Deprotonation of the transition metal hydride (η5-C5Me5)(PMe3)IrH2. Synthesis and chemistry of the strongly basic lithium iridate (η5-C5Me5)(PMe3)Ir(H)(Li)

Organometallics 1999, 18, 2005-2020

2005

Dep r oton a tion of th e Tr a n sition Meta l Hyd r id e

(η⁵-C₅Me₅)(P Me₃)Ir H₂. Syn th esis a n d Ch em istr y of th e

Str on gly Ba sic Lith iu m Ir id a te (η⁵-C₅Me₅)(P Me₃)Ir (H)(Li)

Thomas H. Peterson,^†J effery T. Golden, and Robert G. Bergman*

Department of Chemistry, University of California, Berkeley, California 94720

Received November 23, 1998

Treatment of (η⁵-C₅Me₅)(PMe₃)IrH₂(1) with tert-butyllithium gives (η⁵-C₅Me₅)(PMe₃)Ir-

(H)(Li) (2) as a bright yellow solid. NMR evidence indicates that the lithium iridate 2 is

aggregated in benzene, is converted to a single symmetrical species in THF, and is present

as a dimer in DME. Treatment of 2 with 3,3-dimethylbutane trifluoromethanesulfonate-

1,2-syn-d₂(3-syn -d ₂) gave the alkylated hydridoiridium complex 4a -a n ti-d ₂, which was

converted to the corresponding chloride Cp*(PMe₃)Ir(CHDCHDCMe₃)(Cl) (4c-a n ti-d ₂) by

treatment with CCl₄. Analysis of this material by NMR spectroscopy showed that it was

contaminated with e15% syn isomer. The alkylation therefore proceeds with predominant

inversion of configuration at carbon, indicating that the major pathway is an S_N2

displacement and not an outer-sphere electron-transfer reaction. Protonation studies carried

out on iridate 2 with organic acids of varying pK_aallowed us to estimate that the pK_aof the

dihydride 1 falls in the range 38-41, making it less acidic than DMSO and more acidic

than toluene. This represents the least acidic transition metal hydride whose pK_ahas been

quantitatively estimated. Treatment of 2 with main group electrophiles allowed the

preparation of several other hydridoiridium derivatives, including Cp*(PMe₃)Ir(SnPh₃)(H)

(5a ), Cp*(PMe₃)Ir(SnMe₃)(H) (5b), and Cp*(PMe₃)Ir(BR₂)(H) (6a , R ) F; 6b, R ) Ph). Reaction

of 2 with acid chlorides and anhydrides leads to acyl hydrides Cp*(PMe₃)Ir(COR)(H), and

fluorocarbons also react, giving products such as Cp*(PMe₃)Ir(C₆F₅)(H) in the case of

hexafluorobenzene as the electrophile.

In tr od u ction

While examples of organometallic anions may be

found that span the transition series, most examples

incorporate one or more carbonyl groups in the ligand

system to provide stabilization of the charged metal

center and correspondingly modest pK_a’s for the

hydride.^15-20The fewer non-CO-containing metal anions

known are typically exceptionally reactive,^1-3,5,21-24but

little quantitative thermodynamic or kinetic information

is available on these species.

Although complexes with transition metal-hydrogen

bonds are traditionally referred to as “hydrides”, the

chemical behavior of the hydrogen atom in these com-

plexes can vary from hydridic to protic, allowing transi-

tion metal hydrides to function as Brønsted acids as well

as reducing agents. When the former mode of reactivity

is realized, deprotonation of a neutral transition metal

hydride yields an anionic metal complex as shown in

eq 1. Examples of low-valent organometallic anions are

Previously, we reported that successive treatment of

Cp*(PMe₃)IrH₂(Cp* ) C₅Me₅) with tert-butyllithium

followed by alkyl or silyl trifluoromethanesulfonates

(8) Lee, S.; Geib, S. J .; Cooper, N. J . J . Am. Chem. Soc. 1995, 117,

9572.

(9) Lee, S.; Lovelace, S. R.; Cooper, N. J . Organometallics 1995, 14,

1974.

(10) Leach, P. A.; Geib, S. J .; Corella, J . A., II; Warnock, G. F.;

Cooper, N. J . J . Am. Chem. Soc. 1994, 116, 8566.

(11) Thompson, R. L.; Lee, S.; Rheingold, A. L.; Cooper, N. J .

Organometallics 1991, 10, 1657.

numerous; many have been employed in organic syn-

thesis as well as in the preparation of more highly

functionalized organometallic species.^1-14

^†Present address: Catalyst Skill Center, Union Carbide Corp.,

South Charleston, WV.

(1) J onas, K.; Koepe, G.; Kru¨ger, C. Angew. Chem., Int. Ed. Engl.

1986, 25, 923.

(2) Gilbert, T. M.; Bergman, R. G. J . Am. Chem. Soc. 1985, 107,

3502.

(3) Francis, B. R.; Green, M. L. H.; Luong-thi, T.; Moser, G. A. J .

Chem. Soc., Dalton Trans. 1976, 1339.

(4) Crocco, G. L.; Gladysz, J . A. J . Chem. Soc., Chem. Commun.

1985, 283.

(5) Collman, J . P.; Brothers, P. J .; McElwee-White, L.; Rose, E. J .

Am. Chem. Soc. 1985, 107, 6110.

(6) Bock, P. L.; Boschetto, D. J .; Rasmussen, J . R.; Demers, J . P.;

Whitesides, G. M. J . Am. Chem. Soc. 1974, 96, 2814.

(7) Lai, C.-K.; Feighery, W. G.; Zhen, Y.; Atwood, J . D. Inorg. Chem.

1989, 28, 3929.

(12) Lee, G. R.; Cooper, N. J . Organometallics 1989, 8, 1538.

(13) Ellis, J . E.; Fjare, K. L.; Warnock, G. F. Inorg. Chim. Acta 1995,

240, 379.

(14) Ellis, J . E.; Yuen, P.; J ang, M. J . Organomet. Chem. 1996, 507,

283.

(15) Pearson, R. G. Chem. Rev. 1985, 85, 41.

(16) J ordan, R. F.; Norton, J . R. J . Am. Chem. Soc. 1982, 104, 1255.

(17) Moore, E. J .; Sullivan, J . M.; Norton, J . R. J . Am. Chem. Soc.

1986, 108, 2257.

(18) Tilset, M. J . Am. Chem. Soc. 1992, 114, 2740.

(19) Stevens Miller, A. E.; Kawamura, A. R.; Miller, T. M. J . Am.

Chem. Soc. 1990, 112, 457.

(20) Ryan, O. B.; Tilset, M.; Parker, V. D. J . Am. Chem. Soc. 1990,

112, 2618.

Publication on Web 04/25/1999

2006 Organometallics, Vol. 18, No. 10, 1999

Peterson et al.

(triflates) in pentane solution afforded the corresponding

alkyl and silyl hydrides in good yields.²We describe here

the spectroscopic characterization of the putative Cp*-

(PMe₃)Ir(Li)(H) intermediate, its expanded reactivity

with organic and main group electrophiles, and a

comprehensive study of its properties and chemistry.

Gen er a tion a n d Sp ectr oscop ic Ch a r a cter iza tion

of Cp *(P Me₃)Ir (Li)(H). When a colorless C₆D₆solution

of Cp*(PMe₃)IrH₂(1) was treated at ambient tempera-

ture with tert-butyllithium, an intense yellow color

1

developed immediately. Analysis of this solution by H

NMR spectroscopy showed complicated resonance pat-

terns in each of the characteristic Cp*, PMe₃, and

hydride spectral regions as well as the expected signals

for isobutane. Previous investigations have shown that

protons bound to cyclopentadienyl and phosphine ligands

are capable of being removed by potent bases and

suggested to us that the complex ¹H NMR spectrum

could have resulted from deprotonation at several sites

in the starting dihydride complex. However, integration

of the Cp^*, PMe₃, and hydride regions gave a 15:9:1

ratio, suggesting instead that the Ir-bound hydrogen

had been removed, as we hoped, but the observed

spectrum was the result of extensive aggregation of Cp*-

(PMe₃)Ir(Li)(H) (2) (eq 2).

F igu r e 1. ¹H NMR spectrum of 2 and residual 1 in THF-

d₈(b 1; 4 2).

was sparingly soluble in THF-d₈, but exhibited a much

simpler NMR spectrum than that observed in benzene.

At ambient temperature, single sharp resonances were

observed for the Cp*, PMe₃, and hydride nuclei, in

addition to resonances due to residual Cp*(PMe₃)IrH₂.

Single resonances were also observed for 2 in the ³¹P

and ⁷Li NMR spectra.²⁵Our initial interpretation of

these observations was that good donor solvents such

as THF effected deaggregation to a single symmetrical

species (Figure 1). When this solution was cooled to

7

-101 °C, however, the Li NMR spectrum decoalesced

into multiple broad resonances. This result suggested

instead that dissolution in THF effected rapid aggregate

interconversion at 21 °C so that the observed spectra

were the result of fast exchange.²⁶The addition of 12-

crown-4 as a sequestering agent to a C₆D₆solution of

Previous studies by Gladysz and co-workers demon-

strated that the reaction of CpRe(PPh₃)(NO)(H) with

n-BuLi at -78 °C resulted in abstraction of a Cp ring

proton to form (C₅H₄Li)Re(PPh₃)(NO)(H).⁴Subsequent

warming to -32 °C resulted in rearrangement to the

thermodynamically favored CpRe(PPh₃)(NO)(Li). To

address the possibility that kinetic deprotonation could

occur at a site other than the iridium center, Cp*(PMe₃)-

IrD₂was prepared. Treatment with tert-butyllithium

produced Cp*(PMe₃)Ir(Li)(D) (2-d ), as expected. Analy-

sis of the isobutane product by GC/MS showed that

isobutane-d had been formed (>90% deuterium incor-

poration), indicating that it is indeed the Ir-bound

hydrogen that reacts with tert-butyllithium (eq 3).

1

Cp*(PMe₃)Ir(Li)(H) produced no change in the H NMR

spectrum even upon heating to 75 °C. This implied

either that the barrier to lithium decoordination from

the complex was slow (kinetic stability) at the reaction

temperature or that the strength of the Li-Ir bonds in

the aggregate made complexation by the crown ether

energetically unfavorable (thermodynamic stability).

Attempts to grow crystals of Cp*(PMe₃)Ir(Li)(H) suit-

able for study by X-ray diffraction were unsuccessful.

Diffusion of THF or DME into a benzene solution of Cp*-

(PMe₃)Ir(Li)(H) led to precipitation of a yellow micro-

crystalline solid. Analysis of the DME adduct by ¹H

NMR spectroscopy indicated a composition of [Cp*-

(PMe₃)Ir(Li)(H)]₂(DME). The stoichiometry of the com-

(21) Ruiz, J .; Mann, B. R.; Spencer, C. M.; Taylor, B. F.; Maitlis, P.

M. J . Chem. Soc., Dalton Trans. 1987, 1963.

(22) Bandy, J . A.; Berry, A.; Green, M. L. H.; Perutz, R. N.; Prout,

K.; Verpeaux, J .-N. J . Chem. Soc., Chem. Commun. 1984, 729.

(23) Bandy, J . A.; Berry, A.; Green, M. L. H.; Prout, K. J . Chem.

Soc., Chem. Commun. 1985, 1462.

(24) Alexander, C. S.; Rettig, S. J .; J ames, B. R. Organometallics

1994, 13, 2542.

(25) Gilbert, T. M.; Bergman, R. G. J . Am. Chem. Soc. 1985, 107,

6391.

(26) The possibility that aggregation is unfavored at ambient

temperatures in THF solution but can be observed at lower temper-

atures in this solvent cannot be ruled out on the basis of these

experiments.

Removal of the volatile materials in vacuo from a

benzene solution of Cp*(PMe₃)Ir(Li)(H) afforded a bright

yellow microcrystalline solid in 90% yield. This material

Deprotonation of (η⁵-C₅Me₅)(PMe₃)IrH₂

Organometallics, Vol. 18, No. 10, 1999 2007

Sch em e 1

plex suggested that each lithium atom bridges to a

second atom in addition to the two oxygen atoms of

DME to maintain a preferred tetravalent coordination

sphere. The dimeric [Ru(OEP)(neopentyl)]₂(µ-Li)₂(OEP

) octaethylporphyrin) reported previously by J ames and

co-workers was found to contain two bridging lithium

centers and provides precedent for such a bridging

structure.²⁴

distinguished these pathways in the alkylation of CpFe-

(CO)₂salts by carrying out the alkylation with 1-bromo-

3,3-dimethylbutane-1,2-syn-d₂and 1-bromo-3,3-dimethyl-

butane-1,2-anti-d₂, each of which proceeded with clean

inversion of configuration in the iron system.⁶We

enlisted a similar strategy for our investigation of the

reaction of Cp*(PMe₃)Ir(Li)(H) with alkyl triflates.³⁰

A benzene solution of Cp*(PMe₃)IrH₂(1) was treated

with 1 equiv of tert-butyllithium at ambient tempera-

ture to give a solution of Cp*(PMe₃)Ir(Li)(H) (2). The

volatile materials were removed in vacuo, and the

resulting oil was dissolved in THF. Dropwise addition

of 1 equiv of 3,3-dimethylbutane-1-trifluoromethane-

sulfonate (3, Scheme 1) in THF solution produced a

rapid reaction, as was evident from a deep yellow to

yellow-gold color change. Removal of the solvent and

THF solutions of Cp*(PMe₃)Ir(Li)(H) were stable for

several days at ambient temperature. Benzene solutions

of Cp*(PMe₃)Ir(Li)(H) were similarly stable, but the

aggregated complex began to precipitate after several

hours at room temperature. Heating C₆D₆solutions of

Cp*(PMe₃)Ir(Li)(H) resulted in decomposition to Cp*-

(PMe₃)IrH₂with no detectable deuterium incorporation

2

as determined by analysis by H NMR spectroscopy.²⁷

1

analysis of the reaction mixture by H NMR spectros-

We have not investigated the source of the Ir-bound

hydrogen in this reaction.²⁸

copy showed Cp*(PMe₃)Ir(CH₂CH₂CMe₃)(H) (4a ) and

Cp*(PMe₃)IrH₂(1) in an 8:1 ratio. The alkylation

product was isolated as the bromide by treatment of a

benzene solution of the crude product mixture with

CHBr₃and subsequent chromatography on silica gel.

