfield from those found for

compounds 1-5.

The GIAO calculated chemical shifts for the DFT optimized

geometry IX shown in Figure 10 are in excellent agreement

with the experimental NMR data for 6. The compound has a

structure related to that of 4 and can be envisioned to have been

formed from structure VII (Figure 9) by both removal of the

B4 cage atom and protonation of the endo-sulfur to produce

the thiol group bound at the phosphorus endo-position of IX

(6). The angles around the phosphorus are reasonably tetrahedral

S10-P9-C11 (100.3°); S10-P9-C7 (114.2°); S10-P9-C8

(114.6°), and C7-P9-C8 (104.3°). The P9-C7 (1.774 Å) and

P9-C8 (1.770 Å) are distances shorter than that of the exo-

polyhedral P9-C11 (1.823 Å). The calculated P-SH distance

of (2.144 Å) is longer than the P-S distance calculated in VII

(1.970 Å), and this difference is consistent with the longer P-SH

(2.077(1) Å) versus P-S (1.954(1) Å) distances observed in

Ph₂P(S)SH.²⁹

Figure 9. DFT optimized geometries: (a) VI for endo-6-BH₃-exo-6-Ph-

arachno-6,5,7-PC₂B₇H₁₁(3), (b) VII for endo-6-S-exo-6-Ph-arachno-6,5,7-

PC₂B₇H₁₁(4), and (c) VIII for endo-6-O-exo-6-Ph-arachno-6,5,7-PC₂B₇H₁₁

(5). Selected bond distances (Å) and angles (deg): (VI) P6-BH₃, 1.959;

P6-C11, 1.838; C5-P6, 1.871; P6-C7, 1.864; C7-B8, 1.660; B8-B9,

1.810; B9-B10, 1.810; B10-C5, 1.660; P6-B4, 2.260; BH₃-P6-C11;

106.5; B4-P6-C11, 89.7; B4-P6-BH₃, 163.8; C5-P6-BH₃, 123.2; C7-

P6-BH₃, 123.6; (VII) P6-S17, 1.970; P6-C11, 1.833; C5-P6, 1.858;

P6-C7, 1.867; C7-B8, 1.680; B8-B9, 1.800; B9-B10, 1.800; B10-C5,

1.680; P6-B4, 2.280; S17-P6-C11, 109.8; B4-P6-C11, 90.7; B4-P6-

S17, 159.5; C5-P6-S17, 121.6; C7-P6-S17, 121.1; (VIII) P6-O17,

1.495; P6-C11, 1.825; C5-P6, 1.852; P6-C7, 1.841; C7-B8, 1.690; B8-

B9, 1.800; B9-B10, 1.800; B10-C5, 1.690; P6-B4, 2.282; O17-P6-

C11, 109.1; B4-P6-C11, 95.8; B4-P6-O17, 155.0; C5-P6-O17, 117.9;

C7-P6-O17, 120.5.

comparable to the P-S and P-O distances that have been

observed in phosphine sulfides²⁷and phosphine oxides,²⁸

respectively, but are shorter than those calculated^2afor the

analogous distances in the endo-6-S-exo-6-Ph-arachno-6,7-

-

PCB₈H₁₁(P-S, 2.030 Å) and endo-6-O-exo-6-Ph-arachno-

-

6,7-PCB₈H₁₁(P-O, 1.520 Å) compounds.

(27) (a) Codding, P. W.; Kerr, K. A. Acta Crystallogr. 1978, B34, 3785-3787.

(b) Alder, M. J.; Cross, W. I.; Flower, K. R.; Pritchard, R. G. J. Chem.

Soc., Dalton Trans. 1999, 2563-2573. (c) Piccinni-Leopardi, C.; Germain,

G.; Declercq, J. P.; Van Meerssche, M.; Robert, J. B.; Jurkschat, K. Acta

Crystallogr. 1982, B38, 2197-2199. (d) Grim, S. O.; Gilardi, R. D.;

Sangokoca, S. A. Angew. Chem., Int. Ed. Engl. 1983, 22, 254-255. (e)

Dreissig, V. W.; Plieth, K.; Za¨ske, P. Acta Crystallogr. 1972, B28, 3473-

3477.

(28) (a) Baures, P. W.; Silverton, J. V. Acta Crystallogr. 1990, C46, 715-717.

(b) Galdecki, Z.; Grochulski, P.; Luciak, B.; Wawrzak, Z.; Duax, W. L.

