Acceptor PCP pincer iridium(I) chemistry: Stabilization of nonmeridional PCP coordination geometries

Organometallics 2011, 30, 697–711 697

DOI: 10.1021/om100864g

Acceptor PCP Pincer Iridium(I) Chemistry: Stabilization of

Nonmeridional PCP Coordination Geometries

Jeramie J. Adams, Navamoney Arulsamy, and Dean M. Roddick*

Department of Chemistry, Box 3838, University of Wyoming, Laramie, Wyoming 82071, United States

Received September 6, 2010

The preparation of a series of four-coordinate complexes (^CFPCP)Ir(L) (L = CO, DBU, nbe,

3

coe, MeP(C₂F₅)₂(dfmp)) and five-coordinate complexes (^CFPCP)Ir(L)(L ) (L=L =CO, dfmp, nbd,

0

3

cod, (C₂F₅)₂PCH₂CH₂P(C₂F₅)₂(dfepe); L = PhCN, L⁰= C₂H₄) from dehydrohalogenation of

CF₃

(

PCP)Ir(C₂H₄)(H)Cl with Et₃N in the presence of trapping ligands is reported. (^CF³PCP)Ir(L) and

PCP)Ir(L)₂for L = CO, dfmp have been structurally characterized and establish a distorted-

CF₃

trigonal -bipyramidal coordination geometry for (^CFPCP)Ir(L)₂with a bent PCP unit and inequiv-

3

alent axial and equatorial L coordination sites. (^CFPCP)Ir(L)(L ) systems (L = L = CO, C₂H₄;

L = PhCN, L⁰= C₂H₄) are highly fluxional, with ligand site interconversion free energy barriers

determined by VT NMR of 9.7 kcal mol^-1(L = L⁰= CO), 12.2 kcal mol^-1(L = L⁰= C₂H₄), and

0

3

16.1 kcal mol^-1(L = C₂H₄, L⁰= PhCN). A dissociative site exchange mechanism is proposed.

CF₃

(

PCP)Ir(L) complexes readily undergo oxidative addition reactions. Addition of H₂to (^CF³PCP)-

Ir(CO) reversibly forms trans-(^CFPCP)Ir(CO)(H)₂at ambient temperatures. In contrast, addition of

3

CF₃

H₂to (^CFPCP)Ir(dfmp) affords fac,cis-( PCP)Ir(dfmp)(H)₂as the major product, with an unusual

3

facially coordinated pincer group. VT NMR monitoring of the reaction of (^CFPCP)Ir(CO) with H₂

3

established the initial formation of fac,cis-(^CFPCP)Ir(CO)(H)₂followed by conversion to mer,

3

cis-(^CFPCP)Ir(CO)(H)₂prior to isomerization to mer,trans-(^CFPCP)Ir(CO)(H)₂. The unusual

3

CF₃

stability of (^CFPCP)Ir(L)₂and fac,cis-( PCP)Ir(L)(H)₂complexes is attributable to the increased

3

stability of nonplanar (PCP)M moieties possessing strongly π-accepting phosphorus groups.

Introduction

hydrogen transfer systems based on iridium phosphine pin-

cer compounds, (PCP)Ir.^2-4Key intermediates in alkane

dehydrogenation are (PCP)Ir^Ipincer complexes. To date,

most Ir(I) pincer chemistry has focused on ^RPCP (R= ⁱPr,

^tBu; PCP = 1,3-C₆H₃(CH₂P(R)₂)₂) and resorcinol-derived

^tBuPOCOP (POCOP = 1,3-C₆H₃(OP(R)₂)₂) systems with

strongly donating phosphorus substituents.^2d,g,5It is signifi-

cant that less electron-rich ^tBuPOCOP pincer catalysts are

∼10 times more active than ^RPCP analogues and involve

different preferences for catalyst resting states.^2g,6In light of

these observations, expanding the range of pincer systems,

particularly electron-poor complexes of Ir(I), is clearly of

interest.

There is continuing interest in stoichiometric and catalytic

transformations mediated by pincer transition-metal complexes.¹

Of particular importance are alkane dehydrogenation and

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5476.

In our previous paper we presented the synthesis and

characterization of Ir(III) pincer systems with the strongly

CF₃

π-accepting CF₃-substituted ligand

PCP.⁷A general

property noted in this chemistry was the enhanced Lewis

(4) (a) Goldman, A. S.; Brookhart, M.; Huang, Z.; Krogh-Jespersen,

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B. C.; Scott, S. L. Chem. Commun. 2008, 253–255. (c) Bailey, B. C.;

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r

2011 American Chemical Society

Published on Web 02/03/2011

pubs.acs.org/Organometallics

698 Organometallics, Vol. 30, No. 4, 2011

Adams et al.

acidity and binding of 16-electron (^CFPCP)Ir(X)(Y) centers

3

to form coordinatively saturated octahedral (^CFPCP)-

3

Ir(X)(Y)(L) products. In this paper we report the synthesis

of a number of four-coordinate (^CFPCP)Ir(L) as well as five-

3

coordinate (^CFPCP)Ir(L)₂products. ( PCP)Ir(L)₂com-

CF₃

3

pounds have a distorted-trigonal-bipyramidal geometry

with inequivalent L binding sites. (^CFPCP)Ir(L) (L = CO,

3

MeP(C₂F₅)₂(dfmp)) complexes react readily with H₂to

produce (^CFPCP)Ir(L)(H)₂products. The unique ability of

3

acceptor PCP ligands to undergo a nonplanar distortion in

five-coordinate systems is extended further to the character-

ization of unprecedented facial octahedral products, fac,

cis-(^CFPCP)Ir(L)(H)₂(L=CO, dfmp).

3

Results and Discussion

Dehydrohalogenation Chemistry of (^CFPCP)Ir(L)(H)Cl

3

Figure 1. Molecular structure of (^CFPCP)Ir(DBU) (2) with

(L=CO, C₂H₄, MeCN, PhCN, MeP(C₂F₅)₂) in the Absence

of a Trapping Ligand. Dehydrohalogenation of (^CFPCP)Ir-

3

50% probability thermal ellipsoids and hydrogen atoms omitted

˚

(L)(H)Cl systems (L = CO, C₂H₄, MeCN, PhCN, MeP-

(C₂F₅)₂) using reagents such as KO^tBu, LiEt₃BH, and KH,

for clarity. Selected bond distances (A) and angles (deg): Ir(1)-

C(1) =2.047(4), Ir(1)-N(1) = 2.135(3), Ir(1)-P(1) = 2.1889(9),

Ir(1)-P(2) = 2.1892(9); C(1)-Ir(1)-N(1) = 178.14(13), C(1)-

Ir(1)-P(1)=80.02(10), N(1)-Ir(1)-P(1)=98.44(9), C(1)-Ir(1)-

P(2)=80.43(10), N(1)-Ir(1)-P(2)=101.26(9), P(1)-Ir(1)-P(2)=

158.27(4).

which are commonly employed with donor systems (^RPCP)-

CF₃

Ir(H)Cl, failed to produce either (^CFPCP)Ir(L) or ( PCP)-

3

Ir(L)(H)₂products in the presence of H₂. Complex product

mixtures were observed when L was CO or MeCN. Previous

studies with (^CFPCP)PtCl, using the basic reagent KH,

3

partial reaction was observed (ca. 10% after 72 h). DBU

(1,5-diazabicyclo[4.3.0]non-5-ene) has recently been em-

ployed for (PCP)Ir(CO)(H)Cl dehydrochlorination¹¹and

suggested that the benzylic hydrogens of ^CFPCP are suscep-

3

tible to deprotonation,⁸and similar pincer arm deprotona-

tion chemistry has been reported in related systems.⁹The

milder base Et₃N does, however, readily dehydrohalogenate

was examined for (^CFPCP)Ir(L)(H)Cl systems. Reaction of

3

CF₃

(

PCP)Ir(MeCN)(H)Cl with DBU afforded not (^CF³PCP)-

Ir(MeCN) but rather a red product identified as the DBU

CF₃

(

PCP)Ir(CO)(H)Cl in benzene to cleanly afford (^CF³PCP)-

Ir(CO) (1) (eq 1). Benzylic proton resonances for complex 1

are replaced by a single multiplet at δ 3.29, indicating lateral

symmetry across the plane defined by the meridional (PCP)Ir

unit. ¹⁹F NMR spectra similarly show a single multiplet

at -57.5 ppm.

adduct (^CFPCP)Ir(DBU) (2) (eq 2). Reaction of the Ir(III)

3

acetonitrile complex with 1 equiv of DBU in benzene at

ambient temperature gave a 1:1 mixture of unreacted starting

material and 2. The loss of lateral symmetry due to the

perpendicular orientation of the bicyclic DBU ligand relative

to the (PCP)Ir unit was indicated by diastereotopic benzylic

protons at 3.46 and 3.30 ppm and inequivalent CF₃groups

at -60.2 and -60.6 ppm and was confirmed by X-ray dif-

fraction (Figure 1). Structurally characterized transition-

metal DBU adducts are rare.¹²

The carbonyl IR stretching frequency for 1, 2018 cm^-1, is

105 cm^-1greater than the ν(CO) frequency reported for

(

^tBuPCP)Ir(CO), demonstrating a significant decrease in

CO-metal π back-bonding. The resorcinol pincer deriva-

tives (R-^tBuPOCOP)Ir(CO) (R = MeO, Me, H, F, C₆F₅,

m-{(C₆H₃)(CF₃)₂}) are more electron rich and have

carbonyl stretching frequencies ranging between 1947

CF₃

(

PCP)Ir(CO) Reactivity with CO. Five-coordinate

Ir(I) complexes of the general types (R₃P)_x(CO)_4-xIr(Y)

(Y = H, halide, hydrocarbyl) and (R₃P)_x(CO)_5-xIr^þare

fairly common,^13,14but corresponding pincer complexes

have not been well established. Milstein has reported that

electron-poor pyrollyl-substituted rhodium pincer phos-

phine complexes (^pyrPCP)Rh(PR₃) (R=Et, Ph, Pyr) readily

add CO to form (^pyrPCP)Rh(PEt₃)(CO) and predicted on the

basis of DFT calculations that ^RPCP ligands with stronger

and 1955 cm^{-1 10}

.

Attempts to dehydrohalogenate more electron rich (and

presumably less acidic) (^CFPCP)Ir(L)(H)Cl complexes (L=

3

MeCN, PhCN) with Et₃N in the absence of trapping ligands

were not successful. In the case of the acceptor phosphine

complex (^CFPCP)Ir(dfmp)(H)Cl (dfmp = MeP(C₂F₅)₂),

3

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2009, 28, 1148–1157.

(9) Ben-Ari, E.; Leitus, G.; Shimon, L. J. W.; Milstein, D. J. Am.

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(10) Goettker-Schnetmann, I.; White, P. S.; Brookhart, M. Organo-

metallics 2004, 23, 1766–1776.

(12) (a) Bruce, M. I.; Low, P. J.; Skelton, B. W.; White, A. H.

J. Organomet. Chem. 1996, 515, 65–79. (b) Barkley, J. V.; Davies,

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Article

Organometallics, Vol. 30, No. 4, 2011 699

Figure 2. Molecular structures of (^CFPCP)Ir(CO) (1) and ( PCP)Ir(CO)₂(3) with 50% probability thermal ellipsoids. Hydrogen

CF₃

3

˚

atoms and CF₃groups are omitted for clarity. Selected bond distances (A) and angles (deg) for 1: Ir(1)-C(13) = 1.895(2), Ir(1)-

C(1) = 2.0876(19), Ir(1)-P(2) = 2.2198(4), Ir(1)-P(1), 2.2273(4); C(13)-Ir(1)-C(1) = 179.06(8), C(13)-Ir(1)-P(2) = 100.15(6),

C(1)-Ir(1)-P(2) = 79.59(5), C(13)-Ir(1)-P(1) = 100.44(6), C(1)-Ir(1)-P(1) = 79.85(5), P(2)-Ir(1)-P(1) = 159.340(19). Selected

˚

bond distances (A) and angles (deg) for 3: Ir(1)-C(13) = 1.939(4), Ir(1)-C(14) = 1.941(4), Ir(1)-C(1) = 2.131(3), Ir(1)-P(2) =

2.2435(8), Ir(1)-P(1) = 2.2509(8); C(13)-Ir(1)-C(14) = 96.71(15), C(13)-Ir(1)-C(1) = 171.64(13), C(14)-Ir(1)-C(1) = 91.56(13),

C(13)-Ir(1)-P(2) = 97.65(11), C(14)-Ir(1)-P(2) = 114.35(11), C(1)-Ir(1)-P(2) = 77.76(9), C(13)-Ir(1)-P(1) = 99.71(11),

C(14)-Ir(1)-P(1) = 109.37(11), C(1)-Ir(1)-P(1) = 78.53(8), P(2)-Ir(1)-P(1) = 130.26(3).

π-accepting abilities should favor the formation of the

dicarbonyl (^RPCP)M(CO)₂.¹⁵In accord with this expecta-

tion, addition of 1 atm of CO to an orange benzene solution

of 1 at ambient temperature resulted in a rapid irreversible

in the presence of 1 atm of C₂H₄at ambient temperature

generates a product identified by NMR as the bis-ethylene

adduct (^CFPCP)Ir(C₂H₄)₂(4). The presence of two ethylene

3

ligands was indicated by ambient-temperature ¹H NMR

spectra, which show a broadened (ν_1/2= 120 Hz) C₂H₄

resonance at δ 2.38 integrating to 2/1 with respect to the

benzylic resonance at δ 3.22. While 4 could be isolated as a

white solid by cold filtration from hexane in under 1 atm of

C₂H₄, removal of the volatiles resulted in partial ethylene

loss and formation of an impure oily red-orange product.