Cp*(PMe₃)Ir(CH₂CH₂CMe₃)(Br) (4b) was isolated as

a yellow crystalline solid. Determination of the stereo-

chemistry of the reaction with labeled 3 (3-d ₂) required

prior knowledge of each of the ¹H-¹H coupling constants

in the fully protiated complex Cp*(PMe₃)Ir(CH₂CH₂-

CMe₃)(Br) (4b). The stereogenicity of the pseudotetra-

hedral iridium center in complex 4b results in a

diastereotopic relationship between each pair of protons

on the R- and â-carbons of the dimethylbutyl group

(Scheme 1; Figure 2). In C₆D₆, the two R-protons appear

at 2.27 and 1.44 ppm with each resonance displaying a

16-line dddd pattern, while the two diastereotopic

â-protons are manifest as two overlapping doublet of

triplets (1.19 and 1.11 ppm). In C₆D₆, the R-proton

resonance located at 1.44 ppm was partially obscured

by an impurity which could not be removed by chroma-

tography or recrystallization, and we attempted deter-

mination of the coupling constants in CDCl₃. In this

solvent, both R-proton resonances were well-resolved;

however slow conversion to the chloride complex Cp*-

(PMe₃)Ir(CH₂CH₂CMe₃)(Cl) via halogen exchange was

Ster eoch em istr y of th e Rea ction of Cp *(P Me₃)-

Ir (Li)(H) w ith 3,3-Dim eth ylbu ta n e Tr iflu or o-

m et h a n esu lfon a t e-1,2-syn -d ₂. Previous work per-

formed in this laboratory demonstrated that reaction

of Cp*(PMe₃)Ir(Li)(H) with certain organic triflates

produced good yields of the complexes Cp*(PMe₃)Ir(R)-

(H) (R ) primary alkyl, trimethylsilyl).²We adopted this

method for independent syntheses of compounds of this

class to facilitate our studies of C-H activation by the

16e fragment Cp*(PMe₃)Ir. However, these early studies

did not include an investigation of the mechanism of

the alkylation reactions.

An obvious candidate for the mechanism is a simple

“inner-sphere” bimolecular nucleophilic displacement

(S_N2) reaction of triflate anion by Cp*(PMe₃)Ir(Li)(H).

This should take place with inversion of stereochemical

configuration at the reacting carbon atom of the alkyl

triflate. Alternatively, the reaction could proceed by

sequential “outer-sphere” electron transfer and triflate

loss with products subsequently formed by collapse of

the resulting radical pair.²⁹This process should take

place with significant loss of stereochemical integrity

(racemization) at carbon. Whitesides and co-workers

(27) This indicated that the walls of glass vessels could serve as

proton sources for the decomposition of the complex.

(28) A reviewer has suggested to us the interesting possibility that

the formation of 1 upon heating solutions of complex 2 could result

from disproportionation of 2 to 1 and Cp*(PMe₃)IrLi₂. The fact that

we have never been able to isolate 2 completely free from 1 as well as

the observation of precipitates in standing benzene solutions of 2 lend

additional support to this idea.

(29) Lowry, T. H.; Richardson, K. S. Mechanism and Theory in

Organic Chemistry, 3rd ed.; Harper & Row: New York, 1987; p 487

and references therein, p 409 and references therein.

(30) For a related reference for the use of the neohexyl group in

organometallic mechanistic studies see: Igau, A.; Gladysz, J . A.

Organometallics 1991, 10, 2327.

2008 Organometallics, Vol. 18, No. 10, 1999

Peterson et al.

F igu r e 2. ¹H{³¹P} NMR spectrum of complex 4b in CDCl₃.

Ta ble 1. Cou p lin g Con sta n ts for Com p lex 4b in Hz

(C₆D₆Solven t)

resonance (ppm)

²J _R-R

³J _R-âsyn

³J _R-âanti

³J _R-P

2.27

1.44

10.6

10.7

4.6

4.4

13.6

13.9

4.8

resonance (ppm)

²J _â-â

³J _R-âsyn

³J _R-âanti

³J _â-P

1.19

1.11

13.6

13.5

4.9

13.6

13.5

not observed

F igu r e 3. ¹H{²H} NMR spectrum of complex 4c-a n ti-d ₂

in C₆D₆.

observed. The splitting patterns are most easily resolved

for the R-hydrogens, especially in the ³¹P-decoupled

spectrum, where two 8-line ddd patterns are observed

(Figure 2). The spectra are consistent with two-bond

coupling of the R-protons with each other and three-

bond couplings to the diastereotopic â-hydrogen atoms

14.1 Hz for the downfield R-hydrogen resonance (2.38

ppm in CDCl₃) and 14.1 Hz for the upfield R-hydrogen

resonance (1.71 ppm in CDCl₃). By comparison with the

coupling constants determined for the all-protio system,

this assignment suggests that the R- and â-hydrogen

atoms of each diastereomer³²exist in a relative anti

relationship to one another (4c-a n ti-d ₂, Figure 3).

1

and the bound phosphine. The individual H-¹H cou-

pling constants for the R- and â-hydrogen resonances

were ascertained by comparison of the ¹H{³¹P} spectrum

with the fully coupled ¹H NMR spectrum and are

provided in Table 1.

The smaller H-H coupling predicted for 4c-syn -d ₂

would require that the presence of this material produce

lines appearing between the two doublets seen for R-H

of the anti isomer. Unfortunately, this section of the

spectrum is not completely clean. Spectral simulations

using the J values measured from the perprotio material

predict that the pattern would look somewhat different

from that shown in Figure 3. However, the simulations

require a guess as to the isotope shift on the resonance

positions, and so we cannot rigorously determine whether

the small peaks between the two large doublets are due

to an impurity, to insufficient power to effect complete

²H decoupling in the experiment, or to the presence of

some 4c-syn -d ₂. Even if the smaller lines are all due to

the syn isomer, careful integration indicates that this

would constitute a ratio of about 85:15 inversion/

retention. We can therefore conservatively say that the

reaction proceeds with at least 85% inversion of config-

uration at the reacting carbon center of 3,3-dimethyl-

butyl triflate and therefore occurs substantially, if not

exclusively, by an S_N2 mechanism.³³

The preparation of the labeled iridium complex 4a -

d ₂was effected by the reaction of triflate 3-syn -d ₂with

2 as described for the unlabeled complex. The presence

of complexes with both R and S absolute configuration

at the iridium stereocenter, and the observation of

chloride for bromide exchange in 4b in CDCl₃solvent,

prompted us to perform the coupling constant analysis

on the analogous complex Cp*(PMe₃)Ir(CHDCHDCMe₃)-

(Cl) (4c-d ₂). Therefore, 4a -d ₂was converted to the

chloride complex by reaction with CCl₄(Scheme 1). The

coupling constants for the deuterium-labeled complex

4c-d ₂were determined analogously. However, the pres-

ence of two- and three-bond ¹H-²H couplings compli-

cated a straightforward interpretation and required that

we obtain the ¹H{²H} spectrum as well.³¹The deuterium-

decoupled spectrum of the product 4c-d ₂in C₆D₆is

shown in Figure 3. Once again, the downfield R-H

resonance provides the clearest opportunity for analysis

of the reaction stereochemistry. With one R- and one

â-hydrogen replaced by deuterium, in the absence of ²H

coupling a simple dd pattern for the downfield R-H is

predicted, due to coupling to P and to the (now single)

(32) The presence of stereogenic centers on the R- and â-carbons of

the dimethylbutyl group as a result of isotopic substitution in 3-d ₂gives

rise to four possible enantiomeric pairs of diasteromers in 4c-d ₂. If a

mixture of inversion and retention mechanisms was active in the

present reaction, all four enantiomeric pairs could, in principle, be

observed. Since the method of preparation of the labeled triflate has

in essence “coupled” two of the enantiomeric pairs to each other, an

exclusive inversion or retention mechanism can produce only two

enantiomeric pairs of diastereomers.

3

â-H. From these experiments, J _H-Hwas found to be

(31) Details of the ²H decoupling procedure as well as the coupled

and uncoupled spectra are available at the UC Berkeley NMR facility

website (http://www.cchem.berkeley.edu/college/facilities/nmr/apps/

misc/h2dec.html).

Deprotonation of (η⁵-C₅Me₅)(PMe₃)IrH₂

Organometallics, Vol. 18, No. 10, 1999 2009

Sch em e 2

Estim a tion of th e Acid ity of Cp *(P Me₃)Ir H₂. Data

on the pK_a’s of organometallic complexes are not as

extensive as those available for organic compounds.

However, in recent years several groups have begun to

provide pK_adata for transition metal hydrides.^15-18,20

In general, it is found that thermodynamic acidities

decrease in descending a metal triad and increase from

left to right across the transition series in the periodic

table.³⁴Other ligands attached to the metal center also

have a strong effect on the pK_a, electron-donating

ligands (e.g., phosphines) reducing acidities and electron-

accepting ligands (e.g., CO) increasing them. Typical

examples of measured pK_avalues in acetonitrile solvent

range from 8.4 for Co(CO)₄(H) to 26.6 for Cp(PMe₃)W-

(CO)₂(H). Substitution of Cp* for Cp in the complex

CpMo(CO)₃(H) led to a increase in the pK_afrom 13.9 to

17.1_.A similar substitution in the complex CpFe(CO)₂-

(H) increased the pK_afrom 19.4 to 26.3. Substitution of

a phosphine for CO had an even larger effect. The

acidity of CpW(CO)₃(H) (pK_a) 16.1) is 10.5 pK_aunits

lower than CpW(CO)₂(PMe₃)(H) (pK_a) 26.6).

In light of these observations, we anticipated that

Cp*(PMe₃)IrH₂(1), by virtue of its relatively electron-

rich coordination sphere and position in the transition

series, would exhibit an unusually high pK₁. This

prediction was substantiated semiquantitatively by

quenching studies with various carbon acids. Benzene

solutions of Cp*(PMe₃)IrH₂(1) were treated with 1 equiv

of tert-butyllithium to generate Cp*(PMe₃)Ir(Li)(H) (2),

and the volatile materials were removed in vacuo. The

resulting yellow oil was dissolved in THF-d₈and treated

with 1 or more equiv of a carbon acid of known acidity

(unfortunately, the reactivity of DMSO and CH₃CN

toward 2 precluded their use as solvents for quenching

studies, preventing exact comparisons to previously

measured transition metal hydride acidities). These

experiments demonstrated that 2 is exceptionally basic.

Reaction with diphenylmethane (pK_a) 32.2), CH₃CN

(pK_a) 31.3), and even DMSO (pK_a) 35.1)³⁵afforded

Cp*(PMe₃)IrH₂and the corresponding lithium methide

conjugate bases of the carbon acids in quantitative yield,

as determined by H NMR spectroscopy (eq 4a). While

1

H₂is not often regarded as a Brønsted acid, we found

that it underwent a clean reaction with 2. When a C₆D₆

solution of Cp*(PMe₃)Ir(Li)(H) was placed under 720

Torr of hydrogen, heating at 45 °C for 18 h resulted in

quantitative formation of Cp*(PMe₃)IrH₂and was ac-

companied by the formation of a white precipitate

(presumably polymeric LiH) (Scheme 2). In an analo-

gous experiment, a C₆D₆solution of Cp*(PMe₃)Ir(Li)-

(H) was placed under 720 Torr of D₂and a mixture of

Cp*(PMe₃)IrH₂, Cp*(PMe₃)Ir(D)(H), and Cp*(PMe₃)IrD₂

was detected by ¹H and ²H NMR spectroscopy. No

deuterium was detected in the Cp* or PMe₃ligands

(vide supra). The observation of the three isotopomeric

complexes suggests not only that Cp*(PMe₃)Ir(Li)(H) is

capable of deprotonating H₂but that Cp*(PMe₃)Ir(Li)-

(H) undergoes proton exchange with Cp*(PMe₃)IrH₂to

result in a statistical mixture of isotopomers (Scheme

2).³⁶

In contrast, treatment of the yellow solution of 2 with

toluene did not result in its deprotonation to form

benzyllithium and Cp*(PMe₃)IrH₂. The possibility that

toluene deprotonation was slow rather than thermody-

namically unfavorable, as is often observed with lithium

bases, prompted us to investigate the reverse of this

reaction. When a THF-d₈solution of Cp*(PMe₃)IrH₂was

treated with 1 equiv of benzyllithium, quantitative

formation of toluene and Cp*(PMe₃)Ir(Li)(H) was ob-

served (eq 4b). This demonstrates that the acidity of

Cp*(PMe₃)IrH₂in THF is bracketed by the acidities of

DMSO and toluene.³⁵To the extent that pK_a’s in CH₃-

(33) However, we cannot rule out a contribution to the reaction

resulting from an electron-transfer mechanism that creates a geminal

radical pair that collapses on the time scale of radical inversion.