Acta Crystallogr. 1984, C40, 1197-1198. (c) Mikolajczyk, M.; Graczyk,

P. P.; Wieczorek, M. W.; Bujacz, G. Tetrahedron 1992, 48, 4209-4230.

(d) Cameron, T. S.; Dahle`n, B. J. Chem. Soc., Perkin Trans. 2 1975, 1737-

1751. (e) Bandoli, G.; Bortolozzo, G.; Clemente, D. A.; Croatto, U.;

Panattoni, C. J. Chem. Soc. A 1970, 2778-2780.

The IX structure established for 6 can be viewed in at least

two different ways. If the phosphorus is considered as a cage

atom, then the cluster would be a nine-vertex, 26 skeletal

electron system (n + 4 skeleton electron pairs) and should adopt

a hypho-type structure that can be derived from an icosahedron

(29) Krebs, B.; Henkel, G. Z. Anorg. Allg. Chem. 1981, 475, 143-155.

9

16068 J. AM. CHEM. SOC. VOL. 125, NO. 51, 2003

10-Vertex Phosphadicarbaboranes

A R T I C L E S

by removing three vertexes. The structure in Figure 10 can be

generated in this manner and is quite similar to those observed

for other 9-vertex hypho-class compounds, including hypho-1-

CH₂-2,5-S₂B₆H₈, hypho-2,5-S₂B₇H₁₀^-, hypho-2,5-S₂B₇H₁₁, and

hypho-1-(NCCH₂)-1,2,5-C₃B₆H₁₂.

^{- 30,31}On the other hand, given

the tetrahedral configuration of the phosphorus, the HS(Ph)P

unit could be considered to be a “classical” fragment bridging

the C7 and C8 carbons of the C₂B₆H₁₁dicarbaborane fragment.

In this case, the PhP(SH) would be considered to donate three

electrons to the cage by forming one normal σ-bond and one

dative bond with the C7 and C8 cage carbons. The resulting

8-vertex C₂B₆-framework of the µ_7,8-{HS(Ph)P}-hypho-7,8-

C₂B₆H₁₁cluster would have 24 skeletal electrons and should

therefore adopt a hypho-type geometry that is derived by

removing three vertexes from an octadecahedron.¹⁹The C₂B₆-

framework proposed for 6 in Figure 10 is, in fact, entirely

consistent with those found for other isoelectronic 8-vertex

hypho-clusters, including hypho-C₂B₆H₁₃^-, hypho-S₂B₆H₉^-, and

2,3-Me₂-hypho-S₂B₆H₈.^30,32

Coordination Chemistry of 6-Ph-arachno-6,5,7-PC₂B₇H₁₁

(2a). The reaction of 2a and PtBr₂afforded cis-(η¹-[6-Ph-

arachno-6,5,7-PC₂B₇H₁₁])₂PtBr₂(7, eq 7).

Figure 11. ORTEP drawing of cis-(η¹-[6-Ph-arachno-6,5,7-PC₂B₇H₁₁])₂-

PtBr₂(7). Selected bond distances (Å) and angles (deg): Pt-P6a, 2.254(2);

Pt-P6b, 2.268(2); Pt-Br1, 2.4675(9); Pt-Br2, 2.4687(9); P6a-C11a,

1.823(9); P6a-C5a, 1.823(8); P6a-C7a, 1.839(9); P6a-B4a, 2.221(9);

C5a-B10a; 1.684(13); C7a-B8a, 1.686(14); B8a-B9a, 1.814(18); B9a-

B10a, 1.825(18); P6b-C11b, 1.777(9); P6b-C5b, 1.846(9); P6b-C7b,

1.852(9); P6b-B4b, 2.235(11); C5b-B10b, 1.702(15); C7b-B8b, 1.686(15);

B8b-B9b, 1.814(18); B9b-B10b, 1.747(18); P6a-Pt-P6b, 95.61(7); Br1-

Pt-Br2, 87.38(3); P6a-Pt-Br2, 86.91(6); P6b-Pt-Br1, 89.86(6); C11a-

P6a-B4a, 90.2(4); Pt-P6a-C11a, 104.6(3); Pt-P6a-C5a, 125.0(3); Pt-

P6a-C7a, 122.5(3); C11b-P6b-B4b, 88.7(4); Pt-P6b-C11b, 108.7(3);

Pt-P6b-C5b, 120.9(3); Pt-P6b-C7b, 123.2(3).