The ethylene loss product was not identified. Placing a

benzene solution of impure 4 under 1 atm of ethylene

regenerated a colorless solution and resulted in a sharpening

of the ³¹P pincer broad resonance into a well-defined multi-

plet at 48.5 ppm. Under 1 atm of ethylene, the coordinated

ethylene proton resonance of 4 broadened further (ν_1/2≈ 160

Hz) and a very broad (ν_1/2≈ 300 Hz) free ethylene resonance

was observed at δ 5.15 in a 2/0.5 ratio, which indicated facile

intermolecular ethylene exchange on the NMR time scale at

ambient temperature (see below).

reaction to give a colorless solution of the dicarbonyl

CF₃

(

PCP)Ir(CO)₂(3) (eq 3). Complex 3 was also prepared

3

directly from (^CFPCP)Ir(CO)(H)Cl and Et₃N in the presence

of 1 atm of CO in good yield. ν(CO) bands for 3 appear at

2068 and 2020 cm^-1. Both 1 and 3 have been crystallogra-

phically characterized (Figure 2)

Dehydrohalogenation Chemistry of (^CFPCP)Ir(L)(H)Cl in

3

the Presence of Monodentate and Bidentate Trapping Li-

gands. The reaction of (^CFPCP)Ir(C₂H₄)(H)Cl with Et₃N

3

Despite the relatively intractable nature of (^CFPCP)-

3

Ir(C₂H₄), in situ prepared (^CFPCP)Ir(C₂H₄)₂serves as a use-

(13) (a) Payne, N. C.; Ibers, J. A. Inorg. Chem. 1969, 8, 2714–2718.

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metallics 1986, 5, 766–771. (f) Deutsch, P. P.; Eisenberg, R. Organome-

tallics 1990, 9, 709–718. (g) Abu-Hasanayn, F.; Emge, T. J.; Maguire,

J. A.; Krogh-Jespersen, K.; Goldman, A. S. Organometallics 1994, 13,

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Proft, B. R.; Matter, B. A.; Powell, D. R. J. Am. Chem. Soc. 1999, 121,

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(14) (a) Mague, J. T.; Lloyd, C. L. Organometallics 1988, 7, 983–993.

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Chem. Soc. 1990, 112, 7558–7566. (c) Balch, A. L.; Catalano, V. J.;

Olmstead, M. M. J. Am. Chem. Soc. 1990, 112, 2010–2011. (d) Randall,

S. L.; Thompson, J. S.; Buttrey, L. A.; Ziller, J. W.; Churchill, M. R.;

Atwood, J. D. Organometallics 1991, 10, 683–688. (e) Randall, S. L.;

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Atwood, J. D. Organometallics 1994, 13, 5088–5095.

3

ful precursor to many (^CFPCP)Ir(L)_xsystems (Scheme 1).

3

Indeed, the addition of ethylene as a coreagent in dehydro-

halogenation reactions is often essential for efficient synthe-

ses. For instance, dehydrohalogenation of (^CFPCP)Ir-

3

(C₂H₄)(H)Cl with Et₃N in the presence of 1-4 equiv of dfmp

in the presence of C₂H₄afforded orange (^CFPCP)Ir(dfmp)

3

(5) in high yield. Two ³¹P resonances are observed at 67.3 and

37.1 ppm in a 2/1 ratio and are assigned to the ^CFPCP and

3

dfmp ligands, respectively. 5 has moderate air stability as a

solid and may be stored indefinitely under an inert atmo-

sphere. Addition of excess dfmp (10þ equiv) to 5 in benzene

resulted in the precipitation of colorless crystalline (^CFPCP)-

3

Ir(dfmp)₂(6). Attempts to isolate 6 on a preparative scale

resulted in mixtures of 5 and 6 due to facile dfmp loss under

vacuum. Both 5 and 6 were characterized by X-ray diffrac-

tion (Figure 3).

(15) Kossoy, E.; Iron Mark, A.; Rybtchinski, B.; Ben-David, Y.;

Shimon Linda, J. W.; Konstantinovski, L.; Martin Jan, M. L.; Milstein,

D. Chemistry 2005, 11, 2319–2326.

Cyclic alkene complexes (^CFPCP)Ir(L) (L=norbornene,

3

cyclooctene) were obtained from (^CFPCP)Ir(C₂H₄)(H)Cl

3

700 Organometallics, Vol. 30, No. 4, 2011

Adams et al.

Figure 3. Molecular structures of (^CFPCP)Ir(dfmp) (5) and ( PCP)Ir(dfmp)₂(6) with 50% probability thermal ellipsoids. Hydrogen

CF₃

3

˚

and fluorine atoms are omitted for clarity. Selected bond distances (A) and angles (deg) for 5: Ir(1)-C(1) = 2.118(3), Ir(1)-P(2) =

2.2280(10), Ir(1)-P(1) = 2.2455(10), Ir(1)-P(3) = 2.2546(10); C(1)-Ir(1)-P(2) = 77.90(11), C(1)-Ir(1)-P(1) = 77.57(11),

P(2)-Ir(1)-P(1) = 155.46(4), C(1)-Ir(1)-P(3) = 177.31(11), P(2)-Ir(1)-P(3) = 101.15(4), P(1)-Ir(1)-P(3) = 103.39(4). Selected

˚

bond distances (A) and angles (deg) for 6: Ir(1)-C(1) = 2.1377(16), Ir(1)-P(2) = 2.2602(4), Ir(1)-P(1) = 2.2668(4), Ir(1)-P(3) =

2.3089(4), Ir(1)-P(4) = 2.3120(4); C(1)-Ir(1)-P(2) = 77.16(5), C(1)-Ir(1)-P(1) = 76.54(5), P(2)-Ir(1)-P(1) = 124.211(16),

C(1)-Ir(1)-P(3) = 84.38(5), P(2)-Ir(1)-P(3) = 110.827(16), P(1)-Ir(1)-P(3) = 114.397(16), C(1)-Ir(1)-P(4) = 173.59(5),

P(2)-Ir(1)-P(4) = 98.998(16), P(1)-Ir(1)-P(4) = 101.900(15), P(3)-Ir(1)-P(4) = 101.854(15).

Scheme 1

and Et₃N in the presence of 1 atm of C₂H₄and excess olefin.

Monitoring the solution by NMR after the precipitation of

Et₃NH^þCl^-showed the bis-ethylene complex 4 to be the

only observed iridium species; filtration and concentration

is rapid on the NMR time scale at ambient temperature.

NMR data for 8 are similar to those for 7. Unlike the sharp

CF₃multiplet observed for 7, however, the CF₃resonance

for 8 is significantly broadened and suggests that slower CF₃

site exchange is occurring on the NMR time scale for the coe

adduct.

resulted in loss of ethylene and conversion to (^CFPCP)-

3

1

Ir(nbe) (7) or (^CFPCP)Ir(coe) (8). H NMR data for 7 and

3

8 are consistent with alkene coordination: phosphorus-

coupled vinylic norbornene protons (³J_PH= 5 Hz) in 7

appear as a triplet at δ 4.11, a singlet bridgehead resonance

occurs at δ 3.11, and four separate resonances are observed

for the diastereotopic nbe methylene protons. Vinylic coe

protons for 8 appear as a broad unresolved resonance at δ

5.03, and coe methylene protons are observed between δ 2.53

and 1.27. While norbornene NMR data are consistent with

the solid-state structure shown in Figure 4, single PCP

benzylic and CF₃resonances indicate that alkene rotation

The presence of ethylene in the synthesis of 7 and 8 is

critical: dehydrohalogenation of (^CFPCP)Ir(C₂H₄)(H)Cl

3

with excess nbe or coe in the absence of added C₂H₄resulted

in partial dehydrohalogenation (∼50%) after 20 h and th_þe

formation of the side product (^CFPCP)Ir(H)Cl₂^-HNEt₃

3

(9). X-ray diffraction (see the Supporting Information) and

NMR spectroscopy confirmed the formulation of 9. In the

absence of any added trapping ligand, the addition of Et₃N

to (^CFPCP)Ir(C₂H₄)(H)Cl in benzene produces a 1/1 mix-

3

ture of 9 and the bis-ethylene adduct 4. Complex 9 is

Article

Organometallics, Vol. 30, No. 4, 2011 701

presumably derived from the reaction of chloride (either as

free Cl^-or as an associated chloride adduct such as

(

interest of our research group. In this context, the dfepe complex

12 is similar to the five-coordinate Ir(I) complex (dfepe)₂IrH,

reported previously by our group.¹⁶

CF₃

PCP)Ir(C₂H₄)Cl^-) with unreacted (^CF³PCP)Ir(C₂H₄)-

(H)Cl. This is supported by a separate NMR experiment:

Dehydrohalogenation of nitrile adducts (^CFPCP)Ir-

3

agitating a 1:1 mixture of (^CFPCP)Ir(C₂H₄)(H)Cl and

(RCN)(H)Cl with Et₃N in the presence of excess MeCN or

PhCN does not afford (^CFPCP)Ir(nitrile)_xproducts. In-

3

HNEt₃^þCl^-in benzene at 20 °C resulted in the quantitative

formation of 9 after 20 min. Monitoring the reaction of

3

stead, dehydrohalogenation of (^CFPCP)Ir(PhCN)(H)Cl in

3

CF₃

(

PCP)Ir(C₂H₄)(H)Cl with Et₃N by NMR under 1 atm of

the presence of excess C₂H₄and PhCN gave the mixed five-

3

C₂H₄showed that 9 was present after 8 h (∼50%), but after

24 h it was cleanly converted to the bis-ethylene complex 4.

Dehydrohalogenation chemistry with the chelating trapp-

ing ligands norbornadiene, 1,5-cyclooctadiene, and (C₂F₅)₂-

coordinate complex (^CFPCP)Ir(PhCN)(C₂H₄) (13) (eq 4).

As with other five-coordinate (^CFPCP)Ir systems, the loss of

3

lateral symmetry across the (PCP)Ir unit is reflected by

distinct ¹⁹F CF₃doublets at δ -56.8 and -62.3 and diaster-

eotopic benzylic proton resonances at δ 3.52 and 3.37. An

interesting feature of the ¹H NMR spectrum is the appear-

ance of two broadened singlet C₂H₄resonances at δ 2.60 and

1.76, which may reflect either geminal or vicinal chemical

inequivalence, depending on the orientation of the ethylene

ligand. This issue was resolved by ¹³C NMR and X-ray

diffraction (Figure 6), which revealed that the coordinated

ethylene is above the (PCP)Ir plane and is aligned parallel to

the P-Ir-P plane. Thus, the two resonances are due to

vicinal proton sets directed toward the PhCN and PCP aryl

groups. ¹³C NMR data for the bound ethylene ligand show

PCH₂CH₂P(C₂F₅)₂(dfepe) cleanly affords (^CFPCP)Ir(LL)

3

products (LL =nbd (10), cod (11), dfepe (12)) in high yields.

Complexes 11 and 12 were structurally characterized (Figure 5).

For these chelates, the addition of ethylene as a coreactant is not

required. Designing highly electrophilic metal systems using

perfluoroalkylphosphines (PFAP’s) has been a longstanding

an upfield single carbon resonance at 32.4 ppm with ¹J_CH

=

157 Hz. This coupling is slightly lower than the J_CHvalue

1

III

reported for (^CFPCP)Ir ethylene complexes⁷and is con-

3

sistent with a greater degree of π back-bonding from the

CF₃

(

PCP)Ir^Imoiety.

Figure 4. Molecular structure of (^CFPCP)Ir(nbe) (7) with 50%

3

probability thermal ellipsoids. Hydrogen and fluorine atoms are

˚

omitted for clarity. Selected bond distances (A) and angles (deg)

for 7: Ir(1)-C(1) = 2.089(2), Ir(1)-P(2) = 2.1930(6), Ir(1)-P-

(1) = 2.1995(6), Ir(1)-C(13) = 2.264(2), Ir(1)-C(14) = 2.270(2);

C(1)-Ir(1)-P(2) = 78.53(6), C(1)-Ir(1)-P(1) = 79.38(6), P-

(2)-Ir(1)-P(1) = 142.30(2).

CF₃

(

PCP)Ir(L)₂Dynamics. The fluxionality of five-coordi-

3

nate (^CFPCP)Ir(L)₂systems has been examined by variable-

temperature H and ¹⁹F NMR. While the solid-state struc-

ture of the dicarbonyl complex 3 shows inequivalent CO

1

Figure 5. Molecular structures of (^CFPCP)Ir(cod) (11) and ( PCP)Ir(dfepe) (12) with 50% probability thermal ellipsoids. Hydrogen

CF₃

3

˚

and fluorine atoms are omitted for clarity. Selected bond distances (A) and angles (deg) for 11: Ir(1)-C(1) = 2.097(4), Ir(1)-C(13) =

2.162(4), Ir(1)-C(14) = 2.175(4), Ir(1)-P(2) = 2.2479(11), Ir(1)-P(1) = 2.2744(11), Ir(1)-C(17) = 2.295(4), Ir(1)-C(18) = 2.299(4);

˚

C(1)-Ir(1)-P(2) = 76.80(12), C(1)-Ir(1)-P(1) = 77.50(12), P(2)-Ir(1)-P(1) = 119.02(4). Selected bond distances (A) and angles

(deg) for 12: Ir(1)-C(1) = 2.146(2), Ir(1)-P(2) = 2.2634(6), Ir(1)-P(1) = 2.2751(6), Ir(1)-P(3) = 2.2878(5), Ir(1)-P(4) = 2.2998(6);

C(1)-Ir(1)-P(2) = 77.84(6), C(1)-Ir(1)-P(1) = 76.15(6), P(2)-Ir(1)-P(1) = 126.23(2), C(1)-Ir(1)-P(3) = 96.36(6), P(2)-Ir-

(1)-P(3) = 119.39(2), P(1)-Ir(1)-P(3) = 109.66(2), C(1)-Ir(1)-P(4) = 177.05(6). P(2)-Ir(1)-P(4) = 104.94(2), P(1)-Ir(1)-

P(4) = 101.23(2), P(3)-Ir(1)-P(4) = 83.19(2).