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

Principles and Applications of Organotransition Metal Chemistry;

University Science Books: Mill Valley, CA, 1987; Ch. 3, p 92.

(35) Bordwell, F. G. Acc. Chem. Res. 1988, 21, 456.

(36) Alternatively, reaction with hydrogen could be reversible and

HD formed could scramble H/D into the iridium complex.

2010 Organometallics, Vol. 18, No. 10, 1999

Peterson et al.

with respect to exposure to air and moisture and could

even be recrystallized from an ethanol-water mixture.

The trimethylstannyl analogue was less stable and

decomposed rapidly in solution upon exposure to air or

attempted purification by column chromatography.

Analysis of complex 5a by ¹H and ³¹P NMR spectroscopy

revealed couplings between tin, hydrogen, and phos-

phorus. The observed coupling constants (J _P-Sn) 167

Hz and J _H-Sn) 133 Hz) are consistent with two-bond

coupling and support our assignment of a structure with

an Ir-Sn bond. We anticipated that complexes 5a and

5b might show evidence of an agostic Sn-H interaction,

providing an example of an arrested transition state for

oxidative addition/reductive elimination of Sn-H bonds

to/from the Cp*(PMe₃)Ir fragment. Typical values of

¹J _H-Snfor alkyltin hydrides range from 1500 to 1800

CN and/or DMSO can be extrapolated to THF,^37,38the

first pK_aof Cp*(PMe₃)IrH₂falls in the range 38-41. To

our knowledge, this represents the highest pK_aof a

transition metal hydride yet reported.

With the assistance of A. Streitwieser and J . Krom,

we attempted to determine more precisely the pK₁of

Cp*(PMe₃)IrH₂. The use of cesium bases in THF solvent

systems has been found to minimize ion-pairing effects

on acidities and provide pK_avalues comparable to those

observed in other solvent systems.^37,38Unfortunately,

the attempted reaction of cumylcesium with Cp*(PMe₃)-

IrH₂failed to provide a detectable concentration of

hydridoiridate before the onset of decomposition of

cumylcesium. That cumylcesium (pK_acumene ) 40.7)³⁷

failed to react while benzyllithium (pK_atoluene ) 40.9)³⁷

gave quantitative deprotonation of Cp*(PMe₃)IrH₂sug-

gests that the pK₁of 1 is less than that of cumene (i.e.,

proton transfer from 1 to cumylcesium is thermody-

namically favorable), but steric congestion around the

iridium center inhibits the approach of the tertiary

aromatic base.

2

Hz with J _H-Snfor alkyltin species in the range of 50-

2

70 Hz.⁴⁰However, J _H-Snwas found to be well below

1

the value of 1895 Hz reported for J _H-Snin Ph₃SnH,

which suggests the absence of any significant interac-

tion between the hydridic hydrogen atom and the Sn

center.^41,42Further, complex 5a was found to be excep-

tionally stable, showing no signs of decomposition even

upon prolonged photolysis or heating for 20 h at 195 °C

in benzene solution.

Bor yl Der ivatives. The discovery of transition metal-

catalyzed functionalization of organic substrates medi-

ated by boranes has prompted much recent interest in

the nature of transition metal-boryl complexes.^43-45

These complexes are typically formed via oxidative

addition of a borane to an electronically unsaturated

transition metal center or by the reaction of a transition

metal anion with a boron halide;^43-50recently metal-

boryl complexes capable of alkane activation have been

discovered.⁵¹Though much of the work to date has

focused on the use of catecholboranes, several examples

involving boranes lacking oxygen donor groups are

known.^46,52-56With the nucleophilicity of Cp*(PMe₃)Ir-

(Li)(H) being clearly defined in the present study, we

sought to determine if its reaction with boron halides

could provide entry into a novel class of iridium com-

plexes.

The potassium salt of hydridoiridate 2 can also be

generated by reaction with benzylpotassium in benzene

or benzene-THF mixtures. The resulting complex was

found to be unstable at ambient temperature in pure

THF, undergoing decomposition to a single unidentified

iridium hydride product. Initial studies of the potassium

iridate complex show that it possesses enhanced reac-

tivity in comparison to its lithium congener in related

reactions, though it reacts much less cleanly. Attempts

to deprotonate Cp*(PMe₃)IrH₂with less basic agents

were unsuccessful. Treatment of Cp*(PMe₃)IrH₂with

NaNH₂(pK_aNH₃) 38),³⁵KH-18-crown-6 (pK_aH₂

)

35),³⁵or LDA (pK_adiisopropylamine ) 35.7)³⁹failed to

produce any detectable reaction. This supports our

assertion that the pK₁of Cp*(PMe₃)IrH₂lies above 38.

R ea ct ion s of Cp *(P Me₃)Ir (Li)(H ) w it h Ma in

Gr ou p a n d Or ga n ic Electr op h iles. Or ga n osta n -

n a n es. Cp*(PMe₃)Ir(Li)(H) was found to undergo a

variety of clean reactions with electrophilic main group

compounds. Treatment of a benzene solution of Cp*-

(PMe₃)Ir(Li)(H) with 1 equiv of Ph₃SnCl or Me₃SnCl

resulted in formation of Cp*(PMe₃)Ir(SnPh₃)(H) (5a ) and

Cp*(PMe₃)Ir(SnMe₃)(H) (5b) in 71% and 91% yields,

respectively (eq 5). Complex 5a was remarkably stable

Treatment of a toluene solution of Cp*(PMe₃)Ir(Li)-

(H) at -78 °C with 1 equiv of boron trifluoride-etherate

led to immediate reaction and precipitation of LiBF₄.

(40) Maddox, M. L.; Flintcraft, N.; Kaesz, H. D. J . Organomet. Chem.

1965, 4, 50.

(41) Schubert, U.; Kunz, E.; Harkers, B.; Willnecker, J .; Meyer, J .

J . Am. Chem. Soc. 1989, 111, 2572.

(42) Moss, J . R.; Graham, W. A. G. J . Organomet. Chem. 1969, 18,

P24.

(43) Burgess, K.; Ohlmeyer, M. J . Chem. Rev. 1991, 91, 1179.

(44) Baker, R. T.; Calabrese, J . C.; Westcott, S. A.; Nguyen, P.;

Marder, T. B. J . Am. Chem. Soc. 1993, 115, 4367.

(45) Cleary, B. P.; Eisenberg, R. Organometallics 1995, 14, 4525.

(46) Hartwig, J . F.; Huber, S. J . Am. Chem. Soc. 1994, 116, 3661.

(47) Hartwig, J . F.; He, X.; Muhoro, C. N.; Eisenstein, O.; Bosque,

R.; Maseras, F. J . Am. Chem. Soc. 1996, 118, 10936.

(48) Hartwig, J . F.; He, X. Organometallics 1996, 15, 5350.

(49) Iverson, C. N.; Smith, M. R., III. Organometallics 1996, 15,

5155.

(50) Iverson, C. N.; Smith, M. R., III. J . Am. Chem. Soc. 1995, 117,

4403.

(51) Waltz, K. M.; Hartwig, J . F. Science 1997, 277, 211.

(52) Hartwig, J . F.; Huber, S. J . Am. Chem. Soc. 1993, 115, 4908.

(53) Cundy, C. S.; No¨th, H. J . Organomet. Chem. 1971, 30, 135.

(54) Baker, R. T.; Ovenall, D. W.; Calabrese, J . C. J . Am. Chem.

Soc. 1990, 112, 9399.

(55) No¨th, H.; Schmid, G. Angew. Chem., Int. Ed. Engl. 1963, 2, 623.

(56) Schmid, G. Angew. Chem., Int. Ed. Engl. 1970, 9, 819.

(37) Streitwieser, A.; Ciula, J . C.; Krom, J . A.; Thiele, G. J . Org.

Chem. 1991, 56, 1074.

(38) Krom, J . A.; Petty, J . T.; Streitwieser, A. J . Am. Chem. Soc.

1993, 115, 8024.

(39) Fraser, R. R.; Mansour, T. S. J . Org. Chem. 1984, 49, 3442.

Deprotonation of (η⁵-C₅Me₅)(PMe₃)IrH₂

Organometallics, Vol. 18, No. 10, 1999 2011

Sch em e 3

1

Analysis of the reaction mixture by H NMR spectros-

copy revealed that approximately 50% conversion to a

new iridium complex had occurred. When the reaction

was carried out using 2 equiv of boron trifluoride-

etherate, greater than 90% conversion to the new

complex was indicated by ¹H NMR analysis. The

complex exhibited resonances at 1.95, 1.29, and -17.45

F igu r e 4. ORTEP diagram illustrating the structure of

7a (hydride ligand not located).

multiple recrystallization of the resulting product from

acetonitrile. Subsequently, we found that Cp*(PMe₃)-

Ir(Li)(H) underwent clean reaction with tetraphenyl-

borinic anhydride (Ph₂BOBPh₂) (Scheme 3) to produce

6b in 90% yield unaccompanied by the formation of the

dihydride or other byproducts.

1

ppm in the H NMR spectrum indicative of bound Cp*,

PMe₃, and hydride ligands. The hydride resonance

appeared as a doublet of triplets consistent with cou-

pling to phosphorus and two equivalent fluorine atoms

and suggested a structure involving a bound difluoro-

boryl ligand. Analysis of the complex by ¹³C, ³¹P, ¹⁹F,

and ¹¹B NMR spectroscopy supported a structural

assignment of Cp*(PMe₃)Ir(BF₂)(H) (6a ) for the reaction

product (Scheme 3). The ¹⁹F NMR spectrum showed a

1:1:1:1 quartet (¹J _B-F) 154 Hz) located at -23.2 ppm.

The ¹¹B NMR spectrum gave a 1:2:1 triplet at 23.9 ppm

(¹J _B-F) 160 Hz) further supporting this assignment.

Rea ction s w ith Or ga n ic Ca r bon yl Com p ou n d s.

The ability of Cp*(PMe₃)Ir(Li)(H) to undergo clean S_N2-

type reactions prompted us to investigate whether the

iridate could also be used to generate novel iridium

complexes with electrophilic reagents via nucleophilic

acyl substitution reactions. To this end, we explored

reactions with a variety of organic carbonyl compounds.

When a benzene solution of 2 was treated with pivalic

anhydride at room temperature, an immediate reaction

1

The lack of observable coupling between ¹¹B and H as

1

well as the position of the hydride H NMR resonance

indicates minimal, if any, interaction between boron and

the hydridic hydrogen. The spectroscopic equivalence of

the two diastereotopic fluorine nuclei is consistent with

a complex exhibiting free rotation about the Ir-B bond

at ambient temperatures. Single crystals of 6a for study

by X-ray diffraction were grown by slow cooling of an

acetonitrile solution to -40 °C. Unfortunately, prelimi-

nary data indicated long-range disorder in the crystal

due to interchange of the BF₂and H ligands in the

crystal lattice, thus preventing a meaningful solution

of the structure. Additionally, multiple attempts at

recrystallization could not generate analytically pure

samples of 6a free from dihydride complex 1. Complex

6a was found to be thermally stable in toluene solution,

exhibiting no signs of decomposition upon extended

heating at 135 °C. Interestingly, at this temperature the

complex was observed to undergo H-D exchange with

toluene-d₈.

1

occurred. Analysis of the product by H NMR spectros-

copy showed resonances at 1.82, 1.28, 1.19, and -17.02

ppm, corresponding to the Cp*, PMe₃, tert-butyl, and

hydride functionalities along with resonances for Cp*-

(PMe₃)IrH₂. Removal of the volatile materials in vacuo,

extraction of the crude solid with pentane, and slow

cooling to -40 °C afforded an analytically pure com-

pound identified as the 2,2-dimethylpropionyl hydride

complex 7a by a combination of spectroscopic techniques

(eq 6). The identity of the reaction product was con-

In contrast to the reaction with boron trifluoride-

etherate, Cp*(PMe₃)Ir(Li)(H) underwent complete reac-

firmed by X-ray diffraction. The ORTEP diagram and

positional parameters are provided in Figure 4. In this

structure, the hydride was not located but has been

added to the diagram for clarity. The Ir-C₁₄and C₁₄-O

bond distances were found to be 2.036 and 1.235 Å,

respectively, in the range expected from comparison

with other late metal acyl complexes.^57-61The Ir atom

1

tion with just 1 equiv of Ph₂BBr. The H, ¹³C, ³¹P, and

¹¹B NMR spectra support an analogous reaction product

(6b) containing the diphenylboryl ligand with equivalent

phenyl groups attached to boron (Scheme 3). Complex

6b was obtained in analytically pure form with great

difficulty. Reaction of Cp*(PMe₃)Ir(Li)(H) with Ph₂BBr

to produce 6b was also accompanied by the formation

of Cp*(PMe₃)Ir(H)(Br) and Cp*(PMe₃)IrH₂, and so pure

material was obtained only after partitioning the crude

reaction mixture between pentane and acetonitrile,

selective bromination of the dihydride complex by

titration of the reaction mixture with bromoform, and

(57) Koh, J . J .; Lee, W.-H.; Williard, P. G.; Risen, W. M. J .

Organomet. Chem. 1985, 284, 409.

(58) Bleeke, J . R.; Tesfamichael, H.; Chiang, M. Y. Organometallics

1991, 10, 19.

(59) Bianchini, C.; Meli, A.; Peruzzini, M.; Vizza, F. Organometallics

1991, 10, 820.