2 6-Ph-arachno-6,5,7-PC₂B₇H

₁₁+ PtBr₂f

2a

cis-(η¹-[6-Ph-arachno-6,5,7-PC₂B₇H₁₁])₂PtBr₂

(7)

7

A single-crystal X-ray diffraction study established the

structure shown in Figure 11. Since there were no significant

structural differences, only one of the two independent molecules

is shown in the figure. The complex contains two cis-coordinated

6-Ph-arachno-6,5,7-PC₂B₇H₁₁(2a) cages that are each bound

to the platinum center in an η¹fashion at the endo-position of

the cage phosphorus P6. The geometry around the Pt(II) is a

slightly distorted square plane, with the P-Pt-P angle (95.61(7)°)

being wider than Br-Pt-Br (87.38(3)°) owing to the greater

steric requirements of the bulky cages. The Pt-P bond distances

(2.254(2) and 2.268(2) Å) and Pt-Br distances (2.4675(9) and

2.4687(9) Å) are comparable to those found in cis-coordinated

bis(phosphine)platinumdibromide complexes, such as cis-[Ph₂-

PNHP(O)Ph₂P]₂PtBr₂, (Pt-P (2.241(5), 2.248(4) Å); Pt-Br

(2.472(2), 2.480(2) Å).³³There is little change in the cage

structure upon coordination, with P6-C5 (1.823(8), 1.845(8)

Å) and P6-C7 (1.839(9), 1.852(8) Å) in 7 being somewhat

shorter than the corresponding P6-C5 (1.885(2) Å; P6-C7

(1.888(2) Å) distances in 2a.

Figure 12. Possible rotomers of 7 in solution.

3010 and 3010 Hz) characteristic of cis-coordination.³⁴Likewise,

1

the H NMR spectrum showed two different bridge-hydrogen

and two different CH resonances. The question then arises as

to why two species are observed in solution but only one is

observed in the solid state. One possible explanation is that the

two rotamers shown in Figure 12, where 2a is rotated about

the Pt-P axis, exist in solution, while, in the solid state, only

rotamer A (i.e., 7) is present. In solution, there should be little

difference in the energies of the two isomers, but, in the solid

state, the structure observed for 7 could be favored owing to

π-π interactions of the phenyl rings. Thus, as seen in Figure

The ¹¹B NMR spectrum of 7 showed seven overlapping

resonances, and its ¹³C NMR spectrum exhibited only one broad

cage-carbon resonance. However, surprisingly, even when pure

crystals of 7 were dissolved, both the ³¹P and ¹H NMR spectra

indicated the presence of another species in solution. Thus, the

³¹P NMR spectrum showed two resonances at similar chemical

shifts (-5.2 and -8.8 ppm) in an approximate 85:15 ratio

intensity with both resonances exhibiting ³¹P-¹⁹⁵Pt values (J_Pt-P

,

1

(34) Cis geometry PtX₂(PR₃)₂compounds exhibit a J_Pt-Pof 3300-3500 Hz

1

(e.g., cis-(Me₃P)₂PtBr₂, 3439) while trans geometries showed a J_Pt-Pof

(30) Kang, S. O.; Sneddon, L. G. J. Am. Chem. Soc. 1989, 111, 3281-3289.

(31) Su, K.; Carroll, P. J.; Sneddon, L. G. J. Am. Chem. Soc. 1993, 115, 10004-

10017.

(32) Jel´ınek, T.; Plesek, J.; Herma´nek, S.; St´ıbr, B. Main Group Met. Chem.

1987, 10, 397-398.

(33) Bhattacharyya, P.; Slawin, A. M. Z.; Smith, M. B.; Woollins, J. D. Inorg.

Chem. 1996, 35, 3675-3682.

2100-2600 Hz (e.g., trans-(Me₃P)₂PtBr₂, 2324). (a) Pregosin, P. S. In

Phosphorus-31 NMR Spectroscopy in Stereochemical Anaylsis; Verkade,

J. G., Quin, L. D., Eds.; VCH: New York, 1987; Chapter 14. (b) Goggin,

P. L.; Goodfellow, R. J.; Haddock, S. R.; Knight, J. R.; Reed, F. J. S.;

Taylor, B. F. J. Chem. Soc., Dalton Trans. 1974, 523-533. (c) Favez, R.;

Roulet, R.; Pinkerton, A. A.; Schwarzenbach, D. Inorg. Chem. 1980, 19,

1356-1365.

9

J. AM. CHEM. SOC. VOL. 125, NO. 51, 2003 16069

A R T I C L E S

Hong et al.

distances are shorter than those in 2a, but comparable to those

in the Pt complex 7. The P6-B4 distance (2.206(8) Å) is also

similar to that of 7 (2.221(9) Å).