702 Organometallics, Vol. 30, No. 4, 2011

Adams et al.

Figure 6. Molecular structure of (^CFPCP)Ir(PhCN)(C₂H₄)

3

(13) with 50% thermal ellipsoids. Hydrogen and fluorine

˚

atoms are omitted for clarity. Selected bond distances (A)

and angles (deg) for 13: Ir(1)-C(1) = 2.057(4), Ir(1)-N(1)=

2.088(3), Ir(1)-C(20) = 2.174(4), Ir(1)-C(21) = 2.180(4), C(20)-

C(21) = 1.412(7), Ir(1)-P(2) = 2.2185(10), Ir(1)-P(1) =

2.2243(10); C(1)-Ir(1)-N(1) = 177.88(14), C(1)-Ir(1)-

P(2)=80.30(11), N(1)-Ir(1)-P(2)=97.58(10), C(1)-Ir(1)-

P(1)=78.59(10), N(1)-Ir(1)-P(1)=102.71(9), P(2)-Ir(1)-

P(1) = 123.78(4).

Figure 7. Variable-temperature ¹H NMR spectra (400 MHz,

CD₂Cl₂) of (^CFPCP)Ir(C₂H₄)₂(4).

3

ligands disposed cis and trans to the Ir-C(aryl) bond

(Figure 2), at ambient temperatures single resonances are

observed for the diastereotopic pincer benzylic methylene

protons and CF₃groups in ¹H and ¹⁹F NMR spectra,

respectively, which indicate that CO site exchange is fast

on the NMR time scale. VT NMR experiments have con-

broadened resonance, and further warming to 50 °C results

in progressive sharpening to an averaged ethylene signal at

2.68 ppm. A coalescence at -18 °C (ΔG^q=12.2(2) kcal mol^-1

)

is observed for the diastereotopic benzylic protons. Addi-

tional dynamic information is provided by ¹⁹F spectra, which

show distinct CF₃resonances at -58.7 and -65.3 ppm

at -90 °C and a coalescence temperature of þ30 °C, corre-

firmed this: when (^CFPCP)Ir(CO)₂in CD₂Cl₂is cooled

3

under N₂to -95 °C, a slow-exchange limit is observed with

two distinct benzylic proton resonances at δ 4.20 and δ 3.86

and well-defined CF₃doublets at -61.4 (²J_PF= 75 Hz)

and -65.4 (²J_PF= 72 Hz). Coalescence of the inequivalent

benzylic groups at -70 °C and CF₃groups at -50 °C

corresponds to a site exchange activation barrier of 9.7(2)

sponding to a slightly higher ΔG^qvalue of 12.6(2) kcal mol^-1

.

These observations are consistent with similar exchange

barriers for the rotation of one ethylene ligand and ethylene

ligand site exchange.

The observation of a single ethylene resonance at 2.70 ppm

for one of the ethylene ligands in (^CFPCP)Ir(C₂H₄)₂at -90 °C

kcal mol^-1

.

The presence of a single ethylene proton resonance for the

3

implies that the barriers to ethylene rotation in 4 may be

quite different.¹⁷To investigate this further, a DFT geometry

optimization and subsequent energy calculation for 4 at the

B97-1/cc-pVDZ level of theory was carried out (see the

Experimental Section). While the reaction profiles for ethyl-

ene rotation and dissociation were not examined, the calcu-

lated structure (Figure 8) shows a substantial difference in

axial and equatorial ethylene bond lengths. The significantly

bis-ethylene complex (^CFPCP)Ir(C₂H₄)₂(4) at 20 °C indi-

3

cates that 4 is also fluxional. VT NMR data for 4 in the

absence of free ethylene show dynamic exchange processes

involving both ethylene ligand rotation and ligation site

equilibration (Figure 7).

At -90 °C, separate benzylic CH₂resonances appear at δ

3.89 and 3.67, and three distinct ethylene proton resonances

appear at δ 2.95, 2.70, and 1.73 in a 2/4/2 integrated ratio. ¹³C

NMR spectra at this temperature revealed two ethylene

˚

lengthened C-C bond (1.44 A) and shorter Ir-C bond

lengths (2.18, 2.17 A) for the equatorial ethylene are con-

˚

carbon resonances at 45.1 (¹J_CH= 163 Hz) and 35.6 (¹J_CH

=

sistent with the X-ray structure of the cod chelating analogue

11 (see Crystallographic Studies) and suggest increased

back-bonding and a higher equatorial Ir-C₂H₄rotational

barrier. The C-C bond of the equatorial ethylene ligand is

aligned with the P-Ir-P plane, analogous to the orientation

160 Hz) ppm. The presence of two, rather than three,

ethylene carbon resonances indicates that the δ 2.95 and

1.73 doublets are due to inequivalent geminal, rather than

vicinal, protons, and therefore the associated C₂H₄ligand

has an effective plane of symmetry relating the CH₂groups.

At temperatures above -90 °C all ethylene and benzylic

resonances undergo exchange broadening. The δ 2.95 and

1.73 ethylene resonances coalesce at -10 °C, corresponding

of ethylene in (^CFPCP)Ir(PhCN)(C₂H₄). The orientation of

3

the axial ethylene ligand is canted 41° with respect to the PCP

arene ring and is essentially along one of the Ir-P bonds; the

orientation of the corresponding cod double bond in 11 in

comparison is restricted by the chelate ring to ∼12° out of the

arene plane.

to a rotational exchange barrier of ΔG^q=11.7(2) kcal mol^-1

.

At 20 °C, all ethylene resonances collapse into a single

(16) Schnabel, R. C.; Roddick, D. M. Organometallics 1993, 12, 704–

711.

(17) In the absence of an observed slow-exchange limit, this assumes a

Δν difference comparable to that found for the other ethylene ligand.

Article

Organometallics, Vol. 30, No. 4, 2011 703

Information). The donor PCP complex (^iPrPCP)Ir(CO) has

been reported to readily react with methyl iodide to form a

(

^iPrPCP)Ir(CO)(CH₃)I product with analogous stereo-

chemistry.¹⁹

In contrast to the oxidative addition of ionizable sub-

strates A-B to d⁸square-planar systems, which generally

result in kinetic products with trans A and B groups, the

oxidative addition reactions with dihydrogen proceed via η-

H₂intermediates and lead to kinetic and usually thermo-

dynamically preferred cis-dihydride products. In contrast to

this expectation, Milstein has reported that treatment of

Figure 8. DFT geometry optimization for (^CFPCP)Ir(C₂H₄)₂

(4), showing asymmetrical axial and equatorial ethylene binding

interactions.

3

Scheme 2

(

^iPrPCP)Ir(CO) with H₂reversibly affords the expected cis-

dihydride product cis-(^iPrPCP)Ir(CO)(H)₂, which then

slowly rearranges upon heating at 90 °C under 35 psi of H₂

to trans-(^iPrPCP)Ir(CO)(H)₂as the thermodynamically pre-

ferred isomer. The reaction of (^CFPCP)Ir(CO) with H₂has

3

distinctly different kinetic behavior: exposure of orange

benzene solutions of 1 to 1 atm of hydrogen at ambient

temperatures resulted in a rapid bleaching and the direct

CF₃

(

PCP)Ir(PhCN)(C₂H₄) (13) exhibits slow exchange

formation of trans-(^CFPCP)Ir(CO)(H)₂(15) (eq 6). Removal

3

limit NMR spectra at 20 °C. At higher temperatures, coales-

cence of benzylic CH₂, inequivalent geminal C₂H₄, and CF₃

groups takes place. Kinetic fitting gives identical barriers for

benzyl (16.1(2) kcal mol^-1, 50 °C) and CF₃(16.1(2) kcal

mol^-1, 90 °C) groups and a slightly lower barrier for ethylene

site exchange (15.1(2) kcal mol^-1, 50 °C). The equilibration

of hydrogen rapidly converted 15 back to 1. ¹H NMR spectra

of 15 exhibit a diagnostic hydride triplet at -9.10 (²J_HP

=

19.2 Hz) and a single benzylic resonance which, together with

the chemical equivalence of CF₃groups in ¹⁹F spectra, confirms

the symmetrical trans stereochemistry.

of diastereotopic groups in the asymmetrical complex

CF₃

(

PCP)Ir(L)(L⁰) is not consistent with intramolecular li-

gand site exchange involving L and L⁰in equatorial positions

and supports a dissociative mechanism (Scheme 2). Further

support for a dissociative ligand site exchange mechanism

for (^CFPCP)Ir(L)₂systems is provided by the chelate com-

3

plexes 10-12, which exhibit NMR spectra reflecting a static

five-coordinate environment with inequivalent chelate ends

at ambient temperatures. No changes in NMR spectra for 12

were observed up to 100 °C.

The reaction of the dfmp complex 5 with H₂is quite

different (eq 7). Under 1 atm of H₂, 5 rapidly and reversibly

converts at 20 °C to the dihydride product (^CFPCP)Ir-

3

A dissociative mechanism for (^CFPCP)Ir(L)₂ligand site

3

exchange relates the observed exchange barriers to (^CFPCP)-

3

(dfmp)(H)₂(16), which displays a single complex hydride

multiplet at δ -11.45 as well as diasterotopic benzylic

resonances and inequivalent CF₃¹⁹F doublets. These fea-

tures are inconsistent with either the cis or trans dihydride

Ir(L)-L bond dissociation energies: 9.7 kcal mol^-1for

CF₃

-1

(

PCP)Ir(CO)-CO and 12.2 kcal mol for (^CFPCP)Ir-

3

(C₂H₄)-C₂H₄.¹⁸For comparison, DFT calculations for

stereochemistry expected for a meridional (^CFPCP)Ir pincer

3

(

^pyrPCP)Rh(CO)₂predict that the loss of equatorial CO is

2.2-3.4 kcal mol^-1uphill.¹⁵A higher dissociation energy of

ancillary unit. At ambient temperatures the new species 17

slowly grows in with an associated hydride resonance at

δ -10.18 (∼10% conversion, 24 h), which reaches a max-

imum conversion of 30% after 3 days. No further change in

the 16/17 ratio was observed after 2 weeks at ambient

temperature or after subsequent warming to 80 °C for 1

week. We assign 17 as the minor trans-dihydride isomer mer,

16.1 kcal mol^-1is implicated for (^CFPCP)Ir(NCPh)(C₂H₄),

3

but in this unsymmetrical molecule further data are required

to determine whether benzonitrile or ethylene is preferen-

tially dissociated.

CF₃

(

PCP)Ir(L) Oxidative Addition Reactions. The 16-elec-

tron Ir(I) systems trans-(R₃P)₂Ir(L)(X) commonly undergo

oxidative addition reactions with both polar and nonpolar

reactants. Accordingly, complex 1 reacts with an excess of

trans-(^CFPCP)Ir(dfmp)(H)₂(17). ³¹P decoupling experi-

3

ments and simulation of the hydride resonance for 16 define

a AA⁰MXX⁰spin system with cis hydride ligands (A, A⁰)

coplanar with cis pincer P(CF₃)₂groups (X, X⁰) and a

mutually cis dfmp phosphorus (M). The facial pincer co-

ordination geometry indicated for 16 by NMR data is quite

MeI in benzene to afford (^CFPCP)Ir(CO)(CH₃)I (14) (eq 5).

3

The trans disposition of methyl and iodide ligands in 14 has

been confirmed by X-ray diffraction (see the Supporting

(18) An explanation for the small but significant discrepancy in

activation values for the bis-ethylene system is not readily apparent;

we adopt an averaged value here.

(19) Rybtchinski, B.; Ben-David, Y.; Milstein, D. Organometallics

1997, 16, 3786–3793.

704 Organometallics, Vol. 30, No. 4, 2011

Adams et al.

hydride resonances at δ -11.28 (²J_PH=18 Hz) and δ -11.71

(²J_PH=15 Hz) begin to appear, which are assigned to mer,

cis-(^CFPCP)Ir(CO)(H)₂(19) The cis-dihydride 19 reaches a

3

maximum integrated intensity at 0 °C of 1.5/1 with respect to

18 and then decays as the thermodynamically preferred trans

hydride product 15 forms with warming above 0 °C. After 15

min at 20 °C a 5.9/1 ratio of 15 to 19 is established.

These observations are consistent with a reaction mechan-

ism involving the reversible addition of H₂to (^CFPCP)-

3

Ir(CO) and a kinetic preference for H₂addition across

the P-Ir-P axis to form fac,cis-(^CFPCP)Ir(CO)(H)₂(18)

3

(Scheme 3). At higher temperatures the hydride resonance

for 18 is further broadened due to exchange with free H₂.