2012 Organometallics, Vol. 18, No. 10, 1999

Peterson et al.

is roughly in the C-CdO plane of the acyl group. The

sum of angles around the carbonyl carbon atom was

found to be 360°, indicating symmetric bonding of the

acyl carbon to Ir.

Reaction of 2 with benzoic anhydride provided the

analogous phenacyl hydride 7b in 45% yield after

chromatographic purification and recrystallization. Both

acyl hydride complexes were stable indefinitely in

solution at room temperature under an inert nitrogen

atmosphere, but decomposed quickly upon exposure to

air. In contrast, reaction of 2 with acetic anhydride

yielded Cp*(PMe₃)IrH₂as the sole iridium-containing

product. Although the organic product of this reaction

was not characterized, we assume the dihydride was

formed by proton abstraction from the R-carbon of the

anhydride. The basicity of the iridate complex would

thus appear to limit its use in the formation of acyl

hydride derivatives to reactions with compounds lacking

acidic hydrogens.

The parent formyl complex 7c was obtained analo-

gously in 28% purified yield by reaction of 2 with ethyl

formate (eq 7).⁶²The connectivity of 7c was confirmed

By analogy with the reactions of 2 with acid anhy-

drides, we anticipated that reactions of 2 with organic

carbonates would provide access to the corresponding

alkoxycarbonyl hydride complexes. However, when a

benzene solution of 2 was treated with dimethyl carbon-

ate at ambient temperature, the known complex Cp*-

(PMe₃)Ir(CO) (8) was obtained in a 1:2.2:1.4 ratio along

with Cp*(PMe₃)IrH₂and Cp*(PMe₃)Ir(Me)(H) (9) (Scheme

4). Similarly, reactions of 2 with di-tert-butyl dicarbon-

ate or CO₂both yielded the carbonyl complex 8.

Acyl and alkoxycarbonyl hydrides are believed to be

intermediates in a large number of industrially impor-

tant processes including the Fischer-Tropsch reaction,

the water-gas shift reaction, and olefin hydroformyla-

tion. Consequently, the study of such complexes has

drawn considerable attention.^57-61,63-72We anticipated

that complexes 7a -c would undergo thermal reductive

elimination to produce the transient unsaturated 16e

Cp*(PMe₃)Ir fragment and aldehyde products. While

acyl hydride complexes 7a -c were found to exhibit

varying degrees of thermal stability, they gave complex

mixtures of products, which by ¹H NMR analysis in each

case included at least some of the carbonyl derivative

Cp*Ir(PMe₃)(CO) (8). This pathway, which involved the

unusual overall elimination of R-H across the Ir-C

linkage, was especially evident in the case of the formyl

hydride 7c. In C₆D₆solution, the parent formyl complex

7c underwent clean conversion to 8 via the apparent

elimination of dihydrogen upon heating for 21 h at 45

°C (Scheme 5).

by X-ray diffraction, but long-range disorder resulting

from -CHO and -H interchange in the lattice unfor-

tunately prevented an accurate determination of bond

lengths and angles. Complex 7c was found to be

moderately stable in solution at ambient temperatures

but showed signs of decomposition after several hours.

Somewhat surprisingly, complex 2 was also found to

undergo reaction with benzaldehyde. In a NMR tube

reaction, when a benzene solution of 2 was treated with

1 equiv of benzaldehyde at ambient temperature, con-

version to phenacyl hydride 7b and 1 was observed in

a 1.25:1 ratio. When 2 equiv of benzaldehyde was

utilized, 7b and 1 were formed in a 3:1 ratio. The

increased yield of 7b observed when a second equiv of

benzaldehyde was employed suggested that its forma-

tion was mediated by the formation of adduct 7d , which

underwent hydride transfer to benzaldhyde to give 7b

and lithium benzyloxide (eq 8). To test this hypothesis,

we attempted to trap the benzyloxide ion via reaction

with methyl p-toluenesulfonate. As expected, addition

of benzaldehyde to a solution of 2, followed by the

addition of methyl p-toluenesulfonate to the reaction

solution resulted in the formation of benzyl methyl ether

in 66% yield (relative to 7b), consistent with the

intermediacy of the benzyloxide ion.

We considered the possibility that the targeted meth-

oxycarbonyl hydride 10 might actually be an intermedi-

ate in the formation of 8 from 2 and dimethyl carbonate,

but that this intermediate was unstable, undergoing an

(63) Lilga, M. A.; Ibers, J . A. Organometallics 1985, 4, 590.

(64) Rauchfuss, T. B. J . Am. Chem. Soc. 1979, 101, 1045.

(65) Thorn, D. L. Organometallics 1982, 1, 197.

(66) Tolman, C. A.; Ittel, S. D.; English, A. D.; J esson, J . P. J . Am.

Chem. Soc. 1979, 101, 1742.

(60) Bodner, G. S.; Patton, A. T.; Smith, D. E.; Georgiou, S.; Tam,

W.; Wong, W.-K.; Strouse, C. E.; Gladysz, J . A. Organometallics 1987,

6, 1954.

(61) Milstein, D.; Fultz, W. C.; Calabrese, J . C. J . Am. Chem. Soc.

1986, 108, 1336.

(67) Headford, C. E. L.; Roper, W. R. J . Organomet. Chem. 1980,

198, C7.

(68) Lochow, C. F.; Miller, R. G. J . Am. Chem. Soc. 1976, 98, 1281.

(69) Suggs, J . W. J . Am. Chem. Soc. 1978, 100, 640.

(70) Norton, J . R. Acc. Chem. Res. 1979, 12, 139.

(71) Milstein, D. Acc. Chem. Res. 1984, 17, 221.

(72) Warner, K. E.; Norton, J . R. Organometallics 1985, 4, 2150.

(62) This material can be prepared independently using [Cp*-

(PMe₃)(H)Ir]₂Mg: (a) Golden, J . T.; Andersen, R. A.; Bergman, R. G.

Unpublished results. See also: (b) Golden, J . T.; Peterson, T. H.;

Holland, P. L.; Bergman R. G.; Andersen, R. A. J . Am. Chem. Soc.

1998, 120, 223-224.

Deprotonation of (η⁵-C₅Me₅)(PMe₃)IrH₂

Organometallics, Vol. 18, No. 10, 1999 2013

Sch em e 4

Sch em e 5

the observed products. A similar mechanism has been

proposed to account for reactions involving decarbony-

lation of aldehydes by Rh(I) and Ir(I) complexes.^69,71In

mechanism b, the acyl hydride complex undergoes a

simple concerted elimination to provide the observed

products. While the stepwise mechanism has precedent

for late-metal systems, we believe that it can be ruled

out in the present cases for two reasons. Previous

studies of RH reductive eliminations from Cp*(PMe₃)Ir

(R)(H) conducted within our group have shown that

PMe₃loss is not a thermally facile process.⁷⁹Even if

acyl-for-alkyl substitution facilitated phosphine loss, the

different acyl substituents would not be expected to lead

to the range of thermal stabilities observed in the

present work. In addition, reductive elimination of RH

from Cp*(CO)Ir(R)(H) would generate the 16e Cp*Ir-

(CO) fragment and would be expected to lead to C-H

activation of the solvent, an outcome that was not

observed.⁸⁰

elimination similar to that observed in the thermolyses

of 7a -c (eq 9). We therefore attempted to observe this

In contrast, support for the concerted elimination

mechanism can be obtained by examining the relative

rates for the elimination process. In theoretical studies

of reductive elimination reactions from platinum phos-

phine complexes, Goddard and Low rationalized the

relative rates of reductive elimination of X-Y (X-Y )

H-H > CH₃-H > CH₃-CH₃) on the basis of the

spherical symmetry of the H 1s valence orbital, which

can allow it to simultaneously form H-H and C-H

bonds while breaking M-H bonds.^81,82However, the

directionality of the carbon sp³hybrid requires that it

adopt different orientations for the M-C and C-C or

C-H bonds such that “in the transition state a com-

promise must be reached that is not optimal for either

bond”. This concept of bond directionality can also be

used to explain the relative ordering of elimination rates

(R ) OCH₃∼ OLi (presumed; see below) > H . Ph >

tert-Bu) described above. The directionality of the sp³-

hybridized carbon of the tert-butyl group attached to the

intermediate in a low-temperature NMR experiment.

A solution of 2 in toluene-d₈was frozen in liquid

nitrogen, and 2 equiv of dimethyl carbonate was trans-

ferred into the tube in vacuo. After warming the tube

to -78 °C, it was placed in an NMR probe at -66 °C

1

and a H NMR spectrum was recorded. No reaction was

observed at this temperature. Gradual warming of the

tube did not produce an observable reaction until it

reached 0 °C. After 5 min at 10 °C, approximately 35%

conversion to 8 and 9 was observed without the detection

of any intermediate species. In a similar vein, we

attempted direct observation of the postulated lithium

salt of the iridium carboxylate hydride 11 formed by the

reaction of 2 with carbon dioxide (eq 9). In this experi-

ment, CO₂was condensed into an NMR tube containing

a frozen toluene solution of 2. After warming to -78 °C

for 5 min, the tube was placed in the NMR probe at -66

°C and the ¹H NMR spectrum was recorded. At this

temperature, however, complete reaction to 8 had

already occurred. If iridium acyl derivatives are inter-

mediates in these reactions, these results require that

they are formed in a rate-limiting step and rapidly

decompose to 8.

(74) 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, and references

therein.

(75) Davison, A.; Martizez, N. J . Organomet. Chem. 1974, 74, C17.

(76) Kubota, M.; Blake, D. M.; Smith, S. A. Inorg. Chem. 1971, 10,

1430.

(77) Slack, D. A.; Egglestone, D. L.; Baird, M. C. J . Organomet.

Chem. 1978, 146, 71.

(78) Treichel, P. M.; Stone, F. G. A. Adv. Organomet. Chem. 1964,

1, 143.

(79) Buchanan, J . M.; Stryker, J . M.; Bergman, R. G. J . Am. Chem.

Soc. 1986, 108, 1537.

(80) Extended thermolyses at 195 °C did eventually result in the

formation of Cp*(PMe₃)Ir(C₆D₅)(D), though at a much slower rate than

formation of 8.

Two possible mechanisms that would account for

these elimination reactions are illustrated in Scheme

6. In mechanism a , phosphine loss would generate a

transient 16-electron Cp*Ir(COR)(H) complex which

undergoes subsequent CO deinsertion,^73-78RH reduc-

tive elimination, and phosphine recoordination to give

(81) Low, J . J .; Goddard, W. A. J . Am. Chem. Soc. 1984, 106, 8321.

(82) Low, J . J .; Goddard, W. A. J . Am. Chem. Soc. 1984, 106, 6928.

(73) Casey, C. P.; Scheck, D. M. J . Am. Chem. Soc. 1980, 102, 2723.

2014 Organometallics, Vol. 18, No. 10, 1999

Peterson et al.

Sch em e 6

carbonyl carbon atom (as well as its steric bulk in an

already sterically encumbered ligand sphere) would

require that it undergo significant reorientation to

achieve bonding with the hydride in the elimination

transition state, thereby leading to low rates of elimina-

tion. The phenyl group, however, bonds to the acyl

carbon via an sp²hybrid and can utilize its unhybridized

p orbital in transition-state bonding with the hydride

and would be expected to demonstrate a reduced barrier

to R-elimination relative to alkyl derivatives. Following

a similar argument for the formyl hydride complex 7c,

the spherically symmetric 1s orbital of the acyl-bound

hydrogen would be anticipated to facilitate transition-

state interactions and cause a further lowering of the

activation barrier. Finally, our inability to directly

observe alkoxycarbonyl and lithium carboxylate hy-

drides 10 and 11 could be rationalized on the basis of

the ease with which the oxygen nonbonding pairs can

interact with the hydride with minimal disruption of

bonding to the acyl carbon, leading to even faster

elimination rates.^83,84We cannot, however, rule out the

intervention of η²-aldehyde or η²-arene complexes.^64,85

Given the importance of acyl hydrides in numerous

industrial processes, it would be interesting to deter-

mine the scope of this postulated mechanism as it

relates to other metal complexes.

vastly different chemical properties observed in these

complexes in comparison to their protioalkyl ana-

logues.^86-93Vinyl fluorides are normally quite inert, but

in some cases undergo substitution reactions with

strongly nucleophilic agents via addition-elimination

mechanisms to afford substituted vinyl derivatives.⁹⁴

The reactivity we observed in nucleophilic substitution

at carbon-oxygen multiple bonds prompted us to in-

vestigate the possibility of substitution at activated

carbon-carbon multiple bonds, especially those that

might lead to overall C-F activation reactions.

Complex 2 underwent a clean instantaneous reaction

with hexafluorobenzene to generate the pentafluoro-

phenyl iridium hydride complex 12 in 74% yield (Scheme

7). Complex 12 was purified by column chromatography

and recrystallization. Analysis of 12 by ¹⁹F NMR

spectroscopy showed five inequivalent fluorine nuclei

indicating slow rotation about the iridium-phenyl bond

on the time scale of the NMR measurement. Complex

12 was found to be extremely stable, undergoing no

detectable decomposition upon heating for 20 h at 195

°C. Reaction of 2 was also observed with fluorobenzene,

albeit much more slowly than with perfluorobenzene,

to give the known compound Cp*(PMe₃)Ir(Ph)(H) (13)

in 20% NMR yield along with 1.⁹⁵

F lu or oca r bon s: C-F Bon d Activa tion . The chem-

istry of perfluoroalkyl and perfluorovinyl transition

metal complexes has long been of interest due to the

(86) Banger, K. K.; Brisdon, A. K.; Gupta, A. J . Chem. Soc., Chem.