Unlike 2a, 1a did not react with either PtBr₂or PdBr₂.

Deprotonation Reactions of 1a and 2a. 2a was not depro-

tonated by either Proton Sponge or NaH (eq 9a). However,

according to ¹¹B NMR and computational analysis, when 2a

was reacted with MeLi, a mixture of species was obtained that

contained the 6-Ph-arachno-6,5,7-PC₂B₇H₁₀^-(2a^-) anion as the

predominate product. The calculated chemical shifts (-1.8 (2),

-2.7 (1), -16.5 (1), -35.2 (1), and -38.7 (2) ppm) for the

optimized geometry of 6-Me-arachno-6,5,7-PC₂B₇H₁₀^-in which

one of the two bridge-hydrogens of 2a was deprotonated gave

good agreement with the ¹¹B NMR chemical shifts observed

for the major species present in solution.

PS

6-Ph-arachno-6,5,7-PC₂B₇H₁₁

_{or NaH}8 No reaction

(9a)

2a

^MeLi8

6-Ph-arachno-6,5,7-PC₂B₇H₁₁

Figure 13. ORTEP drawing of trans-(η¹-[6-Ph-arachno-6,5,7-PC₂B₇H₁₁])₂-

PdBr₂(8). Selected bond distances (Å) and angles (deg): Pd-P6, 2.318(2);

Pd-Br, 2.4370(7); P6-C5, 1.813(7); P6-C7, 1.843(7); C7-B8, 1.666(10);

B8-B9, 1.829(12); B9-B10, 1.805(11); B10-C5, 1.678(10); P6-B4,

2.206(8); P6-Pd-Br1, 91.90(5); P6-Pd-Br2, 88.10(5); P6-Pd-P6′,

180.0; C11-P6-Pd, 105.7(2); C11-P6-C5, 109.1(3); C11-P6-C7,

111.1(3); C11-P6-B4, 93.4(3).

2a

-

6-Ph-arachno-6,5,7-PC₂B₇H₁₀

(9b)

2a^-

On the other hand, the 6-Ph-arachno-6,8,9-PC₂B₇H₁₀^-(1a^-)

monoanion was cleanly obtained by the reaction of 1a with

Proton Sponge or NaH (eq 10).

11, the two phenyl rings are in nearly cofacial positions with a

dihedral angle of ∼7° and an interplanar distance of ∼3.5 Å.

These values are quite similar to those that have been observed

in other complexes with π-π interactions between cis-

coordinated aromatic ligands.³⁵This π-π interaction, in addition

to the steric interactions of the cage, may also be a contributing

factor to the larger P-Pt-P versus Br-Pt-Br bond angle.

The reaction of 2a and PdBr₂afforded a product mixture

containing at least two products that were inseparable by silica

gel chromatography. Although it was possible to crystallize

^{PS or NaH}8

6-Ph-arachno-6,8,9-PC₂B₇H₁₁

1a

-

6-Ph-arachno-6,8,9-PC₂B₇H₁₀

(10)

1a^-

Since 1a has two potentially acidic hydrogens, a bridge-

hydrogen spanning B5-B10 and an endo-hydrogen at C9,

mono-deprotonation could in principle yield analogues of either

-

of the structures, Ib₁or Ib₂^-, shown in Figure 14a and 14b.

small samples of trans-(η¹-[6-Ph-arachno-6,5,7-PC₂B₇H_11])2

-

DFT calculations showed that structure Ib₁^-, in which the

bridge-hydrogen at B5-B10 was removed, is 7.6 kcal/mol more

favored than the endo-C9 deprotonated structure Ib₂^-, and

PdBr₂(8) from the crude product mixture, it was not possible

to isolate other products sufficiently pure to allow characteriza-

tion.

-

indeed, the DFT/GIAO calculated chemical shifts for Ib₁

showed better agreement with the experimental data for 1a^-

than those calculated for structure Ib₂^-(Table 1). A comparison

of the calculated bond distances and angles for Ib₁^-with those

found for the neutral compound Ib reveals that the major

structural change that occurs upon deprotonation of the B5-

B10 bridge-hydrogen is a significant shortening of B5-B10 to

1.720 Å and an elongation of B2-C9 to 1.806 Å compared to

their values in Ib (B5-B10, 1.872 Å; B2-C9, 1.738 Å).

The 6-Ph-arachno-6,8,9-PC₂B₇H₉^2-(1a^2-) dianion was pre-

pared by reaction with the stronger base MeLi in DME solution

(eq 11).