Addition of H₂across the C-Ir-CO axis has a larger kinetic

barrier and leads to the formation of mer,cis-(^CFPCP)Ir-

3

Figure 9. Molecular structure of fac,cis-(^CFPCP)Ir(dfmp)(H)₂

(16) with 50% probability thermal ellipsoids. Hydrogen atoms

(except hydride ligands) and fluorine atoms are omitted for

3

(CO)(H)₂at higher temperatures. Stereochemical prefer-

ences for H₂addition across trans-(R₃P)₂Ir(CO)X systems

are well-known.²⁰The mechanism of formation of the final

trans-dihydride product 15 is not certain. Brookhart has

recently reported base-assisted isomerization of cis-(PNP)Ir-

(Me)(H)₂to trans-(PNP)Ir(Me)(H)₂involving deprotona-

tion/reprotonation by adventitious water.²¹Addition of 2

equiv of H₂O resulted in no significant change in the rate of

isomerization from 19 to 15. Calculations by Hall suggest

that an intramolecular “trigonal twist” mechanism connect-

ing cis- and trans-dihydride isomers is energetically access-

ible.²²A trigonal twist mechanism, which requires a facial

PCP distortion accompanying a turnstyle-type twisting of

the P₁, H₁, and H₂groups (see labeling in Scheme 3), should

be favored for electron-withdrawing pincer ligands and is

˚

clarity. Selected bond distances (A) and angles (deg) for 16:

Ir(2)-C(18) = 2.121(4), Ir(2)-P(6) = 2.2904(11), Ir(2)-P(4) =

2.2942(10), Ir(2)-P(5) = 2.3028(10), Ir(2)-H(2A) = 1.51(5),

Ir(2)-H(2B) = 1.51(5); C(18)-Ir(2)-P(6) = 170.99(10), C-

(18)-Ir(2)-P(4) = 77.15(11), P(6)-Ir(2)-P(4) = 105.16(4),

C(18)-Ir(2)-P(5) = 77.05(11), P(6)-Ir(2)-P(5) = 108.97(4),

P(4)-Ir(2)-P(5) = 116.30(4), H(2A)-Ir(2)-H(2B) = 85(3).

unusual and has been confirmed by X-ray crystallography

(Figure 9).

consistent with the low isomerization barrier found for

CF₃

(

PCP)Ir(CO)(H)₂.

Crystallographic Studies. Crystallographic data obtained

for a range of four-, five-, and six-coordinate (^CFPCP)Ir

complexes allows us to compare pincer structural features

with donor PCP systems (Table 1). Following established

electronic effects for phosphines containing π-accepting

3

perfluoroalkyl substituents,^8,16,23Ir-P(^CFPCP) bonds for

3

CF₃

(

PCP)Ir(L) complexes (complexes 1, 2, 5, and 7) aver-

˚

age 2.212 A, which is significantly shorter than the Ir-P

bond length average of 2.296 A for ^RPCP as well as

˚

^RPOCOP systems.^2i,10,24The average Ir-P(^CFPCP) bond

3

The existence of the stable fac,cis-dihydride 16 led us to

examine the course of reaction of (^CFPCP)Ir(CO) (1) with

length for five-coordinate Ir(I) systems (complexes 3, 6,

and 11-13) is slightly longer (2.252 A). The average

3

˚

Ir-C(^CFPCP) bond distance is 2.084 A, which is on the

3

˚

H₂by variable-temperature NMR (Figure 10). Upon mixing

of 1 with 3 atm of H₂in acetone-d₆at -60 °C, a single

product is observed with a AA⁰XX⁰hydride resonance at

δ -9.79 (²J_PH= -157, 33 Hz) which is assigned as fac,

˚

high end of the 2.001-2.102 A range found for donor

pincer structures.

cis-(^CFPCP)Ir(CO)(H)₂(18). When the temperature is

3

(20) Deutsch, P. P.; Eisenberg, R. Chem. Rev. 1988, 88, 1147–1161.

(21) Findlater, M.; Bernskoetter, W. H.; Brookhart, M. J. Am. Chem.

Soc. 2010, 132, 4534–4535.

(22) Li, S.; Hall, M. B. Organometallics 1999, 18, 5682–5687.

(23) (a) Ernst, M. F.; Roddick, D. M. Organometallics 1990, 9, 1586–

1594. (b) Schnabel, R. C.; Roddick, D. M. Inorg. Chem. 1993, 32, 1513–

1518. (c) Butikofer, J. L.; Hoerter, J. M.; Peters, R. G.; Roddick, D. M.

Organometallics 2004, 23, 400–408. (d) Adams, J. J.; Lau, A.; Arulsamy,

N.; Roddick, D. M. Inorg. Chem. 2007, 46, 11328–11334.

(24) (a) Lee, D. W.; Kaska, W. C.; Jensen, C. M. Organometallics

1998, 17, 1–3. (b) Morales-Morales, D.; Redon, R.; Wang, Z.; Lee,

D. W.; Yung, C.; Magnuson, K.; Jensen, C. M. Can. J. Chem. 2001, 79,

823–829. (c) Kanzelberger, M.; Zhang, X.; Emge, T. J.; Goldman, A. S.;

Zhao, J.; Incarvito, C.; Hartwig, J. F. J. Am. Chem. Soc. 2003, 125,

13644–13645. (d) Cartwright Sykes, A.; White, P.; Brookhart, M.

Organometallics 2006, 25, 1664–1675. (e) Ghosh, R.; Kanzelberger,

M.; Emge, T. J.; Hall, G. S.; Goldman, A. S. Organometallics 2006,

25, 5668–5671. (f) Ghosh, R.; Zhang, X.; Achord, P.; Emge, T. J.;

Krogh-Jespersen, K.; Goldman, A. S. J. Am. Chem. Soc. 2007, 129, 853–

866.

raised, coalescence is observed near -40 °C and then a shar-

pening occurs to form a single broadened singlet (ν_1/2

=

22 Hz, T₁=1.72 s) at -20 °C. At higher temperatures this

resonance broadens and coalesces into the baseline by 20 °C.

At temperatures above -20 °C, the resonance at δ 4.54 due

to dissolved free H₂also broadens, due to exchange with 18.

Modeling intermolecular proton exchange between 18 and 1

is not straightforward. However, this exchange process

correlates with the intramolecular site exchange of diaster-

eotopic PCP benzyl protons and CF₃groups. At -60 °C, ¹⁹

F

NMR spectra for 18 show distinct CF₃doublets at -59.9

and -62.3 ppm which coalesce at -20 °C, corresponding to

ΔG^q=10.9(2) kcal mol^-1. Modeling the coalescence beha-

vior of the benzylic protons gives an essentially identical

value of ΔG^q= 11.0(2) kcal mol^-1. At -40 °C, new triplet

Article

Organometallics, Vol. 30, No. 4, 2011 705

1

Figure 10. Variable-temperature H NMR spectra (400 MHz, acetone-d₆) of (^CFPCP)Ir(CO) (1) under 3 atm of H₂, with hydride

3

resonance assignments.

Structurally characterized four-coordinate (pincer)M(η²-

alkene) systems have been reported.^8,25With the exception of

the bulky phosphite compounds (^biphenolPOCOP)Rh(η²-

C₂H₄), all alkene complexes show a significant rotation of

the M-alkene moiety out of the (pincer)M plane. The

norbornene complex 7 exhibits an unusual disposition of

the alkene ligand and the pincer ancillary ligand. Rather than

a simple rotation about the Ir-alkene centroid, the plane

defined by the iridium and the norbornene vinylic carbons is

not rotated but is instead canted 17.3° below the pincer aryl

plane. This distortion tilts the norbornene CH₂away from

the pincer CF₃groups. In addition, the P-Ir-P angle,

142.3°, is not just bent away from the fourth ligand, which

is typical for pincer four-coordinate complexes, but is much

(25) (a) Zhao, J.; Goldman, A. S.; Hartwig, J. F. Science 2005, 307,

1080–1082. (b) Ben-Ari, E.; Cohen, R.; Gandelman, M.; Shimon,

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3190–3210. (c) Rubio, M.; Suarez, A.; del Rio, D.; Galindo, A.; Alvarez,

E.; Pizzano, A. Dalton Trans. 2007, 407–409. (d) Yano, T.; Moroe, Y.;

Yamashita, M.; Nozaki, K. Chem. Lett. 2008, 37, 1300–1301. (e)

Friedrich, A.; Ghosh, R.; Kolb, R.; Herdtweck, E.; Schneider, S.

Organometallics 2009, 28, 708–718. (f) Rubio, M.; Suarez, A.; del Rio,

D.; Galindo, A.; Alvarez, E.; Pizzano, A. Organometallics 2009, 28, 547–

560.

smaller than the 155-159° values for other (^CFPCP)Ir(L)

3

systems, due to a distortion above the (aryl)Ir plane. This

flexibility of the (^CFPCP)Ir moiety also allows the P(CF₃)

3

groups syn to the norbornene bridging methylene to ease

their steric interactions and is consistent with the high level of

ligand stereochemical flexibility reflected in the five-coordi-

nate (^CFPCP)Ir(L)₂structures and in 16 (see below). The

3

706 Organometallics, Vol. 30, No. 4, 2011

Adams et al.

Scheme 3

CF₃

Table 1. Selected Bond Distances (A) and Angles (deg) for ( PCP)Ir(L_ax) and (^CFPCP)Ir(L_ax)(L_eq) Complexes

3

˚

complex

Ir-P(PCP)_av

Ir-C

Ir-L_ax

Ir-L_eq

P-Ir-P

L_ax-Ir-C

L_eq-Ir-C

L_eq-Ir-L_ax

CF₃

(

PCP)Ir(CO) (1)

2.224

2.189

2.237

2.196

2.247

2.264

2.261

2.269

2.221

2.088(1)

2.047(4)

2.118(3)

2.089(2)

2.131(3)

2.138(2)

2.097(4)

2.146(2)

2.057(4)

1.895(2)

2.135(3)

2.255(1)

2.157^a

1.939(4)

2.312(1)

2.192^a

159.3

158.3

155.5

142.3

130.3

124.2

119.0

126.2

123.8

179.1

178.1

177.3

166.1^a

171.6

173.6

173.0^a

177.1

177.9

PCP)Ir(DBU) (2)

PCP)Ir(dfmp) (5)

PCP)Ir(nbe) (7)

PCP)Ir(CO)₂(3)

1.941(4)

2.309(1)

2.046^a

2.288(1)

2.059^a

91.6

84.4

89.4^a

96.4

90.2^a

96.7

101.9

84.2^a

83.2

PCP)Ir(dfmp)₂(6)

PCP)Ir(cod) (11)

PCP)Ir(dfepe) (12)

PCP)Ir(NCPh)(C₂H₄) (13)

2.300(1)

2.088(3)

90.7^a

^aCalculated using the centroids of the alkene ligand.

˚

observed CdC bond length for 7, 1.394(4) A, is similar to

normal to the C(1)-Ir-L(axial) axis toward the arene

group. In complex 6 the equatorial dfmp Ir-P(3) bond

length (2.3089(4) A) is slightly shorter than the axial dfmp

that for the more electron-rich complex [((^tBu) ₂PCH₂CH₂C-

t

2

˚

(H)CH₂CH₂P( Bu)₂]Ir(η -propene) (1.40_þ2(6) A) and longer

than that found for (^CFPCP)Pt(η -C₂H₄) (1.305(7) A).

Ir-P(4) bond length (2.3120(4) A), and both are significantly

2

8,25a

3

˚

Carbonyl complexes 1 and 3 and the dfmp complexes 5

and 6 provide an opportunity to compare closely related

four- and five-coordinated d⁸geometries (Figures 2 and 3).

Complexes 3 and 6, in particular, follow Milstein’s earlier

report of the first five-coordinate d⁸pincer complexes,

longer than the pincer Ir-P bond lengths (2.2602(4),

2.2668(4) A). The remaining five-coordinate structures dis-

˚

play similar angular distortions, though complexes 11 and 12

are further constrained by the chelating cod and dfepe ligands.

The chelating cod complex 11 provides a revealing model

(

square planar, with a maximum deviation from the mean-

square plane defined by iridium and the four attached atoms

^pyrPCP)Rh(PR₃)(CO).¹⁵Complexes 1 and 5 are essentially

for the bis-ethylene complex (^CFPCP)Ir(C₂H₄)₂(4). Alkene

3

coordination in 11 is quite asymmetrical: the double bond cis

to the Ir-C(aryl) bond (equatorial) is significantly length-

˚

of 0.027 A for 1 and 0.034 A for 5. The pincer P-Ir-P angles,

159.3° (1) and 155.5° (5), are canted away from the CO

and dfmp ligands and are within the mean-square plane.

Smaller P-M-P pincer angles correlate with increased steric

interactions; consistent with this, a greater pincer C2 inter-

planar angle twist of 17.3° between the pincer arene ring and the

coordination plane is found for 5 versus that for 1 (13.5°).

The five-coordinate complexes 3 and 6 adopt a distorted-

trigonal-bipyramidal coordination geometry with axial CO

(or dfmp) ligands and pincer C(aryl) groups (3, C(1)-Ir-C-

(13)=171.6°; 6, C(1)-Ir-P(4)=173.6°, tilted away from the

remaining CO (or dfmp) ligand). The equatorial CO in 3 has

angles of C(1)-Ir-C(14) = 91.6° and C(1)-Ir-C(13) =

96.7°, and the P-Ir-P angle is 130.3°. For 6, steric interac-

tions bend the equatorial dfmp phosphorus P(3) away from

the axial dfmp ligand; the corresponding angles are C-

(1)-Ir-P(3) = 84.4° and P(3)-Ir-P(4) = 101.9°, and the

P-Ir-P angle is reduced to 124.2°. For comparison, the

P-Rh-P pincer angle for (^pyrPCP)Rh(PEt₃)(CO) is 128.3°.