Commun. 1997, 139.

(87) Hopton, F. J .; Rest, A. J .; Rosevear, D. T.; Stone, F. G. A. J .

Chem. Soc., Part A 1966, 1326.

(88) McClellan, W. R. J . Am. Chem. Soc. 1961, 83, 1598.

(89) Bruce, M. I.; Stone, F. G. A. J . Chem. Soc., Part A 1966, 1837.

(90) J olly, P. W.; Bruce, M. I.; Stone, F. G. A. J . Chem. Soc. 1965,

5830.

(91) Clark, H. C.; Tsang, W. S. J . Am. Chem. Soc. 1967, 89, 533.

(92) Uson, R.; Fornies, J .; Tomas, M. J . Organomet. Chem. 1988,

358, 525.

(93) Brothers, P. J .; Roper, W. R. Chem. Rev. 1988, 88, 1293.

(94) March, J . In Advanced Organic Chemistry; J ohn Wiley &

Sons: New York, 1985; p 671.

(95) The slow rate observed for the reaction of 2 with fluorobenzene

allowed for significant decomposition of 2 to the dihydride complex 1,

the major product of the reaction.

(83) Preliminary studies of the perfluoroacyl hydride complex Cp*-

(PMe₃)Ir(COC₃F₇)(H) indicate that it undergoes R-elimination at a

temperature intermediate between that of the formyl and phenacyl

complexes 7c and 7b. This observation is consistent with a concerted

mechanism on the basis of the increased s-character on carbon

fragments bearing strongly electron-withdrawing substituents (see

following reference).

(84) Hughes, R. P. Adv. Organomet. Chem. 1990, 31, 183.

(85) We believe that a bimolecular mechanism as has been suggested

by Norton for osmium alkyl complexes can be ruled out in the present

system, as this mechanism requires that at least one metal center in

the reacting pair possess an open coordination site (see ref 72).

Deprotonation of (η⁵-C₅Me₅)(PMe₃)IrH₂

Organometallics, Vol. 18, No. 10, 1999 2015

Sch em e 7

been postulated to be favorable due to the better ability

of a fluoroalkyl substituent to stabilize a negative charge

compared with that of a fluorine atom. In the reaction

with 1,1,1-trifluoropropene, the only possible mode of

elimination occurs at the 3-position to give the η¹-

difluoroallyl complex. However, in the reaction with

hexafluoropropene, elimination can occur at either the

1- or the 3-position, with elimination at the 1-position

being exclusively observed, leading to the vinyl deriva-

tive. In contrast, complex 2 was found to be completely

unreactive toward (trifluoromethyl)cyclohexane and

R,R,R-trifluorotoluene, supporting the proposed addi-

tion-elimination mechanism.

Su m m a r y

This paper has outlined the preparation, solution

characterization, and reactivity of Cp*(PMe₃)Ir(Li)(H)

(2). This complex can be prepared by deprotonation of

Cp*(PMe₃)IrH₂with only the most basic reagents, and

we have estimated the pK₁for the dihydride to be in

the range 38-41. In aromatic solvents, 2 appears to be

highly aggregated, giving complex spectra, but it reacts

cleanly with a number of electrophilic agents, leading

to the formation of novel stannyl, boryl, fluorocarbyl,

and acyl hydrides. The latter have been shown to

decompose thermally via reductive R-elimination, and

we have proposed a concerted mechanism to account for

the observed products. We are currently pursuing the

R-elimination as a synthetic method directed toward

generating novel complexes of iridium with compounds

of aluminum, magnesium and other Lewis acidic ele-

ments.

When Cp*(PMe₃)Ir(Li)(H) was treated with CF₂dCF₂

in benzene solution at ambient temperature, an im-

mediate reaction occurred to provide numerous prod-

ucts. In contrast, reaction of 2 with hexafluoropropene

occurred cleanly to give the perfluoropropenyl complex

14 in 78% yield. Complex 14 showed ¹H NMR reso-

nances at 1.76, 1.12, and -17.01 with coupling constants

supporting a trans orientation of the trifluoromethyl

group with respect to the iridium center. The iridate

was also found to react with 3,3,3-trifluoropropene to

give Cp*(PMe₃)Ir(CH₂CHdCF₂) (15). The identity of this

reaction product was readily deduced from the one-

1

proton dddd signal located at 4.56 ppm in its H NMR

spectrum and its characteristic resonances in the ¹⁹F

NMR spectrum. Unfortunately, attempts to isolate 15

from unreacted dihydride by crystallization or column

chromatography were unsuccessful. Further, attempts

to derivatize 15 by conversion to its chloride with CCl₄

to facilitate purification resulted in decomposition to

unknown products. The perfluoropropenyl and difluo-

roallyl hydrides were found to be thermally stable, the

former undergoing no detectable decomposition upon

heating in benzene solution at 160 °C for 60 h and the

latter showing no signs of reaction after heating for 48

h at 75 °C. Photolysis of the perfluoropropenyl hydride

(14) for 12 h in C₆D₆solution resulted in 30% conversion

to 13-d ₆.

Exp er im en ta l Section

Gen er a l Com m en ts. Unless indicated otherwise, all ma-

nipulations were conducted in a Vacuum Atmospheres 553-2

drybox containing nitrogen purified by a MO-40-2 Dritrain or

1

on vacuum lines using standard Schlenk techniques. H, ¹³C,

³¹P, ¹⁹F, ⁷Li, and ¹¹B NMR spectra were obtained at the

University of California, Berkeley (UCB), NMR facility on

Bruker AMX series 300 and 400 MHz spectrometers. Infrared

spectra were obtained in KBr matrixes on a Mattson Galaxy

series FT-IR 3000 spectrometer and are referenced to a

polystyrene standard. Elemental analyses were performed at

the UCB Microanalytical Laboratory. Mass spectrometric

analyses were conducted at the UCB Mass Spectrometry

Facility on Kratos MS-50 and AEI MS-12 mass spectrometers.

We believe that reactions of 2 with unsaturated

fluorocarbons proceed via addition-elimination mech-

anisms involving carbanionic intermediates. The rela-

tive rates of the above reactions and regiochemistry

observed in the reaction products are consistent with

this mechanism. The mechanism is illustrated in

Scheme 8 and involves the addition of 2 to the double

bond of the fluoroolefin (e.g., hexafluoropropene) to give

intermediate 16 followed by the elimination of LiF to

give the observed products. For the reactions of hexaflu-

orobenzene, fluorobenzene, and tetrafluoroethylene with

2, attack at any reactive position in the molecule gives

the same intermediate. However, for reactions of 2 with

hexafluoropropene and 1,1,1-trifluoropropene, the ob-

served products are consistent with only one regiochem-

istry of addition. This attack occurs at the least hindered

carbon atom, giving the most highly substituted car-

banionic intermediate. Nucleophilic additions to fluo-

roolefins have been studied extensively by a number of

investigators, and this regiochemistry of addition has

NMR spectra were obtained in Wilmad series 505-PP tubes.

Flame-sealing of NMR tubes was effected under vacuum by

connection of the tube to a Kontes stopcock equipped with a

ground glass joint and connected via a Cajon Ultratorr adapter.

Known-volume gas transfers were conducted with calibrated

glass vessels with pressure measurements determined by an

MKS Baratron gauge attached to a high-vacuum line. Pentane,

hexanes, benzene, toluene, diethyl ether, and tetrahydrofuran

and their deuterated analogues were distilled under nitrogen

from sodium benzophenone ketyl prior to use. Methylene

chloride, chloroform, carbon tetrachloride, acetonitrile, and

boron trifluoride-etherate were distilled from calcium hydride.

tert-Butyllithium (Aldrich) was obtained as a solution and was

filtered, concentrated in vacuo, and recrystallized from pentane

prior to use. All other reagents and solvents were obtained

from commercial suppliers and were degassed (liquids) and

used as received unless otherwise noted. Cp*(PMe₃)IrH₂was

prepared by known literature methods.⁹⁶

2016 Organometallics, Vol. 18, No. 10, 1999

Peterson et al.

Sch em e 8

Cp *(P Me₃)Ir (Li)(H) (2). In a typical procedure, Cp*(PMe₃)-

IrH₂(100 mg, 0.25 mmol) was dissolved in 5 mL of C₆H₆, and

a solution of tert-butyllithium (16 mg, 0.25 mmol) in C₆H₆(1

mL) was added via pipet. After allowing the solution to stir

for 15 min at ambient temperature, the volatile materials were

removed in vacuo to give a yellow oil. Trituration with a small

amount of pentane and washing of the resulting solid with

additional pentane provided Cp*(PMe₃)Ir(Li)(H) as a yellow

microcrystalline solid free from residual Cp*(PMe₃)IrH₂. Com-

plex 2 could also be generated as described above and

manipulated as a solution without its isolation. ¹H NMR

analysis of these solutions indicated yields typically exceeding

80%, with small amounts of residual dihydride present.

Alternatively, the oil thus obtained could be treated with an

ethereal solvent (e.g., THF or DME) to generate an adduct that

was sparingly soluble in that solvent. Filtration of the solid

adduct and washing with benzene produced a yellow micro-

crystalline solid that was stable for weeks at -30 °C. ¹H NMR

(THF-d₈): δ 2.08 (s, 15 H), 1.27 (9 H, d, 10 Hz), -19.16 (d,

J _H-P) 28.3 Hz) ppm. ³¹P{¹H} NMR (THF-d₈): δ -43.17 ppm.

⁷Li NMR (THF-d₈): δ -7.32 ppm. MS (EI): m/z 404 (M - Li⁺).

Cp *(P Me₃)Ir D₂(1-d ₂). In a glass reaction vessel equipped

with a vacuum stopcock was placed Cp*(PMe₃)IrH₂(100 mg,

0.25 mmol), 100 mg of dry silica gel, and a stir bar. The vessel

was evacuated on a Schlenk manifold, and degassed EtOD (3

mL) was added via vacuum transfer. After warming to ambient

temperature, the resulting slurry was stirred for 16 h. The

volatile materials were then removed in vacuo, and a second

3 mL portion of EtOD was added via vacuum transfer. After

stirring for an additional 16 h, the reaction mixture was

pumped to dryness and taken into a glovebox. The crude

reaction product was suspended in pentane (5 mL) and was

filtered through Celite. The tan-colored supernatant was

concentrated in vacuo to afford 90 mg of an off-white solid.

Analysis of the solid by a single-pulse ¹H NMR experiment

showed Cp*(PMe₃)IrD₂as the sole product in 90% yield with

greater than 93% deuterium incorporation based upon inte-

gration.

(E)-1,2-Dideu ter io-3,3-dim eth yl-1-bu ten e. In a Parr high-

pressure reactor was placed a solution of 3,3-dimethylbutyne

(5.00 g, 60.9 mmol) and quinoline (300 mL, 2.5 mmol) in

toluene (15 mL). The solution was charged with 100 mg of 5%

Pd on carbon (deactivated with Pb(OAc)₂), and the reactor was

pressurized to 200 psi with D₂and then vented. After repeating

the pressurization/vent procedure a second time, the reactor

was pressurized to 260 psi and was maintained at ambient

temperature for 90 min. The Parr reactor was then vented,

and the crude reaction mixture was filtered through Celite.

The filtrate was subjected to distillation at atmospheric

pressure through a 10 cm Vigreaux column. (E)-1,2-Dideuterio-

3,3-dimethyl-1-butene (2.66 g) was collected (bp 42-44 °C) in

an ice-cooled glass reaction vessel equipped with a vacuum

stopcock. Analysis of the product by ¹H NMR spectroscopy

demonstrated greater than 90% purity with no detectable

hydrogen atoms in the 1-(E)- or 2-positions. ²H NMR analysis

indicated detectable deuterium incorporation (approximately

40%) in the 1-(Z)-position. ¹H NMR (C₆D₆): δ 4.92 (br s, 0.6

H), 1.00 (s, 9 H) ppm. ²H NMR (C₆D₆): δ 5.81, 4.92, 4.81 ppm.

Lit.^{30 1}H NMR (C₆D₆): δ 4.91 (s), 0.95 (s).

3,3-Dim eth yl-1-bu tan ol-1,2-syn -d₂. 3,3-Dimethyl-1-butanol-

1,2-syn-d₂was prepared following a modified procedure of

Bergbreiter and Rainville.⁹⁷In an oven-dried 100 mL round-

bottom flask was placed 40 mL of freshly distilled THF and a

magnetic stir bar. The flask was fitted with a septum and

purged with nitrogen for 5 min. (E)-1,2-Dideuterio-3,3-di-

methyl-1-butene (3.06 mL) was added via syringe, and the

stirred solution was cooled to 0 °C under nitrogen. Borane-

THF complex (9.3 mL of a 1 M solution in THF) was added

dropwise via syringe over a 3 min period. The solution was

stirred for 40 min at 0 °C and 4 h at room temperature.

Methanol (1.15 mL) was then added, and the solution was

recooled to 0 °C. The solution was then treated with 2.55 mL

of 3 N aqueous NaOH solution and 2.8 mL of 30% H₂O₂

solution in succession. After refluxing for 1 h, the reaction

mixture was partitioned between 100 mL of ice/water and 50

mL of Et₂O. The ethereal layer was separated, and the aqueous

phase was washed with four 50 mL portions of Et₂O. The

combined ethereal extracts were washed with two 20 mL

portions of saturated aqueous sodium thiosulfate, and the

thiosulfate extracts were extracted with Et₂O. After drying the

combined ethereal extracts over MgSO₄, the solvent was

removed by distillation through a Vigreaux column and the

residue was short-path distilled (bp 140 °C, lit.⁹⁷bp 140-145

°C) to provide 1.80 g of pure 3,3-dimethyl-1-butanol-1,2-syn-

Deter m in a tion of th e Kin etic Dep r oton a tion Site in

Cp *(P Me₃)Ir D₂. A solid mixture of Cp*(PMe₃)IrD₂(10 mg,

0.025 mmol) and crystallized tert-butyllithium (2.0 mg, 0.031

mmol) was dissolved in C₆H₆(2 mL) at ambient temperature.