2 6-Ph-arachno-6,5,7-PC₂B₇H

₁₁+ PdBr₂f

2a

trans-(η¹-[6-Ph-arachno-6,5,7-PC₂B₇H₁₁])₂PdBr₂

(8)

8

As shown in eq 8, 8 is formed by the reaction of the palladium

dibromide with 2 equiv of 2a. A single-crystal X-ray diffraction

study established the structure shown in Figure 13 in which

two η¹-coordinated 2a cages adopt a trans-geometry at the Pd(II)

center, with P6-Pd-Br angles of 91.90(5)° and 88.10(5)° and

a 180.0° P6-Pd-P6′ angle. The observed Pd-P 2.318(2) Å

and Pd-Br 2.4370(7) Å distances are typical of those observed

in Pd²⁺square planar phosphine complexes, such as trans-

[(C₆H₄Cl)Ph₂P]₂PdBr₂(Pd-P, 2.350(2) and Pd-Br 2.4232(13)

Å).³⁶The P6-C5 (1.813(7) Å) and P6-C7 (1.843(7) Å)

^{2 equiv of MeLi}8

6-Ph-arachno-6,8,9-PC₂B₇H₁₁

1a

2-

6-Ph-arachno-6,8,9-PC₂B₇H₉

(11)

1a^2-

(35) (a) Hirsivaara, L.; Haukka, M.; Pursiainen, J. Eur. J. Inorg. Chem. 2001,

9, 2255-2262. (b) Yang, F.; Fanwick, P. E.; Kubiak, C. P. Inorg. Chem.

2002, 41, 4805-4809.

(36) Coalter, N. L.; Concolino, T. E.; Streib, W. E.; Hughes, C. G.; Rheingold,

A. L.; Zaleski, J. M. J. Am. Chem. Soc. 2000, 122, 3112-3117.

The DFT/GIAO calculated chemical shifts for structure Ib^2-

shown in Figure 14c, in which both the B5-B10 and endo-C9

hydrogens have been removed, showed good agreement with

9

16070 J. AM. CHEM. SOC. VOL. 125, NO. 51, 2003

10-Vertex Phosphadicarbaboranes

A R T I C L E S

7-Ph-11-(η⁵-C₅H₅)-nido-11,7,9,10-CoPC₂B₇H₉(10) complex in

which a Co³⁺ion is sandwiched between formal η⁵-C₅H₅^-and

η⁴-6,8,9-PC₂B₇H₉(1a^2-) anions.

2-

-2 CO, H₂

6-Ph-arachno-6,8,9-PC₂B₇H

₁₁+ CpCo(CO)₂

8

1a

7-Ph-11-Cp-nido-11,7,9,10-CoPC₂B₇H₉

(13)

10

In agreement with their predicted 26 skeletal electron counts,¹⁹

single-crystal X-ray diffraction studies of 9 and 10 established

the 11-vertex nido-cluster structures shown in Figures 15 and

16. The phosphadicarbaboranyl ligands are each coordinated

to the metals in an η⁴-fashion. In both complexes, the hetero-

atoms occupy low connectivity sites on the five-membered open

face of the cluster with the Pt in 9 and the Co in 10 being slightly

distorted above the plane of the other four facial atoms. Similar

η⁴-coordination was observed for the isoelectronic phospha-

2-

monocarbaborane 6-Ph-arachno-PCB₈H₁₀anion in the Pt²⁺

complex 7-Ph-11-(Ph₃P)₂-nido-11,7,8-PtPCB₈H₁₀,^2band in both

this complex and 9, the dihedral angle between the five-

membered open face and the P18-Pt11-P37 plane is ∼73°.

In contrast to 7 where the P6a-Pt-P6b angle is 95.61(7)°, in

9 the P18-Pt-P37 angle has increased to 101.46(5)° consistent

with the expected change in platinum hybridization upon

insertion. The Pt-P bond length in 9 (2.4208(14)Å) is also

longer than those observed in 7 (2.254(2) and 2.268(2)Å).