Due to terdentate bonding constraints, the pincer phosphorus

atoms in 3 and 6 are bent out of an idealized equatorial plane

ened (C(13)-C(14)=1.435(6) A) with shorter Ir-C bonds

˚

(Ir(1)-C(13)=2.162(4) A; Ir(1)-C(14)=2.175(4) A) com-

pared to the double bond trans to the aryl Ir-C bond (axial)

˚

(C(17)-C(18) = 1.375(6) A; Ir(1)-C(17) = 2.295(4) A; Ir-

˚

(1)-C(18)=2.299(4) A). This reflects considerably greater

metal back-bonding from the (^CFPCP)Ir moiety to the

I

3

equatorial ligand. This asymmetry in back-bonding ability

is not observed for dicarbonyl 3 and is only very slightly

reflected in dfmp bond lengths for (^CFPCP)Ir(dfmp)₂(6)

3

CF₃

˚

(Ir-P(dfmp)_ax- Ir-P(dfmp)_eq= 0.003 A) and ( PCP)-

˚

Ir(dfepe) (12) (Ir-P(dfepe)_ax- Ir-P(dfepe)_eq= 0.013 A).

We tentatively ascribe the greater bonding asymmetry in bis-

alkene complexes to a mismatch of optimal back-bonding

and axial alkene orientation. Note added in proof: The X-ray

structure of the bis ethylene complex 4 has now been deter-

mined, which similarly shows an elongated equatorial C-C

˚

ethylene bond (1.40 A) and a shorter axial C-C bond (1.33 A).

The fac-(R₃P)₃Ir(H₂)(X) coordination environment of 16

(Figure 7) is relatively rare.²⁶The Ir-P bond lengths to P(5)

and P(6), which are trans to hydride ligands, are 2.294(1) and

˚

2.303(1) A, somewhat longer than 2.189-2.269 A range for

Article

Organometallics, Vol. 30, No. 4, 2011 707

CF₃

meridionally coordinated PCP systems with trans phos-

phorus groups. These bond lengths reflect the greater hy-

of ancillary coordination geometries opens up new avenues

for future research. In a forthcoming paper we shall report

the application of (^CFPCP)Ir(L)_xsystems to alkane dehy-

3

dride ligand trans influence and are comparable to the Ir-P

values reported for fac-(MePh₂P)₃IrH₃(2.314(2) A) and

˚

drogenation and aldehyde decarbonylation catalysis.

fac-(Me₃P)₃Ir(H)₂(SiHPh₂) (2.308(3), 2.310(30 A).²⁶The P-

˚

(4)-Ir(2)-P(5) PCP angle, 116.3°, is somewhat smaller than

the range of 119-130° found for distorted bipyramidal

CF₃

(

PCP)Ir(L)₂structures (Table 1) but much greater than

the ∼100° angle found in unconstrained fac-(R₃P)₃Ir(H₂)(X)

structures. The osmium piano-stool complex Cp⁰Os(^PhPCP)-

Cl with a PCP P-Os-P angle of 113.2° has been reported.²⁷

Summary

Experimental Section

Interest in terdentate “pincer” ligands with a central aryl

anchoring group is often attributed to their enhanced ancil-

lary ligand stability as well as their preference for a coplanar

coordination environment. This coplanarity is seen in: (1)

three-coordinate “T-shaped” (pincer)M intermediates,^2c,28

(2) four-coordinate square-planar (pincer)M(L) systems,

and (3) six-coordinate meridional octahedral geometries,

(pincer)M(L)(X)(Y). In addition to the ubiquitous square-

planar d⁸Ir(I) systems, (L)₃Ir(X), examples of five-coordi-

nate complexes such as (PPh₃)₃Ir(CO)(H)²⁹and (dppe)₂Ir-

(CO)^þare known;³⁰until now, none containing the (PCP)Ir^I

moiety have been prepared. Following Milstein’s report of

five-coordinate (^pyrPCP)Rh(PR₃)(CO) systems,¹⁵the pre-

General Procedures. All manipulations were conducted under

N₂or vacuum using high-vacuum-line and glovebox techniques,

unless otherwise noted. All ambient-pressure chemistry was

carried out under a pressure of approximately 590 Torr

(elevation ∼2195 m). All solvents were dried using standard

procedures and stored under vacuum. Aprotic deuterated sol-

˚

vents used in NMR experiments were dried over activated 3 A

molecular sieves. Elemental analyses were performed by Desert

Analytics or Columbia Analytical Services. NMR spectra were

obtained with a Bruker DRX-400 instrument using 5 mm NMR

tubes fitted with Teflon valves (Chemglass CG-512 or New Era

CAV-VBP). ³¹P spectra were referenced to an 85% H₃PO₄

external standard. ¹⁹F spectra were referenced to CF₃CO₂-

CH₂CH₃(δ -75.32) and CF₃C₆H₅external standards. The

gases CO (Airgas), C₂H₄(Airgas), and H₂(UHP, Praxair) were

purchased and used without further purification; all other

reagents were purchased from Aldrich and were used with-

sent work demonstrates that (^CFPCP)Ir(L)₂systems posses-

3

sing the strongly π-accepting P(CF₃)₂groups spanning

equatorial coordination sites in a distorted-trigonal-bipyr-

amidal geometry are quite stable. In a simplistic sense, this

pincer distortion allows the acceptor phosphine centers to re-

duce trans ligand competition for dπ back-bonding density.

The unusual hydrogen addition products fac,cis-

out further purification. The complexes (^CFPCP)Ir(CO)(H)Cl,

3

CF₃

(

PCP)Ir(C₂H₄)(H)Cl, (^CF³PCP)Ir(MeCN)(H)Cl, (^CF³PCP)-

Ir(PhCN)(H)Cl, and (^CFPCP)Ir(MeP(C₂F₅)₂)(H)Cl were pre-

pared by following procedures described in the previous paper.⁷

(CF₃PCP)Ir(CO) (1). (CF₃PCP)Ir(CO)(H)Cl (0.500 g, 0.716

mmol) and Et₃N (144 μL, 0.104 g, 1.432 mmol) were dissolved in

15 mL of C₆H₆. The initially colorless solution rapidly turned

orange, and a white precipitate was observed. After the reaction

mixture was stirred at ambient temperature for 12 h, the

volatiles were removed under vacuum, 10 mL of hexanes was

added, and the solution was filtered to remove Et₃NH^þCl^-.

Cooling the filtrate to -78 °C afforded an orange precipitate,

which was collected via cold filtration and dried under vacuum

(0.330 g, 70% yield). Crystals suitable for X-ray diffraction were

grown by slow evaporation from a 1/2 pentafluoropyridine/

perfluoro-2-butyltetrahydrofuran solution. Anal. Calcd for

C₁₃H₇P₂F₁₂OIr: C, 23.57; H, 1.07. Found: C, 23.94; H, 0.71.

¹H NMR (C₆D₆, 400.13 MHz, 20 °C): δ 6.90 (t, ³J_HH=8 Hz, 1H;

3

CF₃

3

(

PCP)Ir(dfmp)(H)₂(16) and fac,cis-(^CFPCP)Ir(CO)-

(H)₂(18) are also consistent with the enhanced ability of

acceptor PCP ligands to adopt a noncoplanar coordina-

tion geometry. The apparent thermodynamic preference

for cis-dihydride coordination in 16 is in contrast with the

preference for the trans carbonyl dihydride product 15.

Scheme 3, besides rationalizing VT NMR results for the

reaction of (^CFPCP)Ir(CO) and H₂, also suggests an explana-

3

tion for the surprising steric sensitivity of H₂addition to

(^RPCP)Ir(CO) (R=ⁱPr, ^tBu), which is indicated by the failure

of (^tBuPCP)Ir(CO) to react with H₂.^2dThe initial formation of

a trigonal-bipyramidal H₂adduct requires pincer bending,

which would force an unfavorable interaction of the syn bulky

^tBu groups. It is apparent that both steric and electronic

influences of pincer phosphine substituents should be consid-

ered in ligand addition reactions to (PCP)Ir(L) systems.

From the standpoint of pincer coordination chemistry, the

ability of acceptor pincer ligands to support a broader range

3

p-C₆H₃(CH₂P(CF₃)₂)₂), 6.79 (d, J_HH= 8 Hz, 2H; m-C₆H₃-

(CH₂P(CF₃)₂)₂), 3.29 (m, 4H; C₆H₃(CH₂P(CF₃)₂)₂). ³¹P{¹H}

NMR (C₆D₆, 161.97 MHz, 20 °C): δ 69.6 (m). ¹⁹F NMR (C₆D₆,

376.50 MHz, 20 °C): δ -57.5 (m, 12F; PCF₃). IR (CH₂Cl₂):

ν(CO) 2018 cm^-1

.

PCP)Ir(DBU) (2). (^CF³PCP)Ir(MeCN)(H)Cl (0.450 g,

CF₃

(

0.633 mmol) and DBU (1,8-diazabicyclo[5.4.0]undec-7-ene,

142 μL, 0.145 g, 0.949 mmol) were dissolved in 10 mL of

C₆H₆. The reaction mixture was stirred at ambient temperature

for 12 h, during which time the solution changed from colorless

to red. Volatiles were removed, and ca. 20 mL of petroleum ether

was added. The solution was filtered away from unreacted

starting material and protonated DBU. The red filtrate was

cooled to -78 °C, and a red precipitate formed, which was

collected by filtration (0.221 g, 59% yield). Crystals suitable for

X-ray diffraction were grown by slow evaporation from a 1/2

pentafluoropyridine/perfluoro-2-butyltetrahydrofuran solution.

Anal. Calcd for C₂₁H₂₃P₂F₁₂N₂Ir: C, 32.06; H, 2.95, N, 3.56.

Found: C, 32.06, H, 2.44; N, 3.56. ¹H NMR (C₆D₆, 400.13 MHz,

(26) (a) Zarate, E. A.; Kennedy, V. O.; McCune, J. A.; Simons, R. S.;

Tessier, C. A. Organometallics 1995, 14, 1802–1809. (b) Bau, R.;

Schwerdtfeger, C. J.; Garlaschelli, L.; Koetzle, T. F. J. Chem. Soc.,

Dalton Trans. 1993, 3359–3362.

(27) Wen, T. B.; Zhou, Z. Y.; Jia, G. Angew. Chem., Int. Ed. 2006, 45,

5842–5846.

(28) (a) Krogh-Jespersen, K.; Czerw, M.; Goldman, A. S. J. Mol.

Catal. A: Chem. 2002, 189, 95–110. (b) Goettker-Schnetmann, I.;

Brookhart, M. J. Am. Chem. Soc. 2004, 126, 9330–9338. (c) Krogh-

Jespersen, K.; Czerw, M.; Goldman, A. S. ACS Symp. Ser. 2004, 885,

216–233.

(29) Bath, S. S.; Vaska, L. J. Am. Chem. Soc. 1963, 85, 3500–3501.

(30) (a) Sacco, A.; Rossi, M.; Nobile, C. F. Chem. Commun. (London)

1966, 589–590. (b) Vaska, L.; Catone, D. L. J. Am. Chem. Soc. 1966, 88,

5324–5325.

708 Organometallics, Vol. 30, No. 4, 2011

Adams et al.

20 °C): δ6.99(t, ³J_HH=8 Hz, 1H; p-C₆H₃(CH₂P(CF₃)₂)₂), 6.88(d,

³J_HH=8 Hz, 2H; m-C₆H₃(CH₂P(CF₃)₂)₂), 3.46 (dt, ²J_HH=18 Hz,

²J_PH=5 Hz, 2H; C₆H₃(CH₂P(CF₃)₂)₂), 3.30 (m, 4H; DBU CH₂

overlapping C₆H₃(CH₂P(CF₃)₂)₂), 2.84 (m, 2H; DBU), 2.42 (m,

(dfmp, 0.489 g, 1.720 mmol) were dissolved in benzene, and the

reaction mixture was stirred at ambient temperature for 20 h.

White Et₃NH^þCl^-precipitated and was filtered away, and the

volatiles were removed, giving an orange oil. The oil was

dissolved in 15 mL of hexane and filtered to remove a small

amount of solid. The solution was reduced to a volume of ca. 5

mL and cooled to -78 °C, precipitating an orange solid (0.312 g,

79% yield). Crystals suitable for X-ray diffraction were grown

by evaporating a hexane solution. Anal. Calcd for C₁₇H₁₀-

P₃F₂₂Ir: C, 22.26; H, 1.10. Found: C, 22.70; H, 1.19. ¹H NMR

(C₆D₆, 400.13 MHz, 20 °C): δ 6.94 (ps. t, ³J_HH=7 Hz, 1H; p-

3

2H; DBU), 2.34 (t, J_HH= 6 Hz, 2H; DBU), 1.44 (br. p, 2H;

DBU), 1.31 (p, ³J_HH=6 Hz, 2H; DBU), 1.13 (br. m, 2H; DBU),

0.88 (m, 2H; DBU). ³¹P{¹H} NMR (C₆D₆, 161.97 MHz, 20 °C): δ

58.0 (m). ¹⁹F NMR (C₆D₆, 376.50 MHz, 20 °C): δ -60.2 (m, 6F;

PCF₃), -60.6 (m, 6F; PCF₃).

CF₃

(

PCP)Ir(CO)₂(3). (^CF³PCP)Ir(CO)(H)Cl (0.250 g, 0.359

mmol) and Et₃N (150 μL, 0.108 g, 1.076 mmol) were dissolved in

15 mL of C₆H₆. One atmosphere of CO was introduced into the

reaction mixture, and it was stirred for 20 h at ambient tem-

perature. The reaction mixture remained colorless, giving a

white HNEt₃^þCl^-precipitate. The salt was removed via filtra-

tion, and the volatiles were removed, giving an orange oil.