The bright yellow solution was then quenched with acetone

(70 mL), and the pale yellow solution was analyzed for

isobutane by GC/MS spectrometry. GC/MS analysis revealed

the presence of isobutane with greater than 90% deuterium

incorporation.

1

d₂in 74% yield. H NMR (CDCl₃): δ 3.63 (m, 0.7 H), 1.45 (br

1

d, 1 H), 0.89 (s, 9 H) ppm. H{²H} NMR lit.⁹⁷(CDCl₃): δ 3.65

(96) J anowicz, A. H.; Bergman, R. G. J . Am. Chem. Soc. 1983, 105,

3929.

(97) Bergbreiter, D. E.; Rainville, D. P. J . Org. Chem. 1976, 41, 3031.

Deprotonation of (η⁵-C₅Me₅)(PMe₃)IrH₂

Organometallics, Vol. 18, No. 10, 1999 2017

(d 1 H), 3.47 (s, 1 H), 1.49 (d 1 H), 0.93 (s, 9 H) ppm. MS (EI):

m/z 104.06 (M⁺, 100), 105.06 (M + 1, 29.46).

mixture was stirred at ambient temperature for 15 min. The

volatile materials were removed in vacuo, and the brown

residue was dissolved in C₆H₆(5 mL). To the benzene solution

was added CCl₄(100 mg, 0.65 mmol), and the resulting

mixture was stirred for 2 h at ambient temperature. After

removal of the volatile materials under vacuum, the crude

chloride was chromatographed on a 10 mm × 200 mm silica

gel column employing 25% diethyl ether in pentane as the

eluent. The leading yellow band was collected and evaporated

to dryness to give 16 mg of 4c-a n ti-d ₂in 24% isolated yield.

¹H{²H} NMR (CDCl₃): δ 2.38 (dd, J _H-P) 3.9 Hz, J _H-H) 14.1

Hz, 0.5 H), 1.71 (dd, J _H-P) 5.3 Hz, J _H-H) 14.1 Hz, 0.5 H),

1.50 (d, J _H-P) 1.8 Hz, 15 H), 1.28 (d, J _H-P) 10.2 Hz, 9 H)

(the diastereotopic â-protons were partially obscured by the

3,3-Dim eth ylbu ta n e-1-tr iflu or om eth a n esu lfon a te-1,2-

syn -d ₂(3-syn -d ₂). 3,3-Dimethylbutane-1-trifluoromethane-

sulfonate-1,2-syn-d₂was prepared according to the method of

Baum for organic triflates.⁹⁸In a 25 mL round-bottom flask

was placed CH₂Cl₂(10 mL), 3,3-dimethyl-1-butanol-1,2-syn-

d₂(200 mg, 1.92 mmol), and pyridine (155 mL, 1.92 mmol).

The flask was fitted with a septum and was purged with N₂

for 10 min. The stirred solution was cooled to 0 °C and was

treated with triflic anhydride (380 mL, 2.25 mmol). The

reaction mixture was warmed to room temperature and stirred

for 30 min. The crude mixture was then poured into a

separatory funnel, diluted with 10 mL of pentane, and washed

with three 10 mL portions of saturated aqueous sodium

bicarbonate and a 10 mL portion of saturated aqueous sodium

chloride. The organic layer was then dried over MgSO₄and

concentrated in vacuo to afford 249 mg of a pale yellow oil.

Analysis of the product by ¹H NMR spectroscopy indicated

formation of the desired product in 55% yield. The triflate

shows signs of decomposition to unknown products upon

concentration and therefore could not be purified. However,

it can be stored indefinitely at -78 °C. ¹H NMR (CDCl₃): δ

4.56 (br d, 0.7 H), 1.74 (br d, 1 H), 0.95 (s, 9 H) ppm.

Cp *(P Me₃)Ir [1-(3,3-d im eth yl)bu tyl]Br . The undeuter-

ated bromide was prepared for determination of the coupling

constants in the NMR analysis. As described in the text, the

analysis of the deuterated complex was carried out for the

chloride (4b). A solution of 2 was prepared by dissolving Cp*-

(PMe₃)IrH₂(114 mg, 0.281 mmol) in 20 mL of THF and adding

tert-butyllithium (0.28 mmol, 1.7 M/Et₂O, 165 µL) via syringe.

After stirring for 30 min 3 (68 mg, 0.290 mmol) was added via

syringe. The resulting reaction mixture was stirred for 30 min

and the volatile materials removed under vacuum. The reac-

tion mixture was extracted with toluene (10 mL) and then

filtered via filterstick cannula. The filtrate was treated with

200 µL of CHBr₃, producing an immediate color change from

gold to bright orange. After stirring for 1 h the volatile

materials were removed under vacuum. The crude product was

dissolved in diethyl ether and purified by chromatography

through a 1 × 25 cm silica gel column. The leading orange

band (15 mL fraction) was collected and solvent volume

reduced under vacuum. The bromide was then chromato-

graphed again using pentane as the eluent. The leading orange

band was collected (10 mL fraction), and the volatile materials

were removed in a vacuum to yield an orange microcrystalline

product. The product was crystallized from pentane and dried

in vacuo to afford Cp*(PMe₃)Ir[1-(3,3-dimethyl)butyl]Br in 37%

yield. Mp: 129.5-131 °C. IR (NaCl): 2946, 2928, 2909, 2861,

1462, 1418, 1376, 1359, 1300, 1280, 1143, 1028, 953, 851, 831,

812, 730, 703, 677, 572 cm ^-1. ¹H NMR (CDCl₃): δ 2.27 (dddd,

J _H-H) 4.8 Hz, J _H-H)10.6 Hz, J _H-H)13.6 Hz, J _H-P) 4.8 Hz,

1H), 1.70 (d, J _H-P) 2.0 Hz, 15 H), 1.53 (d, J _H-P) 10.0 Hz

9H), 1.44 (dddd, J _H-H) 4.4 Hz, J _H-H)10.7 Hz, J _H-H)13.9

Hz, J _H-P) 4.8 Hz, 1H), 1.19 (ddd, J _H-H) 4.9 Hz, J _H-H) 13.6

2

PMe₃resonance in CDCl₃solvent). H NMR (CDCl₃): δ 2.36

(br s), 1.66 (br s), 1.34 (br s), 1.27 (br s) ppm.

Rea ction of 2 w ith H ₂a n d D₂. A solution of 2 (10 mg,

0.025 mmol) in C₆D₆(0.55 mL) was placed in a J . Young NMR

tube. The solution was frozen in liquid N₂, evacuted under full

vaccum, and pressurized with 720 Torr of hydrogen gas. The

tube was sealed, thawed, and maintained at room temperature

1

for 45 min. Analysis of the solution by H NMR indicated no

reaction had occurred. The tube was then heated at 45 °C for

18 h, during which the formation of a fine white precipiate

was observed. Analysis of the tube contents at this time

indicated complete and clean conversion to Cp*(PMe₃)IrH₂(1).

The reaction of Cp*(PMe₃)Ir(Li)(H) with deuterium gas was

effected analogously to the reaction with hydrogen as described

above. After 18 h at 45 °C, the tube contents were analyzed

by ¹H NMR spectroscopy. The ¹H NMR spectrum indicated

the presence of a statistical mixture of Cp*(PMe₃)IrH_2,Cp*-

(PMe₃)Ir(H)(D), and Cp*(PMe₃)IrD₂along with approximately

20% unreacted 2. Removal of the volatile materials in vacuo

and dissolution in C₆H₆with addition of 5 mL of C₆D₆as an

2

internal standard allowed for quantitative analysis of the H

NMR spectrum. This spectrum indicated that deuterium

incorporation had occurred exclusively at the hydride position

of 1 with the exent of conversion from 2 being 80%.

Rea ction s of 2 w ith Ca r bon Acid s. In a typical reaction,

a solution of 2 (8-15 mmol) in 0.5 mL of THF-d₈was placed

in an NMR tube. Subsequently, a solution of a carbon acid

(diphenylmethane, DMSO, or CH₃CN, 2-16 equiv) in THF-d₈

was added via syringe. Analysis of the ¹H NMR spectrum

indicated complete conversion of 2 to Cp*(PMe₃)IrH_2.

Rea ction of 1 w ith Ben zylp ota ssiu m . Benzylpotassium

(6.7 mg, 52 mmol) was suspended in C₆D₆(200 mL), and THF-

d₈(100 mL) was added to effect dissolution. To this solution

was added a solution of 1 (21 mg, 52 mmol) in C₆D₆(800 mL).

A 360 mL aliquot of the red-orange solution was transferred

to an NMR tube and analyzed by ¹H NMR and ³¹P NMR

spectroscopy. The spectrum showed a 90:10 ratio of Cp*(PMe₃)-

Ir(K)(H) and 1 based upon average integrations of the Cp*,

PMe₃, and hydride resonances. ¹H NMR (C₆D₆-THF-d₈): δ 2.17

(s, 15 H), 1.49 (d, J _H-P) 8.0 Hz, 9 H), -19.0 (d, J _H-P) 30.7

Hz, 1 H) ppm. ³¹P{¹H} NMR (C₆D₆-THF-d₈): δ -63.4 ppm.

Rea ction of 1 w ith Ben zyllith iu m . To a solution of 1 (14

mg, 35 mmol) in 0.5 mL C₆D₆was added benzyllithium‚2THF⁹⁹

(7.3 mg, 31 mmol). The yellow solution was placed in an NMR

tube, and the contents were subjected to ¹H NMR analysis.

The ¹H NMR spectrum showed complete conversion of ben-

zyllithium to toluene and 2 as a mixture of oligomers.

Cp *(P Me₃)Ir (Sn P h ₃)(H) (5a ). A solution was prepared by

dissolving 2 (76.8 mg isolated as a solid, 187 mmol) in THF (4

mL). To this solution was added, with vigorous stirring, a

solution of Ph₃SnCl (65 mg, 169 mmol) in THF (2 mL). After

1 h at ambient temperature, the solvent was removed in vacuo,

and the resulting yellow oil was dissolved in pentane (10 mL)

and filtered through Celite. The pale yellow filtrate was

concentrated in vacuo to a volume of 7 mL and was slowly

Hz, J _H-H) 13.6 Hz, 1H), 1.11 (ddd, J _H-H) 4.9 Hz, J _H-H

)

13.5 Hz, J _H-H) 13.5 Hz, 1H) ppm. ¹³C{¹H} NMR (C₆D₆): δ

92.0 (C) 52.5 (CH₂), 33.3 (CH₂), 30.2 (CH₃), 15.3 (CH₃, J _P-C

)

37.0 Hz), 9.3 (CH₃), -3.4 (C) ppm. ³¹P{¹H} NMR (C₆D₆): 39.3

ppm. MS (EI): m/z 568 (M⁺). HRMS calcd for C₁₉H₃₇IrPBr:

568.143390. Found: 568.144568.

4c-a n ti-d ₂. A solution of 2 was prepared by dissolving a

solid mixture of Cp*(PMe₃)IrH₂(50 mg, 0.123 mmol) and tert-

butyllithium (8 mg, 0.125 mmol) in C₆H₆(8 mL). After stirring

for 15 min at ambient temperature, the Cp*(PMe₃)Ir(Li)(H)

solution was evaporated to dryness and dissolved in 10 mL of

THF. A solution of 3-syn -d ₂(30 mg, 0.127 mmol) in THF (3

mL) was added to the iridate solution, and the resulting yellow

(98) Beard, C. D.; Baum, K.; Grakauskas, V. J . Org. Chem. 1973,

38, 367.

(99) Gilman, H.; McNinch, H. A. J . Org. Chem. 1961, 26, 3723.

2018 Organometallics, Vol. 18, No. 10, 1999

Peterson et al.

cooled to -40 °C to produce fine clumps of a white crystalline

material. The supernatant was decanted and the product was

dried under vacuum to afford 5a (89.4 mg) in 71% yield. IR

was filtered through Celite and concentrated in vacuo. The

crude product was then partitioned between pentane (2 mL)

and CH₃CN (2 mL). The pentane layer was decanted and set

aside, and the CH₃CN layer was extracted with a fresh portion

of pentane. The extraction process was repeated a total of five

times, and the pentane extracts were combined and concen-

trated under vacuum to afford a bright yellow oil. ¹H NMR

analysis of the oil showed it to be a mixture of 6b and 1 in a

4:1 ratio. The oil was then dissolved in C₆D₆and titrated with

portions of CHBr₃to convert 1 to Cp*(PMe₃)Ir(H)(Br) and Cp*-

(PMe₃)IrBr₂. The titration was monitored by ¹H NMR spec-

troscopy to determine the extent of conversion of 1 to Cp*-

(PMe₃)Ir(H)(Br) and Cp*(PMe₃)IrBr₂. Complete conversion was

observed after a total of 6.3 mL of CHBr₃had been added. The

volatile materials were then removed under vacuum and the

residue was extracted with pentane. The pentane extract was

pumped to dryness, and the crude complex was twice recrys-

tallized from CH₃CN to afford 40 mg of Cp*(PMe₃)Ir(BPh₂)-

(H) as a yellow crystalline solid. The purified yield for the

procedure was calculated to be 24% based on recovered 1,

though ¹H NMR analysis of the crude reaction product

suggests that the product is formed in an approximate 80%

yield in the reaction.