Consistent with the crystallographically established structures,

the ¹¹B NMR spectra of 9 and 10 each showed seven resonances,

their ¹³C NMR spectrum each exhibited two cage-carbon

resonances, and their ¹H NMR spectra showed the appropriate

BH and CH resonances. The ³¹P NMR spectrum of 9 showed

Figure 14. DFT optimized geometries (B3LYP/6-311G*//B3LYP/6-311G*)

-

of two possible monoanions of 6-R-arachno-6,8,9-PC₂B₇H₁₀^-(Ib₁^-, Ib₂

)

2-

and a dianion 6-R-arachno-6,8,9-PC₂B₇H₁₀(Ib^2-). Selected bond dis-

tances (Å) and angles (deg) for Ib₁^-and Ib^2-. Ib₁^-: B5-P6, 1.998; P6-

B7, 1.984; B7-C8, 1.606; C8-C9, 1.570; C9-B10, 1.733; B10-B5, 1.720;

P6-B4, 2.092; B2-C9, 1.806; P6-C11, 1.888; B4-P6-C11, 93.2; C8-

C9-B10, 107.5, B5-P6-B7, 94.3. I^2-: B5-P6, 2.005; P6-B7, 2.001; B7-

C8, 1.605; C8-C9, 1.498; C9-B10, 1.575; B10-B5, 1.742; P6-B4, 2.297;

B2-C9, 1.608; P6-C11, 1.931; B4-P6-C11, 86.8; C8-C9-B10, 114.8;

B5-P6-B7, 89.0.

three resonances, each of which were coupled to ¹⁹⁵Pt (J_Pt-P

,

the ¹¹B NMR spectrum of 1a^2-(Table 1). An examination of

the dianion structure reveals several significant cage structural

changes compared to either Ib or Ib₁^-. Most notably, in the

dianion, the deprotonation of the endo-C9-H has greatly

increased the bonding interactions of the C9 carbon with its

neighboring cage atoms, with the C8-C9 (1.498 Å), C9-B10

(1.575 Å), and C9-B2 (1.608 Å) distances all being dramati-

cally shortened compared to their values in either Ib (1.577,

3596, 4218, 4236 Hz). The phosphorus resonances of the two

Ph₃P groups showed additional doublet structure (J_PP, 17, 18

Hz) arising from coupling to the cage phosphorus, and accord-

ingly, although not clearly resolved, the cage phosphorus

resonance showed the corresponding triplet fine-structure from

coupling to the two Ph₃P phosphorus atoms.

The reaction (eq 14) of 2 equiv of the 6-Ph-arachno-

-

6,8,9-PC₂B₇H₁₀(1a^-) anion with NiBr₂followed by an

1.774, and 1.738 Å, respectively) or Ib₁(1.570, 1.733, and

oxidative workup produced commo-Ni-(7-Ni-8′-Ph-nido-8′,10′,11′-

PC₂B₇H₉)(7-Ni-8-Ph-nido-8,10,11-PC₂B₇H₉) (11).

1.806 Å, respectively).

Coordination Chemistry of the 6-Ph-arachno-6,8,9-

2-

PC₂B₇H₉(1a^2-) Anion. The reaction of the 6-Ph-arachno-

+ NiBr₂^{(1) -2 LiBr}8

-

6,8,9-PC₂B₇H₉(1a^2-) anion with (Ph₃P)₂PtCl₂gave 8-Ph-7-

2 Li⁺[6-Ph-arachno-6,8,9-PC₂B₇H₁₀

]

2-

(2) O₂, -H₂O

1a^-

(Ph₃P)₂-nido-7,8,10,11-PtPC₂B₇H₉(9, eq 12).

+

2-

commo-Ni-(7-Ni-8′-Ph-nido-8′,10′,11′-PC₂B₇H₉)-

Li₂[6-Ph-arachno-6,8,9-PC₂B₇H₉

]

+ (Ph₃P)₂PtCl₂f

(14)

1a^2-

(7-Ni-8-Ph-nido-8,10,11-PC₂B₇H₉)

11

8-Ph-7-(Ph₃P)₂-nido-7,8,10,11-PtPC₂B₇H₉+ 2 LiCl

(12)

Owing to the C₁symmetries of the 6-Ph-arachno-6,8,9-

9

-

2-

PC₂B₇H₁₀(1a^-) and 6-Ph-arachno-6,8,9-PC₂B₇H₉(1a^2-

)

Likewise, the reaction (eq 13) of 6-Ph-arachno-6,8,9-

PC₂B₇H₁₁(1a) with CpCo(CO)₂at 70 °C resulted in the

oxidative insertion³⁷of the cobalt into the cage to produce the

anions, they are each synthesized as racemic mixtures. Thus,

when a bis-cage complex, such as 11, is formed from one of

these anions, it could result from reaction with 2 equiv of the

same enantiomer (R-M-R or S-M-S complexes) or from

reaction with the two different enantiomeric forms of the anion

(R-M-S).³⁸The single-crystal X-ray diffraction study of 11

(Figure 17) established that two phosphadicarbaboranyl ligands

(37) (a) Miller, V. R.; Sneddon, L. G.; Beer, D. C.; Grimes, R. N. J. Am. Chem.