Hexane (20 mL) was added to the oil, and 1 atm of CO was

introduced, giving a colorless solution with a small amount of

solid. The solid was filtered away and the filtrate cooled to -78

°C to give 3 as an elementally pure white solid which was

collected via cold filtration (0.210 g, 85% yield). Crystals

suitable for single-crystal X-ray diffraction were grown by slow

evaporation from a 1/4 benzene/hexanes solution at -30 °C.

Anal. Calcd for C₁₄H₇P₂F₁₂O₂Ir: C, 24.35; H, 1.02. Found: C,

24.39; H, 0.99. 20 ^oC NMR data: ¹H NMR (C₆D₆, 400.13 MHz)

3

C₆H₃(CH₂P(CF₃)₂)₂), 6.82 (ps. d, J_HH= 7 Hz, 2H; m-C₆H₃-

(CH₂P(CF₃)₂)₂), 3.35 (br m, 4H; C₆H₃(CH₂P(CF₃)₂)₂), 2.07 (d,

²J_PH=5 Hz, 3H; CH₃P(C₂F₅)₂). ³¹P{¹H} NMR (C₆D₆, 161.97

MHz, 20 °C): δ 67.3 (m, 2P; P(CF₃)₂), 37.1 (m, 1P; MeP(C₂F₅)₂).

¹⁹F NMR (C₆D₆, 376.50 MHz, 20 °C): δ -56.2 (br m, 12F;

PCF₃), -77.4 (s, 6F; MeP(CF₂CF₃)₂), ABX δ_A-114.7 (²J_FF

294 Hz, ²J_FP=30 Hz, 2F; (CH₃)P(CF₂CF₃)₂), δ_B-116.5 (²J_FF

=

294 Hz, ²J_FP=68 Hz, 2F; (CH₃)P(CF₂CF₃)₂).

CF₃

(

PCP)Ir(dfmp)₂(6). Complex 5 (20 mg, 0.021 mmol) was

placed in an NMR tube and dissolved in 0.75 mL of C₆D₆. dfmp

(39 μL, 62 mg, 0.218 mmol) was syringed into the NMR tube,

whereupon the solution became pale yellow. After the solution

stood undisturbed for 2 h, colorless crystals began to form. The

reaction mixture was left undisturbed for a total of 20 h. Crystals

suitable for single-crystal X-ray diffraction were obtained from

the tube. Complex 6 is unstable in solution and is highly

insoluble in C₆D₆. Attempts to isolate 6 failed, as the solid

3

δ 6.72 (d, J_HH= 8 Hz, 2H; m-C₆H₃(CH₂P(CF₃)₂)₂), 6.59 (t,

³J_HH=8 Hz, 1H; p-C₆H₃(CH₂P(CF₃)₂)₂), 3.24 (m, 4H; C₆H₃-

(CH₂P(CF₃)₂)₂); ³¹P{¹H} NMR (C₆D₆, 161.97 MHz) δ 47.0 (m);

¹⁹F NMR (C₆D₆, 376.50 MHz) δ -63.0 (d, ²J_FP=79 Hz, 12F;

PCF₃). -95 ^oC NMR data: ¹H NMR (CD₂Cl₂, 400.13 MHz) δ

converts to 5 under vacuum and under an N₂atmosphere.

CF₃

(

PCP)Ir(nbe) (7). (^CF³PCP)Ir(C₂H₄)(H)Cl (0.194 g, 0.278

3

7.12 (d, J_HH= 8 Hz, 2H; m-C₆H₃(CH₂P(CF₃)₂)₂), 6.97 (t,

mmol), Et₃N (0.50 mL, 0.363 g, 3.594 mmol), and norbornene

(0.500 g, 5.311 mmol) were dissolved in benzene. One atmo-

sphere of C₂H₄was introduced, and the reaction mixture

was stirred at ambient temperature for 20 h. Precipitation of

Et₃NH^þCl^-was observed, and ³¹P and ¹⁹F NMR showed the

major species in solution to be 4. The ammonium salt was

filtered away, and the volatiles were removed, giving an orange

oil. The oil was dissolved in 15 mL of hexane and the solution

filtered to remove a small amount of solid, and reduction to ca. 5

mL and cooling to -78 °C yielded the yellow-orange solid 7

(0.112 g, 55% yield). Crystals suitable for X-ray diffraction were

grown by evaporation from a hexane solution. Anal. Calcd for

C₁₉H₁₇P₂F₁₂Ir: C, 31.37; H, 2.36. Found: C, 30.99; H, 2.35. ¹H

NMR (C₆D₆, 400.13 MHz, 20 °C): δ 7.03 (t, ³J_HH=8 Hz, 1H; p-

C₆H₃(CH₂P(CF₃)₂)₂), 6.88 (d, ³J_HH=8 Hz, 2H; m-C₆H₃(CH₂P-

(CF₃)₂)₂), 4.11 (t, ³J_PH=5 Hz, 2H; nbe vinylic CH), 3.38 (ps. t,

³J_HH=8 Hz, 1H; p-C₆H₃(CH₂P(CF₃)₂)₂), 4.17 (dd, ²J_HH=17

Hz, ²J_HP=12 Hz, 2H; C₆H₃(CH₂P(CF₃)₂)₂), 3.83 (d, ²J_HH=17

Hz, 2H; C₆H₃(CH₂P(CF₃)₂)₂); ³¹P{¹H} NMR (CD₂Cl₂, 161.97

MHz, 20 °C) δ 45.6 (m); ¹⁹F NMR (CD₂Cl₂, 376.50 MHz, 20 °C)

δ -65.4 (d, ²J_FP=76 Hz, 12F; PCF₃), -61.4 (d, ²J_FP=77 Hz,

12F; PCF₃). IR (CH₂Cl₂, cm^-1): ν(CO) 2068, 2020 cm^-1

.

CF₃

(

PCP)Ir(C₂H₄)₂(4). An NMR tube was charged with ca.

15 mg of (^CFPCP)Ir(C₂H₄)(H)Cl (0.021 mmol) and 0.5 mL of

C₆D₆. Et₃N (2.8 μL, 0.002 g, 0.210 mmol) was syringed into the

tube, and C₂H₄(1 atm) was introduced into the NMR tube.

After 24 h Et₃NH^þCl^-precipitated. A single major species,

tentatively identified as 4, was observed. For low-temperature

spectra, the benzene solution was decanted away from the

ammonium salt, the volatiles were removed under vacuum,

and CD₂Cl₂was added. 20 ^oC NMR data: ¹H NMR (CD₂Cl₂,

3

J

_PH= 4 Hz, 4H; C₆H₃(CH₂P(CF₃)₂)₂), 3.11 (s, 2H; nbe CH),

400.13 MHz) δ 7.08 (d, J_HH= 8 Hz, 2H; m-C₆H₃(CH₂P-

(CF₃)₂)₂), 6.93 (t, J_HH= 8 Hz, 1H; p-C₆H₃(CH₂P(CF₃)₂)₂),

1.28 (d, ²J_HH=8 Hz, 2H; nbe CH₂CH₂), 0.96 (d, ²J_HH=8 Hz,

2H; nbe CH₂CH₂), 0.55 (d, ²J_HH=10 Hz, 1H; nbe CHCH₂CH),

0.24 (d, ²J_HH=10 Hz, 1H; nbe CHCH₂CH). ¹³C NMR (C₆D₆,

100.61 MHz, 20 °C): δ 157.5 (m; C_Ar-CH₂P(CF₃)₂), 143.1 (t, ²J_CP

3

3.82 (br s, 4H; C₆H₃(CH₂P(CF₃)₂)₂), 2.68 (s, br (ν_1/2=115 Hz),

8H; Ir(C₂H₄)); ³¹P{¹H} NMR (C₆D₆, 161.97 MHz): δ 47.0 (m);

¹³C{¹H} NMR (CD₂Cl₂, 100.61 MHz): δ 140.6 (m; C_Ar-Ir),

125.2 (s; para-C₆H₃(CH₂P(CF₃)₂), 122.7 (m; meta-C₆H₃(CH₂P-

(CF₃)₂), 46.0 (s; Ir(C₂H₄)₂), 39.1 (m; CH₂P(CF₃)₂); ¹⁹F NMR

(C₆D₆, 376.50 MHz) δ -57.9 (br m, 6F; PCF₃), -63.4 (br m, 6F;

PCF₃). -90 ^oC NMR data: ¹H NMR (CD₂Cl₂, 400.13 MHz) δ

1

= 13 Hz; C_Ar-Ir), 124.3 (d, J_CH= 162 Hz; p-C₆H₃(CH₂P-

(CF₃)₂), 122.6 (dm, ¹J_CH=159 Hz; m-C₆H₃(CH₂P(CF₃)₂), 70.1

(d, ¹J_CH=171 Hz; nbe vinylic CH), 45.4 (d, ¹J_CH=148 Hz; nbe

CH), 42.7 (t, ¹J_CH=134 Hz; nbe CHCH₂CH), 38.5 (tm, ¹J_CH

=

1

3

136 Hz; CH₂P(CF₃)₂), 28.4 (t, J_CH= 135 Hz; nbe CH₂CH₂).

³¹P{¹H} NMR (C₆D₆, 161.97 MHz, 20 °C): δ 66.0 (m). ¹⁹F

NMR (C₆D₆, 376.50 MHz, 20 °C): δ -57.8 (m, 12F; PCF₃).

7.03 (d, J_HH= 6 Hz, 2H; m-C₆H₃(CH₂P(CF₃)₂)₂), 6.89 (d,

³J_HH=6 Hz, 1H; p-C₆H₃(CH₂P(CF₃)₂)₂), 3.90 (dd, ²J_HH=18

Hz, ²J_HP=11 Hz, 2H; C₆H₃(CH₂P(CF₃)₂)₂), 3.67 (d, ²J_HH=18

CF₃

(

2

PCP)Ir(coe) (8). Compound 8 was prepared from 0.300 g

3

Hz, 2H; C₆H₃(CH₂P(CF₃)₂)₂), 2.95 (br d, J_HH= 9 Hz, 2H;

(0.430 mmol) of (^CFPCP)Ir(C₂H₄)(H)Cl and 0.50 mL of Et₃N

(3.594 mmol) analogously to 7, except that cyclooctene (0.5 mL,

0.423 g, 3.839 mmol) was used instead of norbornene. After the

reaction solution was filtered to remove Et₃NH^þCl^-and dis-

solved in hexanes, a small amount of solid was removed by

filtration and a viscous red oil was obtained. Further purification

was not possible, and the product was judged to be about þ90%

pure by NMR. ¹H NMR (C₆D₆, 400.13 MHz, 20 °C): δ 7.01 (t,

³J_HH=8 Hz, 1H; p-C₆H₃(CH₂P(CF₃)₂)₂), 6.89 (d, ³J_HH=8 Hz,

2H; m-C₆H₃(CH₂P(CF₃)₂)₂), 5.03 (br s, 2H; coe vinylic CH), 3.36

(ps. t, ³J_PH=4 Hz, 4H; C₆H₃(CH₂P(CF₃)₂)₂), 2.51 (m, 2H; coe

Ir(C₂H₄)), 2.70 (br s, 4H; Ir(C₂H₄)), 1.73 ((br d, ²J_HH=9 Hz, 2H;

Ir(C₂H₄)); ³¹P{¹H} NMR (CD₂Cl₂, 161.97 MHz) δ 45.6 (m);

¹³C{¹H} NMR (CD₂Cl₂, 100.61 MHz) δ 150.6 (s; C_Ar-CH₂P-

1

(CF₃)₂), 139.9 (m; C_Ar-Ir), 124.7 (d, J_CH= 162 Hz; p-C₆H₃-

1

(CH₂P(CF₃)₂), 122.7 (dd, J_CH= 157 Hz, J_CP= 16 Hz; m-

C₆H₃(CH₂P(CF₃)₂), 45.1 (t, ¹J_CH=163 Hz; Ir(C₂H₄)₂), 38.5 (tm,

¹J_CH=141 Hz; CH₂P(CF₃)₂), 35.6 ((td, ¹J_CH=16 Hz, ²J_CP=10 Hz;

Ir(C₂H₄)₂); ¹⁹F NMR (CD₂Cl₂, 376.50 MHz) δ -58.7 (d, ²J_FP=64

Hz, 6F; PCF₃), -65.4 (d, ²J_FP=64 Hz, 6F; PCF₃).

(

PCP)Ir(dfmp) (5). (^CF³PCP)Ir(C₂H₄)(H)Cl (0.300 g, 0.430

CF₃

mmol), Et₃N (0.25 mL, 0.185 g, 1.797 mmol), and MeP(C₂F₅)₂

Article

Organometallics, Vol. 30, No. 4, 2011 709

CH₂), 2.18 (m, 2H; coe CH₂), 1.52 (m, 4H; coe CH₂), 1.33 (m, 4H;

coe CH₂). ¹³CNMR(C₆D₆, 100.61 MHz, 20 °C): δ146.1 (t, ²J_CP

NMR (C₆D₆, 100.61 MHz, 20 °C): δ 147.0 (s; C_Ar-CH₂P(CF₃)₂),

140.3 (m; C_Ar-Ir), 124.8 (d, J_CH= 160 Hz; p-C₆H₃(CH₂P-

1

=

1

3

10 Hz; C_Ar-Ir), 122.5 (dm, ¹J_CH=158 Hz; m-C₆H₃(CH₂P(CF₃)₂),

79.6 (d, ¹J_CH=155 Hz; coe vinylic CH), 38.2 (tm, ¹J_CH=136 Hz;

C₆H₃(CH₂P(CF₃)₂)₂)), 33.2 (t, J_CH= 127 Hz; coe CH₂), 32.6

(CF₃)₂), 122.7 (dd, J_CH= 162 Hz, J_CP= 15 Hz; m-C₆H₃-

(CH₂P(CF₃)₂), 80.6 (d, ¹J_CH=162 Hz; cod HCdCH), 60.0 (dd,

¹J_CH=157 Hz, ²J_CP=22 Hz; cod HCdCH), 40.4 (td, ¹J_CH=136

1

(t, ¹J_CH=127 Hz; coe CH₂), 26.2 (t, ¹J_CH=122 Hz; coe CH₂).