1

(KBr): 3054, 2854, 2114, 2096, 1425, 953, 702, 461 cm^-1. H

NMR (C₆D₆): δ 7.95 (6 H, d, J _Sn-H) 36 Hz), 7.28 (6 H, m),

7.20 (3 H, m), 1.77 (15 H, d, J _P-H) 1.9 Hz), 1.12 (9 H, d, J _P-H

) 9.8 Hz), -17.40 (1 H, d, J _P-H) 30.2 Hz, J _Sn-H) 133 Hz)

ppm. ¹³C{¹H} NMR (C₆D₆): δ 147.3 (CH), 138.1 (CH, J _Sn-C

35.2 Hz) 127.8 (CH), 127.2 (C), 92.4 (C), 23.3 (CH₃, d, J _P-C

)

38.3 Hz), 10.99 (CH₃) ppm. ³¹P{¹H} NMR (C₆D₆): δ -54.6

(J _Sn-P) 167 Hz) ppm. MS (EI): m/z 754 (M⁺). HRMS calcd

for C₃₁H₄₀PSnIr: 754.151314. Found: 754.151705.

Cp *(P Me₃)Ir (Sn Me₃)(H) (5b). To a solution of 1 (100 mg,

247 mmol) in C₆H₆(7 mL) was added a solution of tert-

butyllithium (18 mg, 281 mmol) in C₆D₆(3 mL). The bright

yellow solution was stirred at ambient temperature for 5 min

and a solution of Me₃SnCl (56 mg, 281 mmol) in C₆H₆(2 mL)

was added via pipet. Reaction was observed over a period of

20 min as indicated by a lightening of the yellow color

concomitant with the precipitation of LiCl. The solution was

filtered through Celite and concentrated in vacuo to afford 132

mg of a yellow-gold oil. Analysis of the crude product by ¹H

NMR spectroscopy indicated 91% conversion to 5b. Multiple

attempts to purify this material by recrystallization from

pentane at -40 °C were unsuccessful, as no solid material

could be obtained. Attempts to purify the complex by chroma-

tography on silica gel resulted in complete decomposition to

Meth od B. Rea ction of 2 w ith P h ₂BOBP h ₂. A solid

mixture of 1 (90 mg, 220 mmol) and tert-butyllithium (18 mg,

280 mmol, 1.25 equiv) was dissolved in C₆H₆(5 mL), and the

resulting solution was stirred for 5 min at room temperature.

A solution of Ph₂BOBPh₂(90 mg, 260 mmol, 1.18 equiv) in

C₆H₆(2 mL) was added dropwise over a 1 min period. After

stirring for 30 min at ambient temperature, the crude reaction

mixture was pumped to dryness and the residue was sus-

pended in hexanes (5 mL) and filtered through Celite. The

filtrate was then concentrated under vacuum to a volume of 2

mL, resulting in the precipitation of a white solid, and after a

second filtration through Celite, the filtrate was pumped to

dryness and the crude reaction product was recrystallized from

CH₃CN (1.5 mL) to afford pure 6b (40 mg) as a bright yellow

crystalline solid in 32% yield (first crop). Analysis of the crude

1

1. IR (KBr): 2976, 2913, 2092, 1419, 950, 489 cm^-1. H NMR

(C₆D₆): δ 1.90 (15 H, s), 1.29 (9 H, d, J _P-H) 10.0 Hz), 0.53 (9

H, s, J _Sn-H) 37.8 Hz), -18.08 (1 H, d, J _P-H) 30 Hz, J _Sn-H

)

137 Hz) ppm. ¹³C{¹H} NMR (C₆D₆): δ 92.2 (C), 23.4 (CH₃, d,

J _P-C) 28.6 Hz) 11.24 (CH₃), -5.2 (CH₃, J _Sn-C) 187 Hz) ppm.

³¹P{¹H} NMR (C₆D₆): δ -51.2 (J _Sn-P) 162 Hz) ppm. MS (EI):

m/z 570 (M⁺). HRMS calcd for C₁₆H₃₄PSnIr: 570.104956.

Found: 570.106435.

Cp *(P Me₃)Ir (BF ₂)(H) (6a ). A solid mixture of 1 (152 mg,

375 mmol) and tert-butyllithium (27.5 mg, 430 mmol, 1.15

equiv) was dissolved in C₆H₆(5 mL). After stirring for 10 min

at room temperature, a solution of boron trifluoride-etherate

(108 mg, 124 mL, 760 mmol, 2 equiv) in C₆H₆(2 mL) was added

dropwise over a 2 min period. The solution became dark brown

during the addition of the first equiv of boron reagent and

lightened to a yellow color with the addition of the second

equivalent. After stirring for 30 min at ambient temperature,

the solution was filtered through Celite to remove LiBF₄and

was concentrated in vacuo to afford a dark brown oil. The oil

was dissolved in 1:1 hexanes-benzene (approximately 10 mL)

and was refiltered through Celite to provide a pale yellow

filtrate. Removal of the volatile materials under vacuum gave

a pale yellow oil (119 mg) which slowly crystallized upon

standing at room temperature. ¹H NMR analysis of the oil

showed it to be a mixture of 6a and 1 in an 84:16 ratio.

Recrystallization of the crude product from hexamethyldisi-

loxane (-40 °C) afforded 40 mg of 6a as a white crystalline

solid in a 23% yield containing approximately 10% 2 as an

1

product by H NMR spectroscopy indicated unisolated yields

are greater than 90%. IR (KBr): 2971, 2904, 2088, 1297, 952,

1

701 cm^-1. H NMR (C₆D₆): δ 7.66 (d, 4 H), 7.34 (t, 4 H), 7.25

(t, 2 H), 1.77 (15 H, s), 1.02 (9 H, d, J _P-H) 9.6 Hz), -16.53 (1

H, d, J _P-H) 32.8 Hz) ppm. ¹³C{¹H} NMR (C₆D₆): δ 161.2,

133.9, 127.4, 126.6, 95.3, 22.0 ppm (d, J _C-P)38.5 Hz). ³¹P-

{¹H} NMR (C₆D₆): δ -42.6 ppm. ¹¹B NMR (C₆D₆): δ 93 ppm

(v. broad) Anal. Calcd for C₂₅H_35BPIr: C, 52.72; H, 6.19.

Found: C, 52.73; H, 6.28.

Cp *(P Me₃)Ir (CO^tBu )(H) (7a ). To a stirred suspension of

2 (104 mg, 252 mmol) in THF (10 mL) at room temperature

was added a solution of pivalic anhydride (47 mg, 252 mmol)

in THF (5 mL). Within 5 min, the solution had become

homogeneous, turning from bright yellow to yellow-gold in

color. After continued stirring for 1 h, the volatile materials

were removed under vacuum, and the crude product was

extracted into pentane. The pentane extract was filtered

through Celite and concentrated in vacuo to afford a golden

impurity. Mp: 73-75 °C. IR (KBr): 2972, 2906, 2088, 954 cm^-1

.

¹H NMR (C₆D₆): δ 1.95 (15 H, s), 1.29 (9 H, d, J _P-H) 9.9 Hz),

-17.45 (1 H, dt, J _P-H) 27.0 Hz, J _H-F) 12.0 Hz) ppm. ¹³C-

{¹H} NMR (C₆D₆): δ 95.2 (C), 21.9 (CH₃, d, J _P-C) 38.9 Hz),

10.5 (CH₃) ppm. ³¹P{¹H} NMR (C₆D₆): δ -42.6 ppm. ¹⁹F NMR

(C₆D₆): (22 °C) δ -29.6 ppm (br d with unresolved coupling).

¹⁹F NMR (C₇D₈) (90 °C): δ -23.2 ppm (q, J _B-F) 154.4 Hz).

¹¹B NMR (C₇D₈) (22 °C): δ 23.9 ppm (t, J _B-F) 159.6 Hz) MS

(EI): m/z 454 (M⁺). HRMS calcd for C₁₃H₂₅BF₂PIr: 454.138443.

Found: 454.138992.

1

yellow oil. Analysis by H NMR spectrscopy indicated an 83%

yield of 7a with 1 as a minor impurity. The crude product was

purified by column chromatography on alumina III employing

10% Et₂O in pentane as the eluent. The product eluted as a

yellow band, which was collected, pumped to dryness, and

recrystallized from pentane (-40 °C). The recrystallization

provided pure 7a as very large (>20 mg) yellow blocklike

1

crystals. IR (KBr): 2085, 1574 cm^-1. H NMR (C₆D₆): δ 1.82

(15 H, s), 1.28 (9 H, s), 1.19 (9 H, d, J _P-H) 10.3 Hz), -17.02

Cp *(P Me₃)Ir (BP h ₂)(H) (6b). Meth od A. Rea ction of 2

w ith P h ₂BBr . A solid mixture of 1 (150 mg, 370 mmol) and

tert-butyllithium (25 mg, 390 mmol, 1.05 equiv) was dissolved

in C₆H₆(10 mL). After stirring for 15 min at room temperature,

a C₆H₆solution of Ph₂BBr (100 mg, 407 mmol, 1.1 equiv) was

added via pipet. After stirring for 1 h, the reaction mixture

(1 H, d, J _P-H) 34.8 Hz) ppm. ¹³C{¹H} NMR (C₆D₆): δ 233.1

(C, d, J _P-C) 10.5 Hz), 94.0 (C), 29.5 (C), 19.6 (CH₃, d, J _P-C

)

37.6 Hz), 10.8 (CH₃) ppm. ³¹P{¹H} NMR (C₆D₆): δ -35.5 ppm.

Anal. Calcd for C₂₀H₃₀OPIr: C, 44.20; H, 7.00. Found: C, 44.21;

H, 7.24.

Deprotonation of (η⁵-C₅Me₅)(PMe₃)IrH₂

Organometallics, Vol. 18, No. 10, 1999 2019

Cp *(P Me₃)Ir (COP h )(H) (7b). To a vigorously stirred

suspension of 2 (80 mg, 195 mmol) in THF (10 mL) was added

a solution of benzoic anhydride (44 mg, 195 mmol) in THF (5

mL). After stirring for 1 h at ambient temperature, the deep

orange solution was concentrated in vacuo and the crude

reaction product was dissolved in C₆H₆(5 mL). After filtration

through Celite, the solvent was removed under vacuum to

gas bulb (6.6 mL volume) pressurized to 40 Torr. The tube

was then flame-sealed and maintained at -196 °C until the

time of NMR analysis. The tube was then quickly warmed to

-78 °C in a dry ice-acetone bath, and the contents were

1

analyzed by H NMR spectroscopy at -66 °C. No reaction at

this temperature was observed. The NMR probe was warmed

to -30 °C, and after 30 min at this temperature, no reaction

could be detected. Further warming to 10 °C for 5 min resulted

in 38% conversion to a 1.3:1 mixture of Cp*(PMe₃)Ir(Me)(H)

and Cp*(PMe₃)Ir(CO). After 10 min at 23 °C, complete conver-

sion to the aforementioned products was observed. No inter-

mediate species could be detected. Similarly, a solution of 2

(6.3 mg, 15.6 mmol) in toluene-d₈(400 mL) was treated with

CO₂(26 mmol) condensed into the tube at -196 °C via vacuum

transfer from a calibrated gas bulb (6.6 mL volume) pressur-

ized to 80 Torr. The tube was quickly warmed to -78 °C in a

1

provide an orange oil. H NMR analysis of the oil indicated a

mixture of 7b and 1 in a 5:1 ratio. The crude product was

purified on a 4 cm alumina III column utilizing 25 mL of

pentane (to elute the dihydride) followed by 10% Et₂O in

pentane to elute the phenacyl hydride. Concentration of the

leading yellow band under vacuum provided a yellow oil, which

was crystallized from hexamethyldisiloxane (-40 °C) to pro-

vide 45 mg of 7b as a yellow crystalline solid. The yield after

chromatography and recrystallization was 45%. IR (KBr):

1

2096, 1558 cm^-1. H NMR (C₆D₆): δ 8.24 (2 H, d, J _H-H) 7.2

dry ice-acetone bath and the H NMR spectrum was recorded

Hz), 7.29 (2 H, m), 7.20 (1 H, m), 1.77 (15 H, d, J _P-H) 1.9

Hz), 1.23 (9 H, d, J _P-H) 10.4 Hz), -16.35 (1 H, d, J _P-H) 36.0

Hz) ppm. ¹³C{¹H} NMR (C₆D₆): δ 223.1 (C, d, J _P-C) 11.6 Hz),

154.3 (CH), 129.2 (C), 129.1 (CH), 127.1 (CH), 93.7 (C), 18.5

(CH₃, d, J _P-C) 38.4 Hz), 10.1 (CH₃) ppm. ³¹P{¹H} NMR

(C₆D₆): δ -38.2 ppm. MS (EI): m/z 510 (M⁺). Anal. Calcd for

at -66 °C after a reaction time of 5 min. The NMR spectrum

indicated quantitative conversion to the previously character-

ized complex Cp*(PMe₃)Ir(CO). In an analogous reaction, a

solution of 2 (6.9 mg, 16.8 mmol) in THF (0.5 mL) was added

dropwise to a solution of di-tert-butyl dicarbonate (4 mg, 18

mmol) in THF (2 mL). The resulting yellow-gold solution was

concentrated under vacuum to afford a gold-yellow oil. ¹H NMR

analysis of the oil indicated a mixture of 1 and Cp*(PMe₃)Ir-

(CO) in a 2:1 ratio based upon ¹H NMR integrations.