Soc. 1974, 96, 3090-3098. (b) Maxwell, W. M.; Grimes, R. N. Inorg.

Chem. 1979, 18, 2174-2178. (c) Grimes, R. N. In ComprehensiVe

Organometallic Chemistry; Wilkinson, G., Ed.; Pergamon: New York,

1982; Vol. 1, Chapter 5.5.

9

J. AM. CHEM. SOC. VOL. 125, NO. 51, 2003 16071

A R T I C L E S

Hong et al.

Figure 15. ORTEP drawing of 8-Ph-7-(Ph₃P)₂-nido-7,8,10,11-PtPC₂B₇H₉(9). Selected bond distances (Å) and angles (deg): Pt7-P8, 2.4208(14); Pt7-B2,

2.273(6); Pt7-B6, 2.210(5); Pt7-C11, 2.176(5); P8-B9, 1.928(7); B9-C10, 1.639(11); C10-C11, 1.522(8); Pt7-P37, 2.3164(15); Pt7-P18, 2.3061(16);

P8-Pt7-P18, 108.61(5); P8-Pt7-P37, 118.25(5); P18-Pt7-P37, 101.46(5); C11-Pt7-P37, 151.68(15); C11-Pt7-P18, 88.46(17).

Figure 16. ORTEP drawing of 7-Ph-11-(η⁵-C₅H₅)-nido-11,7,9,10-CoPC₂B₇H₉

Figure 17. ORTEP drawing of commo-Ni-(7-Ni-8′-Ph-nido-8′,10′,11′-

PC₂B₇H₉)(7-Ni-8-Ph-nido-8,10,11-PC₂B₇H₉) (11). Selected bond distances

(Å) and angles (deg): Ni7-P8, 2.1837(6); Ni7-C11, 2.055(2); Ni7-B2,

2.165(3); Ni7-B6; 2.117(3); P8-B9, 1.895(3); B9-C10, 1.652(4); C10-

C11, 1.501(3); P8-B2, 2.008(3); P8-C12, 1.792(3); Ni7-P8′, 2.1692(6);

Ni7-C11′, 2.061(2); Ni7-B2′, 2.169(3); Ni7-B6′, 2.120(3); P8′-B9′,

1.899(3); B9′-C10′, 1.654(4); C10′-C11′, 1.518(3); P8′-B2′, 1.995(3);

P8-Ni7-P8′, 92.13(2); P8-Ni7-C11′, 102.45(7); P8′-Ni7-C11, 97.73(7);

C11-Ni7-P8, 88.35(7); Ni7-P8-B9, 107.41(10); P8-B9-C10, 106.2(2);

B9-C10-C11, 119.0(2); C10-C11-Ni7, 117.54(17); C11′-Ni7-P8′,

89.16(7); Ni7-P8′-B9′, 107.53(9); P8′-B9′-C10′, 106.03(18); B9′-

C10′-C11′, 119.5(2); C10′-C11′-Ni7, 116.16(16); Ni7-P8′-C12′,

124.94(8).

(10). Selected bond distances (Å) and angles (deg): P7-B8, 1.899(3); B8-

C9, 1.632(4); C9-C10, 1.527(3); Co11-P7, 2.1378(7); Co11-C10,

2.003(2); Co11-B5, 2.059(3); Co11-B6, 2.140(3); P7-C12, 1.802(2);

C12-P7-B2, 107.05(12); C12-P7-Co11, 127.86(8); Co11-P7-B8,

111.22(11); P7-B8-C9, 103.34(19); B8-C9-C10, 117.9(2); C9-C10-

Co11, 120.67(17); C10-Co11-P7, 86.26(8).

of the same enantiomeric type (both R-M-R and S-M-S

complexes being present in the P2₁/c unit cell) are η⁴-

coordinated to the nickel center. The nickel center occupies a

four-coordinate vertex in each cage, with both cages adopting

11-vertex nido-structures similar to those found for 9 and 10.

In both cages, all of the heteroatoms are present on the open

pentagonal face and the two cages are twisted 64.9(1)° (as

measured by the dihedral angle between the B1′-B4′-Ni7 and

B1-B4-Ni7 planes) with a 84.00(5)° angle between the planes

of the two open pentagonal faces. Since 11 has two anions of

(38) A modification of the R and S notation for configuration specification is

utilized here. Observation of the phosphadicarbaborane cage from the open

face is thus prioritized from the phosphorus, where the configuration is

specified R, for a clockwise direction, or S, for the counterclockwise

configuration.