³¹P{¹H} NMR (C₆D₆, 161.97 MHz, 20 °C): δ 60.8 (m). ¹⁹F NMR

Hz, J_CP= 34 Hz; CH₂P(CF₃)₂), 34.7 (t, J_CH= 126 Hz; cod

CH₂CH₂), 29.0 (t, ¹J_CH=126 Hz; cod CH₂CH₂). ³¹P{¹H} NMR

(C₆D₆, 161.97 MHz, 20 °C): δ 41.8 (m). ¹⁹F NMR (C₆D₆, 376.50

(C₆D₆, 376.50 MHz, 20 °C): δ_þ-56.1 (br s, 12F; PCF₃).

CF₃

2

PCP)Ir(H)Cl₂^-HNEt₃(9). The reaction between

PCP)Ir(C₂H₄)(H)Cl (0.277 g, 0.396 mmol) and Et₃N

CF₃

MHz, 20 °C): δ -55.6 (d, J_FP=60 Hz, 6F; PCF₃), -59.9 (d,

(

²J_FP=60 Hz, 6F; PCF₃).

(

CF₃

(

PCP)Ir(dfepe) (12). (^CF³PCP)Ir(C₂H₄)(H)Cl (0.421 g,

(0.50 μL, 3.6 mmol) was carried out in the absence of added

ethylene using 10 mL of 95% 1,1-dimethyl-3-butene as the

solvent. After 5 min, a precipitate of 9 began to form. The

reaction mixture was stirred at ambient temperature for 1 h,

and the brick red precipitate was collected via filtration (0.138

g, 86% based on 50% theoretical yield). In a separate NMR

0.603 mmol), Et₃N (0.50 mL, 3.594 mmol), and 1 atm of C₂H₄

were stirred overnight in 15 mL of toluene at room temperature

to give 4 and a HNEt₃^þCl^-precipitate. The salt was filtered

away under 1 atm of C₂H₄, and dfepe (283 μL, 0.840 mmol) was

added to the filtrate. After the reaction mixture was stirred at

ambient temperature for 16 h, a pale yellow solution with a pale

yellow precipitate of 12 was produced. The volume was reduced

to ca. 6 mL, and 12 was collected via filtration (0.454 g, 63%

yield). Crystals suitable for X-ray diffraction were obtained by

slow evaporation from a benzene solution. Anal. Calcd for

C₂₂H₁₁P₄F₃₂Ir: C, 22.03; H, 0.92. Found: C, 21.89; H, 0.99.

¹H NMR (CDCl₃, 400.13 MHz, 20 °C): δ 7.11 (d, ³J_HH=7 Hz,

experiment, agitating a 1/1 mixture of (^CFPCP)Ir(C₂H₄)-

3

(H)Cl and HNEt₃^þCl^-in benzene at 20 °C for 20 min resulted

in the quantitative formation of 9. Crystals suitable for X-ray

diffraction were obtained by slow evaporation from a benzene

solution. Anal. Calcd for C₁₈H₂₄NP₂F₁₂Cl₂Ir: C, 26.78; H,

1

3.00; N, 1.73. Found: C, 27.31; H, 2.90; N, 1.67. H NMR

(C₆D₆, 400.13 MHz, 20 °C): δ 8.73 (br s, 1H; HNEt₃^þ), 6.74

(m, 3H; C₆H₃(CH₂P(CF₃)₂)₂), 3.80 (br d, J_HH=17 Hz, 2H;

3

2

2H; m-C₆H₃(CH₂P(CF₃)₂)₂), 6.99 (t, J_HH= 7 Hz, 1H; m-

2

C₆H₃(CH₂P(CF₃)₂)₂), 4.05 (dd, J_HH= 18 Hz, J_PH= 11 Hz,

2

C₆H₃(CH₂P(CF₃)₂)₂), 3.28 (br d, J_HH= 17 Hz, 2H; C₆H₃-

2

2H; C₆H₃(CH₂P(CF₃)₂)₂), 3.71 (d, J_HH= 18 Hz, 2H; C₆H₃-

(CH₂P(CF₃)₂)₂), 2.31 (q, ³J_HH=7 Hz, 6H; HN(CH₂CH₃)₃^þ),

0.62 (m, 9H; HN(CH₂CH₃)₃^þ), -19.18 (t, ²J_HP=17 Hz, 1H;

IrH). ³¹P{¹H} NMR (C₆D₆, 161.97 MHz, 20 °C): δ 53.1 (m).

¹⁹F NMR (C₆D₆, 376.50 MHz, 20 °C): δ -54.9 (m, 6F;

(CH₂P(CF₃)₂)₂), 2.62 (m, 2H; dfepe CH₂), 2.29 (m, 2H; dfepe

CH₂). ³¹P{¹H} NMR (CDCl₃, 161.97 MHz, 20 °C): δ 72.7

(m, 1P; P(CF₃)₂), 53-43 ppm (overlapping m, 3P; P(CF₃)₂

and dfepe). ¹⁹F NMR (CDCl₃, 376.50 MHz, 20 °C): δ -54.3

(br s, 6F; PCF₃), -62.5 (d, ²J_FP=64 Hz, 6F; PCF₃), -76.0 (s,

6F; dfepe PCF₂CF₃), -76.1 (s, 6F; dfepe PCF₂CF₃), -101

PCF₃), -60.5 (m, 6F; PCF₃).

CF₃

(

PCP)Ir(nbd) (10). (^CF³PCP)Ir(C₂H₂)(H)Cl (0.250 g, 0.358

mmol), Et₃N (150 μL, 0.109 g, 1.076 mmol), and nbd (0.25 mL,

0.276 g, 2.995 mmol) were dissolved in 15 mL of benzene. The

reaction mixture was stirred at ambient temperature for 24 h,

producing a pale yellow solution and a white Et₃NH^þCl^-

precipitate. The salt was filtered away, and the volatiles were

removed. The filtrate residue was dissolved in 15 mL of hexane,

giving a small amount of solid which was filtered off and rinsed

twice with 10 mL of hexane. The filtrate was cooled to -78 °C,

which gave the product as a white solid that was collected via

cold filtration (0.212 g, 81% yield). Anal. Calcd for

C₁₉H₁₅P₂F₁₂Ir: C, 31.40; H, 2.08. Found: C, 31.77; H, 2.19.

¹H NMR (C₆D₆, 400.13 MHz, 20 °C): δ 6.70 (m, 3H; C₆H₃-

(CH₂P(CF₃)₂)₂), 4.28 (br m, 2H; nbd, uncoordinated vinylic

CH), 3.68 (dd, ²J_HH=16 Hz, ²J_HP=12 Hz, 2H; C₆H₃(CH₂P-

(CF₃)₂)₂), 3.28 (d, ²J_HH=16 Hz, 2H; C₆H₃(CH₂P(CF₃)₂)₂), 3.26

(br s, 2H; nbd), 2.34 (m, 2H; nbd, coordinated vinylic CH), δ_A

0.37 and δ_B0.31 (AB, ²J_HH=9 Hz, 2H; nbd CH₂). ¹³C NMR

(C₆D₆, 100.61 MHz, 20 °C): δ 146.8 (m; C_Ar-CH₂P(CF₃)₂),

to -109 (overlapping ABX multiplets, 8F; dfepe PCF₂CF₃).

CF₃

(

PCP)Ir(PhCN)(C₂H₄) (13). (^CF³PCP)Ir(PhCN)(H)Cl (0.400

g, 0.517 mmol), PhCN (0.53 mL, 0.533 g, 5.175 mmol), and Et₃N

(0.720 mL, 0.523 g, 5.175 mmol) were dissolved in 15 mL of

benzene. One atmosphere of C₂H₄was introduced, and the reaction

mixture was stirred at ambient temperature for 24 h. The

Et₃NH^þCl^-precipitate was filtered away, and the volatiles were

removed under vacuum. The residue was extracted with hexanes

(∼45 °C, 25 mL), and the remaining solid was extracted with

several portions of warm hexane. The filtrate volume was reduced

to ca. 10 mL, and a pale orange solid was isolated and dried under

vacuum (0.176 g, 44% yield). Crystals suitable for X-ray diffraction

were obtained by diffusion of hexane into a saturated benzene

solution. Anal. Calcd for C₂₁H₁₆NP₂F₁₂Ir: C, 32.99; H, 2.11; N,

1.83. Found: C, 32.88; H, 2.04; N, 1.58. ¹H NMR (C₆D₆, 400.13

MHz, 20 °C): δ 6.69 (m, 6H; C₆H₃(CH₂P(CF₃)₂)₂and o,p-

3

C₆H₅CN), 6.49 (ps t, J_HH= 8 Hz, 2H; m-C₆H₅CN), 3.52 (m,

1

139.7 (m; C_Ar-Ir), 124.7 (d, J_CH= 161 Hz; p-C₆H₃(CH₂P-

2H; C₆H₃(CH₂P(CF₃)₂)₂), 3.37 (m, 2H; C₆H₃(CH₂P(CF₃)₂)₂), 2.60

1

(CF₃)₂), 122.2 (dm, J_CH= 149 Hz; m-C₆H₃(CH₂P(CF₃)₂),

(br s, 2H; CH₂CH₂), 1.76 (br s, 2H; CH₂CH₂). ¹³C NMR (C₆D₆,

1

66.2 (t, J_CH=132 Hz; nbd CHCH₂CH), 60.8 (d, J_CH= 180

1

100.61 MHz, 20 °C): δ 142.6 (s; C_Ar-CH₂P(CF₃)₂), 140.6 (m; C_Ar

-

1

Hz; nbd HCdCH), 45.4 (d, J_CH=150 Hz; nbd CHCH₂CH),

Ir), 132.6 (dm, ¹J_CH=163 Hz; C₆H₅CN), 131.9 (dt, ¹J_CH=168 Hz,

²J_CH=6 Hz; C₆H₅CN), 128.4 (dm, ¹J_CH=165 Hz; C₆H₅CN), 123.9

(d, ¹J_CH=160 Hz; p-C₆H₃(CH₂P(CF₃)₂), 122.4 (dm, ¹J_CH=158

Hz; m-C₆H₃(CH₂P(CF₃)₂), 119.3 (s; C₆H₅CN), 109.9 (d, J_CH=9

1

41.3 (td, J_CH= 132 Hz, J_CP= 38 Hz; CH₂P(CF₃)₂), 28.0 (t,

1

2

¹J_CH= 181 Hz, J_CP= 20 Hz; nbd HCdCH). ³¹P{¹H} NMR

(C₆D₆, 161.97 MHz, 20 °C): δ 41.3 (m). ¹⁹F NMR (C₆D₆, 376.50

2

1

MHz, 20 °C): δ -56.8 (d, J_FP=64 Hz, 6F; PCF₃), -61.2 (d,

Hz; ipso-C₆H₅CN), 38.2 (td, J_CH= 134 Hz, J_CP= 33 Hz;

²J_FP=67 Hz, 6F; PCF₃).

CH₂P(CF₃)₂), 32.4 (t, J_CH= 157 Hz; Ir(C₂H₄)). ³¹P{¹H} NMR

1

CF₃

(C₆D₆, 161.97 MHz, 20 °C): δ 50.5 (m). ¹⁹F NMR (C₆D₆, 376.50

=

(

PCP)Ir(cod) (11). The procedure for the synthesis of 11 is

MHz, 20 °C): δ-56.8 (d, ³J_FP=60 Hz, 6F; PCF₃), -62.3(d, ³J_FP

64 Hz, 6F; PCF₃).

the same as for 10, except cod (0.25 mL, 0.221 g, 2.084 mmol)

was used instead of nbd. Isolated yield: 0.244 g, (92%). Crystals

suitable for X-ray diffraction were grown by diffusion of hexane

into a saturated benzene solution. Anal. Calcd for C₁₉H₁₅P₂-

CF₃

(

PCP)Ir(CO)(CH₃)I (14). An NMR tube was charged with

a ca. 50 mg sample of 1 (0.076 mmol), 0.5 mL of C₆D₆, and CH₃I

(ca. 0.1 mL, 0.153 g, 1.011 mmol). Upon mixing the solution

immediately changed from orange to colorless. The solution was

transferred to a 5 mL glass vial, ca. 3.5 mL of hexanes was

added, and the solution was slowly evaporated to give clear

crystals suitable for single-crystal X-ray diffraction studies

(0.052 g, 82% yield). Anal. Calcd for C₁₄H₁₀P₂F₁₂OIIr: C,

20.90; H, 1.25. Found: C, 21.16; H, 1.01. ¹H NMR (C₆D₆,

1

F₁₂Ir: C, 32.34; H, 2.58. Found: C, 32.66; H, 2.13. H NMR

(C₆D₆, 400.13 MHz, 20 °C): δ 6.73 (m, 3H; C₆H₃(CH₂P-

(CF₃)₂)₂), 4.87 (m, 2H; cod, noncoordinated vinylic CH), 3.58

(dd, ²J_HH=16 Hz, ²J_PH=12 Hz, 2H; C₆H₃(CH₂P(CF₃)₂)₂), 3.24

(d, ²J_PH=16 Hz, 2H; C₆H₃(CH₂P(CF₃)₂)₂), 2.50 (m, 2H; cod,

coordinated vinylic CH), 2.28 (m, 2H; cod CH₂), 2.15 (m, 2H;

cod CH₂), 1.95 (m, 2H; cod CH₂), 1.47 (m, 2H, cod CH₂). ¹³

C

710 Organometallics, Vol. 30, No. 4, 2011

Adams et al.