C

₂₀H₃₀OPIr: C, 47.13; H, 5.93. Found: C, 47.30; H, 5.96.

Cp *(P Me₃)Ir (CHO)(H) (7c). A solid mixture of 1 (100 mg,

250 mmol) and tert-butyllithium (20 mg, 310 mmol, 1.2 equiv)

was dissolved in C₆H₆(5 mL), and the yellow solution was

stirred for 5 min at ambient temperature. A solution of ethyl

formate (22 mg, 310 mmol) in C₆H₆(2 mL) was then added

via pipet. After stirring for 10 min, the volatile materials were

removed under vacuum and the residue was dissolved in

pentane and filtered through Celite. After removal of the

solvent, the crude reaction mixture was subjected to ¹H NMR

analysis. The spectrum indicated a mixture of the desired

formyl hydride complex 7c and 1 in a 1.7:1 ratio. Recrystal-

lization from hexamethyldisiloxane (-40 °C) provided 30.2 mg

of pure 7c as a white crystalline solid in 28% isolated yield.

The complex may also be purified by chromatography on

alumina III utilizing 25% Et₂O in pentane as the eluent.

Typical yields of unisolated material are greater than 75%.

Mp: 93 °C (dec). IR (KBr): 2713, 2694, 2505, 2138, 1891, 1591,

958 cm^-1. ¹H NMR (C₆D₆): δ 15.25 (1 H, d, J _P-H) 4 Hz), 1.73

(15 H, s), 1.36 (9 H, d, J _P-H) 10.8 Hz), -17.33 (1 H, d, J _P-H

Th er m olyses of Acyl Hyd r id es 7a -c. In a representative

example, a solution of 7a (9 mg, 18.4 mmol) and 1 (2.76 mmol

as an internal standard) in C₆D₆(500 mL) was placed in a

medium-walled NMR tube. The tube was attached to a vacuum

line via a Cajon Ultratorr adapter, and the contents were

frozen in liquid N₂. After evacuating to 30 mTorr, the tube

was flame-sealed, thawed, and then heated for 6 h at 75 °C.

¹H NMR analysis showed no observable reaction. Further

heating of the tube for 18 h at 105 °C and subsequently at

135 °C for 18 h similarly showed no detectable reaction.

Continued thermolysis at 195 °C for 48 h showed 66%

conversion to complex 8. In an analogous experiment, a

solution of 7b (2 mg, 4 mmol) and 1 (0.48 mmol as an internal

standard) in C₆D₆(500 mL) was prepared and heated at 135

°C for 18 h to achieve 15% conversion to complex 8. Similarly,

a solution of 7c (7.2 mg, 16.6 mmol) in C₆D₆(0.5 mL) showed

a mixture of 7c and 8 in 2.2:1 ratio, indicating observable

thermal decomposition between the time of sample preparation

and room-temperature NMR analysis. The tube was then

heated for 21 h at 45 °C. Analysis by ¹H NMR indicated

quantitative conversion to complex 8.

) 32.0 Hz) ppm. ¹³C{¹H} NMR (C₆D₆): δ 219.2 (C, d, J _P-C

)

11.6 Hz), 95.9 (C), 19.1 (CH₃, d, J _P-C) 40 Hz), 9.7 (CH₃) ppm.

³¹P{¹H} NMR (C₆D₆): δ -37.94 ppm. MS (EI): m/z 432 (M -

2⁺). MS (FAB): m/z 433 (M - 2 + H⁺). Anal. Calcd for C₁₄H₂₅

OPIr: C, 38.79; H, 6.04. Found: C, 38.97; H, 6.17.

-

Cp *(P Me₃)Ir (C₆F ₅)(H) (12). To a solution of 1 (106 mg, 262

mmol) in C₆H₆(4 mL) was added a solution of tert-butyllithium

(17 mg, 265 mmol) in C₆H₆(1 mL). After stirring for 5 min at

room temperature, a solution of C₆F₆(102 mg, 548 mmol, 2.07

equiv) in C₆H₆(1 mL) was added, resulting in an instantaneous

color change from yellow to gold. After 3 h at ambient

temperature, the volatile materials were removed in vacuo,

and the residue was dissolved in pentane (10 mL). Filtration

of the solution though Celite and removal of the solvent under

reduced pressure afforded a gold oil which crystallized spon-

taneously upon cooling to -40 °C. The crude product was

recrystallized twice from pentane (-40 °C) to afford 111 mg

of 12 as a pale gold-colored crystalline solid in 74% yield. Mp:

Rea ction of 2 w ith Ben za ld eh yd e. A solution of 2 (10

mg, 24 mmol) in C₆D₆(400 mL) was placed in an NMR tube.

Benzaldehyde (5.4 mg, 5 mL, 50 mmol, 2.08 equiv) was then

added via microliter syringe, and the tube was capped and

inverted to mix the reactants. Reaction occurred instanta-

neously as was evident from a yellow to gold color change.

Analysis of the tube contents by ¹H NMR spectroscopy

indicated a mixture of 7b and 1 in a 3:1 ratio. A solution of

methyl p-toluenesulfonate (10 mg, 54 mmol, 2.25 equiv) in

C₆D₆(200 mL) was then added to the tube. After 65 min at

ambient temperature, no reaction could be detected by NMR

analysis. After 20 h at room temperature, formation of benzyl

methyl ether was detected by comparison of the NMR spec-

trum of the reaction mixture with that of an authentic sample.

The yield of benzyl methyl ether was 67% based upon the yield

of 7b.

NMR Tu be Stu d ies of Rea ction s of 2 w ith CO₂a n d

Ca r bon a tes. In a typical example, a solution of 2 (6.3 mg,

15.6 mmol) in toluene-d₈(400 mL) was placed in an NMR tube,

and the tube was connected to a vacuum manifold via a Cajon

Ultratorr adapter. After freezing the tube contents in liquid

N₂, the tube was evacuated and dimethyl carbonate (14.4

mmol) was condensed via vacuum transfer from a calibrated

88.5-91 °C (dec). IR (KBr): 2912, 2113, 1498, 1427, 948 cm^-1

.

¹H NMR (C₆D₆): δ 1.70 (15 H, s), 0.95 (9 H, d, J _P-H) 10.0

Hz), -16.47 (1 H, dd, J _P-H) 37.1 Hz, J _H-F) 11.4 Hz) ppm.

¹³C{1H} NMR (C₆D₆): δ 92.9 (C), 19.60 (CH₃, d, J _P-C) 38.4

Hz), 10.0 (CH₃) ppm.¹⁹F NMR (C₆D₆): δ -107.2 (d, J _F-F) 31.6

Hz), -111.4 (d, J _F-F) 35.1 Hz), -163.7 (t, J _F-F) 20.6 Hz),

-164.07 (ddd), -165.1 (ddd). ³¹P{¹H} NMR (C₆D₆): δ -44.5

ppm. MS (EI): m/z 572 (M⁺). HRMS calcd for C₁₉H₂₅F₅PIr:

572.124348. Found: 572.124514.

Rea ction of 2 w ith C₆H₅F To Give Cp *(P Me₃)Ir (C₆H₅)-

(H) (13). A solution of 2 (7.42 mg, 18 mmol) in C₆D₆(350 mL)

2020 Organometallics, Vol. 18, No. 10, 1999

Peterson et al.

was placed in a NMR tube. To the solution was added

fluorobenzene (3.47 mg, 3.4 mL, 36 mmol, 2 equiv) via

microliter syring. The ¹H NMR spectrum was recorded after

a reaction time of 60 min, indicating no detectable reaction

had occurred. The tube was then flame-sealed in vacuo and

frozen in liquid N₂. After evacuating the reaction vessel, 3,3,3-

trifluoropropene (4.2 mmol, 14 equiv) was condensed into the

vessel via vacuum transfer from a known-volume bulb. The

reaction vessel was warmed to ambient temperature and was

stirred vigorously for a period of 3 h. During this time, the

solution changed from yellow to gold in color, accompanied by

the formation of a fine white precipitate. The volatile materials

were then removed under reduced pressure, and the crude

reaction product was extracted with three 2 mL portions of

pentane. The hydrocarbon extracts were combined and filtered

through Celite. The filtrate was concentrated in vacuo to afford

1

was heated at 75 °C for 22 h. Analysis of the contents by H

NMR showed a mixture of 13 and 1 in a 1:4 ratio. We have

not investigated the origin of 1 in this reaction, though we

have observed that heating solutions of 2 at 75 °C leads to

formation of 1 via an unknown mechanism (vide supra).

Cp *(P Me₃)Ir (CF dCF CF ₃)(H) (14). A solid mixture of 1

(152 mg, 375 mmol) and tert-butyllithium (25.2 mg, 393 mmol,

1.05 equiv) was dissolved in toluene (10 mL) in a Schlenk flask.

The solution was frozen in liquid N₂, and hexafluoropropene

(5.36 mmol, 14 equiv) was condensed into the reaction flask

via vacuum transfer from a known-volume bulb. The reaction

flask was warmed to -78 °C and was stirred vigorously at that

temperature for a period of 90 min. The reaction mixture was

then warmed to ambient temperature, and the volatile materi-

als were removed under reduced pressure. The crude reaction

product was extracted with two 10 mL portions of C₆H₆, and

the combined extracts were filtered through Celite. Removal

of the solvent in vacuo afforded 146 mg of a dark brown oil

1

98.8 mg of a golden oil. H NMR analysis of the oil showed it

to be a mixture of 15 and 1 in a 76:24 ratio. Multiple attempts

to isolate complex 15 free from 1 by column chromatography

(decomposition) or recrystallization were unsuccessful. Data

for 15: ¹H NMR (C₆D₆): δ 4.56 (dddd, 1 H), 2.26 (m, 1 H),

1.98 (m 1 H), 1.76 (s, 15 H), 1.17 (d, J _P-H) 9.72 Hz, 9 H),

-17.75 (d, J _P-H) 40 Hz, 1 H) ppm. ¹⁹F NMR (C₆D₆): δ -98.9

(d, J _F-F) 113 Hz), -99.2 (dd, J _F-F) 110 Hz, J _H-F) 42 Hz)

ppm. ³¹P{¹H} NMR (C₆D₆): δ -43.25 ppm.

Ack n ow led gm en t. We are grateful for financial

support of this work by the National Science Foundation

(Grant No. CHE-9633374 to R.G.B.). T.H.P. acknowl-

edges a NRSA fellowship from the National Institutes

of Health. We are indebted to Dr. J ennifer Polse for

invaluable assistance with HMQC NMR analyses and

1

identified by H NMR analysis as a 71:29 mixture of 14 and

1, indicating a 78% yield based on recovered 1. Crude 14 was

purified by chromatography on alumina III employing pentane

as the eluent and was subsequently recrystallized twice from

pentane at -40 °C to provide 40 mg (20% yield) of analytically

pure 14 as a yellow crystalline solid. IR (KBr): 2908, 2117,

1

to Mr. Rudi Nunlist for help with H{²H} NMR experi-

1

1625, 1319, 1176, 692 cm^-1. H NMR (C₆D₆): δ 1.76 (15 H, s),

ments. Additional thanks are extended to Dr. Fred

Hollander, Director of the UC Berkeley X-ray Diffraction

Laboratory (CHEXRAY), for crystal structure determi-

nations. We are grateful for a loan of iridium chloride

from the J ohnson Matthey/Alfa Aesar Co., and we would

also like to extend our thanks to Professor Andrew

Streitwieser and Dr. J ames Krom for their assistance

with pK_ameasurements.

1.12 (9 H, d, J _P-H) 10.4 Hz), -17.01 (1 H, ddd, J _H-F) 6.0

Hz, J _H-F) 14.0 Hz, J _P-H) 34.5 Hz) ppm. ¹³C{¹H} NMR

(C₆D₆): δ 94.5.(C), 19.5 (CH₃, d), 10.0 (CH₃) ppm.¹⁹F NMR

(C₆D₆): δ -107.2 (d, J _F-F) 31.6 Hz), -111.4 (d, J _F-F) 35.1

Hz), -163.7 (t, J _F-F) 20.6 Hz), -164.07 (ddd), -165.1 (ddd).

³¹P{¹H} NMR (C₆D₆): δ -41.5 ppm. MS (EI): m/z 536 (M⁺).

Anal. Calcd for C₁₆H₂₅F₅PIr: C, 35.88; H, 4.70. Found: C,

36.10; H, 4.91.

Rea ction of 2 w ith 3,3,3-Tr iflu or op r op en e. To a solution

of 1 (122 mg, 301 mmol) in C₆H₆(25 mL) was added a solution

of tert-butyllithium (25 mg, 390 mmol, 1.3 equiv) in C₆H₆(1

mL). The bright yellow solution was transferred to a 100 mL

glass reaction vessel equipped with a Teflon stopcock and

Su p p or tin g In for m a tion Ava ila ble: Structural data for

7a . This material is available free of charge via the Internet

at http://pubs.acs.org.

OM980945D

Article Doi

Deprotonation of the transition metal hydride (η5-C5Me5)(PMe3)IrH2. Synthesis and chemistry of the strongly basic lithium iridate (η5-C5Me5)(PMe3)Ir(H)(Li)

DOI: 10.1021/om980945d

Source and publish data:

Authors:

Article abstract of DOI:10.1021/om980945d

Full text of DOI:10.1021/om980945d

Products guided by the article

R&D Labs maybe for 226882-81-1

Relevant to this article

Hot Product