9

16072 J. AM. CHEM. SOC. VOL. 125, NO. 51, 2003

10-Vertex Phosphadicarbaboranes

A R T I C L E S

the same enantiomeric type, these cages are related by a

noncrystallographic C₂axis passing through the nickel ion, and

all of the NMR spectral data for 11 likewise indicate that the

two cages are equivalent. TLC, mass spectroscopy, and NMR

analysis of the reaction mixture also indicated the production

of another isomeric complex. This complex could not be isolated

in sufficient purity to allow complete characterization; however,

its more complex NMR spectra suggest that it is most likely

the R-M-S complex.

isomer showing strong donor properties, forming endo-L-exo-

6-R-arachno-6,5,7-PC₂B₇H₁₁(L ) BH₃(3), S (4), O (5), Pt

(7), and Pd (8)) complexes containing Lewis acidic substituents

bonded at the endo-position of the P6-phosphorus. These donor

properties are similar to those recently reported for the isoelec-

-

tronic 6-R-arachno-6,7-PCB₈H₁₁phosphamonocarbaborane

anion.²Thus 6-R-arachno-6,7-PCB₈H₁₁^-and 2 can be consid-

ered anionic and neutral phosphacarbaborane analogues, re-

spectively, of an R₃P donor. The differences in Lewis basicities

found for 2 and 6-R-arachno-6,8,9-PC₂B₇H₁₁(1) is most likely

a consequence of the fact that the phosphorus in 1 is directly

bonded to three electron-poor borons and can readily delocalize

electron density to these atoms, whereas in 2 the phosphorus is

adjacent to two electron-donating carbons that enhance the

phosphorus donor properties. While neutral 1 does not coordi-

nate with transition metals, its dianion readily coordinates to

transition metals in an η⁴-fashion and appears to have an ability,

like the dicarbollide dianion, to stabilize metals in high oxidation

states.

Since complex 11 contains two 6-Ph-arachno-6,8,9-PC₂B₇H₉^2-

(1a^2-) dianion ligands, the nickel has a formal oxidation state

of Ni⁴⁺. Thus the 1a^2-dianion appears to have an ability, similar

2-

to that of the dicarbabollide C₂B₉H₁₁dianions in closo-Ni-

(C₂B₉H₁₁)₂,³⁹to stabilize high oxidation states. The Ni-C11

and Ni-C11′ (2.055(2) and 2.061(2) Å) and the Ni7-B2, Ni7-

B2′, Ni7-B6, and Ni7-B6′ distances (2.165(3), 2.169(3),

2.117(3), and 2.120(3) Å) in 11 are reasonably similar to the

Ni-C (2.077(2), 2.065(2), 2.072(2), and 2.071(2) Å) and Ni-B

distances (2.105(2), 2.086(2), and 2.120(2) Å) in closo-Ni-

(C₂B₉H₁₁)₂.⁴⁰

In conclusion, these studies have resulted in the syntheses

and structural characterizations of two isomers of the first 10-

vertex phosphadicarbaboranes. While DFT calculations showed

that the HOMO orbitals of both isomers have large components

at their endo-P6 positions, the isomers exhibit very different

chemistries, with only the 6-R-arachno-6,5,7-PC₂B₇H₁₁(2)

Acknowledgment. We thank the National Science Foundation

for the support of this research.

Supporting Information Available: Tables listing Cartesian

coordinates for DFT optimized geometries. X-ray crystal-

lographic data for structure determinations of compounds 1a,

2a, 7, 8, 9, 10, and 11 (CIF). This material is available free of

charge via the Internet at http://pubs.acs.org.

(39) Warren, L. F., Jr.; Hawthorne, M. F. J. Am. Chem. Soc. 1970, 92, 1157-

1173.

(40) St. Clair, D.; Zalkin, A.; Templeton, D. H. J. Am. Chem. Soc. 1970, 92,

1173-1179.

JA037799+

9

J. AM. CHEM. SOC. VOL. 125, NO. 51, 2003 16073

Article Doi

Syntheses, Characterizations, and Coordination Chemistry of the 10-Vertex Phosphadicarbaboranes 6-R-arachno-6,8,9-PC2B7H 11 and 6-R-arachno-6,5,7-PC2B7H11

DOI: 10.1021/ja037799+

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Article abstract of DOI:10.1021/ja037799+

Full text of DOI:10.1021/ja037799+

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