3

400.13 MHz, 20 °C): δ 6.75 (t, J_HH= 7.6 Hz, 1H; p-C₆H₃-

(CH₂P(CF₃)₂)₂), 6.68 (d, J_HH= 7.6 Hz, 2H; m-C₆H₃(CH₂P-

¹⁹F NMR (acetone-d₆, 376.50 MHz, -20 °C) δ -62.8 (m, 6F;

PCF₃), -65.0 (m, 6F; PCF₃).

3

2

(CF₃)₂)₂), 3.95 (dt, J_HH= 17 Hz, J_PH= 6 Hz, 2H; C₆H₃-

Dynamic NMR Analysis. All examined fluxional systems

(compounds 3, 4, 13, and 18) were modeled using iNMR.³¹

Dynamic line shape fitting was applied to resonances in the

intermediate exchange regime or at coalescence. Probe tempera-

tures were not calibrated and were assumed to be (2 °C.

X-ray Crystallography. The X-ray diffraction data for all

complexes were measured at 150 K on a Bruker SMART APEX

II CCD area detector system equipped with a graphite mono-

chromator and a Mo KR fine-focus sealed tube operated at 1.5

kW power (50 kV, 30 mA). Crystals were attached to either a

Hampton Research cryoloop or a MiTeGen micromount using

Paratone N oil. The detector was placed at a distance of 5.9 cm

from the crystal during the data collection.

2

(CH₂P(CF₃)₂)₂), 3.43 (dt, J_HH= 17 Hz, J_PH= 5 Hz, 2H;

C₆H₃(CH₂P(CF₃)₂)₂), 0.50 (t, J_PH= 6 Hz, 3H; Ir-CH₃). ³¹P-

3

{¹H} NMR (C₆D₆, 161.97 MHz, 20 °C): δ 49.9 (m). ¹⁹F NMR

(C₆D₆, 376.50 MHz, 20 °C): δ -50.3 (m, 6F; PCF₃), -52.2 (m,

6F; PCF₃). IR (CH₂Cl₂, cm^-1): ν(CO)=2082 cm^-1

.

trans-(^CFPCP)Ir(CO)(H)₂(15). An NMR tube was charged

with a ca. 15 mg sample of 1 (0.021 mmol) and 0.5 mL of C₆D₆.

Hydrogen gas (1 atm) was introduced into the tube, and the

solution changed from orange to colorless upon shaking. NMR

spectra indicated the clean formation of the trans-dihydride 15.

¹H NMR (C₆D₆, 400.13 MHz, 20 °C): δ 6.79 (t, ³J_HH=8 Hz, 1H;

3

p-C₆H₃(CH₂P(CF₃)₂)₂), 6.59 (d, J_HH= 8 Hz, 2H; m-C₆H₃-

(CH₂P(CF₃)₂)₂), 3.28 (m, 4H; C₆H₃(CH₂P(CF₃)₂)₂), -9.10 (t,

²J_HP=19.2 Hz, T₁=9.98 s, 2H; Ir-H). ³¹P{¹H} NMR (C₆D₆,

161.97 MHz, 20 °C): δ 59.7 (m). ¹⁹F NMR (C₆D₆, 376.50 MHz,

20 °C): δ -62.6 (br m, 12F; PCF₃). IR (CH₂Cl₂, cm^-1): ν(CO)

2068 cm^-1, ν(IrH) 2090 cm^-1(sh).

A series of narrow frames of data were collected with a scan

width of 0.5° in ω or φ and an exposure time of 10 s per frame.

The frames were integrated with the Bruker SAINT Software

package³²using a narrow-frame integration algorithm. The

data were corrected for absorption effects by the multiscan

method (SADABS). Crystallographic data collection para-

meters and refinement data are deposited as Supporting

Information. The structures of 2, 3, 9, 11, and 13 were solved

by direct methods, and the structures of 1, 5-7, 12, 14, and 16

were solved by Patterson methods using the Bruker

SHELXTL (V. 6.10 or V. 6.14) software package. All non-

hydrogen atoms were located in successive Fourier maps and

refined anisotropically. Hydrogen atoms for complexes 7 and

12 were located on difference Fourier maps and refined

isotropically. Two sets of anions and cations were present in

the asymmetric unit of 9; the hydride ligands were located and

refined isotropically. Crystals of complex 9 contained two

benzene molecules per asymmetric unit; one CF₃group and

one benzene molecule were partially disordered but were not

modeled. Methyl hydrogens for complex 14 were located and

refined isotropically; one CF₃group was rotationally disor-

dered and was modeled satisfactorily using a two-position

model. The P1 asymmetric unit of 16 consists of three inde-

fac,cis-(^CFPCP)Ir(dfmp)(H)₂(16). An NMR tube was

3

charged with a ca. 21 mg sample of 5 (0.021 mmol) and 0.5

mL of C₆D₆. Hydrogen gas (1 atm) was introduced into the tube,

and the solution changed from orange to colorless upon shak-

ing. NMR spectra indicated the clean formation of 16. ¹H NMR

3

(C₆D₆, 400.13 MHz, 20 °C): δ 6.85 (t, J_HH= 7 Hz, 1H; p-

C₆H₃(CH₂P(CF₃)₂)₂), 6.71 (d, ³J_HH=7 Hz, 2H; m-C₆H₃(CH₂P-

(CF₃)₂)₂), 3.73 (dd, ²J_HH=18 Hz, ²J_HP=15 Hz, 2H; C₆H₃(CH₂-

P(CF₃)₂)₂), 3.08 (d, J_HH= 18 Hz, 2H; C₆H₃(CH₂P(CF₃)₂)₂),

2

1.88 (d, ²J_PH=7 Hz, 3H; CH₃P(CF₂CF₃)₂), -11.44 (AA⁰MXX⁰,

²J_HH=9 Hz, ²J_PH=-161, 32, 19 Hz (to dfmp), ²J_PP=5 Hz (²J_PP

between ^CFPCP and dfmp was not determined), T₁=1.60 s, 2H;

3

Ir-H). ³¹P{¹H} NMR (C₆D₆, 161.97 MHz, 20 °C): δ 38.2 (m, 2P;

P(CF₃)₂), 19.7 (m, 1P; MeP(C₂F₅)₂). ¹⁹F NMR (C₆D₆, 376.50

2

MHz, 20 °C): δ -56.1 (d, J_FP=56 Hz, 6F; PCF₃), -58.0 (d,

²J_FP=60 Hz, 6F; PCF₃), -74.6 (s, 6F; MeP(CF₂CF₃)₂), -110.1

(dd, ²J_FF=309 Hz, ²J_FP=45 Hz, 2F; MeP(CF₂CF₃)₂), -114.2

(dd, ²J_FF=305 Hz, ²J_FP=79 Hz, 2F; MeP(CF₂CF₃)₂).

pendent trans-(^CFPCP)Ir(dfmp)(H)₂molecules. Molecules

3

mer,trans-(^CFPCP)Ir(dfmp)(H)₂(17). After the NMR tube

3

centered on Ir(1) and Ir(3) are well-ordered, whereas two of

the C₂F₅groups associated with Ir(2) are disordered. Assign-

ment of two sets of positions for the disordered atoms led to

satisfactory refinement of the structure. All hydride ligand

atoms were located in the Fourier maps and refined isotropi-

cally. The rest of the hydrogen atoms were placed in calculated

positions and were refined isotropically. In the remaining

structures (1-3, 5, 6, 11, and 13) all hydrogen atoms were

placed in calculated positions.

Computational Details. All calculations were carried using

Gaussian 09 Rev. A.02.³³The density functional theory (DFT)

B97-1 hybrid exchange-correlation functional was used for

geometry optimization and frequencies.³⁴The Dunning cc-pVDZ

prepared from 16 was allowed to sit for 24 h, ca. 10% was

converted to 17. ¹H NMR (C₆D₆, 400.13 MHz, 20 °C): δ 6.81 (t,

³J_HH=7 Hz, 1H; p-C₆H₃(CH₂P(CF₃)₂)₂), 6.66 (d, ³J_HH=8 Hz,

2H; m-C₆H₃(CH₂P(CF₃)₂)₂), 3.41 (br s, 4H; C₆H₃(CH₂P-

2

(CF₃)₂)₂), 2.02 (d, J_HP=7 Hz, 2H; CH₃P(CF₂CF₃)₂), -10.18

2

(br dt, J_HP=20 Hz, 2H; Ir-H). ³¹P{¹H} NMR (C₆D₆, 161.97

MHz, 20 °C): δ 51.8 (m, 2P; P(CF₃)₂), 18.0 (m, 1P; MeP(C₂F₅)₂).

¹⁹F NMR (C₆D₆, 376.50 MHz, 20 °C): δ -59.9 (ps. t, ²J_FP=38 Hz,

12F; PCF₃), -74.2 (s, 6F; MeP(CF₂CF₃)₂), -108.6 to -114.2

(overlapping ABX with 16; MeP(CF₂CF₃)₂).

Variable-Temperature NMR Study of (^CFPCP)Ir(CO) þ H₂.

3

A 15 mg portion of (^CFPCP)Ir(CO) was dissolved in 0.5 mL of

3

acetone-d₆and cooled to -80 °C. Three atmospheres of H₂was

admitted, and after thorough mixing, the tube was placed in

the NMR probe cooled to -60 °C. Spectral data for fac,

cis-(^CFPCP)Ir(CO)(H)₂(18): ¹H NMR (acetone-d₆, 400.13

3

(31) iNMR, Version 3.6.3; http://www.inmr.net.

(32) APEX2 Software Suite, Version 2.2; Bruker AXS Inc., Madison,

WI, 2008.

3

MHz, -60 °C) δ 7.26 (d, J_HH= 7 Hz, 2H; m-C₆H₃(CH₂P-

(CF₃)₂)₂), 7.05 (t, ³J_HH=7 Hz, 1H; p-C₆H₃(CH₂P(CF₃)₂)₂), 4.74

(dd, ²J_HH=16 Hz, ²J_HP=14 Hz, 2H; C₆H₃(CH₂P(CF₃)₂)₂), 4.20

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

M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.;

Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.;

Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;

Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,

T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, Jr., J. A.;

Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,

K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;

Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.;

Millam, N. J.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.;

Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin,

A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma,

K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;

2

(d, J_HP= 16 Hz, 2H; C₆H₃(CH₂P(CF₃)₂)₂), -9.79 (AA⁰XX⁰,

²J_HP=-157, 33 Hz, ²J_HH=12 Hz, ²J_PP=10 Hz, T₁=868 ms,

2H; Ir-H); ³¹P{¹H} NMR (acetone-d₆, 161.97 MHz, -60 °C) δ

46.1 (m); ¹⁹F NMR (acetone-d₆, 376.50 MHz, -60 °C) δ -59.9

(d, ²J_FP=68 Hz, 6F; PCF₃), -62.3 (d, ²J_FP=64 Hz, 6F; PCF₃).

1

Spectral data for mer,cis-(^CFPCP)Ir(CO)(H)₂(19): H NMR

3

(acetone-d₆, 400.13 MHz, -20 °C) δ 7.30 (d, ³J_HH=7 Hz, 2H; m-

C₆H₃(CH₂P(CF₃)₂)₂), 7.08 (t, J_HH=7 Hz, H; p-C₆H₃(CH₂P-

3

(CF₃)₂)₂), 4.66 (m, 4H; C₆H₃(CH₂P(CF₃)₂)₂), -11.30 (t, ²J_HH

=

18 Hz, 1H; Ir-H), -11.72 (t, ²J_HH=16 Hz, T₁=2.79 s, 1H; Ir-H);

³¹P{¹H} NMR (acetone-d₆, 161.97 MHz, -20 °C) δ 57.8 (m);

€

Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.;

Cioslowski, J.; Fox, D. J. Gaussian 09, Rev. A.02; Gaussian, Inc.,

Wallingford, CT, 2009.

Article

Organometallics, Vol. 30, No. 4, 2011 711

basis set was used for all main-group elements; the diffuse

basis set AUG-cc-pVDZ was used for phosphorus.³⁵Figgen

et al. energy-consistent pseudopotentials and correlation-con-

sistent basis set for iridium was used.³⁶The geometry optimi-

zation for the bis-ethylene complex 4 was carried out without

any symmetry constraints; the absence of any imaginary

frequencies confirmed the optimized structure shown in Fig-

ure 8 as an energy minimum.

Acknowledgment. We thank The National Science

Foundation (No. CHE-0457435) and DOE/EPSCoR

(No. DE-FG02-08ER15979) for financial support.

(34) Hamprecht, F. A.; Cohen, A. J.; Tozer, D. J.; Handy, N. C.

J. Chem. Phys. 1998, 109, 6264–6271.

(35) Dunning, T. H., Jr. J. Chem. Phys. 1989, 90, 1007–1023.

(36) Figgen, D.; Peterson, K. A.; Dolg, M.; Stoll, H. J. Chem. Phys.

2009, 130, 164108/164101–164108/164112.

Supporting Information Available: CIF files giving crystallo-

graphic data for complexes 1-3, 5-7, 9, 11-14, and 16 and tables

giving DFT optimization details and coordinates. This material is

available free of charge via the Internet at http://pubs.acs.org.

Article Doi

Acceptor PCP pincer iridium(I) chemistry: Stabilization of nonmeridional PCP coordination geometries

DOI: 10.1021/om100864g